Honing Aluminum Tube

Needs more info about your tubes but....Ball Sizing? Pressing a hard ball through the tube. Expands and smoothes the ID.

Bal-Tec's site explains the process.

HTH, PaulS

I have actually tried this on the inside of a half cylinder of aluminum for optical purposes. With aluminum, smooth and shiny are not the same thing. Aluminum has a very hard outer oxide surface layer. As you sand, you break through parts of that and then gouge the soft metal underneath while the remaining oxide protects other areas. Even fine grits will give a gray pitted surface, although maybe thats shiny enough for what you want. The easiest way to get moderately shiny, but not so smooth surface is careful machining with kerosene.

If you want smooth and mirror shiny, I used a gradual progression of silicon carbide paper down to 3000 grit with kerosene which supposedly prevents forming new oxide. I then used red rouge on a soft buff for final polish, but that is because that is what I had.

If you look on youtube, people have posted all sorts of particular methods of polishing aluminum with all sorts of compounds, but they are all tedious.

Weld seam might be best handled with a straight reamer if it's sizable.

Ok shiny was probably not the best term. Smooth is more important. It will have a low pressure pneumatic seal with am o-ring and piston. The raw tube works ok, but I was thinking with a better than mill finish the o-rings might last longer.

So far I have not worn out an o-ring with the existing units, but I would like to make future ones "better."

"Bob La Londe" fired this volley in news:qlZhr.409$ snipped-for-privacy@newsfe13.iad:

How long are these tubes, Bob?

It takes darned near forever with a long boring bar, but with the right speeds and the right rake on an HSS boring bit, you can get a pretty nice finish.

Get it turned to "round" (sans weld), then use a small flap hone if you want to clean it up.

Remember, I went through this recently with a customer's project, and finally ended up buying an aluminum air cylinder long enough to cut what I needed. But mine was 18" long and 6" i.d. That made it kind of hard to bore with a conventional setup, and I didn't have the time to jig the lathe to mount the work on the cross-slide, and the bit in the spindle, supported by the tailstock.

LLoyd

You have a lot of variables and compromises in there, which I'll leave to others to deal with. I haven't done what you're trying to do.

But this is a good excuse to bring up a related article that may be of some use to other aluminum honers, especially anyone working on model engines. These capital-heavy industrial methods may not be directly applicable but it should be a help to see what industrial users are dealing with when they hone hyper-eutectic aluminum:

Here's more good stuff on honing aluminum from Sunnen:

I think I may have seen aluminium tube with a weld seam but rarely, the stuff I normally get in the size range you mention is extruded so no weld seam. I there a reason why you can't get what you need without the seam.

The seam really is not a major issue. The over all smoothness of the interior bore is what's important.

Finished working length may vary from 10-12 inches.

Yeah, I thought about a round face boring bit, but supporting and doing a

12" internal finish is beyond my skills and equipment. I was just hoping to improve the finish "some"

I may "just" do a flap wheel down the bore and see how that works out. perfectly round is not super critical. it's a low pressure o-ring fit after all.

I recall your project. I read quite a bit on that thread. Glad you got it worked out.

Bob

If you've got a ridge, I'd either do ball sizing or get a helical reamer to get rid of it. If you need to improve the surface finish, ream a little larger, then use a lead lap on it. You need a lap surface softer than the metal you're trying to lap. And like the other guy said, I've not seen aluminum tubing with weld seams, all I've seen has been extruded. If you could get that sort of thing in the sizes you need, you'd be ahead of the game.

Stan

I think that if the seam on the inside is very big, doing your flapwheel alone is going to be very disappointing.

I would either try to do a boring bar mounted on the cross-slide, with center rest to hold the tube in place, or mount the tube on the cross slide and run it past a boring bar that's spinning on the lathe, with center rest fixed to the lathe base somehow, or I would make a boring bar with a pilot that runs down the inside of the current tube (avoiding the seam) and shaves everything evenly.

I suspect the piloted boring bar would be the closest to being within my abilities, and it certainly matches the drawer full of 50-year-old ball bearing sets that I inherited from my uncle. I don't know what would work for you.

I'd bore it out, then look at polishing it with whatever 'soft' tools came to hand.

But first, I'd look for seamless tubing.

Paul Schiller has the right idea. Ball size. MSC sells 10 1 inch balls for $13.6x . So not too expensive to try it. The 2 inch dia balls are not so cheap.

Dan

Why not just use the cylinder hones, that you mentioned, with kerosene flood cooling/lube. Should keep the stones clean.

Cheers,

John B.

How many parts? One or two, no idea. Many? Roller burnisher. Greg O

Neither ball sizing or roller burnishing is appropriate for thin tubes.

I was waiting to see the wall thickness before commenting, based on industry practice rather than my own experience, but I either missed it or it hasn't been stated.

We did a lot of roller burnishing when I was at Wasino. You need some resistance to make it work. I don't think it would iron out a weld seam, regardless. It's used to size and to flatten the peaks of the bore's surface finish.

Similarly, ball sizing. Unless those tube walls are quite thick, I can't see it ironing out a weld seam. It probably would just locally stretch the tube, unless the tube has very thick walls. That doesn't seem likely if it's seam-welded.

.125" wall thickness.

Then I'm skeptical that ball sizing or roller burnishing would iron out the weld. They'd probably just distort the tube.

Lathe jaws machined to match the OD, take a light pass with a boring bar to remove the weld, and roller burnish. A hone will work too, but the roller burnisher will give a much smoother finish.

I have bore many aluminum small engine blocks .010" over size with a Sunnen hone with AN 500 stones and Sunnen's honing oil.

Either way you will need to get the cylinder cleaned up before any type of finish can be done. GregO