Prototype of Crosscut Sled for Angles

[smorgasbord]

This is an idea I had months ago (see this long thread: https://festoolownersgroup.com/threads/woodpeckers-protractor-ruler.71567/ . I still haven't gotten past the prototype stage, but I had occassion to use it recently and was very happy with the results. If it ends up being feasible I might turn it into a real product, but I've got at least a couple more iterations to go through first. Probably easiest to show a picture:



A little bit closer:


The idea is to use a CNC to accurately mill holes for pegs against which your place the fence and lock it down. I have holes for each whole angle, as well as angled for multi-sided polygons up to 20 sides. Here it is setup for a 25º (or 65º) cut.



You can see that the distance between whole angles is pretty large - something like 7mm. That enables use of a simple and cheap taper gauge to dial in any angle in-between. I've got 3 sets of radii, so the 7mm is only for the center arc - the other arcs are slightly more or less, but a known quantity and set up to a nice roundish number. It's easy to use a taper gauge to get 0.5 mm, which would be 0.07º, and even finer than that is certainly do-able.

I drilled holes to angle both ways, here's a setup for 25º the other way:


I've got a few things to work out:
• Will probably use tapered holes/pins so wear affects accuracy less over time
• Make from phenolic or aluminum instead of MDF
• Figure out a better fence lock-down mechanism than the Incra bracklets I'm currently using

And, I've been thinking for months about how to adapt this design to a MFT style top for precise angle cuts with a track saw.

Right now, the angular accuracy is better than I can measure in my home shop. I test by doing polygon angles and cutting wide pieces to see how they fit. And, I don't do the usual cut/flip/cut process which tries to compensate for angular inaccuracies, I cut both sides of each piece with the same setting, so on a 10-sides polygon, for instance, the error seen in the assembled polygon is 20 times the error in any cut.

 

[luvmytoolz]

Great idea!

 

[smorgasbord]

Just a photo showing how a taper gauge can be used to intermediate angles:


Here I've got the fence set to the pre-drilled 22.5º hole for octogons. I inserted another peg in the 22º hole and slid the taper gauge in. Again, in this radii, 7mm is 1º, so the 3.5mm taper reading indicates a 1/2º offset.

Let's say you're cutting some standard 52-38 crown molding and need a 31.62º miter angle for your 92º corner since the carpenter that built your house sucked. Your miter saw's built-in detents aren't right for this cut - you need 30.7º miter and 33.2º bevel (not the "standard" 31.62º miter and 33.86º bevel).

For the miter angle, put a pin in the 30º hole and slide your taper gauge to 4.9mm, then lock down the fence. Each 0.1mm is 0.014º so it's pretty easy to be accurate enough.

 

[Crazyraceguy]

That's a great idea/project. How are you drilling the holes now?

 

[smorgasbord]

That's a great idea/project. How are you drilling the holes now?

My CNC.

Next up is adapting the design into a MFT-type tabletop for tracksaw users. That will be somewhat easier as it won't have backside that needs to be aligned. On the sled, the miter bar needs to at the exact angle relative to the holes (which is why my prototype has it in two pieces today). But, given that one would want the track to ride in the same place and the stock positioned at different angles, where one locates the table becomes a challenge for small shops.