Tailstock center setup question

G-ManBart said:
Minor terminology point, but you are going to be center drilling, not spot drilling the part. Spot drills are most commonly 118* or 135* to match the two most common twist drill point angles. You want to use a center drill which has a 60* cutting angle to match your centers. I suspect this comes up because so many folks talk about "spot drilling" when they're actually using a center drill...they're still spotting holes so it mixes up the terminology.

BTW, actual spot drills are one of the best additions to my shop in the past few years...way better than a center drill for spotting holes you intend to use a twist drill on. I've found you have to be a touch careful getting started if you're using a 118* spotting drill with a 135* twist drill, and vise versa, just easy pressure until the angles even out and it works just fine.

For your project something not mentioned is that you need to know that your tailstock is absolutely centered of you'll wind up with taper in the part. Just using the alignment marks on the tailstock isn't close enough. You either need to do a two collar test bar or bite the bullet and buy a tailstock alignment tool. I got tired of doing the two collar test bar drill, bought the tailstock alignment tool and it has saved me a LOT of time....worth every penny (not too expensive at $65 pretty much anywhere you can find them).

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dml66 said:
I'll be turning a piece of low carbon steel rod, nominal 7mm (0.2756") diameter, 0.003" per foot straightness tolerance. The stick out from the ER25 lathe chuck will be 2-7/8" which includes enough to part off the finished piece. Even though material removal is minimal, 0.003" off the diameter, I'm pretty sure I'll need to employ a tailstock live or dead center. I have very little experience with live or dead centers even though I own both ;).

I know I'll need to spot drill the rod to accommodate the center, should I do that with the rod stick out set to 2-7/8", or chuck it very close, spot drill, then re-chuck to 2-7/8"?

And, live or dead center?

Thank you.
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I first made a tool to easily do this about 50 years ago. I was doing production work turning 3/8 dia stainless stock down to 1/8 dia in one pass. The length of cut was about 4 inches long. No center needed.
I posted this tool on hobby machinist forum on Nov 2017.
Search this forum for. Not a follow rest. With this tool your project
Is super easy. Jim Sehr
 
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dml66 said:
I have one I've yet to use...

Please elaborate
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Near zero cutting pressure eliminates deflection.

Grinding takes only small amounts of material at a pass and this makes it very easy to hit your final size if you only need to remove a small amount of material.

Went back and reread your OP, if this is soft material you may get away with grinding it unsupported.
 
RaisedByWolves said:
Near zero cutting pressure eliminates deflection.

Grinding takes only small amounts of material at a pass and this makes it very easy to hit your final size if you only need to remove a small amount of material.

Went back and reread your OP, if this is soft material you may get away with grinding it unsupported.
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Well then, I'll have to break out the grinder and practice :), I have grits from 60 through 240.

Thanks!
 
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