To avoid these ads, REGISTER NOW!

Drill bits grabbing on exit

E

Everett_45

Member
Joined
Jan 9, 2019
Messages
19
Location
Idaho
Hey guys, at work a while back I was hand drilling 5/8" holes in some 3/16" angle iron. If I remember, I started with a 3/16" pilot and went up to 5/8". At the end of each hole the bit would grab and throw the drill around. I was trying to feed as hard as I could given that I was pushing horizontally while standing, and going relatively slow on the RPM. I had ground the drill bit prior, of course without a gauge or anything. It looked like 118 degrees. I tried slowing the feed and giving it more throttle and even then it grabbed. Eventually it broke through. I've experienced this before, drilling some 1/2" plate with a 27/64" drill. Factory 118 grind on that one.

I've read that you should go real slow on the RPM, I could've been going a little fast there. But my main concern is the grind. Is it true that a 118 degree will grab more aggressively over a 135 degree? Or is the grabbing attributed to my speeds and feeds? Interested to hear what you guys think.
 
To avoid these ads, REGISTER NOW!
OP
E

Everett_45

Member
Joined
Jan 9, 2019
Messages
19
Location
Idaho
ez-duzit said:
Mostly due to the large pilot hole and amateur sharpening job.
Click to expand...

I didn't know 3/16" pilot was large for a 5/8" bit. Smallest I could've gone was 1/8". As for the sharpening job, yes it could have been my fault there but as I said it also happened with a factory ground bit.
 
OP
E

Everett_45

Member
Joined
Jan 9, 2019
Messages
19
Location
Idaho
Zewnten said:
It's ok, don't take anything ez duzit says personal, he acts like an arrogant know it all to everyone even with actual experts, it not just you.

But in answer to your questions I have found 135 degree bits do not grab as bad on the exit and I haven't noticed a need to for a 118 tip if the hole is punched and then pre drilled. Some times if it's grabbing bad and doesn't seem to be technique then I'll finish the hole with step drill from the other side, if I can.
Click to expand...

Thanks, I appreciate the feedback. I never thought of finishing from the other side, I'll have to try that
 
P

PT Doc

Well-known member
Joined
Nov 12, 2010
Messages
3,197
The drill bit will behave like a screw as it exits if you don’t have a solid backer. With an appropriate backer, the drill continues to drill as it emerges out the back of the material being drilled because of this sacrificial material. Look at the back of your aluminum, mild steel after drilling a hole without backer support. That is not round by any means. Now look at the back of aluminum or mild steel drilled with backer support. Very easy to see the difference.
 
X

XCMTB83

Well-known member
Joined
Mar 22, 2015
Messages
108
Location
Iowa
Everett_45 said:
Thanks, I appreciate the feedback. I never thought of finishing from the other side, I'll have to try that
Click to expand...

Machinist by trade here and I have always noticed the 135 degree drills to be more "grabby" compared to 118 degree drills on the exit side of the hole. Completely the opposite of Zewnten's experience. This mainly comes into play if you are hand drilling outside of a drill press and or a milling machine.
 
To avoid these ads, REGISTER NOW!
M

matt_i

Well-known member
Joined
Mar 14, 2008
Messages
10,744
Location
SE Michigan
If you clamp it in a vise that's bolted to the table it just drills thru with minimal drama.
 
M

M635_Guy

Well-known member
Joined
Dec 5, 2019
Messages
4,336
Location
NC
I'm no expert, but I thought a step-drill was the best thing for this thing?
 
C

ChrisLS8

Well-known member
Joined
Jan 16, 2015
Messages
1,964
I'll usually have scrap backer clamped to the backside. I literally drilled 2 hubs out to 17/32 to install much larger 3" extended studs on my track car for the upcoming season and also my new slotted rotors out for 4x100.

I just clamp the old rotors to the backside and it keeps going
 
You must log in or register to reply here.
To avoid these ads, REGISTER NOW!
Top Bottom