View Full Version : variable speed "V" belt

07-12-2009, 04:26 PM
HI All
I am looking for an article posted in The Home Shop Machinist or Machinist Workshop that I lost.
This article is about a variable speed V belt drive system used on a drill press or small mill. This is a simple setup using a double pulley mounted on a jackshaft with a handle for movement. I believe the top and bottom parts are fixed and the center part moves up and down. This happens when the handle is moved and the belt pressure moves the center part up or down and changes the ratio of the pulleys and the speed of the output shaft. I saw one on a drill press many years ago and wish to build on now.
Any help would be welcomed.

07-12-2009, 04:33 PM
My lathe uses this system. I am going to do a similar thing for my mill, using a moped variator, when I find the suitable parts.

07-12-2009, 05:10 PM
Riding lawnmowers use something like this. Started back with John Deere and Bolens back in the '70s. Can't be too complex.

Mad Scientist
07-12-2009, 07:16 PM
If you add a differential to the variable speed pulley and you can go from a 1:1 ratio forward to a 1:1 ratio in reverse without having to shift gears.:)


07-12-2009, 09:09 PM
Thanks for the reply, how ever the drawing shown here is not what I was looking for.
I cannot attach my drawings to show the lay out of what I am describing. Peter your lathe may have what I am looking for could you send a drawing??? The Moped type pulley is driven by speed with a centrifugal system and will not work as a variable speed changer. What I am looking for will either increase of decrease the speed between the input and output by moving the handle.:cool:
maybe they will grant me the option to manage files and I can send the drawings.

Have fun


07-13-2009, 02:12 PM
Hi Tom.

Here is a pic and the factory drawing of my lathe setup. The pic is from when I first bought the machine and needed to source a belt. I do understand that the scooter variator pulleys are centrifugally operated - I was thinking I could cobble a manual control over one and do-away with the rollers.

Click the small drawing for the full-sized version.



http://peterrimmer.myby.co.uk/images/varispeeddrawingsm.jpg (http://peterrimmer.myby.co.uk/images/varispeeddrawing.jpg)

07-13-2009, 06:46 PM

I know exactly the type drive you want to build, I have two machines that use it.

A few points about these type drives..

They aren't the easiest thing to make so it works smoothly without sticking.

They aren't very efficient. V-belt drives generally aren't, but these are worse.

The adjusting lever won't stay in position without locking it down.

Speed control is not really good.

Most of these drives need special, wider v-belts to operate. The belts are stiff and relatively expensive.

Unless you have some reason to want this type drive specifically I suggest a VFD. The machines I have using this drive were expensive in their day and used it because there were no other viable options. Later versions of the machines use electronic speed control.

07-13-2009, 07:20 PM
Variable speed vee belt drives are as common as combines, CVT quads (like my Can Am), and snow machines (like my family's old Skidoo). Combines use them with a control arm to vary the ground speed (like the lathe configuration shown, but usually hydraulically activated). The pulleys have one side that slides in and out on a spline. The drive pulley is controlled by a control arm and a bearing similar to a throw out bearing on a clutch pressure plate (like on a combine) or a set of weights and links that force the sides of the drive pulley together - faster engine speed forces the pulley closed (like on a snow machine). The driven pulley is held closed by a spring which allows the pulley sides to opens up as the drive pulley closes. The range of variable ratio is roughly from 4:1 reduction to about 1:2 overdrive.

A drive belt for a combine might be as big as 3" across the spine while snow machine belts are 2" or less.

07-13-2009, 07:41 PM
MTD mowers used them,IIRC the aftermarket replacements cost $70.

Lovejoy makes preety much anything you would ever want,plus they're online catalog has actual dimensions on the parts-


07-13-2009, 08:17 PM
Thanks for replys I found one on Ebay and bought it.
Great to be able to throw out a question and have many answer it.
I still would like to see the build it yourself article from home shop.:)
have fun

07-13-2009, 08:17 PM
I vaguely remember that HSM article, but I thought it was just an outboard jackshaft that was manually changed? I didn't think it was a Reeves drive?

Most of these drives need special, wider v-belts to operate. The belts are stiff and relatively expensive.

The Vari-speed belts on my Clausing 5914 are about 4 times as wide as a conventional V-belt, and yes, they're very expensive :) You can probably go cheaper if you find a snowmobile belt. At least, I'd assume that snowmobile belts are cheaper than machinery-branded belts.

Unless you have some reason to want this type drive specifically I suggest a VFD. The machines I have using this drive were expensive in their day and used it because there were no other viable options. Later versions of the machines use electronic speed control.

Good advice. Most of us that have VariSpeed machine tools (Bridgeport Varispeeds, Clausing VariSpeed, etc.) wish we didn't :)

07-14-2009, 05:05 PM
This is a test
If it were the real thing you would be dirrected to say hello.


07-14-2009, 05:08 PM
HI George
Thanks it works :D
That is a picture I was sent of what I am looking to build. And if I ever get the article I will.

Have fun

Now to order the other back issues for another projuect.

07-14-2009, 05:12 PM
I can see how the ratios will change with various postions of the double sheave, but how does the whole set up account for the change in center distances for the different ratios?

07-14-2009, 06:43 PM
The belts slide up and down the sidewalls of the Vari-speed sheave as the center distance changes.

That's the primary loss of efficiency, and why they get so hot...

07-15-2009, 10:13 AM
HI All

I hope now that more info is out about the variable speed changer some one will find the article.

Lazlo I do not believe they get very hot as they are used in many different systems. I have been told the shopsmith used them and lawn tractors also use them. These would be running for long stretches of time. I think once the speed is set the friction heat would be no more then a normal pulley. I also plan to use it on a low speed system to end up with about 8 to 25 rpm out put. That's my story and I'm sticking to it.

I need the article to be able to build one!

Have fun

07-15-2009, 06:47 PM
I think I've found it - it has been bugging me since I first saw your request. Took me a while to go through the old issues as it doesn't show up in the indexes.

It is under the "Reader's Forum in the Jan/Feb, 2000 issue of the HSM. The submitter is Rouville Labonte of Portales, NM. He mentions and shows photos of the conversion on a drill press and on a Logan lathe. He says the unit is from a MTD lawnmower.

I seem to remember that he wrote in again giving part #'s but I can't find it.

Let me know if you need more details.


07-16-2009, 01:19 PM
Hi Geoff

you da man that is just what I was describing and I did have that issue.
But there was a construction article posted in either HSM or MW after that and that is what I am looking for so I can build one for my own use.
I am posting the pictures so other may better understand the quest.

Thanks again and have fun


07-16-2009, 01:24 PM

07-16-2009, 02:07 PM
I am posting the pictures so other may better understand the quest.

Thanks again and have fun

Tom, that looks like he added an intermediate jockey-pulley to reduce the speed of a wood-working drill press to metalworking speeds.
In other words, it looks like that's just a conventional V-belt pulley.

Didn't you say you were looking for a variable-speed Reeve's Drive/CVT?

07-16-2009, 02:23 PM
Looks to me like the middle part of the the double-pulley on the idler assembly is free to move up-down, and moving the lever on the left upwards hinges the idler assembly towards the motor and the two belts self-compensate. Clever idea.

07-17-2009, 12:24 PM
My George I think we are on the same page now.

Can anyone find the construction article for building one of these systems?? I was in either Home Shop Machinist or Machinist Workshop.

Have fun

07-17-2009, 04:34 PM
This would seem to be just a variation on a more standard Reeve's drive. The difference is that it's using one more pulley. The premise is the same no matter what....the ratio of the two pulleys changes based on the spacing of the two faces of the pulley. The way that spacing is varied is what changes from one design to the next.

In machine tools this is varied with a lever or other arrangement. I have a Sheldon shaper that slides the motor back and forth on a pair of round rails. In that case the wide VS belt is wide enough that only the motor end has a v-shaped spring-tensioned sheave. The other end goes around a large, flat pulley and the flat portion of the belt is what bears on that pulley. This is probably the simplest design as changing the distance from the motor to driven pulley is all that's needed. I would think that this could be applied to something like a drill press very easily.

In the case of the one in my Bridgeport mill, both ends (drive and driven have spring tensioned sheaves and a lever is responsible for changing the spacing of the sheaves by pulling them apart, directly...and only on the driven (spindle) end. The drive end pulley (on the motor shaft) is spring loaded merely to take up the slack.

In things like snomobiles and ATV's where this has been used for decades, the input throttle of the driving motor varies and centrifugal spring weights on the "primary" side sheave/clutch arrangement determine the rate of change in pulley ratio. In that situation, both the drive pulley and the driven pulley change diameters so you can go from say a 5:1...down to a 1:1 ratio...and keep going to a 1:5 ratio the other direction...giving you *huge* amounts of variability.

I am sure there is some loss...thus the heat generated, on the other hand, these are transmitting up to several horsepower, so the use of one of the standard variable speed belts both allows for this extra HP as well as allowing for changing ratios. This comes with added surface area...and added friction from pulleys that are gripping the belt under tension.

As for the cost....I would say that if a guy was designing one of these from scratch and was not constrained by space, you could design around the belt somewhat and use some item you can find surplus. I found several in a bin at a local surplus place I frequent, some years back...but they didn't fit anything I had. For reference...the standard item for a Bridgeport VS head is somewhere in the $70 range. The much larger belt for my Sheldon shaper was $180 as I recall. I hope mine lasts forever.