Turning the plastics

[Paul Downes]

I have only turned a few acylic/polyester resin pens and am wondering what tools etc. you pro turners use? (this is an unabashed attempt to grease the wheels) I have heard that slow lathe speeds is the name of the game. I have also had a few failures with cracks showing up at assembly but am not sure if they were already present, or were induced by either too tight of a fit or something else. Both were right at the end of a tube.
I notice that a gouge is not the best tool because of the micro chipping. I switched to a skew but it is slowwwww going.

 

[JimGo]

Not a pro, but I use a scraper. Many others use a skew.

Cracks may be due to debris in the tubes, or even a slight bend at the top of the brass tube.

 

[les-smith]

My lathe is usually turning fast enough that it creates a vortex in the shop. LOL I use a Robert Sorby roughing gouge to start with, but first I cut the corners off the blank on the bandsaw before turning. Right now I'm experimenting with heating the acrylic up using sandpaper as I turn it. After I have slightly turned blank I will sand it with the lathe turning with +/- 200 grit paper. I think it softens the acrylic slightly making it easier to turn. This, though, may be a controversial technique. As I said I'm experimenting right now, but I like what I'm getting.

As far as the acrylic cracking upon assembly. I use a small round file to file the tubes before insertion of the parts. I bevel the edges and make really sure there is no CA in the tube. Since doing this I have yet to crack another acrylic barrel.

 

[LostintheWoods]

Another possibility for your cracking problem is having the knurled nut tighter than need be on the mandrel. Its okay to snug it down pretty well initially, but once the blank is round, back it off so that its just tight enough to keep the blank from turning on the mandrel as you shape it. Hope this helps.

 

[DocRon]

I turn them pretty much like i do wood. I start with a spindle gouge, go to a bowl gouge (my all purpose tool) then finish up with a skew. It helps to round off the edges on the belt sander initialy, but not strictly necessary if you go slowly. I am not concerned about slow or fast - I'm in this for fun, not production. Would probably try to find a faster method if I were a production turner.

 

[Malainse]

I drill as slow as the press will go.... I had one burn and crack at higher speed..

I turn wide open and make light cuts with a just sharpened gouge then skew....

 

[johncrane]

1)your cracking could of happened when you drilled the blank if the drill got to hot!
2)your tubes would have been clean to get them on the mandrel, but you can double check them before you assemble the pen. a cotton bud dipped in acetone will remove ca glue
3)make sure you parts get pushed in the tubes straight!
l use a Gouge/scraper/ wet sand.[]

 

[Rudy Vey]

I do quite a bit of plastics and here is my way of doing them (others may use successfully other methods, but this is what works for me).
I use a sharp gouge until about 1/16 before the end size. Then I switch to a sharp skew and finally wet sand from 400 through 2000 grit and polish with automotive or Novus polish. The speed of the lathe is full speed and I drill at about 1500 rpm. The trick is not to try take off too much at a time. And sharp tools, I don't get much chipping with my gouge, but a lot of nice long ribbons.

 

[Geo in Winnipeg]

I drill at about 700RPM. Use water to cool the drill and clear the chips often. If the blank is long enough I don't drill all the way through - just to the right depth then cut it to length. I relieve the corners on the bandsaw, use gouge to 1/16 then skew. I wet sand and polish all acrylics ans resins the same as Rudy. I use a countersink (by hand) to make sure there are no burrs in the tube ends. Always use sharp tools and remember heat is the enemy of plastic. Oh, and I colour the tubes with nail polish - the LOML has a good selection[]

 

[fiferb]

Be careful not to press the parts in too hard during assembly. I found myself giving it a little extra to make sure the nib and finial were pressed in all the way wound up cracking some this way.

 

[Paul Downes]

Well, thank's for the ideas. I usually drill w/water on plastics and also have found it works great on snakewood. I always chamfer the tubes. I suspect the last crack was induced by too much assembly pressure. I have resorted to using the 60 grit gouge[], because I didn't like the way my 1/2"gouge was performing. I wonder if a little lubricant (soapy water) sprayed on the plastic would help with it's machinability? I know this works with other materials. (Might make me look like a paint bomb went off at close quarters.) I think I will be more careful with every step of the process. details,details.......

 

[bob393]

Heat is always a problem when drilling or turning.
To tight a fit with too much presure will do it also.

 

[Rudy Vey]

Originally posted by Paul Downes
<br />Well, thank's for the ideas. I usually drill w/water on plastics and also have found it works great on snakewood. I always chamfer the tubes. I suspect the last crack was induced by too much assembly pressure. I have resorted to using the 60 grit gouge[], because I didn't like the way my 1/2"gouge was performing. I wonder if a little lubricant (soapy water) sprayed on the plastic would help with it's machinability? I know this works with other materials. (Might make me look like a paint bomb went off at close quarters.) I think I will be more careful with every step of the process. details,details.......

I forgot to mention this in my hectic morning. When drilling, I always clear out chips (actually more like ribbons) every 1/8-1/4 inch or so and always dribble water in the hole (2 drops) and on the bit (another two drops) have a small bottle with water by my drill press. When you do a lot of drilling of plastics you get the feeling for the drilling; when your ribbons start to get thick and cling more together it is time for a small break, clear the hole and add water. Since I do this now for several years, I never had a blow-out again. Sometimes, I round over the corners on a disc sander - especially the small acrylic acetate blanks from Berea can be very brittle.

 

[gerryr]

I never touch synthetics with a gouge. I tried a skew and it was just too time consuming and messy with all that stuff wrapping around the blank and mandrel.. I've nothing but a round nose scraper for over a year and the only blow-out I've had was on some really brittle PR. I had some PR blanks from PSI literally explode on me a long time ago when I was still using a gouge.

 

[TellicoTurning]

I start with round nose scraper to round the blank, then switch to skew.. after I saw Ed Davidson's video... I dont get the chipped glass effect that has to be sanded out now with the skew.

The cracking may also be cause by not having your nibs and transmission absolutely square to the tube when you press... I've chipped a few that way... any sideways pressure will cause the edges to chip.

 

[GreggR]

I'm new to this, but I've done a few acrylics. Burned one during finishing (bummer), got drilling breakout, and hated gouges and skews for this material. So here's what works for me, probably not the right way, but it worked for me...

a) Cut blanks 1/8 to 1/4 inch long, drilled almost to break out and cut off. Drill very very low RPM and slow feed, drops of water like listed by others here.
b) Keep it cool when finishing. I polish a little then let it rest, then polish more when the blank is only mildly warm.
c) Bought two cheap HSS chisels - 1/4 and 3/8 (yes wood chisels, not lathe tools), rounded the noses maintaining the rake angle, and honed them to a razor edge on the flat side. They cut great.

 

[YoYoSpin]

Answers are here, grasshopper: http://content.penturners.org/video/epr_sierra_high_res.wmv