Sometimes 3D printing can be cheaper than subtractive machining alternatives. The fixture in my last post cost about $1 in filament. I priced various plastics and aluminum stock from which the fixture could be milled, and always came up with about $30 in raw material. Of course I have to do a lot more printing to amortize the cost of the printer itself.

Using DesPlaines brass frames means losing some of the under frame details present in the OEM plastic frame. Those details were not accurate, but they are very hard to see. To help fill the void I printed some half-frame details since a nearly 12" long part exceeds my printer's build volume.

As Bob stated..”Many smiles were had!”  Hehehehe

The new motor exceeded my wildest expectations I have to say. The normal operating speed may throw folks for a loop for a while…but the engine is just an amazing puller!  And hardly any motor whine.

Even more sad though…I didn’t record anything going UP grade…just down.

DOH!   

Looking forward to seeing what the operators think next weekend!

A Red Caboose GP9 dynamic brake got hammered this afternoon. The printed fixture worked fine, although clamping in the vise needed to be gentle because printed ABS is not as rigid as aluminum.

Curiously, the styrene objected to conventional milling, but was fine with climb milling. It required light cuts and there was considerable spring back.

Here it is fresh off the mill, still in the fixture.

Jim -

Why Cerrobend? Actually, lead shot randomly packed is only 77% as heavy as cast Cerrobend (Wood's metal). The space between round balls must be factored in, although it would be partially filled with epoxy or other less-dense glue.

According to Wikipedia, a random packing of loose balls in a cavity only fills about 63.5% of the volume. The density of lead is greater than Cerrobend, 11.34 g/cm^3 vs 9.4 g/cm^3, but the advantage is lost due to the low packing density.

Grades on the A&O are steep, and we need all the tractive effort we can get.

As for the DB interference, I'm leaning towards making a fixture and milling it out so that the full height above the motor mount is available for electronics. There's a big winter storm heading my way and that might be a good snow day project.

So far I've found FDM 3D printing to be liberating. It lets me imagine new answers to problems that would have been tedious if built-up in styrene or machined on the mill. So far the primary limiters are my imagination and NOOB learning curve with Fusion 360.

The light package mounting block is a variation of an idea I had decades ago for the long hood of an Overland GP30 or 35 (don't remember which.) Back then I got a block of Sculpey modeling clay and packed it in the end of the shell. Then I carved out openings for the various LEDs (all hand-colored blue meanies) and incandescent headlights, also enlarging holes for the various grab irons that poked inside. After sculpting the block was hardened by baking in the kitchen oven.

With the printed blocks I will have to carefully trim the length of brass grab irons so that they don't extend past the inside wall of the shell.

I'm substituting brass detail parts including the handrails, grabs and lift rings since those are delicate and easily broken (the plastic lift rings are far undersize.) The A&O is all about operating sessions, so some innocent but ham-fisted handling of equipment must be anticipated.

All the best,
Bob

Back to the original topic: remotor, and including some benefits.

The effort to install a new, smaller motor in my RC GP9s comes with a benefit to increase headroom inside the shell. This afternoon I milled a TB1935 module to make it narrower, only 1.3." I narrowed it as far as I felt comfortable while holding it in a Sherline vise. It now slips easily in a new RC GP9 shell. So far so good. There are a couple of pinhole leaks in the enclosure, due to voids during injection molding, but not enough to significantly influence bass response. It does, however, now equalize changes in barometric pressure.

Soon a difficulty became apparent. The dynamic brake blister is narrower inside than the shell itself. Rut roh!

Plan A: The DB part has not been assembled, so there are two slots for the exhaust stacks that could be used to hold it in a fixture for milling. That wouldn't be too difficult but the result would be a part that loses the alignment "lip" and reduces the amount of gluing surface. A strong joint is desired because most operators will pick up the finished locomotive by the DB blisters when re-raining after an "oopsie." Stuff happens.

Plan B: After careful measurement I discovered that I had about 0.2" of clearance between the bottom of the speaker and the top of the new motor mount. Originally I planned to center the driver in the DB fan opening, with the passive radiator situated towards the back of the long hood. That wouldn't work since it would interfere with the rear drive tower. However, it can be flipped around 180 and still leave some room for wires.

Either way, I still plan for the primary weight to be Cerrobend poured into the bottom of the OEM fuel tank maybe with the fuel tank taped to the bottom of a pot filled with cold water. The new brass frame also helps.