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on Going Taper

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Alan Gordon 416/07/2020 14:43:42
91 forum posts
3 photos

Good afternoon folks, I have an issue on my S7 turning a taper. My lathe sits on a Myford cabinet. Using a test bar, a DTI and turning the "dumb Bell" I consistently get a taper ! it tends to be smaller at the headstock end. The taper however is variable. I have taken readings using different equipment.The saddle, crosslide and compound slide are smooth with no slack or looseness, As this issue is turning me to drink, I now hope some one can offer advice.

not done it yet16/07/2020 17:28:54
4747 forum posts
16 photos

What do you get with a stout bar, turned in the chuck jaws only?

Martin Connelly16/07/2020 17:32:20
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1401 forum posts
164 photos

Does sound like the part being machined is springing away from the cutter at the thick end.

Martin C

Tony Pratt 116/07/2020 18:23:30
1149 forum posts
5 photos

Loads of posts already for this exact subject, try a search. Tony

Alan Gordon 417/07/2020 11:37:05
91 forum posts
3 photos

Thanks guys, will keep at it.

Howard Lewis17/07/2020 12:52:05
3394 forum posts
2 photos

If the chuck grip is suspect, how about this?

Very firmly grip a piece of large diameter bar through the full length of the chuck jaws, and bore it to suit your test piece.

Mark for No.1 jaw, remove and saw cut along vthe length to use a s a collet.

Replace in the chuck. Fit the test material and grip firmly.

Then turn, as the Myford "cotton reel" method, This will tell you if the lathe bed is twisted (If it is, it will turn a taper )

The Myford instructions will tell you which point needs to be raised or lowered to remove the taper.

Ideally, raising blocks provide a screw adjustment to be made, which should aid the process.

Keep on doing this until the test piece is the same diameter at both ends. The lathe bed should now be free of twist.

If tapers persist, you have eliminated one source and can pursue other causes, such as bell mouthed chuck jaws, badly seated chuck, etc

Howard.

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