High Density Fiberboard

[Scott Felicetti]

I have a project that calls for the use of Medium Density Fiberboard. Strength is a concern. Is High Density Fiberboard better? Readily available? Where to buy. thanks in advance.
Scott

[Jim Becker]

MDF is readily available. "HDF" is not common that I've seen...unless you want 1/4" material and then "hardboard" or "Masonite" would be the same or similar.

MDF with good construction techniques is a strong material with a lot of good qualities including consistency. But it's best to use the right fasteners and pay attention to spans for best results.

[Scott Felicetti]

MDF is readily available. "HDF" is not common that I've seen...unless you want 1/4" material and then "hardboard" or "Masonite" would be the same or similar.

MDF with good construction techniques is a strong material with a lot of good qualities including consistency. But it's best to use the right fasteners and pay attention to spans for best results.

My concern with the MDF is will it hold screws under pressure? Does it flake apart or bend readily compared to regular wood such as Oak or Maple?
Thanks for reply Jim.

[Greg Peterson]

It doesn't flake like particle board. It tends to just break. It can also be dented (corners, edges). As for screw holding, I doubt it will have the same capacity as a hardwood.

MDF is an excellent material in the appropriate application. What are you trying to build?

[Bill White]

There is a product called EXTERA which is an exterior grade fibre board. I used it to "wrap" some columns on our new home. Real tough, and obviously made for exterior uses. Really heavy, but will still flex.
Masonite Corp. used to mfg. a product referred to as "die stock". Extremly hard, heavy, and ridgid. Don't know if it is still available.
Bill

[Kevin Groenke]

HDF, is an odd duck, Primarily used for die boards for rule and die cutting as Bill mentioned. If you can find it, it WON'T be cheap.

MDF is stable and is flat when you get it, but it certainly doesn't have the strength to span a gap or carry a load that solid hardwood has, it probably doesn't even match a quality plywood in that respect. I would guess that it's rigidity is much closer to that of particle board than hardwood. Of course you could go to 1" (or more), I unloaded 10 sheets @1-1/8" this morning... 150 lbs/sheet!!! oowwwweee.

MDF glues on the face and the edge very well, so dado joints work great. You can screw it face-to-face (that doesn't sound so good) without any problem, the screw threads bite into those layers and they'll never let go.

Since MDF is manufactured by compressing subsequent thin layers of wood flour and binder, the edges have a very strong tendency to split if fasteners are used, this applies equally to nails, staples, screws, etc. You can get away with it by drilling a pilot hole the root diameter and the depth of the fastener. Using a tapered drill would be recommended if you're using tapered screws.

There are screws specifically designed to work with mdf which you should be able to track down. These generally have some mechanism at the leading edge of the screw thread which cuts a thread thus reducing the force of the screw leveraging the layers of the MDF apart.

From McFeely's re:Confirmat screws
http://www.mcfeelys.com/confirmat-assembly
If you assemble melamine cabinets or work with particle board or Medium Density Fiberboard (MDF), these unique fasteners have been specially designed to make your life easier. The large shoulder beneath the head locks the shank in position to minimize the possibility of board failure. An extra-long stem on the specially designed screw caps fits a hole in the drive recess, preventing most accidental removal. Screws require a pilot hole through both pieces of material. The 7x50 screws are recommended for use with 3/4" materials. 5 x 40mm screws require a 5mm pilot hole and are used with 1/2" material.


re: SPAX from McDonnely
http://www.mdonnelly.ie/products-page20091.html
MDF Screws

The secure fastener for MDF boards. No splitting and bulging of MDF boards when jointing at the edges or face to face. Special screw geometry allows the connection of MDF boards and thin chipboards without pre-drilling. The special point guarantees spot-on positioning and easy driving of the screw. The slender, countersunk head with cutting ribs easily penetrates into the material.


Here's some good stuff from MDF-info

http://www.mdf-info.org/using/screwing.html
Screwing
MDF has good screw retention strength both in the faces and edges.

Screw types
Most types of screws can be used in MDF but the best results are obtained with two start, parallel thread screws. A high overall screw diameter to core diameter ratio is desirable.


When fixing thin attachments to MDF, use screws which are threaded up to the head. Screws used for panel jointing or the fixing of thicker attachments may have a plain or threaded shank.


Screw position
The positions of screws inserted into the faces and edges of MDF should be decided in relation to board thickness and screw size. As a general rule, screws inserted into the face should not be less than 12 mm from the board edge and 25 mm from the corners. Screws inserted into the edges should not be less than 70 mm from the corners.


Pilot holes
Larger diameter pilot holes than those recommended for solid wood and particleboard are required in both faces and edges of MDF to accommodate the solid core of the screw. As a general rule, the pilot hole diameter should be 85 to 95% of the specified screw core diameter. This requirement is particularly important when screwing into the edges of thinner boards. Pilot holes should be drilled at least 1 mm beyond the expected depth of insertion of the screws into the board. A small counterbore is recommended to prevent any lifting of the MDF surface round the area of insertion of the screw.

The pilot holes recommended when using ISO 1478/1983 Type AB screws are given in the Table. The drill diameters have been rounded off to the nearest 0.5 mm.



G'luck
-kg

[Scott Felicetti]

Kevin,
thank you very much for a great response. The people on this forum are simply amazing. It's a shame I don't encounter such quality people out and about in my daily life.
Be well,
Scott