round corners of square tube?

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

This can be done by hand.

This usually requires a mill or damping jig.

Yours,

Doug Goncz ( ftp://users.aol.com/DGoncz/ )

Read about my physics project at NVCC:

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 use?

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.

--kyler

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.

--kyler

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.

-- Bob May 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 and aluminum.

I think that you can consider this to be your excuse to buy a milling machine. :-)

Good Luck, DoN.

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.

Yup, that's my current plan. It seems so obvious now.

I looked at router tables yesterday. I plan to get one once my attic and garage (shop area) are in order.

Thank you.

--kyler