A Plastic Screw for an N Scale Con-Cor PA

This week I’d hoped to show you the 3D printed replacement Minitrix Crosshead from last week’s post however due to the heavier than normal snows last night I’ve had no delivery today. So this week I’ll share with you something else which should also be arriving soon.

The venerable Con-Cor Alco PA has been around since 1967 and has been improved over the years but the original design, made by Kato under the name Sekisui, can still be found going strong on many layouts; mine included.  One of the things which made this design different from the later is how the chassis sections are fixed together.  The original design had a solid metal section on the top and two metal sections below, one making contact with each rail through the trucks. Between the top and bottom sections is a strip of plastic for electronic isolation.  It’s all clamped together with screws, metal ones on one side to conduct power from the lower section to the top, and plastic screws on the other to isolate that section.  This works well, but the plastic screws, if removed a lot, can easily be rounded off.  Plus if you drop one into the bottomless depths of an exhibition hall they are very hard to replace.

But thankfully I have a solution.

These have been designed to be 3D printed in Shapeways’ Frosted Ultra Detail material to give the required accuracy for the thread and hardness for the actual screw.

Hopefully these will be delivered soon, along with the other parts, and I will be able to share some photos with you next week.  Plus it will be nice to have my Alco PA back on the tracks.

3D Printed Minitrix Cross Heads

Trix produced a variety of locomotives including a range in N scale, dating back to the 1960s, under the name Minitrix.  Many of these shared common parts and it’s one of these for which I’m creating a replacement; a Minitrix valve gear cross head.

This particular cross head will be for the A4 steam locomotive model shown below.

The cross head is the gray slider which connects the piston and the main connecting rod.  This plastic part slides up and down the metal runner as the piston goes in and out, keeping it level and it also connects the valve gear linkage.

As with a lot of the early plastic parts these can become very brittle and start to break up.  Almost all the other parts of the locomotive’s motion are made from metal, the only exception is the crank pin which drives the eccentric rod.  This is also made from plastic and I’ve previously made this as a replacement 3D printed part; you can read more about that here.   You can identify the crank pin in the first image as it’s gray and not silver, just like the cross head.

The original cross head is a very small part and very difficult to photograph up close so the image below is my 3D model of the part, without any modifications.

The cross head is symmetrical so it can be used on each side of the locomotive.  The box section on top has slots in the sides to allow the slider to pass through. Below the box is a pair of rings, the first connects the cross head to the connecting rod and piston.  As these are joined with a pin the connecting rod is able to rotate as the cross head slides back and forth. The second ring connects to the valve gear linkage, again with a pin allowing it to rotate.

The weak spot on these parts is where the rings connect to the box.  If the valve gear becomes jammed and the wheels keep turning a twisting force is applied at this point. If the plastic has started to break up it will simply snap.

In the image below you can see three cross heads with the original on the left.  The middle one has had the weak area under the box strengthened by adding a larger amount of plastic.  The right hand side one has also had the area between the loops strengthened in the same way and it’s this version which I’m test printing.

This cross head fits most of the British outline steam locomotives including the Gresley A3, A4, Standard 9F, Ivatt 2-6-2 Tank and the Ivatt 2-6-0.  Only the Britannia 7P had a different valve gear with a simplified cross head consisting of a folded metal plate.  Minitrix also made two steam locomotive for the American market, a 4-6-2 K4 and a 2-10-0 Decapod.  As the 2-10-0 shared the same chassis as the 9F this also has the same cross head.  The K4 shared the simpler Britannia 7P chassis.

The part has now been printed by Shapeways and I’m expecting it later this week, and once tested will be made available to buy. It’s often these small, seemingly insignificant parts that aren’t glamorous or even particularly interesting, that 3D printing really comes into its own. The ability to modify, improve and manufacture replacement parts at a fraction of the cost of replacing the locomotive means we can keep the majority of our stock rolling, and it’s why I continue to produce these parts.

Shapeways Special Offer

When it comes to internet sales today is considered to be one of the busiest in the year; Cyber Monday!  And not wanting to leave anybody out Shapeways are offering 10% off and free shipping on any purchase over $25.  Ideal if you were considering one of my recently orientated locomotive shells which you can read about here!

This offer is only available today, November 27th 2017, and runs out at 11.59pm PST.

All my Shapeways products can be found in my Shapeways shop here.

All you need to do to get the offer is enter the code ‘MAKEYOURHOLIDAY’ at the checkout, and purchase more than $25.

Happy Shopping!

3D Printing The Right Way Up

In last week’s post I spoke about Shapeways’ ‘Orientation Tool’ for their FUD and FXD materials and my intention to make all my locomotive shells available with this option.  You can read the post here.

My plan was to have both the new orientated models available as ‘Deluxe’ versions and the originals as a cheaper option.  And that’s what I’ve done with the Alco C-855 and C-855B.  However, after working through the other models it became apparent that the price didn’t really change.  By moving the position of parts the price of the model dropped and so the increase caused by using the ‘Orientation Tool’ setting was offset.  So all the other models have simply been converted to have the ‘Orientation Tool’ set for the best quality print by making it print the right way up.

Locomotive shells without the orientation set:

Alco C-855

Alco C-855B

Locomotive shells with the orientation set:

Alco C-855 Deluxe

Alco C-855B Deluxe

Alco C855 Shell Only

Alco C855B Shell Only

Baldwin DT6-6-2000

Baldwin DT6-6-2000 Dummy

Baldwin DT6-6-2000 Shell Only

Baldwin RT-624

Baldwin RT-624 Shell Only


EMD DD35 Dummy

The new locomotive shells I’m working on will all be set to the best print quality from the start and the models will be designed to make them less expensive in the printer.  So for now the ‘Deluxe’ versions just apply to the large Alco C-855s but maybe this will come in useful with some of the HO scale locomotives I have planned, allowing me to offer differently priced versions.

Getting Things The Right Way Round

3D printing locomotive shells with Shapeways has always been a gamble as regards to the orientation of the shell on the print bed.  Understandably, in order keep the cost of the print sensible, the print ended up on its side or totally upside-down as this is the cheapest way for them to print.  The disadvantage is often the best surface finish would be on the underside of the model.

However back in the beginning of October this year Shapeways added their ‘Orientation Tool’ for the FUD and FXD materials allowing the 3D print orientation to be fixed by the designer; me!  You can read more about the tool on my post here.

My original intention was to immediately set all my locomotive shells to print orientated in such a way as to give the best finish possible.  But this does come at a cost,  especially with large locomotives like my Alco C-855 which has a huge volume of space under the shell.  This space needs to be totally filled with support material in order to print the roof.

After experimenting with different compromises and ideas I came to the conclusion that I didn’t want to cut corners; the best has to be available for those who want it but it was unfair to simply push all the prices up to achieve this.  So I have decided to offer both:  prints as they have always been as well as the shells with the orientation which will be set at the higher price.

My new models on Shapeways will be called ‘Deluxe’ and will include the Alco C-855 & C-855B, the EMD DD35 and the Baldwin DT6-6-2000 & RT-624.

Both models will be offered in FUD and FXD materials.  The FXD ‘Deluxe’ will be the ultimate 3D print available.  Hopefully all the models will be available on Shapeways by next week’s post.

As for new locomotive shells designs, well, I may design them differently.  Doing things such as making the roof a separate part would bring the cost down dramatically by reducing the amount of support material needed, but this does raise some stability issues as well as creating a joint which would need to be concealed. However that’s the challenge, and I do have something on the drawing board, but that will have to wait for another post.

A Well Deserved Rest

As you may have read last week, my local club, the Poole & District Model Railway Society, have just had our annual exhibition, and being the Exhibition Manager it has been a busy time for me.  But the show went very well and I think everybody had an enjoyable time.

So this week’s post will simply be to say thankyou to all the visitors, exhibitors, traders and members of my club who worked the show, because it takes all of you to make the exhibition possible. I’m now going to take a few days off.  Next week I should be back to 3D printing projects!