boring oversize parts

I have an aluminum tube that I need to bore about 1" at end out to at least 5.57" -- it varies from about 5.47" to about 5.60". Unfortunately, this is too big to put on my Sherline lathe--it won't fit onto the outside of chuck that I can find for the Sherline. I have this vague notion that there might be some way to do this by putting an end mill in the headstock and rotating the workpiece so that the end mill removes a fairly consistent layer. This doesn't have to be spectacularly precise. I tried this approach, and except that I couldn't figure out a way to get the workpiece to turn consistently (since it wasn't supported), it almost seemed to work.

Does anyone have any clever ways to do what I am trying to do, without breaking down and buying a bigger lathe? Some clever way to mount the tube on a 3.5" OD chuck, for example?

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One piece? Buy a bigger it out...Buy a bigger it out...Buy a bigger it out...Hmmmm.

Reply to
Tom Gardner

What diameter is the tube, now? I remember reading in TMBR about a technique that was very cool if you can figure out how to clamp one end of the tube to a non-moving bench.

1) You find or make a cylindrical plug that just fits inside the present bore. 2) Drill through the axial center of the plug and tap for a (say) 1/2" machine screw (with backup nut). 3) Mill radially into the top of the plug to accomodate a lathe tool and space to hold some swarf. 4) Drill into the plug to accomodate a clamping screw for the lathe tool. 5) Clamp the lathe tool in the plug, thread the 1/2" machine screw with a backup nut and lubricate the OD of the plug. 6) Insert and rotate the plug in your tube. The body of the plug will guide the cutter and keep it at a constant depth of cut. 7) Use a breaker bar to create your new bore. 8) BE the mill.


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If you can find a way to clamp the tube on the compound so that it is centered vertically on the headstock center (you an align it horizontally with the cross feed) you could make a fly cutter sort of tool to bore the inside of the tube.

Or use a four jawed chuck, maybe with the jaws turned around and some blocking to hold the inside of the tube while you bore the other end.

Or machine a two diameter arbor. The larger diameter presses into the tube, the smaller diameter fits your chuck.

Bruce-in-Bangkok (correct Address is bpaige125atgmaildotcom)

Reply to
Bruce in Bangkok

Simple - if the part will fit over the ways.

Make a bit you CAN hold in the chuck. Larger is better. Bore a recess in the face of the bit, big enough that you can reach in with a spanner and turn the heads of four bolts that go sideways to the axis of the lathe, for which bolts you have drilled and threaded holes. In essence you are making a simple four-jaw chuck with outward-moving jaws. The work holding will be poor; if you can live with marks on the inside of the non-machined section make the ends of the bolts pointy.

Mount part and centre, bore (carefully) to suit.

If your part is long you'll have to use/make a steady as well.

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Dangerous way follows: Make a spacer to fit between your internal jays, and the tube. Get a piece of 3/4" hardwood, maybe 6" x 6". Center drill it. Bandsaw it oversize to fit into your tube. Using the tailstock to press the part against a chuck face, turn the OD to just fit inside the tube. Now bore the part to fit over your chuck jaws, being careful NOT to break thru until the final pass. Split the ring in one place.

Install wood adapter over jaws, tube over adapter, tighten, dial indicate OD or ID, TIGHTEN. Turn slowly, light cuts. Duck, cuss, clean shorts.

Reply to
Mechanical Magic

Depends what other facilities you have. Since the tube is larger than the swing of the lathe you are going to have to make the lathe bigger.

Buy a 2" boring head and turn up an adaptor to fit it to the mandrel nose of the Shereline. This is going to be a bit heavy for the lathe to hold but it should manage and can be adapted to fit other lathes or mills you might get in the future.

Remove the tailstock.

Get a piece of 1.5" to 2" thick aluminium cut and drilled to size to make a rising block to lift the headstock up to cope with the diameter of the pipe.

Get another large piece of aluminium to clamp onto the cross slide. Drill for clamps, rough cut a radius in one edge with bandsaw, chain drilling, whatever.

Lock the cross slide gibs (don't want them moving 'till the end of the job). Clamp the aluminium block to the cross slide

Use the boring head to cut a the radiused edge to the radius of the outside of the tube.

You now have a work holder on the cross slide that will hold the tube accurately on centre. Use your third hand/a friend/roller skate/pet cat to steady the far end of the tube. Use the boring head to bore the tube to the right diameter.

You'll probably need to use a sharp HSS bit in the boring head and take small cuts throughout even with aluminium, due to the large diameter you are cutting.

This may be more precise than you want, it is also a lot of work. But it will give the result.

You did ask :-)

Mark Rand RTFM

Reply to
Mark Rand

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