Balancing a pulley

I have a Jet 17 floor standing drill press - not one of my canniest purchases. It shakes fit to bust - it can do accurate work, because the table shakes in synchrony with the head, but I hate using it.

I'm trying to diagnose the problem(s). First off is that that if I take the four stage primary drive pulley off the motor the clattering stops, but with the pulley on (without a belt, just free spinning) it starts again. I stuck the pulley on the lathe and the internal (19mm) bore is about 0.1mm runout from the PCD, best as I can measure. Is that enough to account for the clattering? I'm a bit at sea here, any advice welcome!

Rob

I ran across that situation quite a few years ago. I put the pulley in the 4 jaw, dialed in on the vee grooves, and then bored the hub for an oversized bushing. Then bored the bush to fit the motor. The darn pulley was made some 20 thou eccentric!!

That fixed the problem.

Pete

Firstly, is it balanced statically?

How is the pulley fixed on the motor shaft - keyway or a couple of grub screws?

Is the motor shaft running true?

You should be able to measure run-out at the face of the outermost rim.

Which way is the pulley fixed to the motor? Maybe reversing it is possible? (I don't know if there is a preferred orientation for these things).

Only now consider the concentricity of the pulley bore with the belt grooves, is my advice

I had the same problem which was due to unbalanced mass in the rear of the pulley.

the solution was to make a mandrel and mount the pulley so I could machine the back then turned away the uneven lump off the inside of the pulley.

pmm1

Thanks for your replies. Heres a pic of the pulley: (well at the bottom of this post - haven't figured out how to incorporate inline images on this site). It's about 80mm top to bottom, 19mm bore, with a 6mm internal keyway about 3.5mm deep along the whole length of the bore. The key on the left is 6x6mm and about 30mm long -there's an M8 grub screw in the boss at the base of the pic, which bears on the key. The motor spindle protrudes maybe 35-40mm into the bore. Too much data perhaps!

I'd have a problem boring and bushing because I don't have kit for making an internal keyway, but thanks for the suggestion Pete.

I have no idea if it's statically balanced ndiy. How would I test for that? Obviously even if the pulley grooves were perfectly concentric with the bore the whole thing would be still unbalanced because of the empty part of the keyway - but I have no gut feeling for how important that would be. It's a 4-pole motor, so around 1400 rpm.

pmm1 -no obvious signs of uneveness in this case, but thanks for your suggestion.

Robin

What is the fit on the motor shaft without the key fitted - it should be a snug sliding fit or a very light tap fit .

I have seen pulleys bored oversize and the sliding fit was caused by the key which pulled the whole pulley off centre !

What about the motor bearings - any play there ?

There could be an internal fault in the pulley (fissure) , i would machine up a mandrel so i could mount it in the lathe and spin it up to the operating speed the pulley normaly runs at and see if the vibration occurs -if it does and you cant perceive any runout maybe look at a new pulley .

The amount of metal missing from the keyway groove would have a negligable effect at the speed it operates as the keyway is close to the centre line of the motor shaft .

Ian

An alternative thought to imbalance.

It appears that the motor is single-phase and hard mounted. A single phase motor does not produce a smooth torque, but 'pulses' along at 100 pulses per second. The reaction torque on the stator is transmitted through the hard mount to the machine frame. This may be the principal cause of the vibration.

The pulsing torque will also cause the rotating parts to alternately accelerate and decelerate, particularly as there is very little mass here to act as a flywheel. This can lead to the quill spline 'rattling' when the drilling load is insufficient.

On my old rig I conjured up a resilient mount for the motor to largely overcome the vibration from the hard mounted motor. The spline rattle would need a flywheel or similar on the motor shaft. The best solution is a three phase motor, but perhaps with me, not easily arranged.

You could do the following tests: If it is as described above, the vibration will not alter with belt ratio (spindle speed) and you will hear/feel 100 Hz (two octaves below G(above middle C)). If motor imbalance, and it's a 4pole motor (1475 rpm), the vibration will be at 25Hz unloaded (i.e. once per rev).

.

That ^^^ is, I suspect, the most probable cause of the vibration

Unfortunately that means that even if you have a well-balanced pulley, the dynamic balane will be bad.

To check for 'static balance' you will need some approximation of the watchmaker's Poising Tool.: **LINK**

http://great-british-watch.co.uk/how-to-poise-a-balance-wheel/

Your approximation will depend on the tools and materials you have available ... but it is worth stuying that link, to understand the principle.

MichaelG.

.

Edit: for a basic check it should be sufficient to mount the pulley between [static] centres on your lathe ... you will be at the mercy of friction, but it should reveal any major imbalance.

Edited By Michael Gilligan on 20/03/2017 07:05:54

It can be down to a distorted V belt, this can be because of the belt being under tension while the machine is in storage/unused for a long time, or it can be just the belt, I know I'v got one on my milling machine that needs replacing.

Ian S C

Robin,

It's interesting to see that the current [?] version features poly-v belts

**LINK**

http://www.jettools.com/us/en/p/17-drill-press/716300

If the poly-v pulleys are available as reasonably-priced spares, they would probably be a wise investment.

MichaelG.

If you turn a bit of bar down to a firm fit in the pully and leave it in the lathe then push the pully onto the bar you can then spin it up to speed on the lathe.

If you get vibrations there then the issue is most likely the pully, if you don't get vibration then its more likely to be fit of pully on motor

Robin

Seriously consider Micheal's suggestion changing over to poly-vee drive.  Carving new poly-vee pulleys from solid isn't unreasonably difficult if you don't want to buy.  Pulleys don't need to be very big. I had a Pollard Corona 100A drill, probably of similar size to your Jet, with 1 HP motor which used a poly Vee belt about 1/2" wide. Maybe 5 grooves on the pulleys.  About something under 3" long overall for a 5 step stack. Worked very well. Poly-vee pulleys are easily made if you have an adjustable bed stop on the lathe or a fixed stop with a suitable set of different thickness blocks to step out the groove spacings.

I made one up step by step from a set of disks. Started with a solid bar a bit larger than the smallest pulley. Bored and keyed it to match the shaft. Made the smallest pulley first. Then turned the rest of the bar down to make a mandrel and pushed the disks on one at a time so I was always working on the largest disk. Fixed things together with loctite backed up by small counter sunk socked head screws. Each disk had 4 holes through it running parallel to the bore. Two clearance and countersunk for the screws. Two tapped for the screws holding the next disk.

Sounds like more work but its a defined job. I often find that starting over with something that can jus be made and will work is quicker than trying to sort a defective part or assembly.

Trying to fix an unbalanced, cast, multistep Vee pulley could turn out to be a truly miserable experience. The length means that not only do you have to deal with simple radial imbalance you may also have imbalance along the length of the pulley. Basic radial balance is relatively easily achieved by simple axle on a knife edge or free running bearings et al using the principle illustrated in Michael's posing tool link. But this may not be enough as there could still be compensating imbalances at opposite ends of the pulley so it will still vibrate. Not easily sorted even if you have the gear.

Way back I had to balance up some rotating devices of similar dimensions to your pulleys but less heavy that were intrinsically unbalanced in this manner. Had the use of a simple turbocharger rotor balancing machine with electronic readouts of imbalance but it still took ages and much verbal encouragement. As I recall matters the process was less than intuitive in that adjustments that seemed to be the right way to go about things didn't work out as expected.

Clive.

Edited By Clive Foster on 20/03/2017 10:32:07

Edited By Clive Foster on 20/03/2017 10:35:13

Edited By Clive Foster on 20/03/2017 10:35:57

Clive

MichaelG.

My floor standing drill is one I bought in 1983,when I knew little or nothing about such things,other than that they were better than a hand drill.It is a cheap Taiwan model,spec unknown,but something which has served me well over the years [more than I can say for my rotary table ] It never gave any bother,smooth running and quiet,although it is single phase,of course. Many years ago I managed to drill out 1/2" silver steel to make 3/8" drill bushes,by mounting the blanks in the chuck and the drill bits held in a cheap table vice ! Sounds crazy? maybe,but it worked. We needed 24 bushes to make up a drilling jig.

It sounds like your pulley cone may be bored off center. You should not have that much vibration to contend with.

The other cause might be too much mass in one part of the cone. Not sure how you deal with that.

By the way,I have never replaced my belts on that machine. The bushes worked out fine also.

Robin,

Pop it round one day when you are passing. It's a 10 minute job.

Robin,

As previously suggested, I would have a close look at the belt. I have seen belts on these import machines where there was a definite "step" at the join, others where the thickness varied, both are sources of vibration.

I have made a round poly belt, the sort you cut to length and heat join, and put it on a noisy machine and it was transformed.

Can't be a belt problem

"First off is that that if I take the four stage primary drive pulley off the motor the clattering stops, but with the pulley on (without a belt, just free spinning) it starts again"

<bodge> Is there room to pop a shim made of a bit of beer/coke can between the motor shaft and the pulley to pull it on centre and reduce play? </bodge>

Thanks for your further thoughts on this problem. I'm sure that poly-V belts would be better in the long run, but as JasonB noticed my first trouble is with the clattering which starts when when I mount the pulley on the motor spindle without any belt. That has to be addressed before considering any other refinements to the drive train.

I should probably make a mandrel to fit the pulley and spin it in the lathe as Jason suggested, but given JohnS' kind offer I'll drop by the Lodge when I'm next in the area. Thanks John, I'll PM you.

Robin

Jason

I must have nodded off while reading that bit. Happens all the time!