Tailstock Alignment Question

ddickey

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Realized I was cuting a tape the other day. It was .002" over a 3" length. I've taken a lot of time to level my lathe and it cuts a taper of .0002" over 5" with no TS suppport.
I checked the TS alignment and it is aligned to the headstock both horizontaly and vertically. I then tried turning a peice between centers, there is a taper there also.
I'm sort of confused on what to do next. Do I offset the TS to eliminate the taper or could it be something else?
Also, on my TS i have the normal screws on both side to adjust the horizontal offest but there are two small set screws on the front as well. Not sure what these are for.
 
DD,
You should actually check your lathe for any twist in the bed and headstock alignment before checking for tailstock alignment. Leveling the lathe is a good starting point, but you may find that you actually have to induce some twist to accomplish a cut without taper. I had to do this with my lathe. Tom Lipton has a two part video on how to do this which is pretty good. Check it out here:

Ted
 
I've had to induce some twist. After leveling I took cuts on on my two collar test bar. Made adjustments to the TS feet to get even cuts. After, I made final adjustments on a full length cut. No TS support. I think I've watched that video before. I'll watch it again when I get home.
 
You might find these posts interesting reading. In particular, check out the 2 YouTube vids I referenced by experienced machinists = exact same issue I experienced. Bottom line is if your lathe facilitates headstock re-alignment, look into making that adjustment (assuming if your lathe is determined to be level). I chased my tail in a circle trying to compensate with lathe twist first, but that wa snot the correct order in my case. I am happy to report my lathe is cutting perfectly true now with the headstock taken care of. With that done, THEN you introduce the tailstock alignment into the mix.
http://www.hobby-machinist.com/threads/tail-stock-alignment.53621/#post-446343
http://www.hobby-machinist.com/threads/need-help-lathe-cutting-a-taper.53676/#post-448908
 
I've watched that vid before but thanks for posting it. I read your threads before but I'll have to reread them.
My lathe cuts a .0002" taper over 5". To me that is no taper really. Does this show my HS is aligned? I only cut a taper when I introduce the TS for support even though I've aligned it. Maybe my TS alignment method is faulty. I'm not even sure if my HS is adjustable.
 
I think that's what I said above.
Ted
Apologies Ted, exactly as you said & same video reference. I should have read complete post. Keith Fenner Let's Look Under The Old Girls Apron Part Eleven is another one, same theme.

DD
- 0.0002" over 5" sounds pretty good to me. I'm pretty sure I cannot cut/finish to that resolution myself but I guess its a function of what you are machining.

- re the tailstock alignment, this device was mentioned to me in a prior post. And the universe must have been listening because it coincidentally came on sale, so I decided to splurge.
http://edgetechnologyproducts.com/tailstock-alignment-bar/?utm_medium=googleshopping&utm_source=bc
My tailstock alignment was still set up from my prior best attempt circling dead center arbor with a 0.0001" measuring DTI & a little mirror etc. This thing makes the job dead easy. And because its longer length, any offset discrepancy is magnified which is exactly what I detected. As I mentioned in my post, I learned my tailstock is a bit fussy to lock down (read: I wasn't doing it right). I have 2 setscrews that kind of trap the lateral position. And then 2 more setscrews on the outboard RHS that tighten against the dovetail/gib. Turns out I could alter the tailstock out of alignment just by how I tightened RHS gib screws. Might just be an irritating issue with my lathe. So now after zeroing DTI on headstock bar ring, I traverse to tailstock ring, leave the DTI needle on it to monitor & just alternately snug the screws back & forth preserving zero on dial until its all clamped solid. Unfortunately its one of those tools you probably use once for 5 minutes & then back on the shelf for a month. But it was worth it to me to get this nailed down as I'm doing some toolpost grinding pretty soon. (Sheepishly) I now think this is why I was breaking some delicate and spendy carbide center drills. It probably wasn't defective grinding on their part, it was probably my tailstock/chuck out of whack. Another thought: I guess if you figured out the math it might be a good tool to deliberately move the tailstock to a specific offset position for taper cutting, but haven't tried that myself.
 
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Looks good to me, I just ordered one also.
I've cut a few MT's using TS offset. Seems to work well.
I have those small setscrews also. Mine are on the front of the TS. So you think they need to be loosened first?
 
DD,

I agree with PE, that .0002 in 5" is pretty good alignment, especially for home shop work (if that's what you're doing). If you're making parts for NASA, you may have to improve it some :). Anyway, as you know, now is the time to do the two collar test between centers to set your tailstock alignment. The tool you ordered should work well. If your tailstock alignment works like mine, then yes, you need to break loose those set screws as they basically tighten against each other to lock the tailstock in place.

Good luck and let us know how it turns out.

Ted
 
Well I got the alignment bar today and was a little disappointed in that my TS is in quite good alignment. .0005" over the length of the bar. I guess it proves the stub arbor method I had previously used works fine.
Will probably start over from scratch this spring with leveling. In the meantime keep making chips.
 
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