M911 & M747 on Civvie street

[dogfish7 (R.I.P.)]

The pneumatic actuator canister and rod assembly are very light and the brake plate arm is sufficient to carry the weight.

[JCON]

Very cool!!!

[Beekster]

Feb 21, 2019 19:31:55 GMT -6 dogfish7 (R.I.P.) said:

The pneumatic actuator canister and rod assembly are very light and the brake plate arm is sufficient to carry the weight.

Oh, sure; this isn't a matter of weight.  But shouldn't the canister be mounted to a bracket on the axle, so that the arm is free to move?  Or is what we see in my picture just an outer sleeve affixed to the brake drum assembly?  If the actuating rod which moves the brake shoes is inside, it wouldn't be visible.  I think I see where you're coming from.  A close look at the canister assembly shows molded-in detail of the rod which connects the canister to a lever arm; so on the real rig when the rod is moved in or out from the canister the lever arm pivots which would turn a rod inside the outer sleeve we see, and that rotation would in turn move the brake shoes.  Before I commit to making brackets, I'd sure like to see the internals of this assembly to understand exactly how it moves.

[dogfish7 (R.I.P.)]

I drove Military and Long Haul and saw Pneumatic brake systems up close. You can probably get a PDF of that particular type, but I don't think you'll need to modify that part. It is quite accurate, except for the brake line air hoses, which would make a nice detail feature that would be visible from the rear.
nptel.ac.in/courses/112106175/Module%204/Lecture%2037.pdf

[Beekster]

That tech file is helpful, Dogfish. Thank you, sir! I would still like to see some close-up images to be sure that the mechanism really does hang out there in space, but might just have to go with what I have. Curiously, good walk-around images of the M911 are scarce; not even PrimePortal has much and those aren't the highest resolution. I suppose that my thinking that the mechanism be secured to the axle comes from my Mack projects. Mack attached the brake actuators to the axles, like this on a restored B-series truck:




And an earlier L-series truck:




But on this Autocar 6x6, the front cylinders seem to be out in space like the M911 kit shows; can't tell if the rear ones are attached to the axle:







Question: Since there are two lines to the cylinder, I assume that these are double-action types?

[Beekster]

And at the front end of the truck, that rudimentary engine is now a necessity and I'm cutting/glueing/shaping plastic on it as I write. Pictures will follow later when things are more complete, but the backstory is this: Friday morning after my last post, I was washing the frame to remove the accelerator residue after superglueing some wires. I felt and heard a SNAP and the left fender was broken off. Well, crud...that bites...

I got the fender back on, but it clearly won't survive much handling from here on out if I don't do something to give it further support. That something is the engine, originally intended just to fill visual space just in case someone peers in with a bright light. Now it will be a structural support for the fender, by way of the intake tube from the air cleaner box. I'll extend that with .188" diameter tube, which, handily enough, is the same diameter as the kit's pipe. Attach that to a spares-box airplane wheel turbocharger atop the engine, and as the British would say "Bob's your uncle". At least I hope so. Stay tuned...

[JCON]

Make it work brother!!!

[Beekster]

I've been progressing on my fender support engine, and this is what it looks like now. You can compare with the resin one further back in the thread and see how inaccurate this one really is, but it will be good enough for the extremely limited view angles and will definitely be strong enough to support the fender.





The tubing from the air box pipe to the turbo inlet is laminated from tubing to make a nearly solid piece; more glue surface to ensure a solid bond. The engine pictures illustrate how to go about making a piece like this. It's almost all Evergreen strips laminated together, punched discs, and rod stock cut at various angles and glued together. The plastic glue on the manifold pipe to the turbo is setting up now; when dry I will coat it with superglue, hit it with accelerator, and smooth the contours. This process is exactly what I did to make the DD 8V-71T for the Madill 071 yarder. I was far more precise in measuring and shaping for that engine since it sits out in the open, but this much rougher one is a better example of how to do it. I will follow these same processes if I ever get back to making a Cummins VT8-460 for an IDF M50 or M51 build. I am rather pleased that I have gotten this far with the support engine without busting the fender again since the support engine has been in and out dozens of times to check the fit as work progresses.

[JCON]

That will work fine for the use you need!!! Good job fella!!!

[BUCKY]

Some more nifty work, beekster! Keep it coming!

[JED]

Yet more great work

[Beekster]

Some progress and a setback. I've got the engine/fender area locked down, and have been adding fine wire to the frame to wire the air brake chambers. I'm not adding any air manifolds; just "disappearing" the lines under where the winch deck will sit. I still have to add lines for the front axle and the pusher axle under the winch deck. I'm leaving the wires long so that they can be bent and glued to the brake chambers when the wheels go on for good.






Working with the lines revealed a setback: My rear bogies weren't sitting square to the frame; one side was pushed further forward of the other. There is some slop in the fit of the axles, and when I built everything up I was more concerned about getting all the axle stubs to sit on the same plane so the wheels eventually would too. I didn't think about the location of the bogies otherwise, and when the structure firmed up as I added the drive shafts I thought things would be OK. But it seems that the tight fit of the drive shafts pushed the bogies out of position. This is probably a case of tolerances stacking up as assembly proceeds. The transfer case is a key element, and it goes into the frame at an earlier stage than the bogies. While it fits well, it can move a few thousandths of an inch fore or aft as it is glued in. Same goes for the PTO and the transmission at the front, though to a lesser degree. When the drive shafts go in, this can put stress on the rear bogies and with the slop back there that can push them out of alignment when viewed from above or below.

So, what to do about this? I broke the glue joint (and locating pin) at the front of the drive shaft between the bogies, and then hit all of the joints along the line up to the transfer case with more liquid glue. I pushed the bogies around to line them up better while the joints were soft again, and put the wheels on to sit the whole frame on a pair of wooden blocks to ensure the wheels all touched at the bottom. I then used some steel bars (weights that come in old Japanese 1/700 scale ship kits) to keep the outer faces of the wheels parallel. The result may not be perfect, but it is better, which is what you see in these images.

What did we learn here? Several things. First, ignore the assembly sequence and build the wheels first, leaving off the brake chambers, so that they can be used to help align everything else. Second, as you build try to locate elements like the PTO and transfer case as far forward as they can be pushed. Third, pare down the locating tabs on all the interconnecting axles so that they have some wiggle room to allow all of the components to settle together. Fourth, don't add the torque rods F17 between the bogies and the crossmember between them until the very end when everything else has set solid. Fifth, consider not glueing the walking beams F37 and F38 at all; this will allow the wheels to move a wee bit under the weight of the model. Or at least, don't glue those joints until you are satisfied with how everything else sits together. I will remember all of this when I eventually build the second truck, which is on its way. According to eBay, it was in San Francisco last Friday so I'm hoping that the tracking shows it arriving in Portland and on to Hillsboro for delivery later this week.

[dogfish7 (R.I.P.)]

Some great pointers Beekster.

[JCON]

Or you could have just sliced a small part of the middle of the driveshaft out and glued it back together, reinsert and voila problem solved, no more pressure issues... lol!!!

[Beekster]

Mar 4, 2019 10:36:35 GMT -6 JCON said:

Or you could have just sliced a small part of the middle of the driveshaft out and glued it back together, reinsert and voila problem solved, no more pressure issues... lol!!!

True that!  That is, if I had been observant enough to notice that the bogies were getting all cattywompus in the first place, and I didn't.  I was too focused on the fundamental wheels-on-ground issue and didn't pay attention to everything else. I still may have an issue with the pusher axle wheels, but reworking the mounts and air bags isn't really an option.  If I have to, I will tweak the axle stubs so that the wheels can move vertically a few thousandths to match the rear drive axles.  Getting wheels to sit properly is a challenge with this kit, because without wheels on the frame sits on the differential pumpkins fore and aft.  The front wheels attach with two pins, not an axle stub, so keeping them on for test-fitting is a trial.  I suppose I could glue them on with Elmer's which would hold them just enough for this kind of alignment work.  Another lesson for the next truck, whenever.  Also, the U-shaped drive shaft protector that is part of the pusher axle sits lower than the pumpkins do, so the only way to eyeball everything together is to have raised pieces for the wheels to sit on so that the frame can be leveled.  I'm using scrap wood for that now, but it might be better to build a fixture out of styrene square stock and thick sheet, sort of like a frame lift at your neighborhood service center.  See, the scrap wood can move around, and it would be better for the two sides to be structurally tied together.

Hmmm...looks like I've talked myself into a scratchbuilt frame assembly fixture.  And it's probably worth digging out my M1070 kit and references to see how big to make it.  If I'm cutting plastic, I might as well build something that can be useful for more than one model.

[JCON]

Sounds like you have a plan...

[JED]

Yet more great work with challenges too,keep it up 👍

[Beekster]

Well, that didn't take long at all. Step One of building a truck frame/wheel assembly & alignment fixture is complete:

The basic frame has been cut, squared, and glued together, and the wheel decks cut from .030" sheet.  The frame is solid enough to handle for photography, but still needs to set up completely overnight.  Tomorrow morning I will proceed to Step Two, sanding the frame top and bottom on a flat countertop to ensure those surfaces are flat and parallel.  Evergreen shapes like these often have a bit of a crown to them, so a light sanding will remove that.  Then Step Three, adding the wheel decks and supporting their ends.  I've made those rather long; perhaps too long.  I may cut down the shorter sections a bit more.  I will make a box frame under the end of each wheel deck so that they don't droop, and call it done.  The M1070 tractor is actually a bit shorter than the M911, so it will fit fine.  And the frame for my long-wheelbase IDF Mack DM895 will fit too, should that project ever progress further.

[JCON]

Good!!!

[BUCKY]

It's good that you were able to correct the problem with the skewed parts! Keep up the great work, beekster!!