Heat treat and flatness

Q

Quinn406

Joined
Nov 6, 2021
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Working on my first folding knife design. It will be mostly cnc milled. I will be using cpm 154 for the blade. This will be my first time dealing with heat treated parts and im not sure what to expect. If i buy surface ground material for the blade that starts out perfectly flat, what is going to happen to the flatness as i mill the bevels and heat treat? I do plan to quench with aluminum plates in a press to help with flatness, but how flat will it really be? This will be a very tight tolerance precision knife so ultimate flatness is important. Is some amount of surface grinding typically done after heat treat?
 
Yes you’ll have to do some kind surface finishing after heat treat to remove any discoloration or slight decarb if you do all machining pre heat treat.
 
I start out with precision ground stock and just sand on a granite plate post heat treat. It works fine. I am sure a surface grinder would be handy though... Are you in Montana (406 and all)?
 
Look, I know you think you want to make knives for ecommerce. Lots of upstarts think the same, but they never get any good advice, so I'll help you out.

First, you go get yourself 500 railroad spikes, a coal farrier's forge, and a 3 lb ball peen hammer, a good pair of vice grips, 500 lbs of coal, and a piece of railroad mainline.

You take those railroad spikes and you start forging them into knifes, one by one. Forge them completely to the final knife shape, none of this sissy grinder nonsense. Keep forging until every spike is a knife.

Then you take the knife billets and you start heating them up until they glow enough to where a magnet doesn't stick to them anymore, and dunk it in the creek. Do this for all 500 of them.

Then, maybe, just maybe, you'll be ready to make a knife worth a darn.
 
Mecha said:
Look, I know you think you want to make knives for ecommerce. Lots of upstarts think the same, but they never get any good advice, so I'll help you out.

First, you go get yourself 500 railroad spikes, a coal farrier's forge, and a 3 lb ball peen hammer, a good pair of vice grips, 500 lbs of coal, and a piece of railroad mainline.

You take those railroad spikes and you start forging them into knifes, one by one. Forge them completely to the final knife shape, none of this sissy grinder nonsense. Keep forging until every spike is a knife.

Then you take the knife billets and you start heating them up until they glow enough to where a magnet doesn't stick to them anymore, and dunk it in the creek. Do this for all 500 of them.

Then, maybe, just maybe, you'll be ready to make a knife worth a darn.
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I totally understand where you're coming from, but its just not necessary. I was told something similar when i first got into cnc. I was told i need to start with an old manual bridgeport to learn what machining is all about. I skipped that and designed and built my own cnc mill turn machine, started doing prototype work for drone companies, designed and manufactured a large rc helicopter model, etc. Still to this day ive never touched a manual machine and i have no need to. Why would i need to pound out railroad spikes if i want to design a cnc machined folding knife with titanium cnc milled scales? Whats the point? Do you think john grimsmo pounded out any railroad spikes? I realize he may not be the best example and theres a lot of fanboyism going on to get people to pay what they do for his knives, i never would, but still he started out exactly as i did and made a great knife. He started by teaching himself cnc in his garage and building a conversion, moved on to other cnc related side jobs, made some knife handles for existing knives, one day decided he wanted to design one. I realize theres a lot of douches out there that think they are gonna jump into the knife world and get rich. That isnt me, i am a maker of many things with plenty of experience designing and machining mechanisms. I taught myself cnc from the ground up and i believe i am capable of designing a good knife without pounding on railroad spikes. One thing that i dont have experience doing personally is heat treat and thats what i came to ask about. I mean no disrespect, but i cant say i agree with the idea that you need to start in the stone age to learn a skill that is now commonly done with new technology. My goal is to use my skills to build a knife and have a blast doing it. If i design something someday that people are willing to pay money for as some of the other projects ive taken on, great, if not, dont care. That isnt my primary intention. I love designing and machining, i think building a knife fits into that well and its something ive wanted to do for years.
 
You are asking reasonable questions. As I always say, the details matter.... you are asking broad general questions and the details matter to your answers.

Knifemaking is primarily about solving problems. You need to learn by doing and solve your problems as you progress. Someone else’s experiences and solutions will be different

You need flatness, parallelism and squareness of holes. You will have to surface grind after heat treat
 
Sean Yaw said:
I start out with precision ground stock and just sand on a granite plate post heat treat. It works fine. I am sure a surface grinder would be handy though... Are you in Montana (406 and all)?
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Yep, flathead valley. Sounds good, i do have a surface plate and was planning on hand finishing some blades on, but wasnt sure if heat treat could cause more warp than what could come out easily. Sounds like its pretty minimal.
 
Quinn406 said:
Yep, flathead valley. Sounds good, i do have a surface plate and was planning on hand finishing some blades on, but wasnt sure if heat treat could cause more warp than what could come out easily. Sounds like its pretty minimal.
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Depends on the HT, on the steel type and stock thickness. Some will curve like a banana. If you use professional HT service they should come back flat. I never did cpm154, but there should be someone who can share an advice or two.

On the other topic, have you got the railroad spikes yet? 😁
 
HSC /// said:
You are asking reasonable questions. As I always say, the details matter.... you are asking broad general questions and the details matter to your answers.

Knifemaking is primarily about solving problems. You need to learn by doing and solve your problems as you progress. Someone else’s experiences and solutions will be different

You need flatness, parallelism and squareness of holes. You will have to surface grind after heat treat
Click to expand...
Yeah youre right, a lot is going to depend on the overall process and ill need to experiment to find out what works in my situation. Right now im at the point where i have a good amount of work done in cad and want to start testing some concepts. Working on a unique locking mechanism. Ive ordered some tooling and materials to get started on some parts. I guess one thing i had not decided on yet was whether or not i should spend extra on surface ground material or start with thicker material to flatten at some point which led me to wonder if heat treating ground stock will give something that is still flat. Ill start experimenting and see what works.
 
Quinn406 said:
I totally understand where you're coming from, but its just not necessary. I was told something similar when i first got into cnc. I was told i need to start with an old manual bridgeport to learn what machining is all about. I skipped that and designed and built my own cnc mill turn machine, started doing prototype work for drone companies, designed and manufactured a large rc helicopter model, etc. Still to this day ive never touched a manual machine and i have no need to. Why would i need to pound out railroad spikes if i want to design a cnc machined folding knife with titanium cnc milled scales? Whats the point? Do you think john grimsmo pounded out any railroad spikes? I realize he may not be the best example and theres a lot of fanboyism going on to get people to pay what they do for his knives, i never would, but still he started out exactly as i did and made a great knife. He started by teaching himself cnc in his garage and building a conversion, moved on to other cnc related side jobs, made some knife handles for existing knives, one day decided he wanted to design one. I realize theres a lot of douches out there that think they are gonna jump into the knife world and get rich. That isnt me, i am a maker of many things with plenty of experience designing and machining mechanisms. I taught myself cnc from the ground up and i believe i am capable of designing a good knife without pounding on railroad spikes. One thing that i dont have experience doing personally is heat treat and thats what i came to ask about. I mean no disrespect, but i cant say i agree with the idea that you need to start in the stone age to learn a skill that is now commonly done with new technology. My goal is to use my skills to build a knife and have a blast doing it. If i design something someday that people are willing to pay money for as some of the other projects ive taken on, great, if not, dont care. That isnt my primary intention. I love designing and machining, i think building a knife fits into that well and its something ive wanted to do for years.
Click to expand...

Ain't no knife never been made worth a darn what ain't been caressed by coal and kissed by a hammer! :mad: "Carbon, iron, and heat, what makes a knife real sweet." Now you tell me what in tarnation's a man to do with a knife what ain't been forged by muscle and sweat? This ain't Sally's gumdrop and lollipop factory. Now go on and get to rustlin' up some spikes! Go on now, GIT!


Naw just kidding, I'm just working on my Joad Cressbeckler impression. 😁

 
ChristoDart said:
Q Quinn406 Have you made a knife from start to end?
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Nope, not a complete knife yet but ive been working on some individual parts and machining strategies. 3d milled a couple blade bevels out of both hardened and annealed steal. I actually got a pretty sweet looking finish in 60rc d2 but it went through inserts quick. Definitely not cost effective to do all the machining from hardened material which i figured, but wanted to try it. Will probably do roughing with maybe 10 thousandths of material left, heat treat, then hardmill the finish pass. From there im not sure if i want to clean up on grinder, cnc grind, leave as a milled pattern finish, bead blast, tumble, etc. So many possibilities its hard to land on a specific plan to try. I also spent a day making some various titanium screws. Current lock design im working on requires some very tiny screws and wanted to see how my machine could handle them. Made some m3's that are only 3.2mm long total, 1mm thick head, 2.2mm of shank. Came out pretty nice. Didnt mill the torx socket into head yet, waiting on some very tiny endmills.
 
Welcome Quinn.
Mecha is just having his fun before he paints himself green and goes out to steal Christmas presents from little kids.:D:D:D
His point is that right now, you don't know what you don't know.

CPM154 will usually HT and remain flat. Press plates pretty much guarantee that. You don't need high pressure, just firm pressure on the plates.

I hope you understand the full HT process for stainless steels.
It requires HT foil, a well-controlled HT oven, aluminum quench plates, the proper HT regime (Larrin's book is a great asset here), liquid nitrogen for cryo, and post-HT finish sanding/shaping.
One thing I have had problems explaining to machinists is you don't make a blade, HT it, and then install it as-is. You have to remove a certain amount of surface material post-HT. If machining the blade to high tolerance, you would have to plan .002 to .005 extra thickness in the pre-HT blade. Some makers only profile the blade roughly to shape, drill poilot holes, and then do all final machining post-HT with carbide tooling. This allows exact precision.

Another issue with warp and precision folder blades in HT is that if the blade is completely machined pre-HT it has areas that are not in contact with the quench plates. This allows, and sometimes causes, warp.

The best way forward will be for you to tell us how you plan to make the blade and HT it.
Post a sketch or CAD drawing of your blade and knife plans. There are also some really accomplished folder folks here who may spot errors or improvements on your blade design.
 
Quinn406 said:
Working on my first folding knife design. It will be mostly cnc milled. I will be using cpm 154 for the blade. This will be my first time dealing with heat treated parts and im not sure what to expect. If i buy surface ground material for the blade that starts out perfectly flat, what is going to happen to the flatness as i mill the bevels and heat treat? I do plan to quench with aluminum plates in a press to help with flatness, but how flat will it really be? This will be a very tight tolerance precision knife so ultimate flatness is important. Is some amount of surface grinding typically done after heat treat?
Click to expand...
Of all the times Mecha has posted that advice, yours is probably the most in-depth response...

I do have a couple of suggestions.
Nathan the machinist does a lot of machining in the CPK process. He has posted many details and some WIP on this site. He contributed a chapter to the recent book Next Level Knifemaking by Fry.

Another person who used to post here and on YouTube about machining knives is Aaron Gough.

I agree you probably don't need to forge 500 spikes, maybe just 100...
 
Stacy E. Apelt - Bladesmith said:
Welcome Quinn.
Mecha is just having his fun before he paints himself green and goes out to steal Christmas presents from little kids.:D:D:D
His point is that right now, you don't know what you don't know.

CPM154 will usually HT and remain flat. Press plates pretty much guarantee that. You don't need high pressure, just firm pressure on the plates.

I hope you understand the full HT process for stainless steels.
It requires HT foil, a well-controlled HT oven, aluminum quench plates, the proper HT regime (Larrin's book is a great asset here), liquid nitrogen for cryo, and post-HT finish sanding/shaping.
One thing I have had problems explaining to machinists is you don't make a blade, HT it, and then install it as-is. You have to remove a certain amount of surface material post-HT. If machining the blade to high tolerance, you would have to plan .002 to .005 extra thickness in the pre-HT blade. Some makers only profile the blade roughly to shape, drill poilot holes, and then do all final machining post-HT with carbide tooling. This allows exact precision.

Another issue with warp and precision folder blades in HT is that if the blade is completely machined pre-HT it has areas that are not in contact with the quench plates. This allows, and sometimes causes, warp.

The best way forward will be for you to tell us how you plan to make the blade and HT it.
Post a sketch or CAD drawing of your blade and knife plans. There are also some really accomplished folder folks here who may spot errors or improvements on your blade design.
Click to expand...
Great input here, couple things i had not considered. Throughout my years of learning cnc i followed along with pretty much everything posted by john saunders and john grimsmo (norseman maker) so im pretty familiar with the heat treat process. His blades are RWL 34 which from my umderstanding, cpm 154 is an equivalent that would be much easier for me to get since RWL 34 comes from sweden. My reasoning for that choice of steel is that it seems to be a great performing steel that is a bit more forgiving and easier to machine than some of the other high performance steels. My plan is to build a heat treat oven from fire brick, kanthal coils, thermocouple, controller. Ive build something very similar for curing prepreg cf, just much lower temps. As you said, blades in foil, into oven at 1950, soak maybe 15 minutes, quench between aluminum plates, temper. Had not put much thought into cryo but was wondering if dry ice is cold enough (-107f or so i believe).
The part i had not considered is the lack of contact with the quench plates if the bevels are pre machined. That pushes me further towards doing as you said, profile the blades with some fixturing tabs while annealed, then HT and mill it hard. It will go through inserts faster, but not a huge deal, it will mean less fixturing setups than pre machining bevels and machining a second time after HT. Ill be using toriod cutter with round inserts so they can be rotated to get great use out of the carbide. Im definitely aware of the fact that all surfaces need to be finished after HT, but wasnt sure how deep i needed to go. Sounds like milling hard will eliminate a lot of variables at the small expense of going through inserts faster.
 
I know next to nothing about most things but, if you were making one blade over and over again would milling a negative into quench plates ensure better contact and help eliminate edge warp?
 
No, it would not work, as the blade will be in a foil packet.

I think you are overthinking this. Make some blades and see if you even have a warp issue. You are going to have to make a good number of blades to learn the process, anyway.
Try the blades:
1) Completely done with .003 extra for finish grinding/polishing.
2) 50% done.
3)Leaving a section along the spine that is full thickness (to be removed after HT).
4) As a profiled blank.
 
Everything Stacy said.

On the topic of warping and using plates, warping plagued me until I discovered the issue.

Don't set the blade on one plate and then fiddle-fart around getting the second plate on top with a clamp. Seems one side started hardening on me before the other, because every blade warped some. I always had to straighten what I could then grind flat.

So now I have the plates mounted vertical in a vise. Drop in the packet and crank it shut.

IMG_6437.jpeg
 
Sando said:
Everything Stacy said.

On the topic of warping and using plates, warping plagued me until I discovered the issue.

Don't set the blade on one plate and then fiddle-fart around getting the second plate on top with a clamp. Seems one side started hardening on me before the other, because every blade warped some. I always had to straighten what I could then grind flat.

So now I have the plates mounted vertical in a vise. Drop in the packet and crank it shut.

View attachment 1692605
Click to expand...
Good idea with the pins. I haven't wanted to invest in a horizontal vise, but those pins would make using a vertical vise feasible.
 
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