Wednesday, February 4, 2009

Roubo Bench - part 3: Planning the top

Finishing the base was a major milestone and I needed to stop and take stock of where I was and how to proceed going forward. The next obvious step was to make the top, attach it, then move on to the leg vise and sliding deadman, then drill the holes and Robert shall be your mother's brother. But I'm learning, and knew that making the top is going to require a fair bit of planning before I can get to the planing.

When I was cutting the wood to length for the legs, I had also played around and cut a couple of pieces for the top to length as well. I now realized how stupid that was.

One of the lessons I've learned in this project is to not cut to final length until you have to. You can have all the drawings you want with precise a measurements as your tool will give you, but, unless you’re using a CNC machine to cut your parts, you've got to, in the end, use the measurements of the material and the piece to figure out how big or small to make it. The final measurements will become obvious as you build it.

I actually already knew this lesson but had forgotten it. I learned it when building the tv table. For that project I had never used a drawing at all, and almost never used a ruler. Instead, I had used a rough estimate of height marked out on a stick, subtracted the approximate thickness of my top, then built my first leg to that length. I used that leg to make the other legs, then used the size of the top, derived from the size of the tv going on top of it, to determine the length of the side and front. None of this was measured with a tape measure or ruler. I just used the items themselves. I ended up making a story stick, but then blew that lesson by losing it. [sigh]

I should have re-learned that lesson when building the bookcase when I screwed up the last shelf by cutting it too short. But I didn't realize what I had learned. (or re-learned)

So, now I had to begin with the boards for the top. I cleared my bench top (a weekend in itself) and began laying out which boards went where. I then tested each board by planing it to confirm I was reading the grain right and aligned them so that they all were oriented the same way. I made it so that if I planed them from right to left, my natural direction for planing, there should be no tearout (or as little as possible).

I also put the boards in my initial order and marked them 1-14.

I have just one spare board for the top, so my margin of error is shrinking. I still have to determine, finally, where the boards I’ve already cut to length will go. I have a couple I cut to very short length to be the boards where the planing stop will go and the boards where the wagon vise will sit. But I'm beginning to think that I want final-length boards (which is 60") to be at the top and bottom of my bench. my thinking is that then, when I go to cut off the ends, which I'm planning on doing by kneeling on top of the bench and cutting with a handsaw, I have a guide against which to rest the saw at the beginning of the cut for both sides.

So, I'm imagining it as me up on the top, I have a line drawn from the end of the last board all the way down to the end of the first board with the rest of the boards sticking past the line to some degree. Where I start the cut will be on a second board (second from front, or second from back depending on which side I'm cutting). My saw will rest against the end of the first board (first in back, first in front, depending, etc...) and use that to help me get the cut going straight from the start.

To make this work, I'm going to have to do a few things really right. I'm going to have to get the first and last board lined up perfectly, which means I'm probably going to have to glue the last board all by itself to be able to take the care this will entail.

I'm also going to have to line up, at least on the right side of the bench, the boards for the wagon vise just perfectly too. Effectively, I'll have to line up, at least on the right side, boards 1 (front board), 2-5 (wagon vise) and then 14. The rest I want to leave an inch or so proud of the line and then cut 13-6 to final length. That makes 14" to cross cut as close as I can get to the line. I don't think that's too daunting. I'll then touch up the end grain with some alcohol and my block plane. And if I do that to the ends of the first and last board individually, then I won't have to worry about coming in from both sides, or popping out the ends as the plane leaves the board.

What this means is that I'll have to cut the rest of the boards to about 2-3" too long in order to have the margin for error I'm looking for. I could leave them really long, but I'm going to need some of that length for the wagon vise end. (I’ll explain next post)

But before I do that, there's some more prep work and experimenting I'm going to need to do, namely figure out my wagon vise, and then cut the groove in the front board for the deadman to ride in. This has to all be figured out before I put glue to a single board.

This preparation is essential. It's like cooking Chinese, you have to have all the chopping and measuring done ahead of time, because once you start, it's difficult to stop the process and go back to do something over, or prepare each ingredient only as needed. Once I start gluing up the top, I won't have the work surface to do anything big like figure out the wagon vise, or cut the massive groove I'm going to need for the deadman. Figure this out now, make the prep cuts needed that will be next to impossible with my tools once I glue up, and then git 'er done.

Next I'll talk about all the work I've been doing to figure out how I'm going to build the wagon vise. We're approaching my actual place in the process, so once I catch up, the posts should be a bit shorter, more detailed and perhaps a bit sporadic.


No comments:

Post a Comment

Since this is my blog, for my purposes, if you comment on here, I reserve the right to delete whatever I feel like. But I'm pretty friendly.