Sunday, December 14, 2014

A Square Deal (51)

I find myself working on a Sunday again, which is fine, but I look forward to a day off at some point. hopefully next week.

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Yesterday I finished off with the installation of two of the central pillow blocks an their locking bars - 'drawbars', they could be called. Those attach directly under and into the central tenon on the breadboard end of the slab, and thus are sort of the 'zero' point in terms of slab movement to which they might be subject.

The middle of the slab is held in place with the middle drawbars, while the ends of the slab crosswise are allowed maximal room to float with seasonal movement. You saw in the previous post the lateral room allowed at the post tenon attachment points. I've allowed for 1/4" (6mm) each side.

That left the two other central pillow block locking bars to fit, however their condition is rather different than the other two middles, as, like the post tenons, they attach the top in an area where they are subject to the greatest range of top expansion and contraction. So, they were designed a bit differently. In the next series of photos we are viewing the underside of the table top, so everything is upside down from where it will be normally.

Here are the cast of characters - pillow block to the left, special mortise in the middle, and hammer-headed drawbar on the right:


The drawbar has a hammerhead on one end which fits into corresponding short sliding hammerhead mortise cut into the table. The drawbar slides right through the pillow block, just like the other ones. I feel the sliding hammerhead joint is mechanically much better than a sliding dovetail joint.

The drawbar is dropped into place though an opening:


Then the drawbar is slid outward to engage in the mortise proper:


The above picture shows how much lateral sliding room there is with this connection. It should be plenty.

Once in position, the pillow block, along with two floating alignment pieces on the underside, is slid down:



Once it is down the pillow block just covers the rear portion of the mortise where the hammer-headed drawbar made entry:


An overview of the table slab with both middle pillow blocks and hammerhead drawbars fitted:


Yesterday I fitted the frame to the top, however this was a fit only of the four corners, and the post tenons. These were a tight squeeze - a good fit, but there is not much slop at all (which is what I wanted in those positions as one can expect next to no movement of the top along its grain).

Now it was time to fit the frame with all 8 points of engagement (4 post tenons plus the 4 middle pillow block tenons). The big question was whether the hammerhead drawbars were perfectly centered in the slab, as this would enable the three tenons on each breadboard end (6 altogether) to meet their spots properly.If the hammerhead bars were not perfectly centered, the only recourse would be 'easing' and fudging' the fit, which I would very much prefer to avoid.

Well, here goes nothin':


Success! I felt like I had just landed a remote vehicle on a comet:


This is where all the fussing over precise cut out pays off.

A closer look at the middle connection along the table end finding its way:


A few more checks, then I pushed the frame all the way down:


I was psyched to reach this point in the build!

The hammerhead drawbars will be secured by a peg, and those drawbars are themselves on a slight drawbore:


I'll leave the peg driving until tomorrow however. The next, and nearly final step with this table is to fit the breadboard ends and their associated double-hammerhead ebony keys, which is the plan for tomorrow. Also the leveler feet should be in my hands and I can fit those too. Oh boy! So close now!

I also moved the packing crate construction along for the side table:


All for today - thanks for visiting the Carpentry Way.Net: this thread ends at 52.

5 comments:

  1. Oh, man! You better hurry - I'm almost out of popcorn!!

    ReplyDelete
    Replies
    1. Paul,

      at least you're eating healthy!

      ~C

      Delete
  2. Hi Chris,
    Just a quick question - How the heck do you do that hammerhead mortise???
    Thanks,
    Owen

    ReplyDelete
    Replies
    1. Owen,

      thanks for the question. Prior to this build I had several hammerhead router bits custom made. I used one of them to cut the hammerhead portion of the mortise along with the hammerhead itself.

      ~C

      Delete
  3. Chris, thanks for the quick reply! That's very cool, I've had similar ideas come up for me now and again for different applications, but alway just left it on the drawing board.
    Thanks again for putting in the extra work to show us all where the bar is! Beautiful work!
    Owen

    ReplyDelete

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