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Shimming up tailstock, .020" worth?

greenbuggy

Stainless
Joined
Oct 6, 2005
Location
Firestone, CO
Admittedly I don't always know what I'm doing and can't pretend that I do, but what others do confuses me even more....

I bought a used 17x40 Howa lathe a few months ago. Haven't done much work between centers up until pretty recently, and have realized that the alignment of tailstock to spindle chuck was all kinds of wonky, and that drills have been walking and off center.

So I grabbed a DTI holder I made when I aligned the tailstock on my old lathe, and found that sweeping a dead center in the tailstock, my left-right alignment was within .0010, but up-down alignment was a tad more than .020 off.

So, I cleaned up the ways on the lathe a bit in case there was something there, put fresh oil on them, cleaned off the bottom of the tailstock, still .020 high. Thats when I noticed that there was a slight gap between the top and bottom sections of the tailstock, and after pulling it apart discovered a bunch of oxidized coolant and a pair of precision brand .020 shims, one at the front, and one at the rear of the tailstock base, aligned perpendicular to way travel.

Remove shims, suddenly I can easily get tailstock aligned to where my interapid says I'm damn close to "perfect" in both up-down and left-right planes.

My question isn't how to align the tailstock - I think I've got that covered. My question is, why would anyone shim up the tailstock that much? Is there a practical reason I just can't wrap my head around? My first thought was bed wear, but this lathe isn't worn anywhere near that badly, where it is worn is right next to the chuck (like most lathes, I think), and the ways that the tailstock rides on are in between the ways that the carriage rides on, and hardly worn at all.
 
The lathe may have been out of level when he swept the tailstock.

Or he bolted it to the floor and twisted the bed.

Or he meant to get 0.002" shims and somehow ended up with 0.020" shims and never bothered checking.

Or he wanted to cut a 0.020" taper and rather than doing it the easy way (lateral) he decided to do it the hard way (vertical).

Many possible reasons, none of them good.
 
The lathe may have been out of level when he swept the tailstock.

Or he bolted it to the floor and twisted the bed.

Or he meant to get 0.002" shims and somehow ended up with 0.020" shims and never bothered checking.

Or he wanted to cut a 0.020" taper and rather than doing it the easy way (lateral) he decided to do it the hard way (vertical).

Many possible reasons, none of them good.

Or no one ever told him to "never try aligning your tailstock after hitting that crack pipe". :D

Glad you got it straightened out.
 
Err, shimming the tailstock upwards 0.020" would NOT produce a 0.020" taper. Perhaps a 0.002" one. Unless the tool were above or below the work instead of in front of it.



The lathe may have been out of level when he swept the tailstock.

Or he bolted it to the floor and twisted the bed.

Or he meant to get 0.002" shims and somehow ended up with 0.020" shims and never bothered checking.

Or he wanted to cut a 0.020" taper and rather than doing it the easy way (lateral) he decided to do it the hard way (vertical).

Many possible reasons, none of them good.
 
A drill is just a roughing tool, ram that bitch through the part then bore anything precision.

Iv ran lots of lathes with well worn tailstocks as well as ways.

There becomes a point you run it and know its slop and do not spend time chasing your tail with an indicator trying to fix the machine.
 
A drill is just a roughing tool, ram that bitch through the part then bore anything precision.

Iv ran lots of lathes with well worn tailstocks as well as ways.

There becomes a point you run it and know its slop and do not spend time chasing your tail with an indicator trying to fix the machine.

I thought I made clear that this lathe isn't completely worn out, regardless of what the dolts that owned it before me did.

That said a way off drill bit is far more likely to load up with chips on a single side, break and waste significantly more of my time/$$$ than just setting up the tailstock correctly once would.

A drill might not be a precision tool but I would hope that the live center on my tailstock can be trusted.
 
Now when you swept the quill, was it sticking way out or pulled way back in, you need to check it twice, once way in and once way out, that will show you if the quill is parallel to the bed ways.
 
Did you check for indicator droop caused by gravity????

You have to allow for that..

Does indicator reading change (with your complete DTI setup) when rotated 360, and tip is not in contact with quill (internal droop)?? Indicate off a round bar in tool holder adjusted on center to see if you have some external droop....

Gravity sucks...
 
Gravity sucks...

Agreed

Did you check for indicator droop caused by gravity????

You have to allow for that..

Does indicator reading change (with your complete DTI setup) when rotated 360, and tip is not in contact with quill (internal droop)?? Indicate off a round bar in tool holder adjusted on center to see if you have some external droop....

I'm using an Interapid .0005 indicator, I was advancing the dead center such that I was mid-travel on the interapid before rotating the spindle with my DTI holder so that I was pushed against the spring loading on the interpaid.

If tip is not in contact with anything I do have some very small, almost negligible amount of movement between the +/- sides of the interapid readout, but thats a tiny fraction of the amount out of whack that the tailstock was reading.
 
What others have been trying to tell you is that your procedure is inherently flawed. From what you have told us there is no way of knowing if the tailstock was the right height with the shims, is right now or where it should be. There is flex in the setup you are holding the indicator with, and the the indicator has mass. When it is right side up, gravity pulls everything down, towards the surface it's contacting, when you rotate it over, it's being pulled away from the surface. Depending on how much flex is in the setup holding the indicator, this error can be between a few tenths and a whole lot! It's way more than you might think, I know that. Richard King described an elegant and simple way to truly check center height in another thread recently. I wish I had thought of it, I've always used a level across a test bar, or a surface gage on a flat way to check height of a test bar at two ends.
 
What others have been trying to tell you is that your procedure is inherently flawed. From what you have told us there is no way of knowing if the tailstock was the right height with the shims, is right now or where it should be. There is flex in the setup you are holding the indicator with, and the the indicator has mass. When it is right side up, gravity pulls everything down, towards the surface it's contacting, when you rotate it over, it's being pulled away from the surface. Depending on how much flex is in the setup holding the indicator, this error can be between a few tenths and a whole lot! It's way more than you might think, I know that. Richard King described an elegant and simple way to truly check center height in another thread recently. I wish I had thought of it, I've always used a level across a test bar, or a surface gage on a flat way to check height of a test bar at two ends.

I took a picture of my setup so that it can be critiqued as necessary, I'm open to the suggestion that I'm doing something wrong or could be doing it better and I'd be interested in King's method.

That said, I don't think that I'm wrong to believe that the tailstock was shimmed upwards too much. I could clearly see short, straight drill bits (center drills) walking on the freshly faced surfaces of items I was attempting to center drill, even after the left-right alignment of the tailstock was verified and found to be centered within the limits of my measuring equipment (in this case a .0005 Interapid). Checking the up-down alignment on both top and bottom sides against both left and right sides showed a HUGE amount of variance on both top and bottom sides, consistent with the tailstock being high - I could imagine a relatively small amount of movement due to gravity but not almost .020 worth. Since removing the .020 shim and replacing with a .005 shim my center drills walk considerably less and chip output from both flutes is both A) more consistent between them and B) more spirals out of both, whereas before I was getting chunks out of one and spiral out of the other.

This suggests to me that my tailstock definitely aligned better than I was before, even if I am not perfectly aligned (yet)
 

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no,no,no.....at least it looks like no from the pic

stick a chunk of something in your 3 jaw and take a light cut to clean it up
take an indicator with a holder (could even be an Indicol) and stick on your freshly cut bar
indicate the inside of your tail stock taper opening
 
If you want to find out how much gravity sucks put a piece of stock in your chuck sticking out a few inches, then mount your indicator on your chuck touching the stock sticking out, zero indicator, rotate chuck and watch readings, what ever variation that you have is your compensation amount. You can't indicate off the taper use the body of the center or the hole in the quill.
 
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+1 on indicating the taper inside the quill. I turn a piece of stock to a good size to clamp an indicol on and sweep inside the taper, keeping everything as short as possible with minimum overhang and quill retracted most of the way. But it sounds like you pretty much got the problem licked anyway
 








 
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