Two weeks ago I shared with you my designs for a 3D printed replacement N Scale Minitrix cross head; you can read the post here. This week I have the actual 3D printed cross head to show you.
The design, as pictured below, followed the original closely with the exception of the weaker areas which were strengthened by adding a bit more material.
The actual parts look like this, next to a broken original.
The parts have been cleaned by submerging in Goo Gone for 24 hours, rinsed in warm water and left for a further 24 hours in open air; this is my normal cleaning process for all parts 3D printed in Shapeways’ FUD and FXD materials.
In the image below you can see a new and an old cross head on the slide bar, the slots in the sides are just right to allow the crosshead to slide without being too tight or too loose.
The upper hole on the cross head is for the piston and connecting rod joint and as you can see below this fits together well. The piston is actually a bar with a ninety degree bend in. The bar passes through the cross head then the connecting rod. When it comes to getting the bend through the two parts it needs a bit of a push. This also stops the bar from falling out.
One thing I did learn at this point is the piston bar needs to be fitted after the lower hole is connected otherwise it’s very hard to assemble! So it came out again.
Also, to connect the lower hole, make sure the crosshead is on the slider bar first. Don’t ask me how I know that!
The lower hole connects to part of the valve gear. This time it uses a metal pin. The pin is actually a tube and the end is flared over to prevent it falling out. I carefully un-flared the pin by squeezing it together with a pair of tweezers. Then the remaining part of the old crosshead fell away and I was able to push the pin through the new one. This is probably the stage when the new cross head is most at risk of breaking, so try to make the end of the pin as close to the diameter of the pin as you can. Once it has passed through the pin can be re-flared by pushing in a needle file or something similar. It doesn’t need to be flared much, just enough to stop the pin from passing back through the hole.
The piston bar can now be inserted, completing this part of the assembly.
The wheels and motion can now be inserted into the chassis; this is a really tricky job!
And here we have a repaired Minitrix cross head. The chassis rolls up and down freely and is ready to have the motor and other parts refitted.
I will also try to keep a few in stock, although not until after Christmas, so you can also contact me directly for a set. I will also offer the cross heads in a set, along with my replacement Minitrix Eccentric Rod Crank Pins.
Next week I’ll have another how-to to share with you about coal loads.