Acrylic Roughing

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Jamie

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While roughing down acrylic blanks I get chips or overheating if I take off too much stock and if I cut fine ribbons I'm standing over the lathe for an hour. I rough the blanks to just oversize using a 3/4" roughing gouge, ground with a slight curve, like a spindle gouge (it's sharp!) at a speed of about 700 to 1000 rpm's. Is there a better and faster way to cut through all that plastic?
 
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I just use a round nose. Seems to work ok. I don’t know if it's proper or not, but I move the tool slow enough that it seems to heat up the acrylic allowing for some thick ribbons. As I get closer to final form, I speed up my movements to avoid heating it up.

As far as the roughing, you can always rub the sharp edges against something (driveway in my case) to round off the corners. That keeps me from chipping the corners as much.

Just keep your tools sharp. I normally sharpen a few times while turning any blank.
 
Welcome to the wonderful world of plastic!!!

After you become comfortable with your tools and procedures, you can turn at 4000 rpm and get done 4x as fast.

BTW, if you get BIG chunks to fly off, you take the chance of creating hairline fractures that go down to the tubes and will show up on your finished pen-so DON'T try THAT approach.

(But, then, I ruined scores of dollars of blanks learning that, why take away YOUR financial enjoyment?????!!!)[:D][:D][:D]
 
Like Ed, I turn fast with acrylic (though I only turned a handful so far). You might laugh at me but I find the parting tool to work very well during my rough turning.

Note that my parting tool have a different profile...the cutting part is actually parallel to the handle and the end is NOT shaped like this < (the top is horizontal) so it works almost like a small scraper (just sturdier).
 
I would defintely recommend speeding up your lathe, at least to around 1800 if not 2500 rpm. I use a 1" round nose scraper on just about all synthetics as well as antler. You might also consider building a jig like the one HUT either still sells or did sell that allows you cut off the sharp corners giving you an octagon shape instead of square.
 
Thanks for the advise everyone. I often turn at fast speeds, but on very special blanks, I'm afraid to do anything risky and at high speeds I have blown the blank right off the tube. Hey dare ED, give me a break, I'm a Wisconsin kid to... from Ladysmith, you betcha.
 
So,
ya' retired to TUCK son, Ya' sittin' on a 4tune.

Go ruin some blanks!!!!!!!!!!!!!![:D][:D][:D][:D][:D]

ALWAYS HAVE FUN!!!
 
I turn by plastic at 4k+, whatever my max speed is. After a few passes I look like I had a fight with spiderman with all the stringy crap all over me.[:p][:o)]

Never have had a problem with heat unless its at a low speed.

Plastic = Give it the Nitros and wicked, wicked, scary sharp tools.

Just $.02 worth! [:D]
 
I turn mine on a HF 7x10 metal lathe. I turn them to almost the final size then move to my nova mini to finish them off, sand and polish.
 
Have you ever watched one of the Kip & Rex pen turning videos? I stood all stupified when I saw how fast they rough-turned acrylics. They turn very fast with very aggressive cuts. They knock the end corners off and then turn 1/2" segments down to a rough size. I have always started at one end and see-sawed back and forth across the entire blank slowly getting down to the desired dimensions. I still prefer this method (very smooth across the entire blank, without any 'ripples' that need to be flattened later), but I have sped up my lathe to about 3000rpm and started knocking the end corners down first. This does seem to minimize end-blow outs. While I doubt I'll ever get super aggressive, I have started making deeper, wider cuts. I've noticed that the angle of the cut (bevel) makes a big difference.
 
Something that is different for me is I dont turn square blanks. All of my blanks are cast round, so this eases alot of the stress and shock to the blank.
 
For me, I use a radius skew from start to finish. Like others, I turn at the highest speed I can get out of the lathe. I start with light cuts to knock down the edges and then I go to a peeling cut. That's where I lay the skew flat on the toolrest and peel off about 1/8 inch at a time working my way down the blank. I saw this on Alan Lacer's video and it works for acrylics almost as good as it does for wood.

After I get it close to size, I then go to my normal back and forth cuts until I get it like I like it.
 
Originally posted by tnilmerl
<br />Have you ever watched one of the Kip & Rex pen turning videos? I stood all stupified when I saw how fast they rough-turned acrylics. They turn very fast with very aggressive cuts. They knock the end corners off and then turn 1/2" segments down to a rough size.
Click to expand...

I would imagine this has more to do with trying everything possible to cut down on the video's running length than a recommended method of roughing out acrylic blanks. I'm sure they had several sets sitting ready to go if/when the one they were hogging down blew apart. A few extra blanks at their wholesale price probably isn't even a drop in the bucket of their total video production costs.
 
I use a round nose scraper at the fastest spped available. light cuts till round then more aggressive ribbons until just about final size. Finish with very light cuts from a skew. Whole thing takes about 4 mins, a little more for home brew resins as you will get more break out as it is more fragile that the commercial variety.
 
Charles, I find that I get a lot more catches and blowouts at lower speeds with acrylics.

I crank it up to the highest setting (whatever it is on a Delta midi, I forget), put on a face shield, sharpen my 3/8 spindle gouge on a 150 grit wheel and I go to town.

I don't think I quite hit 4 minutes but I'm certainly less than 8. At least we're not talking about running miles here, I can rough out and finish a dozen acrylic pens in about the time it takes me to puff-wheeze through a mile run.
 
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