## Re: [hobbicast] Shrinkage

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• sentto-1941855-220-962805669-greg_taylor=pullmanind.com@RETURNS.ONELIST.COM on 07/05/2000 10:04:05 AM Please respond to hobbicast@egroups.com To:
Message 1 of 8 , Jul 5, 2000
sentto-1941855-220-962805669-greg_taylor=pullmanind.com@...
on 07/05/2000 10:04:05 AM

To: <hobbicast@egroups.com>
cc:

Subject: Re: [hobbicast] Shrinkage

First, here's what the books say regarding shrinkage: Aluminum small
castings 5/32" per foot and 1/8" per foot for large castings. The reason
for the difference is that you pour large/thick castings at lower
temperatures. With less heat in the melt, you have less expansion of the
metal and therefore less shrinkage in the casting. Brasses and bronzes
shrink 3/16" per foot.

Now, since you like me, probably don't have an expensive shrink rule, try
my
method using decimal fractions rather than common fractions. (3/16) .1875"
divided by (1') 12" =s .015xx. For example, the length of your casting is
to be 7 1/2". Multiply 7.5 x .015 and add the result to 7.5 to get the
length of your pattern. 7.5 + .113 =s 7.6125". Round off to something you

You may want to provide a bit for finish work. I use .02 for shrinkage if
I'm going to do some light sanding and polishing. And I use .03 for a bit
of machining.

Best, Jerry

PS I've been off line for several weeks--fell off the roof, and dinged my
back. It still hurts some but getting better.

foundryman@...

Hi Jerry,
Thank you for posting this more-detailed information for the group to
"digest." I believe that I am understanding all you're saying now! As for
the valve covers I emailed you about casting for me, I would actually have
to make my pattern 22.22" long to obtain a final 22.00" with the
0.125"/12.00" shrinkage factor for the large casting ?! I am assuming that
these valve covers would be considered a LARGE casting due to their final
size of 22.00X5.00X3.50X0.25thick ... am I correct, or would this still be
a SMALL casting?

Thanks in advance! Thanks for the help!

Sincerely,
Greg Taylor :)
Editor Guy/Web Master - Great Lakes Classic AMC Club
http://www.turboforce.com - AMC & Stude Turbo Racing
http://www.turboboost.com - AMC Turbo Power
http://members.xoom.com/glcac - Great Lakes Classic AMC Club
• All: I normally design my part and patterns using Autocad. I scale the part using the shrinkage factor. Then I print the part using a laser printer at 1 to
Message 2 of 8 , Jul 5, 2000
All:

I normally design my part and patterns using Autocad. I scale the part
using the shrinkage factor. Then I print the part using a laser printer
at 1 to 1. I either glue the print out to the wood pattern material and
proceed to cut it out. In some cases I use a divider to pick dimensions
from the full size prints and transfer them to the pattern. A good
laser printer should be within 1/300" (0.0033") and that's close enough
for what I do.

--
James Buchanan
Lexington, Kentucky (The Blue Grass State) USA
Two Truck Climax Locomotive Operator & Builder
• Great on you guys!! Good posts on shrinkage--way beyond my simplistic approach to shrinkage. A shrink rule would be the easy way to go if they didn t cost so
Message 3 of 8 , Jul 5, 2000
Great on you guys!! Good posts on shrinkage--way beyond my simplistic
approach to shrinkage. A shrink rule would be the easy way to go if they
didn't cost so much for my limited use. I want one! After rereading my
post, I realize that I didn't mention the expansion for rapping out the
pattern. As most of my patterns have plenty of draft, 5 degrees, I seldom
have to rap to remove the pattern, but a great reminder for me and all.
Also, I didn't mention my method for grinding a pattern's draft to square or
whatever. As most of my patternwork is decorative, I use the TLAR
Great comments to my post and thanks as I've learned from them.

Best, Jerry

foundryman@...

• Jerry, Was it the fall, or the sudden stop with Terra Ferma that caustd your discomfort. Thanks for the info on Aluminum shrinkage. I ve been told to figure
Message 4 of 8 , Jul 5, 2000
Jerry,

Was it the fall, or the sudden stop with Terra Ferma that caustd your
discomfort. Thanks for the info on Aluminum shrinkage. I've been told to
figure .125 to the foot before, so this confirm's it. Most of the casting I
will do will be Model Engine crankcases, back plates, cylinder head's, etc.
These are in the range of 1.5" wide by 3" tall and long. I'll plan on
.030/.050 max. over size for the pattern. May even back off to .010/.015 for
really small parts. Next comes the question of the pour temprature. I have
an electronic theromo. intended for heat treating that has a range to 2500
deg. F. I guess it could be used. The probe is about 12 to 18 inches long,
so could be hand held if I ware asbestous gloves. I know, they are a health
haz., but I had them in the USAF many years ago, before all the OSHA BS.
According to the Gov., we cant do anything without risk. Oh well, life is a
B_ _ _ _ _, and then you die.

Thanks for the info, and please get well soon, I cant wait for you to
complete the book.

Dirk T.
• ... Jerry; My sympathies on your fall. I m just about to get off crutches myself, after falling off my roof and breaking a hip, about 2 1/2 months ago. Ron
Message 5 of 8 , Jul 7, 2000
At 09:04 AM 7/5/00 -0500, you wrote:
>PS I've been off line for several weeks--fell off the roof, and dinged my
>back. It still hurts some but getting better.

Jerry;
My sympathies on your fall. I'm just about to get off crutches
myself, after falling off my roof and breaking a hip, about 2 1/2 months ago.

Ron Thibault
North Augusta, SC USA
Builder Miinie #2
Captain R/C Combat Ship USS Arizona
http://pages.prodigy.net/thibaultr/
• ... Most of the newer Injets will also print to this resolution. I have an old wide carriage dot matrix printer that also has this good a resolution. I use
Message 6 of 8 , Jul 7, 2000
At 04:19 PM 7/5/00 -0400, you wrote:
>All:
>
>I normally design my part and patterns using Autocad. I scale the part
>using the shrinkage factor. Then I print the part using a laser printer
>at 1 to 1. I either glue the print out to the wood pattern material and
>proceed to cut it out. In some cases I use a divider to pick dimensions
>from the full size prints and transfer them to the pattern. A good
>laser printer should be within 1/300" (0.0033") and that's close enough
>for what I do.

Most of the newer Injets will also print to this resolution. I
have an old wide carriage dot matrix printer that also has this good a
resolution. I use it for printing drawings that are too big for the injet
printer (~ 12" wide by as long as the fan fold paper is).

Ron Thibault
North Augusta, SC USA
Builder Miinie #2
Captain R/C Combat Ship USS Arizona
http://pages.prodigy.net/thibaultr/
• Ron, What is this about military types falling off roofs? I m a retired USAF pilot. My back problems started in 75 when I crash landed a T-Bird on Maui.
Message 7 of 8 , Jul 7, 2000
Ron, What is this about military types falling off roofs? I'm a retired
USAF pilot. My back problems started in '75 when I crash landed a T-Bird on
Maui. My Dr. decided today to send me in for a bone scan to see if I have a
new fracture or two to add to those from the crash. Hope you are about to
get off your crutches and that your hip is on the mend.

Best, Jerry