10mm - not necessarily

[lwalper]

I've got 10mm tubes and, without measuring anything, I drilled a 10mm hole to glue it in. Lo and behold, the resulting hole had so much slop you could drive a truck through it. So, I measured the tube at 0.384 (9.75mm) -- guess I need a smaller drill bit??

 

[KenV]

Check your drill bit -- and check your runout for the drilling process. 0.25 mm is a very very small (.394-.384 is also a very small number)

 

[lwalper]

I was drilling on the lathe with the part spinning in a collet chuck. Everything seemed to be pretty solid and going smoothly. I was drilling spalted maple -- pretty soft -- with a resulting hole measuring 0.420. Maybe it's just the soft wood and tear-out?? With that much tear-out I could probably use a 3/8 (0.375) bit -- it may still come out too big.

 

[Neededwill]

I found a wobble in my 10mm bit 2 weeks ago, only had it for about a month. I was amazed.

 

[ed4copies]

.420"=10.68mm

Somethin aint right!

 

[jimofsanston]

Mica your tubes. I have found that the same kit had slight difference in the OD of the tube. Guess it was a batch issue from the manufacture. I find that more often than you would think that it should.

 

[Charlie_W]

I use calipers on all tubes and select a drill bit as close as possible to 0.010" larger. This leaves a little room for paint. I use epoxy to glue all tubes.
Also. Use a starter bit to give a centered starting point for your bit.

 

[lwalper]

I measured the bit -- it's 0.3944 (10.018mm). Close enough. The tubing is bulk 10mm at 0.3834. That's only 0.011 difference, but the hole I'm measuring is quite a bit larger(0.420). I'm still betting on tear-out in this punky wood. I'm going to try drilling with a 'U' or 'V' (or something in the middle -- 3/8) and see what happens.

I used a center drill to begin and then step drilled (7, 8, 10mm) to desired size.

 

[robertkulp]

I have a 10mm brad point that's garbage. The point is off center and it causes terrible runout. I changed bits to a Colt Pen Turners Bit and it's dead-on.

 

[Pjohnson]

Just had the same issue with my 12.5 mm .... i believe it is run out on my lathe. Not too happy about it, but the lathe is older than most of us. I noticed that most of the run out occurs because i back out the bit to clear the flutes.

 

[lwalper]

So, back at it. I got a different piece of maple -- a little harder and not quite so punky, but still with nice spalting. This time step drilled with a 1/4", 8mm, and then with 0.383 bit (between a "V" and "W") hardening with thin CA between each pass and drilled a nice 0.384 hole. The brass fits like a glove .