# Blum slide drawer box calculation



## bgilb (Jan 9, 2010)

Just wanted to check my sanity on drawer box sizing since it can be confusing. This is 563H slides (and 569, but they're the same). They're the 21" slides for 24" depth cabinets.

1 opening for example is 21" wide. Since I'm using a butt joint, the sides just need to be 21" as far as I know. So that only leaves calculating the front and back, which are calculated as (opening width - 42mm).

42mm is 1.65354" (1" 21/32) just to make it easier (or harder lol). My true material thickness is actually .59 and not .625 (5/8). So the difference of that is 0.035" or 0.07" for both sides.

So any front or back panel will just be opening width - 1.58354" (40.25mm) or (1" - 19/32).

Is that correct? Or does a 1/32nd error on each side even matter?


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## MikeDilday (Feb 21, 2017)

Assuming your front and back are INSIDE butting up to the sides? The sides would be 21". The inside of the box should be opening minus 1-21/32". So your front and back would be 21" minus 1-21/32" and the sides would be 21".


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## TungOil (Jan 16, 2017)

Their instructions are not real clear, but read them a few times and you will get what you need.

https://www.blum.com/us/en/products/runnersystems/tandem/downloads-videos/


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## bgilb (Jan 9, 2010)

> Assuming your front and back are INSIDE butting up to the sides? The sides would be 21". The inside of the box should be opening minus 1-21/32". So your front and back would be 21" minus 1-21/32" and the sides would be 21".
> 
> - MikeDilday


So it sounds like I've got it correct then? Minus using 1-21/32 versus 1 19/32" since my material isn't truely 5/8"


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## pintodeluxe (Sep 12, 2010)

Outside dimensions of the box need to be 21" for 21" slides. 
I more often use 18" Blums with through dovetail corners, and the sides are cut to 18" length.


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## bgilb (Jan 9, 2010)

I'm not using dovetails so that doesn't help me


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## MikeDilday (Feb 21, 2017)

The material thickness does not change anything since the slides mount on the inside of the box bottom and not the outside like traditional slides. If your front and back are opening minus 1-21/32" then it will be correct. The sides can be any thickness up to 5/8. The only dimensions you need to calculate to make the box is the inside measurement between the sides is opening minus 1-21/32" and the box depth front to back is 21". Since you are using butt joints that will be front/back opening minus 1-21/32".


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## LeeRoyMan (Feb 23, 2019)

I keep it simple and subtract 1 5/8" from the opening and never had a problem.


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## RichT (Oct 14, 2016)

The type of joinery doesn't matter. For 21" slides, the drawer box needs to be exactly 21" front to back. Width only depends on the width of the opening and how you space the slides in it.


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## pintodeluxe (Sep 12, 2010)

> The type of joinery doesn t matter. For 21" slides, the drawer box needs to be exactly 21" front to back. Width only depends on the width of the opening and how you space the slides in it.
> 
> - Rich


1+. 
21" slide equals 21" box. This would be true for butt joints or through dovetails, although I suppose it depends which way you butt the joint. I assumed you meant the sides would overlap the front, and there would be a false front attached later.


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## AlaskaGuy (Jan 29, 2012)

Blum Drawer Calculator

https://www.hingmy.com/blumdrawers.php


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## RichT (Oct 14, 2016)

> 21" slide equals 21" box. This would be true for butt joints or through dovetails, although I suppose it depends which way you butt the joint. I assumed you meant the sides would overlap the front, and there would be a false front attached later.
> 
> - pintodeluxe


Sorry, I misread your post. You had already said exactly what I wrote.


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## LeeRoyMan (Feb 23, 2019)

> So that only leaves calculating the front and back, which are calculated as (opening width - 42mm).
> 
> 42mm is 1.65354" (1" 21/32) just to make it easier (or harder lol). My true material thickness is actually .59 and not .625 (5/8). So the difference of that is 0.035" or 0.07" for both sides.
> 
> ...


The tolerances of your side material doesn't matter. 
The -42 mm is for the inside of the drawer.


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