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| Woodworking (rec.woodworking) Discussion forum covering all aspects of working with wood. All levels of expertise are encouraged to particiapte. |
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#41
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Sorry, I didn't think of this until I had posted previous...
Think of it this way as an approximation...the extra force when the blade hits an additional obstruction is essentially same as suddenly grabbing a hold of the blade and yanking downward---if the motor is over-sized, it won't stall but will just keep on pulling until something gives...given the moment arm of the upper axle around the support column, that could well be the place. |
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#42
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On Thu, 23 Dec 2004 20:12:00 -0500, Roy Smith wrote:
In article , Nova wrote: CW wrote: No problem. 2horspower is still pretty weenie. It depends. Most 14" bandsaw have a problem providing enough tension for a 3/4" blade without the frame flexing. Given a situation where a 2 HP motor would be beneficial, unless the saw was designed to handle that size motor, the frame of the saw would most likely flex, dropping the tension on the blade and result in a barreled cut. Hopefully that's the worse that would happen. Grizzly's tech support was iffy on a 1.5 HP on my G1019 and had a definite "no" on a 2 HP. -- Jack Novak Buffalo, NY - USA (Remove "SPAM" from email address to reply) The only time you really need the power and tension is when you're resawing, and when you're resawing, there's usually very little material on one side of the blade. So, it seems to me you could solve the frame flexing problem by having a removable strut which could be fitted as a compression member between the upper frame and the table when resawing. I've never seen such a thing on a bandsaw, but I find it hard to believe nobody else has thought of it before me. Does such a thing exist? I was just thinking of such a thing for my performax 16/32..... |
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#43
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On Fri, 24 Dec 2004 08:49:06 -0500, Nova
wrote: Larry Jaques wrote: Blade friction?!? The motor drives the lower wheel which drives the blade and the upper wheel goes along for the ride. Whether you have a 0.5 or a 5.0 hp motor should make little difference, since the weight of the blade and upper wheel will be the same mass no matter what motor. The blade friction is still there and has to be overcome. Unless the blade slips on the wheels the torque is taken by the frame. Think of it as pushing a rope which is the reason for barreled cuts. but given that it's the same blade running at the same speed on the same wheels, there is *no* difference. now if you use that bigger motor as an excuse to jamb bigger pieces of wood faster through a duller blade, yes you will be loading up the frame. it'd be like putting a big block on a gocart. no problem at idle, but floor it and the motor will tear itself free. |
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#44
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On Fri, 24 Dec 2004 12:53:32 -0500, "George" george@least wrote:
"Larry Jaques" wrote in message .. . On Fri, 24 Dec 2004 08:49:06 -0500, Nova calmly ranted: The blade friction is still there and has to be overcome. Unless the blade slips on the wheels the torque is taken by the frame. Think of it as pushing a rope which is the reason for barreled cuts. I think of it as the wheel pulling the teeth down, into the wood. The majority of the tension on the blade is between the table and the bottom wheel on the downward side. Since the wheels are connected, there may be a very minor amount of "pushing", but the fact that the band is laying on the -outside- of the wheels precludes much of that. Any attempt at pushing would simply make space between the blade and the wheel, and that could come only if there was no tension on the blade at all. No, it is my understanding that barrel cuts are the result of insufficient tension on the blade. How about this: The free-wheeling upper wheel gets ahead of the driven, but loaded lower, causing the blade to bunch into the gap. Doesn't take much difference in speed to start the process, which then increases in effect as the bunched part slows.... the upper wheel is an idler and has less mass than the driven lower. just how is it going to get ahead? |
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#45
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On Fri, 24 Dec 2004 11:57:37 -0600, Duane Bozarth
wrote: Larry Jaques wrote: ... The only part I can see being stressed by having a larger motor would be the lower wheel (major) and its bearing (minor). Startup might be quicker, creating higher initial (and inertial) stress, and it would be able to do more work when making heavy cuts while resawing. The upper wheel and frame are merely used as guides for the band. I just don't buy that C-frame flex thing at all. Wider bands and the higher tension needed to run them would be the only cause of frame stress that I can see. No, I take that back. The frame may have more stress AT the lower wheel bearing mount during heavy cuts. The wheel being slightly deflected upward up would also result in lower tension on the blade, with the tension spring attempting to take up that slack. You've got it except you're overlooking the fact that the blade is pulling on the outside of the upper wheel which is applying torque to the frame...as the motor applies more power to the blade this gets transferred to a higher load which could in extreme case, cause the support to fail... if your saw is *that* underbuilt just throw it away and buy a real saw.... |
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#46
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#47
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Larry Jaques notes:
How could the inertial mass of the blade and aluminum wheel (under 10 pounds would be my highest guess) cause any more tension on the frame than the tension adjustment spring, which is in the hundreds of pounds? I still don't buy it, but I would like to hear the Griz tech's explanation. Me, too. But you've got to realize that Grizz is the one that still recommends using a 20 amp fuse for an 18 amp machine because a 30 amp fuse might allow damage to the motor. IIRC, and I'm not sure of this and can't find what I did with the manual on the jointer, they try to make this a warranty issue. This one wouldn't stand up anywhere, IMO. Charlie Self "Political language... is designed to make lies sound truthful and murder respectable, and to give an appearance of solidity to pure wind." George Orwell |
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#48
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"Duane Bozarth" wrote in message ... Larry Jaques wrote: ... How could the inertial mass of the blade and aluminum wheel (under 10 pounds would be my highest guess) cause any more tension on the frame than the tension adjustment spring, which is in the hundreds of pounds? I still don't buy it, but I would like to hear the Griz tech's explanation. It's not the inertial mass we're talking about here...it's the extra torque exerted by the larger motor when more force is exerted (particularly suddenly) by the blade through the material... I don't agree, all that extra tourque is dilivered to the wood being cut, the upper wheel don't see a thing. All the frame and upper wheel sees is blade tension. I don't see the problem with a bgger motor, 'cept that Grizzly has to put a limit somewhere! Greg |
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#49
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It continues to rotate at its original speed for a few msec after the load
slows the lower. Within the limit of blade/frame flex, it crams. It's rotational inertia that counts. wrote in message ... the upper wheel is an idler and has less mass than the driven lower. just how is it going to get ahead? |
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#50
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Charlie Self wrote:
Larry Jaques notes: How could the inertial mass of the blade and aluminum wheel (under 10 pounds would be my highest guess) cause any more tension on the frame than the tension adjustment spring, which is in the hundreds of pounds? I still don't buy it, but I would like to hear the Griz tech's explanation. Me, too. But you've got to realize that Grizz is the one that still recommends using a 20 amp fuse for an 18 amp machine because a 30 amp fuse might allow damage to the motor. IIRC, and I'm not sure of this and can't find what I did with the manual on the jointer, they try to make this a warranty issue. This one wouldn't stand up anywhere, IMO. One wonders if Grizzly even has an engineering staff. I suspect that the real engineers are not employed by Grizzly and speak little if any English and have never been within 5000 miles of the US. Charlie Self "Political language... is designed to make lies sound truthful and murder respectable, and to give an appearance of solidity to pure wind." George Orwell -- --John Reply to jclarke at ae tee tee global dot net (was jclarke at eye bee em dot net) |
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#52
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On Fri, 24 Dec 2004 17:34:46 -0500, "George" george@least wrote:
It continues to rotate at its original speed for a few msec after the load slows the lower. Within the limit of blade/frame flex, it crams. It's rotational inertia that counts. 1) this is a tiny force in the context of a bandsaw. 2) putting a bigger motor on it doesn't change the upper wheel configuration a bit. wrote in message .. . the upper wheel is an idler and has less mass than the driven lower. just how is it going to get ahead? |
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#53
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In article , J. Clarke wrote:
One wonders if Grizzly even has an engineering staff. I suspect that the real engineers are not employed by Grizzly and speak little if any English and have never been within 5000 miles of the US. I wouldn't put money on that "speak little if any English". My wife stoped a pair of random young people in Nan Ning, CN and asked them in English to take our picture. They both spoke English quite well. |
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#54
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bridger responds:
On Fri, 24 Dec 2004 17:34:46 -0500, "George" george@least wrote: It continues to rotate at its original speed for a few msec after the load slows the lower. Within the limit of blade/frame flex, it crams. It's rotational inertia that counts. 1) this is a tiny force in the context of a bandsaw. 2) putting a bigger motor on it doesn't change the upper wheel configuration a bit. wrote in message . .. the upper wheel is an idler and has less mass than the driven lower. just how is it going to get ahead? You are right, as I see it. I think a smarter question would involve something like what is the maximum useful HP for a replacement motor on a 14" bandsaw. That would probably run up on 2 horses. There's simply not a lot of point in running that blade off a 5 HP motor unless you do constant resawing of ipe or something similar...and I doubt even then. Charlie Self "Political language... is designed to make lies sound truthful and murder respectable, and to give an appearance of solidity to pure wind." George Orwell |
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#55
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wrote in message ... On Fri, 24 Dec 2004 17:34:46 -0500, "George" george@least wrote: It continues to rotate at its original speed for a few msec after the load slows the lower. Within the limit of blade/frame flex, it crams. It's rotational inertia that counts. 1) this is a tiny force in the context of a bandsaw. 2) putting a bigger motor on it doesn't change the upper wheel configuration a bit. My explanation was how the blade begins to flex. You may charge any windmills you care to without changing the basic dynamic equation which anyone who owns the standard 14" bandsaw knows by the sound of the blade slapping on the left - push a rope syndrome - or the right, where the blade slows and flexes at the top of the cut - even under tiny force. It's differential which counts, and in a dynamic system with four sources of built-in-flex - the blade, the frame, the spring and the tires, in conjunction with differential friction on a driven and free-wheel, there's a bit more of that than necessary at times. As to HP limits, my initial in this thread summed up my opinion - wouldn't hurt, but there are better uses for 2 HP, if it is 2HP @ 115, motors than for bandsaws, which are belt and blade limited in their use of torque. Now that I know it's a Grizz we're talking about, my experience with breakage in a number of their castings makes me side with the phone tech. |
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#56
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In article , Charlie Self wrote:
You are right, as I see it. I think a smarter question would involve something like what is the maximum useful HP for a replacement motor on a 14" bandsaw. That would probably run up on 2 horses. There's simply not a lot of point in running that blade off a 5 HP motor unless you do constant resawing of ipe or something similar...and I doubt even then. Actually, I was thinking that a two or three horsepower three phase motor might be useful if you power it with an inverter. As I understand it, the torque would stay the same while you'd be able to vary the speed of the blade. |
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#57
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Greg O wrote:
.... I don't agree, all that extra tourque is dilivered to the wood being cut, the upper wheel don't see a thing. All the frame and upper wheel sees is blade tension. .... How does the torque get delivered to the wood being cut??? |
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#58
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On Sat, 25 Dec 2004 08:13:06 -0600, Duane Bozarth
wrote: Greg O wrote: ... I don't agree, all that extra tourque is dilivered to the wood being cut, the upper wheel don't see a thing. All the frame and upper wheel sees is blade tension. ... How does the torque get delivered to the wood being cut??? The blade is being *pulled* down through by the lower wheel, held fast by friction to the rubber around the wheel. The upper wheel is freewheeling. An old sawmill at Upper Canada Village in Ontario Canada uses a straight blade that cuts on the way down, being pulled by the rotating jointed mechanism at the base. That way the wood is also held fast to the table during the cut. Japanese hand saws cut on the pull stroke. It makes sense. [It's not strictly "torque", which is a turning force, at the wood surface, where the blade is being pulled down with sharp edges into the wood, ripping [tiny] chunks out of it.] Merry Christmas. |
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#59
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I think you missed the (semi) sarcasm mode...
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#61
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On Sat, 25 Dec 2004 08:00:46 -0500, "George" george@least wrote:
wrote in message .. . On Fri, 24 Dec 2004 17:34:46 -0500, "George" george@least wrote: It continues to rotate at its original speed for a few msec after the load slows the lower. Within the limit of blade/frame flex, it crams. It's rotational inertia that counts. 1) this is a tiny force in the context of a bandsaw. 2) putting a bigger motor on it doesn't change the upper wheel configuration a bit. My explanation was how the blade begins to flex. You may charge any windmills you care to without changing the basic dynamic equation which anyone who owns the standard 14" bandsaw knows by the sound of the blade slapping on the left - push a rope syndrome - or the right, where the blade slows and flexes at the top of the cut - even under tiny force. It's differential which counts, and in a dynamic system with four sources of built-in-flex - the blade, the frame, the spring and the tires, in conjunction with differential friction on a driven and free-wheel, there's a bit more of that than necessary at times. heck, if anything a bigger motor should reduce that by slowing down less under load. As to HP limits, my initial in this thread summed up my opinion - wouldn't hurt, but there are better uses for 2 HP, if it is 2HP @ 115, motors than for bandsaws, which are belt and blade limited in their use of torque. Now that I know it's a Grizz we're talking about, my experience with breakage in a number of their castings makes me side with the phone tech. I agree that it wouldn't hurt, and that you'd be unlikely to pull the full 2HP with that saw. my us made bandsaw has a factory 2hp motor on it- although it's an 18" and has a tube steel frame. the only griz bandsaw I ever used was also an 18", and IIRC it also had a 2HP motor on it. I assume that the griz 14" is a fairly generic asian delta clone. |
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#62
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On Sat, 25 Dec 2004 08:13:06 -0600, Duane Bozarth
wrote: Greg O wrote: ... I don't agree, all that extra tourque is dilivered to the wood being cut, the upper wheel don't see a thing. All the frame and upper wheel sees is blade tension. ... How does the torque get delivered to the wood being cut??? by the blade being pulled down through the wood by the lower wheel being turned by the motor. the upper wheel is for tension and tracking only. |
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#63
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Larry Jaques wrote:
snipped I just don't buy that C-frame flex thing at all. Wider bands and the higher tension needed to run them would be the only cause of frame stress that I can see. No, I take that back. The frame may have more stress AT the lower wheel bearing mount during heavy cuts. The wheel being slightly deflected upward up would also result in lower tension on the blade, with the tension spring attempting to take up that slack. The upper and lower wheels move in sync because of the blade tension.. Because the wheels move in sync any stretching of the blade will cause the slack to be on the gap side. The stress on C-frame is also caused by the wheels moving in sync. -- Jack Novak Buffalo, NY - USA (Remove "SPAM" from email address to reply) |
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#64
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On Sat, 25 Dec 2004 23:09:55 -0500, Nova
calmly ranted: Larry Jaques wrote: snipped I just don't buy that C-frame flex thing at all. Wider bands and the higher tension needed to run them would be the only cause of frame stress that I can see. No, I take that back. The frame may have more stress AT the lower wheel bearing mount during heavy cuts. The wheel being slightly deflected upward up would also result in lower tension on the blade, with the tension spring attempting to take up that slack. The upper and lower wheels move in sync because of the blade tension.. Because the wheels move in sync any stretching of the blade will cause the slack to be on the gap side. The stress on C-frame is also caused by the wheels moving in sync. Oh, so it's the stretching that causes the stress? giggle You lost me with your last sentence. What part of synchronization (other than the tension which puts them there) causes stress? ------------------------------------------------------------- * * Humorous T-shirts Online * Norm's Got Strings * Wondrous Website Design * * http://www.diversify.com ------------------------------------------------------------- |
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#65
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Larry Jaques wrote:
Oh, so it's the stretching that causes the stress? giggle You lost me with your last sentence. What part of synchronization (other than the tension which puts them there) causes stress? The blade stretch takes place from the point of the bind to the drive wheel. Because the wheels attempt to move in sync the added length (along with the slop caused ny the slight compression of the tires and frame flex) is transferred around both wheels to the the top of the piece being cut. Although the blade isn't fixed to the frame other than being restricted by the piece being cut, think of the wheels as acting as the cams in a compound bow. -- Jack Novak Buffalo, NY - USA (Remove "SPAM" from email address to reply) |
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#66
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On Sun, 26 Dec 2004 11:38:23 -0500, Nova
calmly ranted: Larry Jaques wrote: Oh, so it's the stretching that causes the stress? giggle You lost me with your last sentence. What part of synchronization (other than the tension which puts them there) causes stress? The blade stretch takes place from the point of the bind to the drive wheel. Because the wheels attempt to move in sync the added length (along with the slop caused ny the slight compression of the tires and frame flex) is transferred around both wheels to the the top of the piece being cut. Although the blade isn't fixed to the frame other than being restricted by the piece being cut, think of the wheels as acting as the cams in a compound bow. Close, but way different. The bow flexes when the bowstring is pulled while the spring expands/releases when the blade is stretched. We're talking opposites of your theory here. The equivalent on the bow is the string, which remains at a fairly stable tension at or near the rest position. Pull the string back 2" and you have the equivalent of the bandsaw blade when the saw is turned off. Release the string and you have the equivalent of the blade during a resaw, slightly less tension and no bow flex. The tension spring in the bandsaw takes up most of the slack and removes the necessity to flex from the frame. Unless the spring is bottomed out (full tension) or released (not involved), the frame isn't stressed much more or less by stretch. ------------------------------------------------------------- * * Humorous T-shirts Online * Norm's Got Strings * Wondrous Website Design * * http://www.diversify.com ------------------------------------------------------------- |
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#67
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Larry Jaques wrote: ... The only part I can see being stressed by having a larger motor would be the lower wheel (major) and its bearing (minor). Startup might be quicker, creating higher initial (and inertial) stress, and it would be able to do more work when making heavy cuts while resawing. The upper wheel and frame are merely used as guides for the band. I just don't buy that C-frame flex thing at all. Wider bands and the higher tension needed to run them would be the only cause of frame stress that I can see. No, I take that back. The frame may have more stress AT the lower wheel bearing mount during heavy cuts. The wheel being slightly deflected upward up would also result in lower tension on the blade, with the tension spring attempting to take up that slack. You've got it except you're overlooking the fact that the blade is pulling on the outside of the upper wheel which is applying torque to the frame...as the motor applies more power to the blade this gets transferred to a higher load which could in extreme case, cause the support to fail... How could the inertial mass of the blade and aluminum wheel (under 10 pounds would be my highest guess) cause any more tension on the frame than the tension adjustment spring, which is in the hundreds of pounds? I still don't buy it, but I would like to hear the Griz tech's explanation. Absolutely right. And, since it is torque and not power that determines the pull exerted on the blade, I guess I have about a 10 horse motor on my 14" Delta bandsaw. Not really, of course. It's only 1 horse. But when I run it in the lowest geared speed for cutting steel, it is putting as much torque to the wheel as a 10 horse motor would at wood cutting speeds. Maybe even more. And I'll occasionally feed heavy steel pieces with enough force to slip the blade on the lower wheel. John Martin |
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