Sunday, July 13, 2008
Bench #3 - Attaching the top, leg vises
I like a row of dog holes as close to the front of the bench as possible. The bench features 5-3/8" thick legs that are flush with the front of the top. I didn't want to place the dog holes behind the legs, which would mean a reach when working narrow pieces, and a bit of a pain to raise up the dog that falls behind each leg. Skipping over the legs was also not an option, since I wanted a hole every 3"-4". That would mean a lot of extra cranking for pieces that fall around the "leg" hole. So my solution was to place a dog hole directly over the leg itself, and mortise the top of the leg for a dog hole. I then bored a hole cross ways through the leg itself so I could reach in and pop up the dog when necesary. The access hole passes completely through the leg so it's easy to keep clean. I also made a dedicated dog that lives in this hole exclusively. It's a tad shorter so when it bottoms out against the ledge in the hole, there is just the right amount of room under the bottom that I can get a finger in there to raise it up.
The dog holes are canted at 2 degrees, so calculating the offset for drilling the dog hole took a bit of thought since the top of the leg would end up buried in the benchtop. Plus, I had to drill at 2 degrees off plumb to get the hole to meet up properly with the access below.
I squared up the dog hole with a chisel. It felt real nice to chop into end grain, since there is no end grain to contend with. I was a little concerned that my solution might weaken the leg. Well, it does weaken the leg since material is being removed. But I'm not worried about it. The short grain section above the access hole is the fragile spot, and with the rest of that massive shoulder distributing the force transmitted through the top, I don't think there's anything to be concerned with.
I managed to get the base flipped upside down onto the underside of the top to mark the tenons for the top mortises. I marked very accurately with a knife and proceeded to waste most of the material with a plunge router.
On the fourth mortise I noticed I was about 1" short of my target depth. My bit just wasn't long enough anyway. I found a bit that was long enough and it just so happened that it had a pattern bearing. So I squared up the top of the shallow mortise (above), ditched the router fence...
...and took the mortise to final depth. What a great technique!
After I squared up the mortise corners I measured the leg tenons with a dial caliper and made sure they would just slide into their mortises. I also drilled the top for the tenon pegs. I didn't want to drop the base into those mortises and remove them more than once. My careful tenon sizing paid off. The top dropped into the mortises like a glove and the shoulders seated nicely. So I marked for the pegs, and setup four spreader clamps to raise the base off the top.
Before I attached the base permanently I routed and installed two 1-1/4" angle irons for the sliding leg vise, one for each side of the bench. I sometimes work from both sides of the bench, so having the ability to place the sliding leg vise on the back of the bench will be a real bonus for my work. The idea for this comes directly from the Woodworking Magazine Blog. Specifically the sliding vise design by Bill Liebold. Thanks Bill and Chris for the info.
Getting the top married to the base was a turning point. It meant the bench itself was done. All that is left is to install the leg vises and throw on some finish. The bench is 36" high. That's a full 3" shorter than bench #2, and I'm already loving it. I think Schwarz's 34" would be a little too low for me. He must have long arms for being 6'4", since my pinky pretty-much grazes the top of this bench. (he mentions in the book that his grazes the top of his 34" high bench) Either that, or I have short arms for 6'1".
That's the leg with the dog hole access.
The sliding vise took a little mocking-up to get the tongue right and tilting-out action correct.
I couldn't simply cut a tenon onto the end of the sliding portion, since the placement of the dog hole strip forced the angle-iron channel rearwards past the thickness of the slide. Adding a tongue or tenon to the back of the slide was the only option. Here I'm clamping on a test piece to check position and thickness. The trick was to find the right height to allow the slide to rise off the runner at the bottom, yet when lowered into position leave enough of the tongue engaged against the angle iron for strength when the vise in engaged.
After I found that magic number I cut the final piece and mortised it so it would slip around the vise screw's nut.
I didn't glue the tongue in place in case it fails in use (I doubt it), but simply ran four 1/2" bolts through the slide and the tongue piece.
For the smoothest possible action on the main leg vise I overdilled the holes in the chop and leg and mortised in Delrin bushings just larger than the screw diameter. These keep the screw from flopping about and provide a smooth surface to rub against. These don't need to be very thick since the screw is not bearing any of the chop's weight.
My original garter design called for brass. I ditched that idea when I found out what brass is going for today. So I used an almost equally expensive material-ebony. Well, it's actually quite a bit less than brass, but it fills the bill nicely, and I had some hiding away for a couple years, so this seemed like a good use for it.
I taped the two ebony halves to a scrap block and chucked the whole works into the lathe. What better way to make perfect circles?
A few scraper cuts later and it was done.
I popped them off the block and drilled holes for attachment screws.
Then I used a router with a circle cutting jig to define the perimeter of the garter's mortise before drilling the through hole for the screw.
The screw engaged the garter perfectly. The ebony garter with stainless steel cap screws (I tapped the wood for 10-24 threads) also looks pretty nice, I have to say.
The leg vise, with roller supports and delrin bushings works effortlessly. I couldn't be happier. In fact, it works so well, that I can grab the end of the hub and give it a spin to open the vise.
It's looking like Roubo's German bench now.