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Drawer Terms and Acronyms

Drawer Terms and AcronymsI've used so many acronyms in my drawings that I'm starting to confuse myself. Hopefully the following will help me to standardize them and help you to decipher my drawings. The image is a modified specification drawing for Blum 554H undermount slides. There is also an image showing how specs change when using the bottom mounting holes. Not all dimensions were on the original drawing and the drawings are not to scale.

Slide Bottom Clearance (BC/SBC) - the distance from the system hole that a slide will mount to, to the top of a horizontal cabinet member. Minimum required BC is the distance from a slide system mounting hole, to the bottom of the slide (lowest point). Used for determining slide to cabinet box bottom, and/or rail/stretcher, clearance. Will the slide work with the layout, will it be reasonably close to horizontal cabinet members. While slide specifications are usually fairly similar, some manufacturers slides won't work with some layouts. One example is Salice under-mounts which require a minimum BC of 42.5/30.5 (top/bottom mounting holes) VS the more standard 37/25 (e.g. Blum)... Note: At least one drawing uses SBO (slide bottom offset) instead of BC (bottom clearance).

Top Clearance (TC) - how much space is needed to install/remove the drawer box. While most slides specify at least a bit of top clearance, this is most important when designing bottom mount drawer layouts - because 3/4 extension bottom mount slides need a relatively large amount of TC.

Bottom mount specifications for top clearance typically assume the drawer box depth is roughly the same as drawer slide length and that the drawer will be pulled straight out. Slide specifications less ~3.5mm will work but require tipping the drawer downward so that the back of the box can clear the carcase when the drawer box wheels go over the carcase wheels. Reducing box top clearance more requires making the drawer boxes shallower than the slides or using full extension slides, i.e. have it so that the back of the drawer box comes past the front edge of the counter-top before the box is removed.

Slide Offset (SO) - the distance from the slide system mounting hole, to the ledge that the drawer box side or bottom sits on. Applies to all bottom and under mount slides. This is a primary variable when designing a drawer layout, or in determining whether or not a manufacturers slide will work with a given layout.

Box Offset (BO) - the distance from the slide system mounting hole, to the bottom of the drawer box (lowest point, typically the sides). Applies to all slides. With under-mounts, this is slide offset (SO) + lip (how much the drawer sides overhang the bottom of the box). With bottom mounts, box offset (BO) is the same as slide offset (SO). Since side mounts have no slide offset (SO), this is the number that matters when designing side mount drawer layouts.

Some drawings only show BO to allow for slight variations in specifications, e.g. '9.5 SO / 13 lip' and '10 SO / 12.5 lip' both have a 22.5 BO. There's also no harm in reducing the '(10 SO /) 13 lip' to 12.5. Note: Inset drawer bottom thickness doesn't matter, only the location of the bottom side of the slot/dado.

Face Offset (FO) - the distance from the slide system mounting hole, to the bottom of the drawer face. Used for calculating face reveal/registration (below).

Overlay and Full Inset Faces
   System: 32 (x n) - 1/2 face gap (typ. 30.5)
   Shifted: its 32 (x n) + 16 - 1/2 gap (typ. 46.5)

Railed Inset Faces
   System: 32 (x n) - (1/2 PT + gap)
   Shifted: its 32 (x n) + 16 - (1/2 PT + gap)

Face Registration/Reveal (FR/B2FR) - the distance between the drawer box top/bottom and drawer face top/bottom. To be able to consistently register drawer boxes to faces, the top and/or bottom box to face reveal (B2FR, TFR or BFR) needs to be the same for every drawer in every drawer stack. While it is possible to center register faces (CFR) without having consistent top or bottom face reveals, true center registered faces have equal top and bottom reveals. Reveals for registration can be calculated as follows:

   Bottom FR = face offset - box offset
   Top FR = face height - box height - bottom FR

Box Side (BS) - the height of the box sides. Typically presented as some multiple of 32mm (plus a constant). While box side height is often the same as box height, box bottoms can run long with the front and back of the box sitting on the top of the box bottom.

Comments [ new ]

Re: Drawer Terms and Acronyms
Posted by Mark on Wednesday, 10-Mar-2021


As an amateur who enjoys building boxes for some DIY projects and a relative newbie to the intricacies of 32MM systems, I really appreciate you sharing all the information on this site. I am struggling a bit with consistently calculating Face Offset (FO) and by extension Face Registration/Reveal (FR/B2FR) as they relate to a Railed Inset cabinet. My assumptions are PT of 19 g of 3 and a Blum undermount drawer slide with 37 SBC. If I use shifted registration to minimize the loss of space with that style of slide, I assume I will mount the drawer slide at the 57.5MM hole and have cabinet bottom clearance of 38.5MM. Back out 3 for g and my assumed FO is 35.5, which doesn’t match either of the numbers in your acronym section. Always the chance I am missing something completely obvious, but any formulae / guidance (in addition to what you already have) would be greatly appreciated. Thanks again.


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Re: Drawer Terms and Acronyms
Posted by Dave L on Wednesday, 10-Mar-2021

Whoops. Face Offset (FO) only covers overlay faces (until I fix it... fixed). For shifted Railed Inset FO is 32 (x n) + 16 - 1/2 PT - gap and your 35.5 FO assumption is correct.

32 + 16 - 9.5 - 3 = 35.5 FO
35.5 - 22.5 BO = 13 FR
295 face - 269 box - 13 FR = 13 FR

I'm not sure how useful that is, basically all it does is verify the numbers on the Railed Inset example drawing.

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Re: Drawer Terms and Acronyms
Posted by Mark on Saturday, 13-Mar-2021

LOL, you're absolutely right that your example drawing is more useful. I had not found that one yet and was going through the math to make sure I understood the various acronyms.

I also think I understand the 22.5 BO (versus the actual 23 BO I calculated from the Blum drawing) to allow for equal drawer face reveal top and bottom of 13MM instead of 12.5 / 13.5. If you are using shaker style drawer fronts and don't want to / can't use the 20MM press fit adjusters, I assume you would still utilize equal face reveals and rely solely on the adjustment mechanisms of the Blum slides to line up your reveals once the drawers are installed?

Thanks again.

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Re: Drawer Terms and Acronyms
Posted by Dave L on Saturday, 13-Mar-2021

The 22.5 box offset works if you use a 12.5 lip/bottom recess. For a 23 BO and balanced reveals the drawer sides would be 1mm bigger.

32 + 16 - (9.5 + 3) = 35.5 FO
35.5 - 23 BO = 12.5 FR
295 face - (12.5 FR x 2) = 270 box

You're right, slide adjusters pretty much negate the need for face adjusters. Balanced face reveals aren't really needed either, but they can simplify predrilling (sub)face and hardware mounting (pilot) holes.

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