Re: [PSUBS-MAILIST] Shrinkage of plexi windows.

[Jon Wallace <jonw@psubs.org>]

Ok Frank, I got my Stachiw book.

Page 834, third paragraph.  Stachiw says the dimensional change from 
annealing "may exceed in some cases 2 percent of original dimensions".  
He goes on to say, "Such a change may be unacceptable for acrylic 
articles machined to dimensional tolerances of < 0.010-in (0.25mm)."  He 
also suggests reducing the internal stresses to less than 200psi prior 
to initiation of machining operations.

There's no mention of which cases may exceed a 2 percent dimensional 
difference.  It's not something that can be calculated and I suspect 
since your thru-hulls are already installed you're just going to have to 
give it your best effort and hope it comes out ok.

Jon


ShellyDalg@aol.com wrote:
> Hi Jon. Ya, the info I got last winter was pretty good about how fast 
> to ramp up the temp. and how long to hold etc, then the cooling 
> process and time and all. It's available from a few sources. Couldn't 
> find the shrinkage though. With the window frames already fabricated, 
> I want to have the finished windows fit with a 1/16 inch clearance. I 
> need to know how big to cut the disks, so they are the right size 
> after annealing them twice. The ID on the frames are 16 and 24 inch, 
> so the _finished_ disks need to be 1/8 inch less. I saw some info 
> where there's only supposed to be a couple of thousandths clearance, 
> but that ain't gonna happen.
> Frank D.



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