Two Tiny Trolleys IV: Mechanism Taking Shape ~ Saturday, January 13, 2007
After taking some time to get the feel for working with brass, I've come back to this project (see parts I, II, and III) and it's staring to come together--actually more easily than I was expecting.
The first step was to cut bar stock into a few blanks the length I needed, 2 3/8", by clamping it into a vise, with just this much plus "kerf" sticking out, and using the edge of the vise as a kind of "half miter" as I cut it with a hacksaw.
I cut a hole for the gear tower of the truck by first drilling small holes to the approximate shape I needed, with my Dremel mounted in it's drill press stand. You can get the holes more exactly where you want them if you make a pilot hole with a hammer an prick punch (you might get by using a hammer and nail). Then I cut out the hole more precisely with a cutting attachment like this:
For this part of the job I didn't bother with the drill press stand--I just clamped the bar in a vise at a convenient angle, and winged it.
To "draw" lines on brass to show yourself where to cut, you can just scribe them with an X-Acto knife (though you might want to retire that particular blade from other uses because I'm sure that'll dull it in a hurry).
The bar now fit snugly onto the truck. Conveniently, its width matched the space between the inside edges of the truck sideframes precisely. Initially, the bar stock rubbed the tops of the wheels and gears, so I ground out wheelwells, like this:
with a grinding attachment.
Eventually, I was able to fit the truck on the bar, and turn the gears by hand without feeling any friction.
I'm holding the truck and brass bar together with bent wires--currently brass, but I'll probably replace them with steel wire later.
I picked up a spare Atlas/Kato motor at a local hobby shop, so now I have two more or less identical motors (dimensionally speaking) for my two trolleys. I cut off the shaft from one end, and attached a worm and flywheel to the other. The worms and flywheels came attached to their own shafts, which in the original RS-1 mechanism were attached to the motor shaft with plastic couplings. They were inconveniently positioned on the shaft for my purposes. I carefully removed them--the flyweels slide off with a little pushing, but I could only remove the worms with a some careful tapping with a hammer and nail. Eventually everything fit like this:
The worms double as sleeves holding the motors' own shafts together with the extra shafts that the flywheels are attached to. The worms only fit loosely on the motor shafts, so I used a dab of cyanoacrylate--if you do this, just make sure to get everything positioned exactly right on the first try, because you won't get a second one, and keep turning the motor by hand for a few minutes just to make sure no stray bit of glue makes the whole thing freeze up.
Now it's all starting to come together:
The motor's just sitting there in this picture; eventually I'll attach it with wire, just like the truck (some of my NScaleTraction@YahooGroups buddies recommend attaching the motors with Silicone Caulk or Tacky Glue--I'm thinking it over). But I couldn't resist a quick test--so I put live wires on the motor contacts, held it in place--and the wheels turned!
So far so good.
Til next time, ding ding!