Machining a Fowler Cylinder Block

[Dan JonesParticipant @danjones77555]

I’ve been wondering this for a little while but I haven’t really investigated it much. Does anyone know how they originally machined the valve faces on the compound over head slide valve cylinder block? The valve faces are both inclined in towards themselves but also inclined downwards towards the crank. To be able to reach right down into the furthest depth of the block/valve face must require a particularly long tool or a machine with a long reach.

Further to this, despite how they did it back in the day, how would people machine it with access to modern techniques and equipment?

Cheers,

Dan

[Dan JonesParticipant @danjones77555]

How did they do it?

[Jeff DaymanParticipant @jeffdayman43397]

Probably done originally with a shaper, in a couple of setups with the block at a compound angle to the ram. I'd be surprised if a positioning fixture or two was not used to position the block quickly at the right angle. Maybe they did one side on one shaper and the other side on a second shaper, with dedicated holding fixtures left set up on each. A gooseneck style tool holder could be made any shape to reach from the ram over walls of the steam chest, where the shaper stroke was adjusted for just the cut length needed for the valve faces. In a shaper you only need the width of the toolholder, plus a small clearance, between end of cut and adjacent wall at each end.

Many factories had rooms full of shapers years ago, before milling machines gained popularity.

The old saying "you can make anything with a shaper – except money" (they are slower than other tools at removing metal)

[JasonBModerator @jasonb]

A modern CNC would be able to do the compound face and with a fine stepover would require minimal lapping, the ports would be the harder ones to cut particularly on the HP side as the face is at a steeper angle so not as easy to get a tool at right angles to it unless the ports were cored and cast in as per the original.

for a model then easier to fabricate the cylinder from many parts so you can do the face and ports while easy to get at, this is Jan Huijgen's 3" Fowler block part way through construction.

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