D-7 Dozer Project

[Chariots of Fire]

With the M-20 prime mover done and the trailer in the design stage I decided to check out a D-7 bulldozer as a load for the unit.  AMT has done a Cat D-8 but it is not that close to the D-7 in several areas.  One that really stands out is the quality of the tracks.  The kit tracks are shaped wrong and the way they connect is nothing like it should be.  So I've set out to make a new and improved set of tracks and then will concentrate on other aspects of the D-7 that will need modification from the kit.  

The tracks started out with preparing a master made of brass stock.  A section of sheet was heated so that the edges could be bent and then the grouser was soldered in place.  With this done a mold was made for casting the several copies that will be needed for the whole track.  

What was needed, however was a way to connect each track plate.  At first I glued to pieces of Evergreen strip stock together in a staggered form and drilled out a hole in each end for the connecting pin.  It was obvious from the start that this would not only be tedious but not very accurate to keep the connections all the same size and in the same place on each track plate. 

Once an initial plate was done and the connectors were glued to the underside, a second mold was done that would include each track plate and connecting pieces to be cast as one.  This ended the need to drill out each connector as well eliminating the problem of duplication.  Below is the process and comparison of the kit tracks with the beginning of the new tracks.

In the photo above is one of the dozer side beams with some of the kit track pieces joined together.  They look clunky and are not shaped correctly.  Below them is the original master for the new tracks, a series of the initial castings and the two connecting pieces and a pin.  The difference in the tracks is obvious.  Now it is just a matter of casting one complete track link at a time.  The mold to the right is for casting the complete piece.  The one on the left was for the initial plate alone.

In this photo I turned the new tracks upside down to show how each one is linked together.  The difference in how each track is linked to the next one in comparison to the kit tracks is clear.  Brass wire was wrapped around a section of pin stock to make rings that would be glued to each end of the pin so that it would not slip out.  The pins on the left have not been cut to size.  Each track section moves easily against its neighbor and will allow the completed track to be wrapped around the idler and drive wheels.

Above is the mold with the top half removed to expose the track plate.  The flash is thin and easily removed.  Not seen are the two connecting pieces that are embedded in the second half of the mold.

Out of the mold and ready for cleanup.  The trick here is to make sure that the casting resin completely fills the voids that are unseen in the mold to the right.  I had to make some small slits in the end of each one so that I could open up the holes to get the resin in.  The mold is very flexible so it make it easy to do.

The bottom of the track complete with the two connecting pieces.  The only thing left is to clean up the little bit of flash and open up the holes for each pin.  To make sure that the part would come out of the mold I coated each hole in the master with MicroClear white glue.  it filled the hole with a very thin veneer that kept the mold rubber from getting in.  A quick twist of an Xacto knife in the completed casting removes the film from each hole once the casting is set.  The holes are then sized with a round file to the right diameter for the pin.

I just received a copy of the Tankograd book on the WW II D-7 so now I have some studying to do!  More to come.

[manayunkman]

Another amazing build, looking forward to the complete mover, trailer and dozer model.

 

Has any of your work been published?

[Chariots of Fire]

Just an occasional photo in modeling magazines that highlight the various model shows in the area.  No real publications.

[Proud Kraut]

Great to have a look at your casting molds. I look forward to seeing many WIP pictures of one more of your projects.

[Chariots of Fire]

3 hours ago, Proud Kraut said:

Great to have a look at your casting molds. I look forward to seeing many WIP pictures of one more of your projects.

Will do.  The M-9 trailer and D-7 bulldozer will be on-going once I get more casting materials.  There are 24 tires and wheels to cast for the trailer alone.

[Chariots of Fire]

On 8/20/2024 at 6:00 PM, Chariots of Fire said:

Will do.  The M-9 trailer and D-7 bulldozer will be on-going once I get more casting materials.  There are 24 tires and wheels to cast for the trailer alone.

Well things change rapidly now and then.  The more I compare the D-7 to the D-8 kit the more I see things that are completely different.  I'm continuing to cast the tracks but will use them on a D-8 buildup instead.  A modeling friend put me onto a 3D printed complete D-7 kit and I have ordered it.  This will allow me to do a good representation of the D-7 and concentrate on scratch building the M-9 trailer.  More to come!

[Chariots of Fire]

The tracks for one side are now complete.  Quite a difference from the AMT kit tracks.  I've decided to build up the D-8 now using the new tracks.  The D-7 is on order and when it comes that will be built as well as the load for the M-9 trailer.  In the meantime here's a look at the tracks done to date.  The first photo shows how each track section is connected to its neighbor.  A piece of 0.080 plastic rod is used as connecting pins.  There are 44 individual track sections and 45 pins just for one side.  Now the other side has to be done!!😆

 

[Chariots of Fire]

FINALLY!  The second set of tracks is done.  I'm opting to use them on the AMT D-8 and will save the D-7 build for another day when my order for a 3D printed kit of one comes in.  In the meantime I'm taking a kit that was partially started and will finish it up with some additional scratch building details.  Nothing has been done in the way of painting yet.  The entire frame and engine will be primed and then painted with CAT yellow.  The tracks will be painted with brown to start with and then highlighted with other colors and metallics to bring out a used look.  A little built up soil here and there will hopefully make it look like it has been working.

I started the makeover with replacing the solid exhaust stack with a piece of aluminum tubing.  The cover will be made moveable.  It's just sitting there for now but will be set upright eventually.  They actually make a photoetch grill for the D-8 that I may get to replace the solid piece and the decal.  Drilling out all of the holes is definitely out of the question!

[Proud Kraut]

The tracks look fantastic, awesome work so far!

[ArtyScout]

It's so YELLOW.😀

 

Semper Fi. 

 

Manny

[Chariots of Fire]

I got the D-7 kit today and it is an amazing piece of work.  Each part is well done and there are no signs of layering on anything.  Smooth as a whistle!  Each piece is still mounted on the material that was used to form it and there are literally hundreds of little attachment points in a very solid lattice arrangement that I will have to remove.  I'll take some photos of them so you can see what they look like.  I did remove the lattice from the Cat 4 cylinder engine just to see what it really looks like and I'm impressed.  It's like putting together a plastic kit but without the instructions!  Thankfully I have done some studying of the D-7 and I have the Tankograd pictorial presentation of it in detail.  The only change I will make is to replace the hydraulics for the cable system of raising and lowering the blade.  That will have to be scratch built.  Stay tuned!

[Chariots of Fire]

Finally got around to taking some photos of the 3D kit of the D-7.  It came in 5 boxes, two shoebox size and 3 smaller ones.  All of the parts are laced together with a lattice type structure.  This all has to be removed.  But the parts are beautiful!

First a look at the AMT D-8.  The tracks are complete and mounted.   In the foreground are the D-7 tracks.  Much smaller in overall length.  The white pins are temporary and hold the end sections and top and bottom track sections together.  The track pads are just about the same as what was done for the D-8

This is what the parts look like in the boxes.  All that latticework has to be removed from each part.  In the back are the blade and pushing frame.  In the center are the two side frames, the seat, floorboard and top of the engine compartment.  In the front is the main dozer frame.  In front of the tracks is the 4 cylinder diesel engine and to the left of it the two cylinder pony motor.

A closeup of the diesel and gas engines.  Great detail and the parts are smooth.

This is a photo direct from the Scale Collectibles website.  It's built up but not painted.  All in all a great kit.

[Chariots of Fire]

Have done a little work cleaning up more parts on the D-7.  The more I get into it the more impressed I am with the quality of the print.  Here's what it looks like by just putting some parts together.  Long way from glue yet because I need to clean the parts well with some detergent and warm water.

Big difference between the D-8 and the D-7.

[ArtyScout]

Cool.

 

Semper Fi.

 

Manny

[Proud Kraut]

Wow, the D8 kit looks really impressive. Great paintwork on the D7 tracks and chassis. Thanks for sharing these WIP pics!

[Chariots of Fire]

10 hours ago, Proud Kraut said:

Wow, the D8 kit looks really impressive. Great paintwork on the D7 tracks and chassis. Thanks for sharing these WIP pics!

Just the opposite, I'm afraid.  The D-8 is in paint.  The D-7 is not, however since posting I painted the dozer blade and a couple of other parts after cleaning them with detergent and warm water.  So far they look great.

[Proud Kraut]

Of course you´re right. Don´t know why I mixed up the designations this morning...

[Chariots of Fire]

Here are a couple of photos of the build so far.  This has been a fun build but thankfully I have the advantage of several photos of a D-7 in the Tankograd volume.  There are no kit instructions at all.  The tracks are complete but will need a bit more weathering.  Other things are just a dry fit for now.

[manayunkman]

Tracks are a work of art.

[ArtyScout]

Nicely done, so far.

 

Semper Fi.

 

Manny

[Proud Kraut]

Your tracks really look made of steel, awesome!

[Chariots of Fire]

Ok.  Basic work is done.  Now it's on to the LeTourneau hoist and power unit for the back.  No real weathering has been done yet.  It needs to look as if it has seen some work and that will be done with some weathering powders reddish in color similar to the M-20.  But this is where we are so far.  The blade is not finished yet either.  The cable sheave that attaches to the blade needs to be made up and it will be easier with the blade off for working.

[ArtyScout]

As always, this is awesome work, and I enjoy the different subjects.

 

Semper Fi.

 

Manny

[Chariots of Fire]

Got a small start on the LeTourneau cable hoist.  The push bar was modified to have the center double sheave and the framework for the upper sheaves has been started.

[Proud Kraut]

Outstanding! Thanks for sharing your work here!