How not to do it

[sparky961]

Recently, I acquired a power hacksaw at an auction. I've been meaning to do up a photo-essay type of thing on this, but I've been rather busy lately with my very ambitious house marketing campaign (thanks again for the visits, guys, even if you're not particularly interested in my home, the blog is starting to be an excellent discussion on the subject of private sale!).

But that's not the point of this post. The blade that came with the machine had a huge chunk out of it that went "ka-thump" at one end of the stroke, so it needed to be replaced. I've been looking for a replacement blade that's around 1" x 12", and I remembered that there was a blade in the pile of things that was on or under the original bench.

So, checking out this blade, I found that it was about an inch too long. I knew that I'd never be able to drill a hole through the blade, so I went online for some advice. There was a posting about "spot annealing" using a blunt piece of steel in a drill... so I tried it with a short piece of 1/4" drill rod. The rod turned blue, and the blade was barely scratched. Attempting to drill it, as was suggested in the posting, just resulted in another drill bit for my scrap pile.

So, I decided to try the torch.... seemed like a good idea at the time - famous last words. Actually, it wasn't that bad. But I digress... I don't have a great torch setup yet, just a barely-adequate little oxy-MAPP set that's insanely expensive to keep filled with O2. But it worked... it was like cutting stainless steel... it just sort of "blooped" away from the place I was cutting, but I managed to get a hole through the thing.

Figuring there must have been a pretty good temper on the piece before I started, I doused the red-hot end of the blade it in a pot of water I had waiting for the purpose.

Great, all good... on to the saw. But wait! What's that "crackling" I hear? The blade shouldn't be making those noises.....

So, I gave it a bit of a flex - SNAP [insert explicative here].

Anyone want to tell me where I went wrong here? How would you put a hole through a pretty hefty hacksaw blade? ???

-Sparky

 

[Alphawolf45]

I'd use a carbide drill or endmill in milling machine or 1/8 inch carbide burr in a Dremel...Your mistake was quenching it made it brittle , it'd worked if you had set it aside to cool slowly.

 

[Mcgyver]

Sparky, when you quenched it you made it dead hard, much harder than it started with.... hard=brittle. - it would have been tempered when you started which is a process that lets the steel down a bit (slightly less hard = slightly less brittle). to anneal, make it soft, it needs a very slow long gradual cool down.

The spinning piece of steel in the DP is something I;ve read about, tried and concluded was BS. Even if you used a small O/A torch to get a small area red hot, the surround metal can act like a quench as it wicks away the heat.

have you tried just drilling it? Before i got a bandsaw i had a homemade hacksaw and would break up and drill lengths of bandsaw blade for it. its was a while ago, but irrc i just drilled it. A hss drill would need resharpening every few holes but it went through

you could also try a masonry carbide bit - best to grind a proper tip on it though

whenever you drill something thin like this take safety precautions - a foot long slender hardened piece of carbon steel is not something you want to grab. I'd have it in a vise, with a piece of wood protecting the vise, and also a stop clamped to the table

 

[Powder keg]

You should be able to do it with a carbide drill. I've drilled files just to see if I could)

Wes

 

[rake60]

As has already been said here the quenching hardened to steel.
It only case hardened it, so you ended up with a piece of steel that
was VERY hard on the outside with a softened interior.

Those properties are very desirable in some cases, such as a key for a
shaft that will be subjected to multiple shock loads.
For a hack saw blade, not so much.

Let's see if I'm intelligent enough to explain the hardening verses annealing process.
Imagine steel as being a very stable fluid. It's molecules are random and it is strong.
When you heat it up those molecules begin to loosen up and line themselves up in an
orderly fashion. That is softening the molecular structure of the steel, but there are
still wild bits that are not following that path of rearrangement.
If you cool it quickly those random bits on the outer surface of the material are frozen
in place resulting in case hardening.
If it is cooled very slowly it allows more time for those outer molecules to line up resulting
in softening or annealing.

Imagine it this way.
If you had 20 strands of wire stretched vertically could you stick your hand through it
without injury?
If you added just 5 random strands of that wires running either horizontally or diagonally
across those lines, would you be as willing to stick your hand through it?

That may be over simplifying it a bit, but it may make the point.

After that lame attempt at an explanation you all know why I never became an
instructor! :big:

But back to the original question, a carbide drill or end mill WILL drill the hardest
of steels. I've used either of them to drill out broken HSS taps many times.

Rick

 

[sparky961]

I had also thought of the idea to grind a hole in it. That's how I got the holes into the stainless steel stock pot that houses my furnace. This would have been what I FIRST tried, but unfortunately, my Dremmel and accessories went to storage with a bunch of other stuff a little while ago.

I like the idea of using a masonry bit to drill it. When I saw people saying "use a carbide drill bit", I was going to reply that I didn't have any - until I remembered that's what's on the end of masonry bits. Any idea if a regular old bench grinder will sharpen carbide?

I'm going to go try that right now!

-Sparky

 

[Powder keg]

Any idea if a regular old bench grinder will sharpen carbide?

It will if you put a green silicon carbide wheel on it)

Wes

 

[sparky961]

Yeah, the "regular old bench grinder" did little but polish it a bit. I'm not sure what the grey wheels are - aluminum oxide, perhaps?

However, I did have a cheap set of diamond files here, and they made short work of the carbide - letting me sharpen them to a bit of an edge.

After that, it drilled pretty much as though it were any other metal...

Also, you made an excellent point about the work holding, Mcgyver. I had it clamped as shown in the picture both times. Like this, even if it did get loose, it would spin and hit the column instead of taking a slice out of my mid-section... or so the theory goes.

-Sparky