Making Tracks

[Chariots of Fire]

The Diamond T M-20 prime mover is going to be hauling a load eventually.  Right now the trailer is in the initial stages of being designed for construction.  Tire and wheels are ready for multiple castings.  In the meantime I opened up one of the old AMT Caterpillar D-8 kits to see if it could be modified into a D-7 cable hoist bulldozer that was used during WW II.  The M-20 hauled these as well as other goods and munitions so it made sense to try and make one up for a loaded trailer.

AMT did the Cat D-8 but its tracks are awful.  Not only do they not look right, they go together wrong as well.  Each track should be connected to the next one with links that are bolted to the track plate above.  After a bit of thought I came up with a way to make new tracks that not only looked right but also went together right as well.

One of the side frames of the AMT D-8 is in the background with the kit tracks in front of it.  In front of them is a first start at making a new set of tracks.  The master track plate was made of brass and plastic hex rods were cut for bolt heads that hold the links to the plate.  The ones you see are too large so before the final track master was made I sanded them off and used a smaller size of hex rod.  The initial mold is on the left for the track plate.  To the right is the second mold that casts the plate and the links all as one.  This makes it possible to do many track plates and links that are all the same.  The links are held together with plastic rods.

In this second photo a first casting of the combined track plate and links has been done.  This is how it looks with the top of the mold removed.  Lots of thin flash but it comes off easily.

Out of the mold the completed track plate looks ok.  But it has some minor flaws that need correcting.  When the mold is filled with liquid resin if it does not completely fill the hidden voids in the mold air pockets result and in turn an incomplete casting.  It happened this time but not severely.  I can fix the void with a bit of putty.  The next casting hopefully will be better.  It just takes patience.

The back side of the link shows that the ends of the links on one side did not get fully formed.  Not serious but this needs to be avoided as much as possible.  In the photos above are the cast tracks so far.  The five completed tracks on the left are from the final mold.  The right four are as I initially made them attempting to make the links separately and then gluing the plates to them.  These first attempts are not as good.  And you can see, reducing the size of the bolt heads made them better as well.  It will take a while to do enough to complete a full set like what is on the left but I'm in no hurry.  I think there is somewhat of an improvement anyway. ?

 

 

 

[Biggu]

Wow, now THAT is modelling. I bet if you made your tracks available to the masses they would sell like wild fire ! What a fabulous improvement , Charles. I am watching this build with excitement and awe. This is going to be epic. Can't wait for more …..

Jeff

[yh70]

your track pads look great, but if you ever build another D8 three aftermarket company's offer replacement tracks for it if you want to save you some time...

[Chariots of Fire]

1 hour ago, yh70 said:

your track pads look great, but if you ever build another D8 three aftermarket company's offer replacement tracks for it if you want to save you some time...

This will probably be the one and only.  I know there are some 3D printed ones out there but they are big $$$!

[BK9300]

Charles, great engineering going on here. You have many skills I have yet to acquire and casting is one of them.  Always educational!

[Rockford]

I can't even drill a hole in the right place! You've got some patience to do that. As with all your jobs it will look fantastic when you complete it. 

[yh70]

21 hours ago, Chariots of Fire said:

This will probably be the one and only.  I know there are some 3D printed ones out there but they are big $$$!

 these were only $60 shipped..and yes they are some at $100 a set.

[Chariots of Fire]

Looks like I'm pretty close on the workup of the tracks.  I may have to tweak the sprocket drive a bit but other than that they will fit just fine.  $60 is not bad.

[hct728(Bob)]

A lot more authentic looking, but all that repetitive work! I'd be tempted to cast a few then assemble a straight strip and cast as a unit for the horizontal sections, maybe the resin could handle a bit of sag when installed. Amazing work again, Charles!

[Chariots of Fire]

3 hours ago, hct728(Bob) said:

A lot more authentic looking, but all that repetitive work! I'd be tempted to cast a few then assemble a straight strip and cast as a unit for the horizontal sections, maybe the resin could handle a bit of sag when installed. Amazing work again, Charles!

Thanks, Bob!  I'm just a glutton for punishment, I guess!  So far I have 22 tracks done of the 36 or so that I need for one side.  Also ran out of casting resin so more is on the way.  

[Russell C]

On 8/18/2024 at 10:52 AM, Chariots of Fire said:

... AMT did the Cat D-8 but its tracks are awful.  Not only do they not look right, they go together wrong as well.  Each track should be connected to the next one with links that are bolted to the track plate above. ...

There's a way to do them wrong in 1:1. Over a decade back when I worked at a steel foundry, one of the jobs was to cast huge track pieces for some open pit mine dragline shovel or something. When molten metal cools, it shrinks a bit, so when the open bolt holes are part of the casting pattern, those holes need to be in the right place after the metal cools, for final machining to be done. Problem was, when the tracks for this job were all pinned/bolted together, instead of laying out in a nice perfect straight line, there was a gradual curve happening, I saw that myself when they were laid out alongside the pattern shop. My boss, the pattern shop foreman was blamed for not planning for the right kind of vents to go into the sand cast patterns, thus causing improper shrinkage. He blamed the metallurgist for not factoring the right mixture of whatever went into the steel to ensure predictable shrink results. Most intense hostile shouting match I'd ever seen in a workplace. Tens of thousands of dollars (maybe more!) of tracks that had to be completely scrapped, there was no way to fix the curve problem. My boss ultimately quit rather than sign acceptance for causing this foul-up.

[Chariots of Fire]

You are right Russell.  Just a bit off on the location of the connection holes and the result is a curve.   I noticed that in what I am doing since each link is cast from the same mold.  Fortunately this can be corrected by a bit of cleanup of the holes where the connecting pin goes.  (Hope I don't get fired!)

[PHPaul]

I 3D printed a set for a 1:16 metal toy I was fixing.  Not the same level of detail, but WAY better than the rubber strips normally used.

[Chariots of Fire]

2 hours ago, PHPaul said:

I 3D printed a set for a 1:16 metal toy I was fixing.  Not the same level of detail, but WAY better than the rubber strips normally used.

With 3D just about anything can be printed nowdays!  I haven't reached the 3D plateau yet except to order some 3D parts from someone who does that sort of thing.

[PHPaul]

Quote

21 hours ago, Chariots of Fire said:

With 3D just about anything can be printed nowdays!  I haven't reached the 3D plateau yet except to order some 3D parts from someone who does that sort of thing.

 

You'd be surprised how easy it can be.  Entry level 3D printers are very affordable, and the design (TinkerCAD) and slicing (Cura) software are free.  I picked up the basic functions of TinkerCAD in 2 or 3 sessions.  If I get stuck on how to do something, there are a multitude of YouTube tutorials.

[Chariots of Fire]

5 hours ago, PHPaul said:

You'd be surprised how easy it can be.  Entry level 3D printers are very affordable, and the design (TinkerCAD) and slicing (Cura) software are free.  I picked up the basic functions of TinkerCAD in 2 or 3 sessions.  If I get stuck on how to do something, there are a multitude of YouTube tutorials.

Thanks for the info, Paul.  I will keep it for reference.  Just made a new piece of the sprocket for the final drive.  Will cast it up in several pieces to get the right thickness.  I'm finding more and more about the D-8 that is nowhere near like the D-7!

[Bainford]

Very nice work. Thanks for showing your process. The tracks look spot on. 

[Chariots of Fire]

Got one side completed!  There are 44 separate pads and links on just the one side with 45 connecting pins.  They fit the D-8 sprockets quite well.  I ground down the drive sprocket just a bit so that the pins fit into the notches better.  Not to get the other side done!!?  Silver tracks are from the AMT kit.  White ones are mine.  I'm happy with the results.

 

 

[BK9300]

No comparison - your new treads are considerably better - like the retainer ring system for your pins, too

[Biggu]

Brian is right. No comparison, apples and oranges ….your new ones are beautiful and will make this kit spectacular !

Jeff 

[gotnitro?]

Fantastic work on the tracks, such an improvement 

[ChrisR]

We need someone to step-up and cast them.

I don't think anybody are selling any at the moment.

[Rockford]

They're absolutely fantastic. You can see the effort that has gone into them, so crisply moulded and proper individual pieces like the real thing, the droop in the middle of the top layer is just so realistic! Your patience has definitely been rewarded there, although I bet you're sick of the sight of them now! Well done for persevering.  

[Chariots of Fire]

3 hours ago, Rockford said:

They're absolutely fantastic. You can see the effort that has gone into them, so crisply moulded and proper individual pieces like the real thing, the droop in the middle of the top layer is just so realistic! Your patience has definitely been rewarded there, although I bet you're sick of the sight of them now! Well done for persevering.  

You got that right, Steve!  A very slooowww process indeed!  I will put them away for a rainy day project!?

[Chariots of Fire]

FINALLY!  The other side is done.  I don't know what happened during the casting process, whether one side of the AMT kit is shorter than the other or not but the second set of tracks has one less plate in it than the original side.  If I put the additional plate in, the tracks are way too loose.  So if nobody counts, they won't know the difference (except that I have now told you all). ?

So here's what they look like on a partially built up AMT D-8.  The kit was one I bought at a show and some of the parts were already together so rather than pull out another kit I decided to do up this one with some additional scratch building along the way.