Well this morning I made a start on the valves for the pair of Edgar T Westbury's Seal engines I am building. Its been a while since my last work on this pair for various reasons but at least I managed to make a start on the valves.
I still have to finish the two flywheels but I seem to have had a bit of a block turning these and instead of ruining the good one I am leaving it alone while I start on something else. The valve stems are very small at only 3/32nd " in diameter (about 2.4mm in dia) and with a little apprehension I made a start by first making a pencil drawing from Edgar T's plans. I find this helps as I at least once have had to focus on the dimensions. Also it helps to clarify my approach to machining order.
I decided it would also be useful to refer to the 1947 Article in Model Engineer for guidance as well as several articles published in Model Engine Builder (American Magazine) but in the end I felt more confused with the different approaches and fixtures shown. So a 'trial' valve was the order of the day (my excuse in case it goes wrong.....then it turns into a 'trial' piece!).
I started by chucking some 3/8" diameter free cutting stainless steel before facing it off then centre drilling. Once done I decided to run a couple of light cuts to check the tailstock was in line. After the first cut I found it to be out about 2 thou over the short length so adjusted it until it ran true.
I first brought the length of the valve to the outside diameter of the valve over its length (except for approximately 1/4" at the live centre/tailstock end) to the design size of 9/32nd" (just over 7mm in diameter). Then working back from the chuck, using the digital readouts, I came to the point where further reduction of the stem was required.
Because of the thin stem I made light cuts (many many light cuts) but whilst it was more work at least I hoped to reduce the possibility of the valve stem doing its own thing and perhaps wrapping itself round the cutting tool! When getting close to the finish size I again checked it was parallel and was disappointed to find about a thou and a half of an inch difference! However running the tool along a couple of times brought everything back to where it was.
I decided to change the disposable insert for the final cut and was glad I did since it gave a nice bright surface. I then decided to try some of the micro mesh sanding pads I bought for my pens finishes and was really pleased with the results! Will definitely use these for metal as well now. They did work better with a little lubrication (WD40 sprayed on).
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The next task was to cut the 45 degree face and to do this I set my top slide over to 45 deg. I used the DRO again to scribe a finish line on the outside of the untouched bar and when repositioning the cross slide to the face end simply kept cutting until reaching the scribed line. Checking the distance again with the DRO's (and magnifying glasses!).
Because of the small diameter of the stem I used my Proxxon tool with its Dremel quick fit cutting disc to cut the tailstock end but oversized. Once this was done the tool was changed to the parting tool and using the DRO to set the point I parted off the valve with the depth of the head a little oversize.
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 DREMEL Multi Tool Accessories SC690 SpeedClic Cut Off Wheel Set Multipack S690 £15.69
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Next time I am going to make a fixture that will allow me to cut the 8BA thread on the end of the valve and also to face off the valve head to dimension, so not quite there yet but I must admit to being pleased at the first attempt! No doubt there are many failures to come with the next 17 needed (or even this one!) so I must not smile too much yet!
Anyway here is a picture for your delectation!
Part finished valve alongside its phosphor bronze valve guide.