Fixed tenon thickness vs. percentage

[Chris Larson]

Hello eCabinets communtiy,

I was wondering what the specific reason(s) are for using percentages rather than fixed values for tenons & dados. My supervisor has asked me about this a couple times and I cannot give him an anwer that satisfies him. He figures that, if the tenon is referenced off of the waste board, why can't it just always be .375" regardless of material thickness? I try to tell him that it is to reduce the margin of error in the machining process, but I don't have much more input than that. Does it have to do with the many complex calculations that the machine is making? Does anyone know how ...(dare i say it?)... other cabinet softwares handle this issue?

Just curiuos, the machine is running well & we are getting good results.

Thanks Thermwood and thanks to Josh Rayburn & Dave Hall in Stamford, CT who have been very helpful,

Chris Larson

[Josh Rayburn]

Hi Chris,
The percentage only comes in handy when you switch from a 3/4" material to 1/2" material (or the opposite). When adjusting the thickness of the material, you've got to consider the thickness of the tenon and the corresponding dado that it will create (with the added fit clearance). That dictates the tool that will be used to machine the operations (dado and tenon thicknessing operations).

By setting the percentage to 55% you get these results:
.725 x 55% = .39875" + 0.015" fit clearance = .41375" which is big enough to be machined with the 3/8" tool instead of the 1/4" tool.
.475 x 55% = .26125" + 0.015" fit clearance = .27625" which is big enough to be machined with the 1/4" tool.
I stuck average thicknesses in there just from experience.

Now as you can see, a fixed tenon thickness would have to be adjusted each time you changed the material thickness that you're working with in order for you to machine the 3/4" material more efficiently by using the 3/8" tool instead of the 1/4" tool. With percentages, you can set it and forget it.

Other software packages give you the option to set the thickness to an exact value OR a percentage, which can come in handy.

Since Control Nesting knows that EVERY tenon and dado will be cut with a "dado" operation, that is, a full 'ring around the rosy' compensating inside the box with the largest tool available that's at least .001" smaller than the width of the box - then you can see how there really is no point in making a fixed thickness useful in the Vulcan world of pure logic.

There are other software packages which give you the option to set the tenon thickness + fit clearance to equal a specific number, say .5" and if that matches a tool that you have (exactly) then it will pick up that tool and make a single pass with it, keeping the conventional side towards the inside of the part. Very clever, and I must say it machines much faster. Maybe TWD will implement this at some point and at that time, the set thickness would obviously become necessary, but until then, it might actually save you a little programming time by avoiding adjustments when changing materials.

Not sure if this helps or not -
jnr

[Josh Rayburn]

I forgot to add this:
The supposed reason for CN making EVERYTHING a comp operation (dado) for the tenon / dado operations is: for example, if you're using a resharpened tool. You can simply adjust the diameter of the tool in your tooling management at the controller, and since the controller looks that diameter up on the fly at each tool change, it doesn't matter what size tool you have, it can still be used.

This also makes it possible to have the tool diameter adjusted in the middle of the job, for example if you don't like the fit clearance on your parts, and you want to loosen it up a little, you can accomplish that on the fly by messing around with the tool diameter that is being called for those comp operations. Otherwise, you would be forced to go back to ecab's and re-twd it, and back through CN to recode it, etc. Saves a lot of time and gives you flexibility.
jnr

[Chris Larson]

Thanks for the quick response Josh. This was very informative. I will translate the CNC verbage so that my supervisor can understand what is going on here.

-Chris

[Scott Marshburn]

All of that is well and good for parts that are being cut on the machine (for example the tendon on the deck and the dado on the ends that receive that tendon) but where the problem for us comes in is the tendons for the face frames that are cut by the machine on the ends. If the material is 3/4 and the settings are 50% then the tendon will be 3/8 if the material is 23/32 then the tendons are 23/64 but if the material is 1/2 the tendons will be 1/4 as you can see the thinner or thicker the material the thinner or thicker the tendons . Our standard dado in our Board stock face frames is 3/8+about 1/64or so for fit.We cut these on the table saw with a custom made blade. So If it were possible to set the actual tendon thickness for face frame tendons that would help allot.

[Josh Rayburn]

Scott,
You can easily reverse-engineer the tenon thickness to be whatever you want by percentage.
If you want a 3/8" groove on .725" material with a .015" fit clearance:
.375" - .015" = 0.36"
0.36" / 0.725" = 49.65%

jnr

[Scott Marshburn]

Josh I Can see what you are saying (Please correct me If I am wrong) but lets say you have drawn up a 50 or maybe even a 100 box job with 3/4 or 23/32 or 11/16 material for the ends and the customer bucks on the price and you say ok we can make all of the ends out of 1/2or 5/8 material. Now you have to change the ends to that material.Thats easy. But now you have to take each cabinet and edit the ends to receive the 3/8 dadoes for the face fraimes.it would be nice If we could set the Tung thickness on the ends to a prescribed thickness.

[Josh Rayburn]

Yes Scott, that's absolutely correct. Thickness percentage works poorly if that is the case. This is why it would be nice to have the option.
jnr