creating repetitive half lap joints

[Hank496]

I am trying to make a deck grate assembly that is made from 1"x1" sticks that have 1" half lap joints.  The parts are joined together and a lattice is formed.  In the past I have made these on a table saw sled that is indexed, and run the work piece over a dado blade.  This has worked out ok, but these have all been small projects (less than 3' long).  This time the grates will each be about 5' long, too long to achieve the accuracy needed to make clean joints.  I really would like to do this with the work being stationary. 

Currently I have a TS55, parallel guides and  Rotex 150 sander.  I think a router solution is the way to go if I can find a way to make accurate repetitive cuts. Anyone have any thoughts?

 

[tbellemare]

You could clamp a bunch of the pieces together and use a router and Guide Stop with the Guide Rail running across.

Tom

 

[waho6o9]

+1 for Tom Bellemare's suggestion. Maybe test on scrap first.

 

[semenza]

Hi Hank,

Welcome to the FOG !  [smile]

Yup I think Tom is on the right track. Might be good to get a couple cauls involved to keep them all down flat and even.  Also either make sure the set up is ultra square across the ends or leave some room at the end of each piece to do a final length  cut after you route them. It would take very little out of square to have the assembly racked.

Seth

 

[Hank496]

Using the Guide Rail was my original thought as well (and it gives me a perfect excuse for a new router!).  But it still is not quite what I need. The way I have been making them is to take a board and use the dado to cut slots and then rip the board to 1" sticks.  A router and TS55 with guide rails improves this part of the process.  However, the key is indexing the cuts so that there is a 1" dado then 1" full thickness and no tolerance creep.  Because the parts are then turned 90 degrees even the slightest variation will not allow the parts to fit together.  The jig I built is ok but after about 30" it builds up about 1/6" so the spacing between dados becomes 1 1/16".  Fitting the parts then becomes very time consuming.

If the 'jaw' on the parallel extension was wider (to allow a 1"/25mm router bit) I could make a 1" peg that would sit in the slot and index the cuts.  I think that may be the solution, to build an extension for the end of the parallel guides that creates an indexing stop.  I've done some searching and it seems there are a lot of homemade parallel guides, but no one has addressed the extensions.

 

[Kevin Stricker]

It sound like it is time to make a better jig for your table saw. Consider a large crosscut sled with a key similar to that used in making box joints.  The key determines the spacing on your boards. You may also want to check out the Bridgecity tool works kerf master for dialing in your dados and creating your jig.

 

[tiralie]

Currently I have a TS55, parallel guides and  Rotex 150 sander.  I think a router solution is the way to go if I can find a way to make accurate repetitive cuts. Anyone have any thoughts?

I have made a lot of half lap joints for trellis. While my stock was 1 1/2" wide x 3/8" I think the same approach would work for you.
I ganged all the horizontal pieces of the grid together squared them up and framed them on a work surface and scewed the frame to the work surface. The frame is sacrificial. I then made a jig for my router that spanned the width of the ganged pieces. The jig was essentially a piece of mdf with an hole cut into it and a key for registration so I could route all pieces in line at the same time. The first route is critical after that you just use the key on the underside to register off the previous groove. I repeated this process for the vertical pieces.
Tim

 

[woodwreck]

I agree with Kevin from having tackled the same task, - the key to repeatability is the box joint jig concept.  The key to making that first indexed cut's determination and accuracy is the Bridge city device/concept.

Sorry about losing the router acquisition excuse.  ;D

 

[unityroad]

I keep my ras for just this kind of work (radial arm saw) picked it up years ago. Its an old crapsman. Good luck what ever you do.

 

[hueburke]

I also agree with woodwreck and Kevin. the box-joint jig, if made well, will solve your accuracy and projection issues. Bridge city's KM-1 is the ticket for set up