Greetings Fellow Woodies:
Ever have one of those days when you look at that piece of woodwork you’ve been nursing for a month and you realize something doesn’t look right. I’ve been working on a hope chest for my daughter for over a month and today I realized that the chest is not square. It’s real close, but its out by a 1/16″. I didn’t notice it until I made the lid for the top. I was trying to make the overhang on the lid equal on all sides. I checked the diagonal measurements on the lid and the case, to make sure they were square. The diagonal measurements were right on! I scratched my head wondering how that was possible.
Well, I collected all the squares that I had in the shop. I checked the corners of the top and they were OK. I then checked the inside corners of the chest. Nope! That’s when I measured the length of the back and the length of the front. The front was a 1/16″ longer than the back. A quick inspection indicated that the dovetails on the front corners had not seated as tightly as the ones in the back.
I checked the two back angles versus the two front angles. The two back angles were equal to eachother, as where the two front angles. So, I had a nice trapezoid. Guess what, the diagonals of a trapezoid are equal.
Well, I called my Dad with this revalation and as usual he put me in my place. He asked me in all the times I ever worked with him did I ever see him measure diagonals. Nope, he always used a square!
Replies
Now all you need is a square square... I have a framing square that my dad gave me and I trusted implicitly just because it was his. What he neglected to tell me was that he had dropped it several times. A few raps on the corner straightend it out. We at least its as square as my new T square anyway. I was going crazy trying to figure out why my cut lines never matched what the table saw was cutting.
Steve - in Northern California
TooPlane and Steve -
many times I can't get my big carpenters squares inside my work, so I make my own squares. Two hardwood boards 24+" long and each with a good jointed edge. Apply glue to each end and clamp. If you don't have a square handy (like out on a job), set the diagonal measurement at 33-15/16 (24" out on each arm) before the glue sets up. If you have a square you trust then use it to set the angle. After the glue sets up, then cut the legs to needed length. Remember that wood moves so check them for square before each use. I generally have several of these laying around and will clamp them inside my work to hold square while assembling other parts.
PlaneWood by Mike_in_Katy
PlaneWood
Good idea Mike, I'll have to try that. Thanks
Steve - in Northern California
Excellent idea Mike. I've got a couple of smaller engineer squares I can use for inside measurments.
Mike, I teach at Katy High, Might you be interested in some ebony?
hello
I have no idea where you are located but yes i'd be interested in some Ebony.
My e-mail is [email protected].
Jim St. John
Heidi's Dad - yeah, if the price is right! Does it make good tool handles?
By the way, my wife works at West Memorial Jr. Hi. We live on Fry road about 2 miles north of I-10.
PlaneWood by Mike_in_KatyPlaneWood
I was up in your area last Friday. Interesting how Fry just tapers off to nothing a few blocks after I-10. You or your wife can call Margret F. here at KHS and leave her E-mail or phone#. I'll get back. Its actually my son's Ebony, so I'll need to check. We have 3,4 &5/4. and a little bit of billet.
Tapers off to nothing? Did you go north or south on Fry?? When I moved here in 1987, Fry Road was a cow path with no stop signs or stop lights. Now it's a 4 lane divided street with stop lights every few blocks. Going north, it goes about 5 miles then quits just after FM 529 at that new High School.
Where I live is part of the old Fry homestead which covered 4000 acres. The original homestead has dwindled down now to about 60 acres and is owned by a Fry descendant. He sold sand off the place till the hole got bigger than the Superdome in NO. Now he's filling up the hole with trees and wood chips. Before he started filling up the hole, he and his friends would try out their machine guns in the sand banks. (this is Texas, folks) I would hear a few zingers going overhead occasionally. Was tempted to fire a few rounds back but didn't.
Later
PlaneWood by Mike_in_KatyPlaneWood
Tell me about "this is Texas folks" I live in SW Hou. and every Dec. 31 at 11:59 & 45 sec. it sounds like an out door gun show in Iraq and goes on for the best part ov an hour.
I was going N. Compared to the 'Homer D's and Wal-mart area, a few houses looks like "tapering down to nothing"
I have alerted Margret F. to fwd. any message to me. They all know about Heidi in the front office anyway.
TOOPLANE, One way to reduce the chance of mis-matches happening as you describe is to make the lid an integral part of the whole construction or carcase. After the basic box is glued up and dried, cut the lid off. Even if the whole is out of scunt, then the top with luck will be out of scunt to match.
Another option might be to make the lid purposely oversize so that nothing is meant to exactly match up anyway. None of this helps with your current problems. Slainte, RJ.
I've seen more sense in an empty wallet. (Anon.)
Good point. I used that method when I built my tool cabinet.
I know that this is pretty elementry but I only use the one square that never leaves the shop. also use only one tape. theoretically they are all the same...Ha!
Miami
What you really need is one square that you use as a master square to check your other squares. Keep your standard in a separate box or protected place. Take it with you when you go to purchase any new square. You can find lots of measuring tools that are surprisingly accurate if you match them against your known accurate master square.
So, what to use as your master square? You can spend a $100 or more for a Starett or Brown & Sharp machinist square which goes out of square the first time you drop it or you can go to an art or drafting supply store and get a $10-12 plastic 30-60-90 drafting square. To prove it's exactly 90°, take two to a glass counter, put the shorter legs on the counter and face the longer legs at each other and butt them together (like a teepee). If the legs exactly butt, you have two perfect 90° angles. Buy one of the triangles and that becomes your standard or master. Now you can check your other working squares--or any you want to purchase--and determine if they are accurate. Keep your plastic master square some place where it doesn't get banged up and you will always have a perfect reference. Use inexpensive squares as your working squares. Check them from time to time. It they get banged up and out of tolerance, cheaper to replace the inexpensive ones than the high priced machinest square.
Buy a couple of smaller triangles to use to check inside corners of case goods.
I guess we all have had an experience with a square that wasn't. When I check a square all I do is put the base on a straight edge of my work bench, or the register stand in the store, and then use a very fine pencil to draw the perpendicular; then I just flop the square and if it's right the perpendicular should not deviate from the drawn line. If it does deviate then it's,out of square. I did this on the check-out table of my local Woodworkers Warehouse store, and NONE of the try-squares I checked were actually square.
The plastic drafting square is a good idea--but check it to be sure it's square. Stranger things have happened. I use a machinists square. I've never dropped it so I don't know if you can knock it out of square. Incra is now making a try-square that is milled out of a single piece of (I believe) aluminum; obviously that could not be knocked out of square. But, of course, they charge enough for that tool to buy three or four machinists squares.
Alan
I'm actually getting a pretty good laugh out of this post even though we have hijacked it to some degree. I like it when I find out I haven't gone completely insane thinking I was the only one with these kind of problems.Steve - in Northern California
A sure fire way to square up larger objects is to use the 3-4-5 triangle. Any triangle with a base of 3 and a rise of 4 will have a hypotenuse of 5. On something like the chest measure along one side 3 units of measure, (inches, feet, mm, miles whatever) and measure along the front 4 units of the same measure from the same corner. Then check the hypotenuse and adjust as necessary to get the 5 units of measure. Now check the diagonals. If the diagonals are off then check the sides and front and back for equal length. With diagonals that match and a 3-4-5 triangle the case will be square. Make sure to use an accurate rule to measure with. We have all built something out of whack only to have it bite us later. All part of the learning curve. RichThe Professional Termite, aka Woodbutcher Extrodinaire
the 3-4-5 method is simply the Pythagoreum Theorum:
A squared + B squared = C squared
A and B are the legs of a triangle, and C is the hypotenuse
3-4-5..... 9 + 16 = 25 while 5 squared is of course, 25
It's an easy method for any triangle, but it's much easier when you use decimal numbers for the math.
When using it to check square I just use whole numbers that are easy to figure in my head such as 3-4-5, 6-8-10, 9-12-15, 30-40-50. This way no fancy math is needed to boggle my brain and slow me down. The KISS method is always my favorite method. Why involve odd numbers and decimals when they are not needed for the task? For this application you are not trying to find an unknown, (the hypotenuse) you are using a known value to check an angle.The Professional Termite, aka Woodbutcher Extrodinaire
Some like it simple, some like to know why things are the way they are... in this case, what is it about 3-4-5 that makes it so.
exactly, the Pythagoreum Theorum (a2+b2=c2)... which is what I stated in my first posting in this thread, look back a couple of messages.
When is a right angle square? When is at 90 degress. If you do a dry fit and measure corner to corner the dimension should be the same. If they are same then glue it up and clamp. While clamping double check the dimensions so that it does stay square. Don't ever trust a tape measure for dimensioning, the hook can come loose and throw you off. Use a folding rule and always Measure twice and cut once. If you have any doubts before you cut the piece than DON'T.
My point in the original post is that just measuring the diagonal does not guarantee that the box is square. The diagonals for the hope chest I made measured the same, but the unit was not square. What I had built was a trapezoid. So, measuring the diagonals only guarantees you have a trapezoid and not a rectangle or square. The only way you can be sure the unit is square is to check opposing angles with a square.
There was a good article in FWW a few months back about making your own squares out of plexiglass. It would be worth the research to find the issue. FOr about $40 youu can build about 5 squares with the longest a little over 4'.
It requires a trip to a plastics store, but if you follow the instructions, you will have squares in a number of different handy sizes that, if put together properly, are actually accurate.
Good luck.
KH
TOOPLANE, if the length of the opposite sides of a rectangle are the same, measuring the diaganols, WILL tell you if it is square. Easy enough to cut the lengths at the same time against a poitive stop, so they will be the same. I agree 100% with the 3-4-5 method, but for me, it is easier to measure/cut the lengths accurately and then measure over the outside corner of the diaganols, than it is to use the 3-4-5 method. Of course, if you're squaring up a house, the 3-4-5 might work better :-)
Measuring the diagonals of a square/rectangle DOES guarantee that the corners are square. A trapezoid only means the sides are parallel. Norm Abrams uses this technique frequently on his show- The New Yankee Workshop
Gary
Try this experiment. If you can do this with a CAD system it is better but it will still work drawn on a drawing board. Draw a horizontal line exactly 6 inches long. From the left end draw a line up 6 in long at an 80 degree angle. From the right end draw a line up 6 in long at a 100 degree angle. Now draw a horizontal line connecting the tops of these two lines. This should enclose the space into a "box". Now measure the diagonals. They will be 7.7135 in long. Both the same length. Question. Are the corners square? Even though the diagonals measure the same the answer is no. In a parallelogram both sets of sides are parallel to each other but the diagonals are different. In a trapezoid the diagonals are the same but only one set of sides is parallel. The post that started this thread stated that he had built a trapezoid because one corner the joint had not closed properly. This is why measuring diagonals alone will not ensure square. Length of sides must also be equal.The Professional Termite, aka Woodbutcher Extrodinaire
You are exactly correct! I made the assumption (silly me) that when making a square box that all sides would be of equal length or a rectangle the parallel sides would be of equal length.
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