Drilling problems

A

andybill

Joined
Dec 29, 2008
Messages
53
Hi, I've been making stock-removal blades from old lawn mower blades, and everything has been going well, except that I can't seem to make a hole in this stuff. I've taken some blades to a welding shop with a good drill press, and all i got was a burnt out little divot and a beat up bit. Any recommendations?
Also, do I need to heat treat these blades? Thanks, I'm just getting started, pretty cool so far!
 
welcome to the forum.to drill your holes get a carbide masonary bit. the blades are already hard, thats why you cant drill through them. i have never tried to make a knife from a lawn mower blade and depending on how you ground the blade will determine if you need to heat treat it or not. if you turned the blade blue you will need to heat treat it. if you buy a $10. membership you can use the search feature and find a lot of answers to your questions and to some you might not have asked yet. it also helps support the site.
 
A carbide bit will take care of the drilling I guess as the steel is hardened. For the same reason you won't need to HT that blade if you didn't overheat it. What ever you use for profiling and grinding the bevels etc. don't allow it to get hotter than you cannot handle. If you want to work with a soft steel you can try to anneal, then shape it, easily drill etc, then normalize then harden and temper... But as it is a mystery steel for me I wouldn't bother to HT it unless you have a big stock of it in your hand and you'll work on this steel mainly...Good luck...
 
Thanks guys. On a few blades, while grinding the bevels, I had small parts of the edge turn red. I'd imagine this has ruined the temper or the heat treatment. I'll check out those carbide bits.
 
If you want to drill a hole in the tng area you might spot anneal the spot you wish to drill. With a wet rag wrapped around the blade portion of the knife heat the spot you wish to drill untill it is red then bury it in kitty litter or wrap in koawool and allow to cool for a hour or so and try to drill it. Depends on the steel and with a mower blade its anyones guess.
 
I would heat the entire blade to 1500F and cool slowly in wood ash or other thermal insulator, this should anneal it and make it machinable. After annealing, it would have to be heat treated again, I do not know the specifics of lawn mower blades, but I figure that they are a simple carbon steel.1500 degrees and a quench in oil should do a decent job, followed by a 400 degree temper.
 
Just use a dremel cut off wheel to cut a small square hole out where you want your pins.
 
Alright, so I've finished some blades, and they take an edge well but don't hold it. I'm going to try heat treating in my kitchen oven. I have two knives, about 7" long. I'm planning on about an hour or so at 400 degrees, until the blades turn straw colored, then air cooled. Some articles I've read say to do this three times. Any suggestions? This is still the lawn mower blade steel. Thanks -Andy
 
andybill said:
Alright, so I've finished some blades, and they take an edge well but don't hold it. I'm going to try heat treating in my kitchen oven. I have two knives, about 7" long. I'm planning on about an hour or so at 400 degrees, until the blades turn straw colored, then air cooled. Some articles I've read say to do this three times. Any suggestions? This is still the lawn mower blade steel. Thanks -Andy
Click to expand...

That's not going to help you at all. Heat treating involves multiple steps.
  • Normalizing-heating to a high temperature, with the temperature being different depending on the type of steel, followed by a slow cool in still air) I usually normalize three times.
  • Hardening-heating to slightly above non-magnetic and then quenching in water, air or oil...what you heat it up to and what you quench it in depends on the steel type.
  • Tempering-heating the just hardened blade in the oven two or three times to a temperature of about 400 degrees F. The actual time, temperature and number of tempering cycles depends on the steel type.

Normalizing reduces stresses in the steel and reduces grain size.
Hardening makes the steel hard and brittle.
Tempering reduces the hardness slightly and increases toughness.

From your post, it appears that you got the steel too hot during grinding and took the hardness out of the blade. Putting it in your kitchen oven will only reduce the hardness further.

The knife needs to be normalized, hardened and then tempered. You'll have to start from the beginning.

Please go to the top of the page and read all of the stickies in the "Newbies-Good info here" thread. Heat treating terms and methods are discussed in many different threads up there. You'll save a lot of time, by taking the time to read them!

In addtion:
Please fill out your profile. You might live extremely close to an experienced maker who will be more than happy to assist you!
 
I apologize for being the bearer of bad news in my previous post. Just look at it as a learning experience. If you don't have the equipment to get the high termperatures required, maybe you'll be lucky and have a friendly maker living near you.
 
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