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drill guide advice #25783 03/04/11 07:14 PM
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Liam O'Neill Offline OP
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I imagine this has been discussed before. I am trying to decide between the Protool drill guide GDP460 (sold by timberwolftools.com) and the Hema ZB 20 (sold by timbertools.com). I want a drill guide primarily for hogging out mortises, I can't really justify buying a chain mortiser at this point. I am leaning towards the protool model since it has a guide fence.

Re: drill guide advice #25788 03/04/11 10:11 PM
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Will B Offline
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Liam,
I don't think the drill guides are designed for hogging out mortises. Usually the largest bit they can handle is around 1", and are meant for lining up long holes for bolts or pegs.

I think you would be drilling twice as many holes as necessary and putting unnecessary wear and tear on a precision tool.

If you can't get a chain mortiser, why not a boring machine (hand-cranked)? Jim Rogers always has some for sale. Otherwise, many of us started with 1/2" electric drills that can handle big bits. For safety and control, I'd recommend a right angle model, like a Milwaukee Hole Hawg.

Re: drill guide advice #25790 03/05/11 12:17 AM
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TIMBEAL Offline
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On really bad days.... I have thought about adapting an electric drill to one of my hand crank machines..... I literally changed gears and the thought does not come up as much anymore. So, that could be an option, I would ask that if you do covert one use a lower quality machine. With a little engineering you could make up one from scratch.

Re: drill guide advice #25792 03/05/11 12:54 AM
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Dave Shepard Offline
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With a little practice, about as fast as a boring machine.



When I can't use the T-auger or boring machine, I use a Hole Hawg 1/2" heavy duty drill. Works well, but noisy, and has a tendency to coast after you let off the trigger.

Last edited by Dave Shepard; 03/05/11 12:54 AM.

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Re: drill guide advice #25796 03/05/11 03:02 AM
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Liam O'Neill Offline OP
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It is my understanding that the centering plate on the drill guide can be removed for using larger auger or forstner bits. One could build a custom plywood centering plate to handle a larger auger, or have one machined. It seems to me that this would work pretty good.

Re: drill guide advice #25797 03/05/11 03:29 AM
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TIMBEAL Offline
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Dave, I pull out the T-auger on occasion. The Hawg coasts to a stop..... just as I become airborne.

Forstner bits, do they really work for morticing? What is the real scoop? Do they wander, how about clearing chips from the hole? Ever have one get stuck in a bore hole?

Re: drill guide advice #25799 03/05/11 06:23 AM
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D L Bahler Offline
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I have used forstner bits to hog out a mortise before, tried it on an ash timber I was just doing some experimenting with, it will become a nice sign post eventually.

I made some mortises in it with a forstner, because I wanted to try it. I used a 1 1/2" bit, and it worked well.
Yes it can very easily wander, you just have to proceed with caution. The fact that you have to stop and clear the chips out when you go very deep is a help here, it helps you keep your hole sighted. The bit's ability to eject chips doesn't work deep in a mortise. You have to manually clean them out every now and then, which can be done by just pulling up the bit and shaking it a bit.
It seems that this would be slower, but a forstner bit can hog out wood much faster than an auger, with a lower power drill.

So my verdict is it can work, but you have to proceed very carefully. I got the bit stuck once, but managed to get it out without too much trouble.

The hardest thing with a forstner bit is to get the initial alignment right, not all of them have a spur in the middle, and even so the spur is pretty small when they do have.

I used a Freud forstner, with a wavy edge and 2 cutters.
But you have to use an extension, since they have short shafts on them.


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Re: drill guide advice #25803 03/05/11 02:52 PM
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Will B Offline
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I think if you modify a drill guide to accept a larger bit you would not only void the warranty but also put more torque on the frame than it was designed for. The manufacturer or dealer should be able to answer this definitively.
Forstner bits get stuck so often, need frequent clean-out and can send you flying that an auger with twist to clean out the chips is preferable, in my opinion. There a "bit" harder to find but Greenlee and Irwin both make auger bits up to 2", I believe. T-auger or boring machine bits are not designed to be used in electric drills with their higher torque and speeds, so caution there.
Drilling half-size holes with a smaller bit will work but doubles the amount of work and chance for error.

Re: drill guide advice #25804 03/05/11 03:18 PM
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D L Bahler Offline
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i should clarify further too..

i am not recommending forstner bits, I am just saying it can be done. I use augers.

On a side not (sort of) I have for a long time been thinking about seeing if I could whip together a dedicated mortise borer. It is not always nice to go for a spin around (or into) a timber!

I have used the half sized hole method before too, it is a good procedure when you are working with some particularly hard to drill wood, like hickory, in which case the torque on a 2" or 1 1/2" bit is very very high.

I've also used the 'mouse ears' method of drilling out the corners with a small bit so that I don't have to clean them out. This only works if the mortise is totally hidden in the joint. It's also a good approach if there is any danger of water getting in the joint, as it can easily drain out. It is a whole lot faster too.


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Re: drill guide advice #25805 03/05/11 03:22 PM
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Liam O'Neill Offline OP
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I suggested the forstner bit only because I was not able to find a 2" auger bit. The plywood centering plate idea came from David Powell at timberwolftools.com. He also told me that the protool drill guide can handle a bit up to 2 1/2" with the centering plate removed. A co-worker of mine has the Hema Zb 20 drill guide and had a centering plate machined to fit his 1 3/8" auger.

I work in a timber framing shop that is equipped with a makita chain mortiser, but wanted to set myself for my own side projects.

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