Motice Help

[ajbell]

Hi All

I am cutting a through mortice for a wedged tenon.

I have predrilled the bulk out with a hand drill and am finishing with
a bevel edged chisel.

I was worried about drilling too close to the knife line so I have prob left too much material (about 4mm)

It is my first time cutting mortices and I am not sure if I am doing it correctly.

1. Do I try to chop the remaining material out by placing my chisel in the knife line and using a mallet?
I have been doing this but it seems to take so much force and I am not sure if my nice LN chisels were meant for such heavy hitting!

2. Do I just take smaller "bites" out of the waste say 1mm at a time and work back to my knife line?

3. Should I need a mallet or should I be able to par back gently to the knife line if the chisel is sharp enough?

The LN chisels come ground to 30deg, I have put a secondary bevel at 35deg and then polished at a further 2deg using a vertias II jig.

thanks for the help

Andy

 

[mr grimsdale]

Hi All

I am cutting a through mortice for a wedged tenon.

I have predrilled the bulk out with a hand drill and am finishing with
a bevel edged chisel.

Mortice chisel (same width as mortice) is best and you don't need to predrill anything up to about 3/4" width (softwood) or say 1/2" (hardwood). Next best is a firmer chisel (same width ditto) which you can use to clean up the cross grain ends, then pick out the long grain sides with a bevel edged chisel perhaps. Whichever you use work from both sides and don't poke anything right through except the tenon.

I was worried about drilling too close to the knife line so I have prob left too much material (about 4mm)

You don't need a knife line for a mortice - you need mortice gauge or marking gauge lines for the sides, and pencil for the ends. Mark right around and do both sides, drill (from both sides, not right through) as close as you can get without going over.

1. Do I try to chop the remaining material out by placing my chisel in the knife line and using a mallet?

Yes at the ends, but only the last mm or so which you save til last. No at the sides which you pare away carefully by hand when you are at the line

I have been doing this but it seems to take so much force and I am not sure if my nice LN chisels were meant for such heavy hitting!

Bevel edged chisels are more for hand pressure than hitting with a mallet. Tapping is OK but if you want to belt something you need mortice or firmer chisels.

2. Do I just take smaller "bites" out of the waste say 1mm at a time and work back to my knife line?

Yes

3. Should I need a mallet or should I be able to par back gently to the knife line if the chisel is sharp enough?

Pare gently just the last few shavings, otherwise bash away, as long as you don't go right through or too far into the sides

The LN chisels come ground to 30deg, I have put a secondary bevel at 35deg and then polished at a further 2deg using a vertias II jig.

So thats a 37º edge. Too steep. It'll still work but you would do a lot better with 30º at the edge, or even less if hand paring and no hitting.
There are endless reports of LN chisels not taking a 30º edge. If true they should be ebayed promptly!

 

[ajbell]

Hi mr G

I don't currently have any mortice or firmer chisels so have no real
choice but to drill and use a bevel edged chisel.

The problem may also be that these are through mortices in the face of a panel (oak 3/4" thick). they are for a horizontal tenon in a shelf which means that the long edge of the mortice (2") is across the grain which I guess is not so easy to remove as it is choping the fibres.

I could not use my gauge to mark the mortice as it is too far from the edges of the panel - but I could have saved my self some time by not marking the ends!

Maybe as you say the sharpening angle is too high but the LN come with a 30deg and suggest a higher secondary angle.

Thanks

Andy

 

[woodbloke]

PM sent - Rob

 

[mr grimsdale]

Hi mr G

I don't currently have any mortice or firmer chisels so have no real
choice but to drill and use a bevel edged chisel.

The problem may also be that these are through mortices in the face of a panel (oak 3/4" thick). they are for a horizontal tenon in a shelf which means that the long edge of the mortice (2") is across the grain which I guess is not so easy to remove as it is choping the fibres.

I could not use my gauge to mark the mortice as it is too far from the edges of the panel - but I could have saved my self some time by not marking the ends!

Maybe as you say the sharpening angle is too high but the LN come with a 30deg and suggest a higher secondary angle.

Thanks

Andy

Right - that's different then. Not a conventional mortice. Should it be called a "through housing"? Not suitable for wedging really as you may split the board.
Knife marks do make sense and mortice chisel no use. Ignore (some of) what I just wrote!

 

[matthewwh]

Hi Andy,

Save your layout lines for taking the final wafer thin shaving to bring the surrounding timber from ‘within a gnat’s’ of the size you want to ‘precisely’ the size you want.

To remove the rest of the material the most important thing is to work methodically and avoid the temptation to be too greedy with a single stroke of the chisel. You shouldn’t need a mallet for any of this job.

Work in from both sides to ensure a crisp finish.

Start with the corners of the mortice, paring off thin shavings at an angle so you have effectively defined the waste with a chamfer at each end (this will help prevent tearing material that you want to keep). You will now see the benefit of having thin edges, slender blades and shallow side bevel angles on chisels. A slim fishtail skew can be handy here for trimming off the frayed fibres so you can see what’s going on.

Next grab a wider chisel and pare back the middle of the waste at an angle, again working in from both sides so you end up with the mortice almost full width at the outer surfaces and narrow at half depth. An alternative way of thinking about it is that you have made a ‘roof shape’ out of the waste on each cheek inside the mortice.

Now bring the angle of your paring strokes down so your roof shape gets flatter and flatter until it is parallel with your knife lines and you have about 1/2mm of material left to pare back (still working in from both sides) to achieve an accurate flat surface.

For the final stroke you can attach an accurately planed block to the outer surface and use it to register the back of your chisel blade while you creep up on the knife line. Tidy up the ends in the same way.

It sounds like a lot of work but it’s not that bad, I still reckon a proper mortice chisel is faster though. With those you only need to mark one edge with a gauge and a mark for each end, the chisel determines the width and because it has three cutting edges it squares the sides as you go. You then make your tenon to fit the mortice (which can be laid out using your mortice chisel as a referance for width - again saving time).

 

[matthewwh]

Agree with what Jacob said above whilst I was typing.

 

[ajbell]

thank guys

I am following a plan for a bookcase in "Fine Woodworking" and everything technique is new to me so progress is slow but I want to learn how to do it properly rather than my usual bodge it approach.

The heavy handed chopping just didn't seem correct, so I will try the approach advised.

Next I need to learn how to cut the tenons, do the wedge, shape the curves on the top rail, ends and bottom rail, cut a rebate and tongue..................etc.

Andy

 

[ajbell]

Matthew

Does it matter that i will parring across the fibres at 90deg - I guess not as it is similar to paring the shoulder on a tenon which is also across the fibres.

The board is approx 50" by 12" so I have been setting it flat on the bench and cutting vertically down after I have drilled the waste out.

I understand the description about the "roof" on the check sides of the mortice but I am unclear about the first step to define the edges of the mortice - can you describe it simply for me?

thanks

andy

 

[woodbloke]

PM replied to - Rob

 

[mr grimsdale]

PM SENT :lol:

 

[matthewwh]

You guess right, the only direction you don't pare in is with the grain.

This would take me about a month in sketchup so you'll have to make do with 'Joel style'!

 

[ajbell]

Hi Matthew

Thanks for the drawing - all is now clear.

I have finished a couple of the mortices using the paring method to form the roof and then leveled the roof parallel to the gauge line.

I don't really seem to get that last wafer thin shaving at the gauge line unless I roll the chisel to get the cut started with the corner of the chisel.
Maybe i have levelled the roof too early.

But it is certainly much better than that constant choping.

Thanks

Andy

 

[Vann]

Thanks Matthew. That's the best (most detailed) description I've come across.

When I get home I'm going to cut and paste that into a Word document and keep for future reference (I've never been able to cut a through tenon successfully ).

Cheers, Vann.

 

[woodbloke]

Matthew's description (and the artwork :wink: ) is excellent and is the way to pare a mortise if a chain drilled series of holes is used to remove most of the waste. I use a router which only leaves the round ends to make square...not too tricky. The beauty of using a router is that the sides of the mortise are parallel in both planes and mortising from each side will produce a through 'hole' - Rob

 

[Jeff Gorman]

Might I respectfully suggest that unless we are making mortises in canal lock gates and suchlike, that direct chopping is a more certain way of making an accurate mortise?

There are some notes on my web site at http://tinyurl.com/yfcl64s

Jeff

 

[woodbloke]

Yes and no I think. Certainly using a mortise chisel was the time honoured way to do the job, but I usually ended up slightly mangling the edges with the chisel, which is of no import for general work where they're covered.
However, when a through show joint is required the exit mortise has to be dead true and the way that I do it is with the router. Provided there's none of the dreaded 'router wobble' in the machining it will produce a dead straight and true mortise - Rob

 

[Jeff Gorman]

Woodbloke wrote:

Yes and no I think. Certainly using a mortise chisel was the time honoured way to do the job, but I usually ended up slightly mangling the edges with the chisel, which is of no import for general work where they're covered.

However, when a through show joint is required the exit mortise has to be dead true.

------------------------

Being brought up in the Cotswold craft tradition where through jointing was common, I was taught the tip illustrated in the fourth and fifth pic down at http://tinyurl.com/yfcl64s . The perimeter of the exit hole is actually cut by the spurs of the mortise gauge and the knife lines at the mortise ends.

Jeff

 

[matthewwh]

Hi Jeff,

First, thank you for the link to your excellent morticing instructions - definitely one to tuck away in the bookmarks. Under normal circumstances I would suggest the same, as did Mr G initially. I think the reason we arrived at the drill and pare method was that the mortice in question is actually a through housing in a panel so traditional chopping would split the surrounding timber.

The original intention was also to wedge it which would have the same effect (unless there has been another misunderstanding and we really mean a keyed tenon which would be entirely appropriate).

 

[mr grimsdale]

Here's my description of morticing (as I was taught)

Much the same as Jeff's, except no levering, and I'm not sure what Jeff's starter trench is for.