> I ordered my very first rockets last week. Since I haven't received
> them yet, I thought I'd start by building my launch pad using Eric
> Ohmit's modification of the Plumber's Delight, a PVC cross and 45
> degree elbow design. The business end of the pad specifies a threaded
> coupler to hold the launch rods.
> 1) Where can I buy rods, what are they called, and what sizes do I
> need for Big Daddy, Silver Comet, Fat Boy, Bull Pup, Skywinder, SR-71;
> and AeroTech Barracuda, Strong Arm, and Initiator?
Try your local Ace hardware store as a source for purchasing material
for launch rods.
There is a locator at that site to help you find the nearest store.
For the small stuff, using up to 1/4 inch diameter rods three feet in
length, I find piano or music wire to be the best choice, it is harder
and more forgiving (less subject to bending) than plain steel or
stainless steel rod. Since music wire is high carbon spring steel it
tends to corrode on storage. As for the corrosion; I find a
synthetic scouring pad is useful for removing the rust that builds up
and the rod can be polished to almost mirror smooth with the same in
just minutes. After polishing I wipe the piano wire rods down with a
clean cloth an then rub them with powdered graphite to reduce
friction. I also find that for long term storage wiping the rods down
with penetrating oil prevents the rust.
Some finer hobby stores also carry piano or music wire. Should cost
you less than $1.00 per piece. I have yet
to find music wire in longer lengths (greater than 3 feet) and in
diameters wider than 1/4 inch.
You could probably find longer plain steel and stainless steel rod
stock is usually 4' by 1/8" diameter and 6' by 3/16" diameter pieces
of steel if you wanted. I have also seen galvanized steel rods at the
hardware store but have not tried using them for rocketry
Be careful with stainless steel rods they are not all the same stuff!
#316 stainless is too easy to bend, try a higher strength alloy such
as 303 (or 304). Brass and aluminum rods are also too easy to bend.
For longer rods try using solid bar stock such as steel drill rod or
precision ground rounds available from McMaster-Carr at:
For a 48" long by 1/8 diameter launch rod try cutting up
something like a 6' long section of 303 Stainless Steel round, part
number 8984K21, cost 2.78 and for a 3/16 diameter rod, try part number
8984K93, cost $3.78. The other alloys and rods with higher quality
(Machine polished) are available but at a much higher costs (2-4
times). Unfortunately as with music wire most plain steel (cheap)
drill rod less than 1/4" diameter is sold in 3' lengths. McMaster
might be able to
obtain longer lengths for you; try contacting them.
> 2) The coupler needs to be tapped for thumbscrews so I bought myself a
> Hanson Home Threading Kit from Home Depot. It comes with taps and
> dies for five popular sizes but no drill bits. The table of hole
> sizes to drill lists some unusual (to me at least) bits:
> #36 2.79mm
> #29 3.50mm
> #25 3.80mm
> #21 4.10mm
> #7 5.10mm
> Where do you buy a set of these wierd size bits? Is there any trick
> involved in tapping a hole or do you just ream it out using a little
McMaster also sells drill bits in wire gauge sizes.
> 3) The design specifies a 2" coupler but Home Depot only has a 1.75"
> coupler in the .5" size. Is there any reason this is not suitable?
> 4) What do folks use for a blast deflector? Would an upside down
> aluminum pot pie pan (about 5" across, I think) work? If this will
> look ridiculous, what would be a better solution?
As for a good blast shield, also in the same issue of "Sport Rocketry"
(p30) is my article on "Ablative Blast Shields". The 6 inch diameter
parabolic (bell/nose cone shaped!) or fluted deflectors I describe
cost only a few dollars to make (molded from floor leveler in the top
or bottom of a 3 liter pop bottle) and should work well on any pad
design. Pictures and descriptions should still be available on the
NIRA web site at:
> 5) This pad is said to be suitable for rockets up to two pounds. What
> will be the launch weight of the heaviest model listed in 1), above?
> Bob Simon (using wife's email account)
> Please remove nospam. to reply by email.