Posts Tagged With: mortising

Mortising Improvements

After reading through Jeff Gorman’s articles on mortising I realized that having geometry problems with my chisel would cause the kinds of prelims I was seeing with crooked mortises I was experiencing.  I thought I should do a little research out in the shop.

To back up just half a step, I was having a couple of different problems with my mortising.

First, and the easiest problem to solve was that I was blowing out the ends of my mortises.  That, frankly, was a self-inflicted injury.  I’ve read Wearing, I know that I’m supposed to leave the door frame members that are going to get mortises over-long to prevent this.  I’ve already milled new stiles for the Byrdcliffe door that are four inches over my finished dimension.  I’ve also realized that I can control where the chisel moves by how I orient the bevel — the chisel always pushes away from the bevel.  In hindsight I probably could have chopped those mortises 1/4″ from the end of the stiles with a little more care (and the bevel facing the end of the mortise/end of the stile).

Mortise End Blowout

Mortise End Blowout

The other main problem I was having was that my mortises weren’t straight or plumb — that is the tenon would lean toward the rear face of the stile.  Part of the solution is to orient the workpiece so I’m looking down the length of the mortise and can watch to ensure the chisel is plumb.  But I gotta tell you, I was doing that and still getting mortises that listed to the starboard.  On top of that, the stiles have a shoulder – a rebate for the stained glass I plan to make – that I was using to ensure that the chisel was straight.

While I was chopping the mortises I notices that my English mortise chisel was getting stuck and I suspected that there was a fatter part behind the cutting edge (no not *me*, not that far back, closer to the edge).  So I measured it, guess what I found?

Chisel Measurements

Chisel Measurements

I found two serious problems with my chisel geometry.  And yes, I know that “it’s a poor craftsman that blames his tools”.

Screen Shot 2014-03-19 at 7.34.24 PM

But there are two very real problems here that I found.  The first is obvious from the tracing of the chisel above, the cutting edge is not straight.  Its angled to one side.  That makes it a sideways wedge and it will push the chisel to the side in the same was as the bevel of the chisel will push it back.  The other problem is less obvious.  You can see from my measurements that the chisel is narrower at the tip than at the midpoint of the bevel (or anywhere, really).  What isn’t obvious is why — someone kissed the side of the chisel on a grinder and the one side of the tip tapers in.  Guess what, another wedge shape that pushes the chisel off plumb.  I can easily re-sharpen the chisel and get rid of the first problem, but correcting the side-taper means shortening the chisel by  1/4″ or maybe a little more.

In the meantime I had to run out to Woodcraft to pick up some Aniline Dye and Gel Stain for the finish work on this project, so I bought a Sorby mortise chisel.  Long story short, it works well and chops a nice straight mortise, but I hate the plastic handle and I’m not impressed with its edge holding.

I laid out another practice mortise, and chopped it using the end-to-end strategy from Paul Sellers’ video.  I ended up with a straight, smooth, square mortise a bit over my intended depth.  Wow, what a relief.

A "true" mortise chisel makes a big difference.  Any straight and true chisel would work.

A “true” mortise chisel makes a big difference. Any straight and true chisel would work.

Here is what I like about the Sorby chisel.  It was in stock at the local Woodcraft store, and is ground straight and true.  It wasn’t cheap, but at $40 it is not unreasonable.  Here is what I don’t like about it.  The plastic handle is just god-aweful.  God-Aweful.  Ick.  The steel is questionable.  The chisel was sharp out of the package, including a micro bevel, so I went directly to chopping my first mortise with it.  After one mortise (and gentle taps, I’m not wailing on this thing for God’s sake) the edge has a couple of little nicks.  It wasn’t badly nicked, and I could certainly cut another mortise with it before sharpening, but I don’t want to sharpen it that frequently.

Nicked edge after one mortise

Nicked edge after one mortise

I flattened the back (it was pretty close) and worked it through up through my 13,000 grit stone.  Then I flattened the bevel and added a micro bevel with a polished edge.  My thinking was that even though the chisel was sharp, with the factory scratches it wasn’t working as effectively as it could.  The second mortise was easier, but the edge still showed wear.  I might get four mortises out of it before I need to re-sharpen.  With my old chisel I cut a dozen practice mortises without it showing the same level of wear.

Sharpened and ready to go (back) to work

Sharpened and ready to go (back) to work

The bottom line is that I think I’m mostly out of the woods on making the mortises for this door.  I have to say, that feels pretty good.  I’m no mortising god, not by anyone’s measure, but things are looking better.

Nice, clean mortise

Nice, clean mortise

I’ve been using a “test tenon” to check my mortises, both to make sure the floor is flat enough that they don’t rock, and that the mortise is snug and plumb.  Even though it looks like there is a small gap on the left side, it’s nice and snug — and clearly straight.  I should be able to get my door frame this weekend, in fact I can probably finish up most of the woodworking on the project and start planning the stained glass.

Test tenon fits properly and is dead plumb

Test tenon fits properly and is dead plumb

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Chopping Mortises

I’ve been reading about chopping mortises, and thinking through my experience last weekend.  I think I have a better perspective on mortising now.

A couple of things I’ve been looking at:

First, watching a few videos is helpful.  This one from Paul Sellers is pretty good, he demonstrates chopping a mortise with both a heavy mortise chisel and a standard bevel edge chisel, starting from one end of the mortise and working toward the other.  The first pass he has the chisel vertical, and the bevel facing in the direction he travels across the mortise.  By the time he gets to the far end (maybe a little sooner) he’s at full depth.  Then he turns the chisel so the bevel is facing in the other direction and works back – starting just past where the mortise isn’t yet at full depth.  But this time, he holding the chisel so the bevel is vertical, so the the chisel is at maybe 30 degrees.

Another good source of information is Jeff Gorman’s web site, the section on mortising has some great pictures.  It does a really good job of illustrating some of the dynamics associated with chopping mortises.  He illustrates really well where the force is concentrated, it’s worth a careful read.

Why does my chisel go wonky?

 

 

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