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Banquo
climber
Amerricka
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Topic Author's Original Post - Jul 25, 2013 - 09:55pm PT
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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.
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Salamanizer
Trad climber
The land of Fruits & Nuts!
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Jul 25, 2013 - 10:04pm PT
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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.
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ruppell
climber
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Jul 25, 2013 - 10:06pm PT
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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.
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Salamanizer
Trad climber
The land of Fruits & Nuts!
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Jul 25, 2013 - 10:09pm PT
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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?
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Evel
Trad climber
Nedsterdam CO
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Jul 25, 2013 - 10:11pm PT
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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?
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Salamanizer
Trad climber
The land of Fruits & Nuts!
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Jul 25, 2013 - 10:19pm PT
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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.
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Banquo
climber
Amerricka
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Topic Author's Reply - Jul 25, 2013 - 10:39pm PT
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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.
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Salamanizer
Trad climber
The land of Fruits & Nuts!
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Jul 25, 2013 - 10:39pm PT
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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.
A close up of the 1/4 in bits.
Close up of the 3/8 in bits.
And here's a close up of my slightly modified..... Oh wait! Gotta keep it PG for Ron ;)
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Banquo
climber
Amerricka
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Topic Author's Reply - Jul 25, 2013 - 10:42pm PT
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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.
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Banquo
climber
Amerricka
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Topic Author's Reply - Jul 25, 2013 - 11:29pm PT
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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.
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Footloose
Trad climber
Lake Tahoe
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Jul 25, 2013 - 11:41pm PT
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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.
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cragnshag
Social climber
san joser
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Jul 26, 2013 - 12:14am PT
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We need to get you out of the garage Dan. Put that whacking to good use on the big stone!
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bhilden
Trad climber
Mountain View, CA
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Jul 26, 2013 - 02:33am PT
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Banquo,
you gotta get rid of that horrible OP hammer. Redo the tests using a BD or A5 hammer. You arms will thank you.
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JimT
climber
Munich
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Jul 26, 2013 - 02:44am PT
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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.
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Banquo
climber
Amerricka
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Topic Author's Reply - Jul 26, 2013 - 09:49am PT
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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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HighDesertDJ
Trad climber
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Jul 26, 2013 - 09:50am PT
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I'm assuming that by 118% faster you mean 18% faster or are you saying it actually went over twice as fast?
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Banquo
climber
Amerricka
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Topic Author's Reply - Jul 26, 2013 - 11:03am PT
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I said "118% as fast" not "118% faster." Perhaps not perfectly clear but I suspect most readers puzzled it out.
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Banquo
climber
Amerricka
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Topic Author's Reply - Jul 26, 2013 - 02:28pm PT
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I drilled two holes using the same, resharpened, 3/8" SDS bit and a sharpened 3/8" A-Taper bit. The procedure was the same as for the earlier test. The SDS bit drilled at basically the same rate (0.00324 inches/blow) while the A-Taper bit drilled faster (0.00386 inches/blow).
So we have:
1/4" SDS 0.00271 "/blow (100%)
3/8" SDS 0.00322 "/blow (119%)
3/8 A-Taper 0.00386 "/blow (142%)
The A-Taper bit is shorter, has shallower flutes, is held more rigidly in the holder and the holder is lighter. Any or all of these may increase the drilling rate.
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HighDesertDJ
Trad climber
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Jul 26, 2013 - 02:35pm PT
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Banquo I said "118% as fast" not "118% faster." Perhaps not perfectly clear but I suspect most readers puzzled it out.
One hole doesn't seem nearly enough to make a real analysis though does it? I could see if you were using a machine that hammered with the exact same amount of force on every blow but there are so many factors, not the least of which is "this 3/8" hole is going to be a bitch I'm gonna hit it harder and faster" even if it's just subconscious.
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Slabby D
Trad climber
B'ham WA
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Jul 26, 2013 - 03:14pm PT
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With HSS bits I've noticed that 17/64" drill significantly faster than both 1/4" or 3/8". I assume this is a result of a thicker bit transmitting more energy to the rock but offset by the additional rock requiring removal as you move to bigger bits. It would be curious to test what the optimal bit diameter is for maximizing depth.
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