Is a J bit the same as a 7mm bit?

[angboy]

It looks like most companies call their slimline's the 7mm and use the 7mm drill bit. But Berea calls theirs a "J" bit. Are they the same thing?

 

[DCBluesman]

We have a Reference section on the upper left hand part of the home page. It links you to http://www.penturners.org/forum/portal.asp?cat=ref . From their you can select the "Decimal Equivalents" link which will give you every wire, letter, European or SAE size for comparison.

In simple answer to your question, the 7mm is .2756" and the J is .2770. I prefer to use a 9/32" bit (more widely available) which is .2812". Russ Fairfield (resident guru) also recommends this bit. [8D]

 

[Fred in NC]

The chart Lou mentioned is very useful. Now let's see ....

A piece of paper from a school notebook is about .003" thick. The difference between the 7 mm and the 9/32" is about .006". So, if you wrap a single layer of paper around the 7 mm drill, it will be the same as the 9/32" !! Not much difference ....

HOWEVER: If you measure the hole made with a 7 mm drill, it is likely that the hole will be a little bigger. One of the reasons is called RUNOUT. Drill presses are not so accurate that they can drill a hole to exact size. The spindle and chuck accuracy come into play. So be careful that you don't end up with a way oversized hole.

The best way, in my opinion, is to drill a test hole and see how the tube fits. Not very scientific, but it works for me !!

 

[BogBean]

I use a 9/32 drill bit for 7mm pen kits but I also use a premium quality polyurethane glue which expands to fill the gap....

 

[Thumbs]

Good point, Chuck! I often use a 9/32; but I've been lucky, I guess, just using thick or medium CA. I rarely use poly glue or epoxy because I always seem to be in a hurry!

 

[epson]

I always use a J bit for my 7mm pens. I use polyurethane glue, and this gives it a little extra room.

 

[Rifleman1776]

I use the expensive 7mm drill bits because that is what the catalog said to use. And I don't want the pen drill police coming after me. And I use really cheap two-part epoxy to hold 'em in. Now, per Eagle's tips, on more expensive blanks, I first coat the hole with CA, let dry, ream smooth, then glue tube in.

 

[angboy]

Thanks for the replies. I printed out a copy of the conversion chart. I actually printed out a second copy that I'm going to give to the people at the ACE up the street. I had gone there to ask them, before I posted here. They had no metric bits and the best they could do was to pull out one of those things that has holes in it so you can see where a bit fits, and then they tried putting various bits through the holes that were listed on that scale as one slightly larger than 7 mm and one slightly smaller, doing this all with the plastic still covering the thingy with the holes and the drill bits they were putting into it, so obviously there was quite a bit of plastic in the equation too! I am curious Frank/Eagle, what is the advantage of using CA glue inside the blank Which CA glue do you use, and when you say you ream it smooth, what do you use to do that? Is that in addition to people referring to sanding the outside of the brass tubes? And while I'm on a role of questions, what is the reason for breathing into the tube before gluing, as I saw mentioned somewhere?

I think I've about reached my allottment of questions for today! Thanks for all of your help!