Drills breaking drilling through Grade 5 bolts

[dnuccio]

i'm having a problem with drills breaking on this job. 1/2-20 grade 5 bolts, 1 inch long that I am drilling a 5/16 hole through the length of. I'm running this job on a Haas VF2. I'm using cobalt 5/16 drills, 135 degree split point at 900 rpm, 5.5 ipm in an ER collet holder pecking every diameter. Using flood coolant at a higher concentration than I typically keep it at. The drill appears to be getting very hot towards the bottom of the hole before it breaks through, the overall length of the bolt including the head is around 1.375 and the drill starts making noise around 1 inch deep. Stopping the drill before it breaks and checking it out, the cutting edge is very worn. I am spotting these holes with a 120 degree spot drill. I do not have thru coolant capability unfortunately. I have 1000 of these bolts to drill so doing it on the bridgeport (to get a manual feel for how the drill is behaving) is not really an option. I'm currently getting 10-15 holes out of a drill. Any suggestions would be appreciated

 

[Milland]

Give MA Ford a call and ask for an applications person, then review the job. I bet they have a carbide drills series that will work well for you.

Drills - M.A. Ford

 

[dandrummerman21]

Carbide.

Something like this:

https://www.mscdirect.com/product/details/58510728

I did just similar yesterday but drilling through the side of hardened 1/2" shoulder bolts, 800pcs. .172" drill 3300rpm, 8ipm, no peck.

Several brands to choose from; guhring, kennametal, yg1, walter-titex, etc.

Do not spot. you can drill with G01 and have it enter the part slightly slower if worried but just go for it.

I didn't look up speeds and feeds; you should for whatever drill you pick; but you need to go with it. It might feel unreasonably fast but it probably isn't.

 

[memphisjed]

slow the rpm down- a lot. go with about 550 rpm (45sfm),

 

[Scottl]

I'm guessing that despite the flood coolant chips are packing in the deeper part of the hole. Can you program it to retract every 0.200" or so? That should allow the coolant to flush the chips off.

 

[dnuccio]

Should have mentioned, I did try some carbide drills on this with little success. Guhring FireX 5/16, ran right at what Guhring reccomends (I don't remember exact feed and speed, but it was in the neighborhood of 3000 rpm and 20 ipm). Got roughly the same life out of that drill.

 

[dnuccio]

I'm guessing that despite the flood coolant chips are packing in the deeper part of the hole. Can you program it to retract every 0.200" or so? That should allow the coolant to flush the chips off.

I've tried pecking as low as every .050" with no change in results

 

[dandrummerman21]

If you still have some firex drills, I would be thinking more like 2000rpm at 14ipm or so.

you didn't mention if you pecked or spotted with it? Again, I would not spot or peck. If you must peck for any reason, it should be a G01 retract rather than using a G83 or G73.

If you are stuck with cobalt drills, I agree with memphisjed that your SFM is too fast. Keep around the same chipload (.006 or so)

Is the hole depth 1" ? or is the thread length 1" so the hole is more like 1.25+?

 

[dnuccio]

If you still have some firex drills, I would be thinking more like 2000rpm at 14ipm or so.

you didn't mention if you pecked or spotted with it? Again, I would not spot or peck. If you must peck for any reason, it should be a G01 retract rather than using a G83 or G73.

If you are stuck with cobalt drills, I agree with memphisjed that your SFM is too fast. Keep around the same chipload (.006 or so)

Is the hole depth 1" ? or is the thread length 1" so the hole is more like 1.25+?

thread length is 1 inch, overall hole depth is around 1.375"

 

[dnuccio]

Update:
Tried a Firex drill, 2000 rpm 12 ipm (.006 ipr) as suggested with no spot or peck and it made it about an inch deep on the first hole and exploded.

 

[cyanidekid]

l'll chime in with the "slow it down with the cobalt" crowd, but add two things, be sure you break completely through any "case hard" layer to full diameter with the spotting drill... thinking def go with carbide for that tool.
second, if your "grade 5" bolts are cheap garbage, they might easily be excessively hard. common defect in low quality stuff. don't know if you have any control over them though. good luck and update us.

(presume you are using a quality brand Co drill, I like the Hertel of that description)

 

[dandrummerman21]

Update:
Tried a Firex drill, 2000 rpm 12 ipm (.006 ipr) as suggested with no spot or peck and it made it about an inch deep on the first hole and exploded.

Well... whoops.

 

[wmpy]

Can you drill half way, flip it, and drill the other side?

I'd much rather make a bolt from scratch than modify cold-headed hardware.

 

[csteen]

Drilling bolts sucks! Twenty or so years ago similar application Letter A drill through 2" long bolt form tap 1/4-28 for grease fitting. Cobalt drills are very brittle compared to normal HSS. Tried carbide like you have but without the through spindle coolant they are like pissing in the wind. Ended up with Ghuring GT 100 Series HSS Tin coated drills running 30SFM and adjusting feed to get a decent chip, if I recall correctly .008 per revolution minimal peck like 2 diameters. Some bolts seemed to be harder than others and some seemed to be made out of whatever was on the floor of the steel mill all mixed together. Good luck!!

 

[Scottl]

I've tried pecking as low as every .050" with no change in results

I wasn't talking about pecking but actually fully retracting the drill. It certainly would slow things down but if it stopped excess drill wear and breakage .........

 

[cyanidekid]

Drilling bolts sucks! Twenty or so years ago similar application Letter A drill through 2" long bolt form tap 1/4-28 for grease fitting. Cobalt drills are very brittle compared to normal HSS. Tried carbide like you have but without the through spindle coolant they are like pissing in the wind. Ended up with Ghuring GT 100 Series HSS Tin coated drills running 30SFM and adjusting feed to get a decent chip, if I recall correctly .008 per revolution minimal peck like 2 diameters. Some bolts seemed to be harder than others and some seemed to be made out of whatever was on the floor of the steel mill all mixed together. Good luck!!

agree about steel, but l'd add if you are getting dulling without chipping stay with cobalt, slow down.

 

[memphisjed]

They make it to 1” your width / depth ratio is on the less than 1 side? If you are clamping with to much authority the bolt (now tube with 1/16 wall) is going to collapse at this very point. Pinching drill and breaking bits.

Slow down - and give a dwell at the 7/8” and 1” pecks.

 

[dandrummerman21]

I also like memphisjed's point above.

I might suggest a "fixture" that is simply a tapped hole. Screw your bolt down until the head makes contact, then drill through it. No real squeezing other than thread tension. And the drill will be pushing it forward so it can't spin out.

zip it back out with a socket when done.

 

[dnuccio]

I also like memphisjed's point above.

I might suggest a "fixture" that is simply a tapped hole. Screw your bolt down until the head makes contact, then drill through it. No real squeezing other than thread tension. And the drill will be pushing it forward so it can't spin out.

zip it back out with a socket when done.

This is exactly what we've got going on, steel plate 1 inch thick with tapped holes for the bolts. The fixturing is solid

 

[Booze Daily]

Drilling purchased hardware is a crap shoot.
I had one job where nothing I could think of worked. Ended up getting a cup of black cutting oil and a chair and sat there brushing oil on after every peck.