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10-28-2011, 07:46 PM #1
How to balance pulleys, etc. "DIY style"
I'd like to find out different methods of rotating parts balancing that don't require any special balancing machinery: just the common machine shop stuff and machines.
I'll need to balance a steel idler 4.750" in dia. x 4.000" long with about 1" bore. The idler is off a vertical belt sander, and it rotates at about 3500 rpm.
Even if you go the "mandrel on the fences" method, how sensitive is it, and how do you know how much to remove from the heavy side?
10-28-2011, 08:11 PM #2
A lollipop on a stick works too.
But for something as long as that roller, a two plane balance device is suggested.
Check the white papers at Balance Technology Inc. or others.
10-28-2011, 08:16 PM #3
If you started with a solid steel round, it is going to be very close to balanced.
If you wanted to remove some of the mass, you could drill 3 - 4 holes all the way through an equal distance from the rim.
Do the "mandrel on the fences" and drill a tiny bit off the bottom when it comes to rest, equal depth on both sides the same distance from the edge.
If you drill too much and the holes go up on several tries, drill the bottom as above. Or melt a bit of solder in the holes, equally on both sides.
If you are using a machinist's level you should get very close. Put it on the machine and run it. Assuming the idler is on a spring loaded mount, if it shakes adjust the belt to run a bit off the edge of the belt and ease a marker up to the face of the pulley until it barely touches for one snick, the mark will be on the heavy side. Drill, put pulley on and run. Repeat if needed.
There is a comedy bit about cutting a bit off a chair leg to make the chair not wobble. It ends with the seat on the floor.
Last edited by paul39; 10-28-2011 at 08:27 PM. Reason: add
10-28-2011, 08:19 PM #4
Use of gob of clay and stick it inside a recess if you can...move the gob and add to it until the sheave or whatever calms down. Use any crude method to approximate the weight of the gob of clay and stick a hunk of two part epoxy or weld a nut or washer on where the clay was.
They make a epoxy repair stick you smash around by hand to mix the two parts...this works great to stick where the gob of clay was. It hardens and stays put...acts as a balancing weight. Does this make sense?
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10-28-2011, 08:24 PM #5
plus, with the clay "additive" method, one can then remove the equal mass from the opposite side.
10-28-2011, 08:29 PM #6
10-29-2011, 04:04 AM #7
and 10k isn't much, a lot of the planes i play with run closer to 30k RPM.
and then there are the single blade competition props...
10-29-2011, 04:14 AM #8
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10-29-2011, 05:02 AM #9
There's a number of balancing tricks you can use for home brew single and two plane balancing. All are equipment intensice even if the equipment is failry simple to build.
Here's a fairly technical explanation of theory and terms.
There's a way to home-brew a silplified DIY balancing machine that uses resonance at a moderate RPM. By use of trial weihts in the form of modeling clay the amount and point of unbalance can be determins right at the location of the correction area. Problem is the sensitivity is limited to about 0.1 oz-in which may be OK for pumps, fans, and motors but excessive for high speed rotating equipment.
One-off balancing jobs should probably be framed out. If the challenge is killing you I'll take a stab at describing the apparatus and procedure but it will take a LOT of words.
10-29-2011, 07:03 AM #10
10-29-2011, 10:38 AM #11
i Balance my surface grinder wheel by running at speed with a dti tip resting on the spindle housing, magnet on the table. The width of needle Burr is a pretty precise measurement. Move the weights and start it up again, more or less vibration. After the first 3-4 goes its easy to know were your going and how much further to go.
Its not pretty and its not instant, but 10 minutes gets it pretty darn good. equally its doing it dynamicaly which is always a improvment over static balancing. Especially when its going to be used as multiple bits mounted together.
10-29-2011, 11:25 AM #12
Lots of interesting solutions above, some of which sail 5,280 feet over my head.
We are not balancing gyro wheels to be certified for flight.
If it is not a big deal to assemble and run, put the machine together with the pulley as is, stand to the side, and turn it on and quickly off, if no or slight shake, turn on again. If it runs OK use it.
If some shake, do my suggestion in #3 above and try again on the machine. You might also check the balance of the drive drum. Also the V-belt pulleys on the motor and drive drum.
If you can't get it to your satisfaction, take all the rotating parts to a race car engine builder or a balancing place.
In 1962 I had all the reciprocating and rotating parts of an MG engine and clutch statically and dynamically balanced by Edelbrock Engineering in Los Angeles. I was amazed at how much metal was cut off the crank and drilled out of the flywheel. The car had the usual 4 cylinder vibration before, and was considerably smoother after, especially near the red line.
I would be curious to know how much balancing is done on belt sanders by manufacturers. I suspect the more you pay, the better the balance.
Last edited by paul39; 10-29-2011 at 11:28 AM. Reason: add
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10-29-2011, 12:50 PM #13
What led you to determine the "need" to balance the pulley?
If this is a machined assembly, it should be (in theory) homogeneous, and close to balanced as it is.
Have you spun it up to expected speed?
10-29-2011, 04:52 PM #14
Very interesting thoughts and advices, everyone. Please keep them coming. Thank you.
10-29-2011, 06:11 PM #15
10-29-2011, 06:36 PM #16
First, I'm really enjoying this thread, particularly the poor man's balancer.
Depending upon application, this may be a dumb question but why does it have to be metal? Why not wood? Not as sophisticated/complicated a solution but in some applications wood is a better choice and with a much lighter weight balance is not as much an issue.
10-30-2011, 01:35 PM #17
I considered this. The original idler was made out of cast iron. Plastic or wood are pretty much out of question for this particular application. Maybe, aluminum, but it'll require a steel hub for the bearings, anyway. So I decided to stay with a steel pulley.
10-30-2011, 06:48 PM #18
I bought an 8 inch wide shop made belt sander for $15 at an estate auction some months ago. I make turned bowls, 8 inch wide is nice for making flat bottoms.
The rollers were made with about 3 inch pipe with a steel strap X welded in each end, bored for an axle, axle welded in and put in sealed bearings bolted to the body. I don't remember if a skim cut was taken on the face of the rollers. It was rusty but the rollers turned smoothly.
It did have some holes drilled for balancing. I have not run it yet, it may shake like a dog pooping peach seeds.
If you like, I can drag it out and take photos.
10-30-2011, 07:45 PM #19
We received a machine that had some 8" dia. x 70" long steel rollers,approx 200 lbs ea. two of which were badly out of balance at 150rpm, they needed to max out at 500rpm.One was on the dancer that controlled the web tension .Only option was to try and balance them.Looking at one end they appeared to be professionally built,however on the other end judging by the welds they had been shortened.To balance std,procedure is to drill a hole in the end cap and insert a rod the correct weight and weld.Didn't see any evidence of that.
I mounted the rolls on a bench using pillow block bearings,one end ridged,the other on a "trap door affair" (one side of the bearing held with a pivot pin the other supported on comp.springs)Clamped a dc motor & controller to the bench with a belt over the roll to drive.Using chalk to mark the heavy side at the sprung end I added weight to the opp side,flipping the roll end to end several times & slowly increasing
speed I managed to get them to run smooth at 1300 fpm.It took over 5 lbs per end.(Of course the plant it came from said they never had any balance problem)
10-30-2011, 08:03 PM #20
We have a lot of scrap blowers 40/50 HP 3' dia.that will lose balance weights get bent/damaged and start vibrating ruining bearings.We have a balance shop down the street now that we send them to now.However at our old plant one of our subcontractors could balance them in place,all he needed was a piece of chalk and a welder and in about half an hour would get them running as smooth as new.He would mark the shaft between the bearings with the chalk using the clearance in the bearings & housing.