Paring knife replacement

[superc]

I kept a paring knife in my tool bin.  Use it at least once every month to cut or score something.  Flimsy thing from Kmart or maybe even Walmart (nah, it has made in USA on it, so not Walmart).  Stamped sheet metal blade.  Bends if you push too hard.  Had another one just like it once, but it snapped 30 years ago.  So anyhow I had cut out a T shaped column backing in 1/4" hot rolled steel plate for my SX2 and I was looking at the left-overs and an idea bulb went off.  Why not make a real shop knife of about the same size to replace the paring knife? 

     I was bored today, So, I did.  I used the bandsaw to rough out the blade shape, then the grinding wheel to put the desired bevel on it.

Some purists may not like my laziness when it comes to how I clamped the blade down when milling my choil, but quick and dirty, and it worked just fine.  Much faster than fiddling around with inch blocks and clamps and more T bolts IMO.

This is my first shop knife in about 50 years.  I made one long, long ago in dad's workshop at home when I was a kid.  It got confiscated by a teacher at public school in NYC when I was showing it off.  He kept it and was seen occasionally using it years later.  In today's world I would sue the bum to get it back, once I got out of jail where they would put me till I was 30 as punishment for bringing such a dastardly device to school, even though I was only 9 or 10.     

The Setup



Close up of the pre cut setup



Cutting (Should my swarf be so small?)



Thing to keep an eye out for!  A mill table capable 3" or 4" vise with a low profile that holds work sideways like I am doing with the Shars vise.  LoL, maybe if I send this picture to Shars they will steal the idea and market one?



The finished knife before hardening or sharpening



Flame hardened to bright orange then cold water quenched (two of these small torches used as only one doesn't throw enough heat for something this big).  Ready for me to oven temper it at 450, then put a razor edge on it.



I haven't decided if I should put a handle or a lanyard on it (maybe both?).  I haven't even decided yet if a shop knife that will spend it's life in a tool bin needs a handle.  One thing I am sure of, while it is possible to snap off the tip, I would really be surprised if regular shop use snaps this blade with a 1/4" spine in two.

[superc]

I wound up doing a 3 hour soak at 530F.  When it cooled all the bare surfaces were a pretty blue, so I am happy.

[Anzaniste]

What did you use to give the blade a 3 hour soak?

[Stilldrillin]

I used to grind my shop knives/ scrapers from old machine hacksaw, blades. 

Love your vice clamp! 

David D

[superc]

I simply chucked it into the oven.  My oven can go a bit higher than that.  Like I wrote, a pretty blue when it came out, so I know the soak was good.

I yielded to feedbacks and put a handle on it using fence post wood and some sheet metal bolts.  Thinned on the grinder, then tightened and peened.  Yeah, crooked holes, I know sorry.



I have never understood why the knife guys put two bevels on each blade.  A blade bevel and an edge bevel.  Must be a reason, but I don't know it.  So here the blade bevel IS also the edge bevel.  Makes sharpening it on an Arkansas really easy and fast. 

Yeah the vise thing.  Probably not approved by my old shop teachers.  Their vise, their rules.  My vise, my rules.  I was a little worried about bolts shearing, but I got away with it.  Had some other bolts that fit standing by just in case.  I thought about sliding the vise out of the way, then messing around with clamps and inch blocks, then I looked at the vise and said, wait a second, would this work?  Yeah it did.  Beautifully too. 

I think there exists a market for a vise or ready made clamp set up like that.  LoL, I may make one if I don't spot one soon on Ebay.  Perhaps with a V cut in the jaws too, so rounds can also be clamped pointing along the X axis rather than the Z or the Y.  Something on the order of a couple of 1 or 2 inch thick steel or iron slabs cut to fit the table, some recessed bolt holes in the along the center axis in the bottom for the T bolts and some bolt holes through the edges like the picture for the hold downs.  Stronger, thicker bolts more resistant to shear forces I am thinking.  1/2 inch or 3/4 perhaps.

[tomrux]

if that is just plain old HRS all the heating up and soaking in the oven wont make a h'penny worth of difference to the hardness.

Tom R

[superc]

Sigh, I lack a brinnel tester, so maybe so.

The ebay ad I bought it off actually had the words hot rolled carbon steel plate, so that raises the question why do you think it won't heat treat?

[tomrux]

normal low carbon steel/mild steel does not heat treat. Just is.
needs to be particular carbon levels before heat treating has any effect.

From Wiki
"As the carbon percentage content rises, steel has the ability to become harder and stronger through heat treating."

.05% to .3% are normal/mild steel

above .3% gets you into heat treatable/high carbon steels.

go too much above 1.75% and you get close to iron. very tough but brittle.
all sorts of other elements are added to produce different characteristics.
Manganese, chromium, silicone and a chemists delight of others.

Tom R

[superc]

So since the Ebay vendors very rarely tell (or know) the specifics of the plates they sell, most of us just do a spark test and confirm steel, then give it a try.  Not much all else we can do.  Regarding the shop knife, who knows.  It is hard and resists filing and getting the little hills and valleys out of the hand held bevel took a lot of stoning, more than some store bought blades have, that's about all I can say.  Yeah, I suppose I could give it a flex test with a breaker bar, but why would I do that for a knife designed for cutting string, tape or opening boxes.  Besides that tests the temper not the hardening.  So beyond noting machine tool marks were hard to file out, I don't know of another test without a Brinnel tester.

[RussellT]

I don't know of another test without a Brinnel tester.

You don't need to be able to measure the hardness accurately but comparing one sample with another might be useful.

If you took two samples - one annealed and one hardened - and put a ball bearing between them and then hit the sandwich with a hammer, the ball bearing would be punched into the samples with equal force.  Comparing the sizes of the dents would show which was harder.

Russell

[superc]

Good trick, thanks.

[ksor]

I think you are much more "in control" if you make them "the Black Smith"-way - but Oh, what a mess and dirty job - look here:

(You have Google translation to the right, just under the menu line - in the combobox! )

http://kelds.weebly.com/smedning.html