MDF carcasses to support fish tank.

[CmdrBond]

Hi.

I'll start this with a little history.

My mum currently has some generic plastic drawer units. On top of one of these she has placed a 40l fish tank .

The fish tank is far too small for it inhabitants (4 fish, 3 of which are goldfish ). So she is getting a bigger tank, 98l, which she wanted to stand across 2 of these units

I have successfully educated her into understanding that this is not a good idea, especially as the first unit is already showing stress fractures.

The problem we then faced is that she did not want to "re-organize" her drawer units. So apart from their sheer expense, we couldn't find anything suitable, so we decided to make some carcasses that take her existing drawers - this keeps her happy.

Now it is just a matter of design.

Overall we are going to build 2 separate (4 drawer) units as opposed to 1 (8 drawer) unit.

Our plan is to use 3/4" (18mm) MDF to make the sides, top, bottom and back, and then probably 1/4" (6mm) MDF for the shelves to take the existing drawers.

The plastic drawers are approximately 13" W x 15 1/2" D x 7" H.

This will give each unit overall dimensions of (approximately) 14 1/2" W x 16 1/4" D x 30 1/4" H

My plan to fix the shelves (as mother doesn't want any gaps between base of shelf and top of drawer - and the drawer side is the same height for its entire length) was to cut a notch in the side of the shelf and horizontal cuts in the front and rear of the side panels (and possibly do the same with the back) and then slot it all together.

My brother suggested a simpler solution, but requiring we reduce the sides and tops to 1/2" (12mm) MDF, then to use the 1/4" to clad the inside of the carcass and then rest the shelf on top of the cladding (for want of a better word). The reason for reducing to 1/2" is because mother does not want the extra 1" (over 2 carcasses) width. Even though it will fit. Because of this I was thinking that the top of the carcass would need to have the extra 1/4" as well.

My question is, based on the scant information I have supplied, do you think

1. I have used the correct materials (MDF) - if not what
2. Each unit will be strong enough to support an evenly distributed load of approx 50kg (98l + equipment across both carcasses)

And what would you recommend being the best way of fixing the sides and top together (bearing in mind I have no specialist equipment, just standard saws and drills).

I am sorry if I rambled a bit - I typed this in competition with the TV on in the background and my wife pestering me every 5 mins. Feel free to ask any questions.

 

[foxhole]

I would suggest 18mm throughout [including shelves] all screwed together to maintain strength, or you risk an empty shell of a carcass collapsing under the weight. Also cheaper , sheets of 18mm are often cheaper than 12/15mm due to quantity sold.

 

[CmdrBond]

OK.

The back panel was going to sit inside the 4 edges as opposed to on their edges as I felt this provided further resistance to the downward pressures and also helped to prevent the shell from tilting.

I did a mock up of one design (all in 3/4" including shelves) in Google Sketchup, here is a screen shot of it. The drawing is slightly exploded to emphasize the joints.

Untitled

• CmdrBond
• 14 May 2012
• 1

What do you think to the way the shelves and sides have been shaped (shelves are identical to the top, the base is the inverse although could also be the same)

 

[foxhole]

Looks fine, though more work than necessary.

 

[JohnD]

I would suggest making a timber table, with timber legs and an 18mm ply top, of a size that the existing drawer units will fit underneath/inside. You can paint or stain the legs to make them blend in.

 

[CmdrBond]

My original idea was just to create a surround for the existing cabinets, but SWMBO decided against that.

While I do have some say over the design regards what I physically can and cannot do, ATEOTD it is not my living room.

I have been doing some thinking on this.

My plan was to use jigsaw like joints throughout the piece, but this is adding complexity. So I am thinking of going for simple butt joints for the shelves, glued and screwed.

I still want to cut into the top and bottom of the cabinet so that weight is still bearing directly on the side panels (and not just some screws) but so that I can also screw in horizontally as well as vertically - as I believe this adds rigidity to the piece.

If I ended up using butt joins all-round with out any interlocking joints, then I think I would screw through the top into the sides, and through the sides into the base.


I am afraid that building 2 MDF carcasses is my only option, and I have managed to convince my mum that it needs to be at least 3/4" (18mm) MDF - for the main structure at least.

So I now have some more questions,

1. Is 3/4" (18mm) MDF sufficient, overkill or not enough, and should I up/downgrade to 1/2" (12mm) or 1" (24mm) MDF for the:
   • The top and base
   • The sides
   • The backboard (considering 1/2")
   • The shelves (considering 1/2")
2. What size screws/pilot hole should I use - I am considering #8x2" (4mmx50mm) for 3/4" (18mm) or #6x1 3/4" (3.5mmx45mm) for 1/2" (12mm).
3. What sort of glue - simple wood glue or something more like epoxy.