Drilling aluminum bronze on a lathe question.

[gcodeguy]

Had a small 30 piece order (35 slugs received). Drill size call-out was for a "Q" drill-.3320. Forget deph, but somewhere near 1.5 deep. Drilled after rough facing and turning. First piece the .3300 go-gage went to within about .3 from bottom. Bored .334 dia. x .48 deep for thread...just to be able to re-bore for nicer looking threads. After first part .330 gage wouldn't go past bored depth. Wall thichkness .053 before finish turning. I thought maybe it was expanding from the heat of drilling and then shrinking when it cooled. Nope. Ran drill back in after finishing part and go gage still wouldn't go. First time in almost 30 years of machining that I have drilled on a lathe, and the hole wouldn't accept a .002 smaller plug gage. Why? I am not surprised when a drilled hole (on a lathe) will accept a .002 LARGER gage. Yes the drill was on size. I measured it, and then had the other lathe programmer measure it. Both of us measured it as the correct size. Coolant was oil.

Drill brand unknown, but said Korea on it. HSS jobber length with a TIN coating on about half of it. Really nice looking point. Looked like it had never been used after I finished the job. Ran a "Q" carbide reamer to depth on a manual lathe to get on size. Brushed oil on reamer for every part. Part was pretty darn warm especially considering how little material it was removing. Ran cold water over one part and go-gage went just fine so no expanding / shrinking to speak of going on.

Considering the length of the flutes, I am wondering if the drill flexed causing the hole to not be straight. Maybe that is why the part got so hot with the reamer. It also looked like there were more chips from the reamer than there should have been. Don't remember my drill feedrate, but I know it wasn't heavy. My best guess while sitting at home would be .005 per rev.

Thanks for any feedback.

 

[JimmyD]

That seems to be a pretty common problem with that material , it seems tough to get a hole to come out to size when drilling or reaming . New , sharp tools help . It does seem to bore much better than it drills or reams , just the nature of the beast . Jim

 

[Bobw]

Measure your drill again.. Ali Bronze is ABRASIVE, VERY ABRASIVE... Toss some nickel in the mix and it just gets worse...

Was just slamming parts in the machine one time, trailer parts, so I wasn't paying attention too much. Drill and ream...

After about 60 holes, the reamed hole was .010 under the drill size... Nicely tapered....

The stuff EATS HSS and Cobalt. It can chew up carbide also, but at least it lasts for quite a while and you can get some
decent speed out of it.

It is some odd stuff, its the only material I can think of where drilled holes get smaller and smaller and smaller.

Its also the only material I won't hit with a deburr tool... Its like 30 second graders scraping their fingernails on a chalk
board, all at the same time. Odd stuff.

 

[HuFlungDung]

The hole gets wavy, rather than undersize, but the effect is similar. Because the wall of the hole has a 'worm thread' imprint, you cannot get a straight pin of the same nominal size to fit. And it does drill very tight to the drill. Perhaps a pass with a reamer would be the solution, but leave adequate material for the reamer to cut a decent chip or it will most likely get stuck.

I've been impressed with what the difference in drilling larger holes in aluminum bronze is, using a HSS twist drill versus and a carbide insert drill. The latter has no issues with the drilling, but the HSS thinks it's pure hell Again, I would advise neutral rake drill lips, not your typical positive rake drill geometry.

 

[DMF_TomB]

alum bronze can be tough to machine
.
i have seen taps break that were not old normally. using sharp new tools helps. wavy hole so a straight gage does not want to go in seems a logical reason why your holes appear undersize
.
i have seen deep holes in castings where drill bit wondered many mm out of position bending the drill bit as it drifted to softer areas

 

[gcodeguy]

Thanks guys. First no need to measure the drill again. Two guys with about 70 years experience between them measured the drill after the job was finished. The drill was TIN coated and still looked brand new. I should have looked at the hole through a microscope so I could see what it looked like. I can believe the "wavy, rather than undersize" statement. Had I looked under the microscope, I would have had a much better idea of what was going on. First time for the job. Won't bother me if I never see it again. LOL. 35 pieces weren't enough for me to spend any time experimenting.

Speaking of abrasive, anyone who has run 25% glass-filled Teflon with uncoated tools knows what abrasive is. LOL

 

[DMF_TomB]

Thanks guys. First no need to measure the drill again. Two guys with about 70 years experience between them measured the drill after the job was finished. The drill was TIN coated and still looked brand new. I should have looked at the hole through a microscope so I could see what it looked like. I can believe the "wavy, rather than undersize" statement. Had I looked under the microscope, I would have had a much better idea of what was going on. First time for the job. Won't bother me if I never see it again. LOL. 35 pieces weren't enough for me to spend any time experimenting.

Speaking of abrasive, anyone who has run 25% glass-filled Teflon with uncoated tools knows what abrasive is. LOL

.
sometimes a hole is not wavy so much but just curved. same thing though a straight gage going in a curved hole will bind as the gage does not want to bend

 

[Limy Sami]

Speaking of abrasive, anyone who has run 25% glass-filled Teflon with uncoated tools knows what abrasive is. LOL

Yeah, then try carbon filled PEEK