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Hard material to drill

J

John 345

Member
Hi ,
Anyone have any ideas on drilling draw bar from a zetor tractor .Got tap size drill through by pilot then 1/2 mm increase till correct size tool steel countersink intially ok then just not cutting, hole about 70mm away from step up bend thought these would be cold bent . Its 25mm x 6omm flat bar. It factory tow bar using in bending set up on press.
 
John 345 said:
Hi ,
Anyone have any ideas on drilling draw bar from a zetor tractor .Got tap size drill through by pilot then 1/2 mm increase till correct size tool steel countersink intially ok then just not cutting, hole about 70mm away from step up bend thought these would be cold bent . Its 25mm x 6omm flat bar. It factory tow bar using in bending set up on press.
Click to expand...

I'm frankly surprised you were able to do that. I just assumed those tow bars were very strong forgings.

If it were me, I'd try and find one with the right hole in the right place.

If not, I'd try carbide drills or maybe a carbide boring head on the mill. Go slow with lots of coolant.
 
I once drilled two 3/8" holes through an angle plate (1.25") for my milling machine. My cobalt drill bit did not make much of a dent in that hardened steel and I did not at that time have any solid carbide bits. However, at a trade show I attended, I had bought a set of drill bits from Mad Dog who are still around I think - and promptly burned the tip off the first one by following their flawed instructions to not use any lubricant and spin the drill bit as close to 2000 RPM as possible. Switched to the spare bit, used lots of lubricant and a much slower speed, and got the two holes drilled. Mad Dog stood behind their warranty and sent me a new 3/8" drill bit. Nice of them.
 
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