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Discussion Starter #1
My press was going 2400 - recently, I had TWO COBALT bits break trying to get thru a GT receiver. This is insane... I've done at least SIX of these.

I suspect Heat Treating issues - but wanted to find out if any of you have gone down to 1600 RPM for routine receiver drilling?
 

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The most obvious first reply is that it depends on drill diameter. Smaller turns faster, larger goes slower. I think I'm set at about 1200 ~ 1300 RPM and my 4mm (or 4.5mm) Cobalt bits have yet to snap off. :cool: It might be a tad slow but I have yet to have a problem so I just leave it be. Don't fix what ain't broke as they say! ALSO........you may be snagging on burrs. Make sure the receiver is supported internally by either the trunnion itself (my choice) or a 1.5" hunk of hardwood. Hope that helps. :grin:
 

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I got the belts on my little Craftsman press set to the slowest speed possible, whatever that is and I don't have a problem breaking bits on any receivers although I've broke a few drilling out the long rivets on some rear trunnions.
 

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For small bits (1/8" and less) I have it set at 1200 rpm. I also put a few drops of tapping fluid on the work and don't really bear down on the bits. Haven't broke a bit yet.
 

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My old craftsman is on the slowest belt pulley(about 800 rpm) and little breakage but i drill real slow with just oil .I don't ever force the drill because i got plenty of time .
 

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I did forget to mention........always back the bit up and out after making some drilling progress. It automatically breaks the chip and helps to clear chips out of ther hole and ALWAYS (unless using carbide) keep things REAL juicy with cutting/tapping oil!!! :wink:
 

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Discussion Starter #8
GOOD data! Thanks brothers... for reference, I'm focusing on the apx 1/8" undersized hole for a rivet.... and clearly, I had the damn press going too fast. The bits were "skating" , not cutting.

I'll try 1600, then reduce it from there... By the way? Drill speed data like this is damn near impossible to find on the net.
 

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The best book in the world. Thicker than a 75 rd drum........ :shock:

"Machinery's Handbook". Latest edition. Get one, it has it ALL between it's covers!!!!!!
 

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the correct speed would be alot faster
for most bits
but i run my hf press as slow as it will go
and just leave it there
 

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CANDYMAN said:
the correct speed would be alot faster
for most bits
but i run my hf press as slow as it will go
and just leave it there
+1

slowest possable speed setting,..
lots of oil,...
drill a bit,.. back out,..drill a bit further,..back out,...
good drill bits(craftsman titanum coated w/ the point),..going to get cobalt drills in the populare rear rivit size.

and support the reciver,...it will bend when you press down on it

use a center punch.

it all helps
 

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Like sex, slow and steady and use plenty of lube...
 

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3.8 x cutting speed (maybe 90 for 4130 steel) divided by drill bit dia.

so, 3.8x90/.125 = 2736 rpm. Center drill and use lube.

This is a standard formula for HSS tooling. If your bit is carbide you can turn it much faster. The big variable here would be your receiver material. Type of steel?
 

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Like I said before............we're going way slow! :wink: :cool:
 

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When you are drilling, watch the metals chips coming out of the hole. Back the drill out to bring a bunch up. You should be getting little flakes (chips). If its powdered metal, you're drilling too fast. Too slow is not good either. The chips will tell you if your cutting spped is right.
 

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I've drilled one or two pieces of metal in my time. Aluminum around 2400 RPM or slower. Hardened steel with cobalt bits 500 RPM or slower. No cheap POS HF TiN drill bits either. Cobalt or HSS. If HSS very slow. My .02
 

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About 600RPM here, never broke one in the receiver, but have snapped a few off on the trunnions.
 

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I checked mine and right now I'm running mine at 1070 RPM. That goes for 2mm up to 10mm for now, Sometimes it DOES feel too slow though.................
 

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My first post here, guys.
I did 500 -600 rpm.
Drilled 2 kits with single regular drill bit with a lot of oil. Not even shaped it
Go slow and do it back and forward to let debree go out.
 

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radkoch said:
I've drilled one or two pieces of metal in my time. Aluminum around 2400 RPM or slower. Hardened steel with cobalt bits 500 RPM or slower. No cheap POS HF TiN drill bits either. Cobalt or HSS. If HSS very slow. My .02
As slow as it will go, and keep the oil flowing. Patience is definitely a virtue when it comes to drilling. I've got the kit demill down to 45 minutes, all rivets, including barrel pressing. If you do a lot of drill work, a "Drill Doctor" is a very worthwhile investment.
 
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