Variable Speed Sanding/Buffing Option

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BobR
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Variable Speed Sanding/Buffing Option

Post by BobR »

Thought I'd share with the group my findings after doing a little research on variable frequency drives (VFD) and compatible motors to use as a variable speed sander/buffer. The VFD is what controls the speed of the motor. It converts AC to DC then converts it back to "psedo" AC using closely spaced pulses (square waves) to approximate the original AC waveform. It's not a perfect replication of the original AC waveform and produces more heat and voltage spikes in the process. It's important to use a motor that was designed to be used with a VFD. Most new motors are compatible, even the general purpose motors. The main benefit of using a VFD besides speed control is constant torque at lower speeds. There may be a better/cheaper VFD than the Automation Direct but I haven't found it. The stuff on eBay is not as good as Automation Direct and is a risk IMO especially with respect to customer service and warranty. You can use an Automation Direct general purpose motor or inverter-duty motor for system costs of $298.00 and $456.00 respectively. The general purpose motor will operate with constant torque down to 900 RPM. The inverter-duty motor will operate with constant torque down to 90 RPM. You do need a three phase 220V AC motor with a VFD.

FWIW, I deep dove the technical specifications of several brands. I found the hardware from Automation Direct to be the best value. It is decent quality and more than adequate for pipe making. You don't need any other accessories such as line filters etc. Those are only needed in a factory installation where line lengths between the VFD and the motor are long. I don't think anyone can beat their prices. Free shipping.

A nice VFD IMO for $186.00 is the GS2-11P0 (1HP). The input is simple 115V which is easy. They do have a version with 220V input if you want that but there is no performance advantage. Both have a 220V , 3 phase output for the motor. I like the potentiometer on it to quickly change the speed without having to add any other controller like Tyler did. You can pre-set up to 7 speeds on the digital keypad. The digital keypad is removable so you can mount the keypad near the motor or somewhere convenient and mount the controller a few feet away to keep it clean which I think is important. They sell various length extension cables for the keypad if you do this. Scroll down to see the different models when you click the link. The third one from the top is the GS2-11P0.

http://www.automationdirect.com/adc/Sho ... Control%29

Here is the Manual: http://www.automationdirect.com/static/ ... /gs2m.html

The GS1 is cheaper but is lacking a few nice options like the removable key pad. You compare: http://www.automationdirect.com/static/ ... ection.pdf

The link below is for the Marathon inverter-duty motors which are good (affordable) motors. I like the Y364 (1800 RPM, 5/8" shaft) for $270.00 which has a 20:1 constant torque rating. That means it will have constant torque down to 1/20th of it's normal operating speed (1800 to 90 RPM). The motor's max speed is ~ 5000 RPM and this controller can run it up to that speed if desired (not recommended though). No problem running constant under full load at 3600RPM. The inverter-duty motors are made to handle high voltage spikes on the leading edges of the pulses inherent in using a VFD (very narrow pulse widths with ns rise times ... the voltage overshoots then settles down). They stay cool at low speeds.

http://www.automationdirect.com/adc/Sho ... 28by_HP%29

General purpose motors on the other hand are a bit cheaper and have a 2:1 constant torque rating. That is, below half the normal operating speed they loose torque quickly. So, for an 1800 RPM motor, they work well down to 900 RPM. Newer general purpose motors have beefed up windings like the inverter-duty motors to handle the extra heat and voltage spikes. Older general purpose motors can get pinholes burned in the motor windings or failed bearings due to the voltage spikes causing arcing over to the bearings which damages them. With that said, a newer general purpose motor will work.

Using this 3/4 HP general purpose motor the whole setup is only $298.00. This motor will work fine and provide constant torque down to 900 RPM (Vs. 90 RPM for the inverter-duty) . http://www.automationdirect.com/adc/Sho ... -P75-3BD18

The inverter-duty motors are an upgrade to the general purpose motor and provide constant torque at slower RPMs (20:1 Vs 2:1 constant torque rating). They do sell a 1000:1 constant torque motor called the black max which will run constant torque down to 1.8 RPM which is nice for removing toe fungus but it isn't worth the added cost, IMO.

VFD's can also be used on a lathe or drill press. http://www.youtube.com/watch?v=nFPX1pW3Sl8

Anyone here done that?
Last edited by BobR on Mon Feb 24, 2014 12:45 pm, edited 4 times in total.
Bob
LatakiaLover
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Re: Variable Speed Sanding/Buffing Option

Post by LatakiaLover »

First rate info. Muchacho gracioso, RobertoR. :D

The whole variable speed approach is something I think every serious pipemaker should look into.
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Red
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Re: Variable Speed Sanding/Buffing Option

Post by Red »

Thanks for sharing that research, Bob. It seems that information on this subject would be plentiful on the web, but it's surprisingly hard to find and distill in a way that's comprehensible and usable to a non-engineer. I've gotten off on rabbit trails before, like dc motors and controllers that run upwards of $600-$1000 or more. I'm sure that a simple inverter is a far more equitable way to go.
dogcatcher
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Re: Variable Speed Sanding/Buffing Option

Post by dogcatcher »

Look at this one, http://www.ebay.com/itm/161060977929?ss ... 1423.l2649

It is an industrial sewing machine motor with a speed controller built in. It does lose power at low speed, but it is works. Find a lathe headstock with threads and you can make your own system for a decent price. I bought a Delta headstock for $34 plus $18 shipping off of eBay, a belt from NAPA, a few bolts and piece of plywood to bolt it all down less than $200. I drilled and tapped a block of wood for a buffing mandrel that screws on the threads of the headstock, cost about 25 cents.
BobR
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Re: Variable Speed Sanding/Buffing Option

Post by BobR »

VFD's are for those that want or need constant torque at slower speeds. YMMV

Plus, in the end, with shipping and extras, you will probably spend at least $298.00 (the "value" version I showed).

Since the motors I showed have 5/8" shafts, it's really easy to set them up as buffers or disk sanders. The Beall arbor or any cheap arbor will attach directly and you're good to go.
Bob
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Re: Variable Speed Sanding/Buffing Option

Post by E.L.Cooley »

I use vfds at my day job regularly. Over the long run marathon motors don't hold up. If I were to invest my money it would be a Dayton motor. Weg holds up the best but are heavy and pricey. Bearing frosting or fluting can be prevented by a motor shaft grounding brush. My preferred brand of drive is a cutler hammer/eaton drive. It looks like you running a 1hp motor?


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E.L.Cooley
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Re: Variable Speed Sanding/Buffing Option

Post by E.L.Cooley »

I am also concerned about the motor that runs down to 90rpm on a 1800rpm motor that would be 3hz or 3 cycles/second. I see the motor does have an bearing end fan however I have never ran an inverter rated motor below 12hz. I would also be Leary of running over 75hz which is nowhere. Lose to 5000rpm. Almost any brand of drive is capable of the ranges you talked about and I've never seen one that would not accept a potentiometer input?


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BobR
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Post by BobR »

Sorry you don't trust the published capability of the motors I referenced. They work as stated. Not all motors are the same and inverter rated is like saying digital ready. You need to look at the specs. Sorry I didn't mention that other VFD's do the same thing and have multiple inputs for pots and such. :)

The whole point of my post was to show an option for a low cost solution.
Last edited by BobR on Mon Feb 24, 2014 8:00 am, edited 2 times in total.
Bob
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Re: Variable Speed Sanding/Buffing Option

Post by caskwith »

I love my variable speed buffer and wouldn't be without it now that I have it. Next project will be a variable speed sander, my current system uses belts and I never change it cos it takes too long, next version will be easier to change so I will actually make use of it.
E.L.Cooley
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Re: Variable Speed Sanding/Buffing Option

Post by E.L.Cooley »

Naw bob I was just saying I'm shocked to see specs like that.


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N.Burnsworth
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Re: Variable Speed Sanding/Buffing Option

Post by N.Burnsworth »

I just recently purchased a variable speed foot pedal and it seems to be working just fine on my 1/2 hp 6" bench grinder. It cost me $27.95 plus $6.00 shipping. My only question now is, can this cause harm to the motor?
Nicholas Burnsworth
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BobR
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Re: Variable Speed Sanding/Buffing Option

Post by BobR »

N.Burnsworth wrote:I just recently purchased a variable speed foot pedal and it seems to be working just fine on my 1/2 hp 6" bench grinder. It cost me $27.95 plus $6.00 shipping. My only question now is, can this cause harm to the motor?

No, but you are controlling the speed by reducing the current to the motor. It loses HP and torque when you do it that way. If it works for your application that's great. Grinding probably doesn't put much load on the motor.

I know I tried something similar on my buffer and it didn't work very well at slower speeds.
Bob
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Vermont Freehand
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Re: Variable Speed Sanding/Buffing Option

Post by Vermont Freehand »

I appreciate the sharing of all the homework you did, Bob, thanks!!

FWIW, I bought a shopsmith with just about every attachment made. It was used and I paid about $1,000, but I sold all the attachments I didn't want for well over $1,000 (after pieced out) and had a handful of attachments left over along with the unit itself. All in all, I made money on it and I now have an adjustable speed motor that I can use for sanding discs, polishing, random drilling, etc. Plus it was made in the 50's and will probably hold up much longer than the cheap stuff made today. Of course bearings will probably be the first to go some day, but an easy fix.
N.Burnsworth
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Re: Variable Speed Sanding/Buffing Option

Post by N.Burnsworth »

I'm actually using it when I do my buffing and polishing. I have a 3600 rpm grinder and I'll slow it down to about 2000 rpm and use an 8 inch buffing wheel which I believe will have a slower surface speed compared to the 6 or smaller size buffs. It seems to be working well.
Nicholas Burnsworth
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BobR
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Re: Variable Speed Sanding/Buffing Option

Post by BobR »

N.Burnsworth wrote:I'm actually using it when I do my buffing and polishing. I have a 3600 rpm grinder and I'll slow it down to about 2000 rpm and use an 8 inch buffing wheel which I believe will have a slower surface speed compared to the 6 or smaller size buffs. It seems to be working well.
The larger the wheel the higher the surface speed. But if it works, it works. Enjoy it!
Bob
BobR
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Re: Variable Speed Sanding/Buffing Option

Post by BobR »

N.Burnsworth wrote:I'm actually using it when I do my buffing and polishing. I have a 3600 rpm grinder and I'll slow it down to about 2000 rpm and use an 8 inch buffing wheel which I believe will have a slower surface speed compared to the 6 or smaller size buffs. It seems to be working well.
the surface speed (in feet/minute) of a buffing wheel = the circumference of the wheel (in feet) X RPM.

The wheel circumference is PI (3.14159) X wheel diameter.
so..surface speed in feet/min (SFPM) is: PI (3.14159) X wheel diameter X RPM
8 in wheel @ 2000 RPM: 3.14 x 0.66' x 2000 = 4144 SFPM
4 in wheel @ 3600 RPM (bench grinder): 3.14 x 0.33' x 3600 = 3769.9 SFPM

Your slowing it down and using 8" wheels actually increased your surface speed vs the 4" buffs
@1200 rpm the surface speed of an 8: wheel would be 2487 SFPM (Rads choice)

Try slowing it down to near 1200 RPM and see how it buffs.
Bob
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Re: Variable Speed Sanding/Buffing Option

Post by N.Burnsworth »

Wow, thanks for your time to break it down for me. I will definitely try bringing it down to 1200 with the 8" and I also have a bunch of 5" buffs that I started with.
Nicholas Burnsworth
Boulder & Briar
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