WoodWorking

All the new semi- synthetic wood products, made from what would otherwise be waste, have their own gotchas, because they don't respond like real wood, in many ways. As you have discovered, MDF (I think the M is for 'medium') won't hold a screw driven into, or even near, an edge.

Luckily, the cheap furniture industry is way ahead of you. Go to an office supply superstore and examine their affordable furniture. You will find a number of variations on a camlock fastener that usually requires you to drive a double- headed screw into the real wood part, from the back, and drill a clearance hole for the screw, and a cross hole for the cam lock, in the MDF part. I swear I have seen the camlock assemblies for sale at home stores. They have to be available, somewhere, and inexpensive.

One other alternative is to homebrew your own, as with a machine screw driven into a large brass pin with a cross- tapped hole.

Or, cross drill where you're going to drive the woodscrew, drive it in, and fill the cross hole with JB Weld or other filled epoxy.

I've also found that it's sometimes sufficient, in low- load situations, to lubricate a woodscrew with a dab of carpenter's wood glue, which makes the screw easier to drive, and once it cures, much harder to remove.

;--

I had a cabinetmaker make a big box for me, of some composite stuff that had a hard syntheic core and two faces of multi- ply veneer. It was, as he claimed, waterproof and strong. But the first drawing I gave him came from a CAD model, and had decimal dimensions to two places, with very loose tolerances. When I'm working in CAD, I don't pay much attention to 'nominal' dimensions, I just make the parts fit each other, and I usually don't know how big they are until I dimension them.

He balked, so I marked up his print with nominal fractional dimensions and no tolerances, then went back and changed the CAD model to the fractional dimensions.

The finished box was exact to the stated dimensions within +/-.005" (~0.12mm) or so, and had no visible gaps or imperfections. I understand that cabinetmakers use knives to mark lines, and saw and drill to the middle of the line.

A carpenter, as opposed to a cabinetmaker, is a lot more sloppy, and may miss a dimension by the width of a carpenter's pencil (yes, the long way, 6mm or so). Of course, carpenters usually work in softwoods, which have hard striations that can cause a nail or a saw to drift off the intended mark, they typically work a lot faster than a cabinetmaker, and they have a specialist 'finish carpenter' clean up behind them, covering gaps and imperfections with precisely fit trim and moldings.

;--

If you're having trouble getting your drill to stay on the mark you want, start with a smaller drill, or stab the mark with an icepick.

-Mike-

You might consider screwing through the mdf to softwood doublers, and using these at joints OR gluing the joints OR drilling a hole though the mdf at 1 inch from the edge of interest, then drilling a hole through to the cross hole from the edge, then placing a drilled and tapped metal stud in the cross-hole, then applying a fixing [machine] screw from the edge to the screw hole in the stud, using it as a custom 'nut'

Brian W

This is not the wrong newsgroup; the fellows in this ng have a wide variety of expertise.

First; as noted by another poster MDF is Medium Density Fiberboard.

Per my contacts at APA (formerly American Plywood Association) MDF is made from wood that was broken down to the fiber level and reconstituted with resin; as opposed to particleboard, which is made from wood particles.

MDF has fairly decent strength, I use it to build shop & garage cabinets, tool racks etc. It accepts paint well; cut & drills without grain influence.

Particleboard is junk for any kind of construction but is great to put under the car in the garage to soak up any oil drips. :)

With respect to your first concern; splitting when drilling & screwing into the edge.

MDF (& several other engineered wood panels) is made by spraying the wood fiber resin mixture onto a large platen / press.

The mixture is pressed to form the sheet.

By nature of the manufacturing process the face surfaces of the MDF sheet are smooth & high density. The density falls as one moves to the center of the sheet & climbs again going towards the other face.

It is this lower density zone that is susceptible to splitting due to "cross grain" tensile forces.

Having experienced this problem, I eliminated it in my projects by:

1) drilling a larger pilot hole than one would normally use. The concept being; split MDF cannot hold much so adjust the pilot hole to eliminate splitting. Experiment with hole size, when in doubt go bigger.

2) increase the length of the edge screws to compensate for "over sized" pilot.

3) use sheet metal screws rather than wood screws, sms have a more constant diameter.....not "wedge" shaped like wood screws

4) if the construction is permanent (or supposed to be) squirt a little wood glue into the hole to "saturate & reinforce" the low-density zone.

Using these techniques I have successfully edge drilled & screwed 1/2" MDF (but more typically I use 3/4" MDF for edge fastening). Stay at least 1" or

1.5" away from an "edge corner" when edge fastening.

wrt to fabrication tolerances:

Cabinet maker better than 1/64" Finish carpenter about 1/32" Rough carpenter with 1/4" always (hopefully) but you can fix it with putty

good luck

Bob

other newsgroups:

rec.woodworking rec.crafts.woodturning

"SS" wrote in news:c1aonv$vun$1 @news.freedom2surf.net:

But I doubt that either would consider MDF to be wood.

what is the diameter of the drill compared to the mdf board? what kind of drill bit?

use a rigid jig, pre-drill with a smaller bit, hold the drill straight, use an appropriate drill bit.

MDF = Medium Density Fibreboard. Joining by screwing into "endgrain" should be accomplished with long non-tapered screws At least twice as long as regular wood screws ). Many designs around & many drive head styles. You will need a rechargeable screwdriver or equivalent & use at least twice as many screws as you would joining regular timber. Take care with design & assembly details. Accuracy: aim for + or - 0.5mm. This is a tough ask but possible with determination. You may need extra steps to achieve this, route edges after saw cutting for example. Pete