smooth finish turning acrylic

[unterhaus]

my experience is that you want to use a super-sharp tool. Everything else is really of secondary importance.

[dlh422]

I'm using the round nose and it's giving me a much better finish. thanks for all the suggestions. Still not where I want it to be when I pull it off the machine but it's much improved from where it was. It's a learning experience.

DH

[samco]

have you tried touching the surface with a flame? (don't know if that would work)

we laser cut acrylic and the heat causes the edge to be transparent/smooth

sam

[bennett71]

DH,
Sam has a great point here. I also cut acrylic with a laser & we "flame polish" the edge to get a brilliant, glass like finish. You might want to try turning a piece in the lathe while hitting it with a propane torch to see what happens. Some of your marks look like normal chatter. Is your machine single phase? You could be getting vibrations in the drive & when the acrylic gets hot & more plastisized from machining, your tool might want to "disengage" & rub the cut. I could be completely wrong here, but from your pics it looks like a harmonic, vibration or rigitity problem to me. Tom

[Paul_S]

You can calculate your feed in IPR for turned finish.

IPR = .0566 x sqr(tool radius) x sqr(desired finish / 125)

.0566 value is for a Ra finish of 125.
For the value for an other desired Ra finish its .0566 x sqr(desired finish / 125).

Of course the finial finish will be no better than the lapped finish on the tool radius.

[ImanCarrot]

I cut acrylic for military applications and get an OPTICAL finish (ie better than anything that can be measured- we're down to fractions of a wavelength of light here on peak to valley values for form and nothing can measure the surface roughness it's so good).

I use a Diamond Turning Lathe with natural monocrystalline Single Point Diamond tools- 0 degrees rake, conical section, -25 deg front clearance and a radius of anything between 0.2mm and 0.5mm depending on the geometry to be cut.

Vibration is my nemesis so I use a strobe and accelerometer to find out where to add weights to the spindle to balance it... one 3mm grub screw (5mm long) can change the vibration characterstics of the machine

[CurtisU]

I've no experience with turning acrylic, love woodturning though and can agree with Tom and Imancarrot, vibration may be affecting your finish. Although I've not intentionally explored it, there is a technique, chatter turning, that produces something that looks like your finish. One man's pleasure, eh?

Here's a guy that tells you how to make a tool for it, there are tools commercially available too.

http://www.hiltonhandcraft.com/Artic...atter_Tool.asp

In addition to the adjustments to speeds suggested by the experienced here, I'd strongly support comments about tuning the rigidity of your setup, since it looks like chatterwork relies on what looks like a "loose" tool.

Hey, maybe you can learn to control it and produce desireable paterns.

Good Luck,
Curtis

[dlh422]

thanks guys for all the comments. I've been pretty busy with some other project lately so I haven't a chance to respond. Nor have I turned much of anything either.. I appreciate all the suggestions. The one thing I did incorporate, I think I mentioned was the round nose bit, it helped alot but I think it can be better. I attempted flame polishing once but I don't know, I may give it another try with the round nose finish. I have a couple of other ideas about eliminating vibrations but just havn't had a chance to get around to it yet However, here is a pic of my latest batch of calls... I don't have them on my website yet but you can see my stuff at www.duckhollers.com....
thanks,
DH

[ImanCarrot]

Here's a couple of pics I turned yesterday on my Diamond Turning Lathe - I skimmed the diameter (to reduce vibration), skimmed one face, skimmed the other then stuck it on my 3 axis turret mill to put some pretty writing on it

This isn't the best finish I can get.. I was only using a roughing diamond tool hehe