drilling big tube sizes help plz

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RAdams

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I recently tried to drill my first set of tubes for a Jr. Gent. i use my lathe to drill and rounded the blank before mounting. I have since found a way to drill on the lathe without rounding the blank.

My problem is this: When i drilled out the body, everything went fine. But when i did the cap at 12 or 12.5 MM or whatever it is, the material was so thin (homebrew PR) that it was bending in my hand. I put the tube inside the blank and laid it flat so it would cool as straight as possible, but one end of the blank was stretched out.

Am i missing something here with these big tubes? Will the squareness of the blank hopefully leave enough "meat" on the blank to correct the problem? Is there a feasable way to drill with a smaller bit first maybe?

Any help would be appreciated!
 
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You using a 5/8" blank? I have no problems with 3/4" square or round, though I have had a few caps soften from the heat of drilling. That means I wasn't paying enough attention and pushed the bit in too fast.
 
I pre-drill with a 10mm bit and then work my way up to 12.5mm. Easier to get the "alignment" with a smaller hole opening. Drill slowly with frequent removal of drill bit in order to help with "ejecting" material from blank.
 
they are 3/4 before i round them. i have a tendency to make them completely round, even if they are off kilter a bit, which leaves me with a little skinny blank. I will try it again with the 10 milly first, and the square blanks, and go slower and remove the debris more often. I sure hope that helps! thanks for the tips!!!
 
Try drilling before turning, there will be more 'meat' on the blank to absorb stresses of drilling. And, with synthetics, heat build up while drilling can be destructive. I use a drill press and back the bit out frequently to clear and cool. I also keep a syringe on hand with water and periodically drip a few drops into the hole.
 
When drilling large holes I tape the bottom of the blank. That gives it more strength to resist cracking and blow out. I drill 1/4" at a time and clear. It takes a little more time but it works. Clearing the chips is essential to keeping the bit and the blank relatively cool. If you don't you will likely blow up some blanks.
:wink::wink::wink:
 
like the others, I drill with a smaller bit and then the final size.

I've had some synthetics get flexible even when just spinning them round to see what they are going to look like (nearly a full inch think).
 
You're drilling too fast, you have to keep the blank cool and it won't do that. You can cool it with an ice cube in some papertower, just keep backing the bit out and cool the bit as well.
 
Rifleman1776 said:
Try drilling before turning, there will be more 'meat' on the blank to absorb stresses of drilling. And, with synthetics, heat build up while drilling can be destructive. I use a drill press and back the bit out frequently to clear and cool. I also keep a syringe on hand with water and periodically drip a few drops into the hole.
Click to expand...

I would do the water thing as well. Take small bites, half a turn on the handle of the tail stock, or less. Takes longer, but............
 
Woodcraft sells some new drill bits by Colt that are German made 5-point brad point bits. The "spiral chutes" (the real work eludes me at the moment) on the bit are very aggressive at removing the material drilled out.

I started using these to drill the blanks and they work like magic and the blank to warm to cause the "melting" issue for me.
 
Backing out often and going slowly make drilling acrylic blanks stay cool. I also dampen the hole if is it wide or deep. I make pill holders that use a 9/16 bit and have not had one get warm or melt. I would drill before rounding blank to keep it cooler.
 
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