drill bits getting dull

[SE18]

Hi
Building a follower rest for my SB9A and drilling thru 1.25" mild steel. Using HSS drill bits. After just one pass, they become dull (using plenty of cutting fluid and withdrawing bit a lot to remove swarf). Tried to grind the bits after watching tubal and someone else's videos but really hard to get the knack as the tips curve around in weird ways and the angles are crazy.

Cheers

Dave

 

[Ray C]

If the bit itself has ever gotten too hot, it may have lost it's tempering and it's shot now. Depending on the metal it's made of, temperatures above 400F (approximately) can change the original tempering.

As far as the angles, try comparing your grind to a known, good bit.

Hi
Building a follower rest for my SB9A and drilling thru 1.25" mild steel. Using HSS drill bits. After just one pass, they become dull (using plenty of cutting fluid and withdrawing bit a lot to remove swarf). Tried to grind the bits after watching tubal and someone else's videos but really hard to get the knack as the tips curve around in weird ways and the angles are crazy.

Cheers

Dave

 

[GK1918]

You said it Dave the knack. Kind of like after the training wheels are off thing your good ta go.
More hard to explain than do but I start with the cutting edge level to the grinder back and
forth lightly and sweep it downwards but keeping the same plane with the wheel and keep
looking at it. Just dont be to aggressive a fine wheel and light cuts. yes I had drill doctors
and I always had the habbit of cutting & saving power cords when they hit the dumster.
So this is a yes I can do thing. Ever watch a sign painter- same thing. Nice steady sweeps.

 

[Ray C]

... stuff snipped... yes I had drill doctors
and I always had the habbit of cutting & saving power cords when they hit the dumster.

LOL: Seriously now, there's got to be more good spare parts inside them than just the pigtail.

 

[SE18]

ok, thanks, I just returned again from the grinder; comparing good bits with mine; the angles are so crazy but the bit is improving bit by bit, I finally got a half decent web at the top and that helped some; but I have a lot more work ahead of me. I need to take a break for a bit.

I'm starting the hole with center drill and the hole diameter will be 5/16 for the follower rest to attach to carriage holes. I made one hole yesterday but that ruined 2 bits. I am in fact using a drill bit half of 5/16 size to get the hole thru then following with a 5/16.

BTW, how much pressure should you apply to the drill's capstan handle, a little, moderate, a lot?

btw, I did so much experimental grinding that the approx 4" long bit is now a 2" long bit

also, another question, the bit was pretty hot as I was taking heavy grindings, so I'm guessing I passed the 400 degree mark; that could be a problem I assume from what someone just said

my drill chart said to use the lowest speed (about 650 rpm) for over 1/2" steel so the pulleys are set for slow

Thanks

Dave

 

[GK1918]

Yes Ray i know it. Its called "when flipping out. Did you happen to see awhile back Mr Pete
flinging one of those drill jigs in the bucket crash thats only getting caught in the moment.

LOL sam

 

[Ray C]

It's very possible the bit is getting too hot as you're grinding it. Once you get the knack down, it can be done in a few moments and never really get warm to speak of. When drilling, use firm pressure but don't muscle it. The curlies should be coming out evenly from both flutes if the bit is sharpened evenly.

Also, the temperature of 400F is approximate but recent reading about heat-treating indicates that moderate tempering (which decreases hardness) start to happen at/about that temperature for many of the common tool steels.

As an aside, when I need to form a new lathe cutting bit and much material must be removed, I dunk the bit in a cup of ice water and really chill it down before making the first pass. Once it gets warm to the touch, it gets chilled down until very cold. You shouldn't need to do this for drill bits though but maybe it's helpful when you're first starting out.

ok, thanks, I just returned again from the grinder; comparing good bits with mine; the angles are so crazy but the bit is improving bit by bit, I finally got a half decent web at the top and that helped some; but I have a lot more work ahead of me. I need to take a break for a bit.

I'm starting the hole with center drill and the hole diameter will be 5/16 for the follower rest to attach to carriage holes. I made one hole yesterday but that ruined 2 bits. I am in fact using a drill bit half of 5/16 size to get the hole thru then following with a 5/16.

BTW, how much pressure should you apply to the drill's capstan handle, a little, moderate, a lot?

btw, I did so much experimental grinding that the approx 4" long bit is now a 2" long bit

also, another question, the bit was pretty hot as I was taking heavy grindings, so I'm guessing I passed the 400 degree mark; that could be a problem I assume from what someone just said

my drill chart said to use the lowest speed (about 650 rpm) for over 1/2" steel so the pulleys are set for slow

Thanks

Dave

 

[Ray C]

... I was absolutely shocked -and then I laughed like crazy!

Yes Ray i know it. Its called "when flipping out. Did you happen to see awhile back Mr Pete
flinging one of those drill jigs in the bucket crash thats only getting caught in the moment.

LOL sam

 

[irishwoodsman]

there is a grinding gage you can use i'm not for sure where you get them but its made for a drill bit, the army taught me how to grind them and i do it by eye anymore but i use a belt sander for mine and it seems to work better for me, and i pick up every broken or dull bit i can fine, you never can have enough. lol)mac

 

[SE18]

Hi Ray, thanks for the tip on lathe bits too, as when I was reading about drill bits, they came immediately to mind.

I rescued a copy of the 19th version of Machinery's Handbook several years ago that someone had placed in the trash before I even got a keen interest in lathe work. I'm spending a lot of time reading it.

somewhere in the book, I'd have to find it the passage, it states that drill bits should not be dunked in water when sharpening. Something about the dunking that causes their molecular structure to be more suceptible to cracking; for some strange reason, lathe bits are OK to dunk in cold water; at least that is what I read