Will masonry bits work for drilling the center of hollow forms?

[Jeremy Leasure]

It seems like the cheapest and quickest option for me is to grab one of those big masonry bits from Lowes or wherever to drill deep into longer blanks. Just wondered if anyone has used them. Other suggestions welcome. I'm hoping handheld mounted in some kind of square block for grip would be ok, my drill chuck is 1/2" so it wouldn't do.

[Scott Hackler]

I would NOT use or try to use those bits. A masonry bit has pretty blunt tips and are really designed to grind away the cement/stone/mortar. If you tried it, you would see that it would tear through the wood and burn as it gets hot. Plus, the masonry bits do NOT have deep flutes up the shaft to funnel the wood away from the point of cutting.

Figure out what size hole you will be wanting to hollow through and buy 1 fortner bit and possibly an extension for that bit. You don't "need" a whole set!

[Harry Robinette]

Plus 1 for Scott's reply, also after using the fostner bit wipe off and ever couple uses run your hone up and down the back side of the cutter it will stay shape for a long time.

[Jeremy Leasure]

Hm. I've tried forstners in end grain with very slow and hot results. I have a whole set of them, and several carbide bits for the ones I use most often. That and an extension would work fine for side grain stuff though.

[Scott Hackler]

Jeremy for what its worth, when I am drilling I have the air hose blowing into the hole constantly to clear out the shavings and to cool the bit! That being said, I have found a big ole 3/4" regular drill bit that works really well....if you can hollow through a smaller hole.

[Ryan Baker]

Masonry drills won't work. They just burn, and fail to cut.

You can get a 12" long twist drill for around $10 or a touch more. Something around 1/2" is good for drilling out the centers of hollow forms. If you need a larger size, a Forstner and extension is really the best way to go. Not all Forstner bits are equal. You should be able to drill end grain without much more trouble than side grain.

The alternative would be to not drill at all and just cut the center out with your hollowing tool of choice.

[James Combs]

I use Forstner bits all the time for end-grain and without any problem. As a matter of fact I can't think of anything that I use a Forstner bit on that isn't end grain. For bowels and other side grain items I generally drill with my gouge then cut from there. I have noticed that if I forget to slow the lathe down to 200-400(depending on bit size) the Forstner doesn't do very well. It gets hot and I think the wood hardens and it doesn't want to cut. If you are having problems cutting end-grain with a Forstner double check your RPM, they are intended for use at fairly slow speeds. If you have a set there should have been a recommended RPM per bit size chart with them, if not I am sure you can find one with a online search.

[Bernie Weishapl]

You've gotten some good advice Jeremy. One other thing is if your forstner bit is dull it will heat and fail to cut. Don't ask me how I know this. I just sent my set in and had a gentleman resharpen them for me. Oh what a difference. Oh and I drill at 250 rpm.

[Thomas Canfield]

I can't remember the demonstrator name at SWAT last year (2011) but he used a masonary bit to make the entry hole very successfully. He said that the reduced diameter of shaft allowed for the shavings to exit without packing, and it did raise eyebrows and questions from audience. I bought one, but you have to sharpen the carbide tip and so far my sharpening is not centered and does not drill very well.

[Rick Markham]

I use a 1" Bosch masonry bit (with carbide tips) to drill my forms. It isn't a "cheap" option by any means, and I'm pretty sure it cost me about $30. It has deep flutes all the way to the shank of the bit, and is about 9" or so long. IMHO, it works better for me than other bits. I realize it's "going against the grain" on here, but forstner bits are too short, and an extension just traps the shavings. This thing is a beast and doesn't flex. As for tear out, if you take it slow at the bottom I don't get any. Like I said, this isn't a "cheap" or "ordinary" masonry bit by any means. I use it all the time because it works much better than any other option I have tried. Different strokes for different folks. Works fantastic in end grain too!

edited to add: I use it at about 200rpm's or less. I could see burning trying it at too high an rpm, but I haven't experienced any burning, screeches a whole lot less that a standard twist drill too!

[Glen Blanchard]

In Mike Jackofsky's DVD, "Making a Hollow Vessel", he addresses this issue specifically. If memory serves, he states that he bought a masonry bit to be used for exactly this purpose, but was not aware at the time that it was designed for masonry work. He states that it works wonderfully, and he has never deviated from using it - even after he found out that he was not using it for its intended purpose. If I remember correctly, the reason he prefers to use these bits is that they don't get clogged up with shavings - so Thomas would be correct in this. Mind you, I have no personal experience with this, but this is what Mike mentioned in his DVD.

[Reed Gray]

Well, there are a couple different types of masonry bits. The cheap ones for the hand drill, and the expensive ones for the larger impact type rotary hammer drills. I would guess that with the tip properly sharpened, they could work fine. The cheap ones have a cutter with a double bevel, like this V. If it was sharpened like a single bevel scraper, I would guess that it could cut fine.

robo hippy

[Scott Hackler]

I guess my experience (and tool box) only has seen the cheap ones because of the times I have used them for drilling though 2x4 sill plates for a strike anchor...well a chucked up piece of rebar would have done a similar rough job!

Maybe I will look into an expensive, carbide.... larger one for this purpose.

[John Keeton]

I guess it depends on one's purpose in drilling the hole. I drill my forms with a 3/8" electrician bit in a Jacob's chuck slipped in the tailstock, but only to establish the bottom and eliminate the nub from hollowing a tad above center. I do withdraw it every couple inches to clear the chips, but I have absolutely no difficulty in side grain/end grain. If it is a shallow form, I have another similar bit I use that I have installed into a handle and I just do it by hand. However, drift is a concern on a deeper form, thus the Jacob's chuck. When I have the form hollowed, I drop the boring bar to center and clean up the very bottom.

[Bill Boehme]

Hm. I've tried forstners in end grain with very slow and hot results. I have a whole set of them, and several carbide bits for the ones I use most often. That and an extension would work fine for side grain stuff though.

Jeremy, the Forstner bits might be dull or they might be getting packed with shavings especially if the wood is wet. The bits need to be backed out very often to clear the shavings. Like masonry bits, not all Forstner bits are created equal. My opinion is that the best available is the Colt MaxiCut Forstner bit made in Germany. It is considerably more expensive than the Asian imports, but cuts amazingly. The size that you need, of course would depend on the size of your hollow forms. I attended a demo by Steve Sinner at SWAT a few weeks ago and he uses a 1½" Forstner bit mounted directly in the boring bar of his hollowing rig. Some of his hollow forms are three feet tall (maybe even more on some of the really large ones) and he is able to bore as deep as he pleases. The most important thing to remember if doing it this way is to perfectly level the boring bar and have it perfectly on center or otherwise you will be bouncing all over the place. For boring a hole without a captive hollowing rig, Colt has extensions with very high precision self locking alignment. I took a class from Trent Bosch earlier this year and he uses a gun drill connected to shop air to bore a hole approximately a half inch in diameter for smaller hollow forms. The nice thing about a gun drill is that it is self-centering. The can be found on eBay and similar auction sites.