PR Turning

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Shamgar

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I have been having lots of problems with making PR and now… turning it.
I was putting 7 drops of catalyst in and all of my blanks cracked from the bandsaw, drilling and so on. I threw all of those beautiful blanks away. Next, I used 3 drops per ounce and I tried to turn a piece without drilling. It took a long time to harden, about 24 hours. While another mold jelled within a few hours I haven’t tried to turn that yet.

I used a spindle gouge, parting tool and round nose scraper to see what the surface would look like. I set the speed at 500-750rpms and use sharp tools. I could not get any ribbons going and the tools would just chew it up, with very little pressure, and leave large and small dimples. Any ideas what I’m doing wrong?
 
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First question is are these round or square? Either way, the lathe speed is way too slow. I turn all plastics at the second highest speed on my Jet mini, about 2600 rpm I think. Others I know turn at the highest speed. If the blanks are square, try sanding the edges down before turning.

And welcome to the IAP. I would encourage you to go the Introductions forum and tell us about yourself.
 
Using a gouge or scraper will unfortunately result in a chipped/pitted surface. It is accompanied by a sound similar to glass breaking or popping. I recommend that you use a skew. If you are not familiar with the skew, I'd practice on some scrap wood first. There are some videos in our library from YoYoSpin that are worth looking at too.
 
I have to disagree about using the gouge. I use a gouge on all of my plastic and would be wiling to bet that I can make the plastic curl just as good as anyone with a skew. The key is for whatever tool you use to be very sharp. I do agree with the scraper causing chips though.
 
I have to disagree about the scraper. I've used it on several PR blanks without problems. With PR, I move my gouges to another room while I turn it.[:D]
 
Comparing commercial plastics/resins and home cast PR (polyester resin)is not comparing apples to apples, although when you speak of plastic you may include home cast PR...I'm not sure. I have been known to cast and turn a few PR blanks. I use 3 drops of catalyst per ounce and have no problems...ready to turn in 4 hours, although I always wait until the next day. I don't round over the corners and I use a skew until the very end then I change to a negative rake scraper.The ribbons are annoying but the final result is worth the hassel...just ask Frank! Sanding is done with MM wet as YoYoSpin does in his video. A roughing gouge works, but if the cut is too agressive, especially before the blank is round, then I feel as if I have been sandblasted. I prefer the skew, but most any tool will work. I know some who turn all plastics, including PR with a scraper once the blank is round.
do a good turn daily!
Don
Originally posted by armyturner
<br />I have to disagree about using the gouge. I use a gouge on all of my plastic and would be wiling to bet that I can make the plastic curl just as good as anyone with a skew. The key is for whatever tool you use to be very sharp. I do agree with the scraper causing chips though.
Click to expand...
 
A negative rake scraper has two bevels...one from the bottom and one from the top... and the cutting edge is between the top and bottom surface of the scraper instead of on the top surface. Take a look at this: http://www.bigtreetools.com/articles/sharpening1.html
Google 'negative rake scrapers' and you will find lots of info. Several high profile turners are now using them. I remove the burr on any scraper I use on plastics. The negative rake scraper does not require the tool handle to be held high with the cutting edge below center. I really like using it.
Do a good turn daily!
Don
Originally posted by gerryr
<br />Don,
Pardon my ignorance, but what is a negative rake scraper?
Click to expand...
 
I use only a gouge on plastics and most woods and don't have any problems with it. It could be because I don't know how to use a skew properly, but I have a lot of blowouts when I use a skew. [:(] Oh, I also have the lathe at its highest speed when I'm turning pens.
 
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