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.

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.

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.

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.

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.

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?

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.

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.

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.

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.

I'd be concered about the setup time for using the guide. I suggest you practice it freehand for a little while, and you'll soon be accurate enough, and faster. CB.

I second Clark's advice.
Before I had a mortiser I used a drill... with a simple square as a guide (or one of Clark's mirrors) - you get good at it.

Liam,

We've used the protool guide with 1 1/2" milwaukee self feed bits to hog out mortises before. These bits are like forstners with lead screws. Milwaukee makes a nice bit extension for these in 3 lengths and the one we already had happened to be the perfect length. I think it was 12", but can't remember for sure. They make 2" self feed bits as well.

As far as using the guide, we just took the center ring out like you said and had no problems. With SF bits, there's no point in making a different sized guide ring, as the bit is built basically like a forstner. It didn't seem to torque the frame overmuch. The depth stop alone makes it an improvement over free hand.

I consider it a viable way to produce mortises in a low to medium production environment. And the guide is still usable for peg holes and other tasks with a simple bit change and replacing the center ring.

I'd forget about forstner bits for mortises -- no lead screw makes it way too much work to drill 4 or 5 inches deep.

And it used to be that those lead screws were replaceable - or at least could be taken out to sharpen.

Back in the good old days we drilled a few thousand this way with a Milwaukee HoleHawg - too much torque, really, to be safe.

Adding a mortise centerline to the layout was very helpful.

We have 2 Protool 460 Guides in our shop and we use them all the time with 1 1/2" WoodOwl bits. It works great and we have never had a problem.


Colton

Good to know that the manufacturers OK the use of larger bits. Thanks for the info.

One way I guide my drilling is with a bullseye (round) bubble level glued on the back end of the hole-hawg or other drill. Gets my body position, hand grip, and 'eyeball' plumb before starting, and helps check plumb-ness while drilling.

The longer the bit (and extension?) the easier it is to be accurate.

A hard knot will try to deflect any bit or boring machine in my experience, at least somewhat. I even built a custom drilling tower as Timbeal suggests, clamped it to the timbers etc, but there is so much torque involved that it would twist and distort in bad knots no matter what.

If perfect mortise walls are an issue, one can drill a little undersize then pare with a chisel.


Pete

Even if the bore holes are "off" you can pare only what needs removing, leaving a section of the bore hole on one side of the mortice.

I was asked a while back what I used for bit sizes, if they were under the mortice size, I found my measuring device and the 1-1/2" bit is right on, not undersized. I like it that way.

I like the idea of the bulls eye level, its nice and low tech. I have tried using the mirror idea (actually a cd upside down) but found it difficult.

I suppose the bulls eye level should work, as long as the timber is true and level.

I use a combo square set to 0, registered in two directions and let it rip. this works as long as the timber is not out of square. I also bore peg holes from the side orientation, not down from the top. I wonder if boring mortice holes from the side would add any benefit? The chips would fall away. Maybe better control of the Hole Hawg?

I tried the mirror, at one time, the last time, the bit got sucked out the exit side and the chuck was pulled into the circle hole in the center of the mirror and it broke into two pieces. Now, I have a mirror in the shop to look into as an aid in extraction of the occasional wood chip.

The Big Al works really well for this. Stood upright, the big heavy fence keeps it really well balanced, and the fence is also very thick, making it pretty accurate in the "other" axis-- the one determined by how much the square is "tipped" forward or backward. I use an 18" long wood owl bit, and normally set the edge of the Big Al 1/4" or so from the side of the bit-- a nice distance for accurate sighting. The Big Al is about 8" high stood upright, so I can drill about 10" deep before the chuck will hit. Rather than using a depth stop or stopping to measure (and maybe scratch my head a bit), I reference the layout lines of the Big Al to determine my depth.

I find this method a lot more intuitive than a bubble level (for me anyway), which requires that you level all of your timbers in 2 axes, and it gives accurate results.

Now if I could just figure out a really suave way of eliminating blowout on the underside... The wood owl minimizes it, but I still usually wind up clamping a piece of 1x. Works great, but it seems the most cumbersome part of the HOLE operation.

I give a little pull back on the bit and brace or drill through the whole bore, when the feed screw exits the back side it just pulls out. Spin the brace/drill in reverse when back back boring on the reverse side. But I still get a little over zealous once and a while, yielding a little blow out.

For through mortises I've always drilled from both sides...

For through peg holes?
I've drilled from both sides...

And I've marked my bits with depth markings (paint marker or similar - needs to be replaced often) - and when I get close - slow down and pull up - this does as Tim stated - strips out the lead and you can flip it over and use a hand brace to finish, or the power drill in reverse.