Long hollow mortise chisel and bit for a door

Re: Long hollow mortise chisel and bit for a door

Cameron......I also have a PowerMatic hollow chisel mortiser and I just went to my shop to check chisel lengths......like yours, the length of my ½" hollow chisel was about 3".......I've never made a front door (so I have no relatable experience) ; but, I think that a 3" deep mortise should give you very adequate strength and should work well for you IMHO.

Re: Long hollow mortise chisel and bit for a door

I was going to say...

I have a number of hollow chisels of various brands and they all are about the same length and will cut about three inches deep.  Another thing to consider is the stroke of your machine.  Even if you find a longer chisel will your machine be able to push it that deep into the wood?

I think 3" is deep enough.  I have cut apart a few doors and don't remember seeing one morticed much deeper than that.  You are getting into what is really  a cross grain connection and if it gets too long the joint may tend to fail because of wood movement.

Aren't M&Ts ...

... traditionally pegged with those fancy offset alignment bores; and not glued for the same reason Barry mentioned--expansion-contraction?

Draw boring a mortise and tenon joint.......

Bruce......I'm not a woodworking historian (so this is my opinion)......but draw bored joints went back to the day where the maker didn't have available clamps of a capacity or number that would allow for that clamp to be used for a prolonged period holding one joint tight......the joints were still glued however (maybe not in large timber framing)......you can still use draw boring to hold your joints tight while the glue sets......but, tight is tight.....and a joint will not get tighter after the shoulders of the tenon are making contact with the mortised member by draw boring or clamping IMHO.

Re: Draw boring a mortise and tenon joint.......

I recently made a couple of saw horses in the timber frame style......I used clamps to hold the joints tight while the glue set......I did not draw bore those joints......once the parts are together, crushing them closer isn't worthwhile or doable.

Re: Long hollow mortise chisel and bit for a door

You may be able to gain an extra inch or so by drilling the deepest mortise you can and then repositioning the chisel and drill to a deeper depth. Don't know if the chisel will hold well with just the inset screw so you may have to add some spacers behind the chisel's collar to power through the wood.

Re: Long hollow mortise chisel and bit for a door

I don't know that 4" is necessary, but if you do 3" with your mortiser, doing the last inch by hand shouldn't be a big deal.

Re: Aren't M&Ts and more ...

These days Schwarz must be the only builder using draw-bored joints as intended. I don't think Roger's joints are more than 4-inches, so they work as glued.

Actually, drawbores aren't intended to pull two members together as an alternative to clamping for a tighter glue joint. They serve as a flexible joint for wood contraction-expansion of the connected pieces. Pre-19th century glue joints tended to fail more often than modern glues. The pin is a spring, holding the joint tight.

However, wood still swells and contracts ... moves seasonally. From what I observe in the comments, the mortiser chisels don't extend much more than 3". The "rule-of-thumb" is to break up a glue joint that is greater than ~3". M&Ts greater than 3-inches depth are still subject to splitting from wood movement. And, or, use drawbores or slip joints for those instances.

The drawbores and flexible pins still provide a solid wood joint in members exceeding three to four inches. Stiles in doors almost always exceed 4-inches in width. I don't remember my source of information, probably a library article, however it was about building doors. [Do I risk saying "traditional" doors?] Drawbored joints are a pain to make, and even Garrett Hack makes them a decoration.

So, make the joint 3 inches deep, or stop the glue at three inches, and ignore the flexible pins. But, for me ... if I go to the trouble and cost, I will build doors to the traditional methods. I will die before seeing the things destroyed by demo fools.

Re: Long hollow mortise chisel and bit for a door

Powermatic drawing with key dimensions:

Re: Long hollow mortise chisel and bit for a door

It's interesting that your diagram shows a useful chisel plunge of 5" for a 3/4" mortising bit. That isn't useful information if the longer bit isn't available. The trouble with the benchtop mortisers that I've owned or used is that they are not heavy-duty enough for big work like entry-door mortises -- either for holding the work or plunging the mortise, unless you're satisfied with the 3" depth, which to me is minimal, for a 6" stile. And, the biggest drawback of benchtop mortisers in my experience is the difficulty of retracting the chisel from a deep mortise. 

On another note, I suggest using a 5/8" or 3/4" mortise for front door construction, and I personally would aim for 4+" in depth.

Ellis

Re: Long hollow mortise chisel and bit for a door

Although I'm responding to your post, Ellis, my following comment is really addressed to all. It's common practice, certainly here in the UK, withr architectural doors for the tenon at the stiles for them to be wedged through tenons. Typically the tenon matches the panel groove which is usually 12 - 13 mm (~1/2"). So, for a 150 mm (6") wide stile tenons would be cut to protrude by about 3 - 5 mm (~1/8 - ~1/4") and the mortice lengthened and angled at the outside edge of the stile to accommodate the wedge. There are different ways to do the wedges; some drive them in at either edge of the tenon, some make a sawcut 5 - 6 mm (~1/4") in from either edge of the tenon, plus a hole bored at the end of the shoulder end of the sawcut and drive the wedge into the sawcut. I prefer the latter method although it's more time consuming.

And then there are considerations such as the end of the tenon and wedges eventually protruding beyond the edge of the stile, or the reverse, the end of the tenon sinking below the stile's edge. I'm not really fond of this consequence with this form of construction, and in truth aesthetically prefer a drawbored M&T. Slainte.