June 12, 2013

Roubo Style Workbench - Part Six

Life has been pretty busy lately so progress on the workbench has slowed a bit. I've continued to find bits of time here and there to move a few steps forward and despite the slower pace things have come a long way since my last update over two months ago.

With the end vise mounted to the top and the dog holes drilled I was itching to start putting it to use. I spent a few minutes turning 3/4" oak dowels into benchdogs by cutting a flat notch in the top and adding a spring loaded bullet catch to keep them from dropping through the dog holes.

With one dog in the end vise and one in the bench I am now able to "pinch" a workpiece horizontally on the benchtop. Here I am smooth planing the legs prepping them for assembly.

Another important feature that needed to be completed before the bench could be assembled was the through-mortise on the front left leg that would mate with the parallel guide of the leg vise.

I marked out the outline of the parallel guide mortise on both sides of the leg and then bored out most of the waste with an auger big in the brace working from both sides to minimize any variation in the drilling angle off of vertical.

I cleaned up the ends of the mortise first. The end grain pine is pretty tough on the finer bench chisels so I used a beefy mortise chisel for this task.

I then pared the side walls down with a bench chisel, again working from both sides.

With the basic mortise roughed out I cut a scrap down to simulate the parallel guide and planed it to just barely fit the mortise. This allowed me to identify any tight spots in the mortise that needed to be pared down just a touch more. After some tweaking the scrap fit nice and tightly all the way through. Not bad for my first hand chopped through-mortise.

Another pre-assembly task was to bore 3 holes in the front right leg that will allow holdfasts to be used to clamp boards to the front of the bench and also provide a great place to store the holdfasts to keep them off the benchtop when not in use.

I also chamfered both the top and bottom of the dog holes. This will help prevent any splintering around these holes and will also reduce the effective thickness of the benchtop down to just under 4" which will help the holdfasts clamp more consistently.

Here is another shot of the benchtop and end vise in action as I clean up the stretchers with the jack plane.

Next come the features that pull everything together... literally. The bench is assembled with drawbore pegs through the mortise and tenon joints which will ensure that this thing will hold together longer than I will. The first step in this process is to drill holes for the pegs through all of the female components. The bench will be assembled with 5/8" oak pegs so I'm drilling 5/8" holes.

Since each leg has a mortise and tenon joint on the inside adjacent faces the drawbore holes are offset a bit to allow each peg to pass completely through the leg.

Here all 4 legs have their drawbore holes drilled waiting for a test fit.

The next step is to test assemble all of the joints clamping them nice and tight.

I then used the 5/8" auger big to mark the location of the holes on the tenons inside of the mortises.

The auger bit leaves a mark lined up perfectly with the holes in the mortise. The magic happens when you offset this mark by about an eighth of an inch towards the shoulder of the tenon.

When the joint is assembled and the peg is driven home this offset ensures that the tenon is pulled into the mortise creating an incredibly tight and strong joint.

In addition to drawboring the legs and stretchers the through mortise and tenon joints between the base and benchtop will be wedged. Here I am cutting wedges from a scrap of oak.

With the wedges cut I started working on the drawbore pegs. I cut the 5/8" oak dowels to length allowing for the thickness of the legs plus a few inches to allow room for the end to be tapered down to ensure the peg is able to navigate the offset between the holes in the mortise and the hole in the leg. In addition to tapering the pegs I also waxed them heavily with paraffin so that they are a bit easier to drive home.

The final step before assembling the bench was to cut saw kerfs into the tenons at the top of each leg. These kerfs will provide a place to drive in the wedges from the top to lock the benchtop to the legs.

Ok... deep breath... it is time to put it all together. I have to admit this was a bit nerve-racking knowing that there is no turning back once I apply glue and start driving in the drawbore pegs.

Big thanks to Mark for stopping over to help with this monumental task. We managed to successfully complete a dry run which helped us sort out the procedure and get the clamps setup and ready to go.

We then took it all apart and then started over with glue. We got the parts fitted together and applied clamps to the base to help pull everything together and then started banging home the drawbore pegs and driving in the wedges to secure the leg-to-benchtop joints.

Watching the joints pull tight as we drove in the pegs was awesome.  Below you can see the tapered ends protruding through to the inside of the leg.

Two of the four corners worked out great. A few pegs split while being pounded in but I had spare pegs ready in case that happened and we were able to drive the busted peg straight through and replace it with a new one.

Unfortunately a few of the pegs also got a bit hung up which resulted in some crazy frantic mallet whacking. This corner suffered some minor issues with a few slivers splitting off the inside of the leg.

The front left leg however went off the rails...quite literally... I suspect the offset on this joint was a bit to aggressive and the peg wasn't tapered enough to allow the peg to make bend the corner and I basically ended up pounding a 5/8" oak peg through a few inches of southern yellow pin and blowing out the whole inside corner. The joint still pulled tight but it is an ugly reminder to be careful with the amount of offset between the holes.

I now had an assembled bench and was itching to put it to work so as soon as the glue had set I started trimming the leg tenons flush with the benchtop.

The handsaw got it close and the low angle jack plane brought it down perfectly flush. The wedges add a cool visual feature to the joint.

At this point in the project the bench was assembled and the end vise was functional creating usable workbench. I still have quite a backlog of pictures and progress to share to catch up to where things are today but I'll stop here for now so that this post doesn't get too long. More to come...

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