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OK, bet some of you will love this question. My Mechanical Engineering degree is a bit rusty, but I can see some of the issues here. (http://www.roymech.co.uk/Useful_Tables/ ... _frict.htm)

I am trying to estimate the amount of force that a drum sander exerts (the expelling force) on a piece of wood. Even the sliding coefficient of friction depends on the normal force (drum to wood, see site above). But it is typically less than the static force. Why am I asking? I want to properly size a DC gear motor for the conveyor belt I am building.

There are several ways to go about this, and I assume it would be necessary to test at least three grits. However, one website indicate that coefficient increased slightly as grit number increases. This suprised me at first, then I remembered surface area of contact. So, who knows.

50, 80, 100, 220. Those would be my test grits.

It seems difficult to estimate the normal force although it should correlate with the amount to take off. Perhaps 1/64" at a time? But who can estimate that? Those with press screw adjusters probably know that 1/4 turn = 1/64" or what ever.

If a board is 65/64" thick, and the machine is set to take 1/64" off, then we have a standard?

It seems to me the best way to do this test is to turn off the conveyor (commercial sander like Jet), insert a slippery material like formica, and then slide the wood through by hand use a 5 or 10 pound scale as the pusher. Noting just how many pounds force are required to make it move, and note if it takes more force to move faster.

Or, someone could read the torque numbers off of their commercial thickness sander... and tell me.

Mike

I think by the time you account for all the variables - grit, conveyor speed, drum speed, new/old sandpaper, hard resinous woods vs. soft dry woods, amount of removal per pass, force of hold down rollers - you're going to end up with a pretty freaking huge range of possible forces.

I say skip the math, and get yourself a 1/20hp or 1/15hp geared DC motor. I think most of the Performax stuff uses a 1/30hp 90v drive motor, so by 1/20hp you should have some headroom without going overkill. My advice is to stay at 1/6hp or below if you want to keep in the range of cheap speed controllers.

My label is a bit scratchy, but I'll see if I can get the torque numbers off it tomorrow.

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Eschew obfuscation, espouse elucidation.

Well, here is some data supporting my initial estimates of around 40-50 in-lbs torque:

http://www.supermaxtools.com/products-s ... anders.php

Yes, they list two torque values on the website, but the users manual says 43.

Mike

Right. I was trying a little humor. But I think I am closing in. Thanks!

Mike

If you're still curious, here's the specs on mine.

1/20 hp Bison DC motor
1:25 gear ratio
40 inch-pounds torque
71 RPM
90 VDC
0.56 amps.

And by approximate quick measurement the belt feeds at about 18 feet/minute. It's about a 23_1/2" wide belt on roughly 7/8" diameter rollers, and though it tracks terrible it doesn't seem to have any problem handling the load. Hope this helps a bit.

_________________
Eschew obfuscation, espouse elucidation.

I found the calculations you would probably use in one of my books: "Manufacturing Processes for Engineering Materials". It would probably be pretty hard to come up with a better answer than just copying off of another design! Some other company has already done the R&D...just copy their answers!

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