Replies

1. 
   RickL | Nov 18, 2004 05:33pm | #1

   Cool...I used a lot of stroke sanders over the years. Mostly a forgotten machine but still can be found all over in wood and believe it or not...metal shops. I recall that article from a very early issue. What you can do is look up the specs for other newer stroke sanders like at Grizzly, Woodworkers Supply. People don't seem to realize a lot of the answers are already out there. The Grizzly has 8" drums with a belt speed of 3500 feet per minute and 1725 rpm motor. The rest, pulley sizes,  can be figured out from the existing info easily. You can google all kinds of math calculators to figure stuff out.

   I can find stroke sanders used cheaper than I can make one and I have all the tools for metal working. The last one I bought for a metalsmith shop I worked at was a nice heavy duty cast Mattison for $700. I couldn't make that quality for several times the price but there's a lot of old ww machines in my area.

   http://woodworker.com/cgi-bin/FULLPRES.exe?PARTNUM=805-874

   Can you make this for machine for less?  I'd be surprised.

1. 
   yona | Nov 18, 2004 09:05pm | #2

   Thank you

   I am familiar with the spec of those machines. I am looking for what you call "math calculations" which is a formula. I think I saw it already once in the FWW but can not find it again.

    

1. 
   RickL | Nov 18, 2004 09:46pm | #4

   As I said before if you do a search on google all the math calculators you could imagine are there not to mention sites with all the basic math information you could ever want.

   http://www.google.com

2. 
   TKanzler | Nov 18, 2004 09:15pm | #3

   You need the diameter of the drum driven by the motor (D), the desired belt speed in ft/min (V), and the motor speed (n).

   Convert belt speed in ft/min to in/min by multiplying by 12, and divide by the drum diameter x pi to get the required drum speed.  Then it's a simple ratio of drum speed to motor speed to get a belt drive reduction (or increase) ratio.

   (V x 12)/(D x pi x n) = ratio

   Assuming 8" dia drum, 3500 fpm belt speed, and 1725 rpm motor, you get

   (3500 x 12)/(8 x 3.14 x 1725) = .96:1 which I would just call 1:1.

   If you leave out the motor speed (1725), you get the required drum speed, which in the above example is 1672 rpm.  If you plan on using a single belt drive, use the largest sheaves you can that don't get in the way.  The grizzly has a 3 hp motor, so at the relatively low shaft speed your talking about, you'd need to run the v-belt fast to keep the tension low, preventing slip, and yielding good belt life.  Two belts of course gives you more flexibility on sizing, but the sheaves get pricey fast.

   HTH

   Be seeing you...

1. 
   yona | Nov 19, 2004 04:48pm | #5

   HTH

   In your first sentence you are missing one important factor: the pulleys sizes (one on the motor and the other on the drum).  1/2" here or there can significantly change the working speed.

   What "ratio" has to do with the calculations? the number of belt are irrelevant also.

   Here is the question: I have a motor at 1750 rpm, 8" dia drum. How do you calculate the pulleys sizes (not guessing or measuring on someone's machine) required to achieve 3500 fpm sending belt speed?

    

1. 
   TKanzler | Nov 19, 2004 06:09pm | #6

   "In your first sentence you are missing one important factor: the pulleys sizes (one on the motor and the other on the drum)."

   You need one to get the other.  I assumed that since I showed you how to calculate the speed ratio of the drum to the motor, you would be able to take it from there, especially since my example, which matches your needs almost exactly, resulted in a 1 to 1 speed ratio.  In other words, the motor sheave and the drum sheave are the same size.  But they can be almost any size you want as long as the ratio of diameters remains the same.

   the number of belt are irrelevant also.

   It's irrelevant to the ratio, but try transmitting 3 hp over a pair of 2" sheaves and a single 3L belt at such a slow speed and see what happens.  That's why I suggested at the end using large diameter sheaves if you want to use a single belt, which is going to be cheaper than a multibelt drive with smaller sheaves.

   Pick a drum pulley diameter and plug into this to get motor pulley diameter.

   motor pulley diameter = (belt speed x 12 x drum pulley diameter)/(drum diameter x 3.14 x motor speed)

   For the above, use belt speed in fpm, diameters in inches, and speeds in rpm.

   Edit: Added units

   Be seeing you...

   Edited 11/20/2004 9:27 am ET by Tom Kanzler

1. 
   yona | Nov 20, 2004 06:39pm | #8

   HTH

   Thank you. You have been most helpful with all of your comments. Your second massage had clarified it all.

1. 
   TKanzler | Nov 20, 2004 10:21pm | #9

   You're welcome.Be seeing you...

2. 
   KeithNewton | Nov 19, 2004 11:35pm | #7

   Are you expecting something magical to happen at 3500 FPM.
   My Okley double belt has a 5 HP on one side and 7.5 on the other. They both have 16" wheels, and run at 1150 RPM for 4817 FPM. Obviously I have plenty of HP to run this larger diameter. I feel that I get a better finish at this speed than the same abrasive on my edge sander at a slower speed.