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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#81
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Testing MOT as electromagnet - this just in
On Jan 20, 8:14*am, "Michael A. Terrell"
wrote: ... * *It's simple: Connect a known value capacitor across the coil. *Put a 1K ohm resistor in series with the generator to the hot side and connect the ground to the other end of the coil. *Then use a scope or AC voltmeter to look for resonance across the L/C pair. That's only simple if you have a capacitance meter. Do NOT use an electrolytic or multilayer ceramic cap. Caps that are physically large for their value like plastic film ones are more likely to be close to their nominal value. http://en.wikipedia.org/wiki/Types_of_capacitor jsw |
#82
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Testing MOT as electromagnet - this just in
Jon Danniken wrote:
Winston wrote: Bob Engelhardt wrote: Winston wrote: The inductance of that coil fell significantly when you lopped off the 'I' core, yes? Yes and no, I supposeG. 'Though I did lop it off, I replaced it with a shorting bar, so it shouldn't be drastically different. Now's the time to break out your $0.99 inductance bridge. I haven't tested this but it looks reasonable: http://www.aronnelson.com/gallery/main.php/v/BinOfBrett/Inductance_meter.jpg.html http://www.aronnelson.com/gallery/main.php/v/BinOfBrett/Inductance_method.jpg.html You can also measure inductances of this size using your PC and tone generating software. Wire up the inductor with a capacitor, apply the tone, and look for the resonant frequency. I did this a few years ago with a MOT, testing the difference in inductance by using different sized paper shims between the "E" and the "I" laminations. There's a webpage describing this somewhere out there, but of course I can't find it right now. I think I made the mistake of saving it instead of adding it to my bookmarks. Bob's soundcard software looks promising. For 29 bucks, it is worth trying IMHO. http://www.daqarta.com/dw_0ass.htm --Winston |
#83
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Testing MOT as electromagnet - this just in
Winston wrote:
The inductance of that coil fell significantly when you lopped off the 'I' core, yes? Can you place a small value sense resistor in series with the 'common' line to your coil? The way I misunderstand magnetic core saturation is that we expect a 'knee' where current begins to increase in a nonlinear fashion in relation to applied voltage. You could set your 'scope up as an X-Y display to show this nonlinearity very clearly. Okay, now that caught my attention, as I've been looking for a way to "notice" saturation when driving the primary of a MOT. I do know that one can view phase angle with an x-y viewing of current and voltage, and I guess it makes sense to look at that same waveform for a change as an indicator of saturation (when phase angle is changed due to an increase of non-inductive current). Thanks Winston, I'm gonna have to play around with this. Jon |
#84
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Testing MOT as electromagnet - this just in
Jon Danniken wrote:
Winston wrote: The inductance of that coil fell significantly when you lopped off the 'I' core, yes? Can you place a small value sense resistor in series with the 'common' line to your coil? The way I misunderstand magnetic core saturation is that we expect a 'knee' where current begins to increase in a nonlinear fashion in relation to applied voltage. You could set your 'scope up as an X-Y display to show this nonlinearity very clearly. Okay, now that caught my attention, as I've been looking for a way to "notice" saturation when driving the primary of a MOT. I do know that one can view phase angle with an x-y viewing of current and voltage, and I guess it makes sense to look at that same waveform for a change as an indicator of saturation (when phase angle is changed due to an increase of non-inductive current). Thanks Winston, I'm gonna have to play around with this. Shore. For A.C. operation, I'd expect that a current transformer would give you much better isolation and signal - to - noise ratio. For D.C. (or A.C.) operation, I'd expect that a Hall Effect Current Sensor would be a better choice, for the same reason. I've used the Allegro ACS756 in some extremely low impedance applications where a sense resistor caused power supply instability. http://www.allegromicro.com/en/Produ...0756/index.asp Highly recommended, though you will need to normalize it's output. (I did that automatically with DAQ gear.) For seven bucks, it is a great value. http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go _button&KeyWords=ACS756&x=0&y=0 --Winston |
#85
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Testing MOT as electromagnet - this just in
Winston wrote:
For A.C. operation, I'd expect that a current transformer would give you much better isolation and signal - to - noise ratio. For D.C. (or A.C.) operation, I'd expect that a Hall Effect Current Sensor would be a better choice, for the same reason. I've used the Allegro ACS756 in some extremely low impedance applications where a sense resistor caused power supply instability. http://www.allegromicro.com/en/Produ...0756/index.asp Highly recommended, though you will need to normalize it's output. (I did that automatically with DAQ gear.) For seven bucks, it is a great value. http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go _button&KeyWords=ACS756&x=0&y=0 Ooh, and up to 100 amps, I like that. Curious as to what you mean by "normalize it's output", though; is this referring to the "typical application" diagram given in the datasheet (sorry I'm rather dense on some things). Jon |
#86
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Testing MOT as electromagnet - this just in
Jon Danniken wrote:
Winston wrote: (...) I've used the Allegro ACS756 in some extremely low impedance applications where a sense resistor caused power supply instability. http://www.allegromicro.com/en/Produ...0756/index.asp Highly recommended, though you will need to normalize it's output. (I did that automatically with DAQ gear.) For seven bucks, it is a great value. http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go _button&KeyWords=ACS756&x=0&y=0 Ooh, and up to 100 amps, I like that. Curious as to what you mean by "normalize it's output", though; is this referring to the "typical application" diagram given in the datasheet Short version: It is a 'single ended' output without a negative supply. You need to subtract Vcc/2 from the output and multiply the result by 25 to arrive at the real reading. Long version: Let's say you power it from 5.0000 V DC. Zero amperes will be represented by a 2.50 V (or Vcc/2) reading between output and ground. An output of 2.54 V would thus indicate a current flow of +1 A and an output of 2.46 V would indicate a current flow of -1 A. 2.54 V - 2.50000 V = 0.04 V 0.04 V * 25 = 1.0 A 2.46 V - 2.50000 V = (-0.04 V) (-0.04 V) * 25 = (-1.0 A) With the data acquisition gear I used, I sensed the Vcc going to the device and wrote an equation that automatically did all the arithmetic for every reading. The log files all showed the current flow in amperes. It worked a treat! If you wanted 'cheap and cheerful', you could put a precision voltage divider between sensor Vcc and ground to provide your multimeter a 'virtual ground', then just mentally multiply the reading you see on the DMM display by 25 to arrive at real amperes. --Winston |
#87
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Testing MOT as electromagnet - this just in
Winston wrote:
Short version: It is a 'single ended' output without a negative supply. You need to subtract Vcc/2 from the output and multiply the result by 25 to arrive at the real reading. Long version: Let's say you power it from 5.0000 V DC. Zero amperes will be represented by a 2.50 V (or Vcc/2) reading between output and ground. An output of 2.54 V would thus indicate a current flow of +1 A and an output of 2.46 V would indicate a current flow of -1 A. 2.54 V - 2.50000 V = 0.04 V 0.04 V * 25 = 1.0 A 2.46 V - 2.50000 V = (-0.04 V) (-0.04 V) * 25 = (-1.0 A) With the data acquisition gear I used, I sensed the Vcc going to the device and wrote an equation that automatically did all the arithmetic for every reading. The log files all showed the current flow in amperes. It worked a treat! If you wanted 'cheap and cheerful', you could put a precision voltage divider between sensor Vcc and ground to provide your multimeter a 'virtual ground', then just mentally multiply the reading you see on the DMM display by 25 to arrive at real amperes. Ah, I gotcha, thanks. I'd probably put a function in my calculator to convert it, unless I was doing a lot of measurements. Jon |
#88
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Testing MOT as electromagnet - this just in
Jon Danniken wrote:
Winston wrote: Short version: It is a 'single ended' output without a negative supply. You need to subtract Vcc/2 from the output and multiply the result by 25 to arrive at the real reading. Long version: Let's say you power it from 5.0000 V DC. Zero amperes will be represented by a 2.50 V (or Vcc/2) reading between output and ground. An output of 2.54 V would thus indicate a current flow of +1 A and an output of 2.46 V would indicate a current flow of -1 A. 2.54 V - 2.50000 V = 0.04 V 0.04 V * 25 = 1.0 A 2.46 V - 2.50000 V = (-0.04 V) (-0.04 V) * 25 = (-1.0 A) With the data acquisition gear I used, I sensed the Vcc going to the device and wrote an equation that automatically did all the arithmetic for every reading. The log files all showed the current flow in amperes. It worked a treat! If you wanted 'cheap and cheerful', you could put a precision voltage divider between sensor Vcc and ground to provide your multimeter a 'virtual ground', then just mentally multiply the reading you see on the DMM display by 25 to arrive at real amperes. Ah, I gotcha, thanks. I'd probably put a function in my calculator to convert it, unless I was doing a lot of measurements. In that case, you can simplify the arithmetic with: ACS758ECB-200B-PSS-T (Straight Leads) OR ACS758ECB-200B-PFF-T (Bent Leads) With your DMM negative lead connected to the center of a stiff, precision 2:1 voltage divider and it's positive lead to pin 3 of the chip, You just multiply the output by 100 to get your reading: +2.000 V = 200.0 A +0.153 V = 15.3 A 0 V = 0.0 A -2.000 V = -200.0 A Seven smackers each. http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go _button&KeyWords=ACS758ECB-200B&x=0&y=0 As a great philosopher once said, "Hell Yeah!" http://www.youtube.com/watch?v=82dDnv9zeLs --Winston |
#89
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Testing MOT as electromagnet - this just in
Jim Wilkins wrote: On Jan 20, 8:14 am, "Michael A. Terrell" wrote: ... It's simple: Connect a known value capacitor across the coil. Put a 1K ohm resistor in series with the generator to the hot side and connect the ground to the other end of the coil. Then use a scope or AC voltmeter to look for resonance across the L/C pair. That's only simple if you have a capacitance meter. Do NOT use an electrolytic or multilayer ceramic cap. Caps that are physically large for their value like plastic film ones are more likely to be close to their nominal value. http://en.wikipedia.org/wiki/Types_of_capacitor I would use the HV capacitor that came from the oven. -- You can't fix stupid. You can't even put a band-aid on it, because it's Teflon coated. |
#90
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Testing MOT as electromagnet - this just in
Winston wrote:
In that case, you can simplify the arithmetic with: ACS758ECB-200B-PSS-T (Straight Leads) OR ACS758ECB-200B-PFF-T (Bent Leads) With your DMM negative lead connected to the center of a stiff, precision 2:1 voltage divider and it's positive lead to pin 3 of the chip, You just multiply the output by 100 to get your reading: +2.000 V = 200.0 A +0.153 V = 15.3 A 0 V = 0.0 A -2.000 V = -200.0 A Seven smackers each. http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go _button&KeyWords=ACS758ECB-200B&x=0&y=0 Even better, thanks Winston. Jon |
#91
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Testing MOT as electromagnet - this just in
Jon Danniken wrote:
Winston wrote: In that case, you can simplify the arithmetic with: ACS758ECB-200B-PSS-T (Straight Leads) OR ACS758ECB-200B-PFF-T (Bent Leads) With your DMM negative lead connected to the center of a stiff, precision 2:1 voltage divider and it's positive lead to pin 3 of the chip, You just multiply the output by 100 to get your reading: +2.000 V = 200.0 A +0.153 V = 15.3 A 0 V = 0.0 A -2.000 V = -200.0 A Seven smackers each. http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go _button&KeyWords=ACS758ECB-200B&x=0&y=0 Even better, thanks Winston. Jon You are welcome, Jon. --Winston |
#92
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Testing MOT as electromagnet - this just in
On Wed, 19 Jan 2011 20:59:16 -0500, "Michael A. Terrell"
wrote: wrote: On Wed, 19 Jan 2011 15:06:08 -0500, "Michael A. Terrell" wrote: Bob Engelhardt wrote: wrote: If I recall correctly when one designs a transformer, you calculate what the ET product is. ... snip So the flux ( B ) depends on the voltage and frequency. And using the same line frequency and the voltage at 240 volts RMS ( much less than the usual 2000 volts on the secondary, you should not have to worry about saturation. ( this assumes you are using AC voltage.). Thanks, that helps! I've been thinking about those 2000 volts. If that's the normal voltage on this coil, it's probably going to take close to that to saturate the core. I mean, wouldn't they design for the core to be close to saturation, to minimize the core size needed? Only at line frequency. With DC exitation the same flux density will be reached when the DC reaches the same level as the normal line freqency magnetising current (i.e the no load current). With DC, the voltage needed to reach this current will typically be about 5% of the rated line frequency voltage provided the magnetic circuit is closed (no air gap) My interest in saturation is 2 fold: I don't want to run beyond saturation 'cause of the extra heat, and at saturation is where the maximum pull will be. Now, about ACC. To use as an electromagnet, I have full-wave rectification, unfiltered. Although the coil's inductance will do some smoothing (I wish my scope was working). My intuition is that the DC component of the current will be determined by the coil resistance and that will produce flux proportional to the number of coil turns. So, the question is whether the DC current will saturate it before 240v. Or be too high for the coil's wire guage. Because the rated line frequency full load current is very much larger than the no load magnetising current, DC excitation will saturate the core long before rated full load current is reached. This applies when the magnetic circuit is as fully closed as in the original transformer. If it is only partially closed with perhaps inferior iron or small airgap, proportionally more current will be needed. But the bottom line is that I'm going to be using 240v max (full wave) and as long as it isn't saturated then, I'll be getting the maximum pull available. 240V should be ample. Jim None of the text you quote was written by me. I'm sorry about the error - it was very bad editing on my part. I hope it has not caused you any difficulty. With apologies. Jim |
#94
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Testing MOT as electromagnet - this just in
The saga continues. Today's testing:
_COIL HEATING_ I used 160v AC into the bridge. Same as used for the first tests I did Wednesday. I assumed a 30% duty cycle (what MagnaBend uses), with 3 seconds on & 7 off. I set up a 555 timer to do this and let it run a half hour. It probably didn't reach steady state by then, but it's unlikely that I'd ever use it longer. The temperature rise was 95C (172F). Pretty modest, given transformer classes are 80, 115, & 150C. Wondering if the 3 second bend time was realistic, I watched the MagnaBend video again & measured the time it took to make a bend. It was about 5 seconds actual bending and 5 seconds or so lining it up. So I ran another test: 5 seconds on, 10 off (33% duty cycle). I ran this for 2 minutes (8 cycles). 8 bends being the most I'd ever do at a time. 85C rise. Then, a balls-to-the-wall test: 250v applied (to the bridge). 5 applications of 4 seconds each & 10 seconds off. 4 or 5 bends is probably a typical job. I usually only do 1 or 2. A small 39C rise. _PULL_ My previous pull/grip/force measurements were done with 120v. Looking for the absolute maximum that I could get, I tried 250v. Knowing that I couldn't measure the full force, I put 3 equal bars on the magnet and loaded one of them (the middle one). It lifted 362 lbs, but was heating up rapidly and as it heated the resistance went up and the current down, reducing the pull. It let go after a minute or so. I didn't intend to run a minute's test, it's just that it took me that long to get the load off the ground. A single bar covering the poles would then exert 3 x 362 = 1086 lbs !!!! Or 290 lbs per inch. The MagnaBend exerts 250 lbs per inch. The temperature rise was 120C. The sustained "on" time was the cause. _SUMMARY_ With 120v applied, the force was 740 lbs (about 200 lbs per in). Although I didn't measure heating at this voltage, it could probably run "forever" (100% duty cycle) without overheating. At 160v, a 30% duty cycle would keep the coil from overheating. Force was not measured. At 250v, the force was 1086 lbs (290 lbs per in). A 47% increase from the 120v force, but with a 108% increase in voltage. Definitely non-linear. A 30% duty cycle would likely be OK (I didn't test to steady state), but the "on" period could not be more than 5 - 10 seconds, with a minute's "on" getting the coil very hot. Were I to actually get around to building a magnetic bender using MOT electromagnets, I would probably include a variac in the controls. It would allow the use of 120v when that amount of force would do, without worrying about heat. But it could be cranked up to 250 when the most force was needed. Now, the next step would be to test other MOT electromagnets to see how much variation there is between them. But that's not going to happen. I'm going to assume a close-enough between them, but check that the secondary turns are close. By dividing the cross sectional area by the wire diameter. Bob |
#95
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Magnabend
Joseph Gwinn wrote:
... The fancy hinges are another matter. In the US, I didn't find any patents assigned to Magnabend, but I bet there are patents somewhere, starting with Australia. ... The thread on the Practical Machinist forum about MagnaBends had a reply from an Australian who had worked with the inventors of the brake and hinges. He posted this link to the patent: http://www.google.com/patents/about?id=n3A2AAAAEBAJ I still don't understand them. Building them would be totally out the question for me. But, I've been thinking about it. The hinge does offer the unique ability to bend at the end of the brake. But the need to make such bends is pretty limited, for me anyhow. Even the MagnaBend video only shows one sequence of bends at the end, and many more along the clamp bar. So, for me, the biggest advantage is the magnetic clamp, which could be homemade fairly easily. And use traditional pin hinges at the ends. The bending bar would have to be stiffer without the hinges in the middle, but that's easy enough. Bob |
#96
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Magnabend
In article ,
Bob Engelhardt wrote: Joseph Gwinn wrote: ... The fancy hinges are another matter. In the US, I didn't find any patents assigned to Magnabend, but I bet there are patents somewhere, starting with Australia. ... The thread on the Practical Machinist forum about MagnaBends had a reply from an Australian who had worked with the inventors of the brake and hinges. He posted this link to the patent: http://www.google.com/patents/about?id=n3A2AAAAEBAJ Wonderful. I knew there had to be a patent. Using information from the patent, I've also found some relevant information in Alan Stuart Bottomley's resume: http://aaybee.com.au/Resume%20Dec%202010.mht.htm I still don't understand them. The patent isn't awfully clear. But the idea cannot be all that complex. It's probably a beefy variation on the invisible hinges used on kitchen cabinets. Building them would be totally out the question for me. That isn't at all obvious just yet. Some of the later hinge designs look perfectly practical for a HSM, being two or three orthogonal pin-in-sleeve hinge joints in mechanical series. But, I've been thinking about it. The hinge does offer the unique ability to bend at the end of the brake. But the need to make such bends is pretty limited, for me anyhow. Even the MagnaBend video only shows one sequence of bends at the end, and many more along the clamp bar. So, for me, the biggest advantage is the magnetic clamp, which could be homemade fairly easily. And use traditional pin hinges at the ends. The bending bar would have to be stiffer without the hinges in the middle, but that's easy enough. Although there has been a thread on using discarded microwave oven power transformers as the magnet, it isn't obvious that this is necessary. Given that the excitation current will be DC, laminated steel is not needed, so one could cobble a magnetic circuit from ordinary mild steel. Joe Gwinn |
#97
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Magnabend
In article ,
Joseph Gwinn wrote: In article , Bob Engelhardt wrote: Joseph Gwinn wrote: ... The fancy hinges are another matter. In the US, I didn't find any patents assigned to Magnabend, but I bet there are patents somewhere, starting with Australia. ... The thread on the Practical Machinist forum about MagnaBends had a reply from an Australian who had worked with the inventors of the brake and hinges. He posted this link to the patent: http://www.google.com/patents/about?id=n3A2AAAAEBAJ Wonderful. I knew there had to be a patent. It's US patent 4,513,475 to Fenton. Using information from the patent, I've also found some relevant information in Alan Stuart Bottomley's resume: http://aaybee.com.au/Resume%20Dec%202010.mht.htm Which led to US patent 4,111,027 (to Bottomley), for the Magnabend itself. Note that 4,513,475 says that the original hinge design of the magnabend was not satisfactory, but does not say why. Joe Gwinn I still don't understand them. The patent isn't awfully clear. But the idea cannot be all that complex. It's probably a beefy variation on the invisible hinges used on kitchen cabinets. Building them would be totally out the question for me. That isn't at all obvious just yet. Some of the later hinge designs look perfectly practical for a HSM, being two or three orthogonal pin-in-sleeve hinge joints in mechanical series. But, I've been thinking about it. The hinge does offer the unique ability to bend at the end of the brake. But the need to make such bends is pretty limited, for me anyhow. Even the MagnaBend video only shows one sequence of bends at the end, and many more along the clamp bar. So, for me, the biggest advantage is the magnetic clamp, which could be homemade fairly easily. And use traditional pin hinges at the ends. The bending bar would have to be stiffer without the hinges in the middle, but that's easy enough. Although there has been a thread on using discarded microwave oven power transformers as the magnet, it isn't obvious that this is necessary. Given that the excitation current will be DC, laminated steel is not needed, so one could cobble a magnetic circuit from ordinary mild steel. Joe Gwinn |
#98
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Magnabend
Joseph Gwinn wrote:
Bob Engelhardt wrote: I still don't understand them [hinges]. The patent isn't awfully clear. But the idea cannot be all that complex. It's probably a beefy variation on the invisible hinges used on kitchen cabinets. That was my thought, then I realized that with cabinet hinges the axis of rotation isn't important. The axis for the MagnaBend hinges has to be the intersection of the clamp plane and the bending bar plane. Building them would be totally out the question for me. That isn't at all obvious just yet. Some of the later hinge designs look perfectly practical for a HSM, being two or three orthogonal pin-in-sleeve hinge joints in mechanical series. Maybe. One thing that troubled me was the patent's description of one axis of rotation intersecting another axis at yet a third axis. The thread on the Practical Machinist forum was started by a guy who was going to make a brake and had made a prototype or mock up of the hinge that he claimed worked. I could try one in pine, just to get the idea. .... Although there has been a thread on using discarded microwave oven power transformers as the magnet, it isn't obvious that this is necessary. Given that the excitation current will be DC, laminated steel is not needed, so one could cobble a magnetic circuit from ordinary mild steel. Yeah, that's a sub-thread in this thread G. I don't think that I want to do that much coil winding. You'd need a couple of hundred turns to keep the current at reasonable levels, and I'd want one at least 24" long. Bob |
#99
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Magnabend
In article ,
Bob Engelhardt wrote: Joseph Gwinn wrote: Bob Engelhardt wrote: I still don't understand them [hinges]. The patent isn't awfully clear. But the idea cannot be all that complex. It's probably a beefy variation on the invisible hinges used on kitchen cabinets. That was my thought, then I realized that with cabinet hinges the axis of rotation isn't important. The axis for the MagnaBend hinges has to be the intersection of the clamp plane and the bending bar plane. Building them would be totally out the question for me. That isn't at all obvious just yet. Some of the later hinge designs look perfectly practical for a HSM, being two or three orthogonal pin-in-sleeve hinge joints in mechanical series. Maybe. One thing that troubled me was the patent's description of one axis of rotation intersecting another axis at yet a third axis. I think I figured the fancy hinge out. They don't come out and say it (in 4,513,475), but they are more-or-less implementing a virtual ball joint: The center of rotation is the intersection point of the three hinge axes. In some variants, one of the hinge axes is a goinometer mechanism (the cylinder-segment bearings). In all cases, the point is to make the center of rotation be outside of the actual hinge mechanism. It takes a minimum of two such hinges to define the axis line about which rotation occurs, just like with ball joints in automobile steering gear. The three-pin hinge (figure 20) isn't stiff against side-to-side motion, so the hinges are provided in pairs, one hinge right-hand the other hinge left-hand, just like gloves. The thread on the Practical Machinist forum was started by a guy who was going to make a brake and had made a prototype or mock up of the hinge that he claimed worked. I could try one in pine, just to get the idea. Sounds like a real good idea. Although there has been a thread on using discarded microwave oven power transformers as the magnet, it isn't obvious that this is necessary. Given that the excitation current will be DC, laminated steel is not needed, so one could cobble a magnetic circuit from ordinary mild steel. Yeah, that's a sub-thread in this thread G. I don't think that I want to do that much coil winding. You'd need a couple of hundred turns to keep the current at reasonable levels, and I'd want one at least 24" long. The MagnaBend patent (4,111,027) gives some coil data in Column 5 Lines 5-12: "A specific construction of the above described tool had a length of 600 mm, a weight of 20 kg. (not including keepers), a coil formed from 22 guage copper wire and weighing 2.4 kg., operated on a 240 volt, single phase, 50 cycles per second AC supply and consumed, intermittently, 4 amps. That specific construction was able to exert a holding force on sheet metal of about 4 tonnes. " Apparently, the Australians used AWG (American Wire Gauge) sizes for copper back then, and probably have gone over to IEC metric wire sizes. In any event, #22 AWG wire with single build (thickness) insulation is 1.972 pounds per 1000 feet, and 2.4 Kg is (2.4)(2.2)= 5.28 pounds of wire, which would be 2,677 feet of #22 wire. The brake is 600mm wide, which is 600/25.4= 23.62" wide, call it 24" or 2 feet. A turn is therefore 4 feet, so 2677/4= 669.4 turns, call it 670 turns. This sounds like a lot, but it is certainly doable by hand, especially if one cobbles together a simple winding machine out of wood and powered by hand. One would wind on a wooden form, not on the iron, just as is done when winding a motor. From a cross-section drawing in the manual, the winding space is 20 by 28 mm (0.787" by 1.102", 0.868 square inches), which will accommodate 1191 turns of single build, so there is space. In practice, one would most likely use double build (to better handle the voltage in a single winding), allowing 1099 turns. There will also be heavy insulation between the coil and the iron; this will reduce the area available for winding. But it looks like we have a viable solution. This, for 220 volt systems. Fewer turns of heavier wire will yield the same magnetic flux in a 120 volt system. Roughly, 335 turns of #19 AWG wire, pulling 8 amps. The ampere-turns product is (4)(670)= 2,680 amp-turns. This yields a 4 metric tones clamping force in a length of 0.6 meters, or 4000/0.6 = 6,667 kilograms per meter, which is 372.5 pounds per inch. Joe Gwinn |
#100
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Magnabend
Joseph Gwinn wrote:
... Which led to US patent 4,111,027 (to Bottomley), for the Magnabend itself. Note that 4,513,475 says that the original hinge design of the magnabend was not satisfactory, but does not say why. I just read the MagnaBend patent* and found it very straight-forward, especially compared to the complexity of the hinge. The original hinges seem like a good idea: they aren't end mounted, so multiples could be used, and they don't project into the axis of rotation. I wonder how they were inadequate. The only shortcoming that occurs to me is that during rotation there is an area near the front edge of the bed that is opened up, leaving the material unsupported. It's a small area, but maybe it's enough to allow distortion in the material. I'd really like to know, 'cause those hinges would be so much simpler to build. Bob * - reading patents is so much easier with 2 monitors. My big one has the drawings, full screen, and the smaller one the description text. No scrolling up and down 'tween text & drawings. |
#101
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Magnabend
Joseph Gwinn wrote:
In article , Bob Engelhardt wrote: Joseph Gwinn wrote: Bob Engelhardt wrote: I still don't understand them [hinges]. The patent isn't awfully clear. But the idea cannot be all that complex. It's probably a beefy variation on the invisible hinges used on kitchen cabinets. That was my thought, then I realized that with cabinet hinges the axis of rotation isn't important. The axis for the MagnaBend hinges has to be the intersection of the clamp plane and the bending bar plane. Building them would be totally out the question for me. That isn't at all obvious just yet. Some of the later hinge designs look perfectly practical for a HSM, being two or three orthogonal pin-in-sleeve hinge joints in mechanical series. Maybe. One thing that troubled me was the patent's description of one axis of rotation intersecting another axis at yet a third axis. I think I figured the fancy hinge out. They don't come out and say it (in 4,513,475), but they are more-or-less implementing a virtual ball joint: The center of rotation is the intersection point of the three hinge axes. In some variants, one of the hinge axes is a goinometer mechanism (the cylinder-segment bearings). In all cases, the point is to make the center of rotation be outside of the actual hinge mechanism. It takes a minimum of two such hinges to define the axis line about which rotation occurs, just like with ball joints in automobile steering gear. The three-pin hinge (figure 20) isn't stiff against side-to-side motion, so the hinges are provided in pairs, one hinge right-hand the other hinge left-hand, just like gloves. The thread on the Practical Machinist forum was started by a guy who was going to make a brake and had made a prototype or mock up of the hinge that he claimed worked. I could try one in pine, just to get the idea. Sounds like a real good idea. Although there has been a thread on using discarded microwave oven power transformers as the magnet, it isn't obvious that this is necessary. Given that the excitation current will be DC, laminated steel is not needed, so one could cobble a magnetic circuit from ordinary mild steel. Yeah, that's a sub-thread in this thread G. I don't think that I want to do that much coil winding. You'd need a couple of hundred turns to keep the current at reasonable levels, and I'd want one at least 24" long. The MagnaBend patent (4,111,027) gives some coil data in Column 5 Lines 5-12: "A specific construction of the above described tool had a length of 600 mm, a weight of 20 kg. (not including keepers), a coil formed from 22 guage copper wire and weighing 2.4 kg., operated on a 240 volt, single phase, 50 cycles per second AC supply and consumed, intermittently, 4 amps. That specific construction was able to exert a holding force on sheet metal of about 4 tonnes. " Apparently, the Australians used AWG (American Wire Gauge) sizes for copper back then, and probably have gone over to IEC metric wire sizes. In any event, #22 AWG wire with single build (thickness) insulation is 1.972 pounds per 1000 feet, and 2.4 Kg is (2.4)(2.2)= 5.28 pounds of wire, which would be 2,677 feet of #22 wire. The brake is 600mm wide, which is 600/25.4= 23.62" wide, call it 24" or 2 feet. A turn is therefore 4 feet, so 2677/4= 669.4 turns, call it 670 turns. Can you be certain the Australians were using AWG and not SWG, it makes a difference. Their video mentions it bending "16 gauge" and their specifications mention 16g/1.6mm which would indicate SWG is in use at least for the metal specs, US metal gauges are thinner for the same number. This sounds like a lot, but it is certainly doable by hand, especially if one cobbles together a simple winding machine out of wood and powered by hand. One would wind on a wooden form, not on the iron, just as is done when winding a motor. From a cross-section drawing in the manual, the winding space is 20 by 28 mm (0.787" by 1.102", 0.868 square inches), which will accommodate 1191 turns of single build, so there is space. In practice, one would most likely use double build (to better handle the voltage in a single winding), allowing 1099 turns. There will also be heavy insulation between the coil and the iron; this will reduce the area available for winding. But it looks like we have a viable solution. This, for 220 volt systems. Fewer turns of heavier wire will yield the same magnetic flux in a 120 volt system. Roughly, 335 turns of #19 AWG wire, pulling 8 amps. The ampere-turns product is (4)(670)= 2,680 amp-turns. This yields a 4 metric tones clamping force in a length of 0.6 meters, or 4000/0.6 = 6,667 kilograms per meter, which is 372.5 pounds per inch. Joe Gwinn |
#102
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Magnabend
I've been following this thread with interest, but not actually planning on
trying to build this type of machine. I think that finding a way to get the 51" $375 Craigslist listing unit delivered would be a worthwhile consideration..but I do understand the curiousity of potentially being able to make a useful machine from salvaged parts. I was thinking that the primary windings may be better than the secondaries, but you likely know better, and the number of turns on the secondary side is much greater than the primary. I haven't looked at a MOT in a long while, but cutting away a primary winding (or either winding) from the E-core, I think that would leave more room available for a custom wound bobbin that fills the entire E-core.. making a much stronger electromagnet.. so it would be a determination of which is the best wire gage to use, and where to get a lot of it, then a method of carefully winding the bobbin (flat, level layers for the highest number of windings). My local motor shop has lent out large spools of magnet wire in the past, then they weigh the spool when it's returned and charge a very reasonable fee for how much weight was removed. If one had a significant number of identical MOTs, doubling either winding onto the E-core may be possible. A second aspect is the mating surfaces of the E-core sections of the core to a separate piece of metal. I'm thinking that the most effective coupling of the two surfaces would need to be very precise for the most effective magnetic transfer to the steel bar.. possibly a very close tolerance smooth/flat surface that a surface grinder might provide. Attachment of the E-cores could then be held securely to the steel bar by tack welding the E-cores in position. I believe that winding the coil to fit directly on the lower section bar would be the best solution, for maximum efficiency. -- WB .......... "David Billington" wrote in message ... Can you be certain the Australians were using AWG and not SWG, it makes a difference. Their video mentions it bending "16 gauge" and their specifications mention 16g/1.6mm which would indicate SWG is in use at least for the metal specs, US metal gauges are thinner for the same number. |
#103
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Magnabend
On Jan 24, 9:13*am, "Wild_Bill" wrote:
I haven't looked at a MOT in a long while, but cutting away a primary winding (or either winding) from the E-core, I think that would leave more room available for a custom wound bobbin that fills the entire E-core.. making a much stronger electromagnet.. so it would be a determination of which is the best wire gage to use, and where to get a lot of it, then a method of carefully winding the bobbin (flat, level layers for the highest number of windings). MOT's are cheap. Usually available for nothing from Microwave ovens that have something wrong with them. So forget winding. Just salvage a HV winding from another MOT, and slip it on in place of the primary. Connect the two windings in parallel or series depending what you have for power to energize the magnet. Dan |
#104
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Magnabend
Wild_Bill wrote:
.... I was thinking that the primary windings may be better than the secondaries, but you likely know better, and the number of turns on the secondary side is much greater than the primary. It's basically a volts-amps choice on the supply. High voltage/low amps using the secondary; low voltage/high amps if the primary. The winding ratio is about 17:1 (2000:120), so for the same amp-turns, you'd need 17 times the current using the primary as using the secondary. ... If one had a significant number of identical MOTs, doubling either winding onto the E-core may be possible. I did this once to get an isolation transformer: I put 2 primaries on the same core. It took a long time to find 2 MOTs with the same winding size. They are very closely fitted, so there is not much margin. I now have 14 extra MOTs as a result of that search (i.e., the 14 are ones that didn't match anything). A second aspect is the mating surfaces of the E-core sections of the core to a separate piece of metal. I'm thinking that the most effective coupling of the two surfaces would need to be very precise for the most effective magnetic transfer to the steel bar.. possibly a very close tolerance smooth/flat surface that a surface grinder might provide. Attachment of the E-cores could then be held securely to the steel bar by tack welding the E-cores in position. I agree. But the MOTs are already pretty flat - they don't want to have air gaps either. I would fasten them in place & then surface grind (Blanchard would be good enough). I believe that winding the coil to fit directly on the lower section bar would be the best solution, for maximum efficiency. I have wound a couple of windings for customized MOTs and it's not something that I want to do a lot of. Bob |
#105
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Testing MOT as electromagnet - this just in
I've been thinking: how much better would pure (regulated) DC be? For a
given magnetization, would the current be less? Or would the heating be less? A previous Reply said that the DC voltage only has to be about 5% of the AC voltage to reach the same level of magnetization. In that case the 200v secondary would only need 100v DC. I'm using more than that, but I'm wondering if it's because the unfiltered DC has so much ripple. Anyhow, I could build a 100v regulator, but would it be worth it? Thanks, Bob |
#106
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Testing MOT as electromagnet - this just in
"Bob Engelhardt" wrote in message ... I've been thinking: how much better would pure (regulated) DC be? For a given magnetization, would the current be less? Or would the heating be less? A previous Reply said that the DC voltage only has to be about 5% of the AC voltage to reach the same level of magnetization. In that case the 200v secondary would only need 100v DC. I'm using more than that, but I'm wondering if it's because the unfiltered DC has so much ripple. Anyhow, I could build a 100v regulator, but would it be worth it? Thanks, Bob I seriously doubt it would be worth it. The MOT is acting as an inductor in this case and it will be smoothing out the current ripple as it is. If you have an o'scope add a 1 ohm resistor in series with a MOT leg and attach the scope across the resistor to monitor the current. You'll need to float the scope (or isolate the AC source to the MOT) as both sides of the resistor will be hot. The waveform will have much less ripple than the excitation voltage waveform. Art |
#107
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Testing MOT as electromagnet - this just in
Bob Engelhardt wrote: I've been thinking: how much better would pure (regulated) DC be? For a given magnetization, would the current be less? Or would the heating be less? A previous Reply said that the DC voltage only has to be about 5% of the AC voltage to reach the same level of magnetization. In that case the 200v secondary would only need 100v DC. I'm using more than that, but I'm wondering if it's because the unfiltered DC has so much ripple. Anyhow, I could build a 100v regulator, but would it be worth it? Why regulate it? A simple filter would make a huge improvement. Connect the cores in series to drop the DC voltage in half. -- You can't fix stupid. You can't even put a band-aid on it, because it's Teflon coated. |
#108
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Magnabend
In article ,
Bob Engelhardt wrote: Joseph Gwinn wrote: ... Which led to US patent 4,111,027 (to Bottomley), for the Magnabend itself. Note that 4,513,475 says that the original hinge design of the magnabend was not satisfactory, but does not say why. I just read the MagnaBend patent* and found it very straight-forward, especially compared to the complexity of the hinge. The original hinges seem like a good idea: they aren't end mounted, so multiples could be used, and they don't project into the axis of rotation. I wonder how they were inadequate. The only shortcoming that occurs to me is that during rotation there is an area near the front edge of the bed that is opened up, leaving the material unsupported. It's a small area, but maybe it's enough to allow distortion in the material. I'd really like to know, 'cause those hinges would be so much simpler to build. Those original hinges looked hard to make, and I wondered if they would tend to jam, especially if a little dirt got into them. Also, the cylinder axes would need to be precisely colinear, or they will tear each other apart. Virtual ball joints will not have this problem. Bottomley has a web site. I wonder if he will answer questions. Bob * - reading patents is so much easier with 2 monitors. My big one has the drawings, full screen, and the smaller one the description text. No scrolling up and down 'tween text & drawings. I have one big display, big enough for side-by-side display, but usually use the space to make the text big. Joe Gwinn |
#109
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Magnabend
In article ,
David Billington wrote: Joseph Gwinn wrote: [snip] The MagnaBend patent (4,111,027) gives some coil data in Column 5 Lines 5-12: "A specific construction of the above described tool had a length of 600 mm, a weight of 20 kg. (not including keepers), a coil formed from 22 guage copper wire and weighing 2.4 kg., operated on a 240 volt, single phase, 50 cycles per second AC supply and consumed, intermittently, 4 amps. That specific construction was able to exert a holding force on sheet metal of about 4 tonnes. " Apparently, the Australians used AWG (American Wire Gauge) sizes for copper back then, and probably have gone over to IEC metric wire sizes. In any event, #22 AWG wire with single build (thickness) insulation is 1.972 pounds per 1000 feet, and 2.4 Kg is (2.4)(2.2)= 5.28 pounds of wire, which would be 2,677 feet of #22 wire. The brake is 600mm wide, which is 600/25.4= 23.62" wide, call it 24" or 2 feet. A turn is therefore 4 feet, so 2677/4= 669.4 turns, call it 670 turns. Can you be certain the Australians were using AWG and not SWG, it makes a difference. Their video mentions it bending "16 gauge" and their specifications mention 16g/1.6mm which would indicate SWG is in use at least for the metal specs, US metal gauges are thinner for the same number. SWG is for sheet steel, while AWG is for copper wire. I did google around a lot, and all indications I found were that they really did mean American Wire Gauge, although I would have guessed that they would use BSG (British WG). The difference between AWG and BWG isn't large. But I feared that AWG really meant Australian WG. Actually, I was surprised to see wire gauge listed, versus diameter in millimeters. If anyone from the Land of OZ is listening, please chime in. Joe Gwinn |
#110
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Magnabend
Joseph Gwinn wrote:
Bob Engelhardt wrote: ... those [original] hinges would be so much simpler to build. Those original hinges looked hard to make, and I wondered if they would tend to jam, especially if a little dirt got into them. Also, the cylinder axes would need to be precisely colinear, or they will tear each other apart. Virtual ball joints will not have this problem. "Eye of the beholder", I guess. Bottomley has a web site. I wonder if he will answer questions. Good idea. I've asked on the Practical Machinist forum. If I don't get an answer, I'll try Bottomly. Or you could. Bob |
#111
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Magnabend
In article ,
Bob Engelhardt wrote: Joseph Gwinn wrote: Bob Engelhardt wrote: ... those [original] hinges would be so much simpler to build. Those original hinges looked hard to make, and I wondered if they would tend to jam, especially if a little dirt got into them. Also, the cylinder axes would need to be precisely colinear, or they will tear each other apart. Virtual ball joints will not have this problem. "Eye of the beholder", I guess. I think that the required precision is the issue. They look like a centerless goinometer mechanism, which requires precision to work well. http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=860 A bunch of hinges should be easier to make, and that's what MagnaBend ultimately went to. Bottomley has a web site. I wonder if he will answer questions. Good idea. I've asked on the Practical Machinist forum. If I don't get an answer, I'll try Bottomly. Or you could. We can work together on the questions to be asked. Joe Gwinn |
#112
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Magnabend
Bob Engelhardt wrote:
... I've asked on the Practical Machinist forum. If I don't get an answer, I'll try Bottomly. ... I just got the reply on P-M: "I have spoken to Alan about the hinges and he has brought a box of the prototype hinges into work today. I think he will write a bit of a story about the Magnabend development over the next week or so. Geoff is away on holiday at the moment (far southwest of Tasmania) where there is no technology, but when he gets back I will see if he want to add something." Bob |
#113
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Magnabend
"Jon Danniken" wrote in message ... I had never heard of these before today, when one of these showed up in the local Craigslist (no connection to the seller). Found a video on youtube, and it certainly does look like an interesting tool. http://www.youtube.com/watch?v=OipSiPSRti8 I don't do enough bending (or have the space) to justify getting one of these, but this caught my eye. Anyone played with one of these before? Jon http://www.magnabend.com/ They are pretty good. We had one at the school shop I attended. They will do thing you couldn't do with anything else. |
#114
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Magnabend
In article ,
Bob Engelhardt wrote: Bob Engelhardt wrote: ... I've asked on the Practical Machinist forum. If I don't get an answer, I'll try Bottomly. ... I just got the reply on P-M: "I have spoken to Alan about the hinges and he has brought a box of the prototype hinges into work today. I think he will write a bit of a story about the Magnabend development over the next week or so. Geoff is away on holiday at the moment (far southwest of Tasmania) where there is no technology, but when he gets back I will see if he want to add something." This is excellent news. I wonder if they realized that they have a fan club. Joe Gwinn |
#115
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Magnabend
In article ,
Joseph Gwinn wrote: In article , Bob Engelhardt wrote: Bob Engelhardt wrote: ... I've asked on the Practical Machinist forum. If I don't get an answer, I'll try Bottomly. ... I just got the reply on P-M: "I have spoken to Alan about the hinges and he has brought a box of the prototype hinges into work today. I think he will write a bit of a story about the Magnabend development over the next week or so. Geoff is away on holiday at the moment (far southwest of Tasmania) where there is no technology, but when he gets back I will see if he want to add something." This is excellent news. I wonder if they realized that they have a fan club. I may know what the problem with the original hinges is: When bending at one end, a major claimed benefit of the MagnaBend, the machine frame will rack a bit, jamming the hinges. Thus the need for a virtual ball joint hinge. Joe Gwinn |
#116
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Magnabend
Joseph Gwinn wrote:
This is excellent news. I wonder if they realized that they have a fan club. Joe Gwinn I'm following this but probably won't be building one. I'm one of those folks that just likes to absorb interesting technology :-) I may even build one or more of the hinges if I can ever] see some "real" sketches. The (what passes for a) dwg on the patent doesn't quite make it. So keep the thread going here or let me know if you take it elsewhere please. ...Lew... |
#117
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Magnabend
In article ,
Lewis Hartswick wrote: Joseph Gwinn wrote: This is excellent news. I wonder if they realized that they have a fan club. Joe Gwinn I'm following this but probably won't be building one. I'm one of those folks that just likes to absorb interesting technology :-) I was thinking of maybe building a one foot wide unit that clamps to a bench, mainly to save on storage space. I don't really need to make that many boxes and pans, so it would be for the joy of building a tool. I may even build one or more of the hinges if I can ever] see some "real" sketches. The (what passes for a) dwg on the patent doesn't quite make it. A good comparison is a gimbal mechanism, but with the rings reduced to sectors and half the pivot bearings missing. http://en.wikipedia.org/wiki/Gimbal_lock So keep the thread going here or let me know if you take it elsewhere please. No plans to move have been promulgated. Joe Gwinn |
#118
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Magnabend
Bob Engelhardt wrote:
Bob Engelhardt wrote: ... I've asked on the Practical Machinist forum. If I don't get an answer, I'll try Bottomly. ... I just got the reply on P-M: "I have spoken to Alan about the hinges and he has brought a box of the prototype hinges into work today. I think he will write a bit of a story about the Magnabend development over the next week or so. Geoff is away on holiday at the moment (far southwest of Tasmania) where there is no technology, but when he gets back I will see if he want to add something." Bob Alan Bottomly (the MagnaBend's inventor) has joined the discussion on the Practical Machinist forum. As to the original hinges ("cup hinges" he calls them), he said they tended to jam when being returned from large-angle bends. Too little engagement after 90 degrees. He also had comments about wire size used for the magnets, but I'm not going to keep repeating what's said & recommend that interested RCM'ers join P-M. Bob |
#119
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Magnabend
Bob Engelhardt wrote:
Bob Engelhardt wrote: Bob Engelhardt wrote: ... I've asked on the Practical Machinist forum. If I don't get an answer, I'll try Bottomly. ... I just got the reply on P-M: "I have spoken to Alan about the hinges and he has brought a box of the prototype hinges into work today. I think he will write a bit of a story about the Magnabend development over the next week or so. Geoff is away on holiday at the moment (far southwest of Tasmania) where there is no technology, but when he gets back I will see if he want to add something." Bob Alan Bottomly (the MagnaBend's inventor) has joined the discussion on the Practical Machinist forum. As to the original hinges ("cup hinges" he calls them), he said they tended to jam when being returned from large-angle bends. Too little engagement after 90 degrees. He also had comments about wire size used for the magnets, but I'm not going to keep repeating what's said & recommend that interested RCM'ers join P-M. Thanks for the P-M cite, Bob. I enjoyed hearing from Alan. At the risk of turning the 'elegant and beautiful' into the 'byzantine and ugly', what would prevent one from designing a current-mode PWM controller so that electromagnets with 'too thick' wire could be driven optimally, with just the proper amount of current for maximum attraction yet not so high as to cause excessive power dissipation? I don't understand the conflict with using multiple MOTs as electromagnets. Every second electromagnet could be driven with opposite polarity so that no repulsion occurs between them, yes? --Winston |
#120
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Magnabend
Winston wrote: Bob Engelhardt wrote: Bob Engelhardt wrote: Bob Engelhardt wrote: ... I've asked on the Practical Machinist forum. If I don't get an answer, I'll try Bottomly. ... I just got the reply on P-M: "I have spoken to Alan about the hinges and he has brought a box of the prototype hinges into work today. I think he will write a bit of a story about the Magnabend development over the next week or so. Geoff is away on holiday at the moment (far southwest of Tasmania) where there is no technology, but when he gets back I will see if he want to add something." Bob Alan Bottomly (the MagnaBend's inventor) has joined the discussion on the Practical Machinist forum. As to the original hinges ("cup hinges" he calls them), he said they tended to jam when being returned from large-angle bends. Too little engagement after 90 degrees. He also had comments about wire size used for the magnets, but I'm not going to keep repeating what's said & recommend that interested RCM'ers join P-M. Thanks for the P-M cite, Bob. I enjoyed hearing from Alan. At the risk of turning the 'elegant and beautiful' into the 'byzantine and ugly', what would prevent one from designing a current-mode PWM controller so that electromagnets with 'too thick' wire could be driven optimally, with just the proper amount of current for maximum attraction yet not so high as to cause excessive power dissipation? I don't understand the conflict with using multiple MOTs as electromagnets. Every second electromagnet could be driven with opposite polarity so that no repulsion occurs between them, yes? You could connect the primaries in series. -- You can't fix stupid. You can't even put a band-aid on it, because it's Teflon coated. |
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