Question and Answers
ABOUT THE
WEST SYSTEM
Introduction
WEST SYSTEM makes widely
known and well-liked "epoxy system." In high-power rocketry, West System
products are used more than any other epoxy system (although not more than
basic "hobby shop" epoxy.) Everyone who tries this system loves it for the
convenience and range it provides. The major disadvantages to the system
are high price and difficulty in mixing small batches.
Questions and Answers
Q: Why is West System better than standard epoxy?
A: Standard epoxy (also called "hobby shop" epoxy) comes pre-thickened and mixes in a 1:1 ratio (one part resin to one part hardner). This means that the hardner part has fillers added to get the 1:1 ratio, making it easier to mix. Unfortunately, the fillers reduce strength and make the epoxy too thick for some purposes. By starting out with unthickened epoxy and using various fillers, you can get the exact qualities needed for different jobs. Also, the West System resin and hardner are typically dispensed from pumps which regulate the ratio, removing the "equal blobs" guesswork.
If you only use epoxy every once in a while and never plan to fiberglass, it's probably not worth investing in a whole system.
Q: Why is West System so expensive?
A: It's actually not that much more expensive than hobby shop epoxy, but you do have a higher initial investment. The investment necessary for general bonding requires you to purchase a larger amount than you might think you need, plus you have to pay for some parts which you will re-use for a long time. If you use a lot of epoxy, you will save money by buying in the larger quantities.
Q: OK, I'm sold. What should I get to start out?
A: First of all, you need to get resin (105) and pumps. Buy the "A" size initially since one pump will dispense about an ounce of epoxy, more than enough for small bonding jobs.
For general bonding, you will also need filler. The best all-purpose filler for high-power rocketry is 404 (high-density). If you want to minimize weight and are boding porous surfaces, you might also want to get 403 (microfibers). 404 is stronger than any other filler for general purpose bonding. The best hardner for general bonding is 205 (fast) which is about the same as 30 minute hobby shop epoxy.
For fiberglassing, you should probably buy 206 hardner (slow) which is about the same as 2 hour hobby shop epoxy. 206 makes a slightly thinner epoxy and gives you extra working time to get all your layers down before they cure fully.
For filling imperfections and building up fin fillets, 407 filler makes
a good choice since it sands easily and feathers out nicely. Other fillers
are good for different purposes, see the section on fillers
below for more info.
Q: Where should I buy my epoxy?
A: You can purchase everything from Rayplex Ltd.
Check out the web cataloge.
Q: I seem to waste a lot of epoxy, even with the
"A" size pumps. How can I reduce this?
A: The pumps do waste a lot since you get about an
ounce from one pump of resin plus hardner. You can mix the parts by hand
if you want to, but this removes one of the main benefits of the system
(easy and accurate mixing). Try to "batch up" little jobs so as to get
several bonds out of a single mix.
Q: West System sells fiberglass cloth, but it's
thicker than I want. Where can I get finer cloth?
A: You can buy finer cloth at your local hobby
shop. (SIG makes several sizes.) Also, the dealer you buy your West System
products through will generally also sell different sizes of cloth. The
cloth is generally not specific to the system, but make sure the cloth you
buy will work with epoxy resin (not just polyester resin). Marine supply
stores will generally not carry the finer sizes.
Q: I'm scared to start fiberglassing. It looks so
hard!
A: Fiberglassing isn't hard, but it is harrowing
the first couple of times. You need to plan ahead, cut out all your cloth
before mixing any epoxy and pick a time when you will not be disturbed.
Don't rush and you will end up with a fantastic result. Be sure to read
the article on Reinforcing Tubes.
Q: Where can I find out more about epoxy and West
System?
A: When you buy your epoxy products, make sure you
get a West System catalog. It has great introductory material on epoxy in
general and their system in particularly. Read the beginning pages and you
will have a good background in epoxy use. You can request a free catalog .
(Even if you don't buy into the system, get the catalog and read it.
Really.)
Also see the article.
West System Fillers
West System makes several fillers which work with their system. The
most useful for high-power rocketry are 404 (high-density) and 407
(low-density).
Part
#
Description
Need
For
105A*
resin
everything
301A
mini-pumps
accurate measurement of 5:1 ratio
205A
"fast" hardner
bonding and filling
206A
"slow" hardner
fiberglassing
404
high-density filler
high-strength bonding, doesn't sand well
403
microfibers filler
light-weight bonding of porous materials
(optional)
407
low-density filler
general filling and filletting, sands
easily
HPR Use: light-weight
porous bonding
HPR Use: general bonding
(best strength)
HPR Use: filling, building
up shapes
USE
FILLER
403
404
405
406
407
410
Bonding
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*
Bonding
with Fillets
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Bonding
Hardware
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**
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Laminating
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**
Fairing
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