Plastic blank chipping

[BobRad]

I was turning my first plastic blank this morning and have problems. I'm using Acrylic Acetate and started with a Woodchuck Pen Pro - which I also have no experience with.

I get nice copious shaving ribbons, but every so often I get a dig in which ends up taking chips out of the blank, or a minor chatter which leaves a bunch of grooves. I switched to a 1/2" scraper which works better but much slower- but even with that I got a bit of dig in.

Part of the problem is that I may just need to get the feel of turning plastic.

However, how should the Pen Pro be place, should the cutting tip be aligned with the center of the mandrel or slightly up or down? Should the tool be held horizontal or tipped?

Should turning speeds by the same as for wood?

 

[bgibb42]

I find, that until the blank is round, chips are a way of life with plastic materials.

For me, I turn at or near the highest speed my lathe will run. You need a sharp tool (with a Woodchuck, that shouldn't be much of an issue), and a light touch. Those three things, along with a bit of practice, and you should be easily on your way.

While I don't personally own a Woodchuck, I have used my Dad's, so I'll say this: I like to hold it so the cutting edge is centered on the material, horizontally, without tipping it either up or down. Again, a light touch will help you until you develop a "feel" for the tool and the material.

Hope this helps!

 

[Monty]

Ditto on fast speed, very light touch and very sharp tool. I prefer a skew to a gouge (as that's what a gouge will do, gouge out your blank if not careful).

 

[seamus7227]

good advise Brian! Bob, i own a woodchuck and have used mine on acrylics, PR, etc., but feel that it is a bit too aggressive on those materials. For me, generally, I will start out using a 3/4 roughing gouge to round the material, then use the skew the rest of the way. Like Brian said, keep your tools sharp, and go slow until you find what works for you. Dont hesitate to try a variety of tools until you find one that suits you. Thats what i did. And just know that you may ruin some blanks in the process but whats a few dollars, right?!:biggrin:


Note: when i said "go slow", i mean be patient, I agree with monty and brian about speed of lathe too! turn it up!!

 

[tim self]

One thing I've noticed using the woodchuck, I will chip plastics if I catch a corner. Just make sure you slow down and keep the curve centered.

 

[Mark]

I use the Woodchuck Pen Pro for roughing and finishing my Acrylics. I've found I don't use my sandpaper anymore. I go directly to MM.

It is very aggressive, so it doesn't take much to take the blank down quickly. You will develop a lighter touch. That will make a huge difference for you.

Good Luck..

 

[BobRad]

For the Woodchuck Pen Pro - do you use a straight or a slightly rounded blade when roughing?

 

[Pioneerpens]

also make sure that as you turn your blank down in size to move your tool rest a little closer...If you are to far back it will also cause it to catch.

 

[BobRad]

"If you are to far back it will also cause it to catch" - that may be part of the problem and a design problem with my lathe limits how close I can get

 

[jskeen]

When turning plastics, I don't even try for nice smooth ribbons until I get the blank within about 1mm of final size. I have too much trouble keeping them from wrapping around the blank and getting in my sight line. I find that the rough little chips that you get when your skew is making that scritch! sound are much easier to deal with as long as you remember to wear a good pair of safety glasses, and have a air hose handy to blow them out of your hair and beard when you are done.

Once I get to within a few thousandths of the size I want, then I will drop the butt of the skew, lay it flatter on the tool rest and kick the handle out to the right to bring the cutting edge closer to vertical, so that it is more shaving the surface of the blank instead of cutting a spiral wedge out of it. By the time I'm down to size, I can usually take the blank off the jet and straight over to the rusty old wilton wet sanding lathe, and start with the MM.

Of course, it took a few blanks getting chunks taken out all the way down to the tube to get good at it, and I still have the occasional oops to keep me humble.

 

[penfancy]

Bob, you may need a smaller tool rest. Go for 4". that way you can always get within 1/8" to the blank even when turning single tube kits.
My trial and error was the same way. It took me 2 months to find out I was too far from the mandrel.

 

[BobRad]

I have a third party small tool rest, but the lathe tool rest holder cannot slide the rest close without playing around a lot and putting it at an angle. I did manage to save the blank by very careful use of a small scraper to fine shave where the jitter marks were and the place where it was badly chipped was where a pen cap was going so it got covered.

 

[easton17543]

I turn mostly Corian, and made this jig for safely rounding over blanks with my router. I doubt this is anything new to you all, but it does help with the chipping issue.

Have a nice day,
Seth

 

[leestoresund]

I just finished turning some acrylic (used for bullet proof cashier guard) using my Woodchuck Pro. Got lots and lots of chipping. I found it best to get the ends turned to rough size before I turned down the center.
Unlike a prior comment I found that, because the blade is slightly rounded, I got fewer chips and dings and grabs if I turned the tool slightly so that the blade was not perpendicular to the plastic and the edge then sort of slid along the little curve before it took the full cut. The blade I am using is a 2" arc so by slanting it slightly it would hit up on the arc before it got to the outside of the arc.
In this case I am putting a decal over it and I did not need to sand it at all.

Lee