Drillema in sizes

[BobRad]

I went to make a Sierra for the first time and it seemed the tube was 10mm so that's what I drilled but it was slightly too small. went and looked it up and found it should have been 27/64". It turns out I had a 27/64" [never used before] so I enlarged it - but I guess cause its more reaming than drilling it caused a lot of friction. Tubes went in fine.

I just wonder why there are pen sizes so close in diameter

"O" and 8mm --- 27/64 and 10mm

 

[DurocShark]

You're generally wanting the drill bit size that is closest to the OD of the tube, but leaving enough space for glue. So even though they are close, the differences are HUGE in the use we're putting them to.

I tend to tinker with scrap to see what size bit works best for a tube. I'd say 75% of the time I go with the recommended size according to the kit's instructions, but the rest of the time I go a smidge smaller. That often means switching from metric to SAE or letter. Or the other way around.

One thing I've found is that drilling on the lathe means less slop in the bit which means a smaller hole from a given drill bit. I had to re-do my chart when I started drilling on the lathe!

 

[ed4copies]

Cause there are "pen-kit engineers" that like ONE size of brass.

Actually, you can use a 10.5mm for the sierra--nice fit.

 

[randyrls]

One thing I've found is that drilling on the lathe means less slop in the bit which means a smaller hole from a given drill bit. I had to re-do my chart when I started drilling on the lathe!

I have the drill size(s) written on the instructions. One size for wood, sometimes a different size for acrylic.

The same bit will drill a slightly smaller hole in wood, slightly larger in acrylic. The blank may also flex slightly after drilling so the hole needs to be larger.

 

[mredburn]

One reason could be the different sized tubes are used to reduce the overall weight of the pen. The Sierra could be made witha 10mm (Cigar) tubes or even 3/8 tubes. And I would speculate they dont want all the parts to be interchangable.

 

[Smitty37]

Different sizes

I've often wondered myself....I look at some kits and would swear they are identical to others but upon checking I find that the tubes are a tad different which means that all of the press fit parts are a tad different and probably won't work interchangably. Then they sometimes seem to do something else to compensate so that identical transmissions can be used. I suspect it is because they don't want the parts to be interchangable.