When the family ran it, College Engineering did back plate castings amongst other things. Unfortunately the lads that bought the business from them only seem to do materials.

Note:- the Ebay supplier that advertizes 'meehanite' won't provide Meehanite certification with the material (I asked them). Therefore it ain't Meehanite, which is a trade marked manufacturing method that involves certificaton.

Edited By Mark Rand on 03/07/2019 22:27:18

Are they happy to sell less than bar lengths Alain?

Might be worth checking out Southwestern steam? They may have selectable over-size offerings (or it may encourage them to offer slightly larger diameter pieces). Not a customer, but have heard/read good reports of them.

Imperfections, such as??

The largest diameter cast iron I have bought from M-Machine was 140 mm diameter, a slice of 2 inch thickness to make a 63 tooth gear of 12 DP.

It was clean, no blow holes or central imperfections and being continuously cast material I would expect that to be typical of all the sizes they sell.

Regards

Brian

These people do laser cutting and say they can do up to 30mm. Normal structural steel would be fine I'd think.

I made a 6 3/4" backplate out of a piece of meehanite which started at about 200mm. There was a hard bit on part of the OD about 1/4" deep, just like an interrupted cut. I was glad to get through it, and doubly glad to have a variety of TNMG16 inserts. I drilled and tapped the CI to fit on a faceplate and did the od and face so it would fit in a four jaw for the rest of the turning. The mess was incredible, despite having magnets set to catch the cast iron dust.

If I ever have to do something like that again, I will try to get a piece of SG iron.

 I bought a 160mm ci blank from a well known supplier for a 160mm chuck and it was under size. It would have cleaned up at 152mm, but I left a bit uncut at 155mm. I contacted the supplier, who immediately refunded my money and said keep it. I reckoned that the three 8mm rear mount screws would be too near to the edge for comfort, so I simply drilled and tapped for six 6mm screws to hold the chuck instead, they could be on a slightly smaller pcd as well as being smaller diameter.

Edited By old mart on 04/07/2019 23:15:37

Seems that from the above posts cast iron is the preferred material for chuck back plates, why is that?

Cast iron is more rigid than mild steel. And it machines very nicely when cutting the thread in it, if a screwed spindle type. But for practical purposes, mild steel will do the job if need be.

That's where theory deviates from practice. Maybe it's because Young's Modulus measures deformation under tension whereas cast iron's greatest strength is compressive? Or its superior resonance damping properties? Either way, I've never had much luck bending good grey cast iron. It usually seems to want to break before it will bend. Never managed to break a chuck backplate though. (One of the few things I have not managed to break over the years )

Edited By Hopper on 05/07/2019 12:15:07