Square problem

[Mike Davis]

I made some end panels for a cabinet. But when I measured and marked the end of the panel I couldn't get or confirm it square. I checked my old rusty trusty framing square and from each side it was different. So I used a 5 foot Starrett machinist's straight edge to check the sides of the panel and they were straight and parallel. Then I tried my Starrett sliding try square with the 24 inch blade, a little better than the framing square but still not right.

I guess I have to add the facts that my shop is too small to be moving this panel around very easily. It is 27 by 76 inches, I built both sides in one panel to cut down on waste and save time. I can't cut it on the table saw, so i am cutting with a circular saw and a good straight edge guide.

So, back to high school geometry for the answer. Geometric constructions 101. :rotflm:

 

[DIYGUY]

Now take your compass and draw a second circle by placing one leg exactly where the original line intersects the opposite side. Draw a new semi-circle and then draw your arcs again. Does the new second line end up on top of the first? If not, one side is not truly parallel with the other ...

Good luck!!

I made some end panels for a cabinet. But when I measured and marked the end of the panel I couldn't get or confirm it square. I checked my old rusty trusty framing square and from each side it was different. So I used a 5 foot Starrett machinist's straight edge to check the sides of the panel and they were straight and parallel. Then I tried my Starrett sliding try square with the 24 inch blade, a little better than the framing square but still not right.

I guess I have to add the facts that my shop is too small to be moving this panel around very easily. It is 27 by 76 inches, I built both sides in one panel to cut down on waste and save time. I can't cut it on the table saw, so i am cutting with a circular saw and a good straight edge guide.

So, back to high school geometry for the answer. Geometric constructions 101. :rotflm:

 

[Mike Davis]

Yep, i already considered that possibility.

Maybe this weekend I can prove this out.

 

[Joe Scharle]

Are you saying that a tape pulled from the top left to the bottom right equals; top right to bottom left, and it's still not square?

 

[mkepke]

Are you saying that a tape pulled from the top left to the bottom right equals; top right to bottom left, and it's still not square?

The diagonal-measure-method requires that the opposing edges be the same length.

If one of the edges is not cut parallel to the other it is possible to wind up with a regular trapezoid (see figure at right). The diagonals are equal length, but the panel obviously isn't square. Sounds like that may have happened here...

-Mark

 

[Mike Davis]

No, i haven't got that far. The panel is laid up rough and I need to trim it to length now, But I haven't been happy with my layout lines. Not confident enough to make the cuts. So, I'm going to use a compass and straight edge to layout the square edge geometrically.

Then I'll check it from corner to corner as confirmation.

Probably being too compulsive/obsessive but there it is.

 

[LeftyTom]

Get a bigger hammer! :rotflm:

 

[EricS]

You can use the 3-4-5 rule. Leg 1 - leg 2- hypotenuse. You can use any measurement as long as the ratio is 3-4-5 for example if you draw a base line strike an arc at 6" from the corner,using the same corner point strike an arc 8" approx 90 degrees from your last mark. now put your compass point on the first mark you made and strike an arc 10" were the 2 lines intersect will be were you draw the line from corner and should be 90 degrees. I think I made it sound more complicated than it really is :eusa_thin. hope this helps



l
x6
l
l
_______8x

 

[Bill Clemmons]

I can't cut it on the table saw, so i am cutting with a circular saw and a good straight edge guide.

Is the reason you can't cut it on the table saw because you don't have the room to maneuver a panel that big? If so, bring it down to my shop and we'll run it through my TS and make sure the sides are parallel. Besides, I love shop visitors. :eusa_danc

Bill

 

[Mike Davis]

Well, that would work Bill. Except I'd have to cut it to get it in my car.

I'll see where I get with it this weekend and if I need to do a final trim I'll see if we can get together.

 

[Bill Clemmons]

Well, that would work Bill. Except I'd have to cut it to get it in my car.

I'll see where I get with it this weekend and if I need to do a final trim I'll see if we can get together.

Yep, that could be a problem. :rotflm: Just let me know if I can help in any way. You're always welcome in my shop.

Bill

 

[sushinutnc]

The diagonal-measure-method requires that the opposing edges be the same length.
-Mark

I was thinking exactly what Joe said and agree with you... but if your opposing edges aren't the same length, then you should just stop right there... impossible to have it square. The diagonal test assumes you've marked the sides to the correct length (that's the "normal" process for laying out the sides of a rectangle). If you can't measure the lengths correctly, forget about the angles!

I'm with EricS... I use the 3/4/5 method. I have used the arc method, but rarely do it... it's not as useful, if you don't have enough waste material for line segment AB (e.g., when attempting to square the edge of a board).

 

[Dean Maiorano]

Screw the boards to the shop floor and use GPS to align them. OK, I'm being silly, please don't hit me...:slap:

 

[Jeff]

No, i haven't got that far. The panel is laid up rough and I need to trim it to length now, But I haven't been happy with my layout lines. Not confident enough to make the cuts. So, I'm going to use a compass and straight edge to layout the square edge geometrically.

Then I'll check it from corner to corner as confirmation.

Probably being too compulsive/obsessive but there it is.

Mike,

Is this a glued up panel or ply? How much of the 26" x 72" panel do you have to play with? What will be your targeted final dimensions when cut to size? How far are you "out of square"; 1/32", 1/16", etc.? Sorry, I'm asking more questions without offering a solution, but I'm curious about your dilemma. I found this step-by-step demo instructive for constructing a true 90 degree angle; it sounds like what you're planning to do.

http://www.mathopenref.com/constangle90.html

Once you're satisfied with the layout lines for that segment perhaps you could use a flush trim router bit and the straightedge to get that line "true" and then reference your other lines from that. :dontknow:

 

[Mike Davis]

Thanks Jeff!

That looks like a much simpler way to achieve the same results. I will try that. :icon_thum

 

[Bill Clemmons]

I found this step-by-step demo instructive for constructing a true 90 degree angle.

http://www.mathopenref.com/constangle90.html

Jeff, thanks for posting that site. Just so happens I've got to square off the ends of a 36" wide table top today, and I was wondering about getting them perfectly square. Great timing! I noticed lots of other math applications at the bottom. :eusa_danc Math was never my strong suit.

Bill

 

[Jeff]

Thanks Jeff!

That looks like a much simpler way to achieve the same results. I will try that. :icon_thum

I hope that helps you out. I've been thinking about it some more (my thinking can be dangerous IMHO). Because you don't have a reference edge to work from then you could work from the center of the panel out towards the edges and forget about whether the edges are true or not (you'll cut those edges to make them true later).

Here's the strategy:

Pick the approximate center (l x w) of the panel. Scribe a circle from that point which will be approximately 26" in diameter (13" radius). From that center point use the straightedge to lay off the intersecting lines to the edges of the circle in an X pattern (the same distance from the center point to the circle intersect in each case). Connect the dots where those X diagonals cross the circle perimeter and they should be a perfect 90 degree angle. Go from there if you're satisfied. :icon_thum

Interesting how much geometry and trigonometry can help us. High School memories prompt the question: "Why do I have to learn this and when am I gonna use it in the future. And for what?" :BangHead:

Good luck and keep us posted on what you find out and the outcomes in your experience.

 

[Skymaster]

Mike; I am in Zebulon and probably too far for ya but if n ya fell like it bring it over here and am pretty sure we can fix it up on my tablesaw with the slider. :gar-Bi

 

[Bob Carreiro]

Mike,
In your case the 3,4,5 method would work great. Measure 36" along one of the longer edges. If the panel is square, the hypotenuse (measurement from the 36" mark to the opposing far corner of the panel forming a triangle) should be exactly 45".
Good luck,
Bob

 

[Jeff]

Mike,

Is this a glued up panel or ply? How much of the 26" x 72" panel do you have to play with? What will be your targeted final dimensions when cut to size? How far are you "out of square"; 1/32", 1/16", etc.? Sorry, I'm asking more questions without offering a solution, but I'm curious about your dilemma. I found this step-by-step demo instructive for constructing a true 90 degree angle; it sounds like what you're planning to do.

http://www.mathopenref.com/constangle90.html

Once you're satisfied with the layout lines for that segment perhaps you could use a flush trim router bit and the straightedge to get that line "true" and then reference your other lines from that. :dontknow:

Mike,

Just curious on the follow-up. Did you get your panels true and square to your satisfaction? Did you find the problem that prompted your original post? Hope it worked out fine.

Bill Clemmons was also thankful for some geometry/math help so maybe he got his project true and square as well.

It's always a challenge and a little bit of wobble, etc. can make it "out of whack". :icon_scra