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I Just Bought And Used One - Worked Well

Here is the review I just today put up on Amazon for this kit I just bought and used:

5.0 out of 5 stars Works Well With Reservations, March 9, 2012

rcarter - See all my reviews

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This review is from: DELTA 17-924 Mortising Attachment with 1/4 Inch, 5/16 Inch, 3/8 Inch, and 1/2 Inch Chisel and Bit Sets (Tools & Home Improvement)

As others have commented, for under a hundred dollars you have a satisfactory mortiser, and without much hassle. I would recommend this kit to anyone who is mechanically-inclined and first does their homework. I was able to use this to bore 24 - 1/2" square x 3/4" deep mortices in heart cherry on a non-Delta drill press without any problem. However, be aware of a couple of serious limitations:

1) The "U" mortise bit holder only has 4-1/2" inside clearance from the quill clamp (top) to the mortise bit clamp (bottom). Measure your drill press from the top of the stop ring at the bottom of the quill, to the bottom of the chuck, and importantly, with that chuck extended to tighten around a 1/8" bit. This is what has to fit into 4-1/2" on this "U" bit holder, the key part of this accessory kit. I could only use the 1/2" mortise bit, because with the chuck extended so far down to wrap around the smallest 1/4" mortise bit, there is not room for it within the "U", at least on my drill press. Fortunately, in my project, for which I bought a used $65 x 3/4 HP x 12 speed x 5/8" chuck drill press, the 1/2" mortise was OK (much bigger augur bit), so I could use this kit without any appreciable down time.

2) You must have a drill press which will allow you to use quite low speed; I ran mine at 600 rpm, and it did not burn up the mortise bit. At 1200 rpm, it instantly heated up, which is a possible explanation for why commentators may be upset about burning their bits. It's mostly about providing enough steady downward force pushing into the wood to create the "square hole." The drill bit inside is really important for clearing out chips and thus keeping the bit cooler. Only use at much-reduced speeds. Be sure you pay attention on keeping the 1/32" clearance between the augur and the mortise bit holder, too!

3) The HP on the drill press is therefore pretty much immaterial. What you do need is a robust travel on the drill press, as depending on your wood, you may like me be putting considerable force onto the crank to get the mortise bit plowed through the wood. If there is a little sideways slop/runout in the travel, it is OK, as once you have initially pronged into the wood carefully with the square bit, the wood prevents the square bit from wandering.

4) The hold-downs are pretty useless if you have any decent width stile, such as a door. The fence is a lifesaver though (I clamped mine to the drill press, as the provided holes didn't fit), and both the fence and mortise bit holder are well-made iron castings, making this a great "old school" solid accessory, the likes of which Delta originally established their brand following.

5) Other reviewers complained about the setup time. Not a problem at all for me, I couldn't see it being an issue, certainly not a show-stopper at all. However, if you buy a used drill press (make sure it fits!), you could dedicate it to mortising, and you would have the best solution.

6) The kit comes with the ability to clamp around four different sizes of quills. I tried this kit on my Delta 32" radial drill press (an older one, not the Delta 11-090 as advertised), and what do you know, it would not fit, ZIP. "The good thing about standards is there are so many of them," even from the same manufacturer who has made this accessory kit for its drill presses. ** WHY do they do this? ** Delta: "WHAT ARE YOU THINKING?" Unless you have a metal lathe, you would need to go to a machine shop and have a set of shims made if your drill press does not match the four sized quills this kit is intended for. Fortunately, three sets are provided in the kit as models.

That is a good comment about drill presses not having the heft for the downward pressure. Buy a used heavy drill press and you can't go wrong, if you are not doing that much mortising. I can see the rationale about getting a dedicated mortiser, though.
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