CPM 3V thickness question

jdm61

jdm61

itinerant metal pounder
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Aug 12, 2005
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In the past, i have used .172 CPM 3V stock for 4.5 long, 1.25 wide field knives and the .207 stuff for a 7 x 1.5 fighter and found both to be pretty much ideal for those applications. My question is about bigger blades. Do any of you have experience with makng say a "bush sword' with blade in the 13-15 inch long by 2+ wide range and if so, do you think that the .207 would be adequate for that "mega machete" application? if so would you temper it to 58 or 60Rc?
 
I've not yet made a 3V blade that long, but I'm very confident that .207" would be plenty thick enough and stand up to a heckuva lotta impact and hard work at 60Rc. I see no reason to temper it down to 58.

You should ask Dan Keffeler about this topic; he's made and tested many large knives/machetes/swords out of 3V and other steels. :thumbup: He's a member here and has a youtube channel, so it won't be difficult to find out what he thinks. (he also happens to a multi-year BladeSports cutting champion, so there's that... ;) )
 
I made exactly what you are describing a few years ago. Gave it to a friend of mine for clearing 4 wheeler trails cutting vines and branches as they drive by. He has abused that knife without fail. 1/4 inch stock 3V, flat grind, heat treated to 59/60 using standard heat treatment from the data sheet but did a triple temper.
 
Thanks guys. I have been impressed with the nasty edge that 3V takes at 60Rc from Peters. I now that regular machetes are a a lot thinner but they are also a LOT softer. I am kndof looking for a bank between those and the WAY thick big choppers that you see some folks make.
I plan to lightly forge and heavily grind a 22" OAL prototype from 2 x 1/4 CruForgeV, so I will get all of the bitching about hand sanding something that big out of the way right up front. :D
 
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The only thing I would be careful with is the acuteness of the primary grind if you're going full height flat and over 2" wide with .207 stock. I'm sure DanK has some data on this, but it may leave the primary fairly thin for a good distance back from the edge...and while it would no doubt be tough in compression and direct loading on the edge, lateral loading (like if a cut is misplaced into a knot, if someone laterally moves the blade to pop a chip out, falling tree / limb traps the edge, etc) may ripple / bend / chip that primary. This could be even more so the case if you add distal taper. I would be more prone to do a saber flat grind at 2" or less in height and then fuller the full stock portion to reduce weight.
 
i was thing of doing a high saber then convexing/blending the transition a bit and doing a tall convex edge.. Kind of like the start of an S grind on a kitchen knife.
Camber said:
The only thing I would be careful with is the acuteness of the primary grind if you're going full height flat and over 2" wide with .207 stock. I'm sure DanK has some data on this, but it may leave the primary fairly thin for a good distance back from the edge...and while it would no doubt be tough in compression and direct loading on the edge, lateral loading (like if a cut is misplaced into a knot, if someone laterally moves the blade to pop a chip out, falling tree / limb traps the edge, etc) may ripple / bend / chip that primary. This could be even more so the case if you add distal taper. I would be more prone to do a saber flat grind at 2" or less in height and then fuller the full stock portion to reduce weight.
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my PD1 camp knife that replaced my slightly smaler but thicker 3v camp knife.. new camp knife is .207 thick and about 2 inch tall and 13 inch of blade mostly flat ground to abut .030 and convexed edge im not sure i wouldnt call it a comp chopper but it sure is great for green tree limbs. just yesterday i cut all the suckers off the weaping cherry (just cut right into the ground) no problems
 
I have made a 16" blade chopper/machete from .145" 3V, 2 actually, and had them heat treated to 60 Rc and they have held up great.
I also have a 24" blade sword I made from .270" 3V at 60 Rc and it is doing just fine. Both are ground pretty thin for knives that size at right around .030" behind the sharpened edge with 30 degree inclusive bevels. I think you could go a little thinner on the edge if you wanted and sharpened to 40 inclusive.
I have had great luck with 3V in large choppers.
 
Just to be clear, I'm not questioning that 3v is great for a chopper or that the edge (apex) will hold up to impact. I'm just considering the primary grind geometry. If my calcs are correct a .207 thick chopper that is 2.25 wide with a full flat grind is about 2.6 dps. Which at half an inch back from the edge would leave it only .046 thick...that's pretty thin for the last half inch of grind if there's going to be any significant lateral loading, no matter the steel. And of course if this is to be a monster chopper, capable of two handed swings, depending on user skill, lateral loading could be significant. Especially since often saying something is 3V makes people start thinking it is indestructable. Again, not questioning that it won't work, just something to consider as you go testing and so forth.
 
Just out of curisotiy, what is the spine thickness on the Browning Crowell-Barker comp cutter? My recollection is that it was not a thick as some custom "race knives". The ESEE Jungles is 3/16. Now those are made from !0xx steel left a tad soft for our purposes. so your mileage may vary, but the are both flat ground as best as I can tell, with the Browming being the full 2i inches wide and have a fairly high convexed edge.
 
The AG Russell listing has it (the Browning Crowell/Barker) at 1/4", but I thought that I had seen it before in 3/16". The Benchmade 171 is .305". Those knives are trying to generate momentum and power from mass in a compact size. On choppers that are 2" wide plus I will grind at least half the height for good cutting geometry. Take that 3V knife heat treated to 60 Rc down to .025" - .030" edge before sharpening and it will likely handle any chopping that you have in mind. If you can stay away from knots in dried wood, rocks or wire you can get away with an edge closer to .015" before sharpening.
 
Granted this was taken very thin, but the testing is always the best way to know when trying new things. While it's very thin at the edge, it's not the apex that failed...it's the primary, and a good bit back.

http://www.bladeforums.com/forums/s...Sword-WIP-36in-CPM-3V?p=14872078#post14872078

Again, 3v is a great choice (especially given how hard it can be taken and still retain toughness), but the grind, edge geometry and thickness seems like it can get tricky in those really big blades. I personally would not feel comfortable extrapolating from a 10" bladed chopper with a relatively neutral balance to a big bush sword over 2" wide out of .207 stock. On the other hand, if there's very clear expectations of how the blade should be used and what should be avoided it's all probably a moot point. From a maker's point of view though / warranty, I wouldn't want to push the limits with such expensive materials without some sort of reliable experience.
 
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Using a Zero FFG calculation is not accurately reflect actual grind. However with a slight adjustment to zffg, you can make a grind - leaving edge thickness before sharpening.

For a 0.207" thick x 2.25" wide blade with edge thickness before sharpen is 0.02". ZFFG is around ~2.35dps against a virtual 2.5" wide blade. Then edge thickness above edge will be (distance/thickness) - 0.25/0.04, 0.5/0.06, 1.125(halfway)/0.092. Then with bevel at 15dps, thickness behind edge will be around 0.027". This geometry would works well for 3V & many other steels with hardness around 59-62rc.

Camber said:
Just to be clear, I'm not questioning that 3v is great for a chopper or that the edge (apex) will hold up to impact. I'm just considering the primary grind geometry. If my calcs are correct a .207 thick chopper that is 2.25 wide with a full flat grind is about 2.6 dps. Which at half an inch back from the edge would leave it only .046 thick...that's pretty thin for the last half inch of grind if there's going to be any significant lateral loading, no matter the steel. And of course if this is to be a monster chopper, capable of two handed swings, depending on user skill, lateral loading could be significant. Especially since often saying something is 3V makes people start thinking it is indestructable. Again, not questioning that it won't work, just something to consider as you go testing and so forth.
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Thank you Bluntcut. I knew the Zero FFG calc wasn't the best, but I wasn't sure how to approximate an actual grind. I appreciate the better numbers.
 
When I was making my first competition cutter I picked a lot of the competitor's brains(Jose Diaz, Dan Keffler). Jose Diaz mentioned to me that he likes flat ground edges for edge stability rather than convex. I guess it has more meat behind the edge. It makes sense once you think about it. I think a convex might cut a little better though being that the shoulders on the edge are rounded.

In regards to the .207 thickness, I wouldn't go that thick. I would think 3/16 would be more than adequate. I'd probably even go thinner with 3v. Swinging a blade around clearing brush is tiring after a while. I want something light, so I can get a lot of work done. I've done 10in long(15in OAL) 1/4in blades and it's even a PITA carrying those.
 
With respect to JG's opinion, I don't think it's too thick, and I would personally prefer even thicker stock to start out with. This way you have plenty of room/thickness to do distal tapers, which make it easy to swing and a joy to use for extended time periods. Get the dynamic balance point out a ways; probably want the "sweet spot" to lie about 1/3 or less from the tip. If you want tip precision and point control, use a pommel to push it all the way out to the tip.

I'll echo the others to leave the edge right around 0.030" thick before sharpening, and then convex the edge on, even though I've never used 3V. Because stiffness and strength are sooooo radically dependent on thickness, this number works across a wide range of steels and hardness for rough use. I.E., even though steel at 60 Rc is much stronger than at 52, ya really can't go much thinner with the (harder) edge anyway- you'd probably need a calipers to tell the difference.
 
He used the word machete. As far as I know the majority of folks who live in rain forests and use machetes every day use stock no larger than 1/8in. Often times thinner. I know he used the word "mega" too which is why I suggested 3/16.

Now if it's gonna be a chopper, hell yeah. You could even go to .300.
 
Anyone know what the thickness is on a Fikes Jungle honey is?
 
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