Here's my first attempt to make a globe valve for my Stuart No. 4 (for the 5/16" inlet piping). I followed George's build here,
http://www.homemodelenginemachinist.com/f31/small-globe-valve-how-make-4377/, but scaled it up 1.5X to better suit the size of my engine.
First step was to take some 5/8" brass and cut the profile for the main body:
followed by some freehand turning then filing of the globe:
I had a template to work to, but this was way off spherical which did cause some problems later. After this experience I'm eyeing one of the toolpost ball turners
The next step was to drill through with a drill the diameter of the valve seat (the smallest of the diameters), then drill with the tap drill size down to the valve seat level, which is around the bottom of the globe. Then I used a small home-made boring bar to remove the angle left by the larger drill, leaving a flat around the valve seat:
The last step in this setup was to tap for the top, screw-in portion. I used the same thread for this as the pipe fittings (5/16" 26 TPI BSB). I suspect that a Model Engineer (ME) 32- or 40-TPI thread would be more appropriate, but I don't have taps or dies in that size.
Then came the screw-in cap part, which consists of a threaded end, a flange which will be cut into a hex, and a profiled neck:
I left drilling the center until I had it parted off, and then screwed into the body. That way, I know the bore is aligned with the body after assembly:
This cap is drilled through with the tap drill size for the thread used on the spindle (I used 5BA, and a 1/8" spindle), then drilled and reamed about half way down for the spindle. An external thread is cut on the end for the gland nut (I think I used 1/4" 26 TPI here).
The third part that makes up the body is the side arm, here being profiled to fit the globe:
While still attached to their parent material, the body is put in the rotary table to drill the side hole. I had a minor boo-boo here:
The rotary table wasn't securely bolted down, because I can't easily get a clamp on the front side. When cutting this hole, the drill caught as it broke through to the bore, and pulled the part up, tilting the rotary table up with it.
The result was a somewhat oval hole, but luckily it's covered by the side arm.
Then I cut the hex flats on both side arm and body:
A final small part is a collar which locates the side arm onto the body when soldering, so here's where we're at:
Here you can just about see the valve seat, which was, luckily, unmarred by the side-wall drilling incident:
The parts were then parted/hacksawed off their parent stock, and put onto a mandrel to drill and tap the newly exposed ends, as well as put a slight 30? profile on the hex flanges:
Time for silver soldering now! All fluxed and ready to go:
and post-solder:
That went into the acid bath for a while.
Not shown here was some threading of the spindle. I used 1/8" stainless steel for the spindle to avoid rust, and threaded the bottom portion 5BA, and a section at the top 6BA to give the handle a flange to sit on.
The handle started live as a bit of 1-1/4" brass bar. I left a generous boss in the middle to give me something to put in a collet later:
then trepanned out a bit from the lower face with a boring bar meant for internal threading:
While still attached, it was partially parted off, and the outer rim profiled:
then parted off completely, and flipped around and held in a collet to trepan the upper surface. I may cut holes or spokes at some point if I decide that this valve is a keeper.
So here's what we end up with:
which, when assembled, looks like:
It's missing the gland cap part that screws onto that top thread, which I haven't made yet.
Blowing through the valve while turning the handle indicates that it seems to form a pretty good seal.
Here's a trial fit on the engine:
I'm quite pleased with how the valve went together, but I'm not sure that it looks quite right on the engine. The globe part seems a bit small to me. Or maybe it's the mixture of styles of the lubricator, T-piece, copper piping and globe valve. It could be time to think about flanges everywhere
So, things I'll do differently next time:
- Make sure the body is spherical. Preferably use a ball turner.
- Maybe give up on trying to profile the side arm to match the sphere. It would be easier to have it just be cylindrical, with just a solder fillet where it joins the sphere.
After this I also have questions!
- How the heck do you choose an appropriate thread for parts like this. So many choices! (BSB, ME, BA, English....). I *think* ME is most appropriate for mating brass parts like this, but 32 or 40TPI?
- What's the best way to get the valve bit fixed to the end of the spindle? Can I silver-solder stainless? Or maybe just center-punch the end of the spindle to lock it on?
Thanks for reading!
Simon