Model Forum / Radio Controlled / Air Models / February 2007

It is pretty odd to state that any aluminum alloy, esp. 6061 which is likely
what you are dealing with, is as "hard as it gets".. there are few aluminum
alloys that would be classified as hard, although high silicon aluminum
might be referred to as such in comparison to softer alloys.

What is a "dremelloid" - is that supposed to be some kind of cute name for a
Dremel tool?

Firstly, high speed steel tools do a better job of cutting soft aluminum
than carbide, although carbide will work okay. How fast are you running your
dremel tool? You should not try to machine/cut aluminum at 8 million rpm.
You need to keep the surface speed of the cutter moderate to avoid heating
and melting the Al at the tool/material interface which is most likely the
cause of your tool clogging. And, a coarser mill is preferred to a fine one,
so if the cutting teeth are of a fine variety and you are running the tool
at high speed there is your problem. Normally, the amount of metal you are
talking about removing should take only a few minutes. You could even rough
saw the opening, then use a small Dremel drum sander on lower speed to
finish cut. You should not be having so much grief with this job, I think
you need to slow down your tool and perhaps use a coarser cutter.

MJD

Very simple my young Padawan alloy porter. You need to keep the carbide
cutter lubricated with paraffin when cutting aluminium. There are a vast
range of carbide porting burrs available with 3mm shanks for cylinder head
work. Google for carbide burrs. For making holes there's a pointed one I use
which tapers over about 1/2" from a sharp point to the 3mm shank. You can
thus make any hole size you like up to the 3mm or hack slots through things.
A quick porting 101 on clogging burrs.

1) Running the burr too fast. The faster you go the quicker the metal
removal but at a certain point the alloy softens as it comes off and the
cutter clogs. My pro porting gear (Foredom) has a variable speed controller.
I can run it up to the clogging speed and then back off a bit. If your
Dremel doesn't you might be a bit stuffed in this respect. With 3mm tooling
it's unlikely to be a problem though. I do most of my work with 6mm tooling
and burrs up to 3/4" diameter so the correct speed is vital.

2) Soft alloy. The better the heat treatment the less clogging you get, in
general anyway. Maybe your alloy is not as hard as you think. Sometimes
however very hard alloy heats up and softens as you cut it so the clogging
problem comes back. Less speed and more lubrication is the answer. High
silicon alloys like LM25 cylinder head casting alloy don't tend to clog
anyway and I do most of my porting dry because it's easier to see what
you're doing. Low silicone forging alloys like HE15 and 30 clog more so you
run wet. Whatever the material you'll always get faster stock removal wet
than dry though.

3) Tooth profile. Teeth for alloy cutting are ideally very coarse i.e. not
many per inch of circumference to stop clogging. Teeth for iron and steel
are much finer. However with lubrication you can use any burr you like and
in fact most of mine are general cut or cross-cut. The coarse cut non
ferrous burrs certainly do remove material at a fearsome rate in comparison
though. I'll use one of those for fast stock removal and then go back to my
favourite general cut oval burr for fine detail shaping. Sometimes it's a
big advantage to not have the stock come off too fast when you're trying to
home in on a shape.

4) Lubrication. Paraffin is the best thing. Any light greasy hydrocarbon
will do just fine though - diesel, kerosene, heating oil etc. Brush on
frequently with an old toothbrush or spray on with a a window cleaner
bottle. Even a clogged burr will miraculously unclog itself as soon as you
chuck a little magic fluid on the job.

Try again with the right techniques and I'm sure you'll find the Force is
with you.