My head was spinning last night

[Michael Cole]

Now, I am fairly well educated, masters degree and lots of extra credits, but am new to this woodworking. I was trying to figure out the dimensions for my cabinets for my shop last night. I am going to build frameless base cabinets using plans from a site on the internet. It is a good site and gives very specific directions on how to figure the dimensions and I am thankful I have it. My problem is that I am using cabinet grade plywood that is 23/32". When you get to those 32nds it taxes your brain figuring the exact numbers! Not sure it matters anyway as I am quite sure I am not skilled enough to cut to 1/32! I think I have all the dimensions figured out and will start working as soon as my wife quits giving me "projects" to do for her. I appreciate all the help I have been given here.

[Dave Richards]

How critical are the exterior dimensions of the cabinets you're making? I do a lot of design work for a cabinet maker who has asked me to use 23/32" for the thickness of plywood for cases. In most situations, the exterior dimensions aren't that critical. I make the lengths of the horizontal pieces to the nearest 1/16 in.. Dadoes to receive those horizontals are always 1/4 in. deep which is plenty. So the horizontals are 1/2 in. longer than the inside dimension of the case. It works out fine.

I do the design and layout work digitally in SketchUp and let the program tell me how big to make the parts.

[David Hawxhurst]

My problem is that I am using cabinet grade plywood that is 23/32". When you get to those 32nds it taxes your brain figuring the exact numbers! Not sure it matters anyway as I am quite sure I am not skilled enough to cut to 1/32! I think I have all the dimensions figured out and will start working as soon as my wife quits giving me "projects" to do for her. I appreciate all the help I have been given here.

that is why i changed to metric. the so called 3/4" ply i've been getting measures 18mm which is a nice easy whole number to work with.

[Peter Quinn]

It's funny how daunting the simple math involved with cabinetry can be at first. I have been using a ruler since I was a child, I tested pretty well in high school aptitude tests for spacial rellations and geometry, I left a Phd program to pursue other things which led me to wood working. Still, the first time I had to lay out a run of cabinets from a set of plans it made my head spin and hurt too. It's mostly nerves and unfamiarity with the salient variables. You don't need a computer program or a Phd in geometry to do this. I've seen some of the most complicated elevations I experienced layed out on a piece of drywall tape in the field! Learn to make a story pole, the rest takes care of itself. Your story pole (mine are usually made on a white piece of poplar or a strip of left over plywood) is a full size drawing that shows where every piece of plywood and solid lands. Cut the pole to fit the run, lay out full scale on the pole, build accurately to the pole, done. I do one for the run, one for elevations, occasionally one for depth too if things are odd or tricky.

if this run is wall to wall and frameless boxes, I'd include loose scribes at each side, and make them at least 1". A loose scribe is just a plywood or solid wood L (solid is easier to actually scribe) that gets screwed to the outside of the case at the end of a run, this allows you to over come out of plumb walls, bad drywall, and the occasional errant sized plywood. On long runs I measure my plywood and will usually add 1/16 to my horizontal parts to overcome my missing 1/32" on each piece of plywood. I'm usually within 1/16" over all on 16' of run that way. On installation I'll usually set a box at each end after leveling the ladder kicks (loose toe kicks that the actual boxes rest on) , then build from one side to the other. When I reach the second side I measure the last cabinet to go in, scribe the necessary amount off the loose scribe on the end box, then shove the last one in. Don't try to fit boxes wall to wall, walls are rarely dead straight and plumb, you need to build in this wiggle room, looks more seamless when you get to doing cabinets for finished space like your kitchen.

[Erik Christensen]

couple of suggestions...

first I use a spreadsheet to reduce the number of math errors in standard calcs - for example - if the cabinet case is A inches wide and I am using slides from XYZ co that are B inches long - what are the lengths of the drawer sides & front/back for the joinery I am using & size of the bottom... once you get the spreadsheet formulas nailed all you have to pay attention to is the height of each drawer and make sure the as-built cabinet width is as specified - all the nasty detailed math is done by the spreadsheet formulas.

second use sketchup to build your cabinet cases, let the space & design drive the exterior cabinet case dimensions and don't worry about 1/16th of slop on the interior - focus on getting cases square and built to fit the room - i then make doors, drawers & drawer fronts to fit the as-built cases

YMMV - others build the other way around to minimize the impact of having assembled cases filling the shop - I am not good enough to build a case to 1/32 accuracy to keep slides from binding but I can build a drawer to those specs

[John TenEyck]

What Peter said. Learn how to use a story pole. Direct measurement is always correct and requires no math.

John

[Michael Cole]

I will have to research the story pole. I read a couple of short articles but still don't quite understand it. About SketchUp - I tried downloading it once to use for USPSA stage write ups and had problems including getting a virus. Is it safe to download? Probably was just a fluke. Recalculated the cabinets again as I keep changing my mind on height. I have a window in the middle of the wall and was trying to be able to get the window trim and a back trim on the counter top. I think I will use the back trim as the bottom trim for the window and make them a little taller.

[Bob Hoffmann]

It sounds like -- at least for this project -- that you are building your cabinet to fit a house wall. Nice -- but, take into account that the house wall is not square and the floor not level. Building your cabinet to fit tight to your wall / window is a daunting task. This is usually done with a filler strip -- that allows a square cabinet to fit an existing wall / window. This filler strip can be cut to match the space between the cabinet and the wall / window -- which will most likely be at an angle, and could also not be a straight line.

Another thing to take into account is that your cabinet and wall / window will expand and contract -- neither are stable and will move in summer to winter. Painters caulk to fill gaps and that allows for movement.

The point that I am making is to make sure that there is some gap in what you are building so that it will fit. I have built stuff that I was sure was the right size to find that it fit in every dimension except one that had to be persuaded to get in place. Building in a filler strip or a way level your cabinet will make it a lot easier to get in place -- and leaving yourself a gap, even without a filler strip -- say 1/8", is a good idea. You may find that that 1/8" is good in one spot, but disappears on the other side.

[Robert Engel]

Michael,

You rarely need (or want) to make cabs this exact, so don't sweat the small stuff!

I'm not an expert, but I've built my share of cabs and I'll tell you, its gets as complicated as you want to make it.
(Now how do I know that???). Here's my take on it:

You didn't give your layout parameters, but even without knowing that, you usually don't have to fret over the exact dimensions because:

1)If the cabs fit between two walls, you're gonna have filler strips on each ends so the doors can open all the way. So there is your fudge factor.
Take distance between walls - 4 or 5 inches and calculate all my cab widths from there. If I'm off due to cumulative error no big deal. Add the fillers to each end and scribe to wall.

2)If cabs have one or more ends open, then its even easier because your cabs just end where they end. Just get them close. If there is a wall on one side and a doorway on the other, leave a couple inches short of doorway to give you some leadway.

If you need an exact dimension, then the width of your bottom will be the total width of the unit minus (2 x 23/32=1 7/16) instead of (2 x 3/4=1 1/2).
But you rarely need to be concerned about building them this close.

I highly recommend the book by Danny Proulx on building frameless cabs.
Good luck!

[Pat Barry]

Michael, you should convert to metric dimensioning. Its incredibly simpler and more intuitive. For example, your 23/32 plywood is actually 18.25 mm. Believe me, convert and it will make your whole project much better . JK

[Rod Sheridan]

Good luck Michael, I'm sure you'll do a fine job.

Time for you to switch to metric and avoid those pesky fractions :-), I converted about a decade ago and haven't looked back

Since you're building boxes, the only critical dimensions are the outside dimensions. That should simplify your predicament.

Regards, Rod.

[Michael Cole]

Have to look into metric conversion!

[Phil Thien]

I just pretend the plywood is the nominal dimension, so 23/32" actual I'd treat as 3/4". You obviously have to accommodate the reduced thickness in your dados, but having a project come out 1/16" smaller (so 23-15/16" wide instead of 24" wide) has never been a problem for me.

For drawers and doors, I cut those parts to actual size after I have the cabinet built, which is really the safest way to do it anyhow.

Sometimes I work in metric but often I have a bunch of fractional dimensions of a space, so I keep everything fractional through the entire project.

[Peter Quinn]

The biggest issue I see is on a wall to wall installation the width at the front of the cabinets is almost always different then the back corners. Framing, drywall buildup, go figure, but if you build them too tight they will not fit. Better to include a loose scribe at each end, learn to scribe, and have a seamless built in look at the front where it matters. Once the top goes on and perhaps a back splash, all is covered and looks great..

[Tom Ewell]

Good advise given so far like don't count on the structure being plumb, level, square or flat. A long spirit level and/or laser level helps to predetermine how bad the room is so you can design in your 'fudge factor'.

Measurements wise, once the design is established, is fairly straight forward, as mentioned above you can adjust for the 3/4" nominal 23/32" fractional stuff, two sides with bottom/top 'butted' to sides is unit width less the 1-7/16.

If you're going groove/dado joinery at the sides then set the depth of the groove/dado so you have a nice number to work with left on the panel...ie. make the cuts so you have 1/2" thickness left on your sides. This will make it unit width less 1"... the dado's of course will be something less than 1/4" deep. (7/32 for you sticklers)

The biggest key I've found is plan ahead enough (cut lists etc.) so each machine setup gets used to cut all parts requiring that setup and it does not hurt to double check measurements while your cutting every so often to make sure the setup is not 'wandering' (bumping the fence type stuff). Resetting to cut a forgotten piece always seems to be a whisker off but not impossible to deal with, better to get it the first go around.

Try to use the same tools for all your measurements be it tape, foldable rule, story pole, squares, etc. or at least check any different measuring devices against one another in case one is really off.

Hardware (hinges/slides) should also be chosen during the planning stage so you can account for drawer/door sizes and any overlay/inset/offset specs required for that hardware.

The inevitable hassle of curvy plywood can be mitigated some with a fixed shelf, back panel and eventual installation with well placed fasteners.