How to fit back on Euro cabinet

[paulhtremblay]

I need advice on fitting (or cutting) the back for a Euro cabinet, constructed with 19mm MDF.

The carcass will have the normal construction for the top, bottom and sides. The top and bottom will fit inside the sides, so that the sides will be completely smooth, with no joints. I want to fit a back inside as well, to keep the sides free of any seams. In other words, if the height of the cabinet is 600 mm, and the width 350 mm, the height of the back will be 600 mm - 19mm, X 300 - 19mm.

My plan is to have the back complete flush with the back (rather than insetting it), and use dowel joints to secure it. Dowel joints should provide the strength needed to mount the cabinet to a wall.

My problem is cutting the back to exact size. Even if the back is smaller by 1/4 mm, you will see a pretty big gap. If the top measures 1/4 mm to large, the top and bottom won't fit tight.

I can't really repeat the cut for the top and bottom, because the large back panel won't fit on the MFT3 table. Anyway, the actual height of the back is shorter than the height of the side panels by the width of the MDF.

Perhaps I should try another design? One traditional technique is to cut the dado 19mm back, leaving a 19mm space between the back piece and the back edges of the sides. One fits in two cleats to drive screws through, in order to hang the cabinet. But that technique seems redundant when I am going to use a full 19mm back panel, itself strong enough to use for securing the cabinet.

I thought about using a rabbet, and then driving in some Miller (through) dowel joints from the back, but I don't think I will have enough surface if I make the rabbet 1/3 the depth of the wood, since I will only have 6 mm for the dowel. I guess I could make the rabbet a full 12mm deep. That would leave a thin 6 mm on the side, but since this 6 mm serves only to hide the back, that may work.

My goals are:

1. Use a much thicker back panel than normal, to add rigidity to my carcass, and to provide a surface to attaching the cabinet to a wall.

2. Keep the sides free from any seams or other joinery, so that I will have a completely flat surface for paint.

 

[E30Mark]

I'd route out a 19mm slot down the inside of the cabinet sides, space this slot 19mm from the  back, and add a couple of scrap bits of wood as spacer /  bearers. You can route out the top & bottom inside faces the same.

 

[Rock]

I would go the dado route but instead of using spacers to screw into, add a french cleat. That's how I hang my shop cabinets, (thought I saw you were working on a cabinet for the shop) works great.

 

[Sparktrician]

If you're intending to wall-hang the cabinets with anywhere near a load on them, the inset back is the way to go, especially if you're using MDF which will blow out far more easily than Baltic birch or any other variant of plywood.  The dado will add strength to the assembly.  I usually use 1/4" ply for backs and inset that by 1/2".  Then I add a 1/2" nailer strip top and bottom in the 1/2" back gap which adds strength to the back assembly.  Much easier to add French cleats with strength this way, too. 

 

[semenza]

  I'd say the dado is the way to go on that. If you are hanging the cabinet directly on the back 19mm MDF, then I would space the dado at least 1/2" in from the back. Last thing you want is the weight on the back tearing the back edge of the dado out. Maybe go the 3/4" space even.  But to save depth inside the cabinet go with a 1/4" back  spaced in 1/2" and hanging the cabinet from added hanging rails.  You still need to attach those hanging rails very well to avoid the same MDF blow out/ tearing problems. 

    MDF has it's place. And is nice to use for some things especially when  just getting started on figuring all this woodworking stuff out but plywood makes a big difference when dealing with things like hanging cabinets.

Seth

 

[Linbro]

If only the sides are seen, rebate the two sides 19mm x 12mm. Then cut the depth of the top and bottom down by 19mm. You can screw and glue your back into the top and bottom and into the rebate - the edges of the back will be covered by the rebated sides.
Lincoln.

 

[paulhtremblay]

Two issues here:

1. Is MDF strong enough to hang the cabinet? Let's say I adopt Lincoln's method, so that can drive Miller dowels right through the back of the back piece through the top and bottom. Miller joints are very strong in MDF (probably the strongest joint for this material, in fact). With this method, there is almost no chance of a joint failure.

The only point of failure would be the screws through the MDF. Imagine that you use a machine to pull the cabinet from the wall. The joint won't come apart, but the screws will eventually pull through the MDF. Could this happen under normal circumstances?

2. If I use the dado method, I need some help with my dados. I just made a practice cabinet, and the dowel joints, made with the Jessem jig, fit fine, but the dado in the back was uneven from board to board, if only by a small amount. This small amount prevented a perfect fit until I chiseled away at the dados.

I used the MFT3 to make the dados. I used the guide stop to make the dado for each piece, and they came out nearly perfect, but not perfect enough.

A better method would be to cut a groove down a 2400 mm piece of MDF, and then, using the parallel guides, rip my stock to the depth of the cabinet. The only drawback is that you can't make stopped dados.

I am using MDF because I want to paint some of these cabinets, and laminate others. I use a 19 mm back to add extra strength to the carcass.

 

[Sparktrician]

Suggest that you look carefully at MDO rather than MDF for both strength as well as ability to take a finish.  MDO is far more resistant to blow-outs than MDF.

 

[Linbro]

Can't see the screws pulling through 18mm MDF - especially if you use one with a large flat head, or use a separate washer. How big is the cabinet, and how much weight will be placed in it?

If you want to dado, you can fit a rebated back into it, instead of trying to get a nice tight fit with the full thickness of the MDF back. You only have to rebate a few mm off the face of the back, then rout a 15mm dado. The shoulders of the rebate will hide the join line.

 

[BBrown626]

I have several MDF wall cabinets with lots of load on them in my garage. Full inset backs are flush to the back edge of the sides, top and bottom. I used 3/4" MDF for all parts of the box. Parts are joined with pocket screws.

If you go with a full inset 3/4" back a good way to ensure a tight fit of the back is to fit the top last. Ensure the front of the top is a perfect fit and then can push the top town tight against the back.  Doing so is easy if you assemble the cabinets with pocket screws, type 17 screws or staples. It won't work with dowels if your committed to using them. 

As I progressed in my cabinet shop I have used a few different methods, including making cabinets with nailers without a back and nailers with 1/4" backs. Those with nailers appeared to be sufficiently strong and I have never had a call-back or failure.

If you are just playing around, I suggest you try an experiment, which I have done.
Build a small cabinet (20" wide?) using each of your construction techniques. Mount it to the wall with a couple 3" screws. Hang from it. Fill it with weights. Challenge somebody to pull if off the wall. You might be surprised at what a cabinet can hold, particularly when made from 3/4" material. Once you see how strong the various methods are then you can focus on the efficiency of your construction.

 

[Rick Christopherson]

I think you are over thinking this, and not realizing just how much surface area the joint of the back encompasses. Just rabbet the back into the carcase and don't worry about dowels or tenons. Keep the joint between the back and sides tight for better glue adhesion.

The total lineal joint is 1800 mm long. So it will easily hold the cabinet without the need for tenons or dowels.

 

[Rick Christopherson]

By the way, MDF gets an undeserved bad reputation as a poor or weak material. However, when it comes to glued joinery, it excels over all other sheet good types. A glued joint in MDF has very similar strength to the MDF substrate itself, as long as the joint is tight.

A low-grade veneer-core plywood will have the weakest joint strength due to the roughness of the joint coupled with half of the joint being end grain (due to the alternating ply directions). A high-grade veneer-core plywood will be much better, especially if it is using poplar as the interior plies, but still slightly weaker than MDF.

There are many projects where I specifically order MDF core plywood because it provides the best joinery, especially when the joints are visible, such as countertops with framed borders. When I use veneer core, it is primarily to reduce the amount of heavy lifting necessary for processing the sheet goods.

 

[AlexThePalex]

Why make the back out of 19 mm MDF? It is not necessary and will make the cabinet much more heavier. Typical european cabinets have the back made out of 3 or 4 mm cardboard. If you insist on using MDF, make it at least 6 mm to keep the total weight as low as possible.

 

[paulhtremblay]

If you are just playing around, I suggest you try an experiment, which I have done.
Build a small cabinet (20" wide?) using each of your construction techniques. Mount it to the wall with a couple 3" screws. Hang from it. Fill it with weights. Challenge somebody to pull if off the wall. You might be surprised at what a cabinet can hold, particularly when made from 3/4" material. Once you see how strong the various methods are then you can focus on the efficiency of your construction.

Good advice. I will do just this type of experiment. I really like modern methods of joinery, but never would have thought pocket screws would work with an MDF carcass. Cool!

 

[paulhtremblay]

By the way, MDF gets an undeserved bad reputation as a poor or weak material. 

Completely agree. MDF is plenty strong enough for the right furniture when done right. The only things I don't like about it are  the dust it generates (oh wait, I now have Festool!); its inability to withstand water; and its brittleness. I had a cabinet ruined because my paint job failed and a jar leaked on it (don't know why my paint job failed). I made a nice 50's style console to fit behind our coach, and was always worried that a bump from a vacuum cleaner nick off a chunk.

Speaking of which, what kind of MDF is the MFT3 made of? It seems absolutely superior to the stuff I get.

 

[BBrown626]

Why make the back out of 19 mm MDF? It is not necessary and will make the cabinet much more heavier. Typical european cabinets have the back made out of 3 or 4 mm cardboard. If you insist on using MDF, make it at least 6 mm to keep the total weight as low as possible.

I buy "ultra-light" MDF. It is much lighter than the regular stuff. I made 4 cabinets today and construction is simpler if you can use all the same material. 
If weight is a concern then 4mm stuff is great for backs. I use thin melamine for backs quite often.

 

[Bob Gerritsen]

Although I cannot judge all the considerations you are dealing with for this project and I'm not sure I totally understand all you've explained, I think I'm with Alex on this one.

A typical euro style hanging cabinets would have a thin back, fitted in a groove with space behind the back for a french cleat or (cheaper and more recent version) some hardware version of the french cleat system. The more recent version would have 3d adjustments which is really quite nice at times. Euro style kitchen cabinets use this and I've never come across those dropping down and they are made of particle board so go figure.

Making a 18 or 19 mm back that is flush to the wall seems overkill as far as thickness goes and demands a perfectly flat and plumb wall wall as the complete back will be touching the wall.

If you do want to take this route however, why not make the back the exact same size as the cabinet interior (meaning: forget the rabbet/rebate) and glue and or screw it. It will be heavy but rock solid.

Still though, I would go with a lighter back but that might be because I just don't see the advantage.

 

[sancho57]

Go to festool TV on U Tube. Eroc has a very good and detailed series on building euro cabs. There are there videos on the subj as well