Help bending and re-strengthening 15n20

[Atlas Knife Company]

My nephew is working on a project for school. It has to do with simple/complex machines. He is building a ballista that shoots a glider similar to that of DaVinci design. We plan on making the bow out of 18" of band saw blade that is most likely 15n20. The bow will be cut in the middle and about 1" bent 90 degrees and welded to the rails for the glider. Each arm of the bow will be about 8" long.

1. How do I anneal the blade so it doesn't snap when we bend it 90 degrees?
2. How can I heat treat it afterwards so it will hold a strong bend at the weld so when the bowstring is pulled back it will spring back like it should?
3. How do I anneal a band saw blade so I can drill a hole in it?

The last one also applies to how I would drill a hole in a hardened metal such as a hardened blank as well as general how-to knowledge.

If welding is a bad idea, we could drill and bolt, but it be more work.

 

[Atlas Knife Company]

And just to answer the question running through some peoples minds, yes, the teacher knows about it and has given an OK. Our initial testing shows that the glider only shoots about 10' - 15'. So don't worry about us making a weapon that he takes to school.

 

[mete]

Don't assume it's 15n20 ,in fact it could be a bimetal blade which would cause problems.
Flexibility is determined by thickness not HT.It's probably HT'd for good flexibility anyway.
If you weld it you'll have problems.If you don't weld you'll make things much easier.
Drill with carbide bit ,it shouldn't be too difficult.
You need to work on that ballista ,15' is poor. After all it should be able to fly it over the castle wall !!! Maybe double or triple the bow like leaf springs of a car .

 

[Atlas Knife Company]

The current flexibility is fine(perfect). The biggest problem is trying to get a 90 degree bend in it. I'm worried it will snap if I try to hammer it flat.

The ballista is very small, only 18" long by 18" wide.

 

[justintyme]

yes it will snap if u hammer it flat. hopefully some1 that understands your project better then i will chime in to help.

 

[Atlas Knife Company]

I know it's a forging question that only a few hundred here could answer in their sleep. Just hoping that someone will. Otherwise, I'm gonna take a torch to it, get it red and start hammering. My nephew has to get the bow done today. The project is due Thursday.

 

[Atlas Knife Company]

That didn't work, lucky I tried on a test piece and not the final bow.

 

[SteelSlaver]

If you get it red hot you should be able to form it to about any shape you please while red hot. If while red hot you bury it in kitty litter and let it cool very slowly you should be able to drill it. Then you need to get it hot enough that a magnet no longer sticks to it (a dull-medium red depending on the light you look at it in), then air cool till it is black again. Then heat it up until the magnet doesn't stick again then just a bit hotter and plunge it in some warm cooking oil. Then as you need a spring stick it in the oven on about 600 for 2 hours. If your oven goes to 700 better yet. Then let it cool. This is a crude HT and will not get the best out of the steel. To do it correctly you need experience or a controlled oven that will reach 1500f and to know exactly what steel you have

 

[Atlas Knife Company]

Thank you. We will do that this afternoon and hopefully get the project finished in time.

 

[Atlas Knife Company]

For the few of you who visited this thread, here is the completed project, including working spring loaded trigger.

It is my nephews job to clean the extra glue off, but I used every one of my knife making tools building this thing, especially my new portaband.