Drilling on lathe question

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Haynie

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May 20, 2011
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I have recently started drilling on my metal lathe. I don't have a chuck for the wood lathe yet.

My problem is, when I get finished drilling the hole is larger than the drill bit. Not a lot but enough to see daylight between the tube and the blank.

I thought maybe there was an issue with my head/tail alignment so i locked in a dead center and a live center matched them up and they touched nose to nose. There is not a lot of throw for my Jacob's chuck so here is my procedure.

Set drill in chuck (tail stock)
put blank in 3 jaw self centering chuck (head stock)
Slide tail to just touching the blank.
Tighten tail stock
start drilling backing out a lot
When I run out of throw I back out the bit and turn off the head
Slide tail until bit into the blank until is touches then back out a hair
Tighten the tail stock
drill
Could
I usually have to do this procedure a couple times before the blank is drilled.

Am I doing something wrong? This same bit on the drill press makes a hole that is perfect for the tube. It slides in no problem but no light shines through.

I have come up with two thoughts
1. Since these are PR blanks the PR is getting hot and maybe expanding
2. My Self centering chuck needs a good tuning.

Any thoughts?
 
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Xander

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Feb 11, 2012
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1) Use the next size SMALLER bit.

When I drill on the lathe I start with a 3/16" bit all the way through the blank. Then I switch to the size BELOW recommended. I check tube fit, then finish with the final size bit.

I always end up on the recommended bit but 'just in case' there is an issue I creep up on it. This way I get a good clean hole that is the right size without being too loose or too tight. I can get 1 coat of paint which just allows me to use epoxy glue with a good close fit.
 

tim self

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Oct 2, 2008
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Atoka, Oklahoma
I drill with a collet chuck (so I know the blank is centered) and sometimes get the same result. My problem, I believe, is bit wander. If the bit is worn more on one side it will not drill properly and allow it to wallow out the hole.

Just my experience.
 

triw51

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Feb 14, 2012
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407 East Cottonwood Drive, Cottonwood AZ
The way I drill on my lathe is I mark center on each end of the blank and make a small indent with a center punch at each center. I put the drill bit in the head stock and line up the center mark with the drill and the live center. I use the live center to push the piece into the spinning drill bit (I hold the blank with pliers). When I am about 2/3 through I rotate the blank. This works great on antler and other odd shaped blanks.
 

rtrimyer

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Jul 8, 2007
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Location
San Antonio, TX, USA.
How fast do you have your lathe set? I was getting the same problem when I was set at a high speed, then I went to the slowest speed and had no more problems. Also, are you backing out and cleaning your bit often? Your shavings could be actually drilling the hole larger. I found when drilling at slow speeds I actually seem to drill faster and my bits stay sharp longer.

Thank you,

Robert
 

Haynie

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May 20, 2011
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Page Arizona
I am drilling at a pretty high speed. Come to think of it the drill press is much slower. Thanks folks. I now have some things to try.
 

frank123

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Feb 5, 2012
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Location
Colorado
Couple of easy things to try to look for a misalignment somewhere if that is the cause.

Extend your tailstock quill all the way (with a taper in it) and see if it still lines up with the point of a taper in the headstock.

Cut a point on a piece of straight round rod and mount it in the drill chuck while it is in the tailsotck and perform the same point to point check.

Put a longer piece of very close tolerance ground rod (drill rod usually works) in the Chuck and run a dial indicator mounted on the cross slide down it to see if it is exactly parallel with the ways (or just move a cutting tool to exact contact with it at the headstock and run it all the way down the ways to see if any clearance is noted iuf you don't have an indicator)

Any alignment problems, if there are any, should show up somewhere in these checks.

Make sure the bit you are using is near to perfect to eliminate any cause of the problem there - doesn't hurt to use a different brand bit of the same size to see if the problem of a tapered drilled hole shows up with it too. Use a starting hole to make sure the bit isn't deflecting off center when it starts drilling (you can usually see this happening with careful observation).
 
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