Blum Tandem Drawer Slides: Question on Drawer Box Measurements - Woodworking Talk - Woodworkers Forum
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post #1 of 2 Old 08-21-2015, 12:46 PM Thread Starter
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Blum Tandem Drawer Slides: Question on Drawer Box Measurements

I would appreciate any insight you guys have on drawer box measurements...especially if you have experience installing Blum TANDEM slides. I recently purchased Blum Full Extension TANDEM Drawer Slides for my bathroom vanity. These are undermount slides. I'm getting ready to start cutting boards for the boxes, but I've run into a dilemma/question with the measurements. The instructions are very explicit about determining the Outside Drawer Width and also for ensuring proper Inside Drawer Width. Below, I'm referring to these measurements as Step #1 and Step #2. Here it goes:

Step #1: How to Calculate Outside Drawer Width
Per the Blum instructions, to determine the Outside Drawer Width, you should deduct 5/8" from the Interior Cabinet Width when your Drawer Thickness is 1/2". The interior width of my cabinet frame is 11". If I deduct the required 5/8", my Outside Drawer Width should be 10 3/8". This seems pretty straightforward.

Step #2: How to Calculate Inside Drawer Width
Per the Blum instructions, the "Inside drawer width must equal opening width minus 1 21/32 for TANDEM to align and function optimally." In my case, that would be 11" minus 1 21/32", which equals 9 11/32". Again, this seems like a pretty straightforward calculation.

However, if I take the inside drawer width of 9 11/32" and add 1" to that for the total width of my two outside drawer members (1/2" x 2 = 1"), that would equal an Outside Drawer Width of 10 11/32". I don't know if you're still with me here, but I'm trying to compare that figure with the 10 3/8" I calculated under Step #1. I am off by 1/32nd of an inch when comparing the two figures. I've read that drawer box measurements need to be exact to work with Blum TANDEM slides. I'm concerned that my calculations are inaccurate in some way leading to the 1/32 difference.

I have one more question that might contribute to or compound my dilemma. The plywood for the boxes is labeled as 1/2" material, but I suspect the actual thickness is less than 1/2" (I will double-check). Does anybody know if the Blum instructions really mean a precise 1/2" when determining Outside Drawer Width? Or do they take the "nominal" effect of dimensional lumber into account already?

Thanks in advance for any guidance you can offer.

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post #2 of 2 Old 08-22-2015, 12:41 AM
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You have to calculate based on the actual thickness of the drawer sides. There are no "nominal" measurements with drawer slides, you need to keep to the 1/32", there is some fudge room but it's needed for adjustments. In essence, the runners attach to the cabinet and the slides mount against the side of the drawer, underneath. These two have to mate correctly, the drawer sides are the only variable since they will be between the slide and runner. The distance from the surface of the cabinet that the runner attaches to, to the inside of the drawer side that the slide goes against, should be 13/16" on each side. You also make the overall height of the drawer 13/16" less than the height of the opening.

Cut a stick that fits perfectly in the width of your opening, make a mark in on each end 13/16". That's where the inside of your drawer sides need to be. You can cut that stick 1 5/8" (13/16"x 2) shorter and it should fit perfectly inside the drawer.
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