Problems with dado

[44henry]

What is the best method for designing and cutting dado's? I have been having a hard time getting my dado's to come out the right size. Even if I specify a width of .765 they are still coming out less than the necessary thickness for .747 stock. Everything else seems right on the money when I cut it out, but the grooves are just not working out for me.

[Gary Campbell]

Alex...
Using one of your existing design files, (the one that you used for the dados) install a v bit & v carve on vector the border of the dado .020 deep. Measure the width very carefully.

IF it is right on the money, install the cutting bit and toolpath as you would for a dado. Remeasure.

If the dado is right on, then you have a design problem.

IF the V line is ok, but the dado is off, your problem is either an improperly measued bit, or deflection either in the bit or the machine.

IF the v line is off, then you have either a design or unit value problem.

In our cabinet panel processing we dont use design software, so most of our dados are cut with the CR command or M2 moves, but it is essentially the same as the design process. They are usually cut .010 over (for glue) the width of the material thickness and seldom vary by more than .005

I am sure that those that have also had this problem, will chime in with their solution.
Gary

[paco]

I always do a test cut (a dado) to see the fit for each batch of material. It's a bit time consuming... but not as much as when an entire set is not fitting properly.

I simply compensate with a toolpath allowance or vector offset. I know/assume my tool to be tight and working my tool with conservative (yet productive) cutting settings.

[magic]

Two other possibilities that make the size wrong are A. The bit is not the size it's supposed to be. Some companies are a little lax when making them to spec. B. Runout on the spindle can make the size larger.

Measure the bit.

[erik_f]

are you running climb cutting or conventional? I have found conventional cutting to usually work out better for most of my work.

[44henry]

Thanks all try all of the above and see if this makes a difference.

[andre]

Alex
I have scratched my head plenty on this.
The first thing is to get all play out of your xy and z axis's
The slightest play will give you dados .015 out easily. Then do like Eric says try both conventional and climb with the same size pocket and you will find one fits differently.
After doing many test with different materials
I find If I add .005 to a dado, with a conventional cut (I believe)I get a good snug fit.
I use a digital calipar and round up to the nearest .01 and add .005.
So .757 become a .765 dado.
But again check all the axis's for play.
For the x car I gently wedged a stick under the motors to ensure a tight fit to the pinion gears.
LOL

[fsrdoug]

If you are doing your cut in a single pass make sure that the bit is a 3/4 inch bit and not one for 3/4 inch plywood as they measure out to .71 inches.
I use a 3/4 inch bit in a single pass and machine along vectors for a snug fit.