Gallery, Projects and General > How do I??

Drilling and tapping in bronze

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sparky961:
Spot the hole before drilling and don't move the table between that, drilling and tapping.  There's no specific reason to do this for bronze other than to eliminate one possible contributor to failure.

I'll second recommendation for a good quality, new tap.  I'd avoid, however, spiral flute because they are the weakest of all taps.  Personally I'd go with a 2-flute spiral point machine tap because they're virtually bullet proof.  If the hole is bottoming I'd start the hole on the mill to keep it square and finish by hand.  Hopefully you have enough hole depth to do this, or it's a through hole (in which case you can tap through on the mill).

This stuff does tend to "close in" on a drill bit if you aren't careful.  Use more coolant or cutting oil than you think necessary and clear chips often.  Neutral rake on cutting tools does tend to help, especially with it wanting to grab and self-feed.  Also use a slower cutting speed (SFM) than you'd expect.  You can go really slow without hurting anything but depending on the alloy some don't like it fast.  Just ballparking it, maybe 1/2 to 1/3 the speed for mild steel.... say 50 SFM or so may seem slow but also gives a nice safety margin.

lordedmond:
Just hope it's not PB1 then your chances diminish


It's looks more coppery than brassy sometimes known as red bronze


Stuart

9fingers:
Thanks so much for all your suggestions guys. I think I now need to ask for your prayers too!

In the meantime I might have the germ of an idea to avoid the problem altogether - needs more thought yet.

Bob

sparky961:
Care to tell us about the past "nightmare experience"?  There might be some things to be learned from that.

9fingers:
I was making some spring collets for a mate. These were for a CNC circuit board drilling machine and held the drills in the tool changer.
I had to turn the OD of the PB rod to about 10mm including a shoulder, then drill through about 8mm resulting in a 1mm wall tube.
Subsequently, a fine slitting saw made part of the tube length into spring fingers.

So about 30mm long, 10mm OD with 12mm shoulder and 8mm bore from memory.

I did not have any collets at the time and so in a three jaw chuck, the weak tube plus the grab of the drill wrote several off.

Even rough drilling  and boring to size caused snatch in the drill and spinning in the chuck.

I got there in the end but poor yield in material and time. He used to make circuit boards for me free of charge and then gave me a one of those horrid "can you just.....?" jobs in return.

Sorry no photos other than those burned into my memory  :lol: must have been 20 years ago at least.

Bob

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