Instructables

Old Dunlap Model 103-0602 wood lathe


Hi,
I have an old Dunlap Model 103-0602 wood lathe. It has step pulleys to adjust the speed. One pulley is on the lathe head and turns the center shaft. The other pulley is on the shaft of the motor. The motor is 1/3 HP ,  1725 rpm's and has a 5/8 shaft. The pulley on the motor shaft is       4", 3 1/4",  2 1/2" and 1 3/4 " .  I am having trouble measuring around the pulley on the head of the lathe are they usually the same size?
Well can anyone help me?

Thanks
Frank

Prfesser3 years ago
The pulleys aren't necessarily the same size---though they probably are---but the difference between two steps must be the same for both pulleys.  For your set, the steps differ by 3/4" on the motor pulley so they must differ by 3/4" on the spindle pulley as well.

By the same token, if the smallest size is the same on both motor and spindle, then the other sizes must be the same as well.

FWIW if you're looking at buying a belt and want to know the size, just use the wife's sewing tape measure.  Wrap it around the largest spindle pulley and the smallest motor pulley, as though it was a belt.  Mark.  Get that size.

Hope this helps!
tall1smokey (author)  Prfesser3 years ago
I want to thank all of you. I think your the best crew ever. Now how do I tell what the RPM's are at the various pulley setups. I need a way to figure out my RPM's and how to lower them or increase them. You guys are the best!!

Thanks
Frank
Prfesser3 years ago
To find the RPM at a given setup, just divide the motor pulley diameter by the spindle pulley diameter. Then multiply that by the motor RPM.

For example, say you have a motor pulley that is 1 3/4" and a spindle pulley that is 4", with a motor that runs at (typical) 1725 rpm.  1.75/4 = 0.4375.  0.4375x1725 = 755 RPM on the spindle.
tall1smokey (author)  Prfesser3 years ago
Thanks , it's nice knowing how to figure that out.

Frank
Most often, the pulleys were the same size, but installed in opposite orientations. You should be able to measure the circumference of each step on the pulley by using a piece of cord or string. Wrap the cord around the pulley and mark the end. Then measure the length of the cord with a ruler or tape measure.
The reason for that, by the way, is that since the belt's size doesn't change you normally want the slack caused by shrinkage in one pulley to be taken up by growth in the other pulley, to maintain good belt tension and friction.

(There are other ways of managing the slack -- spring-loaded idler wheels or intermediate wheels and secondary belts -- but this is the simplest version. My drill press can be set up either with one long belt from motor to drive wheel, or two shorter belts going to an intermediate wheel to get a few more speeds.)

This brings up another question: Is there any way of creating a decent speed control circuit which will work with a 50-year-old capacitor-start motor without losing unreasonable amounts of torque? Or would I have to replace the motor if I want a more modern and precise control system for my drill press? (Or replace the drill press -- but I have sentimental reasons for not wanting to do that.)
The best option would be to purchase a small variable frequency drive (VFD) and wire the motor through the VFD. You would then have virtually unlimited speed control.
tall1smokey (author)  diyoutdoorsman3 years ago
Would a VFD do any damage to the motor ? I heard that you just cant take any motor and make it a variable speed like that. I don't know if its true or not.

Thanks
Frank

VFD's generally are for 3 phase motors, however they do make a small VFD/phase convertor combo to control single phase motors (I actually have 2 of them left over from a previous project). I have used them to control speed on belt grinders in knife makeing shops. You have single phase power on the line side and the VFD/converter will control speed on the line side.

Here is a link with the formula for determining pulley speeds:

http://www.binkyswoodworking.com/PulleyTip.php

tall1smokey (author)  diyoutdoorsman3 years ago
Thank you !! How where can I get and how much do the small VFD/phase convertor combo to control single phase motors cost? I have a 115 volt, 1/3 hp, single phase motor. and that will work?

Frank
The VFD's I got were rated for a 1 HP 240V sgl phase motor and were about $300 a year and a half ago. I got them through a local electrical control equipment distributor here in the Kansas City area. I haven't researched it but you could probably get one through WW Grainger or McMasters. I would inquire at your local electrical wholesale suppliers. They may or may not sell to directly you, but they could certainly point you in the right direction. If there are any local armature shops that sell or repair motors, alternators, generators, etc, they may also be a good source.
tall1smokey (author)  diyoutdoorsman3 years ago
You have been so helpful. I am going to see what I can find out.

Thanks
Frank
tall1smokey (author)  orksecurity3 years ago
Hi, thank you for getting back to me. Would you know how to tell me how to figure out what speed my lathe is turning. The motor is 1/3 HP , 1725 rpm's and has a 5/8 shaft. The pulley on the motor shaft is 4", 3 1/4", 2 1/2" and 1 3/4 " . I guess the other pulleys on the lathe head match those on the motor. I need to know what speed the lathe is turning because I need slower speed for roughing and a faster speed for detail.

Thanks
Frank