View Full Version : Motors, pulleys & movement - not strictly CNC related...

20-09-2011, 04:50 PM
If you had a motor that was powering a spindle other than directly, would it be possible to have the motor fixed while the spindle moves? Vertically only over a short (say 50mm) distance, no horizontal travel required.

More of an idle thought that anything else, but it's been bugging me all afternoon. With pulleys the tension of the belt would change while running; what kind of impact would that have?

Oooh, what if there was an idler that moved in such a way as to maintain the same tension on the belt as the spindle moved up and down? I've just given myself an idea there, assuming it's a viable option...

20-09-2011, 06:37 PM
Is the following system viable do you think?


The idea is for pulley B to be powering something like a circular saw than can be raised or lowered by moving the green bit, either through a lever or stepper-controlled screw, etc.

The reason for this kind of setup is because that same motor could be used to power another tool located nearby - not at the same time, of course. The tool that is not in use could be retracted beneath the table and disconnected from the motor perhaps.

20-09-2011, 09:11 PM
Lots of machinery have pulleys that move in relation to the power source, but they rely on spring loading to ensure the belt remains tight.

It all depends on what kind of power you need to transmit, and the type of belt you're using.
Normal V-belts don't need much tension to grip, whereas as smaller multi-groove belts require a lot of tension to grip.

20-09-2011, 09:44 PM
Spring loading! Why didn't I think of that? Now I feel really stupid...

The original idea came from wondering how to build a table saw, then moved to "ohh what about a router table as well", before settling on the perfectly sensible idea to combine the two...


Realistically if I ever made something like this I'd be using a cheap saw/router from B&Q mounted upside down under a bench, but I enjoy working through these kind of ideas.

20-09-2011, 09:51 PM
Normal V-belts don't need much tension to grip...

And for transferring power for this kind of equipment (saw/router bit etc) a v-belt should presumably be acceptable, I believe? Lathes tend to run on flat or v's?

Oh great. Now my mind just raced into overkill :eek:

Edited to add: Inspired by the old line shaft system for belt driven machines (http://en.wikipedia.org/wiki/Line_shaft)...


20-09-2011, 11:05 PM
How much power you can get through any given belt depends on several factors.

If you search for Gates, they do (or at least did) belt calculation programmes that you could download once registered.