How do you stop cracking paint on Edison motor board?

[marcapra]

I have a charming B-150 Edison Diamond Disc machine. It has rare brown motor board, but the paint has many fine cracks over several parts of the motor board. If I don't do anything the paint will crack off. My motor board is not rusty. Is there a good varnish I could paint or spray over the board to keep the cracking paint put? I was thinking maybe some Damar picture varnish?

[JohnM]

That isn't paint on the bedplate, it's tinted shellac. Not sure how it can be prevented from cracking/flaking. David Teti in Connecticut is the go-to guy for replacing shellac finishes on Edison iron.

[marcapra]

John! Thanks for the tip. You gave me an idea, so I ran down to Home Depot and bought a can of Bullseye spray clear shellac. It's working like magic. The cracked, flaky areas look like they are melting down into the motor board and disolving! Great! Thanks, Marc.

[EarlH]

My folks had a machinist at the house when I was a kid in the 70's. He was a really old guy in those days and looked over a diamond disk machine I had that had a bedplate doing that and the first comment he made was "Edison didn't prep the metal before they painted it, did he? He should have washed the parts better before they were painted" I've often wondered since then about that quick comment and if the problem really is from a slight oil film on the iron parts before they painted them. Some of those grained horns really have problems with the paint staying put as well. Whatever the cause really is, something changed when they went to the black bedplates & horns as they don't do that. Maybe the later stuff was baked on japan.

[martinola]

The difference in durability between the earlier black bedplate coatings and the later colored ones isn't all that surprising. The black color was asphaltum - a black emamel that was baked. Pretty durable stuff.

If you're going to make a bedplate paint out of shellac, one would need a lot of pigment or blends of pigments to create the light opaque color. The more non-shellac stuff you have in the mix, the less sticky it is and therefore easier to crack and flake. Combine that with having oiled machinery above that surface, then you have a real problem keeping it stuck to the bedplate. The original casting may have been prepared well, but oil dripping into cracked shellac over the years will yield the same effect.

I am heartened to hear Marc's report on stabilizing it. Perhaps there is hope after all.

Regards,
Martin