The Craftmans Shop > New from Old

Dore Westbury Mk1 Mill Restoration, finishing and one or two mods.

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Joules:
You can however drag the video time line to skip through, or go back, in YouTube videos.

vtsteam:
Beeshed, it's applied by heating the iron casting with a torch and spinning a rotary brass wire brush held in a drill against it.

Folks should understand that differentially heating an iron casting with a torch can cause it to crack. Cast iron has poor tensile strength, and while heating it uniformly is usually not a problem, heating one section causes that area to expand while the cooler part does not. This cause tensile stress, and cast iron while high in compressive strength, is poor in  tensile strength.

In the video, Canobi is heating only bands on the casting with the torch. Luckily there is a slot running down the casting here, and so axial expansion is easily accommodated without building up a lot of stress.

How much differential heating can be accommodated by a casting will come down to the specifics of casting dimensions and the amount of heat, as above. But it is important to realize that cracking can happen. A better approach is to heat an iron casting more or less uniformly by playing a torch over more than just a small area. And letting the whole cool slowly -- a favorite approach I use when brazing, or welding is heating uniformly, and then to bury the part in wood ashes to cool. These insulate and slow the cooling rate. Castings seem to crack most often in the cool down stage.

Canobi:
Thank you for the info regarding heating iron castings vtsteam, I didn't realise I'd dodged a bullet there. I don't think I'll be doing that to cast iron again, well maybe not until the cold season at least, where I have a ready supply of hot coal ash to bury the hot parts in.


Steel on the other hand is fair game any time and I got round to brassing the arms on a couple of the levers:


I then experimented with a followup heat black session but it was a total fail, so fine sanded the terrible coating off and opted to paint the bolt half instead, which I did along with the aluminium motor mount brackets:


The fail was due to a combination of things. Firstly, there's no way to mask off areas you want to leave untouched , unlike when painting a part. The second was an unknown factor, the steel just didn't want to take the black. I had to use a scotch bright to buff off a light amount of flash rusting before I started heating and coating it so my initial thought was that it was mild steel but could it be a form of stainless perhaps?

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