Drilling bigger holes (HELP)

[PenMakerWillie]

Can somebody please help me. I ruined 5 blanks this afternoon trying to drill holes for a "valiant" pen. The tube sizes are 10mm and 12mm. Everything would be going great until the very tip of the bit broke through the bottom of the blank and that would cause my blank to bust off about a 1" piece off the bottom. It was very frustrating and I would rather not ruin any more blanks doing the same thing. Here's what happened and different things I tried:
#1 - Started drilling the 10mm blank and had it break a corner off
#2 - Same exact thing
#3 - Same thing, nothing changed. Made sure my speed was down, cleared the shavings more, let it cool in the middle, but still broke.
#4 - I tried pre-drilling with a smaller diameter bit. Once I put the 10mm bit back on it kept getting jammed. Ended with the blank breaking.
#5 - Started with the 12 mm only to have the same thing happen. This time I stopped probably every 10 seconds to let it cool, but it still broke.


What am I doing wrong?

Thanks for the help from the pros!

 

[johnnycnc]

cut your blank long (maybe 1/2" longer), drill deep enough for tube length plus a bit (maybe 1/8") but not all the way through the other end.
saw cut the extra off the end, just over desired length, to expose the hole after drilling.

 

[SDB777]

No pro, but I've encountered the same thing(good thing it was just a cheap ERC blank). The only thing I found was to completely remove the drill bit and clean out the excess shavings.(But it sounds like your already doing this)

You using a drill press or the lathe to drill?



Scott (lathe driller here) B

 

[nytefaii]

are you drilling on a lathe or on a press?

are you cutting you blanks the exact length of the tubes?

I always cut my blanks longer than the tubes, because when you are drilling, it can sometimes blowout at the very end when you are done drilling. This way even if it does blow out, you are not wasting the blank. You can still glue the tubes in and then trim/square teh ends.

 

[corian king]

Hello Just like everyone else has said you should always cut your blank a little longer and then trim it down after you drill.Now if you are using a drill press try putting a scrap piece of material under the blank so when you drill through you are going into the scrap I have used this method many times.
Hope this helps!
JIM

 

[alphageek]

You havn't said what kind of material... But I will tell you that the "don't drill all the way" works for me in the few cases where I have a known material with issues (like acrylister).. However, after I got a drill doctor and keep my bits sharp (includeing jr gent at 10.5 and 12.5 mm) I rarely need to do that. If the bit is sharp and I don't force it through the bottom, no issues....

 

[PenMakerWillie]

I'm using a drill press. The blanks are probably about an 1/8" (+/-) longer than the tube length. They are acrylics if this is an unanswered question.

Corian- That sounds like it might work, wished I would have thought of that before I wasted blanks. Will give it a try.

 

[Willee]

Heat and build up of oily material on the drill bit can blow out a blank toward the end.
The deeper you drill the more often you need to clear the drill bit.
If it gets so hot it is smoking stop and let it cool.
Use a paper towel and an ice cube to cool the bit.

Sometimes drilling a smaller hole then chasing it with the larger bit will help.

If you do not have a Drill Doctor get one, learn to use it, and use it often.
Even brand new bits can be dull.

Nothing makes me more frustrated than destroying a blank trying to put the hole thru it.
I now use a lathe and boring bar to cut the larger holes as it generates very little heat as there is no friction or build up of chips.

 

[alphageek]

I'm using a drill press. The blanks are probably about an 1/8" (+/-) longer than the tube length. They are acrylics if this is an unanswered question.

Corian- That sounds like it might work, wished I would have thought of that before I wasted blanks. Will give it a try.

Or give yourself a little more 'room' - say 1/4" or so extra length... Cut it off after drilling and you'll be good to go. Thats always the safe answer.

 

[jpr28056]

One thing I always do to prevent the bottom end blow out is to use a piece of cutoff blank under the blank I'm drilling. This prevents the blow out.

 

[PenMakerWillie]

Thanks everyone for the advice! If it all works out I'll post some pics of the finished product.

 

[dhammis]

I've posted it elsewhere but when drilling acrylics or corian I spray the bit periodically with WD-40. The shavings just slide right out and it keeps the bit cooler. I drill at 500 rpm on the lathe.

 

[gr8danish]

One thing I always do to prevent the bottom end blow out is to use a piece of cutoff blank under the blank I'm drilling. This prevents the blow out.

^^^THIS! Works EVERY time on the drill press! If you are using your lathe to drill the blank, then you will have to make the blank 1" longer than you actually need for your tube.

 

[aggromere]

I used to have problems with blank blow outs and cracking when I drilled on a drill press and switched to drilling on the lathe. Since then I bet I don't have any issues except for maybe 1 in 25 or so and then it is just a little tiny blow out on the exit end. Since the blanks are slightly longer than the tubes it is no problem.

 

[KD5NRH]

What kind of bit are you using? If you can find a set of small, long shank Forstners, I've had good luck using them on the lathe, though finding odd sizes under 3/8" can be challenging, and long shanks even more so. If using twist drills over 3/8", I prefer to start with a 1/4" or 5/16" brad point bit and enlarge the hole in 1/8" or smaller steps with non-brad-point bits.

 

[TellicoTurning]

Like several said above, when I drill on the drill press, I always back the blank with a short length of board under the blank 1. to support the blank, 2. so I don't drill into the DP table... I drill at 1100 rpms on the DP..... most of my drilling is now done on the lathe at 450 rpms... but I've gotten into the habit of drilling just short of the exit and cutting the end off the blank... especially on plastics.

One other check.. make sure your bit is sharp.

 

[Rifleman1776]

I'm using a drill press. The blanks are probably about an 1/8" (+/-) longer than the tube length. They are acrylics if this is an unanswered question.

Corian- That sounds like it might work, wished I would have thought of that before I wasted blanks. Will give it a try.

What Johnny said is best advice. I had surmised you were trying to drill acrylics. Too bad your blanks are so short. I believe your problem will continue. Suggest you limit those blanks to 7mm pens and try wood (yes, some still use wood ;-) ) for large bore models.

 

[randyrls]

If you do not have a Drill Doctor get one, learn to use it, and use it often.
Even brand new bits can be dull.

Repeat what Willee said! If you follow the instructions exactly you will get a drill bit sharper than new. Drill Doctor doesn't work on brad point bits.

Cut the blank roughly in half making sure both halves are about 1/4 to 1/2" longer than the tube. Put a block under the blank and drill to the correct depth.
Hint: Mark the length of the tube on the drill bit. When the mark disapears, the hole is deep enough. Test fit the brass tube before un-mounting the blank.
Trim the solid end of the blank to exact length plus 1/32"

 

[geovtx]

All good tips. When drilling I always use a piece of scrap under the blank and size the boring incrementally. I used 5 smaller bits before the final 9/16. Don't tighten the blank (if you use a vice) too much as it does put pressure an the thin side walls. I use a small air compressor to blow off the chips AND cool/clean the bit. I continually lift the bit and only use light pressure when drilling. I learned this the hard way

 

[bitshird]

Mark the length of the tube on the drill bit with a sharpie permanent marker measure just a tiny bit behind the flutes, not the point, and drill to the mark then cut off the excess and square sand or square the blank as you normally would, be careful using a squaring cutter on Acrylics, sanding them is much safer.

 

[latelearner]

I'm certainly no pro, but after wasting many blanks by blowing out the end, I started cutting them a little bit longer and putting a piece of blue painters tape on the far end. To date,no more blow outs.