Trepanning

I require ideas as to cutting a 3 5/8" hole in 4 x 4 x 1/2" mild plate. Tool design, Speed. Tooling will be 1/4 square HSS. Lathe is 9 inch SBL.

Thanks for any help Doug in Canada.

Hi Diug,

You could chain drill it and then trim up the rough circle on the lathe. Alternative method could be laser cutting unless you are out in the pine forests !!

Mike.

This subject has been discussed in the last few days in this thread.

Les.

Hello Doug,

Probably the easiest is to use a holesaw to cut out the bulk, maybe 3 inch diameter if you have one that size. You should be able to cut through from one side and I recommend backing the job in the chuck with something sacrificial, chipboard of similar.

Turning speed between 50-100 rpm and use coolant on the saw teeth, backing out frequently to clear chips

The alternative already suggested is chain drilling, cutting the between hole links with a cold chisel and cleaning up afterwards. Slow but just as effective.

Regards Brian

Taking on board all of the above, which, in the case of trepanning, require special skills, or buying a hole saw,in the long run it would be just as easy to drill, using your largest diameter and face out from that initial hole, it shouldn't take that long.

Trepanning will work on the SB. Slowest speed possible, ie 5-12 rpm max in back gear and largest spindle pulley. This will keep cut surface speed below 150 feet per min. which is a good max guideline with HSS. Grind the tool as a narrow parting tool with 2-5 deg clearance each side and on the front. On the inside-side, grind slope on the tool bottom toward centre to clear the slot wall. On the outside side, grind slope on the tool also bottom toward centre to clear the slot wall. Top rake about 5 deg front high back low as usual. Use tool sharp and at exact centre height, with lots of oil.

KBC Tools have trepanning tools on their website for hints at the shape to grind HSS to.

I have done similar jobs on my SB 9B.

Good luck, JD also in Canada (near Toronto-where are you Doug)

I regularly trepane 4" discs out of 6" discs of 8 mm hot rolled plate, It's part of the process I go through to make 6" flywheels for my hot air engines, two of these either side, and a centre one with the spokes cut out, the centre one has a hub inserted, and the lot bolted up with3/16 UNF cap screws with the heads counter bored so that the heads are flush with the side of the wheel. Lathe is run at bottom speed of 60 rpm, the tool is HSS. You are then left with a disc about 3 3/4" dia, I cut through from both sides. Ian S C

I don't doubt that a lot of machinists regularly trepan out large diameter holes, all I'm suggesting is, if you haven't attempted it before a half inch thick piece of MS plate is not exactly the best place to start.

Given the medical connotations I suggest a few politicians skulls. This would serve two purposes, you could get lots of practice without actually damaging anything valuable and while you were at it you could take a look see to just double check there is nothing actually in there.

graham.

I usually do it the other way round to what you all seem to be suggesting. Mount the work on the cross-slide, large angle plate screwed into tapped holes, usually a bit of thick plywood screwed to the angle plate and the work screwed and clamped to the lot. Align flat with the face-plate. Mount the cutting tool in a suitable holder bolted to the face plate. It just seems more rigid and the inertia of faceplate helps. Slow speed for big holes, I made an extra large V pulley to sit over the existing one and get about 50 rpm on my DB8.. Made the angle-plate from a bit of 6"x4" steel angle. Accuracy is not usually problem.

Why bother with the opening of skulls Graham, the doctor's knee jerk hammer should produce a characteristic sound of an empty space without all that mess to clean up afterwards. You would miss the practice I must admit, but would it actually be worth the effort?

Think of wheel tapping but with a different result and the test would be a whole lot faster, processing speed would be awesome!

Brian

Edited By Brian Wood on 21/05/2014 12:12:11