Driveshaft Balancing

GFR3SH · Jul 20, 2018

How is true zero imbalance achieved/determined when using a soft bearing driveshaft balancer?

To my understanding, in a perfect situation, both the head stock and tail stock spindles spin at .000" imbalance with a yoke attatched. When a driveshaft is bolted in, and is spinning at .005" imbalance, weight is added and moved around until the dial then reads .000" imbalance. The driveshaft is now perfectly balanced.

In a non perfect situation, because actually getting the dial to read .000" imbalance with just a yoke spinning on the spindle is very time consuming, say it reads .001" before a driveshaft is bolted in. After the shaft is bolted in, and it reads .005" imbalance, is the net total imbalance technically only .004"? Does weight added to the shaft only have to bring the imbalance down to the .001" reading that was there with only the yoke spinning?
Does making the shaft spin at .000" when the yoke alone spins at .001" leave the shaft unbalanced?

eKretz · Jul 20, 2018

You've already got the answer. Yes. Yes. Yes. Best thing you can do is make sure it's zeroed before you start, then you don't have to worry about any of these questions. In addition, depending on the mass of the shaft vs. the mass of the balancing apparatus, your "shifted/corrected" numbers may not correlate. Quality work means doing it right.

DDoug · Jul 20, 2018

I think that when you don't bring the yoke down to .000 (left at .001)

The problem arises when adding in the driveshaft it may (by it's own unbalance)
help the overall unbalance. If you change the timing of the yoke to the rest of the driveshaft, it all goes out the winder.

So you really want the individual parts balanced as good as possible,
so that they can be interchanged and not effect the overall balance.

I have designed balance machine adapters, and we always have them made & balanced to the limits of the machine. Think of the yoke like that.

EDIT:
What problems are you having in getting the yoke balanced ?
When I have balanced things, I find sneaking up on the corrections, so you don't overshoot to work best. If you go "whole hog" and start adding weight/grinding off stuff to the full amount indicated on your machine, re-spin and you find the imbalance moves around, you've overshot.

reedeprintice · Jul 20, 2018

Rubber bearings have a certain "bob" speed usually 1200 rpm tune it there

GFR3SH · Jul 20, 2018

digger doug said:
I think that when you don't bring the yoke down to .000 (left at .001)

The problem arises when adding in the driveshaft it may (by it's own unbalance)
help the overall unbalance. If you change the timing of the yoke to the rest of the driveshaft, it all goes out the winder.

If I understand you correctly, you're saying theres no way to tell if a .001" yoke will make a .001" shaft read .000" or .002"? Therefore, the balance would only be good to +/- .001?

Or, do you mean if the yoke is .001", that imbalance may multipy an imbalance in the shaft, giving no true numbers to calculate on?

Also, 180 degree change of the shaft in an imbalanced yoke will also change the imbalance, umpredictably?

FWIW, the spindle without an attatchment on it spins at .001". Would any adapter zero balanced have to be put back on the spindle in the same orientation then in order to maintain its zero?

I have designed balance machine adapters, and we always have them made & balanced to the limits of the machine. Think of the yoke like that.

EDIT:
What problems are you having in getting the yoke balanced ?
When I have balanced things, I find sneaking up on the corrections, so you don't overshoot to work best. If you go "whole hog" and start adding weight/grinding off stuff to the full amount indicated on your machine, re-spin and you find the imbalance moves around, you've overshot.

Not having problems balancing the yokes, per se. I just dont think my employer wants me spending the required time balancing a yoke to .000". Most of our yokes are .001 or .002. We have about 40 companion plates/flanges, full yokes and half yokes.

The indication on the machine I'm using isnt digital, its by using a felt pen to lightly mark the spindle/feel the vibration in the marker. Then the I stop the machine. The greater the vibration, the darker and shorter the mark is. I put a guestimated weight there based on experience/shaft size/imbalance(I.e, 1710 series shaft, heavy, .010 imbalance, I put the heaviest weight we have on it to start). If it smooths out considerably, but not quite where I need it, I move it clockwise/counter clockwise a bit until it smooths out the most, then I mark it again. Mark in the same spot? More weight, moving? Less weight, or a finer movement of the direction I was going. Complete 180? Less weight. As I get around .002", the marker stops giving definitive responses, all becomes 1 shade or the mark is so long its hard to say for sure where it needs weight to take up the last .002... I generally get the last .002" taken up by trial and error sooner than I definitively take it up by the mark on the spindle.

On some of the yokes theres not much room for grinding, and welding weights on near the outer rotating mass. It would be time consuming to get .000" imbalance given my tooling.

GFR3SH · Jul 20, 2018

reedeprintice said:
Rubber bearings have a certain "bob" speed usually 1200 rpm tune it there

Can you elaborate on this?

Garwood · Jul 20, 2018

GFR3SH said:
If I understand you correctly, you're saying theres no way to tell if a .001" yoke will make a .001" shaft read .000" or .002"? Therefore, the balance would only be good to +/- .001?

Or, do you mean if the yoke is .001", that imbalance may multipy an imbalance in the shaft, giving no true numbers to calculate on?

Also, 180 degree change of the shaft in an imbalanced yoke will also change the imbalance, umpredictably?

FWIW, the spindle without an attatchment on it spins at .001". Would any adapter zero balanced have to be put back on the spindle in the same orientation then in order to maintain its zero?

Not having problems balancing the yokes, per se. I just dont think my employer wants me spending the required time balancing a yoke to .000". Most of our yokes are .001 or .002. We have about 40 companion plates/flanges, full yokes and half yokes.

The indication on the machine I'm using isnt digital, its by using a felt pen to lightly mark the spindle/feel the vibration in the marker. Then the I stop the machine. The greater the vibration, the darker and shorter the mark is. I put a guestimated weight there based on experience/shaft size/imbalance(I.e, 1710 series shaft, heavy, .010 imbalance, I put the heaviest weight we have on it to start). If it smooths out considerably, but not quite where I need it, I move it clockwise/counter clockwise a bit until it smooths out the most, then I mark it again. Mark in the same spot? More weight, moving? Less weight, or a finer movement of the direction I was going. Complete 180? Less weight. As I get around .002", the marker stops giving definitive responses, all becomes 1 shade or the mark is so long its hard to say for sure where it needs weight to take up the last .002... I generally get the last .002" taken up by trial and error sooner than I definitively take it up by the mark on the spindle.

On some of the yokes theres not much room for grinding, and welding weights on near the outer rotating mass. It would be time consuming to get .000" imbalance given my tooling.

What I find really funny is I have joked how OEM driveshafts are made just like you described there.

Some guy just welds a bunch of washers on wherever he feels like and nobody cares that that the tube is .050" out of round and the yokes are crooked.

When I make a driveline I cut all the weights off and use round tubing. Never balanced one and never had a complaint. From class 8 to 200+ MPH rails.

JRIowa · Jul 21, 2018

GFR3SH said:
The driveshaft is now perfectly balanced.

No such thing! We made thousands of driveshafts, if not 10s of thousands. Every customer had their balance specification for balancing. IIRC, most checks were done between 1,500 and 2K RPM with the shaft fully assembled. Our 2 head machine told you where and how much weight to weld on. Just picture a pair of tire ballance on a track.
JR

GFR3SH · Jul 21, 2018

Garwood said:
What I find really funny is I have joked how OEM driveshafts are made just like you described there.

Some guy just welds a bunch of washers on wherever he feels like and nobody cares that that the tube is .050" out of round and the yokes are crooked.

When I make a driveline I cut all the weights off and use round tubing. Never balanced one and never had a complaint. From class 8 to 200+ MPH rails.

I didnt describe how to make driveshafts, I also hardly call having a driveshaft balancer and welding weights on a shaft so that while spinning at 2500 rpm it runs butter smooth at .001" imbalance "some guy just welding weights where he feels like"

Crooked yokes and .050 out of round hasnt ever balanced in my machine. You cant balance a crappily built driveshaft. And when the yokes are square, its 1 in 50 shafts where all the stars align and it doesn't need weights to bring it in even a little.

HuFlungDung · Jul 21, 2018

Garwood said:
What I find really funny is I have joked how OEM driveshafts are made just like you described there.

Some guy just welds a bunch of washers on wherever he feels like and nobody cares that that the tube is .050" out of round and the yokes are crooked.

When I make a driveline I cut all the weights off and use round tubing. Never balanced one and never had a complaint. From class 8 to 200+ MPH rails.

Same here. I tell people I can't balance them, but I can check if the yokes are on square and the tube is 'in wack'. If they want a balance, they'll have to go to the city (2 hour drive), but either way, the driveshaft needs to be straight before it's balanced. So they say "Do what you can to check it, it's unusable as is" so I work on it. Driveshafts that customers notice have a vibration problem, are always obviously out of wack in some easily measurable direction. Either it was hit with a rock or a jack, or some hack 'put it in his lathe' when he shortened it with a chop saw.

Maybe it's just that there's no stretch of road around here that is smooth enough to notice a slight driveshaft imbalance from whatever I can't fix with a straight build

Garwood · Jul 21, 2018

GFR3SH said:
I didnt describe how to make driveshafts, I also hardly call having a driveshaft balancer and welding weights on a shaft so that while spinning at 2500 rpm it runs butter smooth at .001" imbalance "some guy just welding weights where he feels like"

Crooked yokes and .050 out of round hasnt ever balanced in my machine. You cant balance a crappily built driveshaft. And when the yokes are square, its 1 in 50 shafts where all the stars align and it doesn't need weights to bring it in even a little.

Do you use seamed tubing?

GFR3SH · Jul 21, 2018

Garwood said:
Do you use seamed tubing?

Sure don't.

Street · Jul 21, 2018

Shafts that run true help a lot to get something in balance most shafts i have done require a little grinding on the yoke or added weight some however come up just great maybe one in twenty and require nothing.

The reason for imbalance is the centroid of mass does not spin on the centre of rotation.
For you to feel a vibration the shaft must vibrate the diff in turn vibrate the springs to the body vibrate the body to what you feel in the car so a lot of mass to move.
Thats why a shaft a little bit out of balance is not felt in the car.
Its better to get a shaft close as it will be less likely to fail or be hard on bearings.

HuFlungDung · Jul 22, 2018

One of the most critical aspects is getting the yokes in squarely so that the axis through the bearing holes are coplanar. This is because the yokes are in phase at both ends of any one shaft. So any discrepancy in the distance between the bearing caps on one side versus the other means that the tube WILL be continuously stretched and compressed as it rotates. This amounts to vibration which is not properly corrected with weights added, IMO. If you attempt to flame straighten the tube to correct for this error, then you'll have to have a bent tube which is no good. So there is really only one way to do it right and that is to do it right.

JRIowa · Jul 22, 2018

All that I can tell you is how we made driveshafts.
Only a small % were seamless tubing. Most was DOM. All the tubing was cut and chamfered with a Modern tube cut-off machine.
Yokes were pressed and welded in the same machine. About 50/50 on in-line yokes vs 90 deg. What we had the most trouble with was the projection welder for the weights. That was mainly because so of the operators thought it needed adjustment. The welder would be so hosed we'd have to fly somebody in to fix it.
Here's where our balancer came from: Balancers - BTIBTI
JR

HuFlungDung · Jul 22, 2018

90 degrees out of phase is incorrect. Here is a nice video demonstrating why.

Drive shaft velocity - YouTube

DDoug · Jul 22, 2018

HuFlungDung said:
90 degrees out of phase is incorrect. Here is a nice video demonstrating why.

Drive shaft velocity - YouTube

I had to (at least try) to explain to a Mechanical engineer (at least he has the paper) that he just rewelded his broken brush hog drive shaft, why it is
important to get them timed right.
His cobble job was about 25* off.... :ack2:

duckfarmer27 · Jul 22, 2018

digger doug said:
I had to (at least try) to explain to a Mechanical engineer (at least he has the paper) that he just rewelded his broken brush hog drive shaft, why it is
important to get them timed right.
His cobble job was about 25* off....

Doug -

Well, some who got the paper just got the paper. It was amazing to me 48 years ago how some guys working on their senior project really could not do anything of a practical nature. Might have understood theory but could not apply it at all. Then there was a time I had to teach another mechanical engineer at work what a torque wrench was - he was trying to 'help' me and one of my technicians. He was tightening a bolt, the wrench 'clicked' and he kept on reefing - tech damn near decked him. And of course he was a higher level engineer.

Like Will Rogers once said - 'Trouble with common sense is it is not so common'. Goes along with Clint Eastwood's - 'A man has to understand his limitations'.

Of course maybe I should not talk - my welding is not the best in the world at times. I really hate grinding out and redoing to make it right, but that is what I do.

Dale

rj1939 · Jul 22, 2018

I used to retube driveshafts years ago at one of my jobs. Most of them were class 8, wadded up like a rag, when I got them. I cleaned up the yolks as best I could, cut the tube in the lathe, so it was about as square as possible. Assembled it, ran a dial indicator on it, truing as close as possible. I picked a place to start the weld, where I "wanted" it to pull a little, since it was going to anyway.

JRIowa · Jul 23, 2018

HuFlungDung said:
90 degrees out of phase is incorrect.

They made a lot of them for many years. Most of the time is for a 2 piece driveshaft with the center support. I just built the damn things.

The video is kinda neat. Our machine to do that had a 100hp motor on one end and a pump on the other. Those guys had fun. They got to crank on stuff until it broke. Don't know what happened to all that stuff. They've had 3 different owners since I left.

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