Pulley sizes vs RPM?????

[OGYT]

I have an arbor that I have rigged up to hold my four-jaw chuck, in order to smooth the inside of hollowforms with gravel. :cool: I have a two-speed 1/3hp motor that turns 1725 and 1150 RPM with a two inch DRIVE pulley.

That leads me to these RPM Reduction Questions:
Situation Number One: I want to connect the motor to the Chuck arbor which has a 2" DRIVEN pulley, and reduce the arbor speed to 35 to 40 RPM. :eek: (Due to the cast iron shroud on this arbor, it's not possible to enlarge this pulley, either. However, I may be able to attach a larger pulley on the opposite end of the chuck.)
I think it will be necessary to use an intermediate axle/arbor to make such a reduction in RPM.
If I can't enlarge the arbor drive pulley, what size pulleys will be required on the intermediate axle, since one will be a DRIVEN pulley and one will be a DRIVE pulley? :confused:

Situation Number Two: If it is possible to attach a larger pulley to the opposite end of the Chuck Spindle, what would be your suggestion as to pulley sizes? :confused:

Room to mount this contraption is not a problem. :D

[Auzzie turner]

This is on WOW

Anyway, here is what Mr. Jones posted

http://www.csgnetwork.com/pulleybeltcalc.html

Joash:cool::D

[MICKYG]

Al,

Driving Pulley Diameter times (X) Motor Speed in RPM.

take the product of this and then

divide by Driven pulley Diameter will give you what you are looking for.


Regards Mike;)

[Gil Jones]

Drive pulley diameter times motor RPM divided by desired RPM equals driven pully diameter.

[OGYT]

Joash, thanks, but Mr Jones requires belt length to calculate, and belt length doesn't have anything to do with RPM... that I know of, anyway. Yep, it's on WoW, and another forum also. But I still don't have exactly what I'm looking for, but I'm gettin' there.

Thanks, Mike, but the required size of the "driven" pulley is actually what I'm looking for. I guess there are too many configurations possible to have the perfect formula for what I'm trying to do. I can't install a four foot pulley, so I guess I'll have to have a jackshaft in between the motor and the arbor. Having the formula for figuring that is what I need.

Gil, thanks again, Now, how do I re-construct this formula to work a jackshaft into the mess? Do I just have to take a wag as to the jackshaft "driven" pulley, and then figure another time with the same formula?

[MICKYG]

Al,

The two formulas are the same thing one gives the answer in pulley size and the other give the speed in rpm. It looks as if you will need to use two lots of pulleys and shafts to get down to 35rpm with the motor you mention. You could use a reduction gearbox which are readily available in all sorts of reduction ratio.

An other alternative is to get a brush motor and vary its speed by a speed controller which operates by varying the voltage provided to the motor.

Good luck with it, sorry I cannnot be of more help. There are a lot of approaches you could apply to your dilemma to bring about same result.

Regards Mike

[Ian Smith]

OGYT,
I’ll have a crack at this because, whilst I know bugger-all about wood turning, your problem seems to be one of gearing.
Now, if I read you right you have a fixed diameter for both the DRIVEN pulley and the DRIVE pulley of 2 inches.
You have a motor capable of either 1750 or 1150 RPM and you want the DRIVEN pulley to turn at 35-40 RPM.
So if you take the case where the motor is turning as slow as it can (1150 rpm) and the DRIVEN pulley is spinning as fast as you want it to (40 rpm) then you must achieve a reduction of 28.75:1
So in a one-step process this means that the DRIVE pulley must turn a DRIVEN pulley with a diameter of 2x28.75 or 57.5 inches . Any of the previous respondents said essentially the same thing, and that web site that Joash pointed you to makes things that bit easier. It does calculate belt size if you want but it’s not a necessary input or output if you aren’t interested. In any case, you’re looking at a 5 foot pulley if you want to do it in one step or, more practically, a multiple set of pulleys to step it down gradually, and you’re right, the combinations are theoretically infinite but I’m sure that available sizes will soon restrict that.
I have no idea what pulley sizes are available but let’s say you could get your hands on a bunch of 6 inch and 2 inch pulleys then you can get pretty close in three stages as per the sketch. Any set of reduction values which, when multiplied together, give you approximately 28.75 will do the trick

Hope I haven't lead you astray but I think my figures are correct

EDIT - that second figure in the diagram should be 383 not 328

Ian

[Gil Jones]

Ian, looks like we had about the same idea.

[Ian Smith]

Gil,
Ah well, you know what they say about great minds and fools :)

Ian

[Gil Jones]

Ian,
Yup, I do.
Well, now that the world is a safer place, I reckon I will go to bed (1:45am here).

[Skew ChiDAMN!!]

One problem with the proposed ideas, is that for 3 pulley sets (ie. 3 belts) you need 4 shafts, and tensioning the belts can become a nightmare. Adjusting one throws others out, etc. unless you start at the "fixed" end (usually the chuck) and work your way through. It also means that as you work towards the further shafts, they need larger and larger adjustment slots to take up the slack.

One work around is to modify it to use only two shafts :eek: by running some of the pulley clusters on bearings, so they rotate independantly of the shafts. (In pic, these are the yellow clusters.) So long as the two pulley diameters & the belt sizes are kept constant throughout then all the belts can be equally tensioned by adjusting the one shaft. :)

'Tis an old concept, BTW. I first saw it in an old steam-driven sawmill out Emerald (Vic) way, where they used it as a reduction mechanism on their leather flat-belt system... from vague memory they were running 5 or 7 belts and tensioning was done by adding logs as weights!

[JohnM]

A worm drive reduction gearbox could be cheaper, and certainly simpler

[tashammer]

At this rate it will probably be cheaper to buy a hamster and make a treadmill. :D

[Gil Jones]

Skew, that is an outstanding idea!!! Thanks:D
Using 7" and 2" pulleys throughout (and 1150 motor rpm), the final speed would be 26.8 rpm.
Gil

[Harry72]

Dunno, might work... motorbike gear box!
Harley's have a separate Gbox, but even 2nd(or 10th)hand still prob cost a bit.
All these pulleys/shafts and belts would soon add up in cost's too, with a bike's gear box you might be able to incorporate the clutch... just the thing for starting heavy turnings!

[TTIT]

, in order to smooth the inside of hollowforms with gravel. :cool: I think I missed the point here the first time I read your post Al! I haven't heard of this trick before but did you look into lapid$#%$ (rock polishing) rigs? The tumblers they polish semi-precious stones with run at about the speed you want and shouldn't cost too much at all:) - probably less than a bunch of pulleys, belts and shafts!!;):D

[OGYT]

Thanks to all of you for your input. Please see my new thread, "ITs DONE! :D :D :D
Skew, Gil, Ian, Mick. All good ideas, and I've saved and printed them for later use.:D

John, tas, harry, TTIT, Joash. Appreciate your posts! Especially the hamster idea.:D

[jaan285]

hi,
i m working on a project to make a generator to produce 10 KVA
the driving shaft speed is 300 rpm and the driven shaft speed is 1500 rpm. so that ration is 1:5
now, i need to buy pulley for the driver and driven shaft.
i need to find out the size for both pulley with the given data..

can i find some help in that ??

will highly appreciate your help in it.;

thanks.

[RETIRED]

By my calculations you need a 120mm pulley on the driven shaft and a 600mm pulley on the driver.

They will have to be at least triple or 4 row pulleys with matched belts.

The driver speed doesn't seem right to me. What size motor are you using?

[hughie]

One problem with the proposed ideas, is that for 3 pulley sets (ie. 3 belts) you need 4 shafts, and tensioning the belts can become a nightmare. Adjusting one throws others out, etc. unless you start at the "fixed" end (usually the chuck) and work your way through. It also means that as you work towards the further shafts, they need larger and larger adjustment slots to take up the slack.Al,

What I have done is to have middle shaft on a swing arm.So as you apply tension to the last or motor pulley you also tension the middle and headstock belts to boot.

http://www.csgnetwork.com/pulleybeltcalc.html

just put an approx belt length its happy with most any length you use.