Wednesday, 27 August 2014

Garden Gate Project - Part 3 - Top and middle rail with tenons and mortises

More mortises

The top and mid rails required mortises to house the mullions. As the the top and mid rails had already been jointed it was a simple matter of defining a mid point on each and then marking out for each of the mortises.
I normally use a striking knife and undercut with a chisel on my joinery to produce crisp, clean results. The knife line also makes it easy to rest a chisel bevel into.
The pattern bit we have that is 1/2" diameter was measured. The cutter length was 25mm (1") and the bearing thickness was 6mm (1/4"). This dictated the depth that I needed to go to use my method of cutting a shallow clean mortise and cleaning to depth with a router.
Mullion mortises complete

The mortise dimensions are 60mm x 18mm (2.3/8" x a hair under 3/4"). Spade drills and Forstner bit were again used to bore to depth to create some clearance for the router. Then the top of each mortise was carefully chiselled to produce the "routing template". (Again a template could have been made to do this but this is not fine furniture and they are not being mass produced.)
Then simply place the router into the rough mortise and routed away the waste. You still have to clean up the corners with a corner chisel or bench chisel and this was the same as last time.

Cutting the tenons on the cross rails.

The tenons were started to be ripped on the bandsaw and everything was going well until the kerf closed up on the blade. Some reaction wood had caused it to close up. I tried inching it off the blade whilst stopped but ended up pulling the blade off the wheels. The blade would still not come out so I ended up destroying the blade. It was an old one so it was no big deal. On wood this thick it may have been better to crosscut a few relief cuts first of all before ripping the tenon cuts.

As I didn't have a spare blade of the right size I ordered a few more. The rest of the evening was spent sawing the tenons by hand with a Japanese rip saw. Even then the wood was closing up on the blade. Wedging open the kerf with a screwdriver enabled the completion of the cuts.
Cutting the tenons by hand

We have a small crosscut sled that is not really capable of cutting the tenon shoulders accurately on pieces of this length. If we were batching gates out I would make a larger one. However the cross cut sled was still used with some external support to cut within a 1/16" of the shoulder knife lines. Then chiselling to the lines and finishing off with a shoulder plane.
Chiselling the shoulders

Doing this it is possible to get very
clean shoulders

Tenon Router Sled

When cutting large tenons such as those found on entrance door parts or gates like this it is always preferable to take the tool to the work rather than the other way around.
To facilitate this we have a shop made tenon machining router sled made from 1/2" plywood and some scrap walnut. The walnut is jointed to give flat faces to ensure that when the plywood is glued and screwed to it then it remains flat.
There is a large clearance hole in the plywood for the router which is bolted to the sled with countersunk screws.
There is also a slotted adjustable foot which bolts to the edge guide to create an outrigger foot to support the weight of the 1/2" 2000W router.

In use the underside of the plywood is referencing the face of the crossrail. The cutter is adjusted to the desired length to machine the tenon. Only use a smallish diameter cutter for this of around 1/2" or so and take small cuts. As we had already taken a fair amount of the waste away by sawing it only needed the minimum amount of clean up with the router to produce good tenon faces.
The business end of the sled which
is shown on top of the workpiece

Adjustable outrigger foot.
These Sketchup drawings may show you more detail
Side View showing the component and
bench top below.

Top View. The knob is for control as this
is a manually controlled sled and
needs much control

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