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I'm making a set of amateur under-bed "drawers" from scrap. Nothing fancy, just re-using materials from old closet. This is my first project of such scale.

There are intended to be 3 quite large drawers, 130 x 60 x 18cm on the inside. Walls are going to be made from veneered particle board (16mm thick), intended to be held together by 2 or 3 confirmat screws on each side. Bottoms are planned to be made from 3mm thick hardboard.

How do a I make bottom rigid enough in the case of such large drawers?

So far my plan is to:

  1. add 2 narrow crossbeams on the bottom (something around 60 x 5 cm), effectively splitting large 130 x 60cm area into 3 smaller ones - 40 x 60 cm. Having crossbeams pop up from the bottom by 1cm does not worry me that much.
     |----------------------|
rear |      ||      ||      |  front
     |      ||      ||      |
     |----------------------|
           crossbeams
  1. add grooves along all the sides and crossbeams (using router with 4mm bit) and slide hardboard into them.
|     |
|    _|
|   |_   grooves on walls where hardboard slides into
|_____|

If that plan sounds okay, what distance from the edge does the groove need to be and how deep can it go into 16mm thick particle board?

This is an example of what I want to achieve (construction-wise) and what to avoid (sag and breaking):

enter image description here (taken from http://www.instructables.com/id/Fixing-Saggy-Drawers/)

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Bottoms are planned to be made from 3mm thick hardboard.

This is the part you should probably change. If you make the bottoms from something much stouter it will self-support. You could go up to 6mm hardboard, which is significantly stiffer than 3mm, but something like 12mm particleboard/chipboard or plywood would be the superior choice. 12mm and even 18mm board is regularly used in better-quality kitchens for drawers, some of which will be filled with heavy pots and pans. If they can take that they can support the kind of stuff most people store under a bed!

add 2 narrow crossbeams on the bottom

This is also a viable technique. These crossbeams are referred to as muntins and they were the traditional means to support the centres of wide drawers not too long ago.

Wide-drawer muntin

Source: Drawer-Building Basics, excerpted from Chests of Drawers by Bill Hylton, published by Taunton Press.

add grooves along all the sides and crossbeams (using router with 4mm bit) and slide hardboard into them.

You would normally do this anyway with drawer bottoms. But with thinner material like 3mm hardboard in a wide drawer it probably won't prevent the bottoms blowing out (as in the picture you posted) if the drawer has anything weighty stored inside it.

Note that if the bottom is 3mm then a 3mm router bit should be used to form the housing grooves. A 4mm groove in the box of the drawer will make the bottom a very sloppy fit and provide no real support to it. If on the other hand the drawer bottom is a tight sliding fit* the groove will add significant support to the bottom, although it needs to be glued in place for this to work fully.


*Tight enough that you need to tap it home with a mallet.

  • Thanks for your answer! So it seems that superior technique for such a large drawer would be to take 12-18mm sheet, preferrably plywood (because of smooth surface) and securely screw it from below instead of sliding into a groove? Could you please add about grooves depth and offset from the edge if hardboard is still used? Given my scrap contains only 3mm hardboard, what is the reasonable area it can hold in? (e.g. I can add 4 muntins) – Kromster Jun 1 '17 at 7:56
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    I'm not sure what makes you think screwing it from below is a superior technique. Sliding it into a groove seems better to me. If it has a snug fit as Graphus suggests, the groove will support the bottom at every point along the drawer, as opposed to just supporting it at the places where you put screws or fasteners if you screw it from below. Also, the groove hides small imperfections in sizing the drawer bottom. As long as it still fits into the groove, you won't be able to tell if it was a fraction of a mm short, for example. So it will look cleaner, too. – Charlie Kilian Jun 6 '17 at 19:07
  • @CharlieKilian something made me think that 12-18mm thick materials don't work well in dados/grooves in 16mm walls. Looks like my assumption was wrong. Thanks for pointing that out! – Kromster Jun 8 '17 at 8:43
  • Status report: one 8cm muntin worked just fine. The drawer came out strong enough to support ~40kg of tools is cases (load is spreaded evenly across the area). – Kromster Jun 13 '17 at 5:26
  • @Kromster Thanks for the update. Glad it worked so well for you, 40kg is quite a bit of weight for it to support! – Graphus Jun 13 '17 at 19:22

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