I recently glued up 6 file cabinet cases using biscuited butt joints. As I was attaching the bar clamps (Jorgensen) the case which started out square, would go out of square. I undid the clamps, brought it back into square and tried again. The best I could do was to get the cases to deviate from square about 1/16 of an inch over 2 feet. I was wondering if I was tightening up the clamps too much and that was causing the problem. I did go back and verify that the blade on my table saw was 90 degrees to the table and the fence was parallel to the blade. Is there a sequence that should be followed when tightening the clamps? Any suggestions are appreciated.
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Replies
i'm thinking over tightening on the clamps or clamps just a little cocked to the sides
Tommy,
Thanks for the response. I've always had problems with over-tightening things. I'll try a little less pressure next time.
Many times when a frame is out of square during glue up, you can compensate by taking your bar clamps and sliding them slightly over so that they are on a slight diagonal . By doing this, as you tighten the joints together, the diagonal measurements of the frame will "rack" slightly. The more the frame is out of square, the more you will need to rack the clamps. To much racking(and sometimes too much tension/tightness) will cause it to rack too much in the opposite direction. Keep adjusting until the diagonal measurements of the frame are equal.
Just remember a rectangle is a parallelogram with equal diagonals
Does this make sense? I'm having a hard time to articulate this. Major brain fog...
Hi migraine ,
" A rectangle is a parallelogram with equal diagonals " Just curious about that thought , darn you , you are making me think early in the morning ,LOL However a parallelogram to my knowledge also has equal diagonals , so perhaps you may want to rephrase . A rectangle has equal diagonals and square corners , a parallelogram has equal diagonals but the corners are not square . Sorry if it sounds like I am splitting hairs but I learned the hard way as I do on most things. On one project I glued up I checked the diagonals and made sure they were equal , but later discovered it was way out of square . My thought the larger the diagonals the more critical it becomes , for example on a drawer box or cabinet door I check diagonals to get it close to reality but on a larger glue up I use the diagonals and usually stick a framing square into a corner to make sure that I have not created a parallelogram .
dusty
Hi Dusty. Well you got me thinking too. A parallelogram has opposite sides equal but length and width are not the same. The corners are not square and the diagonals are not equal. A trapezoid has 2 parallel unequal length sides, and 2 equal length non parallel sides, this creates a equal diagonal. Peter
Peter ,
Wow thats cornfusing.
uh,huh
http://mathworld.wolfram.com/Parallelogram.htmlhttp://mathworld.wolfram.com/Rhombus.htmlhttp://mathworld.wolfram.com/Trapezoid.htmlAll squares are rectanglesAll rectangles are parallelograms.All rectangles have equal diagonals.All parallelograms are not rectangles.Parallelograms which are not rectangles have unequal diagonals.Rich
Don't ever learn anything new. Rather than give you satisfaction that you know more than you did, it will only confirm you know less than you thought by opening horizons to things of which you had never dreamt and which you now must explore.
Rich14,
Nit picking logic. Your second and third statements are not consistent. Your third statement says "If X is a parallelogram, then X is not a rectangle". You don't mean that (because you are a seeker after truth). A correct formulation of your third statement might be "Some parallelograms are not rectangles".
As pointed out by others, equal diagonals is not the same as ninety degree corners because regular trapazoids have equal diagonals. However if opposite sides are equal and the diagonals are equal, the configuration is a rectangle.
Ron
Ron,Yup. Or I should have said, "Not all parallelograms are rectangles."I was rushing when I wrote that as I was busy with other tasks, including some finishing touches on Unified Field Theory for the lads at MIT and those pesky calls that keep coming in from Condy Rice and her State Dept. team which needs my advice on specifics to solve the problems in the Middle East.But the real distraction was the fact that we were getting ready to go out to dinner and my wife insisted that I actually wear 2 socks of the same color. I continue to work on that, but haven't really figured out how to do it.Rich
Migrane is right about this one.
By definition, a four sided figure is a quadrangle. If a the sides of a quadrangle are parallel, and the top is parallel with the bottom, it's a parallelogram. A rectangle is just a 'special case' where a parallelogram has both equal diagonals and 90* corners.
If you imagine a parallogram racked to the left, it's obvious that the diagonals aren't equal - nor are the angles 90*. As you rack the parallelogram to the right, the diagonals are equal only when the angles are at 90*. If you continue to rack the parallelogram to the right, the diagonals become unequal and the angles are no longer 90*.
'Proving' that a cabinet is square requires that you either;
verifiy that the angles are 90* or
verify that the diagonals are equal
You only need to do one since one implies the other.
Measuring diagonals is more accurate since very few squares are actually square.
Once upon a time (shortly after the earth cooled), I could actually do a mathematical proof of this but that was long ago and those brain cells have long since atrophied. - lol
Hi Dave ,
So lets make sure we got this one nailed . Just because a rectangular shape has equal diagonals may not indicate the corners are square , because you may have a rhombus . Would you agree with that ? I have known that to be the case in real life not just on paper . And if that is an acceptable way of describing the situation , would it be safe to say that when checking our work the diagonals are an indication of equalness but not always squareness . Boy this is way deep ,LOL . When I layout a large job or even if we were laying out a building , simply using the diagonals will not insure the corners are square . In fact even in kitchens and other large areas that will utilize the corner of the room I generally use the 3 - 4 - 5 method to determine if the corner is open or closed and by how much . 3 feet on one wall and 4 feet on the other should measure 5 feet across from one wall to the other . When it measures 5 foot and a half inch you know it is out of square by a half inch , and the corner is open .
dusty
dusty,"Just because a rectangular shape has equal diagonals may not indicate the corners are square , because you may have a rhombus"No.But that would happen if any 2 opposing sides are not equal (in which case it's a rhombOID) and you've got big problems.If you have a 4-sided figure with opposing sides of equal length (each pair may be different) and equal diagonals, it must be a rectangle. If all 4 sides are equal length and the diagonals are equal it must be a square (rectangle). It's also a square rhombus.Rich
Hey Rich ,
You really do seem well versed on this subject . And thanks for replying to the post for Dave . For the sake of people who may still be learning things like how to ensure your project comes out relatively square, would you subscribe to the belief that simply having equal diagonals is not a guarantee that the corners are square ? I certainly use the diagonals as an indicator but a framing square or the equivalent may tell the rest of the story. I would also have to agree with a few of the previous posts that mention bowed and otherwise not perfectly flat materials contributing to out of square works . Unfortunately the reality of materials that we may use is they are not always perfect .Using the materials that we do can create more challenges then the work itself . Have you ever used the 3-4-5 method or the equivalent , or can you share a better way ? thanks for your info
dusty
dusty,Any measurement is only as good as the tool and the technique used. Personally, I use every method I can to assure squareness of glued-up frames. Glue up is notoriously a time of high anxiety. Everything one can do to reduce the uncertainty helps.I use both squares and diagonal measurement. I am absolutely sure of the accuracy of my squares and would never use one that was out of square. Do you know how to test the accuracy of different kinds?While we've all been talking about measuring diagonals here, no one has actually mentioned how to do it. I've seen articles in FWW where the craftsman (?) was measuring with a steel tape. The end was stuck into one corner of the frame and he was loosely looping the tape into the other corner, the way one would rough-measure a room for carpet. No good!Using a rule is very difficult in measuring diagonals. It is very hard to be sure that one has lined up with the inside (or outside) corner. There may be other ways, but I think the best is to "sticker" the corners. The tool is a sliding pair of sticks with the ends cut slightly sharper than 90 degrees. You fit the tool into one diagonal, expanding it snugly into the corners and hold it tight from sliding, then "measure" the other (which will either be too long or won't accept the tool). You adjust the skew of the clamped piece until the tool fits perfectly into both diagonals. After a little practice, the method leaves no doubt whatever as to the equality.Testing with squares after that always confirms squareness (better than they can usually do alone) unless there is something else wrong. And if there is, it immediately becomes obvious.Rich
I agree dusty, but if you have a rhomboid (or a trapizoid), you still have a quadrangle (a four sided figure) but it isn't a parallelogram. By definition, a parallelogram must have:
sides of equal lengths and
a top and bottom of equal lengths.
If either of these conditions aren't met, then the quadrangle isn't a parallelogram and cannot, therefore, be a rectangle since a rectangle is just a 'special' case where a parallelogram has diagonals of equal length (and therefore 90* angles).
The 3-4-5 'trick' is actually making use of the definition of a 30* - 60* - 90* right triangle. For this triangle, the sides are always in these proportions. You could also do the same thing by measuring 10' along two walls and - if the diagonal is 17.07 ft - the walls are at 90*. This works because in a 45*, 45*, 90* right triangle, the proportions of the sides are 1, 1, and the square root of 2 - which is 1.707).
Damn, I haven't really given any of this much thought since I was taking Analytical Geometry in high school. Yo....... Mrs. Slater, how 'bout changing that D you gave me after the first semester. - lol
Dave ,
Why thank you for finally confirming what 30 some years of WW has taught me. You truly are a character . My guess you may not really be a woodworker from your style perhaps you are a teacher , attorney or my real guess a machinist .Enlighten me , please .
cheers ~~~~ dusty
Dusty -
Actually, I am a woodworker and have been for almost 30 yrs. About 10 of those years have been at the serious amatuer/semi-professional level and I 'went professional' about a year ago.
My 'real' jobs have included nuclear engineering (20 yrs), telecommunications engineering (10 yrs), and general contracting. I once considered becoming a patent attorney (I already have a professional engineers license) but gave that up when I realized that no law school would ever accept me........my parents were legally married.
During my engineering career(s), I was a 'jeans and boots' guy. I just couldn't wear the shirt and tie and engineer off the desk. I needed to see, touch, hear, and smell whatever I was working on.
Dave ,
Thanks for the enlightenment , it must be the engineer in you that gave me the machinist feeling . Several close pals of mine are civil engineers and they choose the most useless things IMO to be concerned about . I have heard tell that some of the more cerebral types often get so caught up in the process that they may tend to loose track of the overall objective and goals of completing the project. I have been supporting my family and making a living off my woodwork mostly furniture and cabinets for over 25 years . One thing I have learned , is that I try to continue to learn each and every day so as to continue to grow . For me sharing on this forum is a wonderful thing that many, myself included will learn from the vast volumes of knowledge from folks like yourself and many others actual hands on and life experiences .
dusty
Yeah, that was always one of my pet peeves about the more 'cerebral' engineers I worked with...........they got so caught up in the 'process' that they lost sight of the real job. Being a 'jeans and boots' type was actually a real benefit in many situations. I could understand their problems and still help them keep focused on the real objectives. Understanding the engineering problems also helped me communicate with the construction types so they understood WHY some things really HAD to be that way.
In the nuclear field, I worked with some of the very best and brightest and - in a few cases - it was a definite win-win for both of us. They taught me stuff well beyond what I learned as an undergraduate and I could help them translate a lot of the abstract theory to the real world.
This has become my favorite forum because I find that I can offer opinions and ideas as well as learn a lot. I probably read 4-5 threads for every one I post to. - lol
Awhh, now I'm blushing
Maybe I can help migraine.
Apply glue to the frame joints. Assemble and clamp up. Check the diagonals.
You find the longest diagonal-- there usually is one, by measuring from corner to corner both ways across the item.
You need to 'compress' the longer diagonal a bit shorter by pushing its opposite corners together a bit. By doing this you'll lengthen the shorter diagonal.
Hey presto. Here you have an easy visual memory aid for which way to adjust the clamps to correct the problem-- think of adjusting them to span across the longest diagonal. Therefore whichever pad is at the 'long diagonal' corner needs to pulled away from the frame (or carcase) a bit and the clamp retightened.
Once the diagonals match within a millimitre or so on a large frame or carcase, the next task is to check the job is not in winding and correct for that if necessary. But no-one's asked how to fix that problem so perhaps no answer is required, ha, ha. Slainte.RJFurniture
When I measure the diagonals, I note the difference in the measurements and use a long clamp (or sometimes a smart whack with my hand) to rack the long diagonal by 1/2 of the difference. I other words, if I'm off by 1/4", I rack the long diagonal 1/8" and that brings peace and serenity to my world. - lol
It might very well be that the problem lies in clamping technique, and the guys above have that well covered. However, just to be cantankerous, I'm going to throw a couple other things out there.
Checking your blade and fence is not as reliable as checking the wood that comes off the saw. That's the true test. Your blade and fence could be true, but if your jointer (or planer) is off, the stock won't come off the saw square.
Have you considered using square corner block to aid in your glue up? I made a set of four after seeing them in an article. They can really help, especially with large case goods.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Another proud member of the "I Rocked With ToolDoc Club" .... :>)
forestgirl,
thank you for your suggestions. I did check the wood with two different machinists squares and the cuts seem to be at 90 degrees. I'll have to try to find an article on clamping blocks since it would appear that they would have saved me a lot of time and frustration!
I'm new to the knots discussion and really appreciate all of the feedback, but didn't intend to start a whole conversation about geometry!
Bear59
Bear, here are the ones I made. They might be of limited usefullness with large case goods, but you could build a slightly different version out of plywood and solid stock. I've seen several different plans.
Saw these in Wood Mag, I think. I call them my Blackbird Blocks, after the SR-71 Blackbird, LOL!
It doesn't take much at all to throw something out of square. The edges of these clamps were just a half-smidge off vertical (when laid on flat on the table) and it made a difference for sure. Have you checked your stock by cutting a tall (2") board in half upright and then rolling one side over to check for any discrepancy? I find I can't trust my eyes, regardless of how accurate my square is.
View Imageforestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)Another proud member of the "I Rocked With ToolDoc Club" .... :>)
Thanks for the pictures and the reference. I'll try your idea to cut the 2" piece to see if it does in fact come out square. This was my first time posting anything on Knots after reading it anonymously for a while. I really appreciate your responses to my question. It looks like I'll just have to keep trying to get the technique down. Next project is barristers bookcases so I'm sure I'll get more practice. Thanks again.
They look more like B-2's than SR-71's.
Being a Structual Engineer (although I have not taken the Professional Engineers exam, and have no plans to in the near future) I set up a vertical alignment using Geopak for Microstation (version 7, we have not yet upgraded to V8) Based on this analysis, it can be shown that the rhomboidal interaction of angles will sum to 360 degrees for all cases regardless of distance measured from node A to node B and the correspoding measurement from node C to node D.
Having reviewed numerous shop drawings (as well as created detailed structual sketches for my technicians) I greatly admire the fact that you would hold your picture frames to such a tight tolerance.
I have found that there is too much parity in high school geometry classes, and that with a return to the derivation of basic proofs, situations like these could be avoided.
Hmph! You're right. Oh well, so much for the catchy name.....forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)Another proud member of the "I Rocked With ToolDoc Club" .... :>)
Bear59,
I like to take the risk away of glueing up either non-square or racked by using my sliding sled fense and table saw fense...I know they are square..and the TS is flat. I just put down some wax paper and clamp away.
Forrest Girl brings some good points. If the stock is cut square, paralell and correct dimensions ,then gluing up square is easier. Corner clamp blocks makes sure your clamping square. One other thing, when checking for square with a framing square,the sides must be straight. If their is a slight bow the glue up will appear out of square.This happens most often with long sides where there is some bow in the board.
mike
Why not use those clamp-on squares (like a framing square, but in this case I think they are triangular)? I'm not a woodworker , but I have helped a friend who is make cabinets and he used "squares he clamped on at the corners, if I remember correctly. I have resorted to using a speed square and clamping it in place at a corner.
The problem with a square is that almost none of them are truely 90*. Your typical framing squares can be pretty bad (particularly after they've been dropped a few times) and you have to spend quite a bit of money to get something as good as a machinest square. A square that's off by only 1 degree will give an error of almost 1/4" per foot. In other words, using a framing square that's off by 1 degree on a typical 30" kitchen base cabinet could result in a cabinet that's racked 5/8" - even though it reads 'square'.
The advantage to measuring diagonals on a rectangle is that the only time they can be equal is when the rectangle is square.
Omigod, you're right!! I guess some more brain cells have faded away. - lol
In my own defense, I'll plead excessive fatigue. I spent yesterday at my buddy's ranch in the mountains rebuilding some barbed wire fence that got wrecked in last summers brush fire. Now that the fence is fixed, we'll have to find the cattle after it dries out a little up there.
Although I got the number wrong in my example (it should have been 14.14 ft instead of 17.07 ft), the principal still applies. Measuring out a 3-4-5 (or 6-8-10, or 30-40-50) triangle guarantees a square corner since these proportions only exist in a right triangle.
Do what we do here when we can gety away with it - leave the cattle in the 'long paddock' untill the grass grows back.
Dave
I've recently purchased a set of Bessy 90 degree clamps that keep things as square as can be until you put the diagonal sticks or a square to it. It can still leave a box off square and you end up using a diagonal pipe clamp to tweak it to true. My experience.
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