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Old 03-16-2019, 04:39 PM   #1 (permalink)
 
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Default Messing up acrylic

I seem to be having a terrific problem with acrylic. I have watched the videos and turned a few nice pieces. Lately, however, I haven't been doing so well.

The problem is that the corner of the skew will suddenly "grab" the turning piece. This cuts a groove in the work piece all the way around. Sometimes it is pretty deep and always has a line of chipped-out places in the groove. Sometimes it is salvageable, most often it is not. Sometimes when trying to salvage a blank after this happens, it happens again on the same piece, rendering it good only for trash status.

Here are the solutions I have tried, all to no avail:
- brand new edge on a carbide tool
- freshly sharpened HSS tool
- turned at high speed (~2,000 rpm)
- turned at various lower speeds down to ~500 rpm

I have turned around 100 or so pens but still consider myself to be a newbie so any suggestions or possible remidies will be appreciated. Learning is always a good thing.
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Old 03-16-2019, 05:52 PM   #2 (permalink)
 
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Have to say you do not present the skew the right way then. What size skew are you using. The center to lower half of the skew should be touching the round blank. The roundness of the blank makes the area to cut so thin and small there is no way to get a catch. Unless you are using the skew as a scraper than you twist the skew and cause the catch. There are so many videos on the net that show the proper use of a skew. It really is an easy tool to master and the things you can do with it makes it so useful. Practice practice and you will not be sorry you did.
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Old 03-16-2019, 10:32 PM   #3 (permalink)
 
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I learned recently that a negative rake scraper does a good job on plastics. If you have one or can make one try it. Theres been negative rake carbide inserts available lately, something to check out.
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Old 03-17-2019, 08:13 AM   #4 (permalink)
 
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First of all, I suggest more speed. I do all my (pen sized spindles) turning at 3,700 or thereabouts. Don't know what you've got for a carbide tool, but the 15mm R2 cutter works very well for me (MUCH less apt to catch than the square cutters). It is on a "Magical Skew", which has a hex shaft oriented so that the cutter can easily be help at a skew-like angle (can also be held flat for scraping). I tend to start with a skew-like cut, then once the piece is round, switch back and forth.

I did the same thing with the HSS skew back when I was using that. Hope this helps, as always, YMMV.

Michael
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Old 03-17-2019, 12:12 PM   #5 (permalink)
 
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Quote:
Originally Posted by Gary Beasley View Post
I learned recently that a negative rake scraper does a good job on plastics. If you have one or can make one try it. Theres been negative rake carbide inserts available lately, something to check out.
Now my curiosity is in full bloom. I have looked at the negative rake carbide tool heads and wondered how they are used. Do you use them in the same way as conventional tools? Is any adjustment to the tool rest position needed? I.e. should it be higher or lower than when using conventional tools, and should it be further away from the work piece?
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Old 03-17-2019, 12:14 PM   #6 (permalink)
 
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Quote:
Originally Posted by StanBrown View Post
Quote:
Originally Posted by Gary Beasley View Post
I learned recently that a negative rake scraper does a good job on plastics. If you have one or can make one try it. Theres been negative rake carbide inserts available lately, something to check out.
Now my curiosity is in full bloom. I have looked at the negative rake carbide tool heads and wondered how they are used. Do you use them in the same way as conventional tools? Is any adjustment to the tool rest position needed? I.e. should it be higher or lower than when using conventional tools, and should it be further away from the work piece?
Have a look see.

how to use negative rake scrapper turning tools - Bing
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