Replies

1. 
   jeffpuls | Sep 21, 2021 04:29pm | #1

   One way to get evenly spaced dados/grooves would be to use a handheld router with a 1/8"x 1/8" strip (key) attached to the router base. The key slots into the previous dado/groove and is located such that you get your 3/8" offset.

2. 
   drew_z | Sep 21, 2021 04:30pm | #2

   I would use a tablesaw with a square toothed blade for flat bottomed dadoes. It is time consuming but repeatable and very accurate if you are indexing your fence by just reading your fence gauge. When making custom-spaced bead board this is the method I use and I've found it much simpler than using handheld methods.

3. 
   john_c2 | Sep 21, 2021 05:19pm | #3

   Tablesaw, 1/8 flat bottom blade, sled with a 1/8 key

1. 
   builttolast | Sep 21, 2021 07:01pm | #4

   Thanks man! I knew there was something I was missing…

   So make a sled with an 1/8” key perpendicular to the sled, I guess I should probably use 3/4” ply and cut a dato to receive the key. Maybe 1/4 inch deep and make a 3/8“x 1/8” key?

4. 
   _mj_ | Sep 21, 2021 07:03pm | #5

   Tablesaw, 1/8" flat blade, long spacer bar.

   Cut your first groove then put the board back on the saw..move the fence away, add the spacer, move the fence back into contact and lock it down. Remove the spacer and cut the next groove. Rinse, repeat.

   Another thought; a spacer used on the front fence rail with a stop block would let you move the stop block the same amount each time to slide the fence over. Same result but less cumbersome.

5. 
   [email protected] | Sep 23, 2021 12:29pm | #6

   I didn't see this as a solution, but if its a repeat im sorry. I would use an ⅛" up cut router bit set to depth of course. The key to the repetition is placing a jig into the previous cut slot after the first. Its a great solution snd doesn't require new setups or moving the stock or moving a fence. Be sure to use a board of hardwood as s start so as not to get any blow out st the beginning of the cut.
   Hope this makes it fun for you.

6. 
   [email protected] | Sep 23, 2021 12:37pm | #7

   Here is a nice jig from rockler or you may build one easy since it doesn't have to be adjustable.
   "Rockler Indexing Dado Jig"

7. 
   [email protected] | Oct 20, 2021 07:16pm | #8

   I did globs of this to create groovs in shelves to hold separators of 1/8 masonite for tools etc.I cut a groove in 3/4 inch white covered press board about 2 ft by 2 ft.I installed a 1/8 inch piece of masonite in the groove the hight above the base just less than the depth of the grove you wish to cut.Ease it a bit and apply some wax.Move the fence the distance from the groove equal to the spacing you want between the grooves.In my case I screwed the melamine to my outfeed table.Turn om the saw and raise the blade the height of the groove you desire.Take your finish piece,place against the masonite strip,run your fir st groove,place the just cut groove on the masonite strip and groove away.I cut dozens of grooves this way,1/8,1/4 and 3/8.They were always fast and perfect

8. 
   jharveyb | Oct 20, 2021 10:05pm | #9

   It's not clear if the dados are 3/8" center to center, or 3/8" between the grooves. If the latter, I see only 72 cuts per piece, as each cut and land between are 1/2" wide. Otherwise there is about 100 cuts per piece.
   There is a question here that needs to be answered: how critical is it to avoid accumulating errors? With 100 cuts per piece, a 0.004" error (the thickness of a piece of normal paper) in that 3/8" measurement, if repeated, makes the final groove more than 3/8" out of its theoretical place.
   If accumulated error doesn't matter, and you just need the pieces to be identical, clamp a board to your sled cross-piece ("fence"), run it thru your blade (If the cuts are with the grain, the best would be a flat top blade, which rip blades generally are. If the cut is across the grain, and cut quality is important, you will need to use an ATB blade with rakers (combination blade) and have a not perfect groove bottom.) After grooving it, unclamp and move over 3/8" from the blade, and reclamp. Glue a 1/8" spline in the groove that is slightly lower than your depth of cut. Then as previously mentioned, butt your piece against the stop, make the cut, put the spline in the cut, make the next cut, and continue. This is also how people make box joint jigs.
   If accumulated errors matter, use a test piece with the jig, and see how it performs over the 144 repetitions. If unsatisfactory, adjust the location of the spline by 1/144 of the error. How to do this: When starting, make sure that the jig fence you clamp to the sled fence is about an inch shorter on each end than the fence. If you want to move the jig fence 0.003" left, clamp a block on the left with a 0.003" feeler gauge between it and the jig fence, unclamp the jig fence, remove the feeler gauge, and clamp against the block. THEN check with another test piece. Repeat till it is right enough. Make sure the feeler gauge is against the whole stop block top to bottom, to avoid any error from the stop block not being parallel to the jig fence.
   If accuracy is critical, do a second test piece after the first "right" piece. If it comes out identical, proceed as above. If it doesn't, get rid of it and use the right piece (RP) to space your dados. Put the spline where you can butt the RP against it and butt the work piece against the RP with everything in the right place to make the first dado, and cut it. Put the spline in the RP's first dado, butt the work piece against it again, cut the second dado, and proceed.
   Trying to push a 1/8" router bit thru 2' of wood 144 times would be slow, with poor cut quality along the edges. Push a little harder and you break the bit and potentially ruin the piece. Chip clearance would be so poor that you are likely to have shallower cuts as the cut proceeds, from chip buildup between the piece and the router table or router base.