South Bend 9C Headstock Alignment

D

danjp

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I have a 1947 South Bend 9C horizontal bench lathe with 48" bed that I am having an issue with regarding the headstock alignment.
I am the second owner of the lathe and purchased it from a golf course where it was used to clean up shafts for the mowers so not used a lot.
Most of the bed flaking is still present and there are no dings in the bed and no significant bed wear.
I have the lathe mounted on a 2" laminated bench that is bolted to a concrete floor and to the wall so a very rigid setup.

I have leveled the lathe using a precision level that is .0002/10in so is is level at the headstock and tailstock ends within 1 division on the level.
When I do a 2 collar test I am getting about .004 taper over 8 inches so a lot more than I should be getting. It was larger at the headstock end.

I was able to get the taper out by purposely twisting the bed but did not like leaving it like that as I knew there had to be something else going on.
I needed to put about 0.05" of shims on one side of the tailstock foot to get the taper out over the 8 inches.

So I re-leveled the bed and the then checked the headstock alignment. I used a backplate with a bolt in it that I cut a flat on the head.
I put a test indicator on the carriage and set the indicator to 0 with the bolt closest to the operator. I then rotated the spindle 180 degrees so that the bolt was furthest away from the operator and saw that it was off by a little over .003" so this really surprised me as I did not expect this. This was over about a 6" circumference.
But this confirmed that the headstock was skewed towards the operator and was causing a taper in the 2 collar test by pointing the bar towards the operator at the tailstock end.

So I pulled the headstock off to see if there was anything under it which there was not, and then cleaned all the mating surfaces and put it back in place.
I repeated the test with the backplate and again it was still off by .003".

Since there is no way to adjust the headstock, and I did not want to just start grinding on the headstock I put a 0.004" brass shim under the back edge of the headstock at the inside of the V facing the operator thereby twisting the headstock counterclockwise as viewed from above. I tightened everything back down and checked to make sure the bed was still aligned and then repeated test with the backplate and it was not off by about .0005" from front to back so a lot better.

I then did another 2 collar test and it was better but not perfect so I shimmed the bed at the tailstock end but only needed about .015" of shims to get the rest of the taper out so a big improvement. When I did the 2 collar test after shimming, I was able to get to less than .0005" over 8 inches so very acceptable. I then repeated the 2 color test after aligning the tailstock to the headstock and again I was able to less than .0005" over 8 inches.

Now the lathe is cutting as expected but I still have the shim under the headstock.

My questions are these:

Has enyone else ran into an issue like this and if so how did you fix it?
Is it OK to shim the headstock to get the twist out?
Any ideas on how it got to be this far off?

I should state that I do not know if there was a crash on the machine at some time in the past that may have warped the headstock of even if it was replaced.

Any thoughts or suggestions would be welcome.

Thanks, Dan
 
Possibly the headstock isn't the original as the factory matched the heads to the beds
so yes it's ok to shim where you did to get the results you want
 
danjp said:
I have a 1947 South Bend 9C horizontal bench lathe with 48" bed that I am having an issue with regarding the headstock alignment.
I am the second owner of the lathe and purchased it from a golf course where it was used to clean up shafts for the mowers so not used a lot.
Most of the bed flaking is still present and there are no dings in the bed and no significant bed wear.
I have the lathe mounted on a 2" laminated bench that is bolted to a concrete floor and to the wall so a very rigid setup.

I have leveled the lathe using a precision level that is .0002/10in so is is level at the headstock and tailstock ends within 1 division on the level.
When I do a 2 collar test I am getting about .004 taper over 8 inches so a lot more than I should be getting. It was larger at the headstock end.

I was able to get the taper out by purposely twisting the bed but did not like leaving it like that as I knew there had to be something else going on.
I needed to put about 0.05" of shims on one side of the tailstock foot to get the taper out over the 8 inches.

So I re-leveled the bed and the then checked the headstock alignment. I used a backplate with a bolt in it that I cut a flat on the head.
I put a test indicator on the carriage and set the indicator to 0 with the bolt closest to the operator. I then rotated the spindle 180 degrees so that the bolt was furthest away from the operator and saw that it was off by a little over .003" so this really surprised me as I did not expect this. This was over about a 6" circumference.
But this confirmed that the headstock was skewed towards the operator and was causing a taper in the 2 collar test by pointing the bar towards the operator at the tailstock end.

So I pulled the headstock off to see if there was anything under it which there was not, and then cleaned all the mating surfaces and put it back in place.
I repeated the test with the backplate and again it was still off by .003".

Since there is no way to adjust the headstock, and I did not want to just start grinding on the headstock I put a 0.004" brass shim under the back edge of the headstock at the inside of the V facing the operator thereby twisting the headstock counterclockwise as viewed from above. I tightened everything back down and checked to make sure the bed was still aligned and then repeated test with the backplate and it was not off by about .0005" from front to back so a lot better.

I then did another 2 collar test and it was better but not perfect so I shimmed the bed at the tailstock end but only needed about .015" of shims to get the rest of the taper out so a big improvement. When I did the 2 collar test after shimming, I was able to get to less than .0005" over 8 inches so very acceptable. I then repeated the 2 color test after aligning the tailstock to the headstock and again I was able to less than .0005" over 8 inches.

Now the lathe is cutting as expected but I still have the shim under the headstock.

My questions are these:

Has enyone else ran into an issue like this and if so how did you fix it?
Is it OK to shim the headstock to get the twist out?
Any ideas on how it got to be this far off?

I should state that I do not know if there was a crash on the machine at some time in the past that may have warped the headstock of even if it was replaced.

Any thoughts or suggestions would be welcome.

Thanks, Dan
Click to expand...
I would look at the head stock bearings. Sounds like they worn

Dave
 
Dave,

I did inspect the bearings when I replaced the oilers. I have just a bit of .001" of play in the spindle and the bearing surfaces were pristine.
 
I have shimmed the headstock on several lathes that were level, but cut tapers, in my opinion, the shimming should be done at each end of the headstock Vee way on opposite sides of the Vee, this reduces the thickness of the shim by half for the same result. You say that two collar test was done using the tailstock, that is not the way it is done, also you talk of shimming the tailstock, not sure what you are saying, shimming the tailstock is generally done to make up for wear on the bottom of the tailstock, how did you determine the difference in height between the HS and TS?
 
"leveling" is not leveling, it is taking twist out of the bed.

you can bolt a lathe to the wall, as long as twist is out, it will cut straight.
 
so everyone passed over this, are you using the tailstock when testing for taper?
Have you tried getting the tailstock lined up before doing everything else?

I ask because it seems you did everything before aligning the tailstock if I read that correctly.
 
danjp said:
Dave,

I did inspect the bearings when I replaced the oilers. I have just a bit of .001" of play in the spindle and the bearing surfaces were pristine.
Click to expand...
Most time SB it is 0.000,5 play.
You may need to take out a shim.

Dave
 
Agree with Dave, the last time I checked mine, there was < .0005" of play.
 
Sorry for being a bit confusing. I will try to answer everyone's questions.

I did 2 different 2 collar tests.
I did the 2 collar test in a 3 jaw chuck to check the initial taper and then also did the 2 collar test between centers to align the tailstock after I shimmed up everything. That was the last thing I did. I used a piece of 1.5" aluminum rod about 9.5 inches or so long so I could as close to an 8 inch separation as possible without getting chatter. Final pass was done with a 0.001" cut at a slow speed and using the power feed.

I did not think of using 2 shims on the V to cut the shim thickness in half. Thanks for the pointer.
After I added the shim under the headstock, I verified that the headstock was aligned with the bed using the backing plate with a bolt in it. This was done with all "twist" removed in the bed. Verified that there was no twist using a precision level.

I then did another 2 collar test in the chuck to verify that things got better and they did but it was still not perfect.
At this point I again added shims under one side of the foot at the tailstock end to remove the last of the taper.
The section where I mentioned shimming the tailstock end was putting shims under one side of the foot at the tailstock end of the lathe not shimming the tailstock itself.

Once I was able to get the horizontal taper where it should be, I also verified that vertically both collars were in alignment and they were less than 0.0005" different over the 8 inches. I did this as I was concerned that after adding the shim under the headstock that it would throw off the vertical alignment. Again, all of this was done using a chuck.

After all of this I then did a 2 collar test between centers to get the tailstock itself aligned with the headstock.

I am a little confused about the headstock bearing clearance though. Dave, you mention that the play should be closer to 0.0005" but The SB Bulletin H-4 on Alignment states that there should be 0.001-0.002 clearance and that less than 0.001" clearance can cause chatter due to reduced oil thickness. Mine is right around 0.001" so it agrees with the SB manual for cast bearings. Am I missing something?
 
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