[TCML] Primary support CAD files
huil888 at surfside.net
huil888 at surfside.net
Tue Apr 1 14:03:37 MST 2008
It's great to have a CNC router or milling machine available, but
accurately notched primary supports can be easily made using a radial-arm
saw or a table saw, a length of 1/4" or 3/8" threaded rod ("all-thread"),
a matching nut, and a knob that can be attached to the end of the threaded
rod. The threaded rod is used as a leadscrew to accurately advance the
primary supports across the saw table from cut to cut. If you will be
using 1/4" copper tubing, you will probably need to use a standard 1/8"
kerf width saw blade, and make 2 overlapping cuts to get a notch width of
just under 1/4". If you are using 3/8" or larger tubing, you can use an
adjustable dado blade (either wobble or stacked) to get the correct notch
width in one cut.
First, determine the dimensions for your primary coil and its supports:
ID, OD, number of turns, notch width, notch pitch, etc. Write these
dimensions down! Next, determine the number of primary supports you want,
and calculate the notch offset required between each support to create a
spiral. Cut all your primary supports to length, and use double-sided tape
to secure them together in a stack, with the end of each support offset by
the required pitch from each adjacent support. For a radial arm saw, I
clamp a standard machine nut to the left hand edge of the saw table,
attach a knob to the threaded rod, and thread the rod into the nut. Make
sure you know the thread pitch of the rod! Adjust the saw blade to get the
correct notch depth (cut a test notch in a scrap piece of wood or primary
support material to verify notch dimensions).
Position the stack of primary supports on the saw table so they are
exactly where you want to cut the first notch, and bring the end of the
threaded rod against the end of the stack of primary supports. Make an
index mark on the knob. Carefully make the first cut, and turn the knob
the required anount to advance the primary supports the distance required
for the next cut. For example, assume that you are using a 1/4-20 threaded
rod, a 1/8" wide blade, want notches 1/4" wide, and you want the notches
to be spaced on 1" centers. Each full turn of the rod will advance the
workpiece 0.05". After the first cut, you will have a .125" wide notch.
Turn the knob 2-1/2 turns, and the rod will advance .125", pushing the
stack of primary supports .125". Make your second cut, and you will now
have a notch .25" wide, which will create a light press-fit in soft
plastic like polyethylene. You'll get a light press fit because the
primary tubing is not straight, but bent in a radius which will create
more interference with the notch than if the tubing were perfectly
Next, you want to move the stack of supports .75" (plus one blade width)to
make the first cut for the next notch. .75 divided by .05 = 15, so you
will turn the knob 15 turns plus one additional turn, and make the next
cut. The additional turn is required to compensate for the blade
thickness. Then, make the second notch cut to get the .25" notch width.
Repeat this sequence for the rest of the notches. IMPORTANT! before you
separate the supports, mark them with a sequence number so you can attach
them to your primary baseplate in the correct sequence.
A very similar setup can be made on a table saw, using a crosscut sled.
It takes a lot of words to describe this process, but its really quite
simple and 4-5 photos would clearly show the entire sequence. Done
carefully, you can get results just as good as can be obtained on a
milling machine or a CNC router.
> I'm just about to draw up a plan for the primary coil supports in Visio -
> is there any software out there that can do this for me already?
> I'm looking for something I can print out and attach to the plastic - or
> better still produce a vector file for my buddy's CNC routing table...
> Stephen Hobley Photography
> 317 201 4281
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> Tesla at www.pupman.com
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