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What size Pully
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Author:  Blake Dixon [ Mon Mar 25, 2013 5:29 pm ]
Post subject:  What size Pully
For the Stewmac buffing wheel what size Pully should I put on a 1/4 horse motor to drive the system any ideas?

Thanks
Blake
Author:  Blake Dixon [ Mon Mar 25, 2013 5:50 pm ]
Post subject:  Re: What size Pully
Of course that is to get the desired speed slow enough as to not burn the finish. Also would a 1/4 horse motor be the desired power plant as well?

Thanks
Blake
Author:  LarryH [ Mon Mar 25, 2013 6:04 pm ]
Post subject:  Re: What size Pully
Blake, There are charts on the web that can convert pulley size(s) to your desired RPM. If the motor is just a bare shaft at this time then start with the motor's RPM, choose a cheap small pulley for the motor drive pulley and then choose the pulley for the arbor that gets you the desired RPM.

Understanding that proper RPM is as good a question as what size pulley to use. Also remember larger buffing wheels will have a higher speed at the wheel than smaller buffing wheels but will require more HP to drive them (1/4 HP does seem to be the agreed upon HP for buffing wheels though).

I've also read that the feet per second that the buffing runs at is just as or more important than RPMs.
Author:  gozierdt [ Mon Mar 25, 2013 6:12 pm ]
Post subject:  Re: What size Pully
If you're talking about the SM arbor, they specify the following motor:

• 1725-rpm
• 3/4 horsepower
• 120-volt
• 6.2 amp
• 550 watt
• Includes 1.89" pulley

If you're talking about the 14" buffing wheels they sell, on a different arbor, then it depends
on the pulley size on the arbor.

I think a 1/4hp is a little light, but may possibly work OK. I run Grizzly 12" wheels with a 1725 rpm, 1/2 hp motor,
but to prevent burning I run with a very slack belt- it's pretty easy for me to stop the wheel by pressing too hard,
but I'd rather do that than have it grab the guitar and throw it down on the floor. If you have a choice of motors,
I'd go with the 1/2 hp, especially with the 14" wheels.

What you are really interested in is the buffing media speed as it touches the guitar. It's expressed in Surface Feet
per Minute (sfpm), and is the linear speed of the media relative to the guitar surface. It's a function of both shaft
speed (rpm), and wheel diameter (spfm=Rev/min x pi*dia). If you search on "buffing speed" in the build forum,
you'll get a lot of discussions you can learn from.
Author:  LarryH [ Mon Mar 25, 2013 6:12 pm ]
Post subject:  Re: What size Pully
Blake Dixon wrote:
Of course that is to get the desired speed slow enough as to not burn the finish. Also would a 1/4 horse motor be the desired power plant as well?

Thanks
Blake


To slow the RPM choose a larger arbor pulley and a smaller drive pulley.
Author:  crazymanmichael [ Mon Mar 25, 2013 6:28 pm ]
Post subject:  Re: What size Pully
a 1/4 hp is ok, especiallt for a beginner. if you push too hard you will simply stall the motor instead of buffing trough the finish.

as to sheave sizes it depends on the size of your buffing wheels and the speed of the motor as ell as the vuffing compound you use. using a 1750 rpm motor and 10 in buffing wheels and menzerna compounds, i halve the speed of the motor to give 875 rpm at the wheel; e.g. a 2 and a 4 inch sheaves or a three and a six inch. obviously the small sheave goes on the motor and the large one on the wheel shaft. if you use a higher speed 3450 rpm motor the ratio would have to be 1:4.

these speeds can be easily for the wheel size and compound requirements in your shop.
Author:  B. Howard [ Mon Mar 25, 2013 7:28 pm ]
Post subject:  Re: What size Pully
I think 1/4 HP sounds a bit light. If the wheels bog down when you start to buff you are not going to get a nice polish.
Author:  cphanna [ Mon Mar 25, 2013 9:12 pm ]
Post subject:  Re: What size Pully
Blake,
Pulley size will depend most of all on the RPMs of your motor, as you have no doubt surmised from the previous responses. As to motor HP, you received some good advice there as well. Furthermore, you need to have an idea of your buffing wheel diameter, because different diameters will advance the surface of your buff at different inches per second over your instrument. I know these variables all factor in, but I don't use a power buff, so I can't give you precise advice. I'm just saying that it isn't as simple as asking what pulley diameter. All these other factors play a part. Experienced builders will be able to tell you just what motor power and RPM you need, coupled with a drive pulley size and a buffing wheel diameter to give you the buff wheel speed you need over your instrument. I think Gene Zierdt has come closest to answering your specific question, and also filled in some important blanks for you. Of course, no matter what combination you use, it'll come down to your own sense of touch and pressure while buffing to find out what works for you. But that's the fun part, and practice will yield the results you are seeking.
Author:  Rod True [ Mon Mar 25, 2013 9:51 pm ]
Post subject:  Re: What size Pully
I use a 1/4hp motor and I also have the belt set pretty tight. I can't stop the buffer from hard pushing....I have 12" buffs on my home made buffer. I also run the buff arbor at 1100+/- RPM. The real trick with buffing is to keep the body/neck moving and not stay in one spot very long at all. This is what heats up the finish and can cause trouble.

Blake, welcome from another BC'er...
Author:  Blake Dixon [ Tue Mar 26, 2013 12:58 pm ]
Post subject:  Re: What size Pully
Thanks Rod and others. I guess I should have given you all the goods. I recently ordered the SM buffer with 14 inch wheels and I have a 3/4 hp motor in storage I just thought that was a little over kill however with all the advice I'm hearing, I should be able to use this motor with a loose belt. I have used a buffer in the past however for a much different application. Buffing brass, where heat was not really an issue. I will watch for other posts on this subject to learn from others.

Thanks again
Blake
Author:  crazymanmichael [ Tue Mar 26, 2013 2:49 pm ]
Post subject:  Re: What size Pully
one other nthing to consider is the type of motor. buffing throws off a fair bit of sticky residue. because of this i prefer a tefc motor.
Author:  Robert Hosmer [ Tue Mar 26, 2013 7:01 pm ]
Post subject:  Re: What size Pully
If the first thing you know is your wheel diameter (14"), you can fine-tune things from there by "working backwards".

You need to get an approximation of your desired surface speed (SFPM).
I know you said that you have had previous experience with brass. With the exception of titanium, most metals are gonna do best with speeds well in excess of 5000 SFPM (we used 7000 for brass).
But for the finishes on your guitar, you want to think in terms of the same range of speeds successfully used for plastics; IOW, keep the surface speeds well below 3500 SFPM. For the less-experienced, the slower the better; I have successfully used speeds as low as 1100 SFPM on both finishes (lacquers, etc.) and plastics (such as Lexan). This speed was obtained by using a VFD in conjunction with belt reduction, but it illustrates the point.

Next is RPM of the arbor shaft. Since you now have a general idea of where you want the surface speed (SFPM) to be, you can now determine how fast the arbor needs to spin (RPM).
Stewmac advertises their system as running at 715 RPM at the arbor. With their 14" wheel, this would put the surface speed somewhere in the vicinity of 2600 SFPM. So if you want to emulate the SM setup, strive to keep your arbor spinning at a similar speed.
I have a chart on the wall right here next to the computer; I made it a long time ago because I got tired of recalculating speeds for different wheel diameters, etc.
Looking at the 14" wheel column (with sheave combinations I have used), here are a few (of many) examples that will help keep you in the "safe zone" (under 3500 SFPM) with a 14" wheel.
936 RPM = 3431 SFPM
894 RPM = 3277 SFPM
784 RPM = 2874 SFPM
734 RPM = 2690 SFPM
671 RPM = 2459 SFPM

So the next thing to know is your motor shaft RPM. The motor you have set aside most likely runs at either 1750-1800 RPM or 3500-3600 RPM. (Hopefully you have the one that runs in the lower range, because you're gonna have a bear of a time slowing a 14" wheel down enough for your needs with the higher-speed motor.)

Once you know the speeds of both shafts (motor RPM and arbor RPM), you can determine the speed ratio to correctly size your sheaves (pulleys), then consult your distributor/manufacturer and tell them the ratio you're attempting to satisfy.
To find the ratio, divide the speed of the driver sheave (motor) by the speed of the driven sheave (arbor). Since this is a speed reduction system, your ratio will be greater than 1.
Example: You want to keep it close to the Stewmac setup, so using the 734 RPM arbor speed cited above with a 1750 RPM motor will give a ratio of 2.38 (1750 divided by 734).
An interesting note about the ratio is that it is not only calculated using shaft speeds; it can also be calculated using sheave diameters. The diameter of the driven sheave (arbor pulley) divided by the diameter of the driver sheave (motor pulley) equals your ratio.
I'm not computer-savvy enough to display the formula on screen, but the formula would look like this:
Speed ratio = (motor RPM divided by arbor RPM) = (arbor sheave diameter divided by motor sheave diameter)
Now you can determine which sizes of sheaves will work for your application.
If you already have a sheave on the motor, multiply that diameter by your ratio to determine what size you need on the arbor. Conversely, if you already have the sheave for the arbor, you can divide that diameter by the ratio to size the sheave at the motor.

Example 1: You have a 3.25" sheave already on your motor shaft, and you want to determine the size needed for the arbor.
3.25" x 2.38 = 7.74"
In this case, you should be looking for a 7.75" sheave for the arbor.

Example 2: (This is, for the most part, impractical for your application, but I'll use it to illustrate.) Let's say you have reclaimed a sheave that was once used on an industrial pump. It's an interchangeable-bore design that uses a bushing, so you want to use it on your arbor. You measure it to have a diameter of 10.25"; what size would you need to install at the motor?
10.25" divided by 2.38 = 4.31"
In this case you would look for a 4.25" diameter sheave to place on the motor shaft.

Hope it helps.
Author:  Blake Dixon [ Tue Mar 26, 2013 8:57 pm ]
Post subject:  Re: What size Pully
Thanks again for this wonderful information. I know all of us here benefit from the knowledge of our mentors and newly found friends.

Thanks again for sharing

Blake
Author:  warpedbored [ Sat Jun 22, 2013 11:23 pm ]
Post subject:  Re: What size Pully
All this math makes me dizzy. Keeping in mind that I'm a dumb ass I am building a buffing wheel. I have 12" buffing wheels from LMI, a heavy duty portable shaft from Grizzly with a 3/4" shaft and a 3.25" OD pulley. I'm using a 1/2 HP motor that is 1725 RPM. What size pulley should I use for the motor?
Author:  Colin North [ Sat Jun 22, 2013 11:53 pm ]
Post subject:  Re: What size Pully
warpedbored wrote:
All this math makes me dizzy. Keeping in mind that I'm a dumb ass I am building a buffing wheel. I have 12" buffing wheels from LMI, a heavy duty portable shaft from Grizzly with a 3/4" shaft and a 3.25" OD pulley. I'm using a 1/2 HP motor that is 1725 RPM. What size pulley should I use for the motor?

I was dizzy with all the advice on the forum (which I spent well over an hour reading) so when I made mine with 12" wheels I just aimed at the stewmac SFPM which worked out around 850 rpm.
For that you would need to roughly halve your motor speed, ie use about an 1 5/8" drive pulley on the motor if you can find one that small.
I run 1450 rpm at the motor, and use 3" drive on the motor and 5" on the shaft with a slack belt, so if I push too hard it just slips.
Worked for me. bliss
Author:  warpedbored [ Sun Jun 23, 2013 12:00 am ]
Post subject:  Re: What size Pully
Thank you, any idea where I can find a pulley that small for a 5/8 arbor?
Author:  Stuart Gort [ Sun Jun 23, 2013 12:47 am ]
Post subject:  Re: What size Pully
It's about surface speed. Polishing compounds are designed to be used within a range of surface contact speed to be predictable.

Rpm x diameter (in inches) / 229.2 = surface speed in feet per second.

The full Stewmac polishing system turns 14" buffing wheels at 715 rpm....and I'll vouch for that since I have one and it works great.

715 x 14 / 229.2 = 43.6 fps.

So...43.6 fps or thereabouts is what you're trying to achieve but I can't answer the question without knowing the rpm of the 1/4 hp motor or the Stewmac pulley size.
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