Making a large washer.

[noel shelleyParticipant @noelshelley55608]

The dear old Zeus book will give coordinates ! Noel.

[JasonBModerator @jasonb]

If you need to get a Zeuz book out for that 4 hole pattern, use a rotary table or use a DRO's PCD there is not much hope for you

70/2 should be possible im most peoples heads and then just move that amount in/out/left /right

Edited By JasonB on 18/06/2023 16:15:45

[DiogenesIIParticipant @diogenesii]

..of only it was a square with corners..

[Justin ThymeParticipant @justinthyme24678]

Posted by Nick Wheeler on 18/06/2023 13:31:23:

Were the four bolt holes in the original request?

Because they change how you make the part:

Start with a piece of stock big enough to create the piece

Mark the centre of all three(centre hole, outside edge and PCD) circles.

Draw the centre and outside edges with dividers.

Mark out the PCD.

Drill the PCD

Bolt the piece to a (sacrificial)faceplate using the PCD, and ensure it runs true to the centre mark

Machine the inner and outer edges.

You make several pieces by bolting them to the faceplate at the same time

Ooop's, yes I seem to have omitted that important spec..

I did mark out all the three circles before I started. The problem arose when I used the pillar drill to bore the centre hole out with the hole saw, the pillar drill is so unconcentric it managed to get the not very round hole in the wrong place. See my first image, you can see the scored line .

Never mind, I managed to mount it on the milling machine, and with an edge finder on the inside of the hole I worked out where the centre would be. from here it was very straight forward to get the holes drilled accurately (within a few thou, I quite surprised myself)

I was then able to score a line to where the outer edge will be. From there I have hacksawed and angle grinded it down to a roundish shape.

I'm going to have a good think about how I will lathe this down to its 89mm dia – it's non-roundness is a concern. What speed should I start with? When doing such things turning wood I will keep the speed very low until it gets fairly round. Will I use the same tactic on steel ?

I did spin it and felt 100-150 rpm seemed OK, not sure though

I could get a 3rd bolt in to hold the plated together, should I bother, it seems very secure

[Nigel Graham 2Participant @nigelgraham2]

Hole saws are not intended to be precise. Typically they are building tools used for pipe and conduit ways, drilling water-tanks for their fittings and the like.

Nevertheless they are a valid way to rough out the work provided you select a size that leaves sufficient machining allowance, and I use them fairly frequently for that.

You say your pillar-drill (or bench-drill? They do differ!) is not concentric. Are you sure? A hole saw can give that impression depending on its type, even though its holder's pilot-drill acts as a guide. You can't hope to use a hole saw without that pilot, so it won't enlarge an existing hole without some preparatory work.

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Looking back at other's suggestions, I would start with an octagon or "more-agon", but round the corners off a bit first with a file or angle-grinder, as turning down from sharp corners can be a bit fraught.

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Trepanning can work well provided you can hold the work on both sides of the cut.

This is based on how I machined large rings from 1/2" thick steel plate:

If the work has holes in it, as here, I would drill them and use them to hold the plate to a faceplate with intervening spacers or a scrap of plywood. I would also drill holes in the outer (off-cut) area for further holding. This is so the cut completes without great lumps of steel with razor-sharp burrs suddenly breaking free and possibly causing havoc

The tool shape needs careful thought if it is not to bind. My approach is to start the cut well on the scrap side, in a little way, withdraw the tool and offset it slightly to widen the cut. Take it slow and steady, alternating the trench diameter to give clearance.

Finally unscrew the off-cut from the faceplate and finish-turn the diameter.

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Can this piece be made on a rotary-table and vertical mill? Yes. a ring of bolt-holes concentric with the finished diameters is basic rotary-table work, if the number of holes is a factor of 360º. It normally is!

You can mill the entire component in this way. Set out and drill some holding-screw holes in the off-cut areas (leave room for the heads!) to secure the plate to the table by Tee-nuts. Use a sacrificial plate or spacers as with the lathe faceplate.

Centre the rotary-table under the spindle and set the axis (usually the long one) dial or the DRO if so fitted to 0. Turn the RT to 0º.

Fit the work-piece and spacer(s) to the table.

Now you can drill the component bolt-holes and trepan the ring out by using a slot-drill, with due regard to cut depth for cutter diameter. It's a slow and rather tedious process with large diameters, on a manually-driven rotary-table, but effective.

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Incidentally, if you ever need set out a ring of 4 equi-spaced holes by co-ordinates, or relate a square's diagonal to a diameter, the diameter of a square's circumscribing circle is 1.414 X Diagonal. (Square root of 2 – derived from Pythagoras' Theorem.)

Other polygons and their formulae are available!

Edited By Nigel Graham 2 on 19/06/2023 23:34:01

[HopperParticipant @hopper]

About 100 RPM should do you for that diameter with a HSS toolbit. Could be twice that with carbide, but with the way you are holding the job I would stick at 100 RPM and take it easy. It should clean that nice round shape up pretty easily. It is when you leave it square or even octagonal and you get a harsh interrupted cut that things get interesting.

The two bolts should be sufficient.

[Justin ThymeParticipant @justinthyme24678]

with the thought that carbide is brittle and can shatter. Would it be safer to at least start this 'interrupted' cut with a HSS bit ?

Since I'm going to do this job now, I will use a HSS bit (if they fit the tool holder) , but be interested in your thoughts if this is a valid concern

[JasonBModerator @jasonb]

If you are using carbide just wind in gently with not too deep a cut, plenty of insert milling cutters that don't suffer from interuppted cuts. That's a carbide lathe tool  in my photo, it will also cope better with the mill scale you have on your metal

250-300rpm with carbide which will also put your variable speed lathe's motor in a happier place

Edited By JasonB on 20/06/2023 07:38:59

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