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View Full Version : Replacing the carbide insert on a masonry drill?



adatesman
01-19-2012, 07:25 PM
Admittedly a crazy idea, but do you think it's possible to remove the carbide insert on a masonry drill and replace it with tool steel? Mind you, I'm not asking if it's worthwhile; just if it's possible.

Reason for asking is I dabble in designing mountaineering equipment and pretty much everything suited to drilling in stone has long since changed over to brazed carbide tips on the drills. Unfortunately the carbide tips don't hold up too well when drilling by hand (think: hammer in one hand, drill in the other, give it a smack, rotate a bit and repeat ad infinitim), and HSS drills reground with a chisel point tend to bind in the hole due to the chisel edge not lining up with the margins on the drill. Hence I was thinking of doing a small run of custom drills out of S7 (small= a dozen or so) for some friends for testing, but it just now occurred to me it would be far easier to swap out the insert on a commercially available drill (if possible in the first place).

So, am I smoking crack or did I just find a way to avoid fully machining a dozen drill blanks?

Thanks!

franco
01-19-2012, 07:46 PM
Isn't that doing it the hard way when commercial tool steel star drills designed for the job are still commercially available, e.g.

http://hand-tools.hardwarestore.com/25-96-star-drills.aspx

franco

PixMan
01-19-2012, 07:46 PM
How about you give me the phone number of the guy you're getting your drugs from? They must be kick-ass good!

:D

I would like to think you can still find HSS star drills which are made for the purpose you describe. They are not hard to find.

http://hand-tools.hardwarestore.com/25-96-star-drills.aspx

LOL....the internet, franco beat me by seconds!

Black_Moons
01-19-2012, 07:55 PM
Not bad, though id wonder why you would bother with a masonary drill to start with when all you really need is a bar with a slot ground in the end by an angle grinder cutoff disk or similar and some braze?

Also note that brazing.. anything, will totaly soften it, So you will need some heat treatable tool steel.

adatesman
01-19-2012, 07:56 PM
Ah, probably should have mentioned that the intent isn't to simply put a hole in the rock, but a fairly exact hole in the rock. Specifically 25/64" or 17/64", depending on the size bolt being used. Rawl 5 piece in nominal 3/8" and 1/4" diameters, usually under 3" in length, are common but there's others, including a slew of glue-in epoxied bolts in both standard and metric. And given the alpine setting, dragging a traditional star drill simply isn't going to happen even if you could find the right size.

Sorry for the confusion; lately I seem to be hanging out with climbers, so forgot the application wasn't obvious. :(

PeteM
01-19-2012, 08:09 PM
I think you'll find it easier to make the drill body from scratch, rather than remove a carbide insert (typically brazed in) and deal with the somewhat deformed pocket that is likely left. Starting from scratch also lets you design in the hammering-end of the tool, control the steel quality, give you clean surfaces to chuck up, etc.

RussZHC
01-19-2012, 08:10 PM
From what you have said, I assume current brazed carbide can provide one with those 25/64 and 17/64 holes?

Just asking, have on occasion tried to split rock (for landscaping) via the old fashion route of holes/wedges/feathers and I'd say its tough to hold a hole to an 1/8th let alone a 64th but in my example the actual hole size is not vital to begin with.
Not saying it can be done or isn't done (since why else would you give those specific numbers)...I am also assuming the reason for not using star drills is due to weight?
I guess, what did they used to do?

adatesman
01-19-2012, 08:17 PM
For example, here's a couple bits from the early 1990's when the transition to carbide tips was happening. The top was made by Rawl and the other three likely commercially available and rebranded by climbing gear companies. Note that all four feature the Rawl taper shank, which is long out of date. Also note standard-ish helix on two of them, high helix on one and straight flute on the other. The bottom one is newest and from 1995 and the top two have carbide inserts. Basically I'm looking to make prototypes similar to these, but S7 and straight shank or SDS to fit modern alpine hand drill holders.

Oh, and if I can get away with simply replacing the insert on an off the shelf drill rather than machining from scratch, all the better. If needed the heat treating oven is close to finished, so no worries about hardening.

http://www.supertopo.com/photos/11/26/234119_16059_XL.jpg

adatesman
01-19-2012, 08:32 PM
@Russ- yup, star bits are out due to weight and the fact they don't cut as fast or accurate. Basically we are dropping a 5 piece expansion bolt into the hole in a remote setting in an arguably off-label sort of way and in a life-support manner of use. Drilling 1/64 over nominal seems to give the best compromise between proper tightening torque and accounting for wear on the drill (wear = undersized hole = bolt doesn't go in), hence the odd size requirement. Bear in mind, more often than not these holes are drilled by hand while standing on edges no thicker than a dime with hundreds of feet of nothing below you.... :eek:

Back in the day they used whatever was available, which happened to be tool steel bits made for the purpose. As I said, things hace since shifted to carbide tipped and this pitifully small and insignificant segment of the market has exhausted the old stock and is kinda floundering because of it. The new generation uses battery powered SDS roto-hammers which do fine with carbide, but the older folks and those in designated wilderness areas (read: no power drills of any kind) are left in the lurch.

RussZHC
01-19-2012, 08:55 PM
Right now, think I have to go with Pete on this...not sure that remove and rebraze (?) will get you want you want...so, to me, that leaves a few choices:
1] find a supplier or find out what the material is for a stock (whatever manufacturer) bit (like what you were going to modify) and just plain cut it off and work on the business end, provided the material is suitable
2] go completely from scratch and then all that Pete mentions applies
3] adapt something already out there but without the carbide to start with (mention this because I supposed the argument could be made flute count and pattern could be a variable that could be used to advantage)

It maybe a very small "market" but hey, what if you get a big portion of it? This sort of thing happens a lot with "orphan" sports but someone, somewhere, still has to supply the "basics".

adatesman
01-19-2012, 09:25 PM
Don't think I can argue against any of that, Russ and Pete. Of course considerations on my end are that I'm not sure how my Taig mill will like cutting helical flutes on 17/64" dia S7, and frankly hand fitting a dozen chips of S7 into de-brazed commercial drills for testing might be a PITA but will take far less time than figuring out (and proving out) code for 4 axis milling on a machine not up to the material it's being asked to cut. Bigger mill is on the list, but down the road a ways.... For testing purposes I think hand fitting an insert and then using a toolpost grinder on the lathe would be far easier/quicker than starting from scratch. No? (by which I mean I'm not convinced of it, and until a couple hours ago had planned on going that route)

Mcostello
01-19-2012, 09:56 PM
If he wants a precision hole, shouldn't it be reamed?:)

J Tiers
01-19-2012, 10:52 PM
If he wants a precision hole, shouldn't it be reamed?:)

SOMEONE's gonna get reamed, most likely........;)

Ries
01-19-2012, 11:17 PM
why would removing the carbide tips ruin the drill?
just heat it up til the braze melts, and pull out the carbide.
use a SS wire brush to clean the hot brazing compound out of the slot, then braze in a new HSS insert.
Doesnt sound like rocket science to me.
Sure, you might ruin a couple of ten dollar bits till you perfect the process, but I have de-brazed all kinds of stuff, both intentionally and not, and its not that hard. You just need to figure out what the right amount of heat is, not too hot and not too cold. Probably best to have a smallish oxy-acetylene set and a few different tips to experiment with.

adatesman
01-19-2012, 11:32 PM
Given the number of brazing-carbide-onto-steel threads I've seen in my (not so short time lurking here), that's what I was thinking, Ries. Worst case I figure I slather it all with flux and bits of braze and set it in the heat treating oven to heT and air quench. But I grew up working in a machine shop, not a heat treating shop and realize there's details I've not learned with regard to specific applications like this. Frankly S7 is air cooled and fairly easy to work with, so chances are I'll give it a try regardless pending someone with an authoritative background weighing in with a better idea or reason not to do it. Google's telling me a hot work temper of 900-1000 deg F, which IIRC puts me in silver solder/brazing territory, so worth looking in to for a handfull of pieces.

adatesman
01-19-2012, 11:37 PM
Erm, kindly don't take that as me being argumentative; I just know enough about the subject to be dangerous and sort out good information from well intentioned. :o

Black_Moons
01-19-2012, 11:37 PM
Somehow, I don't see flutes being super important in a hand drill being used as a rock chisel.. Maybe a single turn near the tip so you can sorta dig out debrie... Something like this:

http://i00.i.aliimg.com/img/pb/029/619/231/1260432986343_hz_myalibaba_web13_11314.jpg

If weight is consern, a thined neck would be ideal, And I think extended flutes would just weaken the neck and make it more prone to folding over/snaping in half.

Or maybe something even like this:
http://www.traditionalwoodworker.com/images/1630-050lg.jpg
Except with less of the metal that makes up the outer scoring part.

adatesman
01-19-2012, 11:47 PM
Funny you should mention it, Black Moons, but both those ideas came up in discussions with my beta tester this afternoon. Things get a bit squirrely with the small diameters we're working with, and frankly he had to talk me out of prototyping a 3 and 4 flute drill, based on his experience using them previously (chisel point were easier to maintain in the field).

Mcostello
01-20-2012, 09:08 PM
Interesting coincidence today, watching the show on cable- "Caves under Easter Island" or such and they showed some people rappelling down a cliff face to get to a cave. Guy whips out a cordless drill and makes a hole fairly quickly. Don't know if that would be an idea you could use, but then, admission was free!

Rosco-P
01-20-2012, 09:53 PM
I didn't think modern rock climbing methods used permanent anchors? Instead, wedges and cams. Thought the trend had moved away from drilling and damaging the rock face.

Duffy
01-20-2012, 10:39 PM
FWIW, there is a small company, (about 12 employees,) in Barre Vermont that specializes in rock working tools. I forget the name, but Barre is not a very big place, and once you discount Rock of Ages, it should not be too hard to track down. They make feathers and wedges for rock splitting. I got the impression that they would be small enough to a) talk to, and b) LISTEN to you.

1-800miner
01-20-2012, 11:21 PM
I have been drilling holes in rock all my life. There is no need for spiral flutes on a hand drill steel.I have been in lots of mines seen thousands of drill steels.
Never have I seen a spiral percussion steel.

Ever watch how the old miners used hand steel? Didn't matter if it was a one or two man operation,the details are the same.
Hit it ,turn it, hit it ,turn it.When the steel starts binding from the cuttings pull it out,stick a straw in the hole and blow it out.
Repeat process.

Spiral flutes were developed for rotary drills. All percussion drills still use straight shank steel.

The Rawl drive drills pictured are a misnomer.
Rawl was in the masonary business. they simply converted some of their on the shelf items to the rock climbing market.

Used to rock climb too,before I got old and fat.

adatesman
01-24-2012, 08:22 PM
Sorry folks, got busy with actual work and didn't see the thread got bumped.

Actually, drilled anchors are fairly common nowadays with the advent of so called "sport climbing", where otherwise non-naturally-protectable cliffs (read: no cracks or unstable rock) are protectable with bolted anchors. Kind of along the lines of the climbing gym moved outdoors rather than the traditional "leave no trace" alpine ethic.

Anyway, thanks for the tip Duffy. Oddly enough I've been to Barre and will try and look them up.

1-800miner, I hear you on the stopped climbing due to old and fat thing, and I'll up you with a never-healed-quite-right-shattered-ankle due to hyperextension during a lead fall. :(

And I'm 100% in agreement with you re: spiral vs straight flute. Straight is stronger and given the material removal rates the augering action isn't necessary. I could rant on this for hours, but digging through the welding cabinet I found some phosphor bronze rod that brazes at 1350 deg so figured what the heck and cut the carbide off a masonry drill, ground a .125 wide slot in it and then brazed in a small piece of S7 while letting it heat to 1700 deg for proper hardening. No idea if it'll work, but hopefully will work well enough as proof of concept before I go to the trouble of machining drill blanks.

Hmmm... Should have cooled off enough by now, so on to the tempering...

Thanks all!