How To Miter Cut Aluminum Extrusions?

Yes a milling machine using a slotting saw and held by a fixture to support the outside edges.

A milling machine would be an excellent machine for this, as previously suggested.

I'll propose that you google the term 'cold saw', a sawing devise using a milling type cutting blade.

Your answer will include best support of irregular shapes while clamping, & controlled feed-rate while going through irregular thicknesses.

To hold to a .002 tolerance you will need a jig that can locate your material in exactly the same place repeatedly. Next you will need a saw blade that runs that true. I don't know enough about using a milling machine, but I think your specs are beyond the hand operated chop saws and compound miter saws. You might get by with a very fine tooth blade if you can stiffen the blade sufficiently and feed slowly.

Are you looking for precision angle cuts or length cuts. You have stated precision in thousands of an inch. Precision on the angle of the cut would be in degrees.

For anyone not already aware, an average reasonable Milling Machine in good condition can work to about 1/10000", eg. highly accurate! And my knowledge is 40 years old, so today, they could be even better!!

You need a milling machine set up with a slitting saw on an arbour and a clamping fixture to hold the workpieces. A staggered tooth high speed steel slitting saw about 1/8" or 3/16" thick by 4" dia should work nicely. You can do this work with a small used milling machine, even a hobby type like Grizzly or Smithy will work fine. As far as miter angles go, your fixture for clamping the workpieces could be built on a swivel base like the type found on any common milling vise. Stop playing around with the chop saw and do it the right way :)

Did you ever contact your supplier to see if they could supply you with the extrusions already custom cut ?

It sounds like you lean more towards manufacturing that precision metal working.

If that is the case you should consider anything with a tolerance tighter than +/- .005" to be a purchase part . That is unless there is enough volume to not only "tool-up" but to also have some sort of formal operator training and established procedures for CORRECT machine setup and in process gaging.

It's a real pisser to have a pile of scrap $$ beside a milling machine and an operator looking at you smiling proud as punch of how many pieces he has run not realizing this run of parts will now be made at cost or worse!

With CNC a lot goes good-or-bad in a hurry and .002" with angles is tight.

I have done and still do use the same tools. I have also used 10 inch plywood blades and we resharpened those before a first use. I would not try using a thin blade for .002 tol. I would rough cut with a thin blade, then surface using a machine tool with a table that can repeat at .002. I have used abrasive and carbide cutting tools for the finish. The biggest problem here will probably be the clamping surfaces on extrusions are not accurate enough for .002. The 1/8 wall is very flimsy to expect .002 repeatability.

I would bet there is .002 end play in the saw arbor alone on that chop saw. Add a couple of thou for blade whip and you have a pile of junk.

Others have said it. If it is a long production run and worth doing it yourself hire a competent machinist, let him pick out the best milling and tooling setup he thinks is necessary and let him get to it.

Your best bet, if your material supplier can't supply that stuff within those tolerances, and my bet is he can't he just sells extrusions, is to find a first class machine shop and let them do it. .002 and better is the nature of their business and what they do.

And please, satisfy my curiosity and I suspect that of others, just what are you putting together out of common, cheap, aluminum extrusions that requires those kinds of tolerances? There may be another and possibly better way to do whatever it is you are doing.

j.

AMEN to that question. it sounds like these mitered butts are not being "welded" - and also it sounds like they are not even visible.

can you give us a hint?

I don't know about your .002 tolerance but if you go to Amazon.com, and search for "circular saw blades", you will find dozens of blades in various sizes... some specific to cutting aluminum or cutting non-ferrous metal. I even found 9" Al cutting blades for my miter saw.

Bill

ps I am typically cutting 1/4" round or 1/4" by 1/2" rectangular 6061 in my application.

I also use a carbide tipped blade designed for cutting aluminum with great results. I just do not think that the .002 can be held with the tolerances found in the chop and miter saws I have seen.

What you need is a slow speed metal circular saw. They are called various things from 'Drag Saw' to 'Cold Saw' BROBO-Walden are one manufacturer. The machines have a tungsten steel blade with small teeth with the set provided by grinding the corner off alternate teeth on each side. The are very fast and very accurate; less than .001" in my experience. Aluminium blades are generally 1mm thinner than steel cutting blades, though the thickness varies depending on the blade diameter. You can Hire the saws from tool hire companies, so you can try it out before forking out the several thousand for a new machine! they are a whole new world when it comes to cutting metal!

I agree with the slitting saw suggestions in the other replys.

2 additional suggestions:

1) use a horizontal milling machine

2) mount a rotary table with holding fixture (modified vise to fit your extrusion) to set the angles you need on the bed of the machine.