Hacksaw an octagon 90+mm AF. Mount in 4 jaw chuck and drill / bore 39mm hole. Then mount in 3 or 4 jaw using this hole and carefully turn the 89mm dia.

Edit; Jason beat me to it, can't compete with the pictures either.

Edited By Clive Brown 1 on 09/06/2023 16:17:07

Sounds expensive for a one off. I'd use Jason's method

Having an objectively excessive collection of Starrett hole saws I can generally find one quite close to the needed inside and outside sizes which minimises the amount of lathe work involved.

A certain care is needed when doing the lathe work to stop the nascent washer from twisting out of position in the chuck leading, at best, to misshapen inside and outside diameters. At worst the thing pretzelllises before self ejecting from the chuck.

Which is annoying.

The grooves in the jaws aren't guaranteed top hold the thin part in a secure and stable manner. The job is most at risk when taking the corners off the outside. The more sides you cut initially the lower the knock-knock-knock forces at each corner making it much easier for the chuck to hold properly. Clive Brown advises starting with an octagon rather than square which is what I used to do before getting into hole saw collecting.

Trapping a piece of suitably thick wood, MDF, particle board or similar between the embryo washer and the chuck jaws to act as a sacrificial support can help. No need to make it tight on the centre or terribly round. It just needs to sit under where the tool is cutting.

As with so many such jobs belt and braces set-up is frequently not needed. The job going fine when just held in the chuck. But taking that extra care costs little time when "thats the way you do it".

Clive

Hi Justin look up trepan it’s the easiest way

to cut a large washer out of a flat sheet of metal

in the lathe

hope this is helpful

steve

For holding reasonably thick stock larger than the chuck:

Tap it and screw it on a threaded rod or preferably long bolt with the head behind the jaws.

And remember: Usually the most efficient way to remove metal is sawing. Interrupted cuts isn't doing your machine any favors either.

Edited By Fulmen on 09/06/2023 21:16:56

You could mount the raw material on a relatively small arbor to turn the OD and then make up a beel chuck to bore bthe central hole to size.

Deburring may well have to be a manual opoeration.

Howard

Boring bar would be a good way to open the hole up to 39mm from whatever your largest drill size is. The job is only 3mm thick so not a lot of time involved. Saves the expense of buying a hole saw etc.

And cutting the corners off as Jason shows above is generally easier than trepanning, which is kind of like parting off on a curve so the tool needs to be ground just right for it to go smoothly.

Duncan, I was replying based on Justin's question of what to do if he only had something to make a Ø36 hole. That to me implies he has something that will cut that specific size. The options for that are, in my mind, hole saw, annular cutter or drill, maybe a step drill. I was not suggesting going out and spending money on a special tool for this job. Having a selection of hole saws and annular cutters myself they are what I would use to make a large hole to start with in a 3mm thick plate. And I do have a Ø36 annular cutter if you are wondering.

Martin C

Hi , washer could be made using a bench drill, a vice ,a hacksaw and files.

Maurice