The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > General Truck Forums > Tools, Shops and Shop Safety

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 06-09-2019, 08:29 PM   #1
cadillac_al
Registered User
 
Join Date: Oct 2013
Location: Maine
Posts: 1,825
question about metal for machinists

Today I had to drill out a stripped GM seat belt bolt. Actually started yesterday, I started in the hex hole with a 5/16 bit and it was drilling nicely. After I went down a 1/4" or so I figured I should put a drop of oil in the hole. Why? because when I am in machine shops I see them putting oil around the drill bit while drilling. I figure it's good for cutting or cools the bit or something. I start drilling again and it is drilling fine. I go down another 1/4" or so and I figure I need a 1/2" bit to take the head of the bolt off. I don't have one so I wait until the next day.

Today I figure I don't need a 1/2" bit, all I need is a 3/8" bit to drill out to the threads. I start drilling with a nice Irwin drill bit and it is going through like butter. I went down another 3/8" or so very easily. My gf was watching me and I told her that is the difference between good drill bits and cheap ones. I figure I should put a drop of oil in there so I don't ruin my nice bit. I put 1-2 drops of oil in the hole and start drilling again and it will not drill at all. I can't get one shaving to come up. WTF? This is blowing my mind.

My question for the machinists is, did I heat treat that bolt with the oil and make it impossible to drill? My theory is that the bolt was so hot from that easy yet aggressive drilling that putting oil on it heat treated it. OR, the oil just makes it too slippery to drill? I have used oil quite a few times before and never really knew if it helped or not but I have never seen a drill bit quit drilling immediately after a couple drops of oil is added. I don't mean flooding it with oil I actually count the drops 1, 2, that's enough. Anybody ever heard of something like this?

I suppose I can try that drill bit on something else tomorrow to determine if the bit just suddenly went dull or the bolt got hard.
__________________
76 Chevy K20
76 GMC K15
77 Chevy C10
cadillac_al is offline   Reply With Quote
Old 06-09-2019, 08:47 PM   #2
mongocanfly
Senior Member
 
Join Date: May 2015
Location: Alabama
Posts: 9,636
Re: question about metal for machinists

Cutting oil both cools and lubricates...its either 1 of 2 or both things...the bit is dull or the bolt could be surface hardened...meaning you drilled out the softer center and have hit the hard surface...
I've had issues drilling some bolts...and case hardened is usually the reason...
__________________
Mongo...aka Greg

1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598
Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334
Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563
2013 GMC Z71..daily driver
mongocanfly is offline   Reply With Quote
Old 06-12-2019, 02:03 AM   #3
e015475
Registered User
 
e015475's Avatar
 
Join Date: Nov 2013
Location: Phoenix Arizona
Posts: 450
Re: question about metal for machinists

For the most part, using cutting oil when you are hand drilling just serves to help you clear chips out the flute of the bit. It is very unlikely you put enough heat into the fastener to 'heat treat' it

A lot of larger bits have a chisel point in the middle and only work well with a pilot hole. Did you run out of pilot hole? I start mine with a sharp 1/8" bit all the way to the bottom of the hole.

While it'd be almost impossible to change the hardness of the fastener, you can dull a drill bit pretty fast by overheating it at too high of RPMs and putting a drop or two of oil on it isn't going to make much difference. Different drill bit brands will have different coatings and materials and one might be more robust to higher speed than the other. Look at the cutting edge of the bit and see if there's chunks missing out of the cutting edge or it is a straw color.

Learn how to sharpen a bit on your grinder or buy yourself a DrillDoctor.
e015475 is offline   Reply With Quote
Old 06-12-2019, 12:18 PM   #4
Terrysch
Registered User
 
Join Date: Feb 2019
Location: Ozark, MO
Posts: 374
Re: question about metal for machinists

Cutting oil keeps the temperature down, not increases it.
But a drop will not do that. When you look at machining, the cutting fluid is pouring on the tool and cutting piece to wash away the chips and cool.

There is some new high tech cutting fluids, that do only use a mist. Keeps the machining chips cleaner so worth more as scrap, plus reduces amount of cutting oil purchased and used, which is expensive - oil!!!!!.
But they are only for aluminum - aerospace especially.

I am retired mechanical engineer who worked most of my career at John Deere and Mercury Marine with background in machining steel and aluminum.
Terrysch is online now   Reply With Quote
Old 06-12-2019, 12:25 PM   #5
Terrysch
Registered User
 
Join Date: Feb 2019
Location: Ozark, MO
Posts: 374
Re: question about metal for machinists

Forgot one comment. Sorry.
Mongocanfly gave the correct answer.
Terrysch is online now   Reply With Quote
Old 06-12-2019, 03:06 PM   #6
e015475
Registered User
 
e015475's Avatar
 
Join Date: Nov 2013
Location: Phoenix Arizona
Posts: 450
Re: question about metal for machinists

You might get a kick out of this.........AvE on drilling holes-

https://www.youtube.com/watch?v=QhpOg186fks
e015475 is offline   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 11:56 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2019, vBulletin Solutions Inc.
Copyright 1997-2013 67-72chevytrucks.com