Sorry it has been so long since I have done anything on this post, but because I can only do a little bit at a time at the moment, I waited until I had a bit more to show you all.
So all the snippets for the last few days are now shown.
I needed to produce a friction slide, so that when the engine is running, the handle will be held by friction, but by putting a little pressure on the handle from a radio servo, the joint will slip to its new position, and when stopped, will carry on as though it was still a solid joint.
A little thought had to be put into the selection of friction material. Because it is a fairly high temp and oily area, most friction materials were ruled out, so that left me with basically a choice of two. PTFE or metal to metal.
PTFE was ruled out because it is too slick, and I thought I would have great trouble getting it to act as a stable friction pad.
So after a little more thought, I settled on a steel and phos bronze combination. Both have good wear characteristics and shouldn't be affected by heat and oil.
You have seen a few of these bits before, but I have made a few extras to complete the job.
The friction bits are in fact either side of the slotted link on the left. The steel screw has a pad of PB fixed onto the end of it. The pad has flat on either side of a little stub that fits into the link slot, this effectively stops the screw turning when it is all tightened up. So after the screw is put thru the link, the PB washer is put on, that forms the friction brake. Then the handle, followed by the tensioning device (a spring on a couple of free rotating collars), the spring is compressed or loosened by the little knurled nut, which in turn is locked in position by the fancy handled nut after the correct friction setting is found.
This is what it looks like when assembled.
This is roughly what it will look like on the finished engine.
A view from the top.
So now those bits are made, the engine can be built up. So the engine was stripped of all the unwanted bits for the time being and assembly starts in earnest. It is this part that is the most critical, everything has to be done in the correct order, otherwise you might find you can't fit or adjust certain parts. I will, without fail, find some bits that I have made will require tweaking to get everything running smoothly, but it will just be a little tweak here and there.
The first job is to repack the stuffing glands on the steam chests.
On stripdown, I pulled the old packing out, and found it is rolled up PTFE tape. There is nothing wrong with this method of packing, but being an old fashioned type, I like to use old fashioned techniques that have been used over the last couple of centuries. Also I don't tend to use the new packing string material, that is covered in graphite. I use the real old muck, that is impregnated with a waxy grease, with just a little graphite. I find that when it is set in and the grease has warmed up then solidified, it makes a great steam tight joint, but also a very good self lubricating bearing surface.
So the bits are assembled in the right order, and a strand of packing string is wrapped around the shaft. The string is pushed down inside the stuffing gland and the gland nut is tightened down. You continue to add or remove string until the nut is in by about half it's threads, and the packing is exerting enough pressure to make the shaft slightly difficult to push in and out with your fingers. The gland will soon settle down and become a very good friction free, steam tight joint.
After packing, this is what it looks like. There is enough tightening adjustment on the nut to give many years trouble free steaming. If a whisp of steam starts to escape, a one flat turn on the nut should make the joint steam tight again.
The pair of steam chests ready for going onto the main block.
A thin gasket was fitted between each steam chest and the main block. It was at this time, one of my mods needed a final fiddle with. The slots on the slide valves were deepened slightly to allow the slide valve to lift off it's mating face by about 0.010" (0.25mm). After that the steam chamber was tightened down and valves and linkages were connected up, but the chest covers were left off to allow me to accurately time the engine.
The rear end of the engine was given the same treatment, but also I put on the friction slide.
Because this engine didn't have these bits fitted originally, the linkage operating handle (or the rod it fixed on) was incorrectly made. So to allow the timing to be done, the handle was loctited onto the shaft and the operating linkage was all zeroed up.
After the timing is done, I will drill and pin the joint to make it permanent.
If I am up to it tomorrow, I will set up the timing, and finish off the rebuild.
I do have a few extra bits to make, but they are just decorative requests by the customer, and won't hold up getting the engine to a running state.
Bogs
