Curvy Units and Finishes

[elrajajo]

First post.

Hi, I'm a DIYer converting an an old fibreglass caravan, part of which involves making some new storage and work units out of wood.

We wanted the units covered in Formica-like laminates but after getting some truly outrageous quotes from the laminating companies we've decided to look for DIYable alternatives.

We wanted the units to be curved and are presently experimenting with 2 back to back sheets of 6mm 'bendy mdf'. The first attempt, which involves a quite generous radius seems to be working OK (early days though) but some of the units will ideally require radii of 100mm or less and I'm unsure whether the mdf will go that tight (one of the manufactures - neatform - claim 150mm is the min). Any thoughts or experience on this matter would be greatly appreciated.

Our other consideration is the finish. Covering with Formica-like laminate has many pros but I don't feel confident about applying it on complicated shapes. I read with great interest some forum discussions about 'mirror' finishes on mdf and wondered whether anyone would favourably compare the gloss, toughness and general durability of such finishes with laminates.

I've already learnt many things from reading these forums and will be grateful for any further input from fellow users.

 

[DaveL]

Hi elrajajo,

Welcome to the forum.

I have not made anything with curves like your attempting, but a comment on the finish, paint will not have the same scuff resistance as a laminate. There are different thickness laminates available, the thinner ones will follow tighter cures but are not as robust.

 

[MikeG.]

I would be very sceptical that a Formica laminate could be bent successfully to a 100mm radius without professional equipment. I would certainly have gloves and goggles on as I attempted it, waiting for the splintering.....!!

Mike

 

[jasonB]

You would be better off making the curved doors from several layers of skin ply also called aero ply, if you want a MDF surface then make the two outer layers from 2mm MDF.

Even with that construction its will be quite a job to get the radius you want even with a vacuum press.

If you want curved high gloss doors then you can't beat Parapan which can be thermo formed to any curve you want, I did parts of this kitchen which used Parapan for the doors

http://www.networkinteriors.co.uk/archive/pool-kitchen/

As said above standard thickness formica will be risky to bend at that radius, Decamel or one of the other postforming laminates should go round OK but its not easy to get a good bond laying it by hand.

Jason

 

[FatFreddysCat]

Forget the bendy MDF - on tight radii it tends to give you flats and it takes a ton of glue. In shop fitting we generally use bendy plywood over an MDF former. Glue (PVA D3/exterior) and staple the first layer onto the former then use contact adhesive on the second skin - a first coating to seal the surfaces then a second "liquid" coating before adding the layer (only staple the ends). PVA tends to "belly" the 2nd coat whilst UF/RF glue requires pressure such as a vacuum bag to work. Laminate will bend better if pre-heated with a hot air gun

 

[Oryxdesign]

You can bend a laminate to a 100mm radius, the problem is getting it to stay there whilst the glue dries.
I think to give you some more advice about how to achieve your goal we need to know a bit more about yourself and your capabilities and resources.
Si

 

[elrajajo]

Thanks everyone for genuinely useful ideas and comments, they have led me to many fruitful avenues of research.

Jason - although the Parapan isn't suitable for this project (none of the doors will be curved), I had never heard of the product before but think it looks fantastic - definite use for future. Also, I have some 2mm mdf but find that it is very poor compared to the 6mm bendy variety for tighter curves. As for the different types of laminate - I will be speaking to a specialist in the field tomorrow to find out about tolerances.

Fatfreddyscat (hey, I use to read that mag also btw) Your advice was bang on the money for me given this particular project and my level of skill. As it happened I was in the middle of experimenting with two sheets of bendy mdf where the one had been glued and stapled to a frame. I was just pondering how to go about efficiently clamping the second to the first to ensure the pva properly met, when I decided to come in and see if anyone had replied to my forum question. Your advice re contact adhesive and the two coat method, appears to be great advice: I'll find out in practice tomorrow!

oryxdesign - I'm not a professional woodworker nor even a high level amateur. I carry a only the basic hand and power tools and don't have a large workshop. I'd like to think I'm diligent, thrifty and creative when it comes to building and making things but am always happy to pay for the professionals when I believe the skill set is out of my reach. Using a hot air gun to make laminate bend more - yes. using vacuum bags and such like - no.

 

[FatFreddysCat]

...re contact adhesive and the two coat method...

The first coat (on both surfaces) seals the timber. Bendy plywood can soak up quite a lot of glue. This first coat is left to go off for 20 to 30 minutes until touch dry. After the second coats of glue have been applied join the two pieces whilst the glue is still runny. Start at one end and "roll" the bendy ply towards the other end. Staple as required. Applying whilst the glue is still runny allows a measure of repositioning. You need to add formers behind the ends of the curved sections so that the plywood can be pulled straight. Unsupported edges can bulge which will give you problems when you come to laminate the piece. It also goes without saying that you need to endure that everything is absolutely squre and plumb before laminating.

If you need a change in radius then the second skin of plywood will need to be applied in two or more sections as it can lift where the change of radius occurs.

Use VG (vertical grade) laninate which is thinner than HG (horizontal grade) and to warm the laminate gently with a hot air gun when applying to tight curves. This makes it less likely to crack. You'll also need a very large number of clamps to hold the edges - on an 8ft run we'd use 20 to 30 cramps with flat spreader blocks to hold the edges down. We do this all the time on hotel and hospital reception counters and most of the time it works for us. We often can't use vacuum bags because we can't get 4 or 5 metre long bag to enclose them

 

[elrajajo]

update - Oh well, mostly good with a little annoying bad.

I used the 'fatfreddyscat' method (rolling on two coats of contact adhesive etc) with plenty of dry runs so I was prepared as much as possible. However, once I actually 'went for it' I was really surprised by the amount of glue used and how quickly it was drying. Using a roller was clearly the best method but the grooved mdf just needed more and more: is there such a thing as spray contact adhesive? Would it be easier or cheaper?

Anyway, once the two pieces went together it stuck solid as you would expect, but the top piece snapped just as I was 'rolling' it around the radius :x . I obviously bent the board back a little too much as I attempted to roll it on. It's the sort of thing you learn to get right after a little practice, so I can't complain for a first run.

It leads me to ask this question: what would be the best filler for the narrow gap that now exists along much of the split? Bearing in mind that the unit will be jiggling around a bit as the caravan is being towed, I need something that can flex a bit but hopefully wont shrink back. I was impressed recently with some car body filler (is it David's 39 and 40?) I used to repair the caravan's fibreglass shell - would that be suitable in the mdf?

This unit didn't need to bend around quite so tight a radius as I wanted for the other units but it's convinced me that I would be pushing the bendy mdf too far if I tried to get it around the 100mm diameter. As for the Formica - I spoke to the technicians and feel certain I wouldn't have a chance of getting it to bend or stick. I'll simply have to think of an alternative design: wont be the first time

So any tips re glue and filler will be much appreciated as always.

 

[Night Train]

I'm surprised you managed that with the MDF. Well done.

I would have gone with the thinnest ply I could get 1-2mm.
I'm not sure what else there is around the 100mm bend or how many degrees of bend you needed. If I needed to make 100mm radius I would be looking at a plastic pipe with 200mm bore as a starter to make the former. I would then press the plys into a section of the pipe to form the angle of the bend required. To give an even pressure on the inside of the bend I would wrap some foam rubber or sponge sheet around a bit of pipe of less diameter or a section of the same pipe with a slice taken out. For cramping up I would have a batten on the inside of the pipe and battens outside to cramp to it.


Of course the method would depend on how long the curved section is and what is on each side of it.

I have also wrapped ply around in a tube that has had a section taken out of it and replaced to complete the circle and then used ratchet straps and lots of straight sticks around the outside. When the glue has cured the cut section of the tube id popped out and the rest of the tube can then be removed more easily. That gives me a tube of the right thickness and curvature and from that I cut the curve that I need for joining to straight sections of work.

I will try that in reverse one day. Cut a slot in a tube and then strap it close again. Put the glued roll of ply wood inside and then inflate a car inner tube in it to supply the pressure.

 

[Night Train]

For filling and getting a smooth shiny finish you could try the car body filler all over the face of the MDF. Try on a sample first to ensure that it sticks well.

Build up thin layers and cut back with wet and dry as you would on bodywork. Spray primer onto the clean finshed filler and cut back repeating until the surface is mirror smooth. Then undercoat, cut back and repeat and then top coat etc.

 

[FatFreddysCat]

There is such a thing as spray contact adhesive. A pressurised container is about £100 I believe and the guns run out about the same. The containers are landfill once they're empty. The can't be recharged. The stuff also has a tendency to delaminate with time in our experience so not good for curved work. Avoid!

Best way to spread is to use a toothed glue spreader. Contact glue two pieces of laminate offcut back to back (brown sides inwards), trim to size then saw "teeth" 10mm deep at 10mm intervals across one edge using a coping saw. Cheap and disposable. I make mine in 1in, 2in and 6in widths by about 3 in deep

I was really surprised by the amount of glue used and how quickly it was drying.

Ah, well, now you know another reason for using bendy plywood rather than bendy MDF :roll: The plywood will do a 100mm radius curve but the technique is to screw an end to end batten through the plywood at the start of the curve and apply several more battens as you roll it round the radius, removing previous battens as you go. The plywood skin will need to be slightly longer than the curve and is trimmed off on the table saw or with a rail saw (e.g. Festool) when it's all set. Make up many more curved ribs than you think is necessary, about one every 300mm works well on tight radii. But the technique of using contact adhesive and formers only really works if you intend to leave the formers glued and stapled in place as is normal in sshop fittingwork. If you are trying to produce a curved "shell" without formers then you'll need to go to something like male former + female former + loads of cramps and a UF or RF glue to achieve that end result.

what would be the best filler for the narrow gap that now exists along much of the split?

2-pack body filler such as David's P40 works well under normal circumstances as another poster confirms

On the question of tight radii did you ask the Formica guy how post-formed kitchen worktops are made? That's also decorative laminate although they are done using a device called a post forming press. I reckon you could build a small one using a heater element, some steel angle bar and Tempilac sticks (available from welding suppliers?). The principle is shown here in this page from Art Betterley's catalogue:

You may well need a special adhesive such as PUR (hot melt) or an "iron-on" heat sensitive glue film like that used in Ademco phot mounting presses to achieve your curve. Most of our work goes down to about 160mm radius and we achieve that cold with a bit of extra effort. Not yet done a long 100mm radius, though

I still think that the bendy MDF will tend to telegraph through the top skin of laminate and looks like a series of facets

Anyway I didn't say that curved laminates were easy. If they were easy everyone would be doing it and I'd be out of a job! :wink:

Hope those suggestions help

 

[elrajajo]

Thank you Fatfreddyscat and Night Train for your detailed, creative and very useful contributions - your willingness to spare time and share your experience is really appreciated.

I've had to take a break from the project because of Easter relatives and bad weather but I'm back into it now. I've decided because of time constraints, to give up on trying to make the curve out of ply or mdf, though I will be trying out some ideas later in the summer, probably along Night Train's suggestions.

Instead, I will still be making the same units with the same curves but not out of one singe flowing piece of sheet material. Also I will not be using the Formica or any other HP laminate. We're going to get a little experimental and creative with a material described as flexible veneer (you've probably all heard of it). The difference to standard veneers is the paper backing which makes it much more stable when bending around curves - and it is very bendy.

We will be trying out different stains and varnishes for the finish on the veneers and experimenting with body filler and spray paints on some of the other units. We're also going to try out some 'sign writers vinyl' covered with lacquer or varnish to make a poor man's flexible laminate !?

Hopefully it wont look like a dog's dinner but I'll certainly post the results at the end whatever it looks like.