Constructing the Martin Lewis Little Engines Northern Tender

[Carrdo]

Now working on the roller assembly.

[Carrdo]

A summary of the operations needed to finish the two roller assemblies. There are quite a few of them. I think the photos show the main points.

Just ensure the carrier blocks are well supported internally and well clamped in the vise of the mill as one nearly got away from me in one of the milling operations.

The rollers clear the bottom of the carrier block floor by 0.007" and that is the distance the rollers project above the top of the carrier blocks also.

[Carrdo]

As one can see in this photo, I don't always follow my own design sketches but I like the result.

[Carrdo]

The four wheel trailing truck new rear girder with bottom roller plates attached.

I did not like the existing part so a new rear girder (a cut down 1" commercially purchased channel) was made exactly to the Martin Lewis print.

[Carrdo]

More work on the four wheel trailing truck and further unpleasant surprises.

It is obvious from what I found that the original builder(s) did not possess any type of milling equipment. All of the ends of the inner and outer side frames had been filed, were of an uneven height, were not square and one of the tapped holes had been mis-drilled so that half of the thread came out through the side of the frame. What a mess!

Fortunately, I do have a very large ribbed quality angle plate which has saved my bacon many times and this was pressed into service once again.

The entire trailing truck was set square on this plate and an elaborate clamping system was employed so the ends of the truck were exposed to be able to gingerly end mill the ends of the cast frames both square and level.

The mis-drilled tapped hole was dealt with, as before, by plugging it with a bronze 5-40 NC fastener and then silver soldering it in as I could not rely on the plug to hold sticking half in and half out of the side of the frame. It sounds simple but many lost hours were involved not to mention the nerves involved. After that, I had to re-assemble the angle plate setup once again to re-drill and tap a new hole central to the frame width (as it should have been done in the first place).

But that was not the end of the fun. After producing a new end girder to the Martin Lewis print, one now had to pick up the 8 existing drilled and tapped holes in the ends of the side frames to attach the new girder. Again, I could use the existing old end piece as a drill guide but the old and the new parts did not fit together so that option was out. I would have used the transfer screw method except my transfer screws do not include a 5-40 NC one so I resorted, in desperation, to the tried and true method of trial and error!! It took 4 attempts each one getting me a little closer to the correct hole layout but not close enough. Insane, but I finally got an acceptable drill template.

I did not take any photos of this as I was too distraught by it all.

[Carrdo]

After that little bit of drama, things went rather smoothly.

It was then back to my rather complicated setup as the ends of the trailing truck side frames also have to have a square recess milled across them to accept the bottom roller plates which are attached to the new end girder. Just ensure that nothing moves (as one has to clamp the axles and the side frames separately) and use a sharp cutter and light cuts to minimize any twisting, grabbing or yanking forces.

[Carrdo]

The final drilling and tapping operation to attach the roller assemblies to the bottom roller plates.

Everything is now in place and works as it should. I did made some adjustments which I won't describe to increase the roller gap height so the rollers do not raise the back of the locomotive and reduce the weight on the rear set of main drivers. This locomotive does not have any spring rigging equalization on either the leading or trailing trucks so I cannot shift weight to try and compensate.

The final proof will come when the locomotive is finished and out on the test track.

I am hoping that virtually 100% of the locomotive's weight will sit on the main drivers as I am fighting the scale effect in 3/4" scale (i.e. the weight of a model locomotive decreases much faster than its size as the size of the locomotive is decreased which drastically affects the factor of adhesion which the model can develop). I do not want to have a very slippery locomotive, if at all possible, and the scale effect almost mandates this. If one wants to know why, there is an excellent article in the Model Engineer on this and other factors by Jim Ewins entitled Model Locomotive Research.

It may not be possible to achieve the above and still have a locomotive model which is stable on model track (i.e. one which wants to derail) so I may have to alter things to put some weight on the leading and/or trailing trucks which of course will take weight away from the main drivers. It is all a compromise between the many conflicting factors inherent in both model and full size steam locomotives.

[Carrdo]

Why does this always happen to me!! Moving on from where I left off.

I think the northern chassis is now complete so I wanted to test it out on air. There were some test fittings which came with the original engine so I thought just go ahead and use them. Pretty straightforward, but wait a minute, when I looked closely at the fittings they were a 7/16-24 NS (national special) thread on the cylinder steam inlet fitting and a 1/8 -27 NPS (national pipe straight and not a NPT national pipe tapered) fitting on the air line end. I guess this proves just how old this chassis is.

I didn't have either so I located and purchased the two non standard taps on fleabay. I could have changed everything out to a modern standard and remade the fittings but to keep it original ... I know that NPS fittings are not designed to be used in pressure applications but I have a way around that.

Then things escalated. The air test assembly was not quite long enough to directly fit the cylinder inlet steam lines without adding very short extensions on each branch. And they needed to be slightly curved as well. I could have thrown everything out and remade each branch longer as a one piece unit but do it the hard way again!

I had originally planned and bought a fancy tube flairing kit so as to be able to make a double flair on each of the copper tube ends to but you can't do it with short curved pieces of tubing (you need straight ends) so scratch that and look at commercial compression fittings. Also, the extra 1/4" dia. tubing which I wanted to use was so convoluted, I couldn't use a standard tube cutter to cut short pieces from it so do it the hard way again using a fine jewellers piercing saw to cut the tube by hand by laying the tube on top of the vise jaws. Don't try and hold the tube itself in a vise or you risk squashing or distorting the tube.

None of the above is ever encountered or any explanation given on what to do in such a situation (on any Youtube videos or model engineering articles etc. which I have ever seen) so...

So now having two very short copper tube extensions, the first operation was to fully anneal the copper and then re-circularize the softened ends by inserting a number 13 drill or a smaller size #drill (if the copper tube ends are really distorted) and working one's way back up to a number 13 with light circular tapping on the copper with a non metallic light hammer. This allows one to then install the compression ferrules and the compression nuts.

Half the battle won. to be continued.

[Carrdo]

Some further photos.

And after all that tapping and reforming, the copper pieces were annealed once more.

[Carrdo]

The entire Rube Goldberg inlet tightened and ready for the air line hookup.

[Odyknuck]

Right when you think your gaining on it, always seems to be something to trip you up lol.

[bushav]

I am so glad you posted the above picture. I am just weeks away from the same process. Seeing your setup will make my planning easier. I had not even considered putting a quick connect coupling in the line. I like the way your reversing links are shapped. The Hoffman plans have a blockier shape for the links which I machined as drawn. Your shape is prettier to me. It amazes me how long these locomotives take to build and then how long they are used afterwards. It is really a project of patience.