Bench leg tennon - vise jaw detail

[Robert Trotter]

Hi folks,

Just finalizing my bench construction. I would like your input into whether this mehtod of construction would be OK (strong enough) The bench is for handtools only work.

Top is laminated spruce 105mm thick (about 4") 2000mm x (525+50)mm wide.
The jaws and the front edge strip (in orange) are hardwood. I am thinking of lag bolting the front edge strip to softwood top. the vise jaw will be installed as per LV instructions using bolts.

I will be putting on a LV twin screw as a front vise. I need to attach the rear jaw to the bench and I would like to have the rear jaw and the leg in line. SO I came up with this idea below.

Attachment 68462

Attachment 68463

leg tennon.jpg

leg tennon exploded.jpg

The legs are 105mm square. Cut the legs out for the vise jaw as shown and tennon the remainder of the leg into the top. will this be strong enough joint with the remaining wood for the leg tennon?

Robert

[Robert Trotter]

The first two pictures didn't come out so here they are

overall shot.jpg

leg joint 1.jpg

[Chris Friesen]

Cut the legs out for the vise jaw as shown and tennon the remainder of the leg into the top. will this be strong enough joint with the remaining wood for the leg tennon?

The top will move with humidity changes, and you need to allow for this. The usual technique is to build a standalone frame and then just place the top on it, fastening it to the frame either with a single fastener on each side, or else one rigid fastener near the front and another near the back with an elongated slot.

[Robert Trotter]

Thanks Chris for the reply.
The idea was more like a Roubo or Holtzapffel bench. So no short top stretcher (or whatever the correct term is). Just mortice the legs into the top.

This was one of those big "Thinking things". Then thought I'd try it this way.

Robert

[Hank Knight]

Robert,

Your plan looks very workable to me. As for the top movement, why don't you mortise the front legs into the bench top and not the back, I.E., just let the top rest on the back legs. That way the expansion/contraction of the top is not restricted and is directed to the back of your bench. The front mortises will keep to top from moving around on the base. If you're concerned about tying the leg members together, you could put strechers between the legs front-to-back but not lengthwise. That, with the front mortises into the top should give you all the stablity you need, and I'm not sure you would need it. My bench has front-to-back top strechers only and my top is not fastened to the base at all (I just never got around to it). The weight of the 3" thick maple top keeps it in place and it is plenty sturdy.

My $.02.

Hank

[Robert Trotter]

Thanks Hank for the input.

Woops I made an omition on my quick drawing and left off the tennons on the rea legs. i.e. mortices on all four legs. More like a roubo or Holtzapffel bench.


But I see what you are saying about letting the rear of the top float. I suppose I could just put in the short top stretchers and then sit the top on the front mortices fixing the alignment with the front of the bench and let the back float.

Ummm.. I'll have to decide soon. I am wanting to start this week or next at the latest. You know just get in do somehting otherwise I'll be one foot int grave before I get something deided I am also mulling over whether or not to put in a slot for a wagon vice... better to cut that before assembly. Hummm. Decisions decisions....help!

Robert

[Chris Friesen]

The idea was more like a Roubo or Holtzapffel bench.

I believe the Roubo bench traditionally used a fairly humid bench slab, which would shrink over time as it dried out, thus tightening the grip of the mortice on the leg tenon, as well as slightly pulling the top of the legs inward to form a bit of an trapezoid.

If you do go with this method, the periodic variance of the width of the top will cause the angle of the legs to vary, so plan for that when designing the stretcher joints.

[Robert Trotter]

Thamks Chris for the input.

Robert