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Old 11-06-2017, 02:00 PM   #1 (permalink)
 
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Question "Bubbles" in acrylic/synthetic

I recall seeing a thread that addressed this issue and neglected to Favorite it. I have a blank that is full of them. Not exactly bubbles but pock marks in the material. I read the thread and said, So that's what causes it! I had couple of places today that had minor issues and I had enough material to carefully, with light touches, turn them down. Can anyone help here? What am I doing wrong? Not sure what to use for search words. As always, thanks.
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Old 11-06-2017, 03:43 PM   #2 (permalink)
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Old 11-06-2017, 03:48 PM   #3 (permalink)
 
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I try to make sure and mix the liquid material slowly and I try my best to not make bubbles in the first place before putting the blank/s in the pressure pot. That is what helped me a lot when I make PR blanks and also make sure you have a consistent pressure in the pressure pot until the blanks are hardened.

I have read on this forum and have done it myself that you can fill in the pock marks in the hardened blanks with CA. It might take more than one application to fill the holes.

I wish you the best of luck Woodchipper. I am sure you will get other options/suggestions from other forum members that may help.
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Old 11-06-2017, 04:04 PM   #4 (permalink)
 
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This is not a casting. It is a camo blank from Woodcraft. I'll try to post a picture but not confident it will be decent.
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Old 11-06-2017, 04:19 PM   #5 (permalink)
 
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Here it is.
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Old 11-06-2017, 04:27 PM   #6 (permalink)
 
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Tool chatter... the tool or the blank is vibrating. You can probably feel it. Avoiding Chatter | Tim Bird is more about machining lathes but I think it can apply here too. I'll defer to someone more experienced at resolving the issue to offer up any other suggestions.
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Old 11-06-2017, 04:37 PM   #7 (permalink)
 
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what tool are you using? If HSS its not sharp. If carbide wrong angle or too aggresive.
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Old 11-06-2017, 04:38 PM   #8 (permalink)
 
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That's chip-out (the plastics equivalent of tear-out), the blank is more than likely solid.

A few possibilities for why this might be happening ...

... tool vibration, blunt gouge, blunt scraper, blunt carbide insert, lathe rpm too high causing the tool tip to get hot, trying to take too large a bite, too much pressure (rubbing the bevel too hard against the blank) ...

Approaches to reduce/eliminate the problem ... sharp tools, less pressure, move the tool rest closer to the blank (to reduce overhang and chatter due to vibration), slow down the lathe rpm.
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Old 11-06-2017, 04:42 PM   #9 (permalink)
 
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Either your blank is vibrating, a dull tool, too much pressure or you're cutting too fast.

I catch myself all the time doing one of those things when it happens to me. It is usually, in my case, a dull edge and pushing it a little too much. Or it's vibrating and not tight on the lathe.
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Old 11-06-2017, 04:53 PM   #10 (permalink)
 
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May be all of the above. I have my grinder two steps from the lathe so keeping my tool sharp is not problem. I think I might have been using a round nose scraper. BTW, I did an acrylic blank today and decided to try a 3/4 roughing gouge. When my grandson took a pen turning class, the instructor used a one inch roughing gouge and was fantastic with it. A real craftsman, and not one from Sears. I came out with a much better first-finish and easier to sand and polish.
Will be aware of what is being said here. I do get into a rush sometimes and have to back up and slow down.
Thanks to all.
Edit: Now all I have to do is figure out what it was for, find the bushings and finish turning it.
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