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| Author: | Billy T [ Thu Jan 19, 2012 6:09 am ] |
| Post subject: | Motor Ganging |
I'm in the process of building a thickness sander. I'd like to make a larger drum than say the typical 5". This to keep more paper in the game thus keeping it cooler and cleaner. I have a bunch of ½ hp electric motors and something occurred to me about ganging 2 ½ hp motors together, not necessarily that I would need them after gearing down the sanding drum to meet appropriate SFM (surface feet/minute). Just curious if there's a problem with this. Any comments? |
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| Author: | Cocephus [ Thu Jan 19, 2012 8:20 am ] |
| Post subject: | Re: Motor Ganging |
I made a thickness sander a few years ago that has a 9" diameter powered by a 1/3 hp motor. The pulley on the drum is actually a groove cut into the drum itself about an inch in from the side to accept the v-belt. A 2" pulley is on the drive motor. When I did the math and calculations, I came up with about 900 rpm at speed. I don`t remember what the estimated hp is at the drum, but it takes effort to stall it out. It works very well. If you`re wondering about the construction of the drum, I used a pine 2x12 and laminated the pieces onto a 3/4 steel shaft in a cross-grain orientation. Yes, it`s heavy, but IMHO, the wieght helps it run smoother and being so large, runs somewhat cooler. My pics of it aren`t around anymore and I have it disassembled because I no longer have the real estate in my shop/spare bedroom, and I`m not crazy about using that dust maker in the house, as it can get pretty bad in an enclosed area, even with dust collection. I only use 80 grit paper on it made from a used belt from a wide belt sander. Speaking of width, I made the drum 24" on the abrasive plus whatever else on the ends. I also built the sander to accept up to 4" (IIRC) and down to .010". That way it takes pretty much whatever I feed into it (within reason, of course). Sorry about being so long-winded about this, but I truly miss having it set up and ready to go, hence a severe slow-down in my production. I`ve actually been trying to come up with some sort of idea to get it set up again. Coe Franklin |
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| Author: | David Malicky [ Thu Jan 19, 2012 1:58 pm ] |
| Post subject: | Re: Motor Ganging |
It's generally not a good idea to gang motors--differences in their torque-rpm response and belt-pulley fit (pitch diameter) cause one motor to do most of the work. |
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| Author: | Billy T [ Thu Jan 19, 2012 2:36 pm ] |
| Post subject: | Re: Motor Ganging |
Cocephus wrote: Sorry about being so long-winded about this, but I truly miss having it set up and ready to go, hence a severe slow-down in my production. Don't be sorry bout that! You're giving a lot of empirical information. I could only imagine having to use something like a 9" sander in the house! I was actually thinking about going even bigger like 10"-12".Now I'm thinking about better dust collection. Even though I'll probably be using mine outside. david82282 wrote: It's generally not a good idea to gang motors--differences in their torque-rpm response and belt-pulley fit (pitch diameter) cause one motor to do most of the work. I know with cars that's the way it is. All these double engine'd dragsters from the 50's and 60's never did really well for that same principle. I was just wondering if the same thing applied to torque itself. Electric motors and internal combustion engines have a whole different performance parameter. Vis-a-vis, electric motors have full torque at 0 RPM, where as internal combustion has to be wappped up quite a bit to get anything close to full torque.
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| Author: | David Malicky [ Thu Jan 19, 2012 4:55 pm ] |
| Post subject: | Re: Motor Ganging |
Yup, with AC induction motors, torque is generated by a small % slip from the base frequency, and torque is very sensitive to slip. For example, a 1725 rpm motor develops its rated torque at a slip of ~4% from its 1800 rpm base. If it slips 3%, it generates a lot less torque, or 5%, a lot more. Graphically, the problem is that the curve is very steep at rated (full load) torque: http://www.engineeringtoolbox.com/elect ... d_652.html Direct drive (with couplings) could be used to match the rpms exactly, but motor models don't have identical slip-torque curves, so they'd still fight each other (maybe with high quality motors, identical builds, it could work--I don't know.) As with dragsters, so go sanders! |
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