Taking the dive...need motor advise

hazmat · Post by **hazmat** » Tue May 13, 2008 8:13 am

I'm gonna order this motor today and the rest of the parts next pay day. I figure I can use the motor as/is for shaping until I can get the rest of the parts, so it's a win/win either way.

Thanks for all the help, fellas. Totally appreciated!

hazmat · Post by **hazmat** » Thu May 15, 2008 3:50 pm

Okay, motor's in transit. I'm kind giddy! Another question about some other parts and pieces.

I'm looking at 4-groove pulleys instead of 3-groove pulleys. I'm pretty sure it doesn't make a difference to the machine, just gives me one more speed option. Question is, how does one figure out what step diameters will provide what speeds??

Post by **KurtHuhn** » Thu May 15, 2008 5:47 pm

It's all about the pie!!

or at least pi.

If you know the RPM of the motor, and the size of the pulleys, it's easy.

Assuming:
- the motor is 1725 RPM
- the pulleys have 2", 3", and 4" diameter grooves
- you assemble it right

The pulleys will be aligned so that when the belt is on one pulley's 2" groove, it's on the other pulley's 4" groove. That means that the 3" groove is common.

First you need to find the circumference of the pulleys:
d = diameter
C = circumference

(pi) * d = C

(pi) * 2 = 6.3
(pi) * 3 = 9.4
(pi) * 4 = 12.6

The ratio of the pulleys then are:
12.6 ÷ 6.3 = 2
6.3 ÷ 12.6 = .5
9.4 ÷ 9.4 = 1

So, since the circumference of the small pulley is half the circumference of the large pulley, that gives us a drive ratio of 2:1 if the belt is on the motor's 4" groove (and shaft's 2" groove), and 1:2 if the belt is on the motor's 2" groove (and shaft's 4" groove). The 3" pulley is a 1:1 ratio.

Given that, it's just simple division.
1725 * .5 = 863 RPM
1725 * 1 = 1725 RPM
1725 * 2 = 3450 RPM

The same is useful for finding surface feet per minute (SFPM) of buffers and grinders - a much more accurate measurement than RPM, and is consistent across all belt or buffing wheel sizes.

(EDIT: I effed up the last part. Fixed now.)

Frank · Post by **Frank** » Thu May 15, 2008 9:07 pm

KurtHuhn wrote:It's all about the pie!!

Boysenberry or Huckleberry?

RadDavis · Post by **RadDavis** » Thu May 15, 2008 11:15 pm

Jeez, Kurt, that's a lot of math!

My motor has a 2 inch pulley on it. The shaft on my buffing assembly has a 2, 3 and 4 inch pulleys (or something like that. I know there's a 3 inch one).

I put the belt on the 2 inch motor pulley and the 3 inch pulley on the buffing assembly, and my rpms are 2/3 of whatever the motor is turning.

In my case it's 2/3 of 1725 rpm, or around 1150 rpm.

I figured this out in my head as I was assembling the set up 4 1/2 years ago, so I could be wrong.

I just don't like thinking about pi.

Rad

hazmat · Post by **hazmat** » Fri May 16, 2008 8:07 am

Math lessons at 8am EST make my brain hurt

Thanks for that, Kurt. I think...

hehe

Seriously, it's good stuff to know. I should have been paying more attention in math class instead of playing paper football.

Post by **KurtHuhn** » Fri May 16, 2008 10:01 am

Heh, math is fun.

Actually, math is fun only when used to figure out real-life problems or situations. Math, for the sake of math, is boring for me. I know some folks sure like it though.

It's actually not as complicated as I made it appear, but I figured I'd give the whole story. Teach a man to fish, as they say. If you have whole numbers for your groove sizes, it's simple. When you get into fractional sizes, and odd ratios, then the math really helps. And it's absolutely necessary if want to find the SFPM of your buffing wheel or grinding/sanding belt.

As you said, Rad, it's easy - just use the size of the pulleys as your ratio. 2/3 and 3/2 equals .66 and 1.5 times motor speed.

Jeez, no I'm not a geek or anything, eh?

hazmat · Post by **hazmat** » Fri May 16, 2008 11:13 am

It is good to know. I'm going to need it to figure out which step pulleys I ultimately order. Thanks again.

Frank · Post by **Frank** » Fri May 16, 2008 12:41 pm

hazmat wrote:It is good to know. I'm going to need it to figure out which step pulleys I ultimately order. Thanks again.

If you go with the sizes that Kurt mentioned, 2", 3" & 4", you should be fine for most usages, speedwise. The only downside at 3450 rpm with 1/3 hp motor, is that you'll be losing some torque. This shouldn't be much of a problem if your wheels/discs aren't too large a diameter.

hazmat · Post by **hazmat** » Fri May 16, 2008 2:50 pm

Is there any reason I would need to get up to 3450rpm for any application on a machine like this? The motor I've been using lately for shaping is 1725 and that seems a bit too fast for the finer stuff I'd like to do on it. I have to stop there and go to hand work or I know I'll bork it up ugly.

Post by **KurtHuhn** » Fri May 16, 2008 3:23 pm

Personally, I can't think of a reason to spin a sanding disc or buffing wheel that high for pipe making. That's *really* fast, and the potential for FUBAR is pretty high. However, if you ever want to buff metal, you'll appreciate the higher speed.

hazmat · Post by **hazmat** » Fri May 16, 2008 3:40 pm

That's pretty much what I was thinking. My first "buffer" was actually a 3450rpm grinder that I converted. Understand, "converted" means nothing more than hung some buffs on the shaft and went after it. I'm completely surprised that I never scorched a hole straight through the kit pipes I was making then. Never lost a stem, either.

Frank · Post by **Frank** » Fri May 16, 2008 5:28 pm

You'd probably be better off getting the slowest speed even slower than 863 rpm, rather than a higher top speed of 3450 rpm. It's really handy having a nice slow speed for fine control. That's one of the things I appreciate about my lathe.

kbadkar · Post by **kbadkar** » Thu Sep 04, 2008 4:28 pm

Hey Hazmat, did you ever get your motor and pulley system set up? How did it go? Did you get the Grizzly motor? Which one? Howz it working for you? Does anyone use a double shaft motor for an extra buff or sanding pad? Or do you just run your belt to a double ended shaft in a pillow block? Any useful bits of info can hopefully narrow down the daunting variables.

I'm now trying to piece together a decent sanding/buffing arrangement (starting with Kurt's motor arbor for DA sanding pads). I'm tired of using the wood lathe for all the pipe crafting operations. I've been doing 3 or so pipes at a time on the same operation (drilling, then shaping, then buffing) so I don't have to constantly switch out tooling. It'll be nice to concentrate on one pipe at a time.

hazmat · Post by **hazmat** » Mon Sep 29, 2008 9:00 am

Been out of the loop for a while, sorry I didn't see this sooner. Been a rough couple of months, but that's a whole other story.

kbadkar... I got a Grizzly 1/3 hp 1725rpm motor. I LOVE it. I haven't yet completed the buffing/sanding station, but I have nearly all the parts sitting in a box in my shop. In the meantime, I have the motor itself mounted to my work bench and have been using it for nearly all of my initial shaping. I'm expecting to get it all together here shortly now that I've got some other things back in order. The plan is to mount a shaft in between two pillow blocks with a 3-step pully in the middle. The motor is going to be mounted below to drive the thing, also with a 3-step on it.

I have used a double-shafted motor, but it was way, way too fast for pipe making applications. I did this back when I was first getting interested in making pipes and I had no idea what I was even doing. The motor is now working as a grinder, as was intended