Well, I would be lying if I said that getting the chassis running with all the motion fitted was anything but a trial. Much of it my own doing. I am not sure how but I had scaled the drawing wrong so my many attempts were all destined to failure I just didn’t know it yet. It was mention of the scale size of one of the rods that Ian Allen @lancastrian) posted on the Guild forum that made me double check and find the error. A trial assembly of the final version of the return cranks confirmed that they were indeed almost a millimetre too long between centres.

I confess, that this almost did me in and I nearly consigned the 8F to its box for another decade. Saner heads prevailed and I recalled the drawing, redrew the return crank in Fusion 360 and created an updated working drawing. From there I made a ninth set of return cranks and again I made an error in so much as I predrilled the cranks and the small bosses that I added to clear the ends of the studs protruding above the face of the crank. When I then soldered them together, I hadn’t noticed that the holes were slightly out of line until I tapped them the tapped them and the tap went in at angle. So, I started again and this time I made four return cranks with the view that I could pick the best two.

This was taken part way through making them. – I did trim down the boss on the deeper pair after testing.

Having taken great care in the shape of them I also only drilled a pilot hole in the bosses. Then I clamped the cranks to my Metalsmith drilling plate in the mill vice and drilled right through to ensure that all the holes were aligned.

Next, I used a small engineers clamp to clamp the cranks to my tapping jig to ensure that the tap was aligned to the hole and then they were tapped 12 BA

I also used my homemade tap spinner to reduce the risk of breaking the tap.

Finally, I had two pairs of cranks fitted with miniature studs

A test fit had me heaving a sigh of relief as they fit and the motion turned over under power but there were a few clicks where the bits were catching. I knew that clearance was always going to be tight so I patiently worked my way through the various parts easing them.

They included but were not limited to, filing two etched bolt heads off of the insides of the expansion links; filing the bottom front corner of the new valve blocks to allow a minute amount of extra forward travel; turning the head of the 14ba steel screws that retain the combination lever to the valve block down to the thread thickness while retaining the slot, to allow them to be easily removed. Again, to allow a minute amount of further forward travel; easing the faces of the connecting rods to allow the expansion link to pass without catching. – Incidentally I measured the thickness kit provided connecting rods at 1.7mm and the Premier ones at 1.5mm so had I used the kit rods that problem would have been exacerbated.

I also replaced a couple of 14ba brass screws (which retain the expansion links) with some homemade nickel silver replacements with the view that they would be slightly more hardwearing than the brass ones. In fairness given how little mileage my locos actually do. this may have been overkill on my part.

After all that I had a smooth-running chassis. The tinging noise that you can hear is because I haven’t permanently fitted the retaining pins that hold the radius rod and the combination lever together yet so there is a bit of slop in them.

Well, that proved interesting. I removed the two offending driving wheel springs and I confess that I was surprised when that didn’t fix anything. The restricted movement still remained, so further investigation was required.

Looking a bit closer revealed that the problem was being caused by the compensation beam hitting part of the ashpan/gearbox housing arrangement.

Once I worked out the issue my first thought was how the devil do I get in there to cut out some material to allow more movement. I couldn’t see how I might get a piercing saw in and although I do have a shallow bladed razor saw, that was too deep to go in. The last resort saw wise, was to try a hacksaw blade. That too wouldn’t fit. Then I realised that if I unscrewed the motor retaining ring it might be possible to get a milling cutter in.

I gripped the chassis in the mill vice and with a 2mm two flute slot drill I carefully milled out a slot either side taking care just to go through the two layers of etch without hitting the compensation beam.

Now I just need to refit the spring castings

A friend has asked me to reiterate to anyone joining this thread more recently, that the MOK 8F kit that I am building was bought in 2010 and has been upgraded by MOK at least twice since then. Just in case anyone reading the thread is put off buying an MOK kit by reading my journey.

Additionally, when I started building it back in 2012, I didn’t have much experience (or confidence) in loco building. Hence mistakes were made by me and no fault of the kit through inexperience\lack of confidence. Which I now need to revisit having gained experience and confidence to rectify those mistakes in the meantime.

The latest of them being the realisation that the two rear compensation beams don’t move fully in one direction which leaves the second from the rear axle sitting lower than the others without any upward movement that should be allowed by the compensation beam.

Examination of the chassis has revealed that the issue is caused by my siting of the spring hangers for the second axle so I need to take them off and make adjustments to allow the full range of movement

It also doesn’t help that I had gone so far in building the kit as an LNER 06 but when I bought the whistle of Swindon Built 8F 8425 and decided to base my model on that example instead it required a few changes. Which are again, nothing to do with the quality of the kit as supplied.

When I mentioned them a couple of posts ago, I had also forgotten to post the retaining pins that I had made for the other joints.

I was a little concerned that I had the heads too thick but having looked at the GA and a number of photos, I have them about right.

These, were another little job that was quite satisfying and very therapeutic.

Stepping back slightly Ian Allen posted on the Guild forum that he’d had to add a small piece of brass angle to the rear of the valve guide casting to prevent the valve block from lifting. After making a note of it in my mind to watch out for, I was thinking about the potential problem while shaving this morning and I realised that I had probably solved the problem without realising there was a problem to be solved.

My retaining screw for the combination lever in the valve block is a 14ba steel screw which screws in from the back. The head of the screw protrudes into and slides, in the slot in the rear of the casting which I had enlarged previously.

I had done a similar arrangement on the Princess.

The first one was a success in terms of increasing the range of movement I made it from 5mm Nickel bar and in the end, I made four.

Ultimately leaving me with this

The two valve blocks together

This is the difference that they make in the amount of travel.

One problem solved so onto the next…

After taking a few days off to do a video for the upcoming Gauge IO Guild Virtual show I returned to fitting the motion on the 8F. True to form it continues to entertain and frustrate in equal measures.

I started by fixing the links between the Drop Link, Union Link and Combination lever together with the pins and retaining washers that I made previously for the task.

It was once I had these assembled that I realised that once fitted in place the crosshead travel in the slide-bars was being limited by something and as it was it wouldn’t allow a full revolution of the wheel.

This was the limit of the forward travel. Initially I tried a bit of filing of the combination lever to see if that would allow it to move further forward.

This didn’t make any noticeable difference and I came to the conclusion that it was the fit of the combination lever in the “valve block” (? – I don’t actually know what this part is called)

This is what I came with the kit and I had drilled out the hole which was cast as a dimple on the centre line. I concluded that the hole for the retaining screw was too far forward causing the front of the combination lever to hit the lower front edge of the valve block causing the travel to stop at that point this conclusion was born out when I took it apart because one of the valve spindles had bent under the pressure.

I had also enlarged the side openings in the valve guide castings to allow better fore and after movement of the retaining screw.

Having reached that conclusion I decided rather than try to drill out the existing valve blocks and potentially wreck them that I would make some replacements that were a little longer so that I could set the hole further back.

As is my usual practice these days, I measured the castings that I have I modelled it in 3D.

From there I created a working drawing

At this point I decided to make one to test the theory. If successful I would then document the second one.

I didn’t manage to get the motion fitted although much tinkering has ensued. Time was short yesterday due to other things in life but I did manage to spend time making a number of retaining pins and washers to secure the various links together. The kit does provide a number of what are essentially long rivets for the job but their domed head although very nice are not much like the real retaining pins so having taken the measurement of them off the GA, I turned up something that I think will look better.

I did similar on the Princess but didn’t make any washers just adding a touch of solder at the rear of the joint. This time I felt that washers might help in the event that I need to remove them at any point.

They are turned from 1.5mm brass rod of which I have a lifetime’s supply, in the form of an inherited pack of brazing rods.

It is with much relief that I can report that I have finally made the return cranks to my satisfaction. I turned a couple of thin nickel washers to give me a circle to file to and to space the eccentric rods off the face of the return cranks to clear the bolt heads.

Hopefully I will get the rest of the motion assembled and working tomorrow.

After far too many attempts I am almost there with the return cranks. Both my hand filing and my measuring proved inept, when on one of the attempts I managed to forget to take account of the radius of the big end and the whole thing came out a good 3mm too short. To be fair even if it had been the right length, it looked awful too.

For the next and hopefully last attempt I drilled all the holes and made sure that they would centre over each other on the two layers then I soldered one end together and before adding the bolts I carefully marked up the shape of the crank where it transitioned from the big end to the smaller end.

Next, I gripped the crank at an angle in the mill vice (using a parallel to ensure that the edge line was level and then milled down to my marked line on either side.

After some cleaning up and going around the raw edges with more solder to ensure that they remain as pairs I fitted the retaining bolts. I did manage to rescue all eight from a previous iteration then I dropped three of them as I was fitting them to the new cranks.

After coffee and while typing this post, I decided to have another look to see if I could see any of them and was pleasantly surprised to find two of them. They are so small that I didn’t expect to see them again.

Having soldered them into the holes before cutting the return cranks out I idly wondered just how small hex bolts I could make without wasting lots of material by cutting them from thicker stock. So, I cut a short length of 0.9mm nickel rod and was again surprised that my 3-jaw gripped it. I increased the speed again to approx. 2000 rpm (my lathe supposedly goes to 2500 rpm but I didn’t have it on full speed).

On the first try, I had a little too much stick out and almost immediately the end of the rod bent away from the cutting tool. Undeterred I snipped the bent end off and tried again with roughly 5mm stick out. Using a very light touch to allow the speed of rotation and the sharpness of the tool to do most of the work I was able to reduce the stock from 0.9mm to 0.5mm again I did both ends and transferred it to the pin vice for finishing.

I made a few more just to confirm that the first two weren’t just a fluke.

They do need a touch more finishing with a file to reduce the depth of the head to something more bolt like but that’s the easy bit. The more difficult bit will be holding them and fitting them into holes without them pinging off into the ether…

I have had the most frustrating time since my last post on the 8F. It started when I made my first attempt at improving the return crank offerings in the kit. Like pretty much all etched LMS loco kits, the four retaining bolts (which are in reality recessed into the face of the return crank) are represented as four half etched bumps. Or rather the bumps are full thickness, but the surround is half etched. They usually have a second backing layer to make the return crank up to the full thickness.

The original plan was to drill through the bumps and insert some rod to represent the bolt heads. I confess that I failed miserably to get four holes centred on the bumps. Luckily, I had an additional pair of etched fronts in the spares box which I tried first.

Then I thought perhaps I would make a better job if I drilled out the backing layer and placed that over the ‘front’ layer to leave the etched bumps inset. This I have to say worked perfectly. Sadly, it all fell apart when I soldered the two together. Solder leeched into the holes and filled them completely covering the bumps.

I tried plan B, which was drilling the holes out again and inserting stubs of rod into them. This too failed miserably in so much as the holes ended up offset and the results looked a bit like Marti Feldman.

It was at this point last Monday when I inadvertently rubbed something (I am not sure what but it may have been flux) into my eyelid. It immediately started to itch like mad. By Tuesday morning my eyelid was so swollen that I could barely open it. Tuesday and Wednesday were spent sat listening to audiobooks, with frozen teabags on my eyelid trying to get the swelling to go down. By Thursday I could open my eye a little and I was feeling a bit stir crazy, so decided to go into the workshop and do something.

I started by scanning and importing the outside motion GA from the Wild Swan book into Fusion 360. I scaled it to 7mm scale and sketched the return crank creating a 3D model from it and then from that created a working drawing.

Taking measurements from the drawing for the holes, I transferred them onto some strips of nickel silver which I had cut at 6mm wide. I had prepared 3 strips one for the front layer with 1.6mm holes, one for the back with 0.9mm holes and a third which I drilled with small holes at one end and larger holes at the other. Having something firm to grip in the vice of the Proxxon Mini Pillar drill and using the coordinate tables I was easily and repeatably able to drill the multiple sets of four holes. I also drilled the hole in the other end to tap 12ba for the fixing. More on this later!
At this point I decided to solder them together, then make and fit the simulated fixing bolts. With the view that if I couldn’t get that right at this stage of the proceedings, then there was no point in wasting time filing them to shape.

On my first attempt, I had filed some hex ends on some nickel rod and soldered that into the holes, but this time I decided to see if I could improve upon that. I cut a short length of 1.4mm nickel rod, fitted it in the 3-jaw chuck on the lathe. I would normally have used a collet but the chuck was already mounted so I thought I would see if it tightened close enough to grip such a thin rod. It did so with some movement to spare.

With a very sharp HSS cutting tool, a fast RPM and a very light feed rate, I was able to cut the end of the rod down from 1.4 to 0.9 in one pass. The secret is don’t have too much sticking out of the chuck. I would guess that I had no more than about 6mm protruding. I did this on each end of the rod and then transferred it across to my hex headed pin vice. Using the hex head as an index I filed a short length of the full width rod into a hex to represent the bolt head. Then using my trick of gripping the tail end in a second pin vice to prevent it flying off into space when it cut through, I sawed it off with a piercing saw.

I confess that I found making them quite therapeutic and I got a little sidetracked. I was also amazed at how much of the rod I was able to actually use.

Remarkably quickly I had the eight that I needed and a few for the spares box.

It was kindly pointed out that I had the expansion links fitted the wrong way around. Thankfully they were screwed in from the back to a relatively easy fix, but it also gave me the opportunity to correct something that I had been too lazy to do until I had to unsolder the forked end to swap the expansion link around.

It’s not really visible in the photos but the pin that goes through the radius rod to connect the links which attach it to the reversing gear is flush on the photos in the earlier shots. It now has a protrusion to represent the end of the retaining pin. Which was present all along, but on the inside. This was due to my swapping the radius rods over to get them to better align with the top of the combination lever.

In between the festivities I have been making further progress on the 8F chassis and motion. Way back I had bought a full set of motion from Premier in ignorance at the time that sometimes for whatever reason the kit centres don’t always match those of the Premiers rods. In this case the coupling and connecting rods are fine but most of the others aren’t. I had previously spent some time fitting forks to the radius rods but I hadn’t assembled enough of the motion to check that they would actually fit.

Spoiler alert, they don’t.

Which was a bit of a shame because I had also fitted a sliding block for the reversing links. Hey ho, I still had the kit rods so I made those up.

I had in the past, determined that the Combination levers for my engine should be fluted, whereas the Premier rods are plain. So, they too are in the spares box, as are the Union links because I couldn’t see how I might make them forked.

Returning to the coupling rods, after shortening all the bushes I decided that I couldn’t live with the brass bushed for the two front axles because they ultimately become the ‘crankpin nuts due to lack of clearance on the prototype. So using the nothing looks like steel than steel maxim I made some replacements from steel and I also made up some of the large flanged nuts that retain the rear of the coupling rods.

After this image was taken I did thin down the flanges somewhat.

Next up was recessing the coupling rods at the first pair of holes.

I machined up a stub of bar that was a close fit in the coupling rod holes and fastened them to my Metalsmith drilling plate. Using the stub of ba as a locating pin I was able to adjust the mill tables until it dropped smoothly into the hole and then swap the stub out for a 4mm slot drill which I used to recess the our hole for the flange of the bush.

You will note the black marker spot on the side of the rod. This was to ensure that I didn’t inadvertently recess the wrong end…

Here we are to date with the bits that are fitted so far working without catching or unscrewing them selves when the loco runs in reverse. The next job is the return cranks when I will determine if the Premier Eccentric rod, fits or not.

One of the many things that I love about having a lathe, is the fact that it makes it so much easier to get a consistent result while tackling some of the more tedious tasks in railway modelling.
A task that I have aways found tedious*, is cutting/filing crank pin bushes to length so that they allow some play in the coupling rod and don’t bind or unscrew themselves when running in reverse.

*Mainly because although I can follow a line with a saw without too much difficulty, I really struggle to file surfaces at 90 degrees to the edge.
To get around this on the 8F, I turned up a little Arbor from some mild steel bar (more recycled toner cartridge rod). I threaded the end 10ba and using a 10ba nut, I was able to fit the tapped bush on the end then lock it with the nut and quickly and consistently remove 0.9mm from each one.

I have spent the last week or so fixing a number of mistakes that I made back when I didn’t know any better. For example, I realised when trying to fit the wheels that I had assembled the Premier coupling rods as a pair rather than handed, so one side only fit inside out. At the back of the workbench, I found an old pin punch. I popped it in the lathe and turned a small spigot on the end, to allow me to carefully pop out the rivets and swap the sections of rod around.

Once corrected I was happy to find that the rods ran smoothly in both directions without any sign of binding.

(As an aside I do like the built in motor restraint which is a nice bit of design work.)

The next bit of corrective action took most of a day to sort out. I had previously bent and fitted the two steam pipe sections that fit between the grease separator and the exhaust steam injector. These are made from 3.1mm copper rod which takes a bit of working to shape. Fast forward a few years and the grease separator casting had come adrift from its mounting pad and I hadn’t actually secured the front section of pipe. It was just pressed into the front flange of the grease separator casting. Without paying much attention I soldered the grease separator casting back in place and moved on to more of the motion parts.

While working on these I thought that it might be wise to fit the wheels and check that the Premier coupling rods matched the MOK wheel base and that I had a smooth-running chassis. It was at this point that I realised that the route of the steam pipe prevented the rear axle from moving through its full travel once the motor was fitted – The rear axle sat a good millimetre higher than the front axles. So, I removed the pipe (and the castings at either end) adjusted them and refitted to find that the pipe now hit the tyre on the rear wheel.

At this point I stopped refitting the castings and just kept adjusting the pipe bends. I did much of this with the aid of my vice, a thick-walled steel tube filled with lead and a white rubber mallet. I also made use of the “Markits” BA nut spinner set for making the tight tweaks to the very end bends after finding that the 8BA size just fit over the copper rod. I spent a couple of hours on Christmas Eve and around six hours yesterday before I finally got it to fit in place and clear both rear wheel and allow full vertical movement of the gearbox.

In reality once I come to set the ride height, the vertical movement of the gearbox may be less of an issue but better safe than sorry.