Thin but deep mortise - advise needed

[Helvetica]

The piece is 25mm thick cherry, with a 7mm mortise needed. 70mm deep for a through-tenon. I have bevel edge chisels (Ray Iles) but it’s taking forever and I blew out the side of the mortise on a (thankfully) test piece.

I have a cheap Lidl pillar drill, I drilled halfway with a hss bit, but still the chiselling is slow and fussy. Should I:

1. Get a ¼” mortise chisel and continue by have with an appropriate tool
2. Get an end mill bit for the pillar drill and get as much as I can from both ends before going the chisel route
3. Get something like a two-flute cutter for my router table
4. Something else?

I have 20 of these to cut. Thanks.


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[owen]

Silly question but are you chiselling in from both sides of the timber? It shouldn't be too hard, 35mm from either side is not exactly deep. What's the length of the mortise? 7mm wide 70mm deep by?

 

[MikeG.]

7mm....that's a nuisance. It's unlikely you'll find a chisel that exact width. Why does it need to be 7mm? I have seen 5/16ths chisels, so 8mm would be easier, and a 3/8ths chisel (9.5mm) is common. Paring the sides of 20 deep mortises would be a pain.

You're doing something badly wrong if you are breaking out the side of a piece of 25mm cherry with a 6mm mortise. Could you post a photo so we can try to see what the issue is.

 

[That would work]

Traditionally, a deep mortise would be cut with a Swan neck mortise chisel. But as mentioned above, 35 from each side is not deep and should be fine. I take it the chisel is sharp?
I see you have part drilled the mortise and you say that it is now slow and fussy to chisel... it's probably easier to just chisel as it sounds like the drilling has made the chiseling a fiddle.

 

[worn thumbs]

I'd use the pillar drill and maybe clamp a block to it to act as a fence.You can go at it from both sides and then just use the chisel to lean out the corners and any cusps.A half decent drill bit will do the job "traditionally" mortise chisels would have been used because thats the way things had always been done.Either a hand operated mortiser or a pillar drill would have superseded chisels and an electric mortiser leaves them in the dust.I do own a few mortise chisels but unless I'm feeling nostalgic they rarely get used.

 

[Helvetica]

it sounds like the drilling has made the chiseling a fiddle.

I think this is it, I couldn’t get the drill holes close enough to meet, so the ¼” chisel is struggling to remove material going full width. I broke out the side using the 1” chisel, trying to remove the inside long wall of the mortise. They are sharp - 6000 whetstone.

I think if the pillar drill could make joined cuts, that is where the circles overlap, I could just clean the walls. I find the bit is drifting into the next hole. I’m using a hss bit because I find the wood bit finish is too rough. What would a good quality drill bit - or could I use a router bit and would it give a better cut?

I should have said the mortise width is 6.4mm not 7, should have specified. I’m using it to match the groove made with my axcaliber tongue and groove router bit set.

 

[worn thumbs]

Did you try the technique I suggested with a block clamped to the drill table to determine the position of the workpiece?You can also clamp the workpiece to the block for extra security.Best not to go all the way through from one side and you may want to practice on an offcut.A sharp drill bit helps.

 

[AndyT]

It does start to sound like a quarter inch mortice chisel is the answer.
Ordinary morse pattern drills are designed to drill metal. As you have found, you can't use them for overlapping holes in fairly soft wood. Even in a drill press, they'll dive sideways.

 

[toolsntat]

The best drill bit for doing this job in a pillar drill is a modified twist drill.
You grind it so the outside forms lips that are only slightly above the center point.
This makes it far easier to overlap holes.
Like this but far less spur
https://www.toolstation.com/lip-spur-drill-bit/p47895

Cheers Andy

 

[MikeG.]

7mm....that's a nuisance. It's unlikely you'll find a chisel that exact width. Why does it need to be 7mm? I have seen 5/16ths chisels, so 8mm would be easier, and a 3/8ths chisel (9.5mm) is common. Paring the sides of 20 deep mortises would be a pain........

Did you miss this? 7mm is a peculiar dimension for a mortise. Mortises are almost always the same width as the chisel you use to cut them, so why have you chosen 7mm?

 

[Phil Pascoe]

5/16th mortice chisels are not uncommon and would be about the correct size. 35mm deep mortices? I think you're making hard work of this. As Mike said - what are you doing wrong?

 

[AndyT]

The OP has already said he wants 6.4 mm, not 7, to match a groove. That's a quarter of an inch.

 

[Phil Pascoe]

Yes, sorry - I was thinking of his using 25mm material.

 

[Doug B]

I use the pillar drill quite often for mortises just using router cutters with the drill on full speed, the addition of a cross vice bolted to the pillar drill table allows me to move the timber back & forth to create the mortise, then the ends can be squared up if necessary.

You’d have to go from both sides for a 70mm mortise alternatively you could easily knock up a jig for a router if you have one, worth while if you’ve a lot to do.

 

[Phil Pascoe]

He might struggle to buy a 1/4" router cutter that'll go to 35mm.

 

[Doug B]

He might struggle to buy a 1/4" router cutter that'll go to 35mm.

Not according to google.

 

[johnnyb]

hollow chisel morticers are hard work but would eat this job for lunch. or did he want every method but hollow chisels?

 

[Helvetica]

hollow chisel morticers are hard work but would eat this job for lunch. or did he want every method but hollow chisels?

I am very open to hollow chisel morticers, but I don’t own one. Going to try a straight cutter on the router table.

Ps. Why do so many people talk about the OP in the third person? Don’t you usually address the person who asked the question, instead of everyone else in the room?


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[MusicMan]

Because we're old gits who can't remember who the OP was and can't be arsed to look them up!!

 

[Phil Pascoe]

Ps. Why do so many people talk about the OP in the third person? Don’t you usually address the person who asked the question, instead of everyone else in the room?

Often because we are replying to the previous post, not directly to the OP.