# Thread: Motor, Pullies and Spindle Speed

1. ## Motor, Pullies and Spindle Speed

Ok, I'm working a bit more on my project today and this week as I have quite a bit of free time available to me now. Well, I need some really nice pullies for the vertical mill that I am starting to build. Yeah I could probably go out and buy a nice couple pullies, but I've seen a few ones on here that people have made themselves. I'd like to take on that project and I'm not a engineering student, etc., but I would like a bit of help on this matter. I figured on using a 3VX or 4L belt.

I have a standard 3 phase 220-240v 60Hz NEMA motor 2HP with TEFC and a 3/4" shaft that runs at 1725-1750RPM. I wanted a single phase one, but they were more expensive here and harder to get as the dealer I went to had limited stock. I think what I need is a 4 step pulley on both sides, maybe a 5 step.

Here are a base set of RPM's I would like to be able to accheive:

80, 135, 210, 275, 325, 425, 660, 700, 1050, 1115, 1750, 2100, 2720, 4250

I don't know the caculations involved or the formulae used so I would appreciate help with this.

One last note, my spindle is a 10.750" long 3.375" dia. NMTB #40 spindle.

TYIA,
~gb~

2. Are you talking about a cone stack pulley arrangement?
Like you see on the J head Bridgeports (among others)?

If so, 14 speeds means you'll need a stack of pulleys 14 tall...
Another option is to use a 2 stage setup like you see on some mill-drills.
That would lower the number of pulleys and help with the slower speeds.

Anyway, on to your question, to get the speed ratio, you simply look at the diameter ratio of the pulleys. For most machining purposes you can use the outside diameter of the pulley, but this is an approximation.

So as an example, let's see what you need for your first speed of 80 RPM.
(also realize that this is a somewhat unrealistic speed reduction for a single stage belt - that's why b'ports etc have a back gear)

look at the ratio of the two and you get 1750/80 or 21.875 (just divide)
That means you need a diameter ratio of 21.875 on your pulleys.
If you are slowing down the little pulley goes on the drive side, big pulley on the driven side.

So, if you use a 1" diameter pulley on the motor side (for easy math, can't actually get that with a 4L belt), you'd need a honkin' 21.875" diameter pulley on the spindle. A 2" drive pulley would need a 43.75" driven...

That'd get ya 80 rpm.

Hope that helps,

ciao

lino

3. Ok, yes that was what I was after, and yes I did mean the same 2 stage set up like Bridgeports have, although I would rather narrow down that grouping of spindle speeds to a managable number pullies and of a managable diameter.

~gb~

4. To get your lowest speed using belts might not be manageable. The smallest pulley diameter that is practical is around 3" and the largest maybe 9". This gives a reduction ratio of 3 to 1. Two pulley systems like this give you 9 to 1 and three 27 to 1 but three is starting to get a bit much.

• Ok, 9:1 and 27:1 seem a little bit more managable at those sizes.

I really was thinking of either this:

275, 425, 700, 1050, 2100, 4250

or:

80, 135, 210, 325, 660, 1115, 1750, 2720

trouble is..

I like having the speeds from 2100-4250 around

I mostly do 2024, 6061 and 7075 aluminum and 4130/4140 and 4340 steels.

I don't want to do a VFD yet but will some time, and planned to, just not at the moment.

If I split them into either of these two sets.. would that make any considerable differences?

~gb~