Plasma cutter

T

tim37a

Joined
May 18, 2010
Messages
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Has anyone tried cutting out knife blanks with a plasma cutter? I tried it using 1/8" mild steel and it cut like a charm - much faster than using a 4" grinder and thin cutting discs. I used a plywood pattern and simply ran the nozzle around the edge of the plywood - the resulting blank was about 1/16" larger than the pattern. I'm using S35VN and M390, which wears down any saw blades I have tried. The thing I am wondering about is the heat zone, some of which may not be ground off before heat treat.
Tim
 
We had a similar discussion on another forum.
I did a small test on some scrap and this is what I found

Heres a piece of AEB-L between 3-4mm thick, you can make out the HAZ clear as day
t1HlbJT.jpg


The other two test pieces were 20cv and 154cm

I took a brand new 5/32" chainsaw file straight to the edge of the cut and it skid right off on all 3.
I ground off the bare minimum down to fresh steel and tried the file again...not a problem!
I would say less than a 1/16 was removed in order to get to the soft stuff
ZuB1iXG.jpg


I drilled some holes as close to the edge as i could and that was also not a problem.
pql4KQp.jpg
 
Thanks, FTO_Dude,
That looks like what I got with the mild steel test piece. Since the blank ended up about 1/16" larger than the desired size, I can grind off the affected material and end up in the soft metal ready for grinding the bevels. After the bevels are ground and lightening holes drilled the knife will be heat treated. Now I just have to find a used Hypertherm Powermax 30XP for sale. If anyone knows of one, please let me know.

Tim
 
Hi Tim, Plasma cutter works fine for some steels but not for M390. It cannot take the expansion and contraction from the heat and you will get cracking that sometimes shows up after you have done a lot of work on the blade. The same for CPM S110V. CPM S30V is fine. Be careful of breathing the fumes, especially if Vanadium is in the mix. Phil
 
Hi Phil,
I'm going to use S35VN for kitchen knives. It's a little bit different than S30V - do you think it will be OK? Glad you told me about the problem with a Plasma Cutter and M390 - I can't get M390 but I can get CPM 20CV from NSM which is virtually the same as M390. Will have to see if they have any data on the cracking problem.
Tim
 
Tim, I haven't tried 35VM but so close to 30V I am sure it will be ok. Also don't know about 20CV, just experience with M390 and CPM S110V. Good luck. Phil
 
Phil,
How do you identify or find the heat cracks? Is there a fluid you paint on which soaks into the cracks? Seems like I read about that in a Prop. of Materials class about 40 years ago.
Tim
 
Tim, It is called dye penetrate. It is used to find cracks in welds and engine builders use it to check blocks and cylinder heads. It might work here but in my case the cracks were visible after surface grinding. P
 
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