11/16 or 3/4 ?

[Greg Julius]

I'm using China Birch for the cabinet box and it has a true thickness of 11/16"

I read or saw on a training video that I should specify 3/4" for the material. I'm afraid I can't find the reference to that piece of advice and I am, quite frankly, suspicious of it.

I'm thinking I should create a material that's "3/4" by common name, but specify the thickness as 11/16.

Clearly two 11/16" sandwiched together is 1 3/8" and two 3/4" sandwiched together is 1 1/2" and that differnce is a Whole 1/8". That's a lot of fudge methinks and I think I should be using 11/16" in the material's thickness specification because that's the true thickness.

What's the proper way to define this material?

Thanks,
-g

[Kerry Fullington]

Greg,

If you are sending the files to a router you can design using nominal thickness values and correct material thickness when you write the TWD file for the machine. If you are cutting parts manually it is probably good to use actual material thickness in the design.

[Greg Julius]

What would be the downsides for specifing the material as 11/16 when going to CNC?

It's actually 11/16 and I'm specifying rails and stiles accordingly, shouldn't I just use 11/16 in the thickness?

What I don't understand is if I specify a nominal 3/4 and it's really 11/16, then aren't some parts that abut going to be about a 1/16 off?

[Ralph Balanik]

You should use 11/16 if the material thickness is 11/16 when you write your TWD file. Your blind dado settings and all of your openings use a percentage of material thickness or actual material thickness, if you are not extremely accurate with material thicknesses when you create your TWD files you joints will be sloppy or tight, drawers and doors may not size properly etc.. Being a few thousandths off when you measure your thickness can create a mess of your material and your project. It is advisable to measure your materials just before you create your TWD to cut a project because thicknesses vary significantly enough between batch runs of sheet goods to create significant fitting problems.

When you define materials , if you use actual measurements in you material library, ( speaking from experience), your library becomes cluttered and you find that you are always editing or changing things. This takes a lot of time and can lead to errors. In genral,it will make your design work easier if you use typical thicknesses rather than actual thicknesses in your materials library, and then change the material thicknesses to actual when you create your TWD file for the project. That is my opinion based on my experience.

[Greg Julius]

Ralph, Thank you for your reply.

I'm still learning to get all the Ps & Qs straight.

If I have a stile that's designed to cover 2 - 11/16" sides that are side by side, then that stile needs to be 1 3/8" wide, right? If I design for 3/4", then the stile would need to be 1.5" wide, right?

My fear is that if I use the nominal to design, and at cut time the material is 11/16" and I change it to 11/16, then my stile is going to be incorrectly sized. That's correct, isn't it? How can one "fix" that without having to redraw the face?

I feel that I'm missing something terribly important. Note, I'm not the CNC operator, that's going to be outsourced. I'm just attempting to draw the cabinets the cabinet guy wants.

I'm getting ready to send off my first upper and base set of cabinets complete with boxes and holes and all the trimmings. I'm sure what I get back will be highly instructive

Thanks for the replies everyone and keep them coming. I'm learning from each and every one!
-g

[Ralph Balanik]

Greg,
I did build face frame cabinets in the past but I haven't done so for a number of years, and never using CNC. I cannot offer you an informed response. If something comes back incorrect think of it as a learning opportunity, if it comes back without incident, brace yourself for the next one. If things go without a hitch for a couple of weeks buy a lottery ticket.

[Kerry Fullington]

Greg,

On a face frame cabinet, the face frame is the constant. It defines the width and height of the cabinet.When you change material thickness while writing the TWD the software grows or shrinks every component of the box to adjust for this change in thickness. If your box sides are flush with the outside of the frame, they will remain so and all the decks tops etc. will adjust in width and height. If a partition or shelf is centered in your mid- stile or mid rail it will remain centered.

It is easier to design using nominal thickness just for the sake of your calculations.

If you change your material in eCabinets to 11/16 then you would still need to change material thickness writing the TWD. if your machining shop gets in a unit of material that is a full 3/4"

Material thickness is ever changing.

Your face frame Board stock thickness you have control over.

[Greg Julius]

Thank you Ralph and Kerry again!

I am expecting my first cabinet to go to CNC to be instructive. I am expecting it to be flawed although I'm trying to get as much correct as possible before it goes to the machine. While I'm trying to do as much of the learning vicariously as I can, I'm sure that OJT will fill in a lot of gaps!

I understand that ecabs will adjust a lot of dimensions, but I've got one that I'm worried about. The face frame is going to have a stile that fits between two cabinets.

For the sake of discussion, suppose I have a two cabinet setup. Cabinet A is on the left and cabinet B is immediatly to the right. The right edge of cabinet A will be touching the left edge of cabinet B. I have a single stile that straddles the two edges (that is it covers from the inside of the right end of Cab A to the inside of the left end of Cabinet B).

If I design for 11/16, then I need to make the stile 1 3/8". If I design for 3/4, then I need to make the stile 1 1/2". Is there any way to make that face stile adjust to accomodate the varying thickness of the wood on the cabinet ends? If I can make the face stile adjust, then I'm sold, otherwise I'm at a loss for what to do (except perhaps design for 1.5" stile and place shims between the cabs).

I appreciate both of you (and anyone else who chimes in) helping me get my head wrapped around this subject.

Blessings,
-g

[Kerry Fullington]

Greg,

Your face frame components must remain constant. They determine the size of the cabinet wall to wall. In your scenario you design your boxes at 3/4" thickness and butt them tight behind the 1 1/2" stile.
When the software adjusts for thickness it will shrink each box behind the face frame and you will have a small gap between boxes behind the same 1 1/2" stile but your wall to wall dimension will remain constant.

[Greg Julius]

Kerry,

I was pretty sure that was the case. Thank you for the confirmation.

Thank you for taking the time to explain for me, I really appreciate it!

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