Tube and back painting - oversized drills?

[egnald]

Greetings from Nebraska. My latest project (a Rhinoplastic rainbow of cigar pens) has not been going very well, I back painted my blanks, but still wound up with areas where the tube shows through. I must have somehow scraped the paint away when I was gluing the tubes in - very frustrating.

I have spare tube sets and another batch of blanks on order already. This morning, I found the specialty drill bits for plastics on McMaster-Carr available in inch, metric, letter, and wire gauge sizes. I ordered an "X" (0.397", about 3 thousandths over the 10mm, 0.3937) and a "Y" (0.404", about 10 thousandths over) so I can have a little more clearance to accommodate the paint thickness. I understand that typical paint thicknesses are on the order of 5 thousandths, so if I both back paint and paint the tubes I should still wind up with a snug fit.

Do any of you use over-sized drill bits for working with plastics when back and tube painting? Am I on the right path or are there alternatives that might work just as good as (or better than) oversized drills?

Regards,
Dave (egnald)

 

[carlmorrell]

I have had the same issue. A good investment is a 115 piece drill index. It has both fractional and letter drills. I like to use tamiya paints for backpainting. Been modelling with them since the 80s. Even black I put two coats on. White 3. I wait a day after painting. Even then I still want the tube to slide in easily. Test before glue! I also use Optivisor magnification, a 1/8" camel hair brush and a lot of light.

Here's another thing I do. After painting I keep the blank vertical. After 5-10 minutes, pick it up and wipe off the bottom and move it to a clean place on my wax paper. I feel if I leave the blank horizontal, the paint will migrate to the gravity side!

Certainly not the only way to skin a cat, just my way, YMMV!

 

[Ted iin Michigan]

I've done a fair number of pens with painted tubes and blanks. I've settled in on a process where oversize drills aren't needed. I'm sure we all do a "test fit" before painting and again after. Whenever I suspect the fit is tight enough that it might cause a scratch I'll take a transfer punch (PSI sells them as a "disassembly set" - their part number: PKDISET). I wrap a small piece of 220 tightly around the punch and use it to ream the inside of the blank. It usually does the trick and has a side bonus of smoothing out the inside of the hole.
Also, I used to paint with acrylics and a brush. Now I have 3 cans of spray paint - white, black and grey. I find that these cover well with a thinner coat. While there can be a drastic result difference between the three on the finished pen, you can kind of plan on it whether you want brighter colors, darker or whatever.

 

[jttheclockman]

I am going to double down on what Ted said. I do the same things. Mostly spray paints these days and works well. Do enough pens and you will know when that drill hole is just right.

 

[PaulWitmer]

Likewise, I also follow Ted's and John's processes as described when I need to paint the tubes. A little abrasive and paint resolves any issues I had in the past.
Paul

 

[Curly]

I'll be a maverick and not quite do what the 3 esteemed pen turners before me do. I take a dowel and saw a slit in it and wrap a strip of sandpaper around it starting with some in the slit and the wrap trailing when turned in a drill. Slip it in the hole and spin away moving back and forth but not leaving or dwelling at the mouth of the blank. Basically make a flap sander. Check your fit often to prevent overdoing things. You can do the same with a metal rod but a dowel is pretty easy to slit on a bandsaw or by handsaw.

 

[qquake]

I never use oversize drill bits, and have rarely had a problem. Like Carl, I too let the blank dry vertically. I set it on end on a piece of mesh so the paint can drain out, and air can get into the bottom of the blank.

 

[Charlie_W]

Great advice above!
I second the vote for the 115 piece drill bit set. I measure the tube and find a drill about 0.010 larger.
Primer spray paints. Sometimes I will put the painted tubes in a toaster oven for a bit to cure the paint...200 degrees.
I also prep the tubes first by not only scuffing but also use a flat file and take the "sharp" off the end edges. These sharp edges make a great scraper when sliding into your painted blank....which you don't want.

 

[TonyL]

One should be able to cover/paint the brass and paint the inside inside of the barrels while using the recommended drill size. I am definitely NO expert, machinist, or precision driller. As long as I use epoxy, I very, very seldom risk scraping any paint off. I do slowly twirl the pained tube (coated with epoxy),as I insert it Happy turning with whatever approach works for you.

 

[carlmorrell]

What I have found is to never trust the recommended drill sizes. In fact the last project I worked on called for 7mm drill. No way was that the correct drill bit. I was drilling alumilite and no backpainting required. I ended up using a 9/32. It was the perfect bit for the tubes. 9/23 - 7mm = .0056 inches. Is that considered oversize?

 

[egnald]

Thanks for the input everyone. I guess I am going to have to break out my dial calipers more often. - Dave