Quick acrylic edge clean/polish.

[kiwichris]

Hi-ho,

I scored a few sheets of acrylic and thought I'd make some keyrings for friends out of it...

After a bit of trial and error on feed rates I got the cutting working well but the edges are a little rough/sharp.

Per some things I found on the web I made up a quick'n'dirty polishing wheel from some bits of fabric stacked between two washers but it takes ages to get much progress on the acrylic. I assume I need a cutting/polishing compound of some sort.

So.... Any hits for a quick buff/round/polish on acrylic? Not wanting to go into production, or buy something specialist. I just just want somethign that will mean it doesn't take 15 minutes to polish a 80x25mm keyring!

End result is just to take the sharp edges off and clear up any tooling marks.

Cheers, Chris H.

[mactec54]

kiwichris

You could try & flame polish the edges, You can find on Google a lot about Edge polishing
for acrilic

ACRYLIC SHEET EDGE AND SURFACE FINISHING: Plastic Distributor & Fabricator

[kiwichris]

Originally Posted by mactec54 kiwichris You could try & flame polish the edges, You can find on Google a lot about Edge polishing for acrilic

Hi,

I did see that and give it a go but was looking to round off the edges a bit more than a flame does.

Also, for the record using a small butane torch works well but the protective paper burnt a lot faster than I thought it would!

I'm really looking for a DIY shortcut / replacement for rouge, polishing compound, C93 etc. that I can pick up at a supermarket or local hardware store rather than buying something specialist as I probably wont buy any more acrylic after the free bits are gone.

Cheers, Me.

[RomanLini]

A fine tooth file will get the edge corners rounded, then some fine wet and dry paper, from 600 to 1200 then 1200 with a lube.

[kiwichris]

Hi-ho...

I had a bit more of a play around with this last night and I found it was quickest to scrape the edge and then smooth with a bit if sandpaper then buff...

The small file pinned up quite quickly, whereas using a box knife to scrape the edge was quick and the risk of scratching the surface if I slip is less.

End result is fine for what I want but I am now tempted to get a proper single flute mill for plastic to try out....

[RomanLini]

HSS endmills for metalwork give a clean cut on acrylic, provided they are brand new (sharp) and you run lowish RPMs (like 9k or 10k RPM with a 3mm 4-flute endmill). A squirt of water doesn't hurt either.

[kiwichris]

Originally Posted by RomanLini HSS endmills for metalwork give a clean cut on acrylic, provided they are brand new (sharp) and you run lowish RPMs (like 9k or 10k RPM with a 3mm 4-flute endmill). A squirt of water doesn't hurt either.

Hmmmm.

What sort of feed rates would you be looking for with that?

For the cut I've been running 2 flute 3mm carbide mill at about 7k 300mm/min 0.5mm DOC (small MDF router, can't wait for my big one to arrive!) The cut quality is OK, but there is some chatter marks due to flex in the machine.

For the engraving I'm using 25degree x .2mm carbide engraving tool also at 300mm/min 1mm deep single pass and the result is really nice.

I tried cutting deeper and the tool dug in and pulled things, higher speed on the spindle (Dremel) or feed causes shudder/chatter and lower feed I get a lot of melting / caking of chips in the cut.

I've got some brand new 4 flute carbide cutters I could try, but I'm wondering if you were thinking of higher feedrate than I can do. Max cutting speed on my current setup is only 450-500mm/min.

Cheers, Chris H.

[TDA]

Originally Posted by kiwichris Hmmmm. What sort of feed rates would you be looking for with that? For the cut I've been running 2 flute 3mm carbide mill at about 7k 300mm/min 0.5mm DOC (small MDF router, can't wait for my big one to arrive!) The cut quality is OK, but there is some chatter marks due to flex in the machine. For the engraving I'm using 25degree x .2mm carbide engraving tool also at 300mm/min 1mm deep single pass and the result is really nice. I tried cutting deeper and the tool dug in and pulled things, higher speed on the spindle (Dremel) or feed causes shudder/chatter and lower feed I get a lot of melting / caking of chips in the cut. I've got some brand new 4 flute carbide cutters I could try, but I'm wondering if you were thinking of higher feedrate than I can do. Max cutting speed on my current setup is only 450-500mm/min. Cheers, Chris H.

You should be going at least double that feed (or lower RPM). You are only cutting .843 thou (.0214mm) per tooth per rev at 300mm/m. With that size cutter you would want to take at least 2 thou (.05mm). I would start my feed at 28IPM (711mm/m) at 7k. Since you can't go that fast you might want to try a lower RPM.

Getting chatter marks at .5mm and anything over 300mm/m is odd (especially in cast material). You might want to check if you are climb or conventional milling the parts as your climb side is going to be much harder to get a decent edge out of. Also make sure you have it clamped down well. If it's not that will give you all kinds of tooling marks.

The 4 flute would be even worse as you will have to feed it more material to get a clean cut (My starting feed for this would be 56IPM (1422mm/m) at 7k).

[kiwichris]

Hmmmmm.

Thanks for that info. I can jog at 900mm/min but I've not tried cutting at that speed. I might give it a go and see what happens.

I've got a good handle on feeds/rates for different wood types and some softer plastics but acrylic is a whole new game for me.

I'll post some picks of what I get when I speed up/slow down the cut.

Cheers, Chris H.

[RomanLini]

As acrylic is hard, it generates side forces with cutting. The Dremel will have a lot of flex and always give you some nasty chatter marks. You could convert to a small router with metal frame like an 850W Ozito ($60 at Bunnings with 3yr warranty).

You won't be able to run high feeds with a dremel again as that makes a lot more force and the dremel is too flexible.

Also, you really need to remove chips from the cutting grooves with a permanent air jet if you want a great finish, or cut most of the way then vacuum the chips up, then cut a 0.1mm or 0.05mm final cut to make a clean edge.

Personally I think the Dremel is the real limiting factor!

[kiwichris]

Originally Posted by RomanLini Personally I think the Dremel is the real limiting factor!

I dunno, you've not seen the rest of the machine! :-)

I've got an alloy bracket right down near the pointy end of the dremel which helped a great deal with chatter when I first built the machine but you are right, there is a lot of flex in the case itself and I had to pack out the bearings with epoxy as they were floating around when I first got it.

I'm waiting on a router which is literally on the boat right now, so I'm not going to spend too much time playing with the old router at this point, but it's worth the learning experience to try things out anyway I think.

I picked up some black acrylic offcuts from a local plastics place on Thursday as it's nicer than the (free) white stuff I have. I'll take some pics later on of what I've been up to.

Cheers, Chris H.

[kiwichris]

Me again...

Forgot that I made a video of the engraving part of the process...

Rpm keyring engraving. - YouTube

Rpm keyring engraving. - YouTube

The finish from the engraving bit is nice and clean, it's the profile cutting that's not so hot.

Cheers, Him.