# How to stop cracking of Pen Blanks



## JimmyZ56 (Dec 22, 2010)

I'm fairly new to pen turning.  Currently I'm turning a CSUSA Artisan Jr Retro Pen Kit.  I've manage to crack several pen blanks.  I'm drilling the blanks at 200 RPMs and backing out the drill (12.5mm) numerous times to eliminate chip build up.  I'm thinking of drilling a 5/32 dia hole first and then follow up with the 12.5 mm drill. Any thoughts and/or ideas?


----------



## johnnycnc (Dec 22, 2010)

Is it cracking at the bottom of the hole?
what kind of material is the blank?
fill in some blanks and i guarantee you will  get answers around here.
and just my opinion, but speed the drill up to 500 rpm or more.


----------



## OKLAHOMAN (Dec 22, 2010)

If the blank is acrylic, cut it 1/4 long and don't drill all the way through. Drill it long enough for the tube to fit leaving 1/8" now cut the blank to size...Vola!!! no cracked blank.....


----------



## JimmyZ56 (Dec 22, 2010)

Thanks I'll give it a try.  By The way I"m using Cumaru aka Brazilian Teak


----------



## IPD_Mrs (Dec 22, 2010)

Like John recommended, you would be better off drilling a bit faster.  Also make sure you have sharp drill bit.  If drilling on a drill press make sure you have good support under the blank as well.  Personally I like getting the blank round and drilling when it is in a 3/4" collet.  The collet really supports the side walls of the blank.


----------



## el_d (Dec 22, 2010)

+1 for leaving the blank long and not drilling all the way thru..


----------



## ctubbs (Dec 22, 2010)

A pilot hole would not hurt any.  One less than 1/4 inch or 6mm.  At first I forgot about metric.
Charles


----------



## zig613 (Dec 22, 2010)

Brazilian teak is a very dense wood.  You may be experiencing heat build up when drilling that is causing the cracks.  Sharp bits is key.  You may want to drill part way through the blank, then stop to allow the blank to cool down, then complete the drilling process.  

Wade


----------



## nava1uni (Dec 22, 2010)

I think that the slow speed is allowing heat build up.  Make sure that you have another piece of wood under whatever you are drilling, even if you are going to cut it off.  Sharp drill bit and allow the bit to cut the wood, not the pressure you are applying.  If you press too hard it will compress the shaving and cause cracking.


----------



## Mike5753 (Dec 22, 2010)

To help with heat buildup, in addition to the above comments, I will keep a water bottle handy, and when I back the  drill out,I fill the hole with cold water.  You might end up with a slurry that needs to be cleaned out.

Mike


----------



## jttheclockman (Dec 23, 2010)

Mike5753 said:


> To help with heat buildup, in addition to the above comments, I will keep a water bottle handy, and when I back the drill out,I fill the hole with cold water. You might end up with a slurry that needs to be cleaned out.
> 
> Mike


 

Mike

Here is a suggestion. Switch to denatured alcohol instead of water. Cools faster, does soak the wood with water and have an ill effect on your finish later if the blank is not dried out enough and also prevent swelling up after the blank dries thus making it tough to insert the tube. The alcohol is colder than water and will not have those effects as mentioned and also is great for use when drill acrylics. I use it all the time. Works great.


----------



## mrcook4570 (Dec 23, 2010)

jttheclockman said:


> The alcohol is colder than water



This is a common misconception due to the greater volatility of the alcohol.  You touch the alcohol and it feels cold because it is evaporating.  

Water, however, has a much greater heat capacity (nearly twice as much per gram) and heat of vaporization(more than twice as much per gram), which means that water can remove about twice as much heat as denatured alcohol.


----------



## jttheclockman (Dec 23, 2010)

mrcook4570 said:


> jttheclockman said:
> 
> 
> > The alcohol is colder than water
> ...


 

Say what you will, it does the job and won't swell the wood. Has not let me down yet. I am not a scientist. You maybe right. But I am sticking with it.   Good luck.


----------



## Polarys425 (Dec 23, 2010)

mrcook4570 said:


> jttheclockman said:
> 
> 
> > The alcohol is colder than water
> ...


 
They have a term for that, evaporative cooling. It feels colder, because it is.


----------



## Drstrangefart (Dec 23, 2010)

Polarys425 said:


> mrcook4570 said:
> 
> 
> > jttheclockman said:
> ...


 
BILL NYE!!!!! WHO HAS BILL NYE'S PHONE NUMBER?????????


----------



## brez (Dec 25, 2010)

Jimmy,

There are number of good ideas here. I have found that with difficult woods, or any woods actualy, there are a few key things to do;

1) have a sharp bit. A dull bit can crack any wood.
2) drill at 500 - 600 rpm
3) Back out and clean often. The denser the wood the more often you need to back out and clean. Make sure you clean any shavings that are stuck in the grooves of the bit.
4) Have some support under the blank. This will reduce blowout on the bottom of the blank.

If you take your time you should be able to drill any wood without cracking.

Mike


----------

