From:    Ben Jackson <>
Subject: my track construction technique (long)
Date:    Sun, 31 Oct 1999 14:57:54 PST
By way of introduction, let me describe the sort of track construction
techniques I've been using.  This is the kind of thing I was really
hoping to find on the RBT page.  Hopefully others can send in descriptions
of their methods.

My initial inspiration was the OMSI Gravitram.  I had seen other RBS
before, but it was at OMSI that I realized that I would like to try
actually building something like that.  The basic track is three rails,
one on the bottom and two on the sides, supported at regular (about 6")
intervals with U-shaped rings of the same metal.  For a long time I
thought I was looking at large gauge copper (#8 or #6) connected with
solder, but I realize now that it's probably copper flashed welding rod
with brazed joints.


	5/8" ball bearings, as supplied by the local Ace Hardware for
	$0.80.  That's the largest size they carry (at least until I get
	there and buy them all).

	10ga copper wire, sold by the foot (but horribly kinked due
	to their wire measuring / spooling machine) or in 800' spools
	from Home Depot.  This is easily strong enough to support 5/8"
	bearings (and probably up to 1" bearings) in a three rail
	configuration.  It's not strong enough to make supports out of,
	and it needs more supports than steel.

	Initially I was working with 12ga steel wire, which makes some
	incredibly rigid track and can be used to make supporting
	brackets, but is very hard to work with.

	2' length of 2x12 fir boards for a base.  Mine have warped
	horribly, so I need a new material (or a surface planer, mmm).


	PVC pipe, which I picked up at the Ace Hardware with the ball
	bearings.  I just eyeballed a piece with an OD of about 5/8"
	(bearing) plus twice the diameter of the wire.  I used this
	as a mandrel for making supporting Us and rings.

	Roundnose pliers.

	8" linesmens' pliers.  8" gives enough leverage to cut 10ga
	copper, plus the flat part at the end can straighten kinks
	with enough force.

	Small vise grips, clamps, needle nose pliers, etc.

	Dremel tool for cutting down the coils of wire off the mandrel,
	and lots of other uses, like deburring track (in slow sections)
	and cleaning flux and rosin off of complex joints.

	Bernz-o-Matic micro torch.  About 5" tall, builtin spark lighter,
	flame just big enough and hot enough to work on one joint.

	Craftsman Industrial Soldering Gun.  400wa heat up/150wa continuous.
	3/8" pyramid tip, only weighs 14oz.  Nicest soldering gun I've
	ever used.  Heats up in about 2 seconds, can heat large joints just
	as fast.

	On order:  slip bender!  This will replace pots, pans, cans, etc
	which I've used to make constant radius curves.


	I haven't built any track with the micro torch yet, so these
	methods are limited by the fact that you have to be able to put
	fairly significant force on a joint to solder with a gun.

	As I mentioned above, I make my support rings by wrapping the
	wire around a PVC pipe.  I can do this by hand.  With the 2"
	tail at the end I bend an eyelet with roundnose pliers and use
	that to clamp the coil down.  Then I use a sharpie to mark two
	lines 180 degrees apart and cut off alternating rings with a
	Dremel tool.

	To make track, first I shape 3 wire segments (as close to
	identically as I can, usually with a can or a pot), with a little
	slack left on each end.  I start with the center rail and lightly
	clamp it on top of some scrap wire so it is one wire-gauge above
	the work surface.  Then I use vise grips (or just pliers with
	a rubber band) to hold a U-shaped ring upright and slip it under
	the rail.  With this setup I can solder the rings together by
	pressing the tip of the gun on the center rail, flowing some
	solder onto it to get a good thermal connection to the U and
	then finishing the joint.  Gravity keeps the top of the rail
	about as smooth as possible.  Once I've added all of the rings
	to that rail, I come back and do the inside or outside rail.
	I use spacers (actually needle nose pliers) to hold the wire at
	the right height.  The first joint is tricky, but then I can
	bend the new wire slightly so that it presses against the inside
	of the top of the U for all of the other joints.  I make up for
	the differences in the radii of the inner and outer rails to
	the center by hand as I go along.  On the last rail I check the
	gauge of the track regularly to make sure it's not going to
	pinch the ball.

	For more complex items (alternators, drops, etc) I use whatever
	works.  :-)


	I've made straight track, left- and right-hand curves, U turns
	(where the ball drops and turns to head the opposite direction),
	alternators and funnels.


	I tend to build lots of prototypes, and then try to connect them
	together (without much luck, really).  Without a plan it's easy
	to create simple tracks which have WAY too much drop.

	The hardest part about joining large copper constructions like
	this is that you're soldering on a giant heatsink.  You reach a
	point of wire density where you can't heat up one joint hot enough
	to melt solder either 1) at all or 2) without softening all of the
	surrounding joints first.

	The ball only runs on two rails of the three.  In turns it's
	the outside and bottom rails, and in straight segments it's
	either determined by imprecision in the track construction
	(center rail not perfectly centered) or by the exit of the last

	Smooth joints are very important for good ball speed.

	With two wire track (which I've experimented with) you can loose
	a LOT of energy if you don't have supports close enough together
	to prevent the track from spreading as the ball rolls over it.


	I want to make a few desk-sized RBS.  I think with my soon-to-arrive
	slip bender and my new torch I actually have a chance at making this