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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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#1
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DIY magnetic bend brake - was "Magnabend"
I just made a 2-MOTE (MOT electromagnet) brake as an evaluation of the idea:
-------- I made it small to keep the time, effort, and materials small. But it has an 8-1/2" capacity, which would be enough for a lot of the stuff I do (e.g. electronics project boxes). Unfortunately the results are very disappointing. I ran the MOTE's on 250v (AC into the bridge) and could not quite finish the bend on .040 (about 20 ga) steel. 18ga (.050) started, but only got to about 45 degrees before the clamping bar started sliding back. .030 bent very nicely and although too light for a lot of stuff, boxes in that guage would be useful. So I have definitely ruled out MOTE's for the 24 inch brake that I'd like to make. I'll be thinking about what it would take to wind the coil for that. I expect that it would be painful, but the challenge would be interesting. Bob |
#2
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DIY magnetic bend brake - was "Magnabend"
Bob Engelhardt wrote:
I just made a 2-MOTE (MOT electromagnet) brake as an evaluation of the idea: -------- Oops ... that "-----" was a placeholder for the pic's URL that I forgot to do. http://home.comcast.net/~bobengelhardt/MOTEbrake.jpg |
#3
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DIY magnetic bend brake - was "Magnabend"
"Bob Engelhardt" wrote in message ... I just made a 2-MOTE (MOT electromagnet) brake as an evaluation of the idea: -------- I made it small to keep the time, effort, and materials small. But it has an 8-1/2" capacity, which would be enough for a lot of the stuff I do (e.g. electronics project boxes). Unfortunately the results are very disappointing. I ran the MOTE's on 250v (AC into the bridge) and could not quite finish the bend on .040 (about 20 ga) steel. 18ga (.050) started, but only got to about 45 degrees before the clamping bar started sliding back. .030 bent very nicely and although too light for a lot of stuff, boxes in that guage would be useful. So I have definitely ruled out MOTE's for the 24 inch brake that I'd like to make. I'll be thinking about what it would take to wind the coil for that. I expect that it would be painful, but the challenge would be interesting. Bob You have room to add another coil on each core. If you put the added coil in parallel with the existing coil, I think that would double the holding power. That is "if you don't saturate the iron core". I have no clue where you are an the saturation curve. Mikek |
#4
Posted to rec.crafts.metalworking
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DIY magnetic bend brake - was "Magnabend"
Bob Engelhardt wrote:
I just made a 2-MOTE (MOT electromagnet) brake as an evaluation of the idea: -------- I made it small to keep the time, effort, and materials small. But it has an 8-1/2" capacity, which would be enough for a lot of the stuff I do (e.g. electronics project boxes). Unfortunately the results are very disappointing. I ran the MOTE's on 250v (AC into the bridge) and could not quite finish the bend on .040 (about 20 ga) steel. 18ga (.050) started, but only got to about 45 degrees before the clamping bar started sliding back. .030 bent very nicely and although too light for a lot of stuff, boxes in that guage would be useful. So I have definitely ruled out MOTE's for the 24 inch brake that I'd like to make. I'll be thinking about what it would take to wind the coil for that. I expect that it would be painful, but the challenge would be interesting. BRAVO Bob! I love this stuff! (And I don't often shout.) http://home.comcast.net/~bobengelhardt/MOTEbrake.jpg 1) It did occur to me that the line between the center of your hinge and the gap between the clamping leaf and bending leaf appears off - center a bit, which would cause the workpiece to be lifted unnecessarily. See how Dave used a *piano* hinge? Kewl! http://www.ch601.org/tools/bendbrake/brakeplans.pdf 2) Can you use a permanent magnet to be sure your MOTEs are indeed out-of phase magnetically? (With your head *out* of the path of the magnet, preferably!) 3) As practice for the next design, would you consider removing both of your windings, welding both your cores together and providing a rectangular winding that encloses both center legs? --Winston |
#5
Posted to rec.crafts.metalworking
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DIY magnetic bend brake - was "Magnabend"
Bob Engelhardt wrote:
I just made a 2-MOTE (MOT electromagnet) brake as an evaluation of the idea: -------- I made it small to keep the time, effort, and materials small. But it has an 8-1/2" capacity, which would be enough for a lot of the stuff I do (e.g. electronics project boxes). Unfortunately the results are very disappointing. I ran the MOTE's on 250v (AC into the bridge) and could not quite finish the bend on .040 (about 20 ga) steel. 18ga (.050) started, but only got to about 45 degrees before the clamping bar started sliding back. .030 bent very nicely and although too light for a lot of stuff, boxes in that guage would be useful. So I have definitely ruled out MOTE's for the 24 inch brake that I'd like to make. I'll be thinking about what it would take to wind the coil for that. I expect that it would be painful, but the challenge would be interesting. Interesting experiment. If you have any MOTs left over it might be interesting to ignore the secondaries and hook up three of them with the primaries in series. Jon |
#6
Posted to rec.crafts.metalworking
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DIY magnetic bend brake - was "Magnabend"
"Bob Engelhardt" wrote in message ... I just made a 2-MOTE (MOT electromagnet) brake as an evaluation of the idea: -------- I made it small to keep the time, effort, and materials small. But it has an 8-1/2" capacity, which would be enough for a lot of the stuff I do (e.g. electronics project boxes). Unfortunately the results are very disappointing. I ran the MOTE's on 250v (AC into the bridge) and could not quite finish the bend on .040 (about 20 ga) steel. 18ga (.050) started, but only got to about 45 degrees before the clamping bar started sliding back. .030 bent very nicely and although too light for a lot of stuff, boxes in that guage would be useful. So I have definitely ruled out MOTE's for the 24 inch brake that I'd like to make. I'll be thinking about what it would take to wind the coil for that. I expect that it would be painful, but the challenge would be interesting. Bob Very nice Bob. An observation & comments. The bar you have welded to the front (hinge side) legs of the MOTs will short out a lot of the flux if the MOTs are wired out of phase. This is happening right where the most flux is needed to effectively clamp the work piece. The steel angle piece the MOTs are sitting on will also short flux. Fixing that is trivial - wire them in phase. Is your top clamping bar too thin? A thin bar will saturate and not provide the full force the MOTs are capable of delivering. Adding a block of steel between the center legs and another across the back legs will distribute the external flux more evenly across the unit. This will provide better hold down force especially with a saturating top bar. Don't add any steel which narrows the gap between the center and outer legs of the MOT as this will reduce the external flux available. Art |
#7
Posted to rec.crafts.metalworking
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DIY magnetic bend brake - was "Magnabend"
Rich Grise wrote:
mike wrote: On Feb 12, 12:43?pm, Bob Engelhardt wrote: I just made a 2-MOTE (MOT electromagnet) brake as an evaluation of the ,,, Cool, the way you just go ahead and make things is inspiring. Looking at the picture, I was surprised that one end was left open on the electro-magnets, I thought you'd need it 'capped' to concentrate the flux, but it's been along time since I studied that kind of stuff in school. A "cap" would "short out" the magnetic field - the workpiece itself completes the "magnetic circuit." Cheers! Rich there's no way a piece of 20 guage sheet steel will complete the magnetic circuit. If the work was 3/4" thick tranformer iron, like the missing I's off the E cores, that would be perfect, and the clamping force would be as good as it gets for transformer cores. A keeper plate over the work would help too with getting the most clamping force when using something like transformer cores in a lifting/holding type application. |
#8
Posted to rec.crafts.metalworking
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DIY magnetic bend brake - was "Magnabend"
Bob Engelhardt wrote:
Bob Engelhardt wrote: I just made a 2-MOTE (MOT electromagnet) brake as an evaluation of the idea: -------- Oops ... that "-----" was a placeholder for the pic's URL that I forgot to do. http://home.comcast.net/~bobengelhardt/MOTEbrake.jpg Well it looks like you have room for about twice as many turns on the coils so you should be in petty good shape if you fill the winding space. ...lew... |
#9
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DIY magnetic bend brake - was "Magnabend"
On Sat, 12 Feb 2011 13:52:48 -0800, "Artemus"
wrote: "Bob Engelhardt" wrote in message ... I just made a 2-MOTE (MOT electromagnet) brake as an evaluation of the idea: -------- I made it small to keep the time, effort, and materials small. But it has an 8-1/2" capacity, which would be enough for a lot of the stuff I do (e.g. electronics project boxes). Unfortunately the results are very disappointing. I ran the MOTE's on 250v (AC into the bridge) and could not quite finish the bend on .040 (about 20 ga) steel. 18ga (.050) started, but only got to about 45 degrees before the clamping bar started sliding back. .030 bent very nicely and although too light for a lot of stuff, boxes in that guage would be useful. So I have definitely ruled out MOTE's for the 24 inch brake that I'd like to make. I'll be thinking about what it would take to wind the coil for that. I expect that it would be painful, but the challenge would be interesting. Bob Very nice Bob. An observation & comments. The bar you have welded to the front (hinge side) legs of the MOTs will short out a lot of the flux if the MOTs are wired out of phase. This is happening right where the most flux is needed to effectively clamp the work piece. The steel angle piece the MOTs are sitting on will also short flux. Fixing that is trivial - wire them in phase. Is your top clamping bar too thin? A thin bar will saturate and not provide the full force the MOTs are capable of delivering. Adding a block of steel between the center legs and another across the back legs will distribute the external flux more evenly across the unit. This will provide better hold down force especially with a saturating top bar. Don't add any steel which narrows the gap between the center and outer legs of the MOT as this will reduce the external flux available. Art A workmanlike effort - I'm surprised that it's not satisfactory. A few possible thoughts You've welded the Es to the fixed bar. As Art has pointed out it's essential that these are both N (or both S) Poles. The weld also needs to be machined dead flat - even a few thou gap reduces the holding force. You haven't shown the keeper bar that needs to be placed over the workpiece. This again needs to be flat and at least as thick as the outer arm of the E. With the two old primaries parallel connected and fed from a bridge rectifier The DC component of the rectified AC will be the MEAN value of the supply voltage i.e. 0.9 x RMS value. About 1000uf across the primaries will raise it to near the supply voltage peak value - about 1.4 x RMS. As a final desperate move feed the primaries from a voltage doubler. Leave the rectifier + and - outputs connnected to the windings. Link the two rectifier AC inputs together. Connect the + side of a 1000uf electrolytic to the two joined AC inputs. Connect one side of the supply to the minus end of the winding Connect the other side of the supply to the minus side of the capacitor. This should give you close to 1.8 x RMS supply voltage A further 1000uF connrcted across the winding would raise this to near 2.8 x RMS supply voltage. good luck! Jim |
#10
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DIY magnetic bend brake - was "Magnabend"
On Sun, 13 Feb 2011 08:23:37 -0700, Lewis Hartswick
wrote: Bob Engelhardt wrote: Bob Engelhardt wrote: I just made a 2-MOTE (MOT electromagnet) brake as an evaluation of the idea: -------- Oops ... that "-----" was a placeholder for the pic's URL that I forgot to do. http://home.comcast.net/~bobengelhardt/MOTEbrake.jpg Well it looks like you have room for about twice as many turns on the coils so you should be in petty good shape if you fill the winding space. ...lew... The primary winding of an MOT occupies less than half the window space so the easy solution is to simply install two ex MOT primaries on each E core. With all primaries parallel connected this doubles the ampere turns which will make a substantial difference |
#11
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DIY magnetic bend brake - was "Magnabend"
Lewis Hartswick wrote:
Well it looks like you have room for about twice as many turns on the coils so you should be in petty good shape if you fill the winding space. ...lew... That's a good idea! I have a bunch of MOT's - I might have another 2 with coils that fit. Or not - in the past I've had trouble cross-fitting them to make an isolation transformer. I'll look. Thanks, Bob |
#12
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DIY magnetic bend brake - was "Magnabend"
amdx wrote:
You have room to add another coil on each core. ... That is "if you don't saturate the iron core". I have no clue where you are an the saturation curve. Right ... I don't either. Now that I have my scope working again, I should look into it (I had forgotten what I got my scope out for & this was it). But consider this: assume that in normal use, the xformer runs near saturation (otherwise there is "wasted" iron in the core). Which means that normal current in the primary saturates. At 1.5kw & 120v the primary current would be 12A, more or less. Or .75A in the secondary (2000:120 turns ratio). I don't remember exactly, but I'm pretty sure that as a MOTE, I'm running it higher than that. Bob |
#13
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DIY magnetic bend brake - was "Magnabend"
Winston wrote:
.... 1) It did occur to me that the line between the center of your hinge and the gap between the clamping leaf and bending leaf appears off - center a bit, which would cause the workpiece to be lifted unnecessarily. Good catch. I went to great effort to make the hinge axis on the bend line, but didn't get it quite right. Nevertheless, the clamp resists lifting well enough and fails when the bending force starts pushing horizontally more (after 45 degrees). See how Dave used a *piano* hinge? Kewl! http://www.ch601.org/tools/bendbrake/brakeplans.pdf That is a nice solution for his problem, but not very extensible. First, a piano hinge is WAY too weak for any non-trivial bending. Also, it puts the hinge axis below the bend line, which might not be too bad - I'll have to think about it. That would leave the ends open, like the MagnaBend does. 2) Can you use a permanent magnet to be sure your MOTEs are indeed out-of phase magnetically? (With your head *out* of the path of the magnet, preferably!) Yep, but I want them to be in-phase, to avoid the magnetic shorting that later posts point out. 3) As practice for the next design, would you consider removing both of your windings, welding both your cores together and providing a rectangular winding that encloses both center legs? Well then I'd have to wind a coil. I'd really rather avoid that. Thanks, Bob |
#14
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DIY magnetic bend brake - was "Magnabend"
Bob Engelhardt wrote:
Oh ... of course!! The removed I's! Why didn't I think of that?! Somebody give me a dope smack. Oh, wait ... that won't work: they won't cover the space between the cores. The to-be-bent material needs to be clamped continuously. Bob |
#15
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DIY magnetic bend brake - was "Magnabend"
Bob Engelhardt wrote:
Winston wrote: ... 1) It did occur to me that the line between the center of your hinge and the gap between the clamping leaf and bending leaf appears off - center a bit, which would cause the workpiece to be lifted unnecessarily. Good catch. I went to great effort to make the hinge axis on the bend line, but didn't get it quite right. Nevertheless, the clamp resists lifting well enough and fails when the bending force starts pushing horizontally more (after 45 degrees). I can envision that, now that you mention it, given the axial discrepancy. See how Dave used a *piano* hinge? Kewl! http://www.ch601.org/tools/bendbrake/brakeplans.pdf That is a nice solution for his problem, but not very extensible. First, a piano hinge is WAY too weak for any non-trivial bending. One could always stack regular door hinges side by side, too. *That* is extensible! *And there is prior art*. Also, it puts the hinge axis below the bend line, which might not be too bad - I'll have to think about it. That would leave the ends open, like the MagnaBend does. Interesting, wot? Boring to look at, but very effective. 2) Can you use a permanent magnet to be sure your MOTEs are indeed out-of phase magnetically? (With your head *out* of the path of the magnet, preferably!) Yep, but I want them to be in-phase, to avoid the magnetic shorting that later posts point out. Experiment time! Take two button magnets and place them flat on a table. bring them together *edge on* so that they are 180 degrees out of phase magnetically. (That is, flip one over if they do not attract each other initially). You now have two button magnets snapped together side - by - side and they are magnetically 'shorted out' right? North to South and South to North. Bring a piece of steel down on the magnets axially. What happens? If their fields are really 'shorted out' then nothing happens, right? It's not as if both magnets fly up to the steel or anything. Now repeat the experiment with the magnets *in phase*. (When I do this, only *one* magnet flies up to the steel and the other magnet is *repelled* by the combination!) 'Like' poles repel. Opposites attract. 3) As practice for the next design, would you consider removing both of your windings, welding both your cores together and providing a rectangular winding that encloses both center legs? Well then I'd have to wind a coil. I'd really rather avoid that. It is a lot less time and bother than you imagine. I envision a jig cut from scrap lumber using a scrap 1/2" machine bolt as an axle. A plywood base aligns the axis of your 'winding crank' with your spool of magnet wire. A few hundred turns goes more quickly than you might think. A lot of inspirational work is available on Youtube. --Winston |
#16
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DIY magnetic bend brake - was "Magnabend" - - - Update
Bob Engelhardt wrote:
I just made a 2-MOTE (MOT electromagnet) brake ... I checked the phasing of the MOTE's & they were indeed out-of-phase, meaning that there was some flux shorting through the brake's structure. I put them in phase and tried bending some test pieces. There was a distinct improvement: it will now bend 20 ga (.040 +-), where it would only do .030 before. That's good news and bad news. The good news is obvious, the bad news is now I'm uncertain what to do. Before, I had ruled out using MOTE's - now, I don't know. MOTE's would be easier and faster than winding my own electromagnet in the style of the Magnabend, but just barely strong enough. The other thing I did was look into doubling up the windings by adding a winding from another MOT. The problem is that other windings either don't fit at all, or just fit. The just-fit ones are really too tight to use without damaging them. This is 30 ga wire. Bob |
#17
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DIY magnetic bend brake - was "Magnabend" - - - Update
On Sun, 20 Feb 2011 17:20:54 -0500, Bob Engelhardt
wrote: Bob Engelhardt wrote: I just made a 2-MOTE (MOT electromagnet) brake ... I checked the phasing of the MOTE's & they were indeed out-of-phase, meaning that there was some flux shorting through the brake's structure. I put them in phase and tried bending some test pieces. There was a distinct improvement: it will now bend 20 ga (.040 +-), where it would only do .030 before. That's good news and bad news. The good news is obvious, the bad news is now I'm uncertain what to do. Before, I had ruled out using MOTE's - now, I don't know. MOTE's would be easier and faster than winding my own electromagnet in the style of the Magnabend, but just barely strong enough. The other thing I did was look into doubling up the windings by adding a winding from another MOT. The problem is that other windings either don't fit at all, or just fit. The just-fit ones are really too tight to use without damaging them. This is 30 ga wire. Bob Have you tried adding a big capacitor to boost the rectified volts a bit? Jim |
#18
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DIY magnetic bend brake - was "Magnabend" - - - Update
On Sun, 20 Feb 2011 17:20:54 -0500, Bob Engelhardt
wrote: Bob Engelhardt wrote: I just made a 2-MOTE (MOT electromagnet) brake ... I checked the phasing of the MOTE's & they were indeed out-of-phase, meaning that there was some flux shorting through the brake's structure. I put them in phase and tried bending some test pieces. There was a distinct improvement: it will now bend 20 ga (.040 +-), where it would only do .030 before. That's good news and bad news. The good news is obvious, the bad news is now I'm uncertain what to do. Before, I had ruled out using MOTE's - now, I don't know. MOTE's would be easier and faster than winding my own electromagnet in the style of the Magnabend, but just barely strong enough. The other thing I did was look into doubling up the windings by adding a winding from another MOT. The problem is that other windings either don't fit at all, or just fit. The just-fit ones are really too tight to use without damaging them. This is 30 ga wire. Can you round the edges of the laminations to ease the fit and prevent shorts? -- The more passions and desires one has, the more ways one has of being happy. -- Charlotte-Catherine |
#19
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DIY magnetic bend brake - was "Magnabend" - - - Update
In article ,
Bob Engelhardt wrote: Bob Engelhardt wrote: I just made a 2-MOTE (MOT electromagnet) brake ... I checked the phasing of the MOTE's & they were indeed out-of-phase, meaning that there was some flux shorting through the brake's structure. I put them in phase and tried bending some test pieces. There was a distinct improvement: it will now bend 20 ga (.040 +-), where it would only do .030 before. That's good news and bad news. The good news is obvious, the bad news is now I'm uncertain what to do. Before, I had ruled out using MOTE's - now, I don't know. MOTE's would be easier and faster than winding my own electromagnet in the style of the Magnabend, but just barely strong enough. The other thing I did was look into doubling up the windings by adding a winding from another MOT. The problem is that other windings either don't fit at all, or just fit. The just-fit ones are really too tight to use without damaging them. This is 30 ga wire. The MagnaBend 650E (24" wide) draws 4 amps at 220/240 volts, call it 230 volts AC, which is 4*230= 920 watts. One can simplify the winding task by using a stepdown transformer, if one can come by such a big transformer cheaply enough. I suppose that a MOT or a pair of MOTs would do, a task similar to making a spot welder from MOTs. The general approach would be to remove the MOT secondary winding, and replace it with a new secondary having a reasonable number turns and feeding a fullwave rectifier which in turn feeds a big filter capacitor and the MagnaBend flux coil. The main limit on how few turns the secondary can be is that the voltage has to be high enough the one does not have excessive losses due to the forward voltage drop in the rectifiers, at least 12 volts or so. So there - we found a way to use MOTs. We also need to find out the needed number of ampere turns. Probably the easiest approach (aside from being told the answer by the inventors) is to figure out the ampere-turn product to just saturate a mild (1018) steel magnetic path of the dimensions given in the users guide. Length is 630 mm. Cross section is EI, apparently (to my eye) with standard transformer-lamination proportions. The center leg is 30mm wide. The magnetic pathlength (computed from the cross-section drawing) is 160mm. Needed are the magnetic properties of 1018 steel, which is known. Anyway, this is enough to figure out the maximum possible ampere-turns needed. But it will probably turn out that keeping the coil from melting prevents us from going quite that far. The MagnaBend duty cycle is 30% maximum, and the built-in thermal cutout trips at 70 C. The surface area (not including the clamping bar) is 2(98+45)*630= 286+630 mm^2= 279.3 square inches, call it 280 square inches, so the power loading is 920/280=3.28 watts per square inch. The rule of thumb for air cooling is 0.008 watts per square inch per degree centigrade http://www.vias.org/eltransformers/l...mers_03_11.htm l, we get (0.008)(105-25)(280)= 179 watts can be dissipated in continuous duty, or one fifth of the actual dissipation. The flaw in the calculation is that the transformer rule-of-thumb assumes a spherical object, a reasonable approximation for a transformer, but the Magnabend is instead long and thin. Some empiricism may be in order. Potting the winding in situ may also be useful in getting the heat out of the copper and into the steel, thus reducing the core temperature. But we need to insulate the coil from the iron to withstand something like 1000 Volts AC, for safety. Is there a power tranformer and/or motor designer in the house? Joe Gwinn |
#20
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DIY magnetic bend brake - was "Magnabend" - - - Update
Larry Jaques wrote:
Bob Engelhardt wrote: .... The other thing I did was look into doubling up the windings by adding a winding from another MOT. The problem is that other windings either don't fit at all, or just fit. The just-fit ones are really too tight to use without damaging them. This is 30 ga wire. Can you round the edges of the laminations to ease the fit and prevent shorts? That's a good idea, I'll try it. And I was wrong - this is 26ga wire - still thin, but not 30ga thin. Bob |
#21
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DIY magnetic bend brake - was "Magnabend" - - - Update
Please help me to build electromagnetic bending machine
Please your what'sapp number to contact u easily Mine is +919028710886 |
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