Cutting a large hole out of plate

[Chris Jones 3Participant @chrisjones3]

Hi All, I am trying to cut out a 60mm diameter hole out of a piece of 12mm mild steel plate.

The piece is set up in the 4 jaw chuck on my WM250 lathe and I have ground an HSS tool to cut a slot.

The problem is the tool starts to cut but then digs in and stalls the lathe.

I have tried grinding different angles on the tool cutting edges and adjusted the tool height but have not managed to solve the problem.

Any ideas anyone?

Perhaps a trepanning tool might be the answer?

Many thanks for any suggestions – Chris.

[Chris Jones 3Participant @chrisjones3]

[mechman48Participant @mechman48]

You should be using a trepanning tool with a radius on the front to clear O.D curvature, & some side clearance too… hence your 'digs in & stalls the lathe' scenario. there was a thread not too long a go about trepanning some thin material, with an accompanying sketch of the tool, can't locate it at the mo'… maybe another member could point you in the right direction…

George.

[JasonBModerator @jasonb]

Make the tool a bit narrower with a rounded tip and move it say 0.050 across the work and back while slowly advancing the cut. Go 6mm from each side. This way you have less tool in contact with teh work and no risk of teh sides rubbing.

This is a similar size hole in 10mm plate

The safest way is to actually stop a few thou short of half way and then just hit teh middle and it will open up like a bean tin, no waste piece to fly about and catch something on teh lathe

[Neil WyattModerator @neilwyatt]

That's about as demanding a cut as you can expect any lathe to make. I think your tool need sharper corners and relief right up to the outside cutting edge – it's whole profile needs to be able to fit inside the slot being cut.

Neil

[SteveMParticipant @stevem36008]

An alternative is to use a jigsaw. Some people disregard them for cutting metal but with the right blade(s) and some care it'll cut your mild steel no problem. And it'll be quicker and safer!
Another (and probably the best) option would be to use a bandsaw. Quick, clean, little waste and a near perfect circle with a decent jig. A doddle if you don't need to preserve the parent plate, though it'd need a blade breaking and re-welding/brazing if you do.

Steve

[Ady1Participant @ady1]

digs in and stalls the lathe

backgear would sort your problem. If you don't have such a thing then there's probably a mod

well worth doing, it turns your lathe into a far more versatile machine

Still going to squeal until you get the right tool profile though, I've never done a sideyways parting off job

 

Edited By Ady1 on 13/08/2015 19:37:09

[AjohnwParticipant @ajohnw51620]

I use a tool something like this but cutting tool length and narrower with and increased angle on the end so that the point can be plunged into the work.

it can be used to "face and bore" through material. I've not tried it on anything of your size but it's what I would use.

Looking at the shot you posted I think I can see signs of the tool rubbing on the outer edge. You need a rad on that side of the tool that is smaller than the diameter of the hole you will be left with.

John

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[Ady1Participant @ady1]

Backgear on a var speed lathe

Should also reduce the stress on your motor when doing tuff jobs

Edited By Ady1 on 13/08/2015 19:41:27

[Kenneth DeightonParticipant @kennethdeighton43272]

I would take a cut at the max dia using a tool similar to a parting off tool, about 1/8" wide until it becomes uncomfortable then withdraw and move the tool inwards towards the centre approx.. 1/8" and machine to the same depth then withdraw and move back to the outer dia and continue using this method until I could not proceed with this tool ,then change to a thinner tool and continue as before.

Best of luck.

[Chris Jones 3Participant @chrisjones3]

Thanks Guys for the suggestions.

George – The trepanning tool was a thought but I don't have one at the moment, another job or purchase on the list.

Jason – Yes, OK, I am on to that, back to the grindstone & have another crack at it.

Cheers – Chris.

[Chris Jones 3Participant @chrisjones3]

Ady1 – Backgear,

Yes, the low speed torque on these machines seems quite poor, I have been asking Warco about a set of parts to convert my machine to a VFD drive.

John W1 – "Looking at the shot you posted I think I can see signs of the tool rubbing on the outer edge." –

I have radiused that edge but my hand grinding technique is pretty poor and you can probably see signs of my own inadequacies in that department.

Must try harder. – Chris.

[Chris Jones 3Participant @chrisjones3]

All suggestions gratefully received and will be added to my 'little black book'

Thanks. – Chris.

[JasonBModerator @jasonb]

Found the other photo I was looking for, this is 5/8" bronze. You can see that as well as curving the outside edge of teh tool I have a radiused end and that the kerf is wider than the tool where I move it back and forth across the cut. Not quite so easy to see is the width of the tool narrows slightly as it gets towards the main square body to the sides are less likely to rub. Click image to see it larger

Edited By JasonB on 13/08/2015 20:35:22

[Nigel McBurney 1Participant @nigelmcburney1]

Before you start turning,arrange a way to catch the centre piece,if it drops out and gets caught between chuck jaws and bed or saddle it can do a lot of damage to the chuck,the spindle ,headstock gears,etc etc. one way to catch the centre is to drill a hole through the blank centre and grip a piece of rod in the tailstock drill chuck,so that rod goes through the hole in the blank, If there is no room for the tailstock ,tap a hole in the blank and screw in some studding so that the rest of the studding disappears down the bore of the lathe spindle.

[John OlsenParticipant @johnolsen79199]

Sounds to me like he wants the hole, not the blank out of the middle, so one approach would be to just open out an initial hole with a boring tool until it is big enough. Slow, and a bit wasteful but we are in no hurry are we?

Another approach that I have used is to use a hole saw. One of the good ones like Bluemol, not a cheapy.These are in effect a whole lot of trepanning tools. They do need the lathe going slow, eg back gear if available For deep holes swarf clearance is needed quite often That way you do get the blank as well. Used in the lathe like this, you can get away without the pilot drill if you want a blank with no hole. There is little danger of the blank dropping out and getting hung up, the usual problem is the opposite, eg getting it out of the holesaw afterwards.

John

[KWILParticipant @kwil]

You could also chain drill the whole circle, cut and remove the blank then clean up. Tedious but probably faster than grinding a new parting/boring tool when the present one breaks

[DustyParticipant @dusty]

Another option would be a rotary table and a slot drill in the mill, that is of course if you have the equipment..

[Chris Jones 3Participant @chrisjones3]

John – "so one approach would be to just open out an initial hole with a boring tool until it is big enough. Slow, and a bit wasteful but we are in no hurry are we?"

It just seems such a waste of all the metal. I might be able to make use of that bit in the future, & I hate all those bucketfuls of swarf.

Learning another technique is also rewarding I feel.

Dusty,

YES! a great excuse to save up for a rotary table. Trouble is I keep breaking my small slot drills, I don't seem to have the delicate touch yet.

[Chris Jones 3Participant @chrisjones3]

Jason,

There you go, it works!

Thanks to all for the suggestions.

Chris.

[AjohnwParticipant @ajohnw51620]

Why not make a rotary table ? The difficult part the worm and wheel can be bought. The gashed ones intended for model engineering projects – that's effectively a gear with the teeth at the worm's lead angle. It's also possible to use a gear with the worm at an angle.

The best trick for worm and wheel engagement is to mount the worm in an eccentric but some designs swing it into engagement sometimes in a worm carrier. College Engineering used to do a pretty hefty 5in kit. It suffered a bit when it was Myfordised to fit in the gap but was still pretty good. Better when it was intended to be made on a Boxford.

Castings were widely available but seem to be thin on the ground now. A stick welder and plate steel can be used to solve that problem or machine from solid or even a mix of the two.

John

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[Chris Jones 3Participant @chrisjones3]

John,

Will you stop it! I've got a shelf full of projects in various states of incompletion & each project generates another one or two more projects to enable the one before to be finished.

[vintagengineerParticipant @vintagengineer]

Use a Starret hole saw run slowly and keep clearing the swarf.

[egaParticipant @ega]

I have used hole saws for this kind of job and agree that clearing the swarf is the main problem. More recently I became aware of the rotabroach type of cutter from an article in MEW. Apart from cutting more freely, these have the advantage that they do not require a pilot so the blank is free of a central hole and they cut true to size and leave a good finish. The blank is relatively small because of the greater width of the teeth and they are rather expensive when bought new; cheaper used ones can be resharpened, however.

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