Harden and Temper

[slick95]

Calling on the experts: :bow: :bow: :bow:

I'm having difficultly with a home made fly cutter to cut gears for my Duclos Odds N' Ends H&M. I'm using the instructions from Phil's The Shop Wisdom series but it seems the cutter will not achieve the hardness needed because as I cut the brass gear blank the tip of the cutter rounds off after just a few moments of cutting. On first contact with the blank it cuts nice then just hits and will make a mess if I push it.

Using the Duclos instructions, I am heating the cutter to cherry red and quenching straight down in water until cool. Then I'm heating to a straw color and letting cool without disturbing. The "straw" color may be my problem as I'm not convinced I fully understand what this looks like. I believe it the same as the swarf color I sometimes get from a work piece in the lathe.
Mr. Duclos simply states "Harden and temper the end of the tool to a medium straw color."

The gears are some of the last components to make on this (my first IC engine) and I actually thought it would be easier than some of the other parts (ie crankshaft).

All EARS here for any input/direction you guys can steer me.

Thank you in advance for any and all assistance.

Jeff

 

[black85vette]

Great question Slick and timely too. I have been wondering the same thing but have not hit the point that I actually need to use the info.

 

[Bernd]

Jeff,

First question from me would be "are you sure you are using tool steel that can be hardened? Then there are the 3 grades of quenching, oil, water or air. Which steel do you have.

Once you make a cutter and think it's hardened take a file to it. If the file just slides over without taking anything off then it's hardened. If you remove stock it's not. For a one time use I wouldn't even temper it.

The straw color would be just like what straw looks like when wheat is harvested. A nice yellow gold color.

Hope some of this helps.

Bernd

 

[Peter Neill]

I might get shot down for this, but I've always felt (and found) that the description of 'Cherry Red' as a description of the correct temperature colour for hardening to be mis-leading. The first time I tried hardening something probably about 35 years ago I discovered that the colour required would more aptly be described as a 'Bright Orange' to get it above the upper critical point. So you may find that you simply didn't get it hot enough.

Once you get to the right colour/temperature you need to hold it at this point, and for a small silver steel cutter like you described this would only be around a minute or so, just enough to ensure an even soak into the skin to a reasonable depth. You don't even need to temper if you don't soak the heat for too long.
Also, try using a magnet to check when the temperature is correct. If the steel is still magnetic you're not hot enough, once it loses magnetism you should be in the right place.

Peter

 

[doc1955]

If you find you are using a steel without enogh carbon to heat treat you can case harden it by when you achive a bright red dipping it into hardening powder or if you do not have hardening powder you can use plain old sugar then quench. This will work for cutting brass but not for any thing tougher.

I have built that engine and did make that cutter but I used A2 tool steel and heat treated it.
Good Luck!
Doc

 

[tmuir]

Following what Peter Neill said I've heard of the colour been described as 'cooked carrots' rather than cherry red but I must admit I've only hardened once for a graver and now hearing Peter say hold it at that colour for a minute I'm wondering if I hardened my graver properly as I didn't keep it there for that long.

 

[slick95]

Bernd: I used drill rod and turned it to 3/16 round. I thought that this material was the type I needed. I forgot about the file check technique to verify the results for tempering/hardening.

Peter: Now that you mention it the color I got when heating was more bright orange than the cherry-red. I'm using a propane torch so that orange cool is about as hot as it will go. Also, I'll use the magnet check too for verification.

tmuir: Actually the "cooked carrots" is a better description of the color. Like Peter's description.

Doc and all: I went back to the shop and decided to make a new cutter tool out of 1/4 HHS mini lathe tool. I ground the proper shape with the bench grinder and gave it a try on the brass gear blank and it cut through like"butter" and the shape of the gear teeth look good. I think I'll use this to finish both gears however I still need to learn the temper/hardening techniques and I will apply what you guys have taught me here.

Thanks to all for your help...

Jeff

 

[RobWilson]

Hi if you have a problem judging the temperature of how hot the tool is (color scale is for natural light), with carbon steel if you heat it up until a magnet will not stick to it ( magnet on a stick) its at the correct temperature for quenching. polish tool heat shank until straw color reaches tip and quench to temper, hope this helps

Regards Rob

 

[lugnut]

Jeff, are you going to run your engine on gasoline or LPG? the one I made last year would never really run correctly on gasoline and so now I am attempting to convert it to LPG.
When I made my cutter for the gears I use drill bit and it worked great. Since then I have been playing with making some gear cutting hobs that work really well..

When are you going to post some photos??
Mel

 

[slick95]

Rob: Thanks for the "magnet on a stick" trick. All you guys have really helped me with this heat treating process.

Lugnut: I plan to use gas for fuel. I built the carb/exhaust unit and I hope it all works. I had originally thought maybe a 3/16" drill bit may work for the cutter but wanted to give the tool in the plans a try.
Actually your Odds N' Ends post was my inspiration for the decision to build this engine. It's been fun and not difficult following the instructions (as you said in your post).
I'll post pictures soon.

Thanks to all for the assistance

Jeff

 

[Jasonb]

Then I'm heating to a straw color and letting cool without disturbing.

You should be quenching again as soon as the temper colour is reached, by letting it cool naturally you are in effect annealing the steel - taking it back to unhardened state.

Also after the heating to red heat and quenching are you cleaning the metal back to bright so you can see the temper colours?

Jason

PS you won't see the cherry red well if you are working in a well lit room or in bright sunlight.

 

[Mainer]

A magnet is the most reliable test, but another visual aid is to heat it hot enough so (visually) the sharp edges disappear. That is, if the piece you're heating has a 90 degree corner, when it's hot enough you won't see the line of the corner anymore. But, like "cooked carrots," it's a guess.