Small Poppet Valves

I need to make two poppet valves (the same as used in car engines). The problem is that the stems are only 1/16" in diameter and 3/4" in length.

I've made two that were not a success, the last one with a male centre on the end running in a female centre held in the tailstock chuck. The problem being to get a parallel surface on such a small diameter.

(Almost) any suggestions welcome.

Brian

EXTREMELY sharp tools, DEAD on centre height, ditto light cuts, and minimal end pressure to avoid bending the stem, are the only suggestions that I can offer. This implies HSS tooling.

Howard

Friend of mine made some using HT screws spun in the lathe and attacked with an angle grinder. Posted on an IC engine based website. Have a look on the internet for someone building a half-scale Onan engine and you should find a link to it.

Could use a roller box.

Andrew

By watchmaking standards those are fairly big. If you look up arbor turning, or arbor repivoting you might get some ideas about the tricks and techniques used, but I think Howards advice is correct.

+1 for Andrews roller box, or a running down tool which is a tool with a built in travelling steady. There have been a number described in ME over the years

I have made lots of full size stationary engine valves,a lot of original valves have a material similar to siver steel for the stems and cast iron heads,Amancos and some ruston hornsbys for example,for very small engines the cast iron head would probably not work,though a silver steel stem would be round ,accurate and strong,so why not make the head from stainless steel and thread the component parts and screw them together and lightly rivet over the stem where it protudes through the head,then set the valve stem up in a lathe collet and very carefully skim the seating face of the valve with a very sharp HSS tool. Making a valve from solid rod is not a good idea as the inner core is not very strong when getting down to small diameters,automotive valves get over this problem by forming or forging the head on the valve. The Amanco open crank engine valves also have a valve seat angle of 45 degrees,they work and seal very well ,though often regarded as cheap and crude American engines ,for their time they were a very good engine which started easily ,would run in an absolutely worn out condition,and was an example of lots of capital poured into machines and tooling to produce a very cheap good product from day one of manufacture,the interchangeability of componens was very good,and having made lots of spares,never had a customer complaint about parts not fitting.

You could make a hollow mill to use from the tailstock, it would take the diameter down in 1 operation.
Alternatively if the stock is large enough to take cutting forces set the tool to give the diameter required and make the cut in 1 operation, not multiple passes.

Emgee

Stew Hart has a youtube video of a traveling steady for small diameters that might suite

**LINK**

Rod

I'd suggest drill rod / silver steel for the stems, with drilled discs of same for the heads, tig welded in place. One carefully placed tig fusion weld (no filler) in the centre of the head on the combustion side would seal it and provide more than adequate strength in a valve of the noted size. In this case with a welded joint a threaded fit would be counterproductive. Just a slip fit would be good. Ideally the weld penetration would be at least 80% through the head and well into the stem. After welding the disc is turned and the seal face ground at 45 degrees while holding the stem in a collet.

I made a few this way years ago for Saito 4 stroke RC plane engines (no Saito parts available at the time locally) and as far as I know they are all still running, and I talk to the people I did them for regularly, they never mentioned any issues.

I turned some 3mm diameter x 20mm long stainless ones by turning the blank down in stages (roughly 1/3 of the length at a time) then taking a very light skim over the stem to blend the sections together, but 1.5mm probably won't stand for that.

Joe Pieczynski's approach may be of interest (one deep cut, right to finished diameter):

When I turn parts with small stems I first turn to the head size then turn the stem in one cut with cutting oil and very fine feed. I have done this successfully from a 3/16 blank down to 0.025” and made 100 of them. Leaving the blank a reasonably large size gives you the support.

I'm VERY grateful for all the suggestions and am keeping them in reserve in case my present setup is not successful.

With this, I put a flat ended piece of bar in the tailstock chuck and, without altering the tailstock to bed lock, held a very small centre drill in the headstock chuck and produced a small centre in the piece of bar.

I then fitted my valve blank into the headstock chuck and turned a male centre on it. The theory is that it MUST line up perfectly, but we'll see.

Brian