Shrinkage during HT

J. Hoffman

J. Hoffman

Joined
Jan 1, 2011
Messages
1,798
How much will a blade shrink (if any) during heat treat? I know someone told me to over drill my pin holes by 25% to allow for shrinkage. Now I have a different problem. I cut out my scales, and went a little far with the bandsaw by accident, and I have a small cut into the scale. I'm considering filing the tang down a little bit to make up for the mistake, but I'm also wondering how much the HT is going to shrink it. Thanks for your advice.
Jess
 
By your title I was going to post that it sounds like a personal issue :D

In my experience there is no noticeable shrinking during the HT process. I drill 1/8" and 1/4" in my steel and have to use #30 and #F bits respectively on the scales. I have never had issues with pins going through the holes of the same size in the steel but always have issues with the handle material if I don't enlarge them.

So I would say you will have to make up the difference cutting down the tang or start over on the scales.
 
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Steel actually expands during the hardening process... holes in thicker cross sections shouldn't be noticeably affected.
 
Steel is usually larger after heat treat (because martensite is a jumbled mess), but uneven distortion can make holes go out of round. Though nothing like 25%.

The growth can be noticeable on a long piece, but for your issue I doubt you'll notice much change.
 
There was a Seinfeld episode about this!

I have been reading a lot about steels lately and have noticed you can find information about distortion and such. I think the simple steels can distort more but I'm really not sure.
 
I used to do construction and this is kind of like a left hand monkey wrench, or a board stretcher. Some one is yanking your chain son! :jerkit:

I have had holes that were drilled pre HT that seems to be off after HT but its not from shrinkage but like the others said, more like just the opposite.
It is probably measurable with calipers but have never checked it. I may have to out of curiosity now!:confused: :D:D:D
 
Steel expands...holes shrink. Think of the steel getting bigger all around its profile, and the holes are part of that profile. It is something I have to think about at work, but I hadn't made the connection with knife making because I hadn't read about it anywhere. When I did a search on here (after posting to the thread below) I found that there were several threads on the subject.

http://www.bladeforums.com/forums/showthread.php/843158-The-Dang-Holes-Keep-Shrinking!!!
 
http://www.bucorp.com/files/aisi_d2.pdf
See page 5 for a chart

Dimensional changes depend on steel type , HT .Note the directional component ! The chart for CPM D2 should be different especially the directional component . Some steels like A-10 don't have the directional component . These changes are important in making high precision dies ,etc but not very important in making knives.
 
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