Drilling Hard Metal

[kthree]

We just screwed up. The drilled hole pattern in some gray iron castings was off just enough to not work properly. It was decided to weld the holes closed and redrill. The castings were welded with mig wire instead of nickel rod. The attempt to drill thru the welded spot with a carbide jobbers drill failed. Our radil arm drill was probably a factor in the failure. Our only 'sturdy' drilling option is a Milwaukee knee mill, but the spindle doesn't feed. Redrilling on that machine would be too expensive. We sure would enjoy any ideas anyone would wish to share with us about drilling the hard metal we created. Several years ago an ad illustration in a card deck showed a tri-lobe, straight flute drill, drilling thru a file - if I remember correctly. Does anyone else remember something like that? All ideas, suggestions, and comments will be greatly appreciated. Thanks, K.

 

[MikeHalloran]

Yes, I remember it. I think it's called a 'HardSteel' drill. It uses a lot of pressure and speed to anneal/ melt/ rub its way through. You may notice a blued area around the hole in the file. I'd worry that it might crack your castings.

Got a friend with an EDM machine?



Mike Halloran
Pembroke Pines, FL, USA

 

[CoryPad]

EDM is a great idea.

There are diamond drill bits that aren't insane expensive:

http://www.emuge.com/technical/pdf/cbn_pcd.pdf

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[kthree]

Thanks All for considering and responding to my post. I hadn't even thought of EDM, and even though I've been around CBN, the thought of it in this application had escaped me completly. Really appreciate your help. K.

 

[arunmrao]

You could have used a ms plug to close the hole and then drilled the hole through. welding around the ms plug also would not have posed a problem for drilling.
Under the present circumstance, best advice is to use EDM.Any force used on the casting might lead to cracks.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[kthree]

Thanks arunmrao, appreciate your info. Are you saying ms = mild steel? K.

 

[arunmrao]

Sorry,I should have been clear,ms= mild steel is right

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[030276win]

wat size is the hole..??... u can still use a solid carbide drill with a very slow helix or zero helix (straight flute)...just get them coated with TiAlN, or better still buy a coated drill...

these days the drills if used properly would cut through 60Hrc. But as u mentioned it has to be on a sturdy machine will very low but constant feeds...

alternatively u can use a brazed tip drill...the steel bosy gives it strength and can be used on ur not so good radial drill too..!!!

 

[kthree]

Thanks 030276win. As coincidence would have it, what ended up being done was along that idea. I was whining about my screwup to a friend the other day and he asked me to give him the parts and let him try. He ended up with a carbide end mill on a sturdy machine and constant feed. He drilled 4 holes @ 7/16" dia in each of 52 parts, all with only 2 mills. And more along that same thought... many years ago, the mid 60's I think, in my GFathers shop, while he was busy on a project at the handwork table, two other gents at the knee mill were arguing about speeds and feeds. Without saying a word, GDad put a file in the vise and quietly started sawing on it with a hack saw. He had a pretty good curf in process when the two gents finally saw what he was doing. He didn't finish cutting it, just left it on the table with a curf bout half way thru it. He explained that the files of the day were of higher quality cutting steel then he had when he started his shop in 1919, and because of that he had learned that patience and constant feed pressure can accomplish wonders. Thanks 030276win for taking the time to consider and respond to my post. K.

 

[efini13]

I had a discussion last week of a similar problem with an experienced machinist. He had told me that the harder drills such as carbide and diamond would be less suitable for drilling hard materials because they cant be sharpened as sharp as a HSS drill. The edge of a carbide drill is more brittle than HSS. You might end up using more HSS drills but you can get through the material. Anyone ever heard of this? It makes sense to me. I haven't had a chance to try yet.

 

[tomwalz]

That is styill true but becoming less so with the new micro, HIPed grades advanced binders.

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com