Bit selection for rotary engraver

General Firearms NFA
1

I’m currently in the process of getting lowers engraved for F1/SBR. When engraving the lowers, how does one avoid the anodizing from chipping when using a rotary engraver? Is there a special bit that one uses for this process? Is there some kind of black magic where the metal is heated first prior to engraving?

Currently, I have tried shallow passes, deep passes, high RPM spindle speed, slow travel in the X/Y axis, etc. Bit selection is about the only variable I haven’t tried. For those that use a rotary engraver, what’s the magic sauce? The lowers I’m working on are Type III anodized.

I’m aware that IDENT does laser engraving and Orion uses a rotary engraver to do lowers. For those that have used Orion, was the anodizing chipped around where the letters were engraved? Do you even notice it since they color in the markings?

PS - Speculation and theories as to what may work best are appreciated, but please indicate that it is a theory. I’m really looking for some input from those that know, have done or have experience in this area.

2

Bump.

3

I’m really hoping you aren’t using a dremel (if that is the case then this wont help) and there is no need to heat the surface to be engraved.

True engraving tools for a CNC controlled machine are expensive (around $100 for the tool and $10-18 per insert) and going to look like this : http://everede.net/nine9_2013_index_engr_tool.html.

I’ve done several engraving jobs on type III hard anodized parts and never had any problems with chipping. 5500 RPM 22 IPM at .004"DOC first pass with a second pass at .007" total DOC with a coolant stream for swarf washout. Takes about 5-10 minutes to program, 10-20 minutes to level and fixture part and about a minute and a half of cutting time. AFT regs are a minimum of .003" engraved depth IIRC, but I’ve found that .007" works best for clarity after refinishing with paint, cerakote, durakote etc etc. You dont want all your hard work hidden under a new finish, especially for NFA purposes.

I’ve found that 2 passes give a cleaner edge and no burr in 7075 aluminum parts where as a single pass tends to load a slight burr on the climb side.

4

My first SBR that I made, I had a local shop engrave it for me. It chipped the finish and I wasn’t happy with the large lettering, so after that I always had them laser engraved. The laser was always smaller letters and it looked professional.
Even after painting the engraving black it still wasn’t the prettiest.