View Full Version : OT, making a masonry hole saw?

09-08-2012, 09:17 PM
I need to bore a hole through concrete for a piece of 2" conduit to go through. I am not exactly sure how thick, but probably at least 8". Being the cheap person I am it seems not to difficult to make a hole saw for it. Then again it may be more trouble than it is worth:D. I was thinking of using a length of tubing slightly under the hole size and brazing some carbibe inserts in the end. A couple of questions though.

What type of inserts would be best?
Should they be new ones, or can used ones from the cnc be used?
Would there be a proper angle they should be set at?
Is more better, and how many should I put in there?
When looking at commerical ones I see a long curved slot that runs down it. Anyone know what that is for and will it be needed?
Anything else I should be looking at? It it even worth trying to do this? Thanks.

Tony Ennis
09-08-2012, 10:12 PM
How many holes do you need to make, and how pretty do they have to be?

I bet the answers to those questions guide the solution.

09-08-2012, 11:24 PM
First question is if you have a proper hammer drill. Not a cordless drill with an optimistically named hammer option, but the real thing.

If not the best bet might be to rent the proper drill and bit for whatever minimum time you can find.

09-09-2012, 09:03 AM
I need one hole, and it doesn't have to be pretty. I have a pretty good hammer drill at the house, if it is not up to the task I can get my hands on a better one.

Tony Ennis
09-09-2012, 09:13 AM
Old Timers would use a star drill and a hammer.

09-09-2012, 09:23 AM
Then again it may be more trouble than it is worth the making a hole saw part...to me there are 4 ways, (a) have a professional do it [cost but any grief transferred to them], (b) do it yourself but with professional equipment [rental, less cost, potential for big problems if the unexpected happens], (c) a whole bunch of little holes around the 2" perimeter [not sure if smaller concrete bits are long enough as they tend to be used for installing fasteners], (d) one large hole, 2".

While not having to be pretty, one assumes it has to be within reason regarding collateral damage or cracking in the surrounding areas...if one were thinking jackhammer...IMO (b) is your best option

Edit: to add, IIRC, Dad put a hole in their basement wall to run maybe an inch and a half conduit and the middle portion of the bore through the wall was a fairly neat hole, but both inside and outside needed to have about an 8 inch circle around patched

Bob Ford
09-09-2012, 09:58 AM
Do a search for dry concrete core bits.

Dan Dubeau
09-09-2012, 10:01 AM
Old Timers would use a star drill and a hammer.

Earlier in the summer, I picked up 5 old star drills, 2 grocery bags of c clamps, a couple hammers, 2 grocery bags of heavy duty pegboard hooks, and another bag of various old tools (punches, cold chisels, etc) for $7. That was a good day.

I think I'd lay out the hole, chain drill it, and knock the plug out. I've made hole saws for wood before, but I don't think it's worth the time to try and make one for concrete, when chain drilling with a hammer drill is so fast. I'd make the hole a bit bigger, and spray foam around it.

09-09-2012, 10:33 AM
I'd have to agree with the general sentiment that if you have just one hole to make, and just want to make the hole and be done with it, renting the correct bit or chain-drill-and-chisel may be the overall cheapest and most direct routes.

On the other hand, I do grasp the "do it my own way" approach, or the make-a-tool-to-do-a-job thing, which can have its own sort of fun and satisfaction. One possible approach may be a take off on what you mentioned in your original post. If you start with a tube of about the size of the hole needed, you could braze crushed bits of carbide around the rim. sort of like a diamond drill. I remember someplace used to sell a paste stuff that was paste flux with carbide chunks and brazing filler powder all mixed together. You smear it on and heat to flowing temp with a torch. Persto! you have a core drill. No idea who it was or what the stuff is called, I think it was for water well drilling. Also no idea how well it would hold up as a concrete drill, might do OK for one hole. Probably work better with drill and water flush with no hammering.

Or maybe not.

Be fun to try anyhow. Please let us know what you end up with. Extra points for photos!

09-09-2012, 11:11 AM
For a 2" hole, I wouldn't go with a core bit. Impact style core bits take a huge amount of 'hammer' and torque, and they get hot. They are not all that long in cut so you have to break and remove the core every couple of inches. I also doubt that old metal cutting carbide would hold up for even one hole. I'd rent a standard bit, which with a proper drill will punch a 2" hole in 8 inches of concrete in a couple of minutes (or a wet-run diamond if you really want to core it).

09-09-2012, 01:51 PM
I need to bore a hole through concrete

Around here that means concrete BLOCK basement... just take out a block and cast the pipe in place. Or at least take out the block and bore a solid core conveniently on your driveway or where-ever else convenient.. or do you literally mean cast concrete? Wheres the rebar?

The task you're describing sounds exactly like what my HVAC guy bored to install my new air conditioner in about 90 seconds. Something about the new pipes being bigger and better insulated than the old pipes. A really boring way to do this involves a couple cases of beer and a bored / unemployed / friendly HVAC guy. A much more interesting way to do this involves bartering machinist skills with a HVAC guy. Know how to sharpen drills? He's got dull ones. etc.

Also plumbers. This hole is just a bit larger than the average hole for an outdoor faucet. Plumbers always have some gadget with a broken rivet, or some bizarre wrench that would be a 100 times easier to use if only another foot of length was welded on.

09-09-2012, 02:26 PM
The cutting edge of carbide on concrete bits/hole saws is normally shaped more like a check mark, very different from metal or wood cutting edges. The edge looks more like a dull cold chisel than a sharp wood chisel. I believe it's a softer carbide than that used for metal cutting also, but used metal cutting grade should work fine.

Many of the carbide top concrete hole saws are simply granular carbide bonded haphazardly to the shell.

09-09-2012, 02:41 PM
Hey, I like that idea- prepared granular carbide that will self-braze onto a brazable material. I could have used that a few weeks ago when I needed a custom disc for trimming fiberglass.

09-09-2012, 03:49 PM
I wish is was a block wall I was going through, i am going to assume it as poured concrete, but it is through a foundation of a very old house so who knows what is in there. The star drill looks interesting, do they make them big enough for 2" conduit and do you run them through once and done or run a couple through in steps?

09-09-2012, 04:29 PM
Old poured concrete can be a hard go compared to concrete blocks or recently set concrete. I'm not sure of the time frame, but I think that up to a year or so old it's not too bad to drill. Get a dozen or more years on it and if it was any good from the start, it will be hard as - well, rock.

09-09-2012, 05:35 PM
Yes, you never know what you'll find with concrete. You might try chipping away a bit to get some idea of what you'll be dealing with before deciding on exactly how you'll do it. It might crumble at the sight of a star drill or laugh at anything less than diamond.

You're not likely to run into reinforcing steel in a very old house, but you might run into some large "plums" of granite or other hard rock.

09-09-2012, 05:45 PM
"Very" is a vague adjective. If your house is pre-1940, you can bet that the concrete was mixed on site and that it was "extended" by pitching rocks of varying size into the forms as the pour progressed. Since Murphy NEVER sleeps, you WILL hit one of those rocks-tangent to the side. This will cause your drill to drift and you will use many bad words. THEN you will start another hole and hope to miss the rock, but Murphy is STILL beside you!
I strongly suggest that you bite the bullet, rent a Hilti hammer drill and coring bit from wherever, and have at it. This will cause Murphy to move to some other unsuspecting soul and you will find the softest concrete in the whole wall. It will be done in ten minutes!

Tony Ennis
09-09-2012, 05:52 PM
This will cause Murphy to move to some other unsuspecting soul

oooo another universal law: Murphy can be deflected but not denied.

09-09-2012, 06:22 PM
The house is pre 40's, but I am not sure of when the concrete was poured. I have 1 of 2 spots that I can try to go through. The foundation is hand layed stone, under the kitchen(where I am going through) was only a crawl space at one time. At some point it was dug out and made standing height. The lower half of the foundation is of some poured concrete. This is the area I am going through. I have already put a a 1/2" hole through this spot and it is around 10-12" thick. It went through, not the easiest, but went through.

This is the ideal spot for the hole to go through but the outside of the house there is not the greatest. I have a landscape wall made of stacked stone there. I have already dug down some to the point of where the 1/2" hole should have came out but have yet to see it yet. Maybe a little more digging and I will find it. Even if I get the hole through for the conduit I either have to deal with tunneling under the wall or unstacking it.

The other spot is slightly over from it where I have a set of steps that go to the outside. I was thinking of putting the hole a the bottom of the second step down. It would give me a decent depth. They are also poured concrete, but I don't know how thick it is there at that step. There might have been a big hole left at the top that didn't get formed and just filled up with concrete, which would result in having to go through 16"+. Duffy is also right, I am sure there were rocks thrown in when the mixing was going on. Either place is going to suck.

My other option would be to come up from higher on the house where there is wood then go down with a elbow to under ground. This would then make having to pull the wire through 2 elbows which I didn't really want to do.

Paul Alciatore
09-09-2012, 07:15 PM
If you already have the hammer drill, I would choose the largest bit you have (3/4" or 1") and drill several closely spaced, but not overalping holes on a circle. Then a heavy hammer and chisel to knock out the slug and clean up the sides enough to pass the conduit through. After it is in place, mix up some concrete patch and fill in around it.

Use the time and money you save in your metal shop fun.

09-09-2012, 11:23 PM
The house is pre 40's, but I am not sure of when the concrete was poured. I have 1 of 2 spots that I can try to go through. The foundation is hand layed stone, under the kitchen(where I am going through) was only a crawl space at one time. At some point it was dug out and made standing height. The lower half of the foundation is of some poured concrete. This is the area I am going through. I have already put a a 1/2" hole through this spot and it is around 10-12" thick. It went through, not the easiest, but went through..

You just might be lucky, sounds like a Michigan cellar. Most pre 1940 houses here had a foundation of stone or block when built, but a simple hole with absolutely no finishing as a basement. sometime in the 50s-60s it became common to dig them out and make plumb walls, the -good- jobs were done with block, but normal practice was to simply plaster with concrete, normally it was a layer no more than 2 inches thick.

If they are cut stone, (as in shaped blocks) the foundations are normally no more than one 'block' thick, can chip away at the mortar and slip a block out then use a saw to cut a groove to run your through, then pour a filler in and replace the stone.

Alternate, most acids will dissolve concrete easily. bore small hole through, then use a squeeze bottle with a tube to squirt acid in to dissolve the concrete leaving only foam and sand/gravel to clean out (wet vac time) Drawback to that is that the hole will have an egg shaped profile. I have to say I have never used it on a vertical wall, but have used old acid many times to 'cut' concrete, or make holes through floors for running pipe etc. my most ambitious project using recycled battery acid was a drain trough for the basement. It was surprisingly easy to control depth and shape of cut with it.

09-10-2012, 12:39 AM
You should call about getting it drilled by a professional. It is cheaper than you might think.

Or rent the equipment needed.

09-10-2012, 08:37 AM
I had to drill a 90mm hole into steel reinforced concrete. Everybody suggested that I hire a professional to do it, but:

- The pro's were too expensive.
- The drilling equipment that they use requires that a rail be mounted to the spot to be drilled. This was not feasible.
- The drilling equipment required continuous water cooling, not an option for my kitchen.

So I used my large hammer drill with a cheap chinese cutter:



09-10-2012, 08:43 AM
I first tried my small SDS Plus hammer drill with a smaller cutter, but it didn't advance in the concrete at all and quickly overheated. This concrete is very tough, because it carries the entire structure of the building. I finally bought the larger cutter and used an SDS Max hammer drill. I really had to apply a lot of pressure to have the machine advance. When I reached the rebar steel, sparcs were flying all over the place, but I kept pushing as hard as I can. It took about 5 minutes to get through. I have used two clamps to attach a piece of wood to the other side of the concrete so that the cutter would not break off the surface during exit. It worked out quite well!





09-23-2012, 04:49 PM
Well, I got a hole through the wall. I wish I could report that I made a super cool hole saw and it worked perfectly, but I didn't. I am also glad I did not try to make one for this project. There was about 14" of wall I had to go through. I assumed that this was poured concrete that I was going through, but in reality I think it was a laid up wall of stone with mortar and a small top coat of concrete(I went though the outside basement steps) The first 2" went smooth, with actually a very weak concrete mix. After that was a solid stone covering 85% of where my hole was to go and around 10" thick.

I got a 3/4" masonry bit through one side, and after that it was caveman style. I used a propane torch to help put cracks in the rock and a long chisle and hammer to smash what I could. Slow but steady and the hole went through. One step closer to getting power out to my lathe:D

09-23-2012, 06:20 PM
If you have a drill with a decent hammer action you could make a 2" drill bit from pipe and old carbide inserts. When you get a TC core drill the teeth have a sharp top on them but you soon lose that and the teeth gain a blunt rounded profile - but they still work especially if the aggregate isn't too hard. Make sure you have a good overhang both sides on the teeth (you need no rake) and clear the dust as you go every half inch or so - the commercial ones have a spiral turned in the sides to bring the dust out. Snap off the cores every inch and a half or thereabouts.

If your wall is at all damp you'll have problems with this kind of bit - and they don't cut rebar either unlike diamond core drills.

09-24-2012, 12:21 AM
You're working way too hard. Just use a thermal lance and be done with it in a couple of minutes :) http://en.wikipedia.org/wiki/Thermal_lance

09-24-2012, 01:00 PM
Pulling wires through elbows is pretty easy when you use a LB, LL, or LR. The 1st 'L' means its a 90 degree 'elbow' and the second letter indicates where the removable cover is positioned. Be it Back, Left side, or Right side. These fittings are nice in that they have no radius to them and can fit snugly to whatever they are against.

I have used them on both sides of a wall to get those tight, immediate turns.

Assuming you are running conduit for the whole thing be sure to really slop on the wire pulling compound. You can buy it at your favorite Borg.

09-24-2012, 04:31 PM
It is only going to be conduit for 80' or so. There will be 1 long sweep elbow and then two of the pull elbows you speak of. 1 to get into the garage and 1 on the inside up to the panel. I don't think it will be to bad pulling the wire, it will be a straight shot to the first elbow(which is to get it up out of the ground). I am going to feed a rope through to help. The conduit is also over sized for the wire.