Interior Defects

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Todd in PA

Todd in PA

Member
Joined
Feb 16, 2021
Messages
712
Location
Port Matilda, PA
I've been unhappy with several recent attempts at translucent acrylic pens. The trouble seems to be with the interior of the drilled hole. Has anyone had a problem with this unwelcome "crackle" effect? It appears to be small cracks on the interior of the blank. It's hard to photograph, but in person it's clear these are not on the exterior surface. I'm strongly considering that the unwanted pattern may be the way the paint is curing inside the hole, and not within the acrylic. It only is noticeable with white paint, which reflects the most light. On this pen, I sanded the interior prior to painting, and still got the result shown.

Help or suggestions?

IMG_0861.jpeg
IMG_0860.jpeg

(I know the fittings are shown. It's just a dry fit. This pen is not finished, polished, or assembled. And I likely won't bother, as this look isn't up to standards.)
 
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I use an Acrylic water base paint to paint my tubes and the hole of a blank. I put the paint on a Qtip and put a liberal amount in the hole. I swab it around until I can see there's no dry spots inside. I use a rat tail file to clean out the hole after drilling. I've never sanded or anything else. I've either been extremely lucky or it just works. Good Luck.
 
ed4copies said:
Have you tried different kinds of paint?
Are you always using the same drill bit?
(Isolate the problem)
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I use 2x rustolium. Same but.

I am considering the at paint is old, or the nozzle is part clogged, causing uneven spray. I spray to where the paint is dripping out, then set it on a rack to drip dry.

I will buy a brand new can and use that the next try. The blanks are expensive, so I'm hoping for as many suggestions as I can get.
 
Hippie3180 said:
Crazing from heat. Drilling slowly with a sharp drill and using lubrication should help with that.
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The keep my bits sharp and drill slowly.

I'm not in the habit of lubricant, though I have baby oil right there from Kitless threading. I will be adding that step to my next attempt.
 
KenB259 said:
I always use high temperature engine paint and have never seen the issue.
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May switch to high temp paint. Never thought I'd need it because the only heat exposure is in drilling (prior to paint). But I'm anxious to try what works for others.

Thank you all for various suggestions!!
 
Todd in PA said:
May switch to high temp paint. Never thought I'd need it because the only heat exposure is in drilling (prior to paint). But I'm anxious to try what works for others.

Thank you all for various suggestions!!
Click to expand...
Epoxy an CA gets very hot in their curing process, so drilling is not the only heat source.
 
Todd in PA said:
I drill on the lathe at about 700 rpm. I peck drill a quarter inch and then cool the bit with air by placing the shop vac hose over it until it's cool to the touch.
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Might be worth trying to reduce RPM to about 500 if you can . Cool to the touch should be fine if by that you mean that you can hold onto the bit for a few seconds before having to let go . Your fingertips may be more or less sensitive to heat than mine . If cool to the back of your fingers , it should be more than adequate . I only drill on the drill press , where water serves as adequate coolant and lubricant , although a bit messy .
 
I'm with Wayne - I typically drill around 250rpm. Sure, it's slower, but very little heat is generated, and I'm usually not in a hurry.

And, like Kenny, I use cheap acrylic craft paints to paint the inside of the hole, applied with a Q-Tip, and have never had a problem.

But back to your issue: You have been making great pens for a long time and have not had this problem until recently. If nothing has changed in your process, then you may be on to something with the paint being old.

I would suggest if you want to try using baby oil as a lubricant that you first try it with inexpensive blanks. I do not know if oil residue will foul the CA or epoxy you use to glue in the tube.
 
I am not sure where your blanks are from but I was experiencing this with clear blanks from a European distributor and reached out to the blank manufacturer to discuss as I was sure heat was not my problem, and it was determined that a lubricant I was using was causing a chemical reaction with the acrylic.

If you use any solvents or lubricants with alcohol, ammonia, acetone, etc., as the solvent dries it can cause stress and interact with the outer layer of acrylic and cause stress cracks on the surface.

Heat is the first thing I would try to reduce. If you find that heat is not causing your crazing, look into any cleaning solvents or lubricants you are using for any ingredients that can interact with acrylic polymers.
 
I think I would take a suspect blank and cut a 1/16" inch slice from a shiny/polished side. Sand part of the rough side smooth and apply your paint. After it dries you can inspect through the blank to compare the rough sawed and sanded areas to see if there is any impact. Next, apply your adhesive to the painted surface and let it cure, then examine the results to determine if it is a reaction between the paint and the adhesive you are using.

Dave

PS I do something similar on some translucent blanks by slicing and painting with different colors just to determine the best color of paint to use. The results can be somewhat surprising.
 
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