Issues with painting inside of blanks

[RunnerVince]

Hi all,

I've been trying to up my acrylic game lately, and I'm just struggling. The biggest issue I'm getting is a "crackling" effect on the inside of the blank. I can't tell whether it's the blank itself, the adhesive, or the paint that's doing it, but I've gotten it on pens I've done with both epoxy and gorilla glue. It's driving me mad. I've tried acrylic paints, plain white spraypaint, and the high-temperature white spraypaint that @jttheclockman recommended, and I get the same issues with all three. In all cases, I've given the paint a minimum of 24 hours (up to a week or two) of time to dry. I wondered if it could be something with how I'm sanding, but those don't look like any scratch patterns I've ever seen.

See the picture below. Does anyone know what's causing this, and what I can do differently to avoid it?

 

[carlmorrell]

i got that sort of cracking on a model when the paint was too thick. I was putting white over red and I kept layering it on. I use a very small paintbrush, and tamiya paint. Once I paint the inside, I leave the blank vertical so the paint will not puddle along the length, then after 15 minutes I move the blank and make sure no paint has puddled at the bottom.

 

[jrista]

Are you laying the blank down flat, or setting it up tall, while the paint dries? I always set mine up tall, so that any excess paint will drain out of the blank. Someone else here, a couple years ago, shared this idea of using a simple wire mesh to set the blanks up on, so that the paint would pool below the blank and not around it. I haven't had any problems with cracking...I generally aim for just a thick enough coat to hide any glue or brass.

 

[Curly]

How fast (rpm) are you drilling your blanks at? If too fast some plastics may craze. The same can happen from solvents in some paints or a lubricant if you use some while drilling. The crazing may not show up right after drilling.

 

[RunnerVince]

Replying to everyone at once:

@carlmorrell I'm painting as thin a layer as I can to get coverage.

@jrista I leave them veritcal at least until the paint sets. I like the idea of a mesh so any excess drains away from the blank. I'll see if i have something I can use for that, or maybe buy some of the plastic mesh used in crafting to use.

@Curly I think around 1,200 rpms. I will slow it down to my lathe's lowest speed and take my time for my next blank, and see if that fixes things. I've always tried to take my time, even with the faster speed, but maybe it's a losing proposition no matter what at that speed.

 

[jttheclockman]

Replying to everyone at once:

@carlmorrell I'm painting as thin a layer as I can to get coverage.

@jrista I leave them veritcal at least until the paint sets. I like the idea of a mesh so any excess drains away from the blank. I'll see if i have something I can use for that, or maybe buy some of the plastic mesh used in crafting to use.

@Curly I think around 1,200 rpms. I will slow it down to my lathe's lowest speed and take my time for my next blank, and see if that fixes things. I've always tried to take my time, even with the faster speed, but maybe it's a losing proposition no matter what at that speed.

That is not paint and that is not glue. That is the blank. I would do as you are planning and slow the drill down and advance slowly and clean often. Certain acrylics need more babying. If that is a poured blank with a resin it could be the resin used. When I spray my blank, I hit from both sides and then stand on edge. Never lay it down. It then will pool on the bottom and after a few minutes I will flip it over till it stops pooling I will continue this. usually takes one flip. You should try to drill in the 600 to 700 rpm range. keep the bit cool. I do that with wiping bit down with a saturated rag dipped in DNA.

 

[Curly]

The speed may be the reason then. I would drill at 300rpm or 400rpm at the most. A little water with a bit of dish soap to lubricate and keep it cool. Cover the bed to keep it from rusting, A piece of a puppy pee pad, unused of course, works great.

 

[egnald]

Hmmm. That looks really odd. May I ask what kind of blank that is? Also, are you putting any kind of finish over the top of it? I have had some CA finishes crackle / craze that looked kind of like that. - Dave

 

[RunnerVince]

Hmmm. That looks really odd. May I ask what kind of blank that is? Also, are you putting any kind of finish over the top of it? I have had some CA finishes crackle / craze that looked kind of like that. - Dave

I can't recall other than I think I got that one from PSI. That's an in-process pen that had some other issues, so what you see if the tool finish. I don't as a rule put any finish on acrylic/resin blanks, unless I've overshot with turning and need to add diameter back on, in which case I'll build it back up with CA.

 

[RunnerVince]

The speed may be the reason then. I would drill at 300rpm or 400rpm at the most. A little water with a bit of dish soap to lubricate and keep it cool. Cover the bed to keep it from rusting, A piece of a puppy pee pad, unused of course, works great.

When you say a little water with a bit of dish soap, is that like a drop or two per cup of water?

 

[RunnerVince]

Thank you all for your advice! I incorporated it into my last acrylic pen, and I'm so happy with the results! See below for pictures of what your help allowed me to do. And while one good pen does not a skillful craftsman make, this is definitely a step in the right direction.

To recap:

• I'd already been painting as thin a layer as I could manage, even if it meant doing two coats instead of one in order to get full coverage.
• I'd already been leaving the blank vertical until after the paint sets.
• I slowed my lathe all the way down for drilling.
• I used water (forgot about the dish soap addition, but will try next time) to keep things cool (with the lathe bed covered).
• Haven't gotten any mesh yet, but that's because I'm a big homebody and the craft store is on the other side of town. I got the results I wanted without, but it's a "can't hurt" kind of thing that I will incorporate because it's just good sense.

I'm still not a huge fan of acrylics, but at least now I have confidence that I'm not wasting my time and money when I put an acrylic blank on the lathe. Thanks again to all of you!