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

Search
Go

Discussion Topic

Return to Forum List
Post a Reply
Messages 21 - 40 of total 46 in this topic << First  |  < Previous  |  Show All  |  Next >  |  Last >>
HighDesertDJ

Trad climber
Jul 26, 2013 - 09:50am PT
I'm assuming that by 118% faster you mean 18% faster or are you saying it actually went over twice as fast?
Banquo

climber
Amerricka
Topic Author's Reply - Jul 26, 2013 - 11:03am PT
I said "118% as fast" not "118% faster." Perhaps not perfectly clear but I suspect most readers puzzled it out.
Banquo

climber
Amerricka
Topic Author's Reply - Jul 26, 2013 - 02:28pm PT
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.

Credit: Banquo
HighDesertDJ

Trad climber
Jul 26, 2013 - 02:35pm PT
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.
Slabby D

Trad climber
B'ham WA
Jul 26, 2013 - 03:14pm PT
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.
Banquo

climber
Amerricka
Topic Author's Reply - Jul 29, 2013 - 11:41am PT
HighDesertDJ-

Yes, it is always a good thing to question data. You don't know me, my qualifications (ask if you are interested) or how I might be biased. Heck, I might have been bribed by the 3/8" drill cartel.

The usual way that experimental results are verified is by independent, hopefully objective, investigators trying to reproduce the results. Salamanizer has posted about his experience and similar conclusion but if you doubt our data, you should do tests of your own. If you are objective in your method and analysis, I have no doubt you will arrive at a similar conclusion.

a machine that hammered with the exact same amount of force on every blow

I'd love to see a hammer machine (I considered this but the 3/8" drill cartel isn't paying enough to fund it) and read about the results. A power drill might work. I'd love it if you or somebody else did this test. I don't have a power drill or hammer machine and don't want one.

One hole doesn't seem nearly enough to make a real analysis though does it?

A question deserves a reply. One data point is not enough for an analysis but I actually have 6 data points. I will get around to drilling more holes as soon as the cartel coughs up some more cash.
locker

Social climber
Some Rehab in Bolivia
Jul 29, 2013 - 11:52am PT

The referral to the "Cartel" is fuking HILARIOUS!!!...

LMAO!!!...

ryanb

climber
Seattle, WA
Jul 29, 2013 - 12:07pm PT
In a way, each hole is ~4-600 data points since you are estimating depth per blow. The may be effects from rock type, hole angle, fatigue etc that would change the results but I wouldn't discount this 40% difference on statistical significance...

Have you tried an SDS bit with the sds section of the butt cut/ground off to shorten the bit? Doing this was mentioned in some old threads.

Trying it in a roto hammer would also be interesting...
JimT

climber
Munich
Jul 29, 2013 - 02:02pm PT
You can read this mind-numbing discource on the matter (all 170 pages of it) https://etd.lib.metu.edu.tr/upload/12608282/index.pdf or jump to the conclusions, (the reference to cross section reduction are talking about using smaller diameter drills but still in the same 18mm shank drilling machine):-

"Thinner drill bits are more efficient in softer rock (especially because of length effects), while the thicker drill bits are more efficient in harder rock. In medium rock hardness (around K=2x106 N/m), for cross-section reduction case, the efficiency is not dependent on thickness. When the straight drill bit is observed in medium rock hardness, it can be noticed that the efficiency of it is higher than the thinner ones.
Decreasing length increases the efficiency for bits with a cross-section change, especially for the ones with a cross-section reduction. As a result, for the shortest drill bits (250 mm), the thinner drill bits are more efficient than Φ18 mm even in medium rock."
Banquo

climber
Amerricka
Topic Author's Reply - Jul 29, 2013 - 03:46pm PT
JimT-

Thanks for the link to the paper. I find this stuff very interesting. In the paper, when they refer to hand drilling they seem to mean a hand held drill such as a roto-hammer. I've looked but have never found any studies concerning hand held drills.

On a similar topic, there seems to be no studies of hand held hammer efficiency. One would think that some ergonomics researcher would have worked on this but apparently not. There are some studies regarding curved hammer handles.

I'll go over the paper you linked and look at some of the references it provides.

I hadn't thought about the hardness of the rock being such an important factor. In my mind I am thinking the natural frequencies of the rock and the drill will be important. My gut feel is that although my test block is very hard granite, it behaves somewhat differently than drilling on a larger mass of rock.
Brian in SLC

Social climber
Salt Lake City, UT
Jul 29, 2013 - 03:52pm PT
Interesting stuff.

Thanks!
Banquo

climber
Amerricka
Topic Author's Reply - Jul 30, 2013 - 01:56pm PT
I've been going over the thesis paper and have a few observations.

The blow to the end of the drill produces a stress wave or impulse that travels down the length of the drill bit. The efficiency of transmitting the impulse to the tip of the drill is key to understanding what is happening in my experiment. For hard rock like granite it is most efficient if this impulse is short. For softer rock, a longer impulse is more efficient. Short or long impulse can be envisioned as either time or length. Hitting the end of the drill causes a compression impulse traveling at a fixed speed. This compression wave has a length in both time and distance. The speed is a material property and is constant for steel. The speed or velocity is c=(E/p)^.5 where E is the modulus of elasticity and p is the density. For steel this is about 5000 meters/second or 16,000 ft/sec.

Small diameter drills have a longer impulse so are more efficient in soft rock. Fat drills have a shorter impulse so are more efficient in hard rock.

Any changes in the cross section of the drill cause a portion of the impulse to reflect back. The 3/8" SDS MAX drills have nearly constant cross section so very little of the impulse is reflected. The 1/4" bits neck down quite a bit so a lot of the impulse is reflected back towards the hammer where it reflects again and them reflects yet again at the neck down delivering a series of decreasing impacts to the tip. In soft rock these successive impacts can advance the drill but they do not in hard rock.

In hard rock, the length of the drill has very little effect for a straight shank drill. If a drill has a change in diameter, shorter drills will be more efficient.

The shape of the hammer influences the duration and shape of the pulse.

The drill holder certainly influences the pulse.

For most efficient drilling in hard granite, we would want a short, sharp impulse. Any changes in the drill section (Diameter, flutes, slots) will tend to dull and/or reflect the impulse.

It would be good to do tests comparing different drill holders.

Using my granite block (~100 lbs) probably effectively makes the rock somewhat softer. The difference might actually be more than the 18% I got when drilling in a large mass of rock.
Banquo

climber
Amerricka
Topic Author's Reply - Jul 31, 2013 - 12:46pm PT
I'm thinking that the efficiency of a 1/4" SDS drill might be improved by grinding the change in diameter to a taper. I have no idea if this will work or what the minimum angle is to prevent the hammer impulse from being reflected back.

Probably need Ed Hartouni's help.
Banquo

climber
Amerricka
Topic Author's Reply - Aug 2, 2013 - 07:56pm PT
I know most people are bored with this but it seems interesting to me.

I tried grinding a 1/4" SDS bit down so there is a tapered transition from the SDS part to the drill part. I simply mounted the bit backwards in an electric drill and spun it while I worked it on the bench grinder. It didn't take long and came out pretty good. Its pretty hard steel and the lathe won't cut it.

1/4" SDS bits. The left one is ground down to create a smooth transiti...
1/4" SDS bits. The left one is ground down to create a smooth transition in diameter.
Credit: Banquo

I took Salamanizer's advice and got a grinding wheel. He said Silicon Oxide but I ended up with green Silicon Carbide. Whatever, it works well and I am sure I got the bits sharper than before.

Using the newly extra sharp drills and a Black Diamond hammer instead of the Omega Pacific hammer I found that the ground down 1.4" SDS bit drilled 21% faster than the bit with the shoulder. I really find this hard to believe and think I need to find a volunteer to do a blind test.

Looking back to the first test, the plot I made used a trend line with the intercept set to zero which isn't right since the drilling rate isn't linear when starting a hole. So I recalculated everything and here are the three tests so far:

Test 1, Hand sharpened bits, OP hammer
1/4" SDS 0.00279 "/blow
3/8" SDS 0.00326 "/blow (117%)
Theory: The shoulder in the 1/4" bit reduces impulse efficiency and smaller drills are not as efficient at the stone face.

Test 2, Hand sharpened bits, OP hammer
3/8" SDS 0.00324 "/blow
3/8" A-Taper 0.00386 "/blow (119%)
Theory: The A-Taper bit is shorter and held more rigidly.

Test 3, Wheel Sharpened bits, BD hammer
1/4" SDS 0.00323 "/blow
1/4" SDS ground down shoulder 0.00390 "/blow (121%)
Theory: The in the standard 1/4" SDS bit the shoulder reflects the hammer impulse reducing efficiency.

Test 3 doesn't seem consistent with Test 1 so I want to repeat #3 and have somebody else do the drilling and not let them know which bit is which. However, I am pretty confident that it is good data. I hit one 20 then the other 20 and kept cycling so my hits should have been pretty consistent. I think the difference between 1 & 3 is sharper bits and the way I hold the two hammers. I find I naturally choke up more on the OP hammer. Also, the paper we have been looking at has a section where the author discusses the shape of the hammer and how it affects the impulse and efficiency.

Credit: Banquo
Mungeclimber

Trad climber
Nothing creative to say
Aug 2, 2013 - 08:33pm PT
A 2.5" x 3/8" hole takes 623 whacks


Going to name a route "623 whacks" this weekend. established with a rotohammer!


Sincerely,
3/8" Drill Cartel
Salamanizer

Trad climber
The land of Fruits & Nuts!
Aug 2, 2013 - 09:04pm PT
Now that is interesting. I would have never thought the taper of the drill shaft itself could have any effect on the energy transfer enough to have a significant effect on drilling speed. 21% faster is hardly a nominal difference.

Silicon Carbide is what I meant. The "green wheel".

Are those SDS bits in those drill holders? How does that system work? I had an idea about a drill holder where the bit was inset in the handle shortening the length of the exposed bit. This in theory would shorten the overall length of the drill system and give more control over the drilling itself.
Kinda like a bullpup design for drilling.

Your holders look like they have drill bits that are inset deep in the handle like I'm talking about. Cool!!!

I also thought to have an SDS compatible holder where the bit was held in with a magnet. In theory you could easily replace a bit on lead with one hand and no tools. I'm not an engineer though. But a similar system is used to hold the bit on an apex for power drills and screwdrivers every day.
ruppell

climber
Aug 2, 2013 - 09:36pm PT
I'm interested my man. I've only hand drilled to replace some bolts on Nightcrawler a few years back with Greg Barnes. I've put up a few FA's recently that are fairly bold and should most likely have a few bolts added to them so the sane can enjoy them as well. If you ever finish the prototype I'd buy one off you for sure. As far as this line goes:

On a similar topic, there seems to be no studies of hand held hammer efficiency. One would think that some ergonomics researcher would have worked on this but apparently not. There are some studies regarding curved hammer handles.

I was a carpenter for a long time. I've never see fully curved shaft on hammers like you do on ice axes. Some hammers like the Stileto have a very slight curve at the butt section the helps to set nails up high. If framers haven't started using them I'd say there is a pretty good reason.
cragnshag

Social climber
san joser
Aug 2, 2013 - 09:37pm PT
Banquo will sell you one of his fancy drills, you know. He makes several kinds including one with a deep recess that will swallow most of a 6" SDS bit and leave just enough sticking out to drill a 2" hole. I've tried that one and it works well. The only caveat is that particular drill is too deep for a 4" SDS 1/4" bit.

So the compromise is his standard SDS drill that doesn't swallow as much of the 6" bit so you can still use the 4" SDS.

I think he's off to SoYo this weekend, so he may not respond until next week.

Banquo

climber
Amerricka
Topic Author's Reply - Aug 2, 2013 - 11:25pm PT
My drill holders:

http://freepdfhosting.com/f5b2a6adf6.pdf
http://freepdfhosting.com/ae2b775bc6.pdf
http://freepdfhosting.com/9d223e3d61.pdf

I'd be happy to make one for whoever will cough up some cash. Cragnshag and others are paying $80 for the SDS holders and $50 for the A-Tapers. I can make them pretty much any length.

I've found some really awesome foam handle grip material. A 12" piece of the stuff is priced:

1 - 4 $26.56
5 - 9 $14.61
10 - 24 $11.95
25 - 49 $9.30
50 - 99 $5.14
100 - 249 $4.36
250 - 499 $3.89
500+ $3.56

Geez, that's $2 an inch if I only buy one. I need to get up to the 50 price which means I'd have to sell about 150 to 200 drill holders. Won't happen.
Banquo

climber
Amerricka
Topic Author's Reply - Aug 9, 2013 - 07:48pm PT
Got done with my work early today so I repeated the 1/4" SDS comparison above. I mounted the two drills in identical holders and positioned the foam grips so that I couldn't tell which was which. I mixed them up until I really didn't know which was which and then drilled two holes. 20 blows to one then 20 to the other and repeat until I got to 480 blows. When I was done I pulled the bits to see which was which. The bit ground to a taper was once again faster.

This time it was 27% faster.

The tapered drill went 271 blows/inch or .0037 inches/blow. This was with the BD hammer.

Credit: Banquo
Messages 21 - 40 of total 46 in this topic << First  |  < Previous  |  Show All  |  Next >  |  Last >>
Return to Forum List
Post a Reply
 
Our Guidebooks
Check 'em out!
SuperTopo Guidebooks


Try a free sample topo!

 
SuperTopo on the Web

Review Categories
Recent Route Beta
Recent Gear Reviews