Acrylic success consistency

[philthephlier]

As a fairly new penturner (5 months) and still on the learning curve I have had my share of blown up acrylic blanks despite using sharp tools and varying speeds. I bought a carbide tool from an ebay store called unique tool. It is a 3/4" round carbide insert reground for a relief angle more appropriate for wood lathes. They machine a tapered 16" solid steel shaft and put a golf club handle on it and supply the tool with an allen wrench to loosen and reposition the insert for a fresh sharp edge. I have turned many blanks with it including 6 or 7 acrylic blanks @ 2700 rpm and with fairly light cuts I have not had a failure. The finish it leaves requires very little sanding and the insert hold it's edge very nicely. I have not used the tool enough to need sharpening but I am expecting that all it will need is a minute or two on a diamond stone to get it sharp again.

 

[redfishsc]

Sounds like you found an interesting tool, I'll have to check it out myself.

Here is how I do acrylics. I very, very rarely have blowouts since I "developed" my pattern (based heavily on info from here).

1) Super-sharp skew. Sharpened with a diamond stone, 600 grit. Very quick and easy. I also have the Sheppach so I hone it on the strop, it will shave your arm after the strop. I do not use a spindle gouge on acrylics, even for roughing it out-- it's all done with the skew. I COULD use the spindle gouge but catches are too easy for me with acrylics and gouges.

2) High speeds. I've read that you aren't supposed to turn acrylics at hight speeds--- nobody ever told MY blanks that, I turn every one of them at the highest speed the Delta midi can do (3700?).

3) Rub the bevel, don't be overly aggressive.

4) "feel" the cut. If you start feeling vibration coming from the cutting edge, you may be having chipout. **slow down****.

Move slow but methodically, and imagine the Fur Elise playing in the background to give you the proper mood and attitude for cutting acrylics.

 

[sbell111]

My 'method' is very similar to that of redfishsc.

1) Super-sharp skew. Sharpened with a wolverine jig on a slow-speed grinder. Our sharpening station is very close to the lathe, making it easy to resharpen the tool at any time. I don't use the skew to bring my blank to round, however. I use a gouge for that. Lately, for some reason, I've been using a super sharp fingernail gouge for this purpose. Many times, things go so well with this gouge that I never actually switch over to the skew. This is partly due to my poor technique with the skew.

2) 'Nearly'-high speeds. I don't use the highest speed on our Jet, but the next-to-highest (2630 rpm?).

3) Rub the bevel, don't be overly aggressive.

4) "feel" the cut. If you start feeling vibration coming from the cutting edge, you may be having chipout. **slow down****.

I'm totally on board with his #3 & #4. If I try to rush the process, I will destroy what I am working on. I light touch and the willingness to back off and stop the lathe to see what's happening is the stuff, for me.

 

[reddwil]

I've never had on blow out while turning, my problem is drilling them. Just when I think i've got it figured out, I lose one.

 

[redfishsc]

I drill solely on the lathe. I do not even own a drill press (the shop I work at has a HUGE drill press but I never use it for blanks).

I hold the blank using the longnose jaws on a Barracuda chuck, and I put the drill chuck/bit in the tailstock.

Drill at 500 RPM, and I'd drill slower if I could, but the Delta midi only goes as low as 500.

Drill slow, purge often, and if you really struggle with it, you can use mineral spirits (some have recommended even kerosene) as a lubricant. The spirits is oily enough to act as a lube yet will actually evaporate, not interfering with the glue later. Some use water to lube but I've tried it and it's not nearly as effective as the mineral spirits. Keep the spirits in a mustard-squeeze bottle and just dribble it on the drill bit (or if using the drill press, dribble down into the blank hole).

Beware the exit!!! If you get in a hurry near the end you will cause the blank to "self feed" and get jerked up onto the drill bit and shatter the end---- even when drilling on the lathe. Gotta move slow.

 

[reddwil]

Beware the exit!!! If you get in a hurry near the end you will cause the blank to "self feed" and get jerked up onto the drill bit and shatter the end---- even when drilling on the lathe. Gotta move slow.

Thats where I have my problems, on the exits. I usually cut my blanks longer and stop a 1/8 short when drilling. Then trim. It works but the extra steps are a headache

 

[redfishsc]

Just remember to drill s-l-o-w, generate as little heat as possible (using mineral spirits if possible as a cutting lube), purge the dust every 1/8" ESPECIALLY as you approach the bottom.


Here is a trick---- use white out (or perhaps even a piece of duct tape or masking tape) and mark the length of the blank on your drill bit. In other words, when you see the mark on the drill bit getting close to the TOP of the blank, you know JUST when the bottom of the drill is hitting the bottom of the blank. This will be your time to get exceedingly paranoid, careful, and overly protective. Drill slow and make a slow exit.


I struggled with this for a while. If, in desperation, you give up on acrylics, buy a jaw chuck-- it's very hard to beat the Barracuda (or Cuda 2) from PSI, and use this to drill on the lathe. The PSI chucks come already with longnose jaws which work perfect for drilling blanks. I've drilled many, many more blanks this way than with a drill press, and I have a LOT better success at it.

Why? I suppose because I can use the handwheel on the lathe to very gently and slowly advance the drill bit into the blank.

 

[mbuckley52]

more tricks

When I make ( I cast my own blanks now) and drill my own blanks. I bought a special drill at a local turning store, the flutes are open more so it will clear out the drilled acrylic. (not sure if I can mention the store). just use you drill press and go up and down a lot to clear the bit.

than once you have glued the tube in they blank, try sanding the square edges on a belt sander, this takes off the corners and makes them easier to turn. i hook up the shop vac for this , it makes a mess, I use a roughing gouge that is very sharp and take small bites, if you get the right angle the acrylic will come off in long strips, it sometimes gets rapped up around the blanks and you have to stop the lathe and clear it off.
I run my lathe about 1200 rpm and take small bites until you get the feel for it.
once you know the feel it will be a lot easier.

As a fairly new penturner (5 months) and still on the learning curve I have had my share of blown up acrylic blanks despite using sharp tools and varying speeds. I bought a carbide tool from an ebay store called unique tool. It is a 3/4" round carbide insert reground for a relief angle more appropriate for wood lathes. They machine a tapered 16" solid steel shaft and put a golf club handle on it and supply the tool with an allen wrench to loosen and reposition the insert for a fresh sharp edge. I have turned many blanks with it including 6 or 7 acrylic blanks @ 2700 rpm and with fairly light cuts I have not had a failure. The finish it leaves requires very little sanding and the insert hold it's edge very nicely. I have not used the tool enough to need sharpening but I am expecting that all it will need is a minute or two on a diamond stone to get it sharp again.

 

[dntrost]

Lucky I am ignorant

I guess I am lucky I didn't read much before turning my first acrylic. I find drilling on my drill press no real issue I clean every 1/4 - 1/2 inch. I turn same speed as wood and do keep my tool as sharp as I can just have a grinding wheel I sharpen it with. But so far no blow outs. I did melt one by sanding at full speed now I sand at 500rpm through all phases of sanding.

 

[Buzz]

I prefer to drill on the drill press. The blank being vertical means that the hole can get an occasional squirt of water from a sprayer bottle to help keep everything cool.

I never attempt to drill all the way through (at least not since having blow-outs in my first few attempts), I drill deep enough to accommodate the tube and then dock the blank to length.

Turning is at full speed on a Jet mini (3,300 rpm) and I use a roughing gouge and skew.

I don't bother to change speeds for finishing either, although I would if I had VS. I use the coloured pads sold for acrylics/resins and use plenty of water. A shallow ice cream container on the bed beneath the blank keeps things reasonably clean and dry. Final buff is with white diamond.