NS class 5000

Chassis construction (finally!)

After all the preparatory work on the chassis and the gearbox I was at long last ready to assemble the chassis. It may seem a long way to get there and it truly was. But it is a good thing to ponder all possibilities and interdependencies between chassis and gearbox before the final assembly so you can always retrace your footsteps. This is my first loco for which I changed the original drive substantially and it paid off to take my time. At least I now have the confidence to assemble the frame. There we go...

In the closing stages of the preparatory work I mentioned that I soldered three axle bearings in place. The remaining seven holes were reamed larger than strictly necessary giving all other bearings a play of say 0.5 mm. What is the fun of it? Well, once I hook up the frame in the chassis jig with the witness axles in place the loco frame will be fixated by the three "datum" bearings already soldered in place (yellow circles)

the two middle axle bearings fixate the lateral position of the frame (red arrow)
one bearing on the rear axle fixates the longitudinal position of the frame (red arrow)

The seven somewhat oversize holes allow the witness axles to algin the remaining bearings correctly once the coupling rods are placed on the outer end of the witness axles. Then I know that all bearings are in one level and they are also in line with the axle centres.

The frame plates in the jig with the seven remaining axle bushes separately on the witness axles.

I took the coupling rods out of the etch and found their crankpin holes pretty much oversize. I had a spare set of crankpin bushes from Alan Gibson at hand which fitted like a glove over the provided DJH crankpin. I decided to use them to narrow the holes in the coupling rods. I reamed the holes in the coupling rods and soldered the bushes into the them.

Note: the bushes are made of steel and steel is more difficult to solder than brass. I used 450C in the iron, "S39" flux and took the time to heat it well. Eventually the solder flowed and adhered.

Lower rod done, upper rod original. The difference in hole size is clearly visible.

◄ On the crankpin and virtually without play.

Undoubtedly I will need to ream these holes again after frame assembly, but at least I will know then that it will all work with the least amount of play.

To test if all five holes on one side are equally spaced and aligned with the five corresponding holes on the other side I laid both coupling rod with their faces opposing over five crankpins. They should line up perfectly.

Well, it is a good thing that I checked. Four holes were okay, the fifth was a bit off. When carefully measuring both coupling rods one turned out to have been bent. I realign the coupling rod until it was straight again. Then they went stood the test flawlessly. One important source of trouble eliminated!

Coupling rods on, bushes inserted and aligned

Somehow this setup reminds me of a galley ship.

I lined the frame up approximately in the middle of the jig and moved the seven loose bushes into the frame holes. Six went in without any form of resistance, the seventh just would not fit happily. With some wriggling it went in, but it immediately popped out when I blinked my eyes.

So I took the whole thing apart again, widened the offending hole and reassembled the chassis again. Now it all came together nice and easy.

Then the whole frame was soldered together, carefully avoiding uneven build up of heat.

I did not clean the soldered spots for superfluous solder at this stage. The frame should yet be tested for proper running and if need be resoldered. Until then just the faces of the axle bearings should be freed of solder.

I added the wheels and coupling rods. Despite my high hopes the chassis did not run immediately without binding. That would have been the holy grail, but it was not to be. On the other hand, movement was already so free that I saw no reason to retrace my steps but sufficed to search for the offending holes.

This was the way I took out the remaining deficiencies.

First: the holes of axle number four are left untouched. The fourth axle (from right to left, right is the front of the loco) will be the driving axle and any excessive play here will translate to all four other axles. So I will allow no more play in them then the minimum necessary to revolve around their crankpins.
I removed the crankpins from the first, second and fifth axle.
I added both coupling rods on the remaining four crank pins on the third and fourth axle and tested if the chassis would run without binding. It did. Now that was a good start.
I added one crank pin on the second axle and tested, added the other crankpin on the second axle and tested. I reamed one hole a little and got a good result. I now had three axles running without binding.
I now added the crank pins to the first axle in the same way, reaming a bit more until content
and finally treated the fifth axle.

When it happened that new binding occurred, and it miraculously did despite all care taken, I retraced my steps and corrected. Now is the time to iron out all issues. My aim was to obtain a free running chassis with the least amount of play possible.

At last I had a free running chassis.

Having come to this stage I could my attention tot the final assembly of the drive train and join it with the chassis