Replies

1. 
   RickL | Aug 23, 2007 06:59pm | #1

   Machine shop would be your best bet. Bushings must be as wide as your arbor flange or you will distort the blades. Plenty of 5/8" bushing around but the OD is too small.

   The DIY option is to get some alumium in the thickness you want and mark the center and drill it out. It doesn't have to be round. It can be square. You can make it an octagon to get more depth or scribe a circle before you drill it and bandsaw or sabersaw the circle.   Alumium cuts nicely on a table saw or chop saw with a negative hook blade. Most chop saw are fitted with one already. This is from real experience not arm chair theory.

   I much prefer my horizontal slot mortiser as I make mortises in both rail and stile and insert a loose tenon. Gets rid of all the problems of machining tenons altogether. I can be putting a frame together before you even set up your tenon cutter. The Domino is the portable version of my slot mortiser.

   
   

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   Edited 8/23/2007 3:16 pm ET by RickL

2. 
   MikeHennessy | Aug 24, 2007 03:26pm | #2

   You can go the machine shop route, but be aware that spacers made in this fashion are matched to a set of saw blades. Change blades, and the spacers probably won't work because the teeth on the blade are wider than the saw plate, and that measurement is not necessarily consistent between blades. If you dicide to go with shop made spacers, take your blades to the machinist so he can determine the thicknesses needed to space them properly.

   I have had great success just making my own spacers out of scrap materials of various thicknesses. I cut mine with a hole saw on the drill press. Various thicknesses of plywood (signboard), tempered masonite, thin steel and aluminum sheet. I can get any thickness by mixing/matching these spacers. I can also use the spacers that came with my dado set along with my home made ones for fine tuning. Again, remember that the total width of the spacers must be more than the desired thickness of the tennon since the teeth overlap the saw plate. IIRC, my blades require spacers a little over .2" wider than the tennon. Oh, and you can't beat the cost of these spacers. ;-)

   I have a chart that I keep near the blades/spacers listing the proper combinations for the sizes I use most. Note also that if you use a mortiser, your tennons must be sized to properly fit the mortise made with your particular bit. And that ain't necessarily exactly 1/4", 1/2", etc.

   You need to be able to adjust your dado blade to fit your work, since wood is somewhat variable in dimension. Same with tennons. Adjustability is a valuable feature that is harder to get if you have spacers machined. You can make them a little bigger by adding additional spacers, but you can't make 'em smaller.

   Mike Hennessy
   Pittsburgh, PA

1. 
   bob k | Aug 24, 2007 04:53pm | #3

   Thanks, Mike. I had been wondering if there was a reason why I couldn't just make spacers out of MDF, plexi and delrin scraps. Anyone? I'm going to give it a try using two ripping blades. I'll probably get a set of thin dado shims that are available at all the tool stores to fine-tune the fit.

1. 
   MikeHennessy | Aug 24, 2007 05:13pm | #4

   Don't know why two rip blades wouldn't work so long as they leave a square-bottomed kerf -- never thought of it before. I use the two outside blades of my dado set.

   The only limitation on what material you use for spacers is that, whatever it is, it shouldn't compress when you tighten the blades. I made mine about 4" in diameter and that works well.

   You may need to consider dealing with your throat plate as well. I use a zero-clearance plate with interchangable inserts. I've made inserts for 1/4", 1/2" and 3/4" (+/-) dadoes, and I use these for tenons as well.

   Mike HennessyPittsburgh, PA