Hi There Gents.

I have done a lot to make a converter plate for my old Herbert 4
Preoptive take a Forkardt Chuck which is in excellent condition.

I have made a plate in half inch mild steel, - as a trial to see if I
can make one using more appropriate materials, like cast iron later.
I have fitted it to the flange on the Herbert and have been able to
turn it down to an accurate diameter. The flange has a recess to
locate anything bolted to it and this isn proving to be the problem,
as if I take it off now, I don't know if I can bolt it on again
centrally as I have it mounted on countersunk bolts and these will not
be available if I turn it over to get at the back. The Old Herbert
Inspection Number is: 94-2949.B.

Do you think an inch thick plate turned to match the Herbert flange
and then turned in situ to match the Forkardt with a small flange
that fits into the hole in it's backplate, drawn on by the mounting
bolts threaded into the plate, will be OK? Is there any approved
design for these things. I am thinking of taking the final design to
a proper machine shop to get the recess turned out, but I need to
know what the DIN number for that Herbert flange is I have seen lots
of converter plates for sale but they always quote the specification
of the mounting and apart from the diameter which I have measured at
19.03 mm as far as I can see and the holes in it form an equalateral
triangle 7.88 cm radius. I don't have the definitive size. I cannot
take these measurements to an engineer and risk saying, please make me
a plte like this.

Costing only 20 pounds I have discovered a cast iron disk of over an
inch thick and the right sort of diameter. It is a spare dumbell in a
sports shop and so I am going to look round the car boot sales for a
cheaper one.

Does anyone know what the spec. of thisHerbert mounting flange
actually is, please?

Thanks a lot George.