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I've been experimenting with engraving cover plate material with a 60 degree V-bit at a depth of .020" to .040" (9000 RPM at 19 ipm). The chips pack into the slot and can't be removed with air. Tried two passes and it's better but not by much.

Any tips?

What material are you engraving? It could be that you're feeding too slowly. Also, pick up one of those segmented flexible air nozzles to point at your bit.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Kinda pricey, but these Cold Guns work. Common usage in the aircraft machining industry. Works on plastic, soft aluminum, other materials. Will freeze your fingers if you're not careful. If your shop is not air conditioned the moisture in the air will condense on the hose in big fuzzy crystals. You'd have to watch to make sure water didn't drip on the wood after you shut them off. You do need a big air compressor to keep it fed.

http://www.airtx.com/cold_air_guns/

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"Act your age, not your shoe size" - Prince

I'm with Andy - 19 IPM is pretty slow.

Thanks guys.

The material is cover plate vinyl. Two air jets but you have to watch the pressure or you'll blow a bubble under the protective skin. I have a cold air gun but have never found a use for it. I assume this would cool the plastic enough to keep the chips from melting into the cut?

I'll try bumping up the feed. Maybe program some lines at increasing speeds and try cutting some scrap.

The most success I've had so far is re-cutting the engravings with the spindle slowed down to 2000 to try and drag the bit through the cut to clear the chips.

I've never cut vinyl but with other plastics increasing the feedrate usually does helps. Increase it enough to avoid melting.

I'm guessing at 9krpm something in the 75 to 125 ipm range as a test.

Let us know how the cold air gun works too. I doubt it would help but it would be interesting if it does.

_________________
http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

I couldn't find my cold gun. It's buried somewhere. The best results so far have been to replace the bit with a fresh one, dial down the RPM to 5000 and the feed to 8 ipm. This results in a chip free cut.

That's odd. I would think raising the feedrate would load the cutter more and dissipate heat. I guess it is all relative though right.
Feedrate vs RPM.

Yeah, I'd like to run the tool a lot faster but I did test cuts varying the spindle speed in 500 RPM increments and there was a huge difference. Did the same tests with feed speeds too. Learned a lot.

I use alcohol all the time on gummy materials that are prone to melting. The fast evaporation takes away heat vertu quickly.

How are you feeding the alcohol?

How do you manage the fire risk? I've always wondered about that one. I think Datron uses alcohol cooling on their machines. https://www.youtube.com/watch?v=khwX1vE9rrA

We use lab bottles like this. It's just a squirt here and there. Enough to keep the cutter wet.

http://www.amazon.com/gp/aw/d/B003OBYX6 ... SBFMBAH25K


The fire risk is minimal in my situation at work because everything surrounding is metal and enclosed. We also have flood cooling which would put out any fires should that happen. It really doesn't require a lot of alcohol I would keep a fire extinguisher close by in a woodworking environment.
Of course don't do anything you're not comfortable with and it's at your own risk. It does work well though.

Oh and we use lab grade isopropynol 99 percent.

What type of tool are you using? I used single flute counter sinks for engraving, much better finish than engraving bits. I used them in UHMW, lexan, glass filled ultam and aluminum.

The cutters from Precisebits work really well on everything, especially if you use high speed and do a cleanup pass.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

So far I've tried a single flute Amana insert bit, Precise bits 60° engraving bit and a traditional flat grind engraving bit. I'm sticking with the Precise bit for now because it's part of our master tool set.