I’m looking for advice on the best approach for a project.
I have a four pound sledge I’d like to re-profile into a “double diagonal” hammer for Blacksmithing. Similar to a cross pein hammer, but this would entail creating two tapering heads (each at a 45 degree angle to handle) on opposite sides of the head. I know I’ll lose significant mass in the process and I’m ok with that.
The head is likely a medium carbon steel (4140 or similar). I see three viable approaches of increasing refinement:
1- Use an angle grinder with a cutoff blade to remove the bulk of the unneeded material, then grind off the remainder up to the profile line. Using the KMG is also an option.
2- Cut along a profile line (x4) using the metal-cutting bandsaw, then grind to a finished profile using an angle grinder and/or the KMG.
3- use a fly cutter on the Bridgeport to cut the sides in directly.
Forging one from scratch or reforgjng the head is also an (albeit much slower) option.
Questions
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Are the bandsaw blades and/or the fly cutter suitable for medium carbon steel like 4140?
Do you see options advantages or flaws with any of the later approaches?
Metal Shop’s rule of thumb is 55 HRC being the upper limit of hardness we allow to be machined. We have hardness checking files, use one of those to see where it’s at.
The main thing we’re trying to keep down is hardened metal debris from getting anywhere near the machined surfaces in the 'shop, so if it’s close to 55 make sure you’re really thorough with your clean up.
From the tables I could find I saw that 4140 could be as hard as 58 so you’ll definitely need to check and see if they annealed it a bit or left it at full hardness. You may want to anneal yourself and then re-harden to taste anyway.
I’d use the Bridgeport because I’m lazy and all of the other methods would be a PIA (either metal dust from grinding or the difficulty with work holding and getting a good cut on the bandsaw).
My main concern would be is the surface hardening process the hammer went through when it was made. You’d be removing a lot of that surface area exposing the softer metal underneath - which like, swords is desirable so to doesn’t shatter or break while the outer edge/surface is hardened. If you heat treated the whole head then just quenched the hardness would be uniform. I’m sure with your blacksmithing experience (BS abilities! ) you’ve done case hardening before.
I agree Bridgeport would probably be best, you can get cutters for just about any hardness when machining that outer layer - but you’d still have to do the surface hardening issue.
I will fully anneal it before starting (regardless of approach) so the metal would be easier to remove. A long hot tempering would bring the steel to around 25 Rockwell.
I plan to anneal, reshape, reheat and quench both heads (but not the body) in oil, and then temper back for toughness.
Annealed, it should be around 25 Rockwell.
Quenched in oil will take it to 50’s (59 for a water quench).
Tempering at 400F will drop that back down to 42.
My phone’s Heat treat app considers the machinability of 4140 as only “fair” but does not go into specifics as to why or what problems might be lurking.
I can’t say anything for sure, but I’ve been taught that in general a saw will be the fastest material removal, followed by drilling, then milling, then grinding.
If I’m thinking of the shape correctly, a wooden v-block would be easy to make and help you hold the 45deg angle when you run it through the bandsaw. Then grind it to the finished shape.
I’d tend to agree, if the metal is soft enough. Saws tend to do worst with harder materials, however.
The cuts themselves will be straight, but at an odd compound angle (45 degrees to the sides and tapering towards the hammer head) which will make fixturing for cutting with the mill awkward, too.
You are missing the one where you create a jig and just let it drag behind your vehicle as you drive.
If you can get it fitted up, you would probably get it done quickly on the Bridgeport with the shell mill. Especially if you take into account the power feed.
Shell Mill (which has carbide inserts), 20 to 50 thou per pass (depending on how machinable “fair” is ) and powerfeed. It may take a bit but there won’t be much “work” besides waiting and listening to the Bridgeport purr.
With no machined surfaces it might be difficult to clamp in the mill vice, and it will be time consuming to mill it. I would probably go the cutoff wheel route.
A while back I needed to cut some railroad track. I ended up buying this blade to do so, its good to HRC 45. Based on light reading, annealed 4140 is 192HB(Brinell Hardness).
This is a direct length to the proper blade sized for the bandsaw we have in metal shop. It cut smooth as butter on the railroad track which was lightly used(read as work hardened).
Did we acquire this blade or was it purchased by you? I’m interested in doing exactly what @HankCowdog did to a 3 lb sledge hammer from Harbor Freight.
With “perfect being the enemy of good enough”, I ended up just using an angle grinder and a new cutoff blade (for the reach). Refined that cut with a grinding wheel and a 60 grit (IIRC) sanding flap disk (mostly to strip off the black paint and smooth the non-working surfaces).
Went surprisingly quickly/well. Keep a quench bucket of water handy to keep it cool or plan on removing the handle and re-heat treat.
@coloneldan - I can work through the process with you one evening if you’d like. Next week would be better than this week.
) you’ve done case hardening before.