Incra LS Positioner Fence on Table Saw Crosscut Sled

[Rick Kruger]

I'm working on doing just that so that I can run a series of shallow 6mm (0.236") dados in some 12mm Baltic birch plywood (BBP). I have six grooves to cut on six sides which will become the sides of storage racks for some divider boxes for sorting and storing fasteners. 6mm BBP will inserted and glued into the grooves as shelf guides/supports. I will be using a standard combo blade on my Sawstop Jobsite saw with a 1/8" kerf. The first cut will be made for all the grooves and then the LS will be use to shift the cut enough to make the resulting width a nice fit for the 6mm BBP.

I have a DeWalt dado set but the narrowest it will cut is 1/4" (0.250"). I considered using just one of the two outside blades to get a flat bottom, but figured out the "bats ears" bottom left by the standard combo blade works just fine.

My approach is to add an extension onto my crosscut sled onto which the LS base will be mounted. I have the 17" LS model but the fence is too wide for my sled, so I will use the fence from a Kreg bandsaw fence that I'm not using on my bandsaw.

I've been thinking about what hazards this configuration/use might present. Such as trapping the BBP between the blade and the fence. These are not thru cuts, but dados. The nominal method of guiding the stock would be with a miter gauge (Incra 1000SE) but that seems less secure than holding the stock on the sled. The miter gauge would have to be moved from the left miter slot to the right once the stock is moved over to the right for the last few dados and the stock will be less than fully supported on one side for each cut. Having the stock supported on both sides of the cut for all of the cuts seems like a good
situation.

Pictured below are the parts set up as the mount will end up. I'm working on making braces to hold the extension to the sled and there are challenges caused by a mismatch between the LS fence mounting screws and the Kreg fence "T" slot.

I would like to hear your thoughts about the veracity of this approach and in particular hazards that should be anticipated.

Rick

[David Buchhauser]

Hi Rick,
I think you're on the right track. I have a 25" version of the LS that I was planning on mounting to a rip sled on the sliding attachment to may table saw. I think the key is to make sure that the fence is parallel to the miter slots on the table saw. Since you are only using the LS as a precision stop, perhaps you don't really need such a long fence. And depending on the width of your material, perhaps the LS could be mounted closer to one of the edges of the sled. For this operation, I don't think you need to worry about trapping the material between the blade and fence.
David

[Rick Kruger]

Hi Rick,
I think you're on the right track. I have a 25" version of the LS that I was planning on mounting to a rip sled on the sliding attachment to may table saw. I think the key is to make sure that the fence is parallel to the miter slots on the table saw. Since you are only using the LS as a precision stop, perhaps you don't really need such a long fence. And depending on the width of your material, perhaps the LS could be mounted closer to one of the edges of the sled. For this operation, I don't think you need to worry about trapping the material between the blade and fence.
David

Yes, I will be aligning the LS fence with the saw kerf in the sled. There is no direct way to align it with the miter slot, at least that I've thought of. The kerf was cut using the blade after the sled fence was aligned using the 5-cut method and I have verified that it produces square cuts.

And yes, the fence may not need to be so long since, as you say, it is really only a precision stop. I had not thought of that .

Thanks,

Rick

[Rick Kruger]

It is done, the LS Positioner is now mounted on my crosscut sled and is ready for some trial cuts. Checking things out with my 6" machinist scale shows it is set up correctly. My layout and drilling was not up to snuff, so I had to enlarge the hold down knob holes to get the fence lined up with the near edge of the saw kerf.

Now to see if it does what I'm after with the slot widths. Thankfully, I have ample scraps to try it out on before going to the real box sides.

Rick

[David Buchhauser]

Rick,
That looks like nice setup. I will be looking forward to some photos of the results of your efforts.
David

[Rick Kruger]

Yes, results. Gotta say I'm very pleased. I ran three trials, running all six dados through the first pass, incrementing the LS for each position and making the cut. The slots measured 0.135".
LS First Pass 06-16-19 640.JPG

Then, returning to the starting position, incrementing the fence to the right by 0.100", which is what the photo above shows, the offset ready to make the second pass. Because I a just learning how the LS works, I set up a 2" travel dial indicator against the fence and used it to set the position. It took a couple of tries, due to backlash and when the clamping lever is closed to the final locked position, it shifts the assembly by 5-10 thou.

First two passes turned out pretty good, except there were a couple funky ones, 0.246", 0.255" and 0.242". It turns out the screw clamping the right side of the fence to the LS ram was loose, allowing the fence to move in and out. I feel fairly sure the funky ones were due to this movement.
LS First Two Trials 06-16-19 640.jpg

After tightening that screw, the results were a little better, except the last groove was a little undersized. Not so much that it couldn't be used as is, just a bit tight (0.233"). On this trial, I used the LS leadscrew to make the position shift after the first pass and then checked it with the indicator. I did shift it about 5 thou. due to the locking clamp changing the reading. I am not sure what caused that last one to be undersized, but during all this I did notice some small chips (bigger than sawdust) on the sled, so maybe something got between the stock and the fence (even sawdust could do it).
LS Third Trial 06-16-19 640.jpg

I think I'm ready to run some of my box pieces. I did make several extras because it is inevitable that I'll mess up some.

Rick

[David Buchhauser]

Rick,
It looks like you are getting it dialed in. I will look forward to seeing photos of the finished boxes.
David