Understanding Pen Drilling

**Luke Maddux** · 15th June 2015, 12:11 AM

There was a time when I said I would never turn another pen. I have since gone back on that. I enjoy being able to make a pen as a last minute, semi-casual gift, and I also enjoy having pens made of woods which I appreciate at my own disposal. So I want to be able to get it right...

Part of what made me hang it up before was the fact that I have a tremendous amount of trouble drilling the blank correctly and subsequently installing the tube. The hole is always too small and if I try to carefully ream it I end up making the hole wider in parts and something always goes wrong. I actually went through three $8 pen kits today just trying to get a blank mounted.

I have a set of Colt bradpoints and I also have a 7mm pen blank bit which is also made by Colt. I find that when I am drilling blanks at 7mm with the dedicated pen bit, which I do on my lathe, I am not really having any problems. The tubes slide right in and glue securely. But as soon as I try to make an 8mm pen, it all goes south. I'm using the 8mm bradpoint bit that is part of my set.

So is there something fundamental that I'm missing here? Is the reason that the 7mm pen-specific bit is marketed that way because it is ever so slightly oversized to accommodate the outer diameter of the brass tubes? That would explain why the 8mm size gives me so many problems. If this is the case, I will just buy an 8mm pen bit. I want to have that option because there is a kit I like which is an 8mm bore.

Otherwise, what am I doing wrong? This is such a basic step in the pen making process and it's giving me ridiculous amounts of trouble and actually costing me quite a bit of money.

For people who know the pen item numbers at carbatec, I am having success with Pen 1 and Pencil 1, which are 7mm bore kits, but am failing miserably with Pen 9, which is an 8mm kit.

Thanks a lot in advance,
Luke

**Ironwood** · 15th June 2015, 07:39 AM

I always measure the tubes with my vernier callipers and then find a drillbit which is .4 or .5mm oversize using the callipers to measure it also.

If your drill set only has full mm sizes, you might have to look at getting some in between sizes.

**Treecycle** · 15th June 2015, 02:21 PM

Is the 8mm drill the one recommended by Carbatec for this kit? They don't have any instructions on their site for the kits they sell, so do they come with the kits?
As Ironwood says, there are many weird and wonderful sizes required for different kits so you can end up with a good collection of drills if you start turning a few different kits and they won't necessarily match up with your standard metric sizes.
The other problem you can have is wood movement. Even if you use the recommended drill size, after drilling the hole the wood will close in and the tube doesn't fit. If you leave it overnight and drill again it will often be okay as it has taken out that little bit of shrinkage.

**Luke Maddux** · 15th June 2015, 04:57 PM

Originally Posted by Treecycle

Is the 8mm drill the one recommended by Carbatec for this kit? They don't have any instructions on their site for the kits they sell, so do they come with the kits?
As Ironwood says, there are many weird and wonderful sizes required for different kits so you can end up with a good collection of drills if you start turning a few different kits and they won't necessarily match up with your standard metric sizes.
The other problem you can have is wood movement. Even if you use the recommended drill size, after drilling the hole the wood will close in and the tube doesn't fit. If you leave it overnight and drill again it will often be okay as it has taken out that little bit of shrinkage.

I thought about wood movement. I still find it strange that this would only be a problem with the 8mm kits.

Yes, Carbatec recommend an 8mm bit.

Unfortunately I don't have Verniers. Otherwise I might be able to adjust accordingly.

Maybe I need the next size up in imperial. I don't know...

**Luke Maddux** · 15th June 2015, 04:58 PM

The next size up in imperial is 21/64... That will be a REALLY easy one to find...

**Rod Gilbert** · 15th June 2015, 06:52 PM

Hi Luke,
I am not an expert in pen sizing
21/64 shouldn't be hard to find any decent hardware should have a full range of sizes in stock most of the larger stores should be able to help you.
Regards Rod.

**dai sensei** · 15th June 2015, 10:06 PM

Hate t tell you, but the 8mm tubes also need a different pen mandrel shaft, unless you have cone bushes

**daryl1** · 12th July 2015, 04:59 PM

I recently purchased slid pen kits from GPW and the 8mm drill bit as per the tube size. Had exactly the same problem. Tube would not go right thru and jammed when inserting after applying glue. Kit manufactures should know the issues and rectify before offering for sale. This kit was a Dayacom and not the resellers fault.

**DaveTTC** · 12th July 2015, 10:03 PM

11/32 might be easier to come across. If my maths is right that would be about 8.7mm

A set at carbatec http://www.carbatec.com.au/brad-poin...13-piece_c8910

Some on ebay http://www.ebay.com/bhp/brad-point-drill-bits

Dave TTC
Turning Wood Into Art

**Les in Red Deer** · 13th July 2015, 01:39 AM

Carbatec bits are infamous for being over sized.

Les

**bookend** · 21st July 2015, 12:23 AM

I don't use bradpoints. I use standard metal drills - Sutton viper bits or Frost for the sizes you are talking about.
They work well.

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