Cutting steam valve ports

I have been reading an ancient ME from 1953. Author "LNWR" has an article describing making jigs to cut valve ports.

The gist is that the first jig is held with a clamp and guides drilling the holes for studs to eventually hold the steam chest (and before that locate the second jig). The first jig also guides drilling most of the meat out of the valve slots.

So far so good.

The second jig has correctly sized slots (made by filing) and has matching punches to cut the ports. The described use is to scribe the outline of the slot and then remove the jig to "CHIP OUT THE SLOTS AS NEAR AS POSSIBLE" thence replace the jig and follow with the punch (which is dead square on the end)

How do you reckon the author would have gone about "CHIPPING"?

Article in Vol 108 no 2696 page 116

https://archive.org/details/Model_Engineer_Vol_108_No_2696/page/115/mode/2up

Edited By Russell Furzer on 13/07/2022 12:42:24

small cold chisel or cape chisel , likely. Not much done anymore, but a major part of repair and casting machining back many years (and die sinking , back more than a hundred years).

Many ops, including sheetmetal cutting, can be done very fast with correct / practised used of chisels with work held firmly in a vise.

Quite common years ago for steam ports to be cut by drilling and using a small cold chisel to remove the unwanted material, LBSC describes the process several times in various write up's. I've only seen it once on a Molly that we think was built in the 1940's. On this engine the slide valve recess and the flutes in the coupling rods had been cut the same way and a very good job indeed the builder had made of it, better than some I've seen milled!

I think there may be a how to do it in the Titch book by LBSC, certainly in one of his write ups he gives a sketch of a small chisel to make, helpful back in the days of a lathe only equipped workshop where milling facilities were limited.

Dave

Come to think of it , seen a Fayette as well with chisel cut ports, not as neat, but it had still run ok for about fifty years!

Given that the article was written in 1953, before more modern machines, such as Milling machines, were available,more work had to be done manually, with the reduced precision that sometimes ensued.

It might well be my lack of skill, but given the choice between producinbg a port by drilling and then using a hammer and chisel, or milling; the machine would win every time.

Old time fitters produced fantastic work, but spent a lot of time on it, but consistent repeatability would be less easy to achieve.

Howard.

I like many had heard about the use of cold chisels but as a knee jerk reaction dismissed them as old hat. However now I am getting on a bit in model engineering years I have begun to see the value in old techniques which very often are far quicker than more modern methods when it comes to one off work, which is most of what we do.

For example I have seen a few write ups for ways to shorten rivets to the correct length for use involving jigs to hold the rivets and heads so then may be milled and so on. However, and I take no praise for this as it wasn't my idea, if a piece of material is reduced to the legth required for the rivet and a rivet sizes hole is drilled. The piece may be held in a vice, the rivet inserted horizontally and the end struck of with a cold chisel. So simple. OK it's not in the cutting keyways realm but it makes me wonder that I'm missing out on many more simple short cuts employing the humble cold chisel. Cutting sheet along the top of the bench vice would be another.

regards Martin

It used to be said that a good fitter could work to within 0.005" with a hammer and chisel.

Sometimes, a short piece of sheet can be narrowed, by being held in a vice and using a chisel on it.

Unlike using bench shears, it doesn't bend! Just needs the burr filing off.

Howard