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Simple math and the demons that haunt me

Posted by joeabbott on January 12, 2014

I wanted to complete three parts to the project: correcting an edge band, trimming panels to final dimensions, and start building the doors; let’s see how that went!

P1060074Edge band

In the warm light of the shop, the mismatch (see yesterday’s post) looked far less egregious than I thought it had. For the majority of the panel, the alignment was spot-on, but somehow it drooped a bit on one corner; probably by less than an eighth of an inch. So I decided to mechanically level that area, rather than cut off the entire edge band and try again.

First, I pulled out a sander and started going at it. Well, for the overall amount of material that had to be removed, it would have taken a long time, so I abandoned that approach and got out my trusty plane. I tested the depth of cut on a test piece and was happy so I started in on my panel: riiiip … a big chuck got pulled out. Oh my! I tried again (please, don’t ask why) and … riiiiip. Another chunk.

Holy cow! I was planing along the direction of grain and the bamboo was behaving oddly. I’m not sure if I was catching a “node” (one of the grassy nobs in the bamboo stem) or what, but I now had two divots in the wood band. I was about the get out the saw and take off the band when I determined that the divots weren’t deeper than the mismatch … I might be able to sand plane (ed. note: correction 1/13/2014) it out.

And so for a looooong time, I went from 60 grit, to 80 grit, to 100 grit, and then to 220 grit and removed a bunch of wood. In the end I was happy with how it looked but my confidence in my planing technique is sorely shaken. My sanding skills … well, they’re fine.

Final dimensions

P1060079I then found I had the same problem with panel two as I did the first one: the strand plywood used in the body was slightly thicker than the vertical grain plywood used on the edge bands. Not surprising, but it forced me to get out the #5 jack plane and start leveling.

I did this the other day, so my plane was tuned and I was ready to dig in.

For this exercise, I planed the panel somewhat across grain: more along a 45° angle from the edge to the center of the panel. As with the prior panel, this both took a long time but went better than I thought it might. Maybe this was instilling some confidence back to me in my planing techniques.

I mocked up a quick picture … not to scale … that shows what I’m talking about. In the image below, the purple center rectangle represents the strand center panel; the green rectangles are the edge bands; this would be and end-on view. My job was to flatten the purple to be level with the green. Or, level enough.

image

After I had the back of the panel suitably flattened, I went back in, measured the cabinet base, and came out to trim the edges on panels to be within 1/4” of the final dimensions. Rather than take all the width off one edge, I took about 1/4” off both far and near sides so the width of the edge bands remained consistent.

At this point I have a small amount to trim off the end and sides, but I’ll wait until I attach it to the top and then use a router and pattern bit to chase along the existing edges. I brought the top panels up and put them in place along with a slightly longer than necessary center edge. Today I’ll start gluing this up! Yes, I could have started gluing it up yesterday but I always like to sit on things a day or two and make sure I’m not missing something. The next step is a big one!

#Exciting #Scary

P1060080

Doors

imageThe last part of the project I wanted to address was the doors, and this is where the simple math comes in. For those who don’t like or refuse to use math, this really is simple and it’s just because I’m a knucklehead that I made a mistake. Let’s do this quick!

For the doors, I wanted a 2” wide band on each side of each sliding door, like the picture to the right. The rest would be the strand bamboo.

We’re going to have three doors on each side that slide along two tracks. Considering one side of the cabinet, the two doors on the ends slide on the back track, the door in the middle will be in the front track. Here’s a top-down view of what it will look like:

image

As you can see in the sketch, if you look at the cabinet from the front on, I want the bands on the center panel to be the right size to hide the bands on the back panel.

Question: How wide should I cut the panels?

This is the simple math. With the inside dimension of the cabinet being 69.75”, we should be able to answer this easily. I’ve added labels to the sketch to help us:

image

If you are looking from the front, you would see:

Width of Edge Band 1 + width of Panel 1 + width of Edge Band 2 + width of Panel 2 + width of Edge Band 3 + width of Panel 3 + width of Edge Band 4

And you’d know that all of those widths added together would amount to 69.75”.

Next, we know that all the panel widths are the same … that is, Panel 1 and Panel 2 and Panel 3 will all be the same size. The Edge Bands will also all be the same size, too … not the same as the panel dimension, but Edge Band 1 = Edge Band 2 = Edge Band 3 = Edge Band 4 … in terms of width. This means we can write the sentence above more generically to say:

Width of Edge Band + width of Panel + width of Edge Band + width of Panel + width of Edge Band + width of Panel + width of Edge Band = 69.75

If we count up the “width of Edge Band” we see there are 4 of them; and if we count up the “width of Panel”, we see there are 3 of them. So we can write the sentence as:

(4 x width of Edge Band) + (3 x width of Panel) = 69.75

Earlier I stated I wanted the width of the Edge Band to be 2”, so that gives

(4 x 2) + (3 x width of Panel) = 69.75

or

8 + (3 x width of Panel) = 69.75

I hope this isn’t going too fast, but it leaves us with 61.75 divided by three to determine the width of a panel … meaning each panel would be 20.583”. Which is just over 20 9/16”.

And so I promptly cut all the panels at 20.25”.

Please don’t ask. I seriously went through all the math above, all the calculation, all the factoring and considering, all the hooo-haw, and then cut the boards over a quarter inch shorter than I had wanted. To say I was displeased is something short of the emotion I was feeling at the time.

How could I have messed that up? I don’t know, Just did. Welcome to my demons, my world: ‘A’ for planning, ‘C’ for execution. <insert frownie face here>

But, all is not lost. Math to the rescue!

I have my equation, it’s just that some of the sizes I’d planned on aren’t what they were originally intended to be:

(4 x width of Edge Band) + (3 x width of Panel) = 69.75

If we insert 20.25” for the panel width, I see that I just need to cut my Edge Bands slightly bigger …

(4 x width of Edge Band) + (3 x 20.25) = 69.75

(4 x width of Edge Band) + 60.75 = 69.75

(4 x width of Edge Band) = 9

Edge Band = 2.25”

So where I’d originally planned for the edge bands to be 2” in width, I merely need to make them oversized by a quarter inch and no one will be the wiser. Yes, even writing this here in a blog on the Internet, no one will be the wiser. Seriously … who will read through this much math anyways?

Coda

Today I cut the edge bands for the doors. I’ll need to cut door pulls into them, so I am not sure how far along I’ll get … the pulls will be tricky business (for me). Stop in later, I’m sure I’ll have pictures and pretty sure it won’t involve applied mathematics!  Thanks for dropping in.

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2 Responses to “Simple math and the demons that haunt me”

  1. When ever my cut boards come up short I blame it on the ruler I bought at Menards.

    • joeabbott said

      I wish it was that easy. The problem came when using my circular saw and rail guide: to saw exactly on a line, I end up placing the rail _on top of_ the mark I measure. As I was cutting a lot of these panels for doors, I ended up making a “story stick” (I wrote about these at length in an earlier post). Anyhow, the rail is 7.25″ wide, so I had to add that to subtract that width from my 21 9/16″ panel dimension. Somewhere in basic subtraction I rounded down instead of rounding up. I was just concerned about “wasting lumber” and wanted a rough cut very close to a final dimension: this plywood costs well over $200 a sheet. So, to save 3/4″, I ended up botching the cut altogether. Oy.

      Happily, the method I wrote about to increase the edge band dimension is super-easy and will be just fine. Still, even a Menards ruler would have done better than I did!

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