Turning polymer clay, what am I doing wrong?

[DigBaddy72]

My wife has recently started to make polymer clay blanks for me to turn. We've had 4 out of 7 blanks break, chip, peel, blow out so far. I'm wondering what we are doing wrong? I've included two pics to show the symptoms. I suggested she work the clay more. I've let the blanks cool longer (upwards of 5 days after taking them out of the oven). I use carbide tipped tools when turning clay and turn at about 1500 rpm. If anyone can throw out some suggestions or tips, I would GREATLY appreciate it. Things are starting to get a little frustrating. She is making some really cool looking blanks, only to have them ruined because they break during turning.

 

[TBCbushings]

I use a skew to turn mine..Some people only use sand paper..Not sure what one is better...Just my .02

 

[builtbybill]

I would try to make the blanks as close to finished size as possible, before baking, so that there will be less material to remove during turning. This will allow you to do it with sandpaper and not have to use tools. Also, thinner material will result in more consistent curing during the baking.

Again, just my $0.02!!

 

[epigolucky]

I've only turned one PC blank ever, so this is definitely not the end all be all answer by far. But I turned mine with wicked sharp skew and as fast as my lathe could go - I went very slow taking very light cuts. I could have probably finished 2 pens in the time to took me to get the 1 PC blank to the proper dimension. Hope this helps.

 

[Charlie_W]

I am assuming these blanks were made on the tube. As others said, make the blank closer to finished size. Have your wife roll the blank on a piece of glass , tile or granite....something smooth with the bushings as your stop gauge. I would wrap the bushings with some tape to increase the diameter slightly. Roll till the blank is the size you set with the tape. Bake as usual.

As for turning, since there is very little to take off, as said, sanding is one method. I used a skew but instead of in traditional skew mode, I put a burr on one edge and used it as a scraper taking off thin shavings. If you are going to sand, leave a little big to account for that. Also, take into account how thick your finish is going to be. I used a CA finish.

Good luck! It is great that you two can make this a collaborative effort!

 

[edstreet]

Problem is not from the carbide, rpm, how long after they are baked (silly concept and very wrong to think it changes after cooking from baking ).

 

[Skie_M]

Use very very sharp tools ... make sure you bake for the proper amount of time at the right temps, and take VERY light cuts ....


Or just grab some Abranet and go at it, the results will be quite a bit better.

You should be able to turn it at any speed, as long as your polyclay was properly heat cured, but I went ahead and turned it at around 2000 rpms.


Remember that your polyclay is NOT glued to the tube inside, and don't go gorilla on tightening down your tailstock or you'll pop the clay loose from the tube.


You may want to check out my thread on Tie-Dyed Pens. I go through my entire procedure from how I mix my clays, application to tubes, baking temps and duration, turning, and finishing on the lathe.

 

[DigBaddy72]

Thanks for all the replies! I'm hoping my wife and I can apply some of these techniques this weekend. I'll update this post with any progress!

 

[plantman]

After I bake my tubes, and while they are still hot, I drop them in a bowl of cold water to shock them. Now when you remove them from the water you can take them directly to the lathe and turn them. I should mention that I usually turn my blanks on a mini metal lathe with tooling, and have much more control over pressure, speed of cut, and depth of cut. I also turn some on a mini wood lathe with standard tools. Make sure that your clay is pressed tightly on the tubes !!! Rolling, using the bushings, is an excellent idea also and will give you uniform thickness and little to be taken off by turning or sanding. Jim S

 

[Skie_M]

Put some tape on the bushings to give you a little material to actually take off when sanding ....


Shocking your polyclay from hot to cold may not be the best idea .... they can turn brittle if you do that, but if the technique works for you, then it works!