Replies

1. 
   oldusty | Aug 30, 2008 05:35pm | #1

    Hi Patrick  ,

            Is the material a true 3/4" ? Is the cut a true 3/4" ?

            When you say it was too tight , how much you talking ?

           It could be the finish that makes it thicker . 

     edit : I re read and 2 playing cards was the better fit

           Every now and then some ply is on the thick side and it won't fit into the dado , depending on the amount ,I can shim my dado set on the TS ,you can  make two passes as you did , heck it's only one cabinet . I've probably taken a belt sander to a few as well , never have used pre finished ( yet ) .

           

                         good  luck           dusty

   
   

   ---

   Edited 8/30/2008 10:42 am ET by oldusty

1. 
   stpatrick | Aug 30, 2008 06:14pm | #3

   Good morning Dusty and Richard,

   Technically the router bit is 23/32  , so .71875 and the mic says the ply is .7250. The bit seems fine on unfinished ply, so i was assuming the finish must be  just thick enough to make it not fit. With the 2 card shim the fit is perfectly snug.  I have a dado set but was using the router because i do not have  a slider and my sled is only 24 inches wide.

   Richard, i may try that next time (kitchen, if the mrs. approves). I like the idea of the additional glue surface.  Is this joint good for ply or better for solid stock?  Also, should i put the indented groove on the bottom or on the top face of the shelf, or does it matter strengthwise since it will be locking??

   Thank you both, Patrick

   Edited 8/30/2008 11:18 am by stpatrick

1. 
   thumbnailed | Aug 30, 2008 07:02pm | #4

   Patrick,

   There is a large variation in plywood thickness, depending on core material, national source, maybe even the time of year the ply is layed up, and the care of the personnel doing the work. I had a shipment of bookmatched 3/4 ply, sequentially numbered, that was apparently randomly laid on a mixed lot of 18 and 19 MM cores. If it weren't for too tight a deadline, I'd have sent it back. Also your cutters will vary a little, especially after a few sharpenings. The sized tongue on the shelf elements, notch usually down, as mentioned above, is usually the best solution. Other possibilities include splines or biscuits. If the part will be carrying little or no load, you can often use screws, if the sides will be covered or concealed, as in built-ins. As to that card solution, try a little two-sided carpet tape, the thin kind. The adhesive is pretty agressive, and it is pretty useful in many situations.  

2. 
   SgianDubh | Aug 30, 2008 07:12pm | #5

   For heavy load bearing shelves put the tongue at the bottom for strength. I suspect you can see why easily enough.

   Obviously for carcase tops and bases the tongue side of the panel faces towards the centre of the cabinet.

   For intermediate vertical dividers I normall put the tongue side of the panel where it is least seen.

   A note on construction. Make the tongue just a hair shorter in length than the depth of the channel, housing, slit or dado. This way the shoulder of the joint closes up tightly.

   I think that about covers it, except I can say that if you're dealing with panels that vary fractionally in thickness then make the tongue to suit the thinnest panel. Panels that are a hair  thicker will end up with tongues just a hair too tight. Use a shoulder plane to skim the tongue to fit. It takes just a few moments. Slainte. Richard Jones Furniture

1. 
   stpatrick | Aug 30, 2008 08:12pm | #6

   43213.6 in reply to 43213.4 

   "For heavy load bearing shelves put the tongue at the bottom for strength. I suspect you can see why easily enough."

   Richard, you give me too much credit - - - it didn't become obvious to me until you made me think about it, as my "gut inclination" was just the opposite, but i was not focusing (as i should have been) on the aspect of which was stronger.  Once you pointed it out, i kinda went "well,  of course; how silly of me!"

    

   Gentlemen, thanks to all . . . . . but was i right to be nervous about the one hand hold and the other too close to the bit?

   And Thumbnailed, thank you; since i don't have to thickness them,  i had just ASSUMED (yes, i remember what Sr.MaryHolyWater said) sheet goods would be standard - - but again, just ignorance on my part - - but i won't make that mistake again (but i'm sure there are plenty more out there for me to "discover" on my journey thru ww'g).

    

   You guys are Aces in my book. Patrick

1. 
   SgianDubh | Aug 30, 2008 08:52pm | #7

   I forgot to answer an earlier question of yours. I use the joint with man-made board materials of all sorts and with solid wood; even though there's a lot of end grain to long grain glue joints in solid wood the joint is still pretty strong.

   Hell, my solid wood roll around tool box is made with these joints in 1/2" thick stock and it's held together for over twenty five years. By roll around I don't mean just a bit of gentle rolling around the workshop. It is picked up and put in the back of a car or van, and dumped on the floor at the next place, and has been transported across the Atlantic twice in a container as well as moved to various houses I've lived in.

   I'd say that if the joint is tough enough for all the mistreatment my poor old tool box has suffered over the years it's pretty tough. However the joints were, how shall I say, executed precisely and snugly. If they'd been a sloppy hack job I don't think they'd have lasted. Slainte.Richard Jones Furniture

2. 
   SgianDubh | Aug 30, 2008 05:50pm | #2

   Consider  this approach. Make a groove, channel, slit or housing (dado) that's less than the thickness of the plywood. Then cut a tongue to match on the shelf, carcase top or bottom, divider, or whatever.

   True, it's two cuts with a router, but the joints go together reliably, are tighter, and there's more rigidity in each joint because the parts are better locked due to the fact that there are more locking returns. Slainte.

   View Image

   Richard Jones Furniture

3. 
   [email protected] | Aug 31, 2008 07:42am | #8

   To answer your original question:

   With the guide in place, put a couple of peices of scrap up against it and clamp them down. 

   Lossen the guide, and move it far enough to put your shims between it and the blocks that were clamped up against it. 

   Put the shims in there, snug the guide up against them, and clamp it down. 

   You should have just moved it the thickness of the shims. 

   I cut such dados with two guides and a pattern bit.  I set one guide where I want the top edge of the dado, then put a piece of scrap of the right thickness up against it, (off cuts from the shelf work well), and set the other guide against the scrap.  You now have two guides set up parallel to each other with the distance between them equal to the thickness of the shelf.  Route out the dado with a pattern bit, and the width of the dado matches that of the shelf. 

1. 
   stpatrick | Aug 31, 2008 04:48pm | #9

   JnF, thank you.  I was using a Festool (can i say that word here?) saw guide rail as my fence, and only a single fence since i assumed the plywood bit and the plywood were the same.  I couldn't figure out how to move the fence 25/1000's but i suppose i should have used the cards, put the srap block up to it, clamped them, removed the cards and moved the festool rail to the new location . . . . and i would have had i been making a much wider dado/rabbet, but here it was just a SMALL amount more that i needed . . . . . that i kept saying "there must be an easier way that is escaping me, how do the big boys do this?"

    

   Gentlemen, i appreciate all of your time and advice. Patrick