Calculations for building 3 rail cabinet door with raised or shaker panels
user-6925001
| Posted in General Discussion on
I would appreciate some guidance on the calculations for building tall pantry doors that will require 3 rails instead of 2. It will have 2 floating panels, but require a horizontal rail in the center of the door for structural integrity to prevent bowing under the weight of the tall door. For example, the door height is about 68 inches and the 3 rails will be about 23 inches. How do I calculate the dimensions of my floating panels for the cabinet door, assuming that the rails and stiles are 2 1/4 inches wide, with a standard 3/8 inch mortise depth and a 1/16 inch expansion gap on each side of the 3 tenons. Thank you.
Ellis
[email protected]
Replies
Dry assemble the door and just measure for your panels. K.I.S.S.
Thank you for getting back to me so quickly. I was hoping for a quick and dirty arithmetic formula to work out my calculations in advance for all cabinet doors. Basic 2 rail cabinet doors are easily worked up using on line website calculators after feeding in your opening, rail and stile widths and overlay. Unfortunately, few people pay much attention to the 3 rail doors today, but I'm confident that there is a quick and easy arithmetic formula out there to bang these doors measurement out quickly, after considering rail and stile width/length along with your 3/4 overlay in this specific situation.. Many thanks and I will follow your advice if no one comes up with the formula.
Formula Schmormula.
OTTOMH:
Width of panel = width of door -2(width of stiles) +2(overlap)
Height of panel = (height of door -3(width of rails))/2+2(overlap)
DO NOT DO IT THIS WAY - it is a recipe for pain. Instead do what @_MJ_ said.
MJ & Rob are right - if you work theoretically to a plan (or make a detailed arithmetic plan, which is basically the theory) you provide the gremlins with lots of opportunity to persuade you towards errors.
We humans tend to live in an environment that's 10% direct experience mediated by 90% of memetic stuff swirling about our brains. The brain stuff likes to trump (!) the experience stuff, given half a chance.
Your drawings, sketchup or other plan can distort reality both when it's made and when you apply it. But if you start with some fundamental reality, such as measuring the door rail and stile lengths against the hole into which the door they make will go, there is far less chance of a memetic theory-gremlin substituting a wrong length for a correct length.
And once you have that directly-measured set of rails & stiles made into a door frame, you can use it to directly measure the required dimensions of the panels.
Many are wary even of the memetic device of numbers! They instead compare one thing to another, with one of them as the story stick that tells the other how to continue the story without resort to what we might these days call "alternative number facts". :-)
Lataxe
Cultists are evil. They are designed to create mental health problems.
I make door frames about 1/16 oversize all around so I can fit it perfectly after assembly. Once the frame is dry assembled, I measure and cut the panels. Another dry fit, then glue up, then final fitting.
Do not try to use math to cut parts ahead of time.
Make the rails and stiles 2” wider than the depth of the groove (2 3/8”). Subtracting 4” from the width gets you the rail length and panel width. From the height gives you panel length.
If you’re looking for simplicity, make a couple sticks 1/8” thick.
Mock up the door, put each stick in the groove bottom and clamp where they overlap.
I build 3 rail doors pretty often. My formula is:
Height (68") - total rail thickness (3 x 2 1/4" = 6 3/4") divided by number of panels (2) + panel tenon length x2 (3/8" x 2 = 3/4") - expansion gap x2 (1/16" x2 = 1/8") = panel length
68 - 6.75 = 61.25
61.25 /2 = 30.625
30.625 + .75 = 31.375
31.375 - .125 = 31.25
Divided evenly, your panel length is 31-1/4".
For offset panels, like in the photo, the total panel length is 62 1/2" (31.25 x 2) which you can cut however you want ex: 22-1/2" and 40". The rest of formula doesn't change. The formula works for as any panels as you choose to have.
Panel width is rail length - 1/8"
Rail length is total door width - stile thickness (4.5") + plus stub tenon length x2 (3/4")
*Make sure your stub tenon lengths are actually 3/8". Freud and Whiteside bits are 13/32, not 3/8". That changes the formula to:
Door width - 4.5" + 13/16". That's a difference 1/8" on double doors, which can really screw up your gap.
Ignore the people who say "don't use formulas and fix it at the end". That's exactly what you shouldn't do. Build it right the first time.
Mr GE,
You pine:
"I build 3 rail doors pretty often. My formula is: (snip) .....
Ignore the people who say 'don't use formulas and fix it at the end'. That's exactly what you shouldn't do. Build it right the first time".
The thing is, you've achieved right first time via a lot of practice ("I build 3 rail doors pretty often"). When one is an amateur building a first-time thing, the approach you recommend with that number-heavy "formula" to 3 decimal places is an unnecessary minefield and likely to produce wrong-first-time.
Did you get it right first time with the actual first-time door you built? Perhaps you did - but that makes you exceptional. :-)
For most of us, it's better to sneak up on a first-time project via careful checking of reality. Theories and "formulas" so often miss those pesky little quirks that reality likes to throw at us.
Lataxe
OK, well, first off, the OP mentioned that these were 3/4" overlay doors, not inset doors. Every other response to this thread seems to have missed that, because building doors slightly larger than the opening and trimming to fit is how you SHOULD build inset doors. But since these are overlay doors, there's no benefit.
Second, the OP asked about a formula for finding panel dimensions. My formula is for panel dimensions and rail lengths. Advising the OP to build a door slightly oversized and trimming it down doesn't help him or her in any way because the question was about panels, not doors.
Third, there is no room for error on rails. If the rails are too long, the door will be too wide. If the doors are already drilled for cup hinges, you can only remove meat from the opposing stile which will be noticeable if it's more than 1/16" (Believe me, I know)
Fourth, the OP is building multiple doors, not a single door, and wanted a formula that would work for all the doors. Sneaking up on the correct size is fine for a single door, but unnecessarily tedious for multiple doors. A formula that gives you the correct dimensions of all parts is far simpler.
Lastly, it's not hard math:
A panel width is 1/8" less than the rail length
A rail length is total door width minus 3-11/16" (for freud or whiteside bits and 2-1/4" stock)
A panel length is established by desired visible length + 11/16"
I included all steps in the formula so the OP would know how I got there, but ultimately, the above numbers are all you need to know. If adding fractions or converting decimals to fractions is difficult, there are literally hundreds of fraction calculator apps.
It's way easier to build everything right the first time. With overlay doors, chasing bad dimensions only detracts from the finished product. Also, most cup hinges are three-way adjustable, so if your doors are off by a fuzz, the can be adjusted.
Some might recommend a CAD program and cut to those measurements. However, cutting to those tight tolerances assumes you can also build your cabinet to those tolerances. I can't do this and don't know any hobbyist who can.
I agree with MJ above, do a dry fit and measure panels to that size. Also, build the door an 1/8th oversize, then fit your door to the existing opening. There's a FW video series that covers this. It covers a small cabinet, but the principles remain the same.
This forum post is now archived. Commenting has been disabled