3/8" SDS drills faster than 1/4" SDS

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Banquo

climber
Amerricka
Topic Author's Original Post - Jul 25, 2013 - 06:55pm PT
So the wife is working late so I went down to the garage and got out two brand new SDS bits and two brand new drill holders. I sharpened both bits to a similar shape. The 1/4" bit is a DeWalt made in Germany. The 3/8" bit is a Makita made in Japan. I whacked the 3/8" drill 40 times then hit the 1/4" drill 40 times, repeat, repeat, etc. After every 80 whacks I cleaned the holes. I used a heavier hammer than my usual Yosemite hammer. Hard granite block.

After I got some depth, I started measuring the depth to the deepest part of the hole.

Turns out the 3/8" bit went 118% as fast as the 1/4" bit. I think a 1/4" hole is only faster because you don't have to drill so deep.

3/8" bit went 0.00321 inches per whack
1/4" bit went 0.00271 inches per whack

A 2.5" x 3/8" hole takes 623 whacks
A 1.25" x 1/4" hole takes 461 whacks

Boy, those are nice drill holders.

Credit: Banquo
Credit: Banquo
Credit: Banquo
Credit: Banquo
Credit: Banquo
Credit: Banquo
Ron Anderson

Trad climber
Soon to be Nipple suckling Liberal
Jul 25, 2013 - 07:00pm PT
maybe its the larger cutting surface of the 3/8??
Salamanizer

Trad climber
The land of Fruits & Nuts!
Jul 25, 2013 - 07:04pm PT
Yep, after hand drilling hundreds of holes I've figured this one out myself. My theory is that the 3/8 in bit allows for looser tolerances, thus giving room for larger chips to be removed with every blow along with allowing more material to be self cleaned by the rotation of the bit.

Just a theory, but to the same depth, 3/8 in definately drills faster than 1/4 in. Thats fact! 1/4 inch just goes in quicker in a pinch because I'm only drilling to 1 1/2 depth instead of 2 1/4 with the 3/8.

Interesting stuff eh.

I still think a modified SDS drills at least as fast as an HSS. But you only have to sharpen the SDS about every 12 holes or so. Doubt you'd get that far with HSS.

Edited to add: You're only getting about 2" with 600 blows? I was used to getting about 2 3/8 with about 600 blows using an unmodified SDS bit.
After slight modification I'm getting the same depth with about 450 blows.
ruppell

climber
Jul 25, 2013 - 07:06pm PT
Maybe it's more force being applied on the hammer swings. To get it truly accurate you would have to use the same amount of force on each swing. Something a human will never be able to do. It is a really interesting test though. I like salamans theory about it. And yes those drill holders are sweet.
Ron Anderson

Trad climber
Soon to be Nipple suckling Liberal
Jul 25, 2013 - 07:07pm PT
of course time can also be slightly modified,, especially on those freaky-deeky leads where yur EXTRA inspired to get sumpn in QUICK LOL! I remember tapping a 1/4 in NOOOOO time once.
Salamanizer

Trad climber
The land of Fruits & Nuts!
Jul 25, 2013 - 07:09pm PT
You'd have to get an adverage after hundreds of holes to be somewhat accurate in your data, which is more or less what I've done.

I actually count every hole I drill. Nothing else to do I suppose. Is that freaky/wierd?
Evel

Trad climber
Nedsterdam CO
Jul 25, 2013 - 07:11pm PT
It sure didn't seem faster Tuesday! I wasn't counting though. Did put in two 3/8x3" top anchor bolts in about 20 mins with my rig which is a modified spline drive to SDS adapter.

Nice drill holders Dude.

How are you sharpening carbide bits?
Ron Anderson

Trad climber
Soon to be Nipple suckling Liberal
Jul 25, 2013 - 07:11pm PT
Sal,, yes that is weird..;-)
Salamanizer

Trad climber
The land of Fruits & Nuts!
Jul 25, 2013 - 07:19pm PT
Carbide bits can be sharpened with a Silicon Oxide grinding wheel.

It's the green wheel.

You have to get the angle right on the tip. Much less than you'd expect, or the tip will chip or shatter easily. Also you have to grind slowly with water near by to frequently cool the bit. If it gets too hot, it quickly becomes brittle and you'll shatter your bit on the first hole for sure.

Much experimenting I've done with many bits I've destroyed. I'll try and take a pic of one of my modified bits.
Ron Anderson

Trad climber
Soon to be Nipple suckling Liberal
Jul 25, 2013 - 07:23pm PT
just make sure its PG!^^^^^^^;-D
Banquo

climber
Amerricka
Topic Author's Reply - Jul 25, 2013 - 07:39pm PT
How are you sharpening carbide bits?

I get cheap flat diamond files. Made in China ~$10 for a set on Amazon. Seem to last a long while and fit in the drill kit.
Salamanizer

Trad climber
The land of Fruits & Nuts!
Jul 25, 2013 - 07:39pm PT
The first two are 1/4 in bits. The one on the left is unmodified, slightly used. The one on the right is modified with a correct angle. I put a more severe angle on the 1/4 in bits than the 3/8. It speeds drilling time and does not shatter as easy as 3/8 would. The two on the left are 3/8, slightly used and modified. Both have drilled at least 10 holes.

Credit: Salamanizer

A close up of the 1/4 in bits.

Credit: Salamanizer

Close up of the 3/8 in bits.

Credit: Salamanizer

And here's a close up of my slightly modified..... Oh wait! Gotta keep it PG for Ron ;)

Banquo

climber
Amerricka
Topic Author's Reply - Jul 25, 2013 - 07:42pm PT
You're only getting about 2" with 600 blows?

A vertical hole keeps more dust which may slow it down. The block on the work bench isn't as rigid as El Cap so that may slow me down. I wasn't trying to hit hard, just be consistent.
BJ

climber
Jul 25, 2013 - 07:42pm PT
Nice job wacking it in the basement while your wife was gone
Banquo

climber
Amerricka
Topic Author's Reply - Jul 25, 2013 - 08:29pm PT
When I sharpen a carbide bit, it is really sweet how much faster it drills.

I wasn't whacking in the basement. I was in the garage silly.
Footloose

Trad climber
Lake Tahoe
Jul 25, 2013 - 08:41pm PT
Sal, you could've been a engineer!

I drilled my first bolts last season.
Fun stuff. Since I only had to do a half dozen.
cragnshag

Social climber
san joser
Jul 25, 2013 - 09:14pm PT
We need to get you out of the garage Dan. Put that whacking to good use on the big stone!
bhilden

Trad climber
Mountain View, CA
Jul 25, 2013 - 11:33pm PT
Banquo,

you gotta get rid of that horrible OP hammer. Redo the tests using a BD or A5 hammer. You arms will thank you.
JimT

climber
Munich
Jul 25, 2013 - 11:44pm PT
A friend who works on (big)rock drill development says itīs because the core of the 3/8" is stiffer and sends the shock from the hammer better into the cutting faces.
Banquo

climber
Amerricka
Topic Author's Reply - Jul 26, 2013 - 06:49am PT
the core of the 3/8" is stiffer and sends the shock from the hammer better into the cutting faces.

I've heard this and think there is some validity to it just like drilling on a solid cliff seems to go faster than drilling on my block. I have been told that solid drill stock will drill faster than a spiral drill.

The OP hammer has never left the garage where I use it for banging on all kinds of things. It, like my BD hammer, is somewhat soft steel which is nice for not dinging things up too much.
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