whats the best depth to reverse engraving?

[Kev Mayger]

Where’s Rodney when you need him eh?

[Rodney Gold]

Heh , here!!!

We laser it and just frost the surface , but it depends on the effect you want , our engraving flouresces with no “edge” effect. If you want the edge effect , IE glowing single cut lines you must use a bit with a shallow angle , preferrably 45 degree which is somewhat problematic cos the pex is bound to vary in thickness if its cast and small changes in depth have big changes in line thickness . To compromise , use a shallowish bit and go in a mm or so. You dont have to go in deep at all.
You actually normally dont want extremely clean cuts so we dont use any coolants if rotary engraving so the cuts are somewhat “frosty”
A good strategy is to do fills , like the solid inside of a letter , at a lot shallower than the outline. This does 2 things , 1) less stress on the cutter and a smoother surface without milling marks and 2) surrounds the glowing letter with a brighter line
If you leave the mask on the pex and engrave thru that , you can do marvellous things with various paints and have a colour edge lit sign.
The plastic masks arent good for this , so if it has plastiuc , strip it off and lay down some paper based vinyl application tape.
Be real careful with cast pex , it generally has no better than a 10% thickness tolerance and can vary between 7-9 mm across a piece. Extruded acrylic doesnt laser well at all and is not the best for this application if rotary engraved as it cuts a little too clean. BE VERY CAREFUL cleaning the stuff afterwards , do NOT use meths or solventsa , the pex is VERY stressed cos of the machining operations and can easly craze with solvents.
You can backpaint the acrylic too and laser/engarve thru that for glowing letters on a coloured background. You can also slectively apply vinyls etc – can do some nice things with edgelit.
We have moved from those low voltage tubes to leds for our edgelit. They can be fitted in thin channels and are very cheap.

[Westcoast Sign Guy]

I use an engraving bit 35 to 45 deg angle. I usually use 1/2″ acrylic at a depth of 1/16″ to 1/8″

[Kev Mayger]

Cheers guys, exactly was i was after. Another fine piece of advice from the signboards.