Let's Make Some Furniture! - Fixture First

This is the second in the a series of posts I'm writing about the process I'm taking as Asa and I build our living room couch.

The Progress So Far

Here's the first test build I made with a saw and a miter box:

With the first test build a success, I talked it over with Asa and we decided that trying to repeat this process 5 more times with a saw and our cheapy miter box will take too long and be labor intensive enough that we may just give up.

So, we got ourselves a Porter Cable circular saw. It uses the same battery packs that the drill we got uses:

Brand spanking new

We got a circular saw because of its portability and size. Our tiny apartment doesn't have enough space for a table saw, so this guy will be our go to guy for the hundreds of cuts we'll be making.

As much as I'd like to jump right in, mark up the lumber, and start cutting away, my inexperience with a circular saw means that I really should do some research first.

Table saws are nice because they have a lot of features built into them that help you make square cuts. The guard rails, blade depth, and blade angle settings on most table saws do that for you.

Look at all those knobs and buttons I can't use :*(

This thing would definitely make short work out of all the lumber I need to cut up. Unfortunately, it's not the right time or place for manly power tools like this.

So then how can I make sure that I can get good consistent cuts with a circular saw and a leftover length of 2x4 from the test build?

I figured... I'll need to make a fixture.

Let's Make a Fixture

Fixtures are great. From my time overseeing factories at HP, I learned one big lesson: Fixtures make all the difference in making sure you're doing what you intend to do.

The difference would be in trying to freehand a bunch of cuts or letting the fixture do most of that work for me.

Given my inexperience with the tool, I'll opt to spend an extra day figuring out how to make a fixture with what I've got:

  • (1) 8' length of 2x4
  • A box of screws
  • A saw
  • A miter box

My requirements for this fixture:

  1. Holds wood in place securely
  2. Fast to make adjustments
  3. Kept wood square
  4. Protect Apartment from Damage
  5. Don't want to go back to Lowe's for more wood
  6. Fixture doesn't reduce safety (I like my fingers)
  7. If the saw kicks back, jams, fails, etc... it'll fail gracefully and safely

After doing some looking around online, I found some good designs and suggestions for making a track for my circular saw:

https://www.google.com/search?q=circular+saw+track&oq=circular+saw+track&aqs=chrome..69i57j69i60.5231j0j7&sourceid=chrome&es_sm=91&ie=UTF-8

Unfortunately, none of them would work in my instance for one reason or another. The biggest reasons being requirement #5 above. So I instead started sketching up some ideas instead.

Everything I sketched up just seemed too overcomplicated. It required many lengths of wood that I simply didn't have (requirement #5).

So, I decided to instead just start building something and trusting that a good design would arise organically.

I start off by clearing off my workspace (the floor, notice the tile I'm hoping not to damage - requirement #4).

Then I just start laying bits of scrap wood together to see if I can tetris out a solution... and lo and behold, one did come up.

It turns out that when you stack two pieces piece flat and place a third on edge, the differences in width and depth of the 2x4's create a a 1/2" ridge:

This creates a perfect track that clears all the stuff on the saw on the right (the motor sticks out) while leaving the left side clear for the wood to drop after it's been cut.

Having two 2x4's on top of each other @ 3" more than clears the the maximum depth setting on the saw (requirement #4); a track is easily created to keep my cuts straight (requirement #3); and the center of gravity and action for the saw (where you hold it and push) sits over the larger portion of the foot and on the wood (requirement #6 and #7) so it tends to tip into the guide and the saw blade tends to tip into the wood and not away from it.

I keep the main length of 2x4 on the bottom as long as possible to maximize moment of inertia. Moment of inertia is the physics behind why tight rope walkers hold long poles. The longer the pole, the slower things rotate. Therefore, the longer the bottom piece of lumber, the more stable it'll be.

So, given that the saw blade rotates clockwise (so the teeth rotate towards you as you push away to make the cut), if it catches or kicks, the extra weight on the far end will help keep things from flying at me.

You can see it here as I begin to make cuts. The cutting space will be in the middle, leaving room for me to kneel on one end of the track - so that I can use my body weight to hold everything down:

The idea is that as I cut, I'll be pushing the saw away from me. If I slip, then the natural reflex is to push the saw out and away. The saw itself has a safety feature (I tested this a few times) which quickly stops the blade if nothing's squeezing the trigger all the way.

The pivot point is at my knee where I'm kneeling on the track, so any type of squirreling around will be at the far end (which I can fix with weights or jam into a corner of the room):

From a top view of the work area, you can see how this thing works. There's a gap that's just wide enough for a 2x4 to fit into. I adjusted the cuts manually until it was just tight enough to have a bit of friction, but not so much that I need to hammer pieces in.

Viewing the fixture from the end where I'll be kneeling on it, you can see where I'd insert the 2x4. The cut side pokes out to the right, and the drop side is on the left.

From here, I can slide and tap each 2x4 until it's in the right spot. Once there, I push the circular saw away from me while keeping the foot of the saw against the right guide.

Nice and simple! In the next post, I'll show the results from trying to use this thing.

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