Dial Test Indicator Mystery?

[simpsonrl]

I use an interapid 0.0001” indicator model 312B-1. I have noticed that when centering something in the lathe jaws, it matters what direction the lathe spindle rotates. For example, if you rotate the lathe forward and adjust until you get “0” movement, and then rotate the lathe in reverse, I get about 0.0003 to 0.0004 movement in the indicator. (indicating that am not quite centered up)
At first, I thought that the pivot maybe had a little side to side movement and the direction that the stylus moved across the surface effected the side load on the stylus, thus causing the differing readings. However, I recently made a roller with ID and OD cut with out removing from the chuck. It was highly polished and for grins, I put the indicator on the inside bore and then the outside diameter both on the near (operator) and far (back) sides of the part which has the effect of the part sliding by the stylus in both directions depending on where the indicator is located. As long as the chuck was rotated either by hand or at 70 rpm (slowest I can go), it read perfect in run out. No perceptible needle reading what so ever. But when I rotated the chuck in reverse, I got about 0.00035” run out. It did not matter where the indicator touching the part (front or back). In this case, since the part had not been out of the chuck and was highly polished, there were no surface finish related “noise” to muddy the water so to speak.. it was easy to see and the indicator reading were clear…
So now I think it must be something with the spindle bearings… Could there be a slight amount of slack in the bearings (say maybe a couple of tenths) and as you rotate the spindle, the bearing biases itself toward one side? i.e, trying to climb up the high side so to speak and moving the spindle axis a little. Then when you rotate the other direction, you get the same effect and it moves the spindle axis in the opposite direction?
That’s about the only thing I can come up with. It was clearly related to the spindle direction, and not to the mounting or friction of the stylus on the part.
Maybe I need to tighten the spindle just a little? By the way, this is a Grizzly G4003 lathe about 20 years old. I am the only owner and have taken very good care of it. I know the Chinese lathes are not the best in quality, But I have had no reason to complain on this one and have thoroughly enjoyed in over the last 2 decades..

Look forward to your thoughts…

 

[eKretz]

Tighten your spindle bearings, and prepare for the assault.

 

[Matt_Maguire]

When rough setting a 4 jaw (or X-X then Y-Y on a mill) I’d go back & forth. Then when doing the final adjustments I’d always rotate the same direction.

Good luck,
Matt

 

[D Nelson]

The indicator sagging
Don


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[simpsonrl]

The indicator sagging
Don


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In this case, the indicator was not moving. (assuming you meant like if the indicator was held in the chuck and you were indicating in the tail stock and the indicator turned upside down). I was simply traversing the indicator from the front of the part to the back of the part.

 

[Matt_Maguire]

In this case, the indicator was not moving. (assuming you meant like if the indicator was held in the chuck and you were indicating in the tail stock and the indicator turned upside down). I was simply traversing the indicator from the front of the part to the back of the part.

Changing lathe saddle or mill table directions can do that, but in my experience interapid indicators handle it better than most other DTI's do.

Good luck,
Matt

 

[jim rozen]

Tighten your spindle bearings, and prepare for the assault.

Put the indicator on the part. Push/pull the spindle and note the TIR.

 

[EPAIII]

I was not familiar with that model indicator. So I looked it up. Here it is for others who may be wondering.

Search Results

It is a Dial Test Indicator or DTI so it operates with a swinging arm. OK.

This is a classic case where swapping something around or reversing something will give us information about what is going wrong. In this case, you can reverse the position of the DTI by mounting it from the rear of the cross slide. Leave the swinging arm at the SAME ANGLE but approach the item in the spindle from the rear. This position reverses the direction of the force on the DTI's arm with each direction of spindle rotation.

First make another test cylinder as you did in your post above. Then check it just as you did before. I assume you will get the same results; OK with forward rotation and a bit off with reverse rotation. Now, check and see if it acts the same way when the DTI is mounted at the back and facing in the opposite direction when the spindle is rotated forward and reverse.

If you get the same results, OK with forward spindle rotation and a bit off with reverse rotation, then it is not the DTI. It is probably the spindle bearings, as you suspect. I am not familiar with that model lathe. What kind of spindle bearings does it have?

If it does point to the spindle bearings I would suggest that you always check concentricity by rotating the spindle in the forward direction.

 

[D Nelson]

Put another indicator on another part of the chuck so it isn’t being biased by the direction and watch both indicators. do they show the same thing ?


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[eKretz]

Either way, the actual runout shouldn't be changing unless it's a spindle issue. The indicator reading could be changing and that would be normal. In other words indicating with the spindle turning one direction the indicator could be zeroed and stay zero as the spindle is turned. Turning the spindle the other direction could make the indicator read -.0003" and stay there at -.0003" as the spindle is turned. That would be normal. He's saying the TIR is different. I.E. zero runout in forward and .0003" runout in reverse. That points to the spindle for me.

 

[tdmidget]

A .0001 indicator in a Grizzly machine is pure fantasy. Test indicators are for relative measurement, not actual. This just indicates the thrust in the opposite direction. Use a .001 indicator and get to work. In B4 the lock.

 

[BT Fabrication]

its the holder flexing.........

 

[simpsonrl]

Put the indicator on the part. Push/pull the spindle and note the TIR.

I do get some movement when pushing or pulling the spindle. Of course spindle bearings would show this effect. However, in my experience, everything flexes when you apply force, even the cast iron of the lathe. So some slight movement is expected just from spring in the material and maybe some twist in the bed. this is a 12x 36 lathe and about 1,000 lbs. so it is not over large and stiff. it is on a concrete floor, but only 4 inches thick.

Believe it or not, when leveling the lathe a few years ago, I could set the level on the cross slide and actually see it move as I walked toward the lathe from flex in the floor. (that Damn level will drive you crazy!)

 

[simpsonrl]

I was not familiar with that model indicator. So I looked it up. Here it is for others who may be wondering.

Search Results

It is a Dial Test Indicator or DTI so it operates with a swinging arm. OK.

This is a classic case where swapping something around or reversing something will give us information about what is going wrong. In this case, you can reverse the position of the DTI by mounting it from the rear of the cross slide. Leave the swinging arm at the SAME ANGLE but approach the item in the spindle from the rear. This position reverses the direction of the force on the DTI's arm with each direction of spindle rotation.

First make another test cylinder as you did in your post above. Then check it just as you did before. I assume you will get the same results; OK with forward rotation and a bit off with reverse rotation. Now, check and see if it acts the same way when the DTI is mounted at the back and facing in the opposite direction when the spindle is rotated forward and reverse.

If you get the same results, OK with forward spindle rotation and a bit off with reverse rotation, then it is not the DTI. It is probably the spindle bearings, as you suspect. I am not familiar with that model lathe. What kind of spindle bearings does it have?

If it does point to the spindle bearings I would suggest that you always check concentricity by rotating the spindle in the forward direction.

Ahh, this is the exact test I did. And it was most certainly related to spindle direction and not direction of the indicator sliding on the part.

These are tapered roller bearings. According to the book they actually should have some preload.

 

[simpsonrl]

A .0001 indicator in a Grizzly machine is pure fantasy. Test indicators are for relative measurement, not actual. This just indicates the thrust in the opposite direction. Use a .001 indicator and get to work. In B4 the lock.

Agreed.. I have noticed this for several years. most of the time it does not matter. hell surface finish defects are deeper than that.. But I thought it was the indicator and maybe needed cleaned. But this recent experience with a nearly perfect part, actually showed the indicator to be very stable and repeatable in its reading.

 

[dian]

somebody explain to me how the change in direction can cause runout in the bearings. the spindle might get displaced, yes, but runout?

 

[eKretz]

It was already (partly) explained by tdmidget. Reversing the spindle can change thrust forces on the bearings, making the balls ride on a different part of the race. A lathe that has been run a long time on its original bearings will wear grooves in the races where the balls track, and they won't necessarily be true to the original unworn surface. So running in one direction (likely forward, which many lathes spend the vast majority of their time in) the balls are running in their worn track. Running in reverse the balls shift a bit and run at least partially in the unworn part of the bearing or run on part of the unworn section and part of the worn section. This will of course be exacerbated by bearings that are not adjusted correctly.

After hearing the manufacturer and the fact that this lathe is over 20 years old, it may be time for a new set of spindle bearings. I would try tightening them up first though.

And to be fair, it doesn't sound like OP expected the Grizzly to attain perfection. He is just wondering what is going on because he noted a discrepancy. It is a good sign that he is probably a fairly observant and attentive fellow. I think I would probably advise to tighten the spindle bearings and stick with the .001" indicator also.

 

[jim rozen]

I do get some movement when pushing or pulling the spindle.

Right but HOW MUCH.

The spindle position could cam based on the rotation direction. The side to side clearance when you push/pull
will tell you how much it could be more or less. If the shift in position on the indicator when you reverse rotation
of the part is about the same as the spindle clearance, there's your answer.

 

[eKretz]

I do get some movement when pushing or pulling the spindle.

Right but HOW MUCH.

The spindle position could cam based on the rotation direction. The side to side clearance when you push/pull
will tell you how much it could be more or less. If the shift in position on the indicator when you reverse rotation
of the part is about the same as the spindle clearance, there's your answer.

His complaint is not just a shift, it's a change in runout. Zeroed in one direction, .00035" runout in the other.

 

[DDoug]

His complaint is not just a shift, it's a change in runout. Zeroed in one direction, .00035" runout in the other.

Chasing .00035 movement on a Griz homeshop lathe....

This is a trolling thread.....