I've been looking all over for 25mm square aluminum tube and finally
found some at
The problem is that the
1mm round corners aren't nearly enough to fit the receiver I'm
trying to mate.
As a test, I hand filed the corners and the tube slipped in nicely.
I'd like to learn a clean way of doing this. (Yes, I realize
grinding or sanding can make it fit but I want something precise.)
I can imagine using something like a very small router bit to shape
the corners. Is a mill the right tool for this? What kind of bit
would have the shape I need?
Get an ordinary router carbide "round over" or "quarter round" bit of the
desired radius (1/16 or 1/8 for example) with a guide wheel on the bottom
of the bit.
Then use an ordinary router to run down the edges of the aluminum stock.
Routing against bit rotation tends to leave a furry finish on aluminum.
Routing with bit rotation leaves a mirror smooth finish on aluminum.
Otherwise a the carbide bit mounted in a router is going to remove the
aluminum material every bit as easily as it would remove wood material,
particularly given you are only shaving off a small amount.
Only other thing to watch out for is that you don't thin the wall
thickness of the aluminum right on the corner to the extent it compromises
the structural integrity of the aluminum tube. To that end, select the
smallest bit radius that will accomplish your objective.
Dennis van Dam
I've been trying to think of how I could jig my (Craftsman plunge) router
to perform this task efficiently. I keep thinking that it would be
easier to chuck the router bit in my drill press (I don't have a mill yet
but I'm looking for an excuse.) and then set an open vise so that I can
just feed the tube between the bit and one (smooth) jaw of the vise. Or
I might use two pieces of angle iron (one with a cutout for the bit) to
form a channel for the tube.
Is that a reasonable approach? If so, should I take advantage of the
press' ability to run much slower than the router? Which speed should I
Thanks for all of the advice!
BTW, I'm trying to make tubes that will easily slip into the receivers
on a Trek bicycle trailer so that I can make my own conversions.
Right now I'm using one inch tube that's hammered into place and is a
real pain to extract. I don't mind kludging a prototype but I want to
do better. (It's good exercise.) I'm also considering making some
conversion kits for friends and such a solution would not be sufficient.
Now I hope to make the square corners into an advantage by only rounding
the portion that slides into the receiver. That should keep me from
inserting the tube too far.
Having a too large inside radius can easily be cured by making up a short
broach to square up the inside. Don't forget to insure that the broach has
a initial taper to make sure that the broach enters the end of the tubing in
a square fashion.
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works every time it is tried!
[ ... ]
Not without a *lot* of careful modification. Drill presses have
the chuck mounted to the spindle via a taper (perhaps two, with many
drill presses having a female Morse taper in the spindle, and an arbor
which fits the spindle taper and the chuck's taper.
In any case -- these tapers (especially the one on the chuck)
don't deal well with side loads, which are a part of the milling which
you want to do. As a result, there is a very high chance that the chuck
will come free (with its cutter), while still spinning rapidly, and
start bouncing around the shop, looking for flesh to cut with the tool
in the chuck. And it tends to happen so rapidly that you probably won't
be able to do anything about it until after the chuck settles down with
the very battered cutter still held in it.
Note that the router uses collets to hold the cutters, *not*
drill chucks. Among other problems, the jaws of a normal drill chuck
won't grip the hardened shank of a milling cutter (or probably a router
bit, either). There are drill chucks made by Albrecht which have a
diamond grit to hold such hardened shanks, but you will find that they
cost more than your whole drill press. :-)
Note that there are milling machines which use a Morse taper,
(with Morse Taper collets) but the spindle of the milling machine is
hollow, to allow a drawbar to pull the Morse taper into the spindle, and
to hold it firmly.
You should not use a drill press for this at all.
If you gain access to a milling machine, there are
corner-rounding mills available designed to work well with both steel
I think that you can consider this to be your excuse to buy a
milling machine. :-)
Stick your router in a router table. Plan "B" would be to set the tubing
into dado cut into a piece of plywood and rig some end stops.
I keep thinking that it would be
The round-over bits have a ball bearing on them to prevent you from cutting
too deep. No fence required.