Drilling bronze

[Dan Pierson]

I started making the guard for my long delayed knife using Mark's initial sample
of stabilized maple burl (yes Mark, I will finish it some day ).

Took a bar of 1/4 silicon bronze I bought from AKS and face milled part of
it flat then cut off about 7/8 for the guard, marked and center punched it
then tried to drill an initial hole to start milling the slot. The HSS drill (.156),
just spun and managed to get a shallow depression in the stuff. Tapping
fluid made it hard to find the depression so it got sort of oval as I missed but
didn't help the cutting at all.

Do I need to anneal this? Did I work harden it while face milling? Is there
something else I'm obviously doing wrong?

 

[1066vik]

silicon bronze is hard stuff.
one trick I learned some time back for drilling hard things - get a masonry bit, touch up the edges with a diamond to be sure it's got a clean sharp profile, and use it with lots of tapping fluid.
cut slow and it should be able to carve out your hole - although it might be a shade oversized as those bits are often slightly oversized.
another, more expensive option would be to try a cobalt bit.

 

[Rusty McDonald]

Just go slow Dan, It's some gummy stuff to work with much worse than brass or NS. Just finished one using Si Bronze.

 

[Nathan the Machinist]

It probably isn't so much gummy as it is hard and strong. I have made the mistake of writing programs treating it like brass which resulted in much sphincter puckering and slapping of red buttons...

I think you can anneal it by heating to 1000 and water quenching (though you'll want to double check that). A regular HSS bit should be fine, though silicon bronze is quite abrasive, so HSS will dull quickly. You can expect to need a high penetrating force. Dull bits won't cut. A pilot hole the size of your web will reduce the power requirements of your drill press. I've not processed the stuff much, but it pretty much always squeaks a little when I do.

 

[Gene Martin]

Nathan is rifght. Heat it until it looks black under the flame, then water quench. That makes it much easier to anneal. Silicon bronze is indeed tough stuff, but the work is worth it. If you are using a propane torch it will take a little time to heat it. It seems to just suck up heat.

Gene

 

[Dan Pierson]

If I anneal it I'll just set my Evenheat to 1000-1100 F, let it sit (15 minutes?) and water quench it. Seems simpler than using a torch.

Edit to add: I did check the annealing range on the web. Seems to be 900-1250. I'm ignorantly assuming that it doesn't really matter what temperature within that range I pick.

 

[Will52100]

I've used a good bit of it and never had to aneal. Of course it's a pain to polish comparied to nickle silver and brass, but it's woth it. I do use carbide end mills and ti coated drill bits most times though.

I would sugest getting a drill doctor, I don't have very many dull bits since I got one and most materials like Ti and bronzed you realy need a sharp bit. I've seen them from the factory that were dull, though not too many from US companies.

 

[oilburner]

I've worked with the stuff just about everyday for the past 4 months, and done a lot of it now and then before that. Building a custom railing with the material. We just drill it, no need to anneal. Your bit is probably just a little dull. With a good bit you will do just fine. And as a cautionary side note, if you decide to drill a pilot hole first, make sure it is no bigger then the web of the final bit. If it is, the bigger bit will just kind of "augger" it's way through it in about 1 second, either braking the bit, or pulling the part out of the vice/mess the part up. Good luck with it. Mark.