Machining lexan or polycarbonate

[Patternboy]

Good night everybody,

I am trying to machine lexan (.5"th.) and I don't know what would be the best way to cut it. I am making L shape brackets around 24"x24"x 4" I am using an Onsrud cutter 3/8" Dia. 2 flutes straight, I tried different feed and spindle speed and I am getting melted chips, my toolpath is a contour, my stepdown is .125".
Thank you

[stevespo]

Yes, getting the feeds/speeds right is the key. I bought some inexpensive single flute carbide (straight) cutters and got decent results. I believe I slowed my router down to 10K RPM and was using cutting speeds of 60-90 IPM. Similar stepdown of .125" with a .250" diameter bit. With the slower RPMs, the tradeoff is you get more "scalloping" along the edges, but a lot less melting. You can always try and go back with a slower finishing pass and take a very light cut.

Another thing that helps is to run some compressed air at the bit to help keep things cool. If you can do it, a fine mist of water also helps out - but I run dry due to my MDF workboard.

Steve

[CalG]

WAX the cut line with stick wax. The saw guys sell it. Just apply like tracing the outline with a crayon. A little lube goes a long way.

CalG

[Patternboy]

Good day all, thanks for your reply,
CalG, it's very hard to follow the cut line with a stick wax when I am cutting 8 pieces at once like nesting, my sheet is 48"W.x 42"D. See attachment.

To stevespo,
I am using also a solid carbide cutter, I set the rpm at 1200 and feed at 75/ipm, didn't work, change rpm and feed two or four time and same thing melting the lexan. I can't use liquid because like you I have MDF workboard.

[judleroy]

Use a 1/4" carbide two flute spiral upcut router bit. They sell them at lowes now adays. 10-to25,000 rpm. Cut feed depends on router rigidity. Maybe 50-200ipm. 1/4" depth of cut. You can go the whole 1/2" with a good setup.

[Patternboy]

Good day judleroy, I have tried with a spiral upcut in the past and if you don't have a vaccum table to hold your piece down, it will lift it up while it's cutting especially if it's only .25" th.
Thanks

[judleroy]

Use the thin 3m 2 sided tape to hold down your parts or sheets. You can still clamp the edges of a sheet but the tape will hold the center down where you are cutting. The tape can be removed by rubbing an edge till its free and then just pull it off. Make sure you leave the protective coating on your polycarb till after the tape is removed.

[CalG]

PatternBoy

For situations such as your requirements I have had very good results by making a "quasi-dry run" A spring loaded scribe point is put in the machine spindle that etches a light line showing the tool path.( I've used the tapping aid plungers, but have also made my own device.) Its a simple mater to retrace the scratched lines with the lube wax.
This tracing is really good confirmation of your program too.

Just an idea....

[mc-motorsports]

Try using HSS cutters, carbide might not hold a sharp enough edge causing rubbing which is probably some of the reason your melting chips. Other than that, a blast of air/coolant to get the chips out will help a lot, as high pressure as you can deal with.

HSS will flex a lot more than carbide, only disadvantage in this situation.

MC

[Geof]

I think part of your problem, maybe most of it, is the straight flutes; the chips are not being ejected and are just packing in the cut.

I have pound GARR 242M series cutters, micrograin carbide high helix two flute very good for lexan because they do have a very sharp cutting edge which prevents rubbing and the helix pulls the chips up out of the cut.

If you are doing a lot of these I suggest you make an aluminum cover plate to hold the lexan down so you can use a helix cutter and take a good cut at a fast feed.

[trooper55]

i use an onsrud 63-712 which is a 1/8" single flute up cut solid carbite and it works great very clean cuts and holds it's edge very well but it will pull the material up. But i have tried they down cut version i think is the 62-712 and that works well too because it still ejects some of the chips and puts down presser on the part. Just have to use some air to help get the chips out.