This week I have an update to share with you regarding my N Scale Minitrix eccentric rod crank pin replacements.
Back in September of 2015 I wrote a post about repairing Minitrix steam engines which had suffered with broken eccentric crank pins. You can find the post here. These fit A3, A4, 7P (Britannia), 9F, US K4 and US 2-10-0 Decopod steam locomotives.
The crank pin, as illustrated below, has a square peg which fits into the actual wheel and a hole which receives a steel rivet linking it to the eccentric rod.
Although these worked and allowed the repair of the locomotive they did have a few issues. Their small size made them rather delicate and it was easy to break one when attempting to refit the rivet. So I originally offered spares in each pack as it was almost certain to happen on your first attempt.
This lead me to improve them by slightly increasing the size of the loop and the size of the rivet hole as shown below, the newer Mk2 pin is at the back.
This did help and made it much easier to reinstall the rivet. But the issue of re-flaring the rivet was still a problem and I was finding it hard to do as I couldn’t get a supply of new rivets. This lead me to start cutting part of the loop away to leave a ‘C’ shape which could be forced over the rivet. As it is a ‘C’ shape it would not fall back off the rivet and the rivet didn’t need to be un-flared in the first place. The original peg, what was left of it, could be cut away and the new one could simply be clipped in.
But it was hard to cut the hoop in just the right place without braking the hoop. This lead me to upgrade the model again to include three Mk2 parts with a complete hoop and three Mk3 parts with a ‘C’. Below you can see the Mk2 and Mk3 crank pins. Supplying both, I thought, would give you the option as I was unsure as to how well the Mk3 ‘C’ type would work .
Then in June 2017 when Shapeways restructured their pricing system this model became rather expensive as each individual part had an additional $1 handling charge added to the cost. But the answer is my new Mk4 version of the crank pin which you can see below.
The crank pins are now supplied in a frame. Although they are not attached to the frame they are 3D printed in the configuration shown above and the loops prevent the cranks from falling out. The whole model is therefore treated as one piece.
There are eight cranks in each model, allowing for spares, and all have the ‘C’ shaped end which I’ve now used successfully on every loco I’ve repaired since printing the first ‘C’ shaped crank. Also having spoken to several of my customers they confirmed they didn’t use the cranks with the full hoop at all.
And as the cranks are now held together it makes them easier to not lose! When you need one simply cut the restraining hoop.
The new Mk4 crank pins can be found here.
Next week I’ll have an update on some of my 3D printed couplings.