Shelf sag

[grim_d]

Last dresser I did I doubled up the 18mm MR MDF. No sign of sagging as yet. giving me 36mm shelves. Could route / cut a 10mm grove both sides for 20mm box pre glue up.

I do that often, good for making chunky "legs" and end panels, it probably will sag a bit over time but you'd expect there not to be a huge load on a dressing table so should be minimised.

I think the sad truth is mdf is fundamentally unstable for long spans so the best solution is that use short spans or multiple supports as in kieth 66s design

You are absolutely right. The other sad truth is that our hands are tied, if someone is paying thousands of pounds for me to make them something nice then I don't want it to look like crap in a years time.

 

[Erie Fred]

I have a set like that.
I have been thinking about cutting new pieces (old are too warped to save)
and gluing down some thick paper product to the underside, as that is in tension, and maybe will provide support.

 

[Turbo]

I really hate MDF, expensive for what is effectively sawdust & glue, dust is horrible, will not hold a screw, poor strength & very easy to split.

There is good plywood out there, its pot luck if you can get it. I bought 2 sheets of 18mm last week from a local builders merchant, flat & true, really nice veneer on the outside & no voids in the middle. It only cost me £40 a sheet, during lockdown we were paying £70 for pure rubbish!

Very tempted to go back & buy a few more sheets for stock.

 

[knighty]

is the shelvs are 26mm thick, how about routing out some 20mm groves into the bottom of it and epoxying in some 20x3 flat bar?

 

[sako243]

I really hate MDF, expensive for what is effectively sawdust & glue, dust is horrible, will not hold a screw, poor strength & very easy to split.

There is good plywood out there, its pot luck if you can get it. I bought 2 sheets of 18mm last week from a local builders merchant, flat & true, really nice veneer on the outside & no voids in the middle. It only cost me £40 a sheet, during lockdown we were paying £70 for pure rubbish!

Very tempted to go back & buy a few more sheets for stock.

I had an interesting one where I picked up 6 sheets of OSB to form a base for my log shed roof. Put two up and it covered the 5.2m span perfectly. Eh... Triple measured and yup the sheets were 2.7m not 2.4m. Shame I had only two out of the 6 because it meant I didn't have to cut a sheet down. Phoned up the chap in the builders merchant and explained and said can I have some more of the 2.7m ones. He thought I was high until he went out back and sure enough the old ones down the bottom were longer than the others. The supplier never said they were 2.7s or special order so everyone kept quiet and I got the bigger sheets which meant much less ripping down.

 

[JohnH]

Blockboard, though you dont see it much these days. Lighter than MDF and Ply as well.

 

[Pond frog]

I really hate MDF, expensive for what is effectively sawdust & glue, dust is horrible, will not hold a screw, poor strength & very easy to split.

There is good plywood out there, its pot luck if you can get it. I bought 2 sheets of 18mm last week from a local builders merchant, flat & true, really nice veneer on the outside & no voids in the middle. It only cost me £40 a sheet, during lockdown we were paying £70 for pure rubbish!

Very tempted to go back & buy a few more sheets for stock.

Get back and buy them you know you’ll regret it if you don’t

 

[grim_d]

I really hate MDF, expensive for what is effectively sawdust & glue, dust is horrible, will not hold a screw, poor strength & very easy to split.

There is good plywood out there, its pot luck if you can get it. I bought 2 sheets of 18mm last week from a local builders merchant, flat & true, really nice veneer on the outside & no voids in the middle. It only cost me £40 a sheet, during lockdown we were paying £70 for pure rubbish!

Very tempted to go back & buy a few more sheets for stock.

Depends on the MDF, builders barn and trade MDF is awful stuff.

Higher grade like Medite MR or Finsa MR or even Medite Optima or Finsa Hidrofugo are very different animals indeed. Significantly more dense, easier to machine, the dust is far reduced because of its density. (I extract anyway)

It gets a bad rap for screw holding because most people are using cheap lower density MDF, using the wrong screws (you should only ever use coarse thread if you are screwing into MDF) and they are not using a pilot hole.

I recommend Spax-M screws if you're interested.

It's easy enough to find reasonable Ply if you are painting or edge finish is not of concern (or you are banding), eucalyptus ply is quite nice for general purpose but If you are after consistent layering so it looks nice when displaying the edge or want nice face veneers in lighter colours then your options are significantly reduced now. Birch ply was the go to but it's hard to come by now because it was mostly Russian

That horrible red/pink Chinese hardwood junk from the builders merchant is truly dire, the veneers are thinner than a fag paper and most of it isn't actually glued down, more filler on it than an old ford.

There are some alternatives coming onto the market such as Garnica globulus maple but not many places stock it yet, it will be hilariously expensive and if their efficiency range is anything to go by there will be some significant quality issues.

I did see a company down south doing some birch ply alternatives, and the price was decent, but they are 500 miles away from me....

 

[grim_d]

is the shelvs are 26mm thick, how about routing out some 20mm groves into the bottom of it and epoxying in some 20x3 flat bar?

Not against it though It would need to be grooves In two sheets then glued together so as not to disturb the face veneer.

Would also need to work out at what point it becomes more cost efficient to just use actual wood.

 

[MattF]

Would also need to work out at what point it becomes more cost efficient to just use actual wood.

Why not just cost/quote for ply or proper wood, & save the grief of MDF?

 

[grim_d]

Why not just cost/quote for ply or proper wood, & save the grief of MDF?

As we've discussed, real wood (particularly hardwood) and it's associated labour cost is simply out of budget for most.

Ply is often unsuitable, this really depends on the project and again, ply that is suitable is often out of budget...ply isn't a great deal better for bendyness either.

Veneered MDF that can be cut to size straight away Vs the cost of buying, dimensioning, and gluing up then 2nd dimensioning enough hardwood to even get to the point of cutting it to final size would just blow the budget away, were talking large bookcases, fitted wardrobes etc not coffee tables (I tend to use real wood and steel on my smaller stuff)

Wood is also inherently unstable, it comes with a whole host of its own issues.

Every path to the end result comes with its own challenges and issues, my particular challenge in this Instance is "can I figure out a cost effective way to make the specified material perform satisfactorily within my defined parameters"....the answer might be "no" but I'll never stop trying to provide a better product and service

In short...

For a project where oak is specced then real white oak is about 2.5x the cost of oak veneer MDF for an inch thick and about 2x the cost for half an inch thick, before the considerable extra labour cost.

 

[Newlands]

When I say "as the shelf bends" I don't mean the shelf will deform (it will, but that's not the point) I mean, imagine what will happen to the rod, as the shelf is loaded and it begins to bend. If the rod is bang on the centre of the board, it will just bend. If it's towards the top of the board, it'll be compressed, if it's towards the bottom, it'll be in tension. For maximum impact, it'd need to be as far to the bottom as possible (or below the bottom!)

Yes, if the rod was placed right on the neutral axis. But if it is placed in a groove of variable depth, as initially suggested, then tensioning the rod will put a pre-load on the timber, exactly like a guitar truss rod. And guitar truss rods definitely work - you can see a very visible deflection when you wind them up.

 

[mtt.tr]

Block board?

Even if it's just for the smell of wee that it gives off