how to make a proportional divider for drawing


WARNING! Power tools, including drills and saws,
are extremely dangerous and can cause injury or death!
Use at your own risk! Let me show you how to make a proportional divider. You want to use a piece of good quality wood. This is oak wood, but you can use maple, or any other good quality hardwood. Inexpensive pine wood tends to split, and is actually harder to work with. So, get a piece of wood like this. This one is at least 14 inches long. That’s how long our proportional divider is going to be. So, I will put a mark here, at 14 inches. This is where we’re going to take
our proportional divider from. And then the other thing I’m going to do is put a halfway mark at 7 inches. Then the next thing is to put a line down the center of this piece of wood, exactly down the middle. Really take your time on this and make sure that it’s a nice straight line right down the middle. So, I’ll put a little mark halfway and then take a straight edge. So now I have 14 inches marked off, the halfway marked off, and a line down the center. Now we’re going to drill holes on one half of that. So between here and here, we’re going to drill holes, like so, all the way through. And then, we’re going to put it on a table saw and rip off a couple of strips to make your proportional divider from. But it’s really important that these drill holes are exactly on the mark. And if you try to just drill them straight like that, the drill bit tends to walk a little bit and your lines won’t be straight. To start, I’ve got a small Phillips-head screwdriver. You could use a nail in place of that, but this little Phillips-head screwdriver works great. What I’m going to do is start about halfway, and move just slightly off-center, and that’s where our first hole is going to go. So really take your time, and make sure that that point is exactly on that line, stand it up, and just hit it with a hammer a couple of times. That is going to allow us to… When we start to drill, if we drill into that hole, it’s going to keep it exactly where we want it. Now that I’ve got that first hole marked, we’re going to put another mark about every half inch. So I’ll just make some marks. There’s where I need to put all the drill holes. Right on the line. Now that I have all those marks there, I’m going to use my drill and drill holes. Even though we’re only going to take two strips off, and we really only need to drill about that deep, just go ahead and drill all the way deep, and that way you can cut four of these strips and choose the best ones. Usually, the top one you’ll discard, because when you start the drill, it sort of tears it up a little bit. So, now we have all the holes drilled, and we’re ready to rip this this way. We’re going to use a table saw. You could use a hand saw if you don’t have a table saw, and just cut it by hand along a line, but that’s going to be really hard. So if you do have a table saw, you should use one, if you know how to use one safely. OK. So now let me re-measure and cut these exactly 14 inches long. Let me cut that real quick. Now I’ve cut these to 14 inches. The next thing is to put the screw through, and it doesn’t matter what hole we pick. I’ve got just an assortment of screws. This one is a little short, this is a wing screw, with a wing nut, and you can find these anywhere. The thing that will really help is if you can find one of these gasketed washers. Because what I’ll do is I’m going to first put a washer there, then I’m going to put it through one of the holes, and then I’ll put the gasketed washer on next, with the rubber facing out, and then put another washer on. And what happens is when you tighten this down, it will squeeze that gasket and it will grip the screw better. What that does is that it means when you tighten this down, it’ll stay tight. We can wiggle it all day long
and it’s going to stay tight. It’s not going to loosen up like this will do without a gasketed washer. So now I’ve got the screw in there, and that’s going to hold it dead straight so that these are exactly lined up. That’s why we want to go ahead and put that screw in. You can even tighten it down. It doesn’t matter what hole, but put it in one hole. Then the next thing is we’re going to take some masking tape and just tape the whole thing together. See how I’m pulling that real tight? So that doesn’t move. And you even could do it down here on this end. Now that that’s got the screw in it and we’ve got tape, now we’re going to cut these ends, or just sand them. And there’s two ways you can do that. One, we can just literally try to cut it, like that. So that what we’re going to do is cut a point, but that can be hard. The other thing to do, which takes maybe more time, but there’s nothing to it, is get the heaviest sandpaper you can find — maybe not the heaviest, but this is 60-grade — and just start sanding, like that. Do both ends. It’s going to take a long time, but when you’re done, you’ll have
a fantastic proportional divider. Just going to keep on sanding like that. The other way is to cut it, or use power tools or something. But this is the way that anybody can do it. And if you don’t even have any of this heavy sandpaper, or you don’t want to spend any money on it, then take this and go out on a sidewalk, on a concrete sidewalk, and just drag it on the sidewalk. It may take a long time, but eventually you’ll get a nice point, as you can see I’ve started to get already. And we’re going to put a point on both ends. I’m going to do a combination of the two. I’m going to cut it and then sand it. But you don’t have to,
you can just sand it all the way down. So I’ve taken a saw and just taken it almost to the point, and then I’ll do the rest with the sandpaper. So that’s basically done. Before you take your tape off you want to make sure that that point right there—
See if I split it apart? You want to make sure that one’s not longer than the other. So if that one’s slightly longer, then I’ll just sand on this side until it is exactly equal. It should round right onto the crease so that those are exactly the same length and have a nice, sharp point on the end. So don’t take this tape off
until you’ve examined that point and made sure it’s dead right. So that’s a good one there. It should have a nice, sharp point. Take your time on the sanding. That’s what’s really going to make
this a good proportional divider. Or not so good. Checking both sides… and we’re all set. Now we can take the tape off. So now all the tape’s off, and we don’t want to touch these points again. You can check and see how well they’re lined up. If you don’t like your point, then you can tape it again and sand it again. But don’t try to sand this without putting tape on it to hold it perfectly together like that. Then I can just very gently, without touching the point, just sand the rest of the edges. So there it is. There’s your proportional divider. Ready to go. This is the end you measure with, and that’s the end you plot with. Usually.

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