M-20 Prime Mover

[Firemodeler1]

A new project is now on the workbench.  Started in on a 1/25 scale M-20 prime mover.  Evergreen stock and brass or various sizes and shapes will be used to create the model.  Biggest challenge will be the Hercules Diesel engine that will have to be done.  There are some decent sources of information out there including Tankograd and a walkaround by Dave Doyle publications.

The molds for making 10 12:00 x 20 tires are now done.  The tires in the photo are 3D printed that are being used as masters.  Will post pics as progress continues.

[Mark Deliduka]

That looks fantastic so far! Bring it man!

[Jmarc]

NNNNNNNNNNeat start !

[Firemodeler1]

Got a small update on progress.  Tires and wheels have been cast and work has commenced on the suspension.  The rear suspension consists of active springs, torsion rods and two floating axles.  The springs are made of strip brass, soldered together at the ends starting with the shortest first.   The torsion rods are made of brass tubing.  With those done front springs and the front axle will be next.  After that the cab will be worked on.  One door is done including the brass hinges.  The cab itself will take some additional alteration before the doors can be hung.

[Firemodeler1]

Here's a look at all of the parts that make up the front and rear springs and axles.  They are ready for mounting on the chassis.  The universal joints are 3D printed from Down Range Productions.  They sort of snap together and are easily modified for the driveshafts.  The odd thing in the right front is a template for drilling the lug nut holes in the wheels.  Each one has 10 lugs so getting even spacing is a bit difficult.   A paper template of 10 segments was drawn to scale and taped to a piece of brass sheet.  The center hole was drilled first and then the 10 lug nut holes were drilled out afterward.  The center plastic piece fits into the center of each wheel which gives the template a positive location for the lug nuts.

[Firemodeler1]

Got the front end put together finally.  Little adjustments here and there to make it the correct track.  Tie rod and steering is also done.  The wheels are held on to the axles with small bolts and washers.  inside the axle tubing is a piece of plastic rod that was drilled out for the bolts.  The wheels spin freely on the brass bushings inside each wheel.

[Firemodeler1]

Got a bit more done but the adjustments necessary to get the radiator, hood pieces an cab to all be where they should be has been a challenge.  I blame that on drawings that probably have just enough slop in them that when enlarged to the proper size are just enough off to mess things up.  The drawings were sized to the wheelbase but there was no way to compare the location of other components.  All part of the scratch building process.

[AP40rocktruck]

Solid workmanship, Great topic so many possibilities!

[Mark Deliduka]

Brilliant work so far! You have some mad skills here man!

[Firemodeler1]

A quick update on the M-20.  The radiator, hood and cab now can be located accurately on the frame.  The cab is mounted with screws secured to a cross member and the cab floor.  The hood and radiator location relate to the cab.  Some tweaking of the hood pieces needs to be done and hinges for opening need to be attached.  The cab doors are already hinged and open and close.  The cowl vent opens in closes with a lever inside the cab.  Side pieces are still needed for the radiator.

[AP40rocktruck]

Superb craftsmanship, great to see others working in mixed media for a scratch build!

[Firemodeler1]

HI, Richard.  I see you like highway trucks as well as the military venue.  Here's a scratch built one that was done in 2009.  Lots of brass in the frame and chassis but with a sheet plastic cab and body.  Brass hood, fenders, doors, bumper.  Resin cast tires.  Turned aluminum headlight buckets.   It's 1/25 scale and Is a 1928 Pierce Arrow 7 ton dump.  That's the real one in the background of the photo.    Interesting side note, there was a brass ID plate on the side of the frame which said that if speeds exceeded 25 mph it would void the warrantee..

 

 

[AP40rocktruck]

Awesome, The Peirce Arrow is so overlooked in scale modeling.  

Thanks for sharing

[AP40rocktruck]

You asked about louvers, here is what mine look like after being laser slit & pressed.  These are for my M-20 in 1/24.  .012" brass, not .030".

[Firemodeler1]

WOW!  You are light years ahead of me in this work.  I can understand the use of a laser to make the slits.  But moving the metal afterward so uniformly and even requires some special tools.  Can you elaborate a bit, please?  It would be wonderful to add louvers like yours to my M-20 but the best I can do at this stage is some quarter round plastic.  

[AP40rocktruck]

19 hours ago, Firemodeler1 said:

WOW!  You are light years ahead of me in this work.  I can understand the use of a laser to make the slits.  But moving the metal afterward so uniformly and even requires some special tools.  Can you elaborate a bit, please?  It would be wonderful to add louvers like yours to my M-20 but the best I can do at this stage is some quarter round plastic.  

So those brass louvers & the press to form them were fabricated in 1998-ish.   I need to make a new tool (press) as the original one was damaged when I moved in 2006.  If I remember correctly, in 1998 it cost me about $2000 in time & materials to make the forming die.  Plus another $800 to have the brass laser slitting done.  Not a cheap way to fabricate one piece of a model. 

In terms of how the die or tool worked in the press, one side had the raised shape for the underside of the louver & the top plate had an opening cut to the perimeter dimensions of the louver.  This was repeated with exact spacing to form a row of 30 louvers.  The reason the sheet of brass is so much larger than needed was 1, to have enough surrounding material to allow for the stretch to take place with out distortion of the surrounding metal.  2, so that 4 alignment pins could be cut into each piece of brass, where these are needed to align the 30 slits correctly for good louver formation.  3, those alignment pins must be far enough apart so it does not interfere with the final shape of the parts (hood side panel) can be cut from the stock.  

The tool / die was machined out of D2 and was not heat treated.  For only 8 parts I wasn't willing to spend more on heat treat & super finishing, or my time to do the work.  D2 after heat treat is miserable to polish out especially in such small spaces.  A big part of making the tool, was allowances for brass thickness & understanding how soft brass moves at room temperature during stretch.  

If you are going to use 1/4 round, I strongly suggest making the hood sides out of styrene instead of brass.  Even with a jig, getting 30 in a perfect row, evenly spaced and twice with styrene to brass would be difficult at best.  

Hopefully this gives you some direction or ideas.  

Rick

[Firemodeler1]

Thanks, Rick for your explanation.  Far more than I would be capable of doing.  As far as the quarter round is concerned, I have had it work quite well in the past.  I made a decal first with the spacing and alignment horizontally.  I use a chopper to get the quarter round all the same length.  The decal is laid on the brass and stays there permanently.  A small bit of AC on the decal line helps hold the quarter round in place.  After painting the seal is complete.  Here is the process on the finished Diamond T wrecker I did a couple of years ago.  The hood on this one had 24 louvers, the last 6 of which were longer than the rest.

The photo below shows the bare hood with the louvers on clear decal paper.  This was trimmed close and transferred to the hood side. Quarter round pieces are to the left.

[Firemodeler1]

Made a bit of progress in the past few days.  Things are beginning to come together.  Next up is to get the front fenders done.  Renshape will be used to carve them out.  Brackets will hold them in place on the frame.

[AP40rocktruck]

Well the work with the decals for spacing is a great idea (I might steal that process) and the results show for it.

[Firemodeler1]

Fender work was done today.  To begin the fender profiles were glued to the Renshape blank and roughed out using a bandsaw.  Then the top edge was sanded smooth using a disk sander.  After that was done the bottom side was thinned out with a sanding drum in a Dremel.  The outside edge was left so that it could be rounded off by hand.  The right fender is done.  The left one still needs the edge sanded round.  The curved part of the hood side needed some adjustment to fit the fender contour but that is expected sometimes in scratch building.  It will still have to be done to the left side as well.

[Jmarc]

NNNNNNNNNeat !

[Firemodeler1]

Additional work done on the cab and fenders.  Headlight buckets were cast of two part resin and pinned for mounting.  The cab side vents are done along with the drip edge and two grab handles.  A dashboard was made up of Renshape and Evergreen sheet stock.  The gage cluster is a decal and the knobs and switches are common pins.

[Firemodeler1]

Progress is steady with things beginning to fall into place.  The fenders are mounted but removable, hood is set and pinned but removable, the "louvers" are done, windshield glass is in, dash is in and doors are done.  Wipers are also done and set in place.    Lower splash panels at the fenders have been glued in and fixed to the frame. 

[Firemodeler1]

As of yesterday, this is what the rig looks like in paint.  Cab details being finished up with shift lever, auxiliary shift lever, transfer case lever and hand brake and steering wheel.  A fire extinguisher will be mounted on the cab back and then the seats will be set permanently.

[Firemodeler1]

Work continued to get the battery compartments and fuel tanks mounted on running boards.  This is where we are as of today.  Now is the time for the winch construction.  The winch cable was strung from the front pintle and through the loops toward the rear.  Cable is not heavy enough.  Need to find a better substitute.