two collar testing question

trying to center the tailstock with the headstock. onheavy 10 made a test bar .750 round with 1.250 collars on each end 9 in. apart in the center of the collars. got both ends to measure the same . at this time 1.220 +- .001 depending on my mike setting; but very close. however when i use a indicator on the tops of the collars; the tailstock end is around .006 higher than the headstock collar. is the tailstock too low or are the ways worn at that area??

More likely the base of the tailstock is worn. Its not uncommon to have to shim them up to match the headstock.

You said the tailstock end is higher and then asked if the tailstock is low, so I'm confused. Tailstock ways are not typically worn and it should be somewhat visible if so. Did you level the lathe/check for bed twist at all. Twisted bed will throw off the collar test. I've also heard that the TS is sometimes set higher than the HS when new to account for wear. It'd be easy to bring the TS up close to the HS and check for height differences between the two, making some assumptions about wear at the HS end where it is more common.

This is the reason the 2 collar test fails. It does not show the cause of the error. If you can afford a lathe, you can afford buying test bars. They are not expensive.

what i'm trying to say about the height is: with a dial indicator, the collar at the tailstock is .006 higher than the headstock collar. therefore, if the tailstock is setting too low on the ways., by .003 (i think), the height of the collar will be higher. would not a .003 shim correct the issue , or, would it be a .006 shim?? i'm confused

You did not say where your dial indicator is mounted, guessing on the tool post?

If the tail stock is too high, then how can adding shims to RAISE it further make it lower?

Very common to see the tailstock axis lower than the spindle axis due to wear. Usually a combination of tailstock base wear plus quill/quill bore wear, not necessarily TS way wear.

The quick solution is adding a loose shim between the tailstock casting and the tailstock base.

The more permanent fix is a bonded and scraped shim in the same location after scraping the bottom side to the ways. Have to get the quill axis pointing in the right direction (albeit perhaps at the wrong height).

Depending on whom you ask, adding Turcite or Moglice or Rulon to the bottom side of the base isn’t recommended because they reduce clamping friction too much.

BTW the ideal TS quill alignment is not truly coaxial with the spindle. The quill axis should point a few tenths upward and a few tenths forward when extended. This counteracts both gravity and tool pressure without causing problems drilling or reaming.

I think you're going to have to give us more background on your methodology.

As a sanity check, slide the tailstock up to the headstock with centers in each and see how they match up. If the centers are sharp and "clean", 0.006 should be fairly obvious. You can insert a steel rule between the two centers, oriented vertically - if the centers are matched vertically, the rule will remain vertical.

Bad application of the collar test.

Use the 2C test to make the machine turn straight without tailstock....in the case of SB shim or adjust bed foot to get it right... A bar of mild steel ~1.5" diameter about 8" long so that when its chucked has about 6" sticking out...

Then once you got it turning straight, chuck up another piece of scrap with about 2" sticking out and turn it to the EXACT diameter of the tailstock quill.

Now you have a direct comparator to set the tailstock to....use an indicator attached to the carriage to go over the top and side.

Using a bar like you are tells you nothing about how the tailstock is actually pointing....used SBs almost always point down and away.

I'm still having trouble with how wear caused the tailstock to raise up. Is it possible someone switched the tailstock at some point?

Yes...OR someone may have in error stuck shims between the base and body of the tailstock....happens all the time because guys will use an indicator in the spindle and then read it backwards and add shims....no kidding.

iwananew10K said:

Bad application of the collar test.

Use the 2C test to make the machine turn straight without tailstock....in the case of SB shim or adjust bed foot to get it right... A bar of mild steel ~1.5" diameter about 8" long so that when its chucked has about 6" sticking out...

Then once you got it turning straight, chuck up another piece of scrap with about 2" sticking out and turn it to the EXACT diameter of the tailstock quill.

Now you have a direct comparator to set the tailstock to....use an indicator attached to the carriage to go over the top and side.

Using a bar like you are tells you nothing about how the tailstock is actually pointing....used SBs almost always point down and away.

Click to expand...

Please don't tell people bad info. The sequence is simple. Make bed straight, then head stock parallel to bed, then TS. You don't twist the bed because the head stock is not parallel. When doing any alignment, a reference is needed. In the case of the lathe, it is always the bed, then everything else is measured and adjusted to that. It is very possible that either the spindle line and or the tail stock line is out of plane with the bed or each other. Anything out of plane will create a tapered cut. No correction can be made if you don't know where the problem lies.

Derek Smalls said:

If the tail stock is too high, then how can adding shims to RAISE it further make it lower?

Click to expand...

Yes I'm still struggling with the TS being "higher" means it's low when the OP says he used a dial indicator on the tops of the collars (assuming by running the carriage back and forth with the DI mounted in the toolpost). Every DI I've seen rotates clockwise as the plunger is pushed, resulting in increasingly larger/higher readings. So "higher" on the TS end would be plunger pushed in further which would mean the TS is higher if measuring the top of the bar, not lower. Where's the communication breakdown?

iwananew10K said:

Bad application of the collar test.

Use the 2C test to make the machine turn straight without tailstock....in the case of SB shim or adjust bed foot to get it right... A bar of mild steel ~1.5" diameter about 8" long so that when its chucked has about 6" sticking out...

Then once you got it turning straight, chuck up another piece of scrap with about 2" sticking out and turn it to the EXACT diameter of the tailstock quill.

Now you have a direct comparator to set the tailstock to....use an indicator attached to the carriage to go over the top and side.

Using a bar like you are tells you nothing about how the tailstock is actually pointing....used SBs almost always point down and away.

Click to expand...

This is actually really good info.

This application of the 2c test is a great way to set a machine up to very reasonable accuracy if you don't own a precision level, South Bend outlines this in their manuals. If you do own a good level, more checks can be done and used together with the 2c test to really map out bed and alignment issues.

The method outlined to check tail stock height and attitude is also spot on.

Bigger picture, unless this error that you think you have found affects your work, I would't worry about it too much. Unless you are drilling very small holes or turning very small diameter shafts between centers, it's not gonna have any real affect on making parts.

I think Steve's point may be....if you've twisted the bed slightly to get straight turning from the chuck, due to slight HS misalignment or wear, then setting the TS by comparison up near the HS might not result in straight turning between centers with the TS further away. Thus the OPs method of test turning between centers is also valid for setting the TS position. Some might say more valid and should be checked at the position the TS will be in for the project at hand, if high precision is required.

I will qualify that with my own experience which is knowing my bed has a slight twist because I have a level but not currently having a stand/floor bolting arrangement that allows me to correct it. It turns well enough in the chuck, but if I were going to turn something between centers that needed to be spot on I'd use the OPs method at the same TS position after getting close using other methods, likely the stub of equal diameter to the quill method.

porthos said:

trying to center the tailstock with the headstock. onheavy 10 made a test bar .750 round with 1.250 collars on each end 9 in. apart in the center of the collars. got both ends to measure the same . at this time 1.220 +- .001 depending on my mike setting; but very close. however when i use a indicator on the tops of the collars; the tailstock end is around .006 higher than the headstock collar. is the tailstock too low or are the ways worn at that area??

Click to expand...

The Two collar test tells you only one thing, the cutting tool is at equal distance from the axis of the spinning cylinder along the two ends of the cylinder. Nothing else. The rest of the geometry is unknown, you could be moving at a 360-degree helix and still pass the test. As others said, flat straight bed, start from there, Machine Tool Reconditioning : Edward F. Connelly : Free Download, Borrow, and Streaming : Internet Archive

dee
;-D

thanks guys: you are making my novice head hurt. i'll figure it out

I agree with Greg, Iwan and Derick. (and the others for the most part) I just saw thescale method last year. Pretty cool way that shows it's off, but not how much. Sharing ideas is cool..

I have successfully using the 2 collar test for 50+ years test new and worn machines. Using tests bars inside the tapers is also the way the new machine builders do it. With out photo's and being there we are all guessing at the problem and for Steve to criticize people who have successfully used the 2 collar method he needs to calm down a bit. As someone said. We do not know if someone has shimmed the machine. The OP can dismantle the TS and take some pictures. Take a flashlight and look under the headstock and see if there are shims. Take some photo's of the bed and headstock tailstock. A worn machine wil give you all sorts of weird info. Doing the 2 collar test is a simple and cheap way to test the machine. The spud test for tail stock works for me and again have been using it for 50+ years. I always make sure the machine is level . aligned first unless it was a short bed and it's sitting on a table before doing the tests.

Take a look at page's 30 - 35 and 53 and 54.

file:///C:/Users/richa/Downloads/Testing%20Machine%20Tools%20%2528Dr.Schlesinger%2529%20(2).pdf


I just did the tests at the last class and took some photo's. It wasn't ideal as the machine was a small spindle hole and he didn't want to cut his aluminum bar stock. We showed it to prove the point on how to. The machine was like new and tested within .0002" Many time I find that someone swept the headstock to Tailstock and the shimmed it but they didn't know that indicators and indicators rod sag with they turn over.

I had a dummy assistant tech teacher once tell me the bed of a lathe doesn't twist and he always shimmed headstocks to straighten them out so it would cut straight. The OP may have bought one of his machines or from some other dummy who did.

Steve if you would like to discuss this in person I will be teaching classes in Austria in November for BIAX Germany.

SB headstock is not adjustable....soooo, you make yourself crazy leveling it, then stick your test bar in the spindle and find its out.....then what??

In use all that is relevant is how it turns...its a worn,used machine...you set it up as best you can to turn straight for the first 6" or so and then do what we do and compensate from there...unless you are planning an actual rebuild.