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Straightening Acetyl Rod

Ron Hofer

Hot Rolled
Joined
Jul 7, 2007
Location
Brookfield, WI
I want to use 1/8" acetyl rod as a axle of sorts, but what I got from Speedy Metals has a slight bow to it. When I put 1/8 brass tube in the frame, it spins freely, but the acetyl binds a bit. Straightening by hand bending helped but not enough. Way back when, I used to straighten brass music wire by putting one end in a stationary vise, the other in a vice-grip and pulling it straight. Would that work with acetyl?

Is there some technique I haven't thought of? Thanks in advance.

Ron
 
A thermal stress relief cycle while fully supported in a straight metal tube might work, but you'd have to control temperatures carefully. Search the plastic manufacturer's literature to see what they say, or contact a tech rep for help.

OTOH, taking a larger rod and turning a straight section from it using a box tool or similar may be more effective, depending on how much time you're willing to spend making the box tool and dialing in the process.
 
A thermal stress relief cycle while fully supported in a straight metal tube might work, but you'd have to control temperatures carefully. Search the plastic manufacturer's literature to see what they say, or contact a tech rep for help.

It can be annealed. I've done it before and it's pretty easy. Here's what Dupont has to say:

Although most applications do not require annealing,
in applications where tolerances are extremely
critical, annealing has been successfully used. It is
also used for checking machined parts for dimensional
stability. Annealing is the process of raising
part temperature prior to use high enough so that
most of the internal stresses will be relieved in a
short time—usually less than one hour. Annealing
can also be useful in the prototype stage to examine
the tendency of a part to warp so that design changes,
if necessary, can be made to eliminate or minimize
the warpage. Common methods of annealing are
as follows:
• Air Annealing
In an air circulating oven, the parts are heated
to 160 ± 3°C (320 ± 5°F) for 30 min plus 5 min/
1 mm (0.04 in) of wall thickness. It is important
that parts be uniformly heated and the oven capable
of controlling the circulating air temperature
to ±3°C (±5°F).

• Oil Annealing
Parts annealed in a recommended oil* circulating
bath at 160 ± 3°C (320 ± 5°F) will require
15–20 min to come up to temperature plus
5 min/1 mm (0.04 in) of wall thickness. Again,
uniform heating is important, and the parts should
be restrained from contact with each other or the
walls of the bath.
As parts are flexible at elevated temperatures, they
should be handled carefully to prevent deforming
and allowed to cool slowly in an undisturbed
manner. Stacking or piling should be delayed
until parts are cool to the touch.
• Partial Annealing
Partial annealing is sometimes adequate instead
of full annealing described above. Partial annealing
is accomplished by raising the temperature
of the part 28°C (50°F) above the maximum-use
temperature for a period of 1 hr.
When testing a part for a one-time short-term
exposure to high temperature, such as paint bake
oven, neither full annealing nor partial annealing
may be appropriate. In such a case, testing with
the part in the installed condition at the actual
temperature and for the actual time is much more
meaningful. Testing at a higher temperature or
for a longer period of time could throw out a
perfectly good application.
*Recommended Oil Suppliers:
U.S.A.
“Primol” 355 – Exxon
“Chevron White Oil
No. 15” – Standard Oil Co. of California Western
Operation, Inc.
“Nujol” – Plough, Inc.
Europe
“Primol” 292 and
“Majoline” 238 CRA– Exxon
“Ondina” 33 – Shell
 
Thanks very much for the tips, you three. I opted for Milland's suggestion and the result met my exacting critical standard: 'close enough for government work.' Again, many thanks.
 








 
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