Reverser part 7

I shall begin this update with a picture from Sir Nigel Gresley's overhaul images available online, I've probably said this before, but for anyone building a Gresley pacific, A1/3 or 4 the SNG online blog is a wealth of information.

I begin with this image of SNG's reverser sleeve, its thrust plate and what Don calls the nut although a threaded shaft probably is more suitable but nut is shorter...:)

The sleeve can be seen at the back, this is the part that pivots in the top of the reverser stand. We then see the bronze nut ( you can just see the thread at the top inside) which is sitting on top of the thrust plate. The sleeve and thrust plate are bolted together with the 4 large bolts enclosing the nut in between. in model terms these bolts will be 10BA and the ball raced thrust washers will be a part of the bronze nut itself, no need for ball races here.

Don begins with the sleeve, so shall we. Don states to start with a 5/8 sq length of steel and machine it down to 9/16 sq, that would be nice, alas the smallest that I had left was 3/4x 1/2 in gauge plate and so there I started. Not as bad as it may sound as gauge plate is a lovely metal to machine, once machined to the required size ( I machined it extra long) it was clocked in the 4 jaw. The spigot seen is 15/16 long, 3/8 OD and bored out to 1/4", the base needs to be 3/16 thick as does the thrust plate. In case it's not obvious I am making both the sleeve and thrust plate in one go and the state as seen is the sleeve base has been left over the required thickness and the thrust plate is slightly over its required 3/16 and, of course, both 9/16 sq. I have also knocked off the corners ready for hand filing of the rads later. My thinking is, that I save time is doing the basic machining while the parts are still attached to each other.

The job was then parted off and reversed in the 3 jaw ready for the machining of the 1/2 x 3/32 recess into the thrust plate. There will also be the same-sized recess machined into the bottom of the sleeve base, it's here within both recesses when bolted together that the nut will be held.

The last part to do at this setup was to part off the thrust plate, machine the sleeve base down to size and repeat the cutting of the 1/2 x 3/32 into it. With that done, the thrust plate was turned upside down and reamed together with the sleeve, the result seen here.

It was then time to machine the recesses that encapsulate the sleeve and drill the 4 No.51 holes, which would then be ready for 10BA bolts to hold the parts together.

This picture shows the recess being machined in the thrust plate, with the 4 N0.51 holes already done. These were drilled using the rotary table and with the sleeve and thrust plate clamped together.

After both the sleeve and thrust plate had had their recesses machined. I then bolted the two together trapping the sleeve in between the now 4 pillars checking that the sleeve turns easily. I wanted to fit a thrust bearing here as per full size but couldn't find anything that small commercially, we are talking 1/2 OD 1/4 ID and approx 0.040 wide, I haven't given up, so for now I have a bronze spacer of that size fitted in its place. Note that nut is overlength in this picture, left until I was happy with everything else, the sleeve is to size though.

Next, we move on to the more tricky part, not helped by an error in the drawing, we are,of course, talking about the fulcrum. A few things to point out why I believe that Don has this wrong. First Don has the fulcrum placed in the centre of the sleeve, a quick glance at The photo I posted above showing SNG's workings will show that the fulcrum sits lower down on the shelf. The next problem is that the sleeve and thrust plate when fitted assembled to the stand sit above the front face plate, it has to as it won't sit inside the stand itself. Don's own GA of the stand shows this. A third and more important reason is that the fulcrum point centre as drawn by Don sits 0.750 above the front face plate, however, the sleeve and thrust plate which we know sits above the plate are 0.375 for the base and then 0.468 from the base top to fulcrum middle, giving us a total 0.843 which, of course, won't fit, we also need a small gap between the two as the sleeve pivots above the front face plate, hope that makes sense.

Having decided to move the fulcrum lower down I then gave some thought as to how I was going to make this part and hold it square on the sleeve while silver soldering. Don suggests making a jig or even doing it by eye, his eyes were clearly better than mine..:) I chose a different method as described below. First, we have the 5/32 spigot (overlength) and a length of 3/8 brass machined down to be 0.500 long, I made it a few thou over this for later truing if required. I chose brass to make life a little easier for the next stage.

Ok, so I planned to drill through the brass fulcrum with a 3/8 drill thus giving me two parts, this is very much a Heath Robinson approach but I didn't want to waste time filing a scallop as Don suggests. I anticipated that the part would not stay still while drilling and so wrapped it in tape to give some grip and also cut a deep channel into some plywood which would close around the part when tightened fully in the machine vice. This worked surprisingly well leaving just a small burr at the bottom

With the fulcrum now in two parts I then needed to decide where to make the pivot point along the sleeve, before committing to drilling I test-assembled the parts and checked that where I planned to place the pivot point gave me enough room for the reverser to move fully fore and aft and also that the sleeve sat just above the stand front face plate. I came to 0.300 above the sleeve base, which looks ok to me. Here we see the sleeve trapped between the vice jaws, packed under and then drilled 5/32, I then placed one half of the fulcrum on the spigot to check for fit.

I then dry-assembled the parts to check all was ok. Note that the sleeve and base sit close to one side of the stand, this is as per full size.

I include this picture just to show that before silver soldering the parts together I machined a small amount out of the spigot centre. I did this to reduce the work of the cutter that I'd use to machine the centre away, choosing a mill cutter over a drill bit. Note also the two bearings in the background.

It was then time for the big heat-up, well, not that big but still a possible problem if I got it wrong. After fluxing the parts I used an old rusty clip which is perfect for these little jobs, as the fulcrum was a good fit to the sleeve the clip alone held the parts squarely for heating.

With the part joined I placed it in the 3-jaw and machined out the spigot centre, I started with a smaller 5mm cutter first, finished with a 1/4 and then reamed through. I then held the part by the over-length spigot to true up the fulcrum if required, they were pretty good anyway so I just removed the few thou that had been left oversize.

With the handle now made and painted we have a working reverser, I looked at a number of reference photos before deciding on how to finish the handle. I have seen red which, of course, is BR days, seen what looks like painted and unpainted, IIRC FS today is unpainted with a brass plate on top. I've seen flat tops and domed. I have gone for black taking note of the red handles which are worn down to bare metal where the driver's hands make contact and fitted a shallow dome just because I like it.

I still have the fine detail to add, the same goes for the backhead, plus not forgetting I could now make the reach rod, decisions, decisions..:)

Lastly a short video has been posted in the video page of the reverser working