Drawer Box Tolerances with Undermount Slides

A discussion of drawer dimensions, material thickness, and slide specifications. December 7, 2008

I am starting to use Blum undermounts for 1/2'' thick drawer boxes. The spec sheets say to subtract 5/8'' from the inside of the cabinet opening if you are using 1/2'' material. The material my boxes are made out of (Baltic birch) actually measures closer to 7/16'' thick. Will this change the formula for my drawer box sizing? Blum lists several different formulas for sizing boxes, based on drawer material thickness, but they did not list one for boxes less than 1/2'' thick.

Forum Responses
(Cabinetmaking Forum)
From contributor R:
I build my own 1/2" ply drawers all the time, and my ply runs under too. I've not had any problem - the slides allow a fair amount of slop. If you are really worried about it, just subtract 11/16ths.

From contributor M:
I don't think 1/16" is going to kill you, especially if your drawer face is overlay vs. inset. As long as the action is smooth, you'll be fine. It is annoying, though, that so much of this hardwood ply available is not to their full measurement. I often use a "3/4 inch" birch ply that only measures 11/16", but it is strong, clear and $18/sheet cheaper than anything else I can find. Once you get used to the hassle, it's not that bad.

From the original questioner:
Thanks. I am just concerned about the tracks being in a bind if the boxes are too big. As much as I pay for these slides, I want them working at the best performance possible.

From contributor B:
You will be fine with subtracting 5/8" from the opening. We are a drawer manufacturer and that is what we subtract when orders are given as opening sizes. We do a lot Baltic birch drawers.

From contributor D:
The Tandem guides we use base the drawer box size on the inside width (the front and back length), not the outside of the box. They come in two models for 5/8 max material and 3/4 max material. We use the ones for 5/8 and are good for any material up to that size. The Blum literature specifies an amount to deduct from the cabinet opening that gives you the size of the front and back. The only time we have run into problems with this is when we outsource drawers, they usually want the box exterior width so we have to calculate that when we usually do not.

From contributor N:
Take a few minutes and make up a small sample to put your mind at ease.

From contributor H:
Contributor D is right. The Blum instructions give you the drawer front and back dimensions, not the overall drawer dimension. You can have sides up to 5/8 added to this dimension without problems. We build our drawer with 1/2 pre-finished ply sides and 1/2 bottoms and 3/4 pre-finished ply for the fronts and backs. The bottom is pocketholed to the sides and is the same width as the front and back. Check the archives and you will find some drawings on how I do it. We use up a lot of scraps from our cabinet gables and backs for these drawers and they can be assembled in less than a minute.