cutting Lexan on my CNC (4:30 in Hawaii... & I'm praying for a quick response...)

[iSign]

hey guys, I just ran out to but some 3/16" clear acrylic for some second surface signs I need to make tomorrow & the material I was offered was all warpy!!

I've not seen such crap, but I guess I'm used to cast acrylic & didn't know this supplier had quoted me an inferior product, extruded acrylic (I actually never knew about it even)

Anyway, they had Lexan & it was nice and flat so I bought it.

One of my signs is covering a door & there is a 2-1/2" diameter lock I need to rout a hole for, plus several of these signs are where someone could accidently run there finger along the edge, & get cut, so I wanted to run a conic bit around the perimeter of each blank & then cut through with an endmill to give a nice beveled edge...

But, I've never cut Lexan on my router!!

...and the fist time I tried cutting it on my panel saw ...well, you don't wanna know... although I did buy a new blade & now that's not a problem... but it does lead me to wonder what kind of learning curve may be waiting for me now...

So, ideas are great, but I really hope someone has done this & can confirm what differences I might want to consider regarding the tool, or feeds & speeds.

...oh yeah, I was also hoping to run a test tonight

 

[Fred Weiss]

I don't think I'll be much help since the closest I ever came to machining Lexan was machining Delrin.

The main thing to realize is that despite its bulletproof characteristics, Lexan (generically polycarbonate) is a low energy plastic in the same family as polypropylene and polyethylene. It will tend to grab, pull and stretch, so whatever you would do to compensate for that is what you should do for the Lexan.

Going from memory ... it's been more 15 years, you should

• use cutters with the most clearance to prevent clogging and to allow for chip removal
• add extra passes to your cutpaths so you are making shallower cuts
• speed up your rpms
• slow down your feed rate

 

[iSign]

thanks for the reply Fred, I will finish setting it up, check back here one last time & give it a whirl.

I have a 1/4" single flute up-spiral I usually use for acrylic, & I'll try out my small 90 degree conic first. I'll probably run the spindle at 18,000 which is fairly common for most of what I've done, but maybe try 100 ips, instead of the usual 150 - 200.

I'll also probably set the depth around .085 to take 3 passes on 1/4" Lexan (my new pieces are 1/8" & 3/16", but I have a test scrap of the same GE Lexan, so I'll test with that in case the test fails & I want to return the 2 sheets & look at another Acrylic supplier tomorrow.

 

[Techman]

yes, there is cast and calendared plastic sheets

as you observed when cutting it with saw blade.. it melts.. and then the chips rebonds itself.

Lots of air to provide cooling and chip removal. Air gun with a concentrated blast ... Slow feed,, and a large high speed spiral bit cutting in the proper direction. That means no climb cutting..the spiral bit will pull the chips out. Run it slow too. maybe multi passes will help

Mill cutting is better and means the feed goes counter to the cutter rotation. usually it will carry heat away better.

Make sure the corners do not collect chips. They will melt and rebond into a big old melted gob. Flame polish the edges if you want them really pretty and shiny.

Make sure the chips fall onto the scrap side of the cut. use feeds and cutter direction to do this. Leave the paper liners on to prevent scratches. The chips will be sharp. As you found when you cut it those chips are messy and get into every thing.

 

[GB2]

Doug..I've never tried Lexan in the router but I'd agree with Fred's advice. My router's maximum is 54 IPS and from my instinct I'd definately not start out higher than 100. I do have some lexan on hand if you wanted me to try something but I guess you could trial and error just as well!

 

[iSign]

thanks guys... I'll go see what I come up with!

 

[astro8]

What techman says plus if you have a good vacuum table (so you know your parts aren't moving) after you cut through you can do a small clean up pass if you think your edge is a little frosty.

I leave the spindle at 18,000...some say to use water mist as well as this will cut down on your rewelded chips but I don't use it as my mist is setup with cutting fluid for aluminium.

I've cut a fair amount of polycarbonate and found that different brands cut differently, even older versus newer sheets cut differently...

I've even cut polycarb thinking it was acrylic and it cut well...so ignorance is sometimes bliss.....

 

[sfr table hockey]

I might be too late for your answer but I cut lexan with my router for my table hockey surfaces. I use a scrap of MDF or any scrap wood for the underside of the lexan and use an up spiral 1/4" bit. I cut mainly the 1/8" thickness and it cuts real nice. With the up cut spiral bit you will just need to sand the top edge a bit. You can actually cut the 1/8" lexan with a pair of sissors for trimming.

Lexan won't chip like regular acrylic does when cutting. Because its so thin you just have to make sure it is held down secure when cutting.

 

[CustomRide]

Our flatbeds have a creasing tool option and it will actually cut lexan buy running multiple passes on it....its a creasing wheel may want to check into the bits or heads available for your unit for future use.

 

[Westcoast Sign Guy]

I cut poly-carb as much as I do acrylic.

Cut poly-carb on your router table the same way you do acrylic. You won't have any issues. I prefer single flute down or up spiral bits, the best bits are Belin, expensive but they do the job and well

BTW- I made the same mistake you did on the panel saw. best thing to do is use those substrate clamps if you have that, or lay a plywood board over what you are cutting and cut both at the same time. A lot of times it's better to use a hand router & a straight edge to make your cuts on poly-carb

1/4" CED single up spiral 15k RPM @ 2.5 IPS (Belin)
1/8" CED single up spiral 18 RPM @ 1.14 IPS (Belin)

 

[iSign]

well I had a fun night of running all my machines that I usually don't run myself anymore... finished my print files, got some prints rolling, got my Lexan cut files ready & ran some tests, then cut my 2 full sheets of material with an engrave pass with the conic tool, for my bevels, & the router offset pass with my endmill to cut out just outside of the bottom of the V groove... everything came out perfect at 100 ipm & 18000 rpm... even coated out some MDO which I haven't done in a real long time & that looks like glass... it's nice to do some production work for a change!

 

[PGSigns]

Doug
I got a lot of good info from this site on feeds, speeds, and tooling for cutting plastics. http://www.plasticrouting.com/
Jimmy

 

[iSign]

Thanks Jimmy!
I really need to spend more time researching what is available in that site... I just started reading some really cool stuff & remembered the time... gotta go to work! ..but thanks again