Casting on Smooth Tube Fails

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vtgaryw

vtgaryw

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Jul 24, 2012
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Milton, VT
I've had a number of failures trying to cast PR on a smooth painted tube. Specifically, I'm casting a bottle cap on a Sierra style pen.

First fail was using a mandrel, and you could see the separation on the ends of the tubes from the PR as soon as I put a little bit of pressure on the tailstock. I switched to a set of TBC bushings, and much better. Came out nice, no milky areas where it separated. I did get a little separation though when I pressed the cap into the tube.

So, is it hopeless trying to use PR on a smooth tube with nothing to grab? Or do I need to let the blank cure for, like months? (this one cured for a week)

I've noticed how hard PR is after a year or so. But will longer curing fix this problem, or do I need to use Aluminite and a pressure pot?

Thanks,

Gary
 
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Sounds as though your failure is in the turning and not the casting. I cast and turn a lot of blanks clear cast with poly resin...snake skins and labels which are stuck to the tubes and clear cast. You need to figure out how to correct your technique. Are the ends of the blanks squared correctly and accurately? What tool are you using? How fast are you turning? Are your tools sharp...really sharp?

Pressing the pen parts into place can be a problem, as you have discovered. The parts must be started completely straight. The section that goes into the tube can be sanded a bit smaller and glue used to hold it securely in place. CA is not the best choice for this. I use loctite thread locker (blue or red) when I do this.

Getting in a hurry is not an option when casting, turning, or assemblying acrylic.

I find a gouge, spindle or rough out, to be way to aggressive for poly resin as well as other acrylics. I use a skew. Actually, I use a skew on all pens of all materials.

I don't think using alumilite is your answer.

Do a good turn daily!
Don
 
Agree with the squaring of the blank to the tube so you are not pushing on the PR. Also, I file and sand the inside of the tubes so I can push the parts almost all the way in my hand. A couple of tiny spots of epoxy applied with a toothpick will lock parts in place after pressing them in. Tight fitting componets actually swell the brass tube and cause the separation.
Hope this helps.
 
+3 on the squaring of the tubes AND sanding the inside of the brass tube for an easier fit. I use a small dremel sanding disk in my drill press to clean the tubes out.

sharp tools help also


Harry
 
Are you using the tubes that already powder coated white? Casting on powder coated tubes will not work. It will separate on the ends like you are describing. The powder coating is harder than regular paint and will not expand, Sanding the inside of the tubes like others have sand will work. I lost 12 watch blanks from using some black powder coated tubes.. Expensive lesson. If you are clear casting do not use alumilite, It comes out yellowish.
 
Thanks for all of the advice, and here, a few clarifications:

I've only had this problem on smooth painted tubes. I square the ends perfectly. I'm having problems on tubes I bought pre-painted (black), but I don't know if it's powder coat or paint, the vendor didn't specify. But based on what people are saying, it sounds like it's an adhesion problem with the paint.

Sanding down the inside of the tubes sounds like a good way to go to avoid problems in assembly. It only occurs on the ends, so I don't suspect my turning technique, I do a lot of acrylics and a lot of my own casting and don't have problems with anything other than smooth painted tubes. I have tried both a skew and an EWT carbide.

For painting your own tubes - what type of paint? Acrylic or enamel?

Thanks,

Gary
 
When it comes to paint, your probably going to have to experiment a little. I've had most acrylic paints react with the resin and bubble and wrinkle up as it cures. I think oil based is probably your best bet if your painting a scene. If it's just spray painting a back ground you can probably use enamel. I would suggest getting something to seal the paint like a clear spray of some type. They make some artist sprays for sealing painted pictures and chalk drawings. Good luck!
 
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