another Blum undermount slide question

[Justin Ludwig]

The blum formula boils down to subtract 5/8" from the opening for 1/2" drawer box material, to within a few thousands of an inch once you convert it to SAE. Frankly the difference in the plywood doesn't much matter on those slides but you could subtract 11/16" to make up for the 1/32" undersized plywood 2X if you really care to. My guess is if your sides are 1/8" off the slides either you miss measured the opening or the widths are not exactly right. But when you nail the numbers in both cases, use exactly 1/2" material, and use the 5/8" subtraction the drawers slip on like a glove...and not OJ simpsons gloves. If the drawer wont fit you must.....adjust it!

PS: I have run a very thin kerf up the bottom of the sides of a few drawer boxes in my past when the fit was just a bit too snug. You don't see this with drawer faces in place on applied fronts, drawers that are too narrow are a bigger problem on 563's than a bit too loose, so always err on the a little too big side if things are odd to measure, like 23 and "almost but not quite 3/8"....better to round up the width than down IME.

Peter nailed it.

I subtract 11/16. I can use 1/2 or 5/8" material and it doesn't make a difference. When using 1/2" material, there is side to side play when the drawer sits on the slides NOT locked in place. Reference your back drilling jig to the outside of the box in either case. Create a spreadsheet with a formula to calculate your box pieces so all you have to do is enter your opening width and cabinet depth.

[Max Neu]

If you base you're formula on the inside box dimensions you won't get any side to side play,or snug fits,all the discrepancies get shoved to the outside,which doesn't affect the operation of the slides.

[Justin Ludwig]

If you base you're formula on the inside box dimensions you won't get any side to side play,or snug fits,all the discrepancies get shoved to the outside,which doesn't affect the operation of the slides.

That's true but you lose a little of the width of the drawer doing it that way; though, I doubt there's enough loss to constitute anything of worry for even the pickiest of clients (watch my next job be someone who walks around with a magnifying glass).

[Max Neu]

That's true but you lose a little of the width of the drawer doing it that way; though, I doubt there's enough loss to constitute anything of worry for even the pickiest of clients (watch my next job be someone who walks around with a magnifying glass).

I am more concerned about the drawers working properly than cheating someone out of a 1/16" of drawer space.

[Ellen Benkin]

Maybe I cheated but I sent the measurements for my drawer openings to a company that made all my drawer boxes. After reading all these responses I am glad I did!! The boxes also came with the notches and holes in the right places. Worth every penney!