Hollow chisel mortising - does it have to be this difficult?

[Larry Spitz]

I have a Delta 14-070 drill press and a Delta 17-905 mortising attachment. I am having lots of different problems in my first real attempt at using the mortising attachment. At the moment I am using a

3/8" chisel. It is as sharp as I can make it.

1. I find it very difficult to clamp the collar of the chisel holder around the split ring bushings in such a way as to keep it the split in the bushings aligned with the split in the collar and to keep both halves of the bushing aligned horizontally.

I have replaced the 5/16-18 nut and bolt supplied with a piece of threaded rod and two pairs of jam nuts and it is better now, but still slips from time to time.

1. I am running the drill press at its slowest speed (250 rpm) instead of the recommended 650-2000 rpm because of the awful screeching noises I get at the higher speed and the amount of heat generated at the chisel tip. I actually have not tried any speed above 650 because my ears could not stand it.

1. The interior of the chisel gets packed with the shavings from the drill bit and not only don't the shavings fall out of the open side of the chisel by themselves, they have to be pried out with an awl which means that each 3/4" deep mortise takes 5 or 6 sequences of drill-stop drill press-clear shavings-start drill press-drill. Really boring (pun intended) and inconvenient.

I have waxed the inside of the chisel, basically by mortising a block of wax. This helps, but not too much.

I have tried using this mortising attachment in pine, maple and matai. All with approximately the same results. Are there tricks I should know? I have RTFM-ed several times. Is this a bad mortising attachment? Should I buy another model? Or should I go back to doing my mortises by hand or router? (My current project involves several linear feet of mortise,

1/4" from the edge of the workpieces. This seems an ideal application for a hollow chisel mortiser.)

Any advice appreciated.

Cheers,

Larry

[charlie b]

You might want to sharpen the bit as well as the chisel. You did sharpen the inside of the chisel with one of those cone sharpeners right? And you only polished the outside faces of the chisel, not "sharpen" them?

If the bit isn't sharp it will tear out wood rather than creating fine curlies. That may be why all the clogging.

If you "sharpened" the outside of the chisel you may have created a tapered chisel, narrower on the cutting end and fatter above the area that you "sharpened". That'll make pushing the chisel down into the wood harder.

Then there's the gap between the bit and the chisel. Too much and the bit may wander - and rub the inside of the chisel. You can blow out the bottom of a mortise that way. If the gap is too small, the end of the bit rubs on the inside of the end of the chisel, generating enough heat to burn both the bit and the chisel. Try The Forty Cent Method for setting the bit/chisel gap.

your stock isn't flat it can be hard to mortise, the part moving as you apply pressure. Hollow chisel mortisers don't do curved holes well at all.

If the stock isn't secured well and can move, even a little, you've got the same problem. The hold downs on the drill press mortising attachments

- how shall I say it - SUCK? Clamp the part if you can - and as securely as you can.

charlie b

[Larry Spitz]

Yes, I used a cone sharpener even though the Delta manual says not to. On the outside all I did was break the burr off with a fine diamond stone.

I haven't sharpened the bit (yet).

using.

I couldn't agree more. The work is well clamped with a toggle.

[Leon]

And did you polish the 4 outer sides of the chisel also?

Now you see why most that start out this way quickly graduate to the dedicated mortiser if they continue.

The screech is normal. Dedicated mortisers do this also. A little TopCote on the bit inside the chisel will help for a little while. Use hearing protection. You should have hearing protection in your shop, right?

I would start with running at the proper speed and then maybe considering getting a better quality set.

[Leon]

You need to polish the outer sides of the chisel to a mirror finish. This will greatly decrease friction when plunging.

[Lew Hodgett]

OK, a question.

Plan on building a small table using M/T. It is going to be a one shot deal so investing in a dedicated mortiser doesn't make sense.

Based on this thread, a drill press attachment is a loser, so what is the best approach?

A router /w/ a jig, then clean out corners /w/ a chisel maybe?

Lew

[Leon]

Router and jig will work but I used to use a forstener bit in a drill press to hollow out the bulk and clean up with a chisel. Be sure to use a fence so that you holes go in a straight line.

[Lew Hodgett]

Can do that.

Matter of fact, as soon as I hit the send key, the thought occurred to me.

Thanks.

Lew

[Chris Friesen]

There's nothing that says mortices need to be square (unless they're visible, then it's a personal preference thing). For me at least, rounding over the tenons to match the mortices is quicker than squaring up the mortice.

Chris

[charlie b]

Not sure why they waste time and your money with those "free" drill press hollow chisel mortising "accessories".

Why not go with loose tenons. Mortises are fairly easy to do with a plunge router and a spiral bit. Mortise both parts, make up a couple of feet of tenon stock to match the length and width, round over the edges with the router and a quarter round bit and cut off what you need.

Trend makes a M&T jig that is so so for doing the tenons but real easy for doing mortises.

Or, if you've got a good fence for your plunge router and like to make jigs, consider making this one, or a variation of it

charlie b

[Lew Hodgett]

Have a good set of carbide forstner bits and a decent fence for the drill press.

As Leon suggested, seems pretty straight forward.

What do you think?

Lew