Repairing the edge of MDF cabinets to securely hold screws. Tempoary fix.

[dbhost]

So I am finding deeper issues with the MDF cabinets in the camper. Most notably, Sportsmobile attached this black plastic T molding in slots routed in the edge of the MDF, THEN they used 2" screws to attach the cabinet door hinges to the MDF through the T molding and the routed slot. this has the effect of there only leaving about 1" supported by the MDF. The T molding moves, a LOT, and with humidity does a poor job supporting the joint. I end up with crumbly gargabe edges and cabinet doors that want to fall off. I would like to reinforce these edges and just, reinstall the doors as is for now. The question is, how? I try not to work with MDF, and I want the van campable until spring when I anticipate the truck will e ready and my UC should be in remission and I can camp the truck for a while...

As a reminder, my intent i to rebuild the cabinets entirely using better materials, and the MDF cabinet pieces as templates.

[twistsol]

Add a hardwood face frame to the cabinets, glue and screw it to the MDF and add a spline if you want to go crazy with it. Then attach the cabinet door hinges to the face frame. Bonus, your cabinets get 3/4" deeper

[dbhost]

Hmmm. Interesting idea. I wonder if the slot is narrow enough for biscuits to work... And here I was thinking about maybe filling the void with something like Durhams rock hard water putty... If it weren't for the slot for the T molding, a simple drill and fill would be in order, but no, they had to combine MDF with a slot and then screw holes...

[LCHIEN]

Screws into the edge of MDF is asking for trouble.

How about ikea style knock down fasteners?


took me a bit of searching they are called barrel bolt or cross lock dowel fasteners

Relies on metal to metal threads instead of metal to MDF threads. the MDF is compressed over a larger area to carry the load instead of the pullout force on the thread splitting the MDF. Use a forstner to drill a blind hole for the dowel/barrel nut It does take some accurate drilling - A tall drill press so you can drill the edge holes perfectly perpendicular to the barrel hole (a good use for the saddle squares BTW for marking).

Typically you center the dowel nut about an inch from the edge which will clear your slots for the edging and give sufficient meat to hold onto.

[dbhost]

I am trying to repair in place, not build new. I get what you are going for, these are frameless cabinets and the doors screw straight into the cabinet sides. Stupid design, but it has held up for the last 30 years. I just need 2 more before it comes out and gets totally redone...

[cwsmith]

I like Loring's suggestion, as it will at least provide some integrity to the bolts. My experience with MDF has been minimum, to say the least as I really dislike the material. I've come to find that the only way to fasten it securely for any use is to have whatever bound together in a manner that sandwiches the MDF between two materials that have integrity, like a bolt, washer and nut, or a barrel fasterner, or place a screw with hardwood strip to fasten into, or even a metal strip like aluminum or steel with the MDF in the middle.

More than 30 years ago I turned the attached garage in my last house into a family room. Had a small wall furnace put in and decide to surround that with a simple bookcase, with lower cabinets on each side of the heater. Friends suggested I use MDF as price of lumber were, as they are now, rather inflated. Afterall they said, all those home improvement shows are using it.

Well I bought a sheet of it. It was messy to cut because it's only glue and dust. No integrity to it whatsoever. Even a small horizontal trim piece, 3 x 18 x 3/4 sagged. Vertical pieces bowed out and without tie-rods you couldn't put a shelf between two vertical sides. To fasten my shelves, I had to bore two holes at each end of each shelf, placing the disc two-inches in from each shelf end. Glue in the hardwood disks and then drive my bolts through the sides, fastening them into the shelf discs., much like using barrel nuts. I made a vow never to use MDF for anything, except perhaps as backing inserts on my drill press table. (Note that I had tried just drilling holes in the verticals, push in guides and use those right-angle shelf support with pins, that allow shelf adjustments. The shelves would sag loose, pulling the pins out of their location holes, and on some the holes would elongate, and the pins would fall out.)

CWS

[LCHIEN]

this one:


is threaded for 1/4-20 bolt, is 5/8" long so it can be put in a 5/8" deep hole in the bottom of a shelf and not break thru the top The hole is offset 3/8" from one end so that the connecting bolt can be centered in 3/4" think material.

A 1/4-20 flat head bolt can be used to be flush on the outside fastener with a countersink..

Lots more metric choices.

[d_meister]

The barrel nuts suggestion is a good one. You could also make your own from hardwood dowels. Use a forstner bit with a depth stop, and drill in the adjacent area of the existing fasteners. Cut plugs from the dowel, and glue it in the hole, being careful to orient the grain perpendicular to the existing screw hole. If you use 3/4" or larger, it's harder to miss and also spreads the effective reinforcement and load bearing over a larger area.
Using good hardwood dowels like oak with clear visible grain is best. Dowels all were birch, once upon a time (in my area), but now they tend to be poplar.
I've reinforced stripped holes by injecting epoxy, and then placing the screw coated with a release agent in the hole and then attaching the hardware with the screw after a full cure. I've used Boeshield T9 as a mold release in the past, but I've let it fully dry before using the fasteners. it's best to experiment with a scrap experiment model, since you have to remove the screw that forms the new thread in the epoxy before attaching the hardware. A good product to start experimenting with is the paste wax most of us have. I haven't tried it.

[LCHIEN]

I considered recommending/suggesting making cross dowels from wood, but then you'd have just 3/8" of engagement of a wood screw in hardwood.
The commercial metal cross dowels are cheap and will hold really well.

[dbhost]

Undoubtedly screws in MDF is a problem waiting to happen. These are 30 year old cabinets, and apparently the MDF on the corners are simply failing... I want to camp this thing before I pull it apart and rebuild the cabinets.

[dbhost]

Okay here is a thought, and it is probably an incredibly stupid thought, but hear me out...

Drill, MARK, so I get the depth right, and fill the screw holes. Let that cure.

Epoxy the T molding in place, squishing epoxy in the middle where it seems to have spread a touch. There are only a few very small areas where a tiny amount of adhesive was used from the factory. My thought process is the T molding if epoxied in place will take the brunt of the abuse vs screw holes in the MDF. If I can stop the movement before it gets to the MDF it should be stronger. Oh and clamp the areas where it has spread to hopefully allow the epoxy to get a bite on the whole shebang...

THEN pick some screws at least 1/2" longer, drill pilot holes so I am not pushing too much wood. Reinstall the now sitting on the van floor cabinet door back into the cabinet. And lastly create a snap closure strap to hold the door closed in transit. I am NOT going to go with fancy catches as it has friction catches that do not work... Sportsmobile uses snap straps on a lot of the smaller doors, I think I will just make and use 2 for the bigger door...

[capncarl]

When I got my motorhome the cabinets were like you were describing, some damaged from spill liquids on counter tops and just general MDF idus. Rather than go to all the trouble with dowels and screws I was able to simply glue a fresh piece of hardwood to the edges and hold it in position with a nail gun using finishing nails. Tops were finished with Formica glued on top of the old, and on top of the new hardwood. If finished out nice with minimal work and lasted until I tore everything out and redesigned the whole mess. If you overthink it, it will drive you crazy.

[d_meister]

There are a number of methods highlighted on YouTube. The "saturate with crazy glue" option looks good. Maybe use wax paper on the cauls

https://www.youtube.com/watch?v=ItH6XeHwyIQ

[dbhost]

Will watch this tonight... I am looking to repair in place and again, I want it on a temporary 2 year or so basis until I strip it down and use the existing cabinet pieces as templates.

[capncarl]

I find it hard to “drizzle on a generous amount” of superglue at more than $6 per ounce. I’m not denying that superglue works because I actually use it on probably 3 out of every 5 Tiny Trees and Tiny Mushrooms that I carve. It might put you in the poor house though.

[dbhost]

capncarl I think it all depends on how you define generous. But yeah, Superglue can get spendy... Which is why I was thinking epoxy, but that is kind of, well thick to apply into small gaps...

[cwsmith]

Isn't that 'particle board' and isn't 'particle board' made from ground wood scraps, which are something much more course and binding than MDF, which is just 'dust'. I know it's been about thirty years since I tried it for the only time, but as I recall there's not any fiber to it at all. Using wood glue or even superglue the only substance or integrity to the material will be the glue itself.

CWS

[dbhost]

Well, the resin that has been holding the particle board together for the last 30 years has done its job. I am just looking to skate by for a year or two more before we pull the cabinets and copy them using real honest to goodness wood...

[dbhost]

So it might be incredibly stupid of me, but I am going to try. Push sawdust into the holes as best I can, squish some Liquid Nails max in the holes / slot, and insert T molding and let it cure, at least 1 week. THEN drill & fill, and THEN I can reinstall the cabinet door complete with a restraint strap so it won't fling itself open and pour the pantry contents onto the floor when I make a turn.... I hope.

[dbhost]

The drill press has found a new home.