The On-Line Magazine of Rideable Model Railroading
© November 24, 2012
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The "Gumz" Turret Valve Part 2
continued from Part 1
Written by Charles Reiter
continued from Part 1
The square valve handle mounting section was cut using a collet spinner on the milling machine. This allowed me to hold the 1/8 shaft and keep support close to the tool. Of course for a few they can even be filed to a close enough square. Once the handle is on you will never see it again. The bonnet is made in two parts. Cut the 1/2” hex stock to the .312” length first. Then drill and tap it to 3/8-24. I drilled and then parted off with a thin blade, but as you drill deeper all it takes is a little chip under one cutting edge and the drill wanders off the center. So drilling and threading individual pieces improves the quality. After threading the “nut” I used a 3/8” end mill to make a .093” recess on one end. This engages the cap part. Then I made the caps out of 1/2 brass rod. I decreased the diameter to .480” to get a tiny step for the silver braze. I cut .130” thick blanks because it suited my tooling but making the .24 protrusion and 3/8 diameter step, then parting it off is an excellent method. The important part is to make the .24 part clean because it compresses the Teflon seal, and get the .015” step at 3/8” sized properly to engage the diameter of the relief in the “nuts”. I then mounted the cap by the .24” part and filed a radius on the top edge. Now the caps get fluxed and silver brazed onto the nuts. After cleaning them up, mount a piece of the 3/8-24 rod in the chuck. Screw a bonnet on and using a center drill and drill put a #29 hole through the bonnet. The hole will come out on the true center, since it references the threaded feature. Deburr, wire brush, and assemble the parts.
Handles were made by cutting a piece of 1/8 thick sheet into squares about .875 square. These were then stacked in groups of about 5 or 6 and “pressure plated” between centers. I then mounted the round blanks in a collet with a stop in it, a pot chuck would be the same, and drilled a center hole at .093. I then mounted the disks on a pin protruding from a piece of .875 rod and with a little cap over the pin to allow the tailstock to clamp the disk knurled the edge. Then back to the collet to add detail by thinning the thickness, leaving a thick center and outside edge. The square holes were broached with a .093 square piece of tool steel .75 long. It was turned to a .093 round lead in with an angled cutter that left “teeth” at the corners. This was hardened and then with a lot of lubricant pushed through the handle holes in an arbor press.
The square holes were then dressed up with a little square file. The disk wheels were then further detailed by adding six 0.125 holes. The holes were made using a drilling jig that is like a cup with the holes in the bottom. Once the wheel is set in the jig the first hole is drilled and a pin inserted to index it. The rest is drilling and deburing. I did try threading the valve rod and threading the handle to fit, then using the center screw to lock it but did not like the resulting fit.
To connect the valves to the various points Dave simply had added a 1/4-40 mpt union to each of the tailpieces. Since I like to make as much as I can myself I chose to make little unions as integral fittings. The first ones were made as little flat ended ferules with nuts that had a 1/4-28 thread in them. That worked well except the ferules connected to the inside of the piping by brazing. The nut is truly captive stuck between the ferrule and the pipe. All that piping was 3/16 inch except the whistle valve which threaded on directly with a coupler. The next installation was improved by adding short lengths of 5/16-24 thread to the tailpieces. While a little touchy to braze on, it allowed ferrules to be made that would slip over the end of the 3/16 copper tubing, and the nuts could be slid up the pipe afterward. All of this is straight forward lathe work.
The valve group works really well and the only leaks were at the packings. Those were stopped with a quarter turn tightening. The flat face connection of the unions, seal reliably and don’t require any pull back when disconnecting.
I have been extremely pleased with the performance of the original unit built by Dave Gumz (seen below) on his Mason and with my version as installed on my Shay.
Written by Charles Reiter
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The On-Line Magazine of Ridable Model Railroading