Anodised Material Engraving

19 Nov 2015 16:40 #65519 by Micromet
How do cnc-ers get rid of the edge burrs produced when engraving anodised aluminium?
Even diligent emery paper sanding using 3000 grit can still take the anodising off the edges of small objects such as dog-tags before the burrs are removed. As an alternative, I've just test sprayed engraved dog tags with clear acrylic paint - when dry I will see if emery papering that down will take away the burrs before getting to the anodised surface. I can then polish up the acrylic with my range of fine paint polishes.

Does anyone have a better idea?
19 Nov 2015 18:08 #65528 by mgenton
use a single edge engraver (carbide) no more than .010 depth per pass and keep you Chip Per Tooth .0005 - .0002

say if your running at 10000 rpm that would be 5.IPM and your Z feed should be half your XY
you can use cutting fluid but it your not flushing the chips away with enough volume just use a little air blast
19 Nov 2015 18:36 #65532 by Micromet
OK - so some things I'm doing right.
Single edge carbide engraver tool - tick
Running at 11000 rpm - nearly a tick
Did single pass at 0.05mm - guess that's a tick if 0.010 is in inches

However - looks like my feedrate was wrong - had it set to 400mm/min.
Z penetration was 100mm/min might be a bit slow but for this application - only had 3 separate curves to do and the burrs were all around the curve.

But the acrylic coating appears to work - just need to let it harden before papering it back.
20 Nov 2015 02:28 #65556 by mgenton
what are you using for a spindle ? if you have a router then thats your problem it will oscillate (not run true) and you might be rubbing with the backside of the tool instead of cutting
and 6061 is gummy that could be part of your problem if it is 6061

other than that engraving needs a sharp tool and take it slow if you dont need the depth use a drag tool i make mine out of 1/5 carbide and spring loaded it , you can buy diamond drag tools

you could make a dry pass or take another skim cut to clean up
if you want you can profile cut it to finish a couple tenths should be fine .0002 just remember to climb cut
20 Nov 2015 11:34 #65568 by Micromet
Hi Mgenton,
As you might guess - this is all new to me - so bear with me. MY cnc machine is one of those chinese 3020T engraver/routers. I'm using 60 deg carbide single flute cutters. Don't know which aluminium it is - doubt if the pets4tags firm that sold them do either.

Never though about using a drag tool - although that would mimic how hand engravers do it - will get some of the diamond ones and work out how to spring load them - not at the stage yet where I can make my own although I do grind my own lathe tools.

But thanks for the good advice.
20 Nov 2015 12:08 #65569 by cncbasher
check the alignment and runout of the spindle , some are terrible ( read all )
the usual cure is to replace the bearings with german made ones.
they are drop in replacements , but not cheap

time taken to rectify the spindle is well worth it in results .
also as has been said , use harder aluminium for engraving , the softer types will gum up real quick
( most engineering aluminium )

make sure your engravers are sharp too ,
in some cases depending on how i want it to look , for example machine front panels i use a standard small endmill
rather than an engraver

sometimes a drag cutter in a springloaded holder is better ( easy to make )
20 Nov 2015 12:11 #65570 by Micromet
I noticed that spring -loaded diamond drag engraving tools seem to be quite expensive and, oddly, only seem to be available from the US - at least my search on ebay seems to show. I did find a DIY effort to produce a spring-loaded tool on the internet
So I thought I might travel that route.
My question is - can I use any type of diamond tipped cutter forcnc drag engraving e.g. a general workshop diamond glass cutter? I have lathe and milling machine facilities so I can modify any commercial cutter to fit.
20 Nov 2015 15:06 #65572 by andypugh

Micromet wrote: can I use any type of diamond tipped cutter forcnc drag engraving e.g. a general workshop diamond glass cutter? I have lathe and milling machine facilities so I can modify any commercial cutter to fit.

I would imagine that, dependent on the design, the concentricity of the tip of the diamond to the shaft might be important.

I wouldn't expect to be able to use a wheel-dressing diamond, for example.
21 Nov 2015 15:13 #65609 by Micromet
Does the concentricity matter if the tip is not being rotated - just dragged? Any concentricity means that the engraving might be slightly displaced in the X or Y plane - but that applies to the whole image - its just an affine translation of all points. Providing you don't rotate the diamond point between operations on the same image - it should be OK.
21 Nov 2015 20:49 #65624 by cncbasher
drag knifes are slightly off centre to allow them to kick in one direction , diamond point cutters meant for glass don't work
all that good ,unless on glass of course ,

i sometimes just grind a carbide mill cutter thats been broken , using a diamond wheel on my grinder .
well you have to use the scrap somewhere
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