8mm button head tests

Search
Go

Discussion Topic

Return to Forum List
Post a Reply
Messages 1 - 36 of total 36 in this topic
Banquo

climber
Amerricka
Topic Author's Original Post - Feb 24, 2013 - 05:54pm PT
Minerals, who posts here on ST, sent me some 8mm button head anchors to test. I have been trying different drill sizes to see what works with them. But first some dimensional data:
Credit: Banquo

The split in the 8mm anchors increases the width of the shank by 22% while for 0.25” anchors the increase is 40%. So the increase is proportionally less for the 8mm anchors. The increase in diameter for the 8mm is 0.069” while for the 0.25” anchors it is 0.095” so the increase isn’t just proportionally less it is actually less. The 8mm isn’t just a scaled up 0.25” anchor which makes sense to me because of dimensional problems of scale. For a round section, the bending stiffness (moment of inertia) increases as the diameter to the fourth while the bending strength (section modulus) increases as the diameter to the third power. If you simply scaled up a 0.25” anchor it wouldn’t simply be proportionally strong or hard to drive. I am sure there are fabrication issues in scaling up also.

Next comes figuring out drill sizes. Carbide tipped masonry bits (SDS & A-Taper) are all oversize per ANSI B212.15 (which I found posted on some website and you can too). I am guessing that carbide bits are oversize so that a 1/4” rod or bolt will always fit in a hole drilled with a 14” bit. HSS twist drills are all just a bit undersize since a drill always makes a hole just a bit larger than the drill’s largest diameter.
Credit: Banquo

Test #1) Drilled with 8mm SDS and tested in pullout using a steel hanger which pried a bit. I had to use a 2 pound hammer in my effort to beat it into the hole. It crumpled and the head was flattened. I managed to mushroom and squash the anchor until the hanger was tight. It pulled at 960 pounds.
#1
#1
Credit: Banquo

Test #2) Drilled with 5/16” SDS and pulled with test fixture. I only got this one in about half way when it bent over. It pulled at 1960 pounds.
#2
#2
Credit: Banquo

Test #3) Was drilled too close to the edge of my granite block and spalled off the side so no result.
#3
#3
Credit: Banquo

Test #4) Drilled with an 11/32” HSS bit. I managed with much pounding to get this one all the way in and I tested it in pullout. My fixture broke at 2780 pounds. I couldn’t reattach to it so I chopped it.
#4
#4
Credit: Banquo

Test # 5) Drilled with an 11/32” HSS bit and tested in pullout with a hanger (some prying). It took much beating to get in and pulled at 2740 pounds.
#5
#5
Credit: Banquo

Test #6) 11/32” HSS tested in shear with a hanger. I mashed the head beating it in. The hanger broke first and then the head popped off with a maximum load of 4550 pounds.
#6
#6
Credit: Banquo

Test #7) Drilled with a 23/64” HSS bit and tested in pullout. It went in nicely and pulled out at 2720 pounds.
#7
#7
Credit: Banquo

In conclusion I would say that the 23/64” drill worked nicely but is very close to a 3/8” drill. Anything smaller than a 23/64 HSS (0.358”) bit is too small. There is a small range of drill sizes that will work since the largest dimension at the split is 0.385”. I would rather go ahead and put in a 3/8” bolt if I am drilling a hole of this size. A 3/8” carbide bit would drill a hole that is too large for the 8mm anchor. A 9mm carbide bit might work but they are pretty rare and I haven’t found them in the USA. Although the steel used in the 8mm anchors seems pretty soft to me, the capacity is certainly good if you can get the hole size right.

Spreadsheets as CSV in case anybody wants to open it in a spreadsheet:


ANCHORS,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,
Split Shank Size,8mm,,"1/4"" x 1-1/2""",,"1/4"" x 1-1/4""",,,,,,,,,,,
,mm,in,mm,in,mm,in,,,,,,,,,,
Overall Length,45.97,1.810,41.73,1.643,34.98,1.377,,,,,,,,,,
Penetration Length,40.94,1.612,38.28,1.507,31.78,1.251,,1.169,,,,,,,,
Shank Diameter,8.03,0.316,6.07,0.239,6.10,0.240,,,,,,,,,,
Largest Split Dimension,9.78,0.385,8.48,0.334,8.53,0.336,,,,,,,,,,
Length of Split,27.89,1.098,22.00,0.866,21.84,0.860,,1.272,,,,,,,,
Difference Between Shank & Split,1.75,0.069,2.41,0.095,2.44,0.096,,,,,,,,,,
,,1.218,,1.397,,1.400,,,,,,,,,,
DRILLS,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,
Recommended Drill,"1/4""",,"1/4""",,"5/16""",,8 mm,,Nov-32,,23/64,,9 mm,,"3/8""",
Type Measured (Carbide),"1/4 "" A-Taper (USA)",,"1/4 "" SDS (German)",,"5/16"" SDS (German)",,8mm SDS (China),,HSS,,HSS,,Don't have one,,"3/8"" SDS (German)",
,mm,in,mm,in,mm,in,mm,in,mm,in,mm,in,mm,in,mm,in
Measured Drill Dimension at tip,6.83,0.269,6.83,0.269,8.38,0.330,8.48,0.334,8.69,0.342,9.09,0.358,,,9.98,0.393
ANSI B212.15 (maximum),6.60,0.260,6.60,0.260,8.51,0.335,8.45,0.333,,,,,9.2,0.362,10.11,0.398
ANSI B212.15 (minimum),6.81,0.268,6.81,0.268,8.31,0.327,8.20,0.323,,,,,9.45,0.372,9.91,0.390
Published Size,,0.25,,0.250,,0.3125,8,,8.73,0.34375,9.13,0.359375,9,,,0.375
Actual/Published Size,,108%,,108%,,106%,106%,,,99.5%,,99.6%,,,,105%

Rhodo-Router

Gym climber
sawatch choss
Feb 24, 2013 - 07:18pm PT
thanks Banquo!
mike m

Trad climber
black hills
Feb 24, 2013 - 07:30pm PT
Buttonheads are always bomber.
Strider

Trad climber
ಠ_ಠ
Feb 24, 2013 - 07:56pm PT
Do you archive the data from your tests anywhere else, where they are all accessible in one place?

This is awesome info to digest and I appreciate the effort to put it together!

-nick
mike m

Trad climber
black hills
Feb 24, 2013 - 08:14pm PT
^^^Agreed. Most of the buttonheads I see are really old and are in varying states of deterioration.
Ron Anderson

Trad climber
Soon to be Nipple suckling Liberal
Feb 24, 2013 - 08:16pm PT
stronger than i thought.. Interesting info..
mucci

Trad climber
The pitch of Bagalaar above you
Feb 24, 2013 - 08:34pm PT
Thanks for the detailed report Dan!

Jesus, 8mm would be tough to send home if you were sketched out on lead!




How about a well placed 5/16th x 3/4" machine head rivet, pull and shear numbers? More of those on Yo walls than any other piece of metal.

Mungeclimber

Trad climber
the crowd MUST BE MOCKED...Mocked I tell you.
Feb 24, 2013 - 08:46pm PT
Banquo, I echo what Mucci said, if you have the time and inclination. I will definitely read the results and buy the drinks. :)






This below mimics everything I have heard about the 8mm Fixe split shafts. Essentially it's a crap shoot, and why would anyone crap shoot when they need it for upward progress. shame too. The old Rawl 5/16" were great on SMC hangers for lightweight work. you could pre-plug the splits into the hanger hole and have it stay. I have a few still, but I'm not doing enough back country work apparently. :)

Test #2) Drilled with 5/16” SDS and pulled with test fixture. I only got this one in about half way when it bent over. It pulled at 1960 pounds.
Scrubber

climber
Straight outta Squampton
Feb 24, 2013 - 08:46pm PT
Stronger than I thought too. Most of the ones around here have been replaced in the last decade or so. There's not much left of them after 20 years in our wet, coastal environment. I have seen the occasional stainless steel one over the years. No idea as to their cost or availability.

As someone who has pulled well over a hundred of these things to replace them with stainless wedge type anchors, I've made an interesting observation. Many of the split-shaft (compression) bolts I've removed have had one or both sides of their split partially or completely fractured prior to me removing them. This is conceivably due to the forces involved in beating the bolt into a tight fitting hole. (The cracked portion has clearly been rusting for some time before I got to it.)

Did any of the ones you sucessfully pulled show signs of cracking?

K
bhilden

Trad climber
Mountain View, CA
Feb 24, 2013 - 09:52pm PT
I did a little math:

5/16" = .313"

8mm = .315"

So, it looks like 8mm = 5/16" or did everybody already know that?
Clint Cummins

Trad climber
SF Bay area, CA
Feb 25, 2013 - 01:14am PT
Nice work and analysis, Dan.

Minor point: it looks like Excel is up to its usual tricks - it has replaced 11/32 with Nov-32. Putting it in quotes '11/32 should help.
Don Paul

Big Wall climber
Colombia, South America
Feb 25, 2013 - 04:20am PT
Great work Dan. I'm a little surprised by picture #5 were you're pulling the bolt straight out from the rock. I thought bolts had no strength in that direction and could come right out, but you tested it at 2700 lbs. Someone else scared me by showing how easy it is to just pop them out with a chisel.
healyje

Trad climber
Portland, Oregon
Feb 25, 2013 - 04:26am PT
The old split-shank buttonheads out at Beacon are some of the most durable and hardest steel I've ever encountered. If the old homemade hangers on them weren't shite they'd still completely bomb.

Couldn't get them out with tuning forks and I finally tried my battery-powered Sawzall with a brand new Lennox blade that will cut a stud like swiss cheese - the blade burned to nothing making little more than a scratch on the buttonhead. Bummer there aren't better hangers on them.
rick d

climber
ol pueblo, az
Feb 25, 2013 - 06:04am PT
dan-

if you want to try a couple rawl 5/16 for tests let me know I have about a dozen (would like to keep a few). The best test for them is a hand drilled hole.

rick
tucson, az
Banquo

climber
Amerricka
Topic Author's Reply - Feb 25, 2013 - 07:27am PT
Do you archive the data from your tests anywhere else, where they are all accessible in one place?
I am not very organized in this regard.


Did any of the ones you sucessfully pulled show signs of cracking?
I didn't see any. The steel is very soft and malleable. I wouldn't expect cracks.

5/16" = .313"

8mm = .315"

So, it looks like 8mm = 5/16" or did everybody already know that?
I don't have any 5/16" to measure but the 1/4" shanks are 0.239" so I suspect the 1/4" size means they will fit in a 1/4" hole. The 8mm shanks are actually 8mm. A 5/16" may or may not have a 5/16" shank. This is what happens when there are no standards.

Someone else scared me by showing how easy it is to just pop them out with a chisel.
Having pulled a few 1/4" anchors myself, I know that some old ones can be pulled with little effort while others are very hard to pull. New 1/4" anchors tested 3340 lb in shear and 1860 pullout.

if you want to try a couple rawl 5/16 for tests let me know
Sure would, I'll send you my address. A couple to measure and then test in shear and tension.
Roughster

Sport climber
Vacaville, CA
Feb 25, 2013 - 07:34am PT
I always find this stuff really interesting, so thank you for posting it! I have posted this before but I will say it again. I once put a bolt into Table Rock, which is rock of the shittiest quality that is still boltable, that wiggled and spun. I just couldn't get it to tighten down all the way.

I decided to pull it, instead of just removing the inside stud and sealing to see just how "bad" this placement was. I spent the next 4 hours absolutely wailing on it with a 5 lbs sledge hammer funk device. I even started funking up and down and left and right which made the hole huge, and I still couldn't get it to pull.

I finally gave up, unscrewed the bolt from the sleeve and patched the hole, but from that day forward, my confidence in bolts was that, beyond the weird / freakish which I do recognize happens on occasion, they are frickin unbelievably bomber if you get them all the way into a hole.
slabbo

Trad climber
fort garland, colo
Feb 25, 2013 - 08:00am PT
I have placed quite few 5/16 over the years, both rawl and Fixe. Most of these were hand drilled and i always flared the hole slightly to prevent fracture. Whether this compromised strength, i don't know, but the Fixe especially would not go all the way in without the flaring.

most of these bolts certainly seemed bomber enough and were fall tested but you never know and for sure at 20+ years, they are due for replacement anyway.

I noticed Fixe ? hangers for your test. Do you think that the added thickness was a factor with such short bolts ?????

john
guyman

Social climber
Moorpark, CA.
Feb 25, 2013 - 08:30am PT
I hate 3/8 button heads... when the head has many hammer hits, beware!

The head can and will be worked, it will break off.

Kris S was getting lowered and cleaning the draws at Church Dome, "Jacobs Ladder" was the route if I recall.... its slightly overhung... he was swinging in to grab the draw, grabbed it and the top (the head) broke off!!!!! It didn't even hold at all!



Banquo

climber
Amerricka
Topic Author's Reply - Mar 25, 2013 - 10:52am PT
supertopo member "rick d" sent me two 5/16" anchors to test and as a bonus two old Star Dryvins.

Two Star Dryvins and two 5/16" split shank anchors
Two Star Dryvins and two 5/16" split shank anchors
Credit: Banquo

I am interested in testing the Star Dryvins even though the voice in my head says there is no point since they are considered to be bad by one and all. ASCA says:

The Star Dryvin is the only sleeve-and-nail bolt we found. This anchor, once commonly used in sandstone, utilizes a lead sleeve and a steel nail. You tap the sleeve in the hole, and then hammer the nail in, spreading the sleeve. In the best rock the 3/8inch Dryvin only holds 1400 pounds in shear and less than that in pullout. In sandstone, where Dryvins were thought to be a good alternative for drilled angles these bolts are unbelievably weak-we pulled one out with our fingers.

Rickety and somewhat expensive at $2 each, there's no excuse for ever using a Dryvin. If you see a star icon on a nail head that's embedded in a sleeve, yank the sucker out and put in a real bolt.

If I do test them , I would like to try one in shear and one in pullout. I would expect the same results for the two lengths in pullout but the longer one might be better in shear. What to do?

The 5/16" anchors are interesting in comparison to the 8mm anchors. The stated sizes are very close but the 5/16 has a smaller actual shank diameter and a larger dimension at the split. I think it is designed to be placed in a 5/16" carbide hole which is slightly larger than 5/16. Anybody know what drill was specified?

Anchors: 8mm, 5/16" and two 1/4"
Anchors: 8mm, 5/16" and two 1/4"
Credit: Banquo

8mm Fixe, 5/16 Rawl, 3/8" Star Dryvin, 1/4" Powers
8mm Fixe, 5/16 Rawl, 3/8" Star Dryvin, 1/4" Powers
Credit: Banquo

Updated dimension table.
Credit: Banquo

CSV of spreadsheet.

ANCHORS,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,
Split Shank Size,8mm,,"5/16"" x ?",,"1/4"" x 1-1/2""",,"1/4"" x 1-1/4""",,,,,,,,,
,mm,in,mm,in,mm,in,mm,in,,,,,,,,
Stated Diameter,8.00,0.315,7.94,0.3125,6.35,0.250,6.35,0.250,,,,,,,,
Overall Length,45.97,1.810,43.31,1.705,41.73,1.643,34.98,1.377,,,,,,,,
Penetration Length,40.94,1.612,39.24,1.545,38.28,1.507,31.78,1.251,,,,,,,,
Shank Diameter,8.03,0.316,7.72,0.304,6.07,0.239,6.10,0.240,,,,,,,,
Largest Split Dimension,9.78,0.385,10.24,0.403,8.48,0.334,8.53,0.336,,,,,,,,
Length of Split,27.89,1.098,28.07,1.105,22.00,0.866,21.84,0.860,,,,,,,,
Difference Between Shank & Split,1.75,0.069,2.51,0.099,2.41,0.095,2.44,0.096,,,,,,,,
Split Dim./Shank Diam.,,1.218,,1.326,,1.397,,1.400,,,,,,,,
,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,
DRILLS,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,
Recommended Drill,"1/4""",,"1/4""",,"5/16""",,8 mm,,"11/32""",,"23/64""",,9 mm,,"3/8""",
Type Measured (Carbide),"1/4 "" A-Taper (USA)",,"1/4 "" SDS (German)",,"5/16"" SDS (German)",,8mm SDS (China),,HSS,,HSS,,Don't have one,,"3/8"" SDS (German)",
,mm,in,mm,in,mm,in,mm,in,mm,in,mm,in,mm,in,mm,in
Measured Drill Dimension at tip,6.83,0.269,6.83,0.269,8.38,0.330,8.48,0.334,8.69,0.342,9.09,0.358,,,9.98,0.393
ANSI B212.15 (maximum),6.60,0.260,6.60,0.260,8.51,0.335,8.45,0.333,,,,,9.2,0.362,10.11,0.398
ANSI B212.15 (minimum),6.81,0.268,6.81,0.268,8.31,0.327,8.20,0.323,,,,,9.45,0.372,9.91,0.390
Published Size,,0.25,,0.250,,0.3125,8,,8.73,0.34375,9.13,0.359375,9,,,0.375
Actual/Published Size,,108%,,108%,,106%,106%,,,99.5%,,99.6%,,,,105%
rick d

climber
ol pueblo, az
Mar 25, 2013 - 01:21pm PT
dan-
we actually tested two 1" x 1/4" dryvin's in concrete at Geir Hundal's house and got a respectable 800-900lbs shear out of them.

I can see if I can the OD of a 5.10 --5/16" bit to guestimate the hole size.

A photo image of the heads will also reveal the "R" for rawl.

From standing on 100's of 3/8" dryvins I believe the stats will be pretty good when said and done.

lead shields man. woooohooo
Banquo

climber
Amerricka
Topic Author's Reply - Apr 8, 2013 - 05:45pm PT
I got around to testing the 5/16" Rawl button heads. I drilled with a 5/6" German SDS bit. The anchors went in OK but took some solid pounding to drive. They didn't bend mash and crumple like the 8mm ones did. They seem to be harder steel. There was some spalling near the surface as they went in but the results were good. Probably stronger than whatever hangers they might be placed with.

The tension test resulted in a rather impressive 5250 pounds.
5/16" Rawl and 5/16" SDS bit
5/16" Rawl and 5/16" SDS bit
Credit: Banquo
5250 pounds
5250 pounds
Credit: Banquo

The shear test nearly pulled through the 1/8" angle I used to load it. This resulted in an astounding 7370 pounds.
Spalling
Spalling
Credit: Banquo
Credit: Banquo
7370 pounds
7370 pounds
Credit: Banquo
Greg Barnes

climber
Apr 8, 2013 - 06:58pm PT
Yip! No surprise....when people ask my advice on pulling 5/16" buttonheads, it's simple: "Don't mess with them unless you really need to."

The main trick if you really need to pull them (and you don't feel like lugging a 4 foot crowbar around) is to use pins to drive them out a little ways, then tap them back in (not quite flush). Repeat 15 or more times and they pull out - you basically use the buttonhead to break out rock until it pulls.
rick d

climber
ol pueblo, az
Apr 8, 2013 - 07:42pm PT
wow, just wow.

so the real rawls were (are) the schiznick.
Roger Brown

climber
Oceano, California
Apr 8, 2013 - 07:50pm PT
Dan,
I have been lurking here reading every post. I wanted to post several times but didn't. It is really cool you are doing these tests. One thing for sure; holes power drilled are really tight. As a construction worker I have power drilled my share of holes. Even in concrete, which is much softer than granite, button heads go in hard:-) I have even seen people at work "ream" the hole out a bit to make them go in easier. I have pulled a bunch of button heads during bolt replacement and I have come to realize that power drilling can lead to quite a wide spectrum of results. Like "Scrubber" mentioned a few posts back, a lot of bolts come out with fractures and those fractures have been there a long time. I too think they received those fractures during installation. I also think those placing the bolts saw that beating the hell out of the bolts just didn't seem right either. I think people started reaming out the holes to keep from damaging the bolts. Especially the larger sizes. These folks were just trying to get the job done the best way them could, but I fear they might have reamed them out the way I and other construction workers did. We just ran the drill around in a circular motion. I just realized this past season that that method just gives you a cone shaped hole. Bigger at the bottom and tapering up to the top. Well, last season when I found myself running low on 1/4" button heads to replace I decided to replace 5/16" when I ran across them. What a surprise to find many of them coming out as easy or easier than the 1/4" ones. In fact most of them are kinda short. I always pictured them as being these big old bomber things. After I found the bad button heads I started pulling other stuff. I found that if a wedge bolt had a bunch of threads showing, that usually meant that it never tightened up, it just got tight because it ran out of threads. Those generally came out without too much trouble. Cone shaped hole? This season I am going to keep track of which ones come out easy. Keeping track won't be hard, (I bag and tag everything anyway) I am kinda bummed out because I don't want to find what I think may have happened. What do you think Dan? Does it make sense that people would ream the holes out and maybe get it wrong? What do you folks think? Anyone know a route power drilled and reamed out to get big button heads in? E-mail me with the route name. I will start a list and erase the e-mail. Like I said, the 1/4" bolts in the Valley are becoming rare and I have the time and resources:-)
Roger
Banquo

climber
Amerricka
Topic Author's Reply - Apr 8, 2013 - 09:24pm PT
Roger-

No need to lurk, you are amongst friends here.

Obviously, I think the 5/16" Rawls are terrifically strong if placed in good rock and in a good hole. In Yosemite the rock is usually good so the variation is probably the hole. I think some of the confusion is that the size of carbide drills is larger than the stated size and for HSS drills, it is actually less than the stated size. Carbide drills are pretty much standard these days for climbers although a few old trollish climbers are hanging onto their HSS drills.

If you have encountered old 5/16 button heads that pulled easy, I would suspect the holes were drilled oversize. If a climber in the old days drilled a 5/16 HSS hole, he would probably find that he couldn't pound the 5/16 anchor in. So he went to his next size up which was probably a 3/8" HSS.

5/16 = 0.3125"
HSS 5/16 measures 0.3100"
5/16 carbide measures 0.330"

5/16 Rawl shank is 0.304"
5/16 Rawl at widest point is 0.403"

I just don't think you could get the deformed 0.304" shank into a 0.3100" hole.

At 0.403" at the split the anchor will stick in a hole drilled with a 3/8 HSS bit but will have less capacity. It will have almost none in a hole drilled with a 3/8 carbide bit.

3/8 = 0.375
3/8 HSS = 0.372"
3/8 carbide = 0.393"

Anyway, stated anchor sizes indicate the carbide drill size that is right for the hole with the exception of the bizarre 8mm Fixe anchors.

What would be of interest is if you could judge the size of the hole that the anchor was installed in. I've tried measuring hole sizes but I think it is hard to do accurately. The best way to do it would be to carry HSS and carbide drills in various sizes and see which fit in the hole. If you had a 3/8 HSS bit, I would bet it fits in the hole if the 5/16 anchor pulled easily.

Perhaps some old drillers will tell us what size drill they used and we can go replace the ones that were placed with the wrong drill. The wrong drill would be anything but a 5/16 carbide.

All of the holes in my tests and every hole I've ever drilled in rock was hand drilled. I think drilling with a power drill is like riding a helicopter to the top of a peak - a lesser experience.

As for workmen wobbling the drill to wedge shape the hole, I don't doubt it happens but would be impossible to detect without load testing. If an anchor is critical and the safety factors are small, they are often proof loaded which is the only way to know for sure if they are good.

Also, I'd be happy to help you out with your rebolting if you ever need a hand, just ask.

Dan
Banquo

climber
Amerricka
Topic Author's Reply - Apr 8, 2013 - 09:31pm PT
Anybody that places bolts must understand that getting the hole diameter right is critical. The scary thing for me is clipping some bolt and wondering if the guy who drilled the hole knew what he was doing. Most any reasonably new anchor these days is good in Yosemite granite if the hole is the right size.
bhilden

Trad climber
Mountain View, CA
Apr 9, 2013 - 12:56am PT
Dan,

first off, thanks for all the great work! Very cool!

If you are looking for something to test, how about the difference in strength between wedge bolts with "cut" threads versus "rolled" threads. All the data I read is that "rolled" threads are much stronger as the bolt stock is basically intact and isn't cut into as with "cut" threads. Could be interesting.

Here are some references on the subject:

http://cr4.globalspec.com/thread/35903/Thread-cutting-vs-Thread-rolling

http://www.3si.org/forum/f42/any-metallurgists-out-there-want-explain-why-rolled-threads-better-than-cut-326274/
JimT

climber
Munich
Apr 9, 2013 - 02:21am PT
We´ve drilled and measured plenty of holes, partly for QC testing bolts and because we use test blocks to check the bolts actually go in. But only machine drilled obviously so hand drilled may well be different.
Split-point masonry bits with two cutting edges drill a hole which isn´t round but has a special triangular form called a Reuleaux triangle. Even though it measures the nominal diameter at any point you can´t actually fit a round bar of this diameter in the hole. The difference can be huge, a 12mm hole of this type could theoretically only accept a 10.1mm round object.
This also occurs with 4 flute bits but is less extreme.
The effect has been used in engineering to drill not-round (mostly square) holes for over 100yrs using a special drill chuck called an Oldham coupling
The amount of variation from out-of-round varies with the rock and the machine used to drill with and for anchors which need a more accurate hole like self-tapping concrete screws there are specially sized close or matched tolerance bits made, Hilti for example supply a 0.2402" bit for hard concrete and a 0.2260" one for soft for use with their 1/4" Kwik-Con screws.
To partly overcome this effect the standard for carbide-tipped drills requires them to be over-sized, a nominal 1/2" bit has a min size of 0.520" for example.
Dingus McGee

Social climber
Laramie
Apr 9, 2013 - 07:49am PT
The "oversized" 3/8 inch SDS drill bit becomes too small for placing a 0.375 inch diameter Hilti bolt when the carbide across the tip measures less than 0.386 inch. Yes, Jim the drill bit drills a hole smaller than its size! Rock does not drill like steel with the bit held in a drill press.

Banquo

climber
Amerricka
Topic Author's Reply - Apr 9, 2013 - 08:31am PT
bhilden - Rolled threads are generally stronger because of the residual compression stress created at the root of the threads which counteracts the tension stress concentration that happens there. There are very few cut threads in the world, not only are they weaker, they are harder and more expensive to make. I've never seen an anchor bolt with cut threads - which doesn't mean they don't exist of course. If you know of a brand or type that has cut threads, I's like to look into it.

JimT - There is no perfectly round hole and I am sure mine are not perfectly round. They look round to the eye though. The pointed tip of the bit helps keep it centered. The amount of out of roundness probably has to do with the shape of the carbide tip. If you look at the 5/16 German SDS in the first photo above, you can see that it has a small centering nipple and a wide shoulder both of which help keep the hole round and the bit aligned. I don't know if there is much difference between a power drilled hole and a hand drilled hole but hand drilling would seem to be more precise. All my tests are hand drilled because that is the way it is done where I climb.

Anyway, holes aren't round and they aren't straight either.
Roger Brown

climber
Oceano, California
Apr 9, 2013 - 08:35am PT
Dan,
That is some great information. I will measure the hole sizes this season. I put together a small shop next to the garage and have been making stuff for bolt removal. I will make something to hang off the harness to measure hole sizes. I have long said, "it's the hole, not the bolt" Sure, there is the occasional bolt that has rusted so skinny it comes right out, but usually I figure it's the hole. But, hey, these guys were drilling this stuff on lead by hand. I am amazed at some of the bolts that have been placed. I used to have a lot of bolts break while trying to pull them. With new methods that seldom happens now. I do find a lot of bolts that are cracked or half broken when I get them out and the ones that do break only have a small shiny spot at the break. Maybe the best bolts are the ones with hard to drill, sloppy holes and the bad ones are the ones drilled from good stances with tight holes. Someday when I get old, I'll sit down and go thru these boxes of bolts/hangers and see if there are answers just waiting to be found:-)
Roger
locker

Social climber
Some Rehab in Bolivia
Jun 5, 2013 - 05:23pm PT


BUMP for a better AMERICA!!!...


Gobie

Trad climber
Northern, Ca.
Sep 14, 2013 - 01:38am PT
I was curious to see where the 5/16 Rawl buttonheads had ended up in our world so I did a Google search tonight and found this feed. In the late 90s I found by dumb luck a small box of these behind the counter at an REI in Sacramento. They didnt even know what they were for and gave them to me for less then a dollar each. Since they were no longer in production they were like precious ingets. Curiosity got the best of me so I picked up a climbing magazine and began to call climbing shops in areas where I knew that hand bolting was the norm. I ended up calling a shop in WA that had two boxes behind the counter. I purchased every one and ended up with close to 150. I paid my tribute to the godfather (EC Joe), maybe 50. They have all been placed and were all done with a Rawl hand drill with the 5/16 chisel bits with a single twist. I can say with confidence that to this day I would trust everyone of those bolts. Only one out over 100 was botched and that was done by my X wife because she couldnt aim straight. All the holes were started by tapping quickly to get in a flaring pattern to start the whole and make sure that no dinner plating occured and then drilled straight within 1/4 of the depth of the bolt and blown out. When they were tapped in it was critical to understand that physics only allows the bolt to go in so far for each hit regardless of how big your hammer was or how hard you hit it. Knowing instinctively what the mass=force ratio factor was is critical to how the bolt went in. Usually about 10-12 solid blows with a 20oz hammer never intending to drive the bolt fully in just a few blows. It is interesting to see confirmed what I already knew to be true in that these things are bomber. BITD I drilled a few holes in a 40lb boulder nad dropped tested these things just to see if they would hold up as well as 5 piece rawl bolt (they were the schiznic back then). Interestingly enough they held up just about as well and after many drops it was always the sling or the hanger that crapped out first. BTW, we always used an epoxy under the hanger to seal the holes and to prevent the freezing effect.
rincon

Trad climber
SoCal
Sep 14, 2013 - 07:55am PT
Credit: rincon
Banquo

climber
Amerricka
Topic Author's Reply - Sep 14, 2013 - 08:56am PT
There is still confusion about anchor sizes and even more about what drill to use for what anchor.

The old Rawl drills had an odd taper. About half the embedded length was tapered and about half was straight. I have no idea why. The old Rawl drills came in numbers rather than diameters. I have seen old box sets of Rawl drills and anchors where both the drills and anchors used the number system. At some point they seem to have switched to inch sizes for anchors and drills. This may have been when an ANSI standard for drill diameters appeared or when somebody got the rights to the US name.

The Rawl bits below say made in England and there is still an English company http://www.rawlplug.co.uk/. So at some point the size system changed and a US company appeared.

The Star drills used a taper similar to A-Taper but it had a steeper angle and was smaller. The Star drills all seem to come in inch sizes. and are oversize like the ANSI standard.

Anyway, you really must get the right size drill for whatever anchor you use. If you don't use whatever drill is specified for the anchor, testing is your only option. The guys making their own HSS drills need to be careful. A smaller hole may not always be better.



Star and Rawl bits and holders. Left to right the holders are:  <br/>
Rawl...
Star and Rawl bits and holders. Left to right the holders are:
Rawl type (unmarked) with stuck bit
Rawl for 6-8-10-12-14
Rawl type (unmarked)
Star
Star
Credit: Banquo

Rawl holder with 10 &#40;0.200"&#41; and 12 &#40;0.250"&#41; bits.
Rawl holder with 10 (0.200") and 12 (0.250") bits.
Credit: Banquo

3/8 Star drill &#40;0.395"&#41;
3/8 Star drill (0.395")
Credit: Banquo
Gobie

Trad climber
Northern, Ca.
Sep 14, 2013 - 09:46am PT
At the tiem it didnt seem like we had that many choices. I cant even remember now where we would order the drill or bits from. I still have one handle with a bit so far in it that it will never be removed so at some point I must of picked up a bit that didnt match the handle, or I was freakin out and smakin the crap out of it if thinking this would lead to my survival somehow. Anyways, I heard Largo say once in a VHS climbing video "if something seems wrong, it probably is". Just like other areas of rockcraft, bolting requires skill and intuition and common sense. It seems like most people that struggle with this stuff have had no real experience with mechanical stuff or construction. In short, when your pounding it in it just feels good. How could something that feels so right be wrong?
Messages 1 - 36 of total 36 in this topic
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