Sorry this is so wordy.
Me and large cases apparently don’t agree. I’m building a 6.5′ ft tall bookcases and cabinets for a downstairs builtin in the garage. The cabinet has a fixed shelf at ~3′. The dado for the shelf was cut before the sides were separated. The widths of all sides were cut at the same time on the same saw & setup. All lengths were cut together also, and verified for square. I preassembled, checked for sq. and everything was ok. I glued & screwed it together (it’s ok the sides are hidden by other units). The diagnals matched, and top and bottom were checked with a framing square. Now I happened to check the shelf for square against the sides. One side was ok. But the other was off ~3/32″ at 24″.
How could only 1 side of the shelf not be square if the dados were cut at the same time, and the top & bottom are square, and the other side of the shelf is square with the sides? Does anyone (everyone) know what’s going on with this?
Thanks.
Replies
Have you checked to be sure that the shelf is perfectly flat? It is possible that it has some sort of twist or bow towards one end. Secondly, could the shelf possibly be slightly too long for the space? If its a fraction too long, being forced into the unit would cause it to bow somewhere.
Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.
Yep, I checked that also, and made sure the dados were a fat 64th deeper
than necessary just so bowing wouldn't be a problem. I still have a 2nd one to glue up so I'll triple check that one. Thanks.
Is the shelf fully seated into the dado? Or, was the shelf accurately sized to be the exact width as the dimension from the bottom of one side dado to bottom of the other side dado?
How did things look during the dry-fit?
Just another thought (because this has happened to me in the past). Be sure when cutting dadoes on the table saw that you firmly put pressure over the blade as you slide the sheet goods. Otherwise, part of the dado will be "shallow" and you won't notice it up until the glueup and the one side will be out of square.
Scott
From long experience in many shops, the first thing you should check are your squares. Most squares aren't square and some can be out by a lot.
John W.
If most squares are out, What do you check them against?Though he did say he measured the diagonals and they were the same.
Pythagoras got it right long ago.http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Pythagoras.htmMark
Measure it with a micrometer, mark it with chalk, cut it with an ax.
I agree with JohnW.
If the case comes up sq. by measurement, and as long as you can verify that the one side and/or the shelf are straight(not bowed), I would look at the square. To test it, place the tongue(16") against a straight rip on a piece of plywood, mark a line down the length of the body(24"), flip the tongue over the opposite side and mark a line right next to the first. The difference between the lines is twice the err of the square . Some will say to put the body of the sq. against the wood, but, the longer the lines, the more evident the discrepancy is.If the sq. shows an acute angle, take a small punch or wide nailset, and punch the inside angle of the sq. The punch will push steel(or alum.) out, and open the sq.
If the sq. shows an obtuse angle, punch the outside angle of the sq.
If it doesn't work the first time, do it again on the opposite side.Sorry to bore the vets here, but that's always a good tidbit.You didn't say how you cut the dados, but since you wrote that you cut them and then ripped the sides apart, I'm guessing you used a router?
I think the answer is in these previous posts.Here's my own summation:1) If you are using a router, take special pains to make certain the dado is dead-on square with the sides. 2) If you are using a full width dado that exactly fits the shelf, consider instead using a quarter inch wide dado , then rabbeting the shelf to fit.3) When you measured the diagonals, assuming you did the whole bookcase, did you also also measure the diagonals from the fixed shelf to the top, and again to the bottom of the
book case. Always do this measuring at the dry fit stage, so you can see what the problems are, then come up with a solution. I would say, it just has to be that fixed shelf.4) As John suggests, do check that square. Post again, if you don't know how to do that. Good luck.
Ok thanks for all the replys. The dado was cut with a router plywood bit so there wasn't as much of a problem with the depth as there could have been. The long (~ 7 ft.) case didn't have a back on them when I glued up ( I usually do that), so the sides were 'free wheeling and not consistenly parallel with each other. After I set them up the shelves were level and I suspect they'll be sq. with the sides after a back is put on them.
I already checked my framing squares for square. First post thanks again for the responsiveness.
safety tip o' the day - keep your good three fingers away from the saw blade and be sure to wear a saftey monocle over your one good eye.
I have done that! I am not sure what happened.. I used sliding Dove tails for the shelves... Off a bit.. For my Grandaughter.. I wanted it really nice.. She NEVER noticed but I told her ther was a problem.. About 5 years now and it still looks OK with all the books on it..
She was REALLY happy.. Well.....
I believe that Howie nailed it, your dado's may not be a consistent depth. This often happens when the stock is not perfectly flat. Long stock has more of a predisposition to bow. Easy fix next time you dado. Make a table saw insert from wood with a slight hump at the middle of the blade area. The stock will ride over this hump , the dado blades will cut the same depth all thru the length.Apparently when dadoing the entire width of the panel the panel did not lay flat at certain points .
My dado inserts are about 1/16" high in the middle, blended in by sanding to the saw table height. I get dado's of the same depth whether The stock is completely flat or not.
mike
I like your idea of a "bump" in the dado insert. The question is, how did you build the bump into the insert?I have never seen this idea before. Why don't you write it up, and send it to a few magazines? They're always looking for stuff like this (sometimes desperately).
I bandsawed the bump, then sanded it on a disk sander. The transition between the bump and the level portion has to be smooth on the infeed side. Otherwise it would be like hitting a step.The outfeed side is not critical.
I only submitted one of my hairbrained ideas ( wife calls it that ). Never heard a reply.Though I posted it here and a couple of other forums and people liked the idea.
That was a post on cutting doors,laminate, veneered panels etc without tapeing or scoring to elimanate chipout. Example, clamp a straight edge on the door bottom. Install a sharp 40 tooth blade in handheld circular saw. Set the depth for about 1/8". Now you make a scoring cut by pulling the saw backwards. The guard has to lifted and kept off the door or it will leave a mark.Not a problem if you use a straightedge that the saw rides on top of.
After the scoring cut, set the blade for one tooth below the door thickness and push the saw as normaly done.I do this for plastic laminates and veneered panels or doors, anything that might chip. 44 years and 100,000 doors later , none of em chipped.
mike
If you really want to get your thing published, here's my suggestion: Call 3-4 mags, and ask the name of the editor responsible for the section of the mag that does tips (Methods of Work is the title used at FWW). Get the mailing address of that editor (sometimes they are not in the home office). Send an old fashioned letter (one page) outlining your idea -- a description following the lines of your two posts here would be just fine. Lead off the letter with an explanation of the problem you are solving. It would help if you included one or two photos (stapled to your letter) -- nothing fancy necessary, snapshots will do. Then sit back and wait for 4-5 months, until some harried editor has the time to contact you (include your email address in the letter).Good luck.
Thank's , my wife and grandchildren like your idea. I'll give it a try, the kids want to see grandpops name in a magazine. I hope it is just months, I'll be eligible for social security next year.
mike
I had this same problem on an entertainment center, and the culprit was the inconsistent depth of one of the dados. Apparently, the sheet tipped up a little when passing over the blade. I now cut all my dados in sheet stock with a router and straight edge. You can purchase bits that are exactly the same size as today's "3/4" plywood. 23/32.
Jeff
Do think it will be that noticable (to you yes),it dosent seem that critical to me .Just my two cents.Cheers.
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