What size dovetail cutter? Mitutoyo test indicator

[pontiac428]

Check out the workshop practice series on metal finishing. It's a great bathroom read, broken into small sections covering all types of techniques.

The folks who really strive for the rainbow are the ones to pay attention to. There is some hocus-pocus like adding leather and bone to the mix, that may help create some detail, but the basic case hardening salts do the job, too.

 

[Eyerelief]

I have experienced as well as read about case coloring fading over time. I have clear coated some old gun restores I have done to preserve what is left of their original finish.

If your interested, here is an article out of field and stream talking a little about the old school method of charcoal, bone and leather as well as using chemicals
https://www.fieldandstream.com/blogs/the-gun-nuts/the-best-case-color-finish-for-your-shotgun/

I mean, it’s on the internet so it has to be true right?

 

[dkemppai]

""Create a hard, wear-resistant surface on carbon steel parts. Sprinkle compound over a heated part, heat again, and cool in quenching fluid""
I'm very concerned about quenching.

Carbon diffusion within steel takes time and temperature. Something like 20 minutes at 2000F to get the carbon .050", or some such nonsense. (Those aren't exact numbers, obviously). Half the time at 2000F will get you half the depth. Again, these aren't exact numbers. Dropping the temperature slows the process down, etc.

So, heating it red (say 1500F), and holding it there for 5 minutes with case hardening compound won't get a very thick 'hard candy shell'. The 'soft nougat center' will keep it from cracking when quenches.

If you're looking for scratch resistance, all you need is a few thousandths. If you're going to post HT grind, you might want .010". That might take 5 minutes at 2000F, but you'll most likely need a test sample to dial your procedure in.

Honestly, I'd try a test sample first. Heat up a block and hold it at 2000F for 10 minutes with the cherry red on it and quench it. Cut it open, hone the cut edge flat and etch with ferric chloride (or similar). You should be able to see the difference between the grain structure.

(Somewhere I have a slug of mild steel with M2 TIG welded onto it, ground and etched. I'll post a shot of that if I can find it...)
Edit: Found an image. One is M2 on low carbon, the other is ~H13 (massive grain structure) on low carbon. The low carbon is HRC10-15. The M2 is HRC65 (Slug 3). The H13 ~HRC55 (Slug 2). The alloys steel etch darker. With case hardening, that darkness will only be a few thou, to maybe 10 thou thick.

If you do a sample you have a pretty good idea what you'll get.

 

[Janderso]

Carbon diffusion within steel takes time and temperature. Something like 20 minutes at 2000F to get the carbon .050", or some such nonsense. (Those aren't exact numbers, obviously). Half the time at 2000F will get you half the depth. Again, these aren't exact numbers. Dropping the temperature slows the process down, etc.

So, heating it red (say 1500F), and holding it there for 5 minutes with case hardening compound won't get a very thick 'hard candy shell'. The 'soft nougat center' will keep it from cracking when quenches.

If you're looking for scratch resistance, all you need is a few thousandths. If you're going to post HT grind, you might want .010". That might take 5 minutes at 2000F, but you'll most likely need a test sample to dial your procedure in.

Honestly, I'd try a test sample first. Heat up a block and hold it at 2000F for 10 minutes with the cherry red on it and quench it. Cut it open, hone the cut edge flat and etch with ferric chloride (or similar). You should be able to see the difference between the grain structure.

(Somewhere I have a slug of mild steel with M2 TIG welded onto it, ground and etched. I'll post a shot of that if I can find it...)
Edit: Found an image. One is M2 on low carbon, the other is ~H13 (massive grain structure) on low carbon. The low carbon is HRC10-15. The M2 is HRC65 (Slug 3). The H13 ~HRC55 (Slug 2). The alloys steel etch darker. With case hardening, that darkness will only be a few thou, to maybe 10 thou thick.

If you do a sample you have a pretty good idea what you'll get.

Very interesting

 

[pontiac428]

I think case color fades from lack of a protective oil film. I have stuff in the bottom of the Kennedy chest that still looks good after 90 years, so I'm not sure that it is an issue.

One of the reasons I thought this would be cool is the quench can be skipped. You don't need to quench to fix the gas precipitates into the matrix if you prevent oxygen contact (which is one reason for bone/leather, to absorb O2), so the part can be cooled slowly if it is sealed in a foil envelope. The trick of putting small parts in an altoids can packed with case mix does similar, by using an excess of carbon/cyan/nitrogen feed to consume unwanted oxygen despite the leaky container. So the point was that you could cool the part slowly in your HT oven, retain a hard surface, and get cool rainbows to boot. My thoughts are the heat, dip, and quench technique described on the can s for quick and dirty jobs on small parts, making it look easy so more people try the product.

 

[Janderso]

So the point was that you could cool the part slowly in your HT oven, retain a hard surface, and get cool rainbows to boot

I like this idea.
I did read that case hardening tool steels can cause micro cracking.
Since there will be no quench, maybe I can get away with it.
Or I may just blue the parts and be done with it

The small piece is A2. If I had to do it all over again I would have used different materials.
It's all about learning by the seat of my pants.

 

[pontiac428]

A2 is not meant to be quenched, it is air hardening, so that may be part of the cause. The part geometry is definitely your root cause though.

 

[Janderso]

Finished the top piece, re-cut the spring steel sheet. I went with .024” vs. the .020”
The knurled knob locks with just a bit of pressure. I couldn’t be happier how that came out.
Just need to drill and tap holes to mount the dovetail piece then I’m going to make a new base. Then I’m done, maybe.
The jury is hung on the metal finishing method.

 

[Janderso]

Well shoot, I learned something today.
This material for the knurled knobs is W1.
I drilled and inserted a piece of HSS then surface ground it to finish. This will be the mating surface fir the knurled knob to have a fine adjustment fir the indicator.

I decided to weld a tip on the end using a broken drill bit for filler rod.
I assumed all would be annealed so I then went to put an #8-32 thread on and found it was too hard to work.
I decided to just cut it off with a parting tool.
I barely put any pressure on and it snapped off.
W1 gets hard without putting it in water. Who knew? Not me.

 

[dkemppai]

I decided to weld a tip on the end using a broken drill bit for filler rod.

Yep, the M2 drill bit 'filler' will be hard after the weld. ~65HRC... ...It's a nice little trick