[dlh422]

Attached is a pic of the cnc lathe that I got this year. It uses a horizontal laminate trimmer as the cutting tool. I've been turning wood and acrylic and using a triple fluted upcut solid carbide router bit. It removes the material well enough I suppose but leaves a rough surface. Does anyone have any suggestions on what type of bit to use to get a smooth, or at least as smooth as possible finish. Perhaps an v-grooving bit. I'm tired of sanding and polishing. especially the acrylic.

thanks,

dh

[Pat2000]

Can you give any more details as to what kind of finish you are getting?
You might want to reduce the cutting speed if possible if you are getting burning/whitish marks, maybe drop down to two flutes? to help with swarf removal and maybe use coolant if thats not going to be too messy for you, do you have an air-line? we use them a lot at work to blow the swarf from the flutes,

I mill quite a lot of acrylic at pretty slow speeds compared to routing, hope that helps but you need to detail the problem a bit more!

[dlh422]

thanks, I actually have a couple of video clips which might help but haven't been able to attach either one, even zipped. and I'll get some close ups of the finished pieces too. I'll get more details for you but have a hungry 4 yr old yanking on my arm at the moment. thanks for the reply.

[dlh422]

Pat,
Attached are a few more pics. One of the machine, and two of the parts. One of the parts is polished and next to it is how it comes off the machine. As you can see it's rough, whitish and includes the swirl tracks. I don't use coolant and I suspect it would be pretty messy and I'm sorry nor do I have an an air-line either. I still can't attach the video clip. It must be too large.
thanks,
dh

[dlh422]

well, not all that whitish but mostly just rough with the swirl tracks.

[JoeFL]

It looks like you might be turning a bit too fast.. I'd try slowing it down a little.

I also agree with Pat on using a 2-flute tool and compressed air directed at the cut area for cooling/swarf removal. See if that doesn't help...

Nice work, by the way.

-Joe

[ger21]

If it's cutting on the end of the tool, you're going to have a very hard time getting rid of it. I'd recommend using the shortest tool possible, to minimize deflection, and make sure it is extremely sharp. Have you tried a round nose 2 flute bit?
http://www.pricecutter.com/product.a..._A_cn_E_243667

[dlh422]

yes, it is cutting on the end of the tool. I haven't tried anything but the flat end bit. I thought the v-groove might be good but I'll give the round nose a try too. The router is removable so ultimately the best solution may just be to remove it and mount a stationary cutting tool. I'll have to have that machined though.

thanks for suggestions.

DH

[chan luci]

Hi,
I have lots of experience in acrylic turning. High speed is a MUST. And after the final cut, you can use a smooth silk or synthetic cloth to wipe part when the job rotates on the turn machine. Repeated run gives an excellent glossy and transparent finish.
Let me know the outcome of the result.

[Pat2000]

Sorry dh not to get back to you, interesting parts you're making, it seems that cutter deflection may be one of your probs?, hard to see quite tho, so go with that short cutter if you can, bigger shank on the cutter maybe? have fun!! where do you get that kind of greenish shade of Acrylic, I do like Acrylic it has such a juicy transparency!!

[dlh422]

I've been meaning to get back with an update but just been covered up... I ended up ordering a round nose like ger21 recommended. In fact it should be in today so I'll give that a try and see if it helps. I'll post an update when I get some results.

there's a place called delvies plastics that I've been ordering my acrylic from. They have a pretty good selection of colors to choose from to so it's lots of fun.

thanks,

[scubanick]

looks kinda like some duck calls we are making

[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