MDF & Plywood

[rbarnold]

Hi All,

Could someone please tell me what the differences are (strength and stability) between MDF & Plywood of the same thickness?

I have been getting plans for Jigs etc., for my shop from the USA and they all specify Plywood, when I thought MDF would be just as good.
Asking the suppliers of the plans in the USA has resulted in no replies, so I thought I would ask you guy's since you seem to know a bit
Any other info on this subject would also be welcome (except of course that the dust is dangerous)

Thanks in advance
Roger:confused:

[gazaly]

My belief is the durability of ply, especially for something used as often and in the fashion that a jig is, would far outweigh MDF. Also MDF is alot heavier than ply, and I wouldn't have thought as strong.

My thoughts only.

Cheers.

GAZALY

[Johnno]

Gazaly - and any others who would care to get in on this discussion - I'm currently investigating new doors for our kitchen cupboards.

The originals are standard rail & stile with raised panels, only not very well made - also finished (sprayed, whatever) after assembly so that the panel was locked in place. Obvious results - split panels, grotty-looking marks where raw wood has been exposed when the panel has shrunk, and oil/dirt stains on those raw wood patches. Tassie Oak was wood and the finish was unknown clear lacquer.

Would like to replace with solid doors, and am investigating supplies of basic materials in Canberra. First cab off the rank offers me 17mm MDF with Tassie Oak veneer. "Don't worry about the weight, mate, everyone makes cabinet doors out of this now!"

The hinges are those things labelled ' Contintental ' - I'll have to buy a Forstner bit to install them, so I can't see any problem with screws pulling out of the MDF. Are there any other problems I am creating for myself?

Should I still be looking for veneered ply rather than MDF?

Any constructive advice will be appreciated

Johnno2

[marcusl]

We had this discussions the other day at work. Whether to use mdf or plywood for shelving? No choice really - plywood for it's strength. But as for jigs well...???

I'll avoid giving an opinion and quote from this article

http://www.taunton.com/finehomebuild...ges/h00016.asp

"A 3/4-in. sheet of MDF-core plywood, for example, weighs about 100 lb., a big drawback if you're hefting panels over a table saw by yourself. A particleboard-core panel is roughly the same. According to the Hardwood Plywood and Veneer Association (www.hpva.org), an industry trade group, both MDF- and medium-density particleboard-core plywood show "excellent" flatness and surface uniformity, compared with only "fair" or "good" ratings for veneer-core panels. Dimensional stability, screw-holding and bending strength of MDF or particleboard panels, however, are rated as "good" or "fair," compared with the "excellent" marks that veneer-core panels get. Plywood made with engineered-wood cores should cost somewhat less than comparable veneer-core panels."

Hope that helps

marcus

[marcusl]

johnno

http://www.rainforestinfo.org.au/goo...#anchor1493581

This site mentions 'outgassing' from plywoods and MDF that use urea formaldehyde - suggests exterior grade ply (which uses phenol formaldehyde) even on interiors, to avoid potential health risks....so it's not only the dust that might be a hassle.

thought it might be of interest

marcus

[echnidna]

Personally i wouldn't use ply for jigs , its just a waste of money.
Ply is a little stronger than mdf but mdf is nice and stable and ideal for jigs, It also is unlikey to delaminate if it gets wet but ply will. A coat of laquer or poly is a big advantage as it prevents moisture uptake and preserves any notes or info on your jigs.

[kenmil]

I'm with you Bob. Jigs are basically throwaway items and ply is way too expensive for that.