drilling 660 bronze

Houndogforever · Apr 8, 2021

Now that my lathe is making parts, I know at some point I will be making some bushings out of this stuff.
It's SAE660 bronze and the final bore is .750+.0007/-0.0
I will need to drill this hole about 2-1/2" deep and it will be a thru hole.

I run 2 different styles of these, but that changes outside dia, not inside.

I figure an 11/16 drill thru and then bore it to size.
I make about 75 a year, and have for over 5 years.

I do NOT have high pressure coolant, however I am fairly certain I can get low pressure coolant to atleast go thru the internal passages. Not sure how much pressure that would be, but I reckon flow would be fine.

So how would you guys get that hole in there to start off?
Thanks

Dan from Oakland · Apr 9, 2021

Any reason to not start with cored stock rather than solid? Then you can just go after the ID with a boring bar. Cored stock in that size range is about .030 under or over nominal. Given the cost of bronze bar these days, there is no reason to not use cored stock. No need for high pressure coolant to flush chips. I would only use coolant as a way to keep the part cool so you can hold size on the bore and not worry about thermal expansion.

Mtndew · Apr 9, 2021

660 is butter compared to Ampco 18. Flood coolant will be fine.

BT Fabrication · Apr 9, 2021

if you can find material as a tube, id go that way, if not bronze is $$$$$$$$$$$$$$$. if you drill, regular HSS drills are fine. drill 0.030" under then reamer to size. 2 ops and its done. a little coolant helps and you will be on size or max a couple tenths over. id avoid boring bars unless you need to.

david n · Apr 9, 2021

BT Fabrication said:
id avoid boring bars unless you need to.

I'd avoid reamers unless you need too.

..............I flippin hate using reamers..............

660 ya say? It's the 12L14 of the bronze world.....................HSS with flood coolant will work just fine.................boring............use a nice small tool nose radius.

Houndogforever · Apr 9, 2021

I'll tell you, it has been 22 years since I last had a cnc lathe and I didn't even THINK about cored stock.

I reckon I should search for material first, then figure out the methods.

thanks guys.

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drilling 660 bronze

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