WM210V Tailstock question

[weston1968]

The lathe is an education. The tailstock was 0.006" high and was angled down over 0.100" at 210 mm. I took the bottom off the tailstock, shimmed the back up and machined the part down 0.006" with a taper to bring up my 210 mm lathe test bar closer to the center on headstock. I got the tailstock within .0.001" at the tailstock, but the test bar now angles down 0.015" at the end of the 210 mm test bar.

My question is: what is considered acceptable drop at 210 mm from the tailstock? I am afraid of trying to fix this taper because I would need very thin shims before machining.

I found the spec attached in a WM220 manual. It pretty much says everything should be within 0.001". I ordered some very thin shims and got all of my measurements under 0.001". I was driven nuts by the top half of the tailstock not being exactly flat (my assumption), so as I tightened the rear adjusting screws the settings would change as the top half rocked on the base. I wound up having a 0.002" shim on the front and a 0.023" shim on the back between the two halves of the tail stock. This was after I had machined the base down. This works well, as tightening the adjustment screws does not effect the any of the measurements any longer. The whole setup is very repeatable. I lucked out in that the horizontal was perfect.

 

[WCraig]

I think we need pictures of how you are measuring this drop. Is it possible the test bar is just sagging?

Craig

 

[WobblyHand]

I think we need pictures of how you are measuring this drop. Is it possible the test bar is just sagging?

Craig

Or is the test bar straight? Or is the taper on axis? Try rotating the bar 180 degrees and see if the answer is the same. Lots of things can be off and they all contribute to the error.

Getting a tail stock to line up is amazing tricky, I started to do this on my mini lathe and stopped because I didn't want to make it worse than it was. There wasn't a true reference surface that I could find. Everything was seemingly tilted. Was an exercise in too many error terms and uncertainty in identifying the dominant error sources. The only reference surface I knew to be "true" were the ways everything else was suspect.

 

[weston1968]

The test bar has a morse 2 taper that plugs into the tailstock, the other end of the test bar has a center hole on it. My lathe headstock has a Morse 5 taper and at first, I used a Chinese MT5 to MT3 adapter and an old American MT3 center. The Chinese MT5 to MT3 adapter was off with a TIR of 0.005". I bought a four-jaw chuck and mounted a straight shank center and got it to less than 0.0005". I then used a Starret dial gauge to run along the top of the bar. Once I machined the tailstock and got the heights identical, I ran the dial gauge along the side of the bar and was able to adjust the tailstock to within 0.001". I now was within 0.001" on the tailstock. I then inserted shims into the gap between the two pieces on front of the tailstock to get the test bar up to the middle of the center on the headstock. I then took the shims and used them to machine a taper on the tailstock. I had to do this twice to bring the bar up from over 0.100" low to 0.015" low.

I measure the drop by putting the test bar using the Starret gauge on the top of the bar near the headstock and slowly moving the test bar away from the headstock. The gauge now drops 0.015".

The bar feels solid in the tailstock and I do not see it dropping that much just from its weight.

I am used to my old Logan lathe where everything just lined up and there was no taper at all in the tailstock using the same setup.

 

[WCraig]

Is the 0.015" deviation repeatable? If you rotate the test bar 180 degrees, do you get the same result?

How long is the test bar? Even the smallest burr or other imperfection in either the test bar or the MT socket could easily lead to that kind of deviation over a long-ish test bar. If you extend the tailstock quill and measure between it and the carriage, is it parallel to the ways?

Craig

 

[weston1968]

The test bar is 210 mm long ( 8.3" ). It is entirely repeatable no matter how many times I take the bar out and rotate and reinsert. I continued to machine the tailstock base and brought the test bar. drop to 0.002". The center to center is now lest than 0.001" horizontally and vertically.

I still do not know what I should expect for a drop in the tailstock. I was unable to find what is acceptable anywhere.

The reason I am trying to get to zero error is I have a project where I need to bore holes accurately. When I started I chucked a 12 mm endmill and was boring a 13.7 mm hole. After I got everything aligned I was boring a 12.6 mm hole which means I have a total off center mismatch of 0.007", unfortunately this is not good enough. I did this work around: I used a center drill which will give a good center regardless of how far off I am. I then used a 12 mm drill bit figuring it would follow the hole. This gave me a 12.02mm hole which is within the tolerance I need. I just need to modify the design to accept the 18 degree taper on the end of the drill bit.