Steamin plywood to shape & Yatton VoF build

[maxi-model]

I am in the process of building a laser cut plywood kit. It requires the roof sections to be "steamed" into their simple single plane curved shape by prior binding to a suitable curved former. In this case a surprisingly structurally rigid metal Tesco loo brush container - its exactly right dia', 9 cm (a little undersized, the actual diametre of the curve is 14 cm, to allow for the material to "relax" after forming") and right length, 26 cm (Sorry, too much information ). The roof sections are made from 1.6 mm ply, so fairly stout but at no risk of breaking/splitting when being bent "cold" to the former's circumference prior to steaming.

Here is/are my problem(s). I have no experience of employing this shaping/bending technique, I do not want to risk ruining the parts through ignorance - No matter how I try I cannot get the material to hold its fully curved shape "cold" before steaming, I cannot devise a simple mechanical means to hold it uniformly and fully to shape due to its 1.6 mm material thickness. I have not risked soaking them prior to steaming. The usual option of employing stout rubber bands, to bend the roof sections down onto the structure they are to be bonded to is not an option - the roof material is insufficiently pliable and the structure it is being bonded to is not of sufficient strength or the correct design to employ that technique or use an IP engineering roof fitting jig either. This is not a complaint as to the kit's design, when bonded and in place on its chassis the whole structure will be very strong and secure. Anyway a glue bond alone, even if structurally possible, would not be sufficient. The roof sections have to be formed to a circumference they will hold prior to fitting and bonding.

I cannot find a tutorial to advise on this method of bending plywood at this scale. Big bits of heavy duty furniture yes, 1.6 mm ply sheets no. Anybody out there with experience of this technique who can advise or point me to a suitable tutorial or forum topic here or elsewhere that deals with this authoritatively. Thanks in anticipation. Max

P.S. I have contacted the supplier and I am sure the will provide advise. But I am an impatient old soul so I thought I'd ask here too

 

[Gtarling]

Soak the chosen piece of thin ply in warm water for an hour or two, bind it tightly to the chosen former with elastic/crepe bandage or elastic bands, allow to dry overnight, remove from former and glue in place, clamping it tightly.

G.

 

[playmofire]

You steam the piece of material before bending it to shape, I think. Professionally, this is done in a steaming cabinet I believe. Otherwise, soaking in boiling water should work or holding in the steam from a boiling kettle (watch out for burnt hands!). Years ago I bent a strip of ply to fit round the curve of a viaduct but can't remember which method I used but it was probably the boiling water one.

 

[maxi-model]

Soak the chosen piece of thin ply in warm water for an hour or two, bind it tightly to the chosen former with elastic/crepe bandage or elastic bands, allow to dry overnight, remove from former and glue in place, clamping it tightly.

G.

Thanks for the suggested alternative. However, any form of clamping as a final process, as stated, is probably not an option. I'd thought about doing this way to get to the desired curvature but prefer to stick to the kit's suggested steaming method and instructions. I do not wish to post a picture of the actual structure or parts as this would identify the maker and may lead to unwarranted comments regarding any perceived deficiencies, by others, in its design. It's a good solid design, so long as you have the roof sections fully formed to near the correct curvature prior to bonding. Max

 

[maxi-model]

You steam the piece of material before bending it to shape, I think. Professionally, this is done in a steaming cabinet I believe. Otherwise, soaking in boiling water should work or holding in the steam from a boiling kettle (watch out for burnt hands!). Years ago I bent a strip of ply to fit round the curve of a viaduct but can't remember which method I used but it was probably the boiling water one.

The instructions say bind to the former first then steam over a pan of boiling water for 4 minutes. I cannot find a way to hold it to the former fully and uniformly in the correct shape in its dry state. The material's resistance to bending (though no risk of snapping) is making it difficult to find a mechanical means to achieve this. This has included using wooden battens along the side edges and tie straps to secure. can't get it tight enough and everything keeps popping out of place while I try. Using washing line and tying up like a parcel doesn't work either.

One though that crossed my mind was to bolt the battens, to hold down the roof sides, to the former. However the former's cylinder needs its end cap in place to maintain its structural integrity. Certain vital lack of access there (OK I could fabricate an internal support but that's getting a bit complicated). Yes, I could pre-assemble the battens/bolts using star washers to help stop the bolts rotating when I tighten up to secure. Got plenty of nuts and bolts, M3/4/5/6 but no star or spring washers to match Max

 

[JimmyB]

maxi-model , as an alternative to steaming, what about thin longitudinal cuts on the underside 5 - 10 mm apart about half the thickness to the plywood. When content it will bend, glue the cuts a layer of paper (to stop the wood sticking to the former) and wrap around the formed, I would use "cable ties" to hold it in position.

 

[maxi-model]

maxi-model , as an alternative to steaming, what about thin longitudinal cuts on the underside 5 - 10 mm apart about half the thickness to the plywood. When content it will bend, glue the cuts a layer of paper (to stop the wood sticking to the former) and wrap around the formed, I would use "cable ties" to hold it in position.

Interesting idea Jimmy. I would hold off on trying though, unless all else fails, till I have spoken to the supplier. There is a risk, due to my hamfistedness and inexperience, of causing issues with the parts that could result in the need for replacements. I have seen this actually done as laser etch engraving on some ply parts use for sharply curved parts to form things like duckets on brake vans.

One side of one of the the roof sections has some etched detail that would mean one would have to be very careful as to the depth ones cuts. It also could cause a "plank" effect that may not be possible to sand out due to risks of deleting the roof's etched surface detail. Cable ties have been tried but one needs to add a battens along the length of the piece being steamed to ensure one does not end up with "wavy" edges. Max.

Edit - If I were to make the cuts Jimmy what would be the best way to do this - A razor saw against a straight edge, with a small fine cut triangular file used after to give more of a "V" profile to the cut, or Stanley scoring blade (usually for plastics). I also have a "Bare Metal" scoring scribe, for cutting shut lines in plastic. None of the above

 

[Greg Elmassian]

Confusing.

So from post #1 you have a nice metal former, or at least the right diameter
Also you say you cannot fully shape it prior to steaming - ok, you just put tension on the the best you can, and start steaming.
But you continue to say rubber bands are not strong enough... ok I get that, but then you say your form is not strong enough.. that is the key.

Stop... get a stronger former... and yes you may have to steam bit by bit. Clearly someone did succeed with the method they presented.

I would look to find a piece of heavy walled plastic pipe or something stronger. you could even fill your metal former with concrete.

It seems your issue is strength of your former.

For steaming, a large dutch oven with a cover on the stove with some water in the bottom boiling will work, or you can get an steam iron and hold it close to the wood. If you have a person with an espresso machine, it will produce large volumes of steam.

But first I would get the form working. With a strong one, you can definitely apply pressure. I would resist soaking the wood, as it might delaminate.

Greg

 

[Paul M]

Seems like you're not going to be able to bend it in one go, so do it small stages, there shouldn't be any feal rush. Try putting in the microwave for a while, the glue will soften and then you can start to bend it. But as I said take it slowly

 

[maxi-model]

Thank you all for your inputs.There are some interesting tips and guidance but none I would want to try without further advice from the maker, due to my lack of understanding of the basic steaming technique and with this material's thickness. I think we will leave it there as looking at the replies, while all helpful, none actually describe the process I need to understand to proceed with any confidence.

Part of the problem is that this kit is unique in my experience as the roof section cannot be clamped/bound directly to a separate or integral support frame to get it to bond and conform to the curvature required. Nor is it of the type where longditudinal strips are used to form the roof with filling and sanding back to provide the final curved and finished form. These are the only two construction types I have come across in common use, barring pre-formed styrene and metal, after many kit builds over the past 15 years. In either 16 mm and 15 mm scales. Live and l learn, as my dear father used to tell me, frequently.

I'll have a word with the guy who engineered the kit this week as they should know. If the worst comes to the worst I will try to get him to provide pre-formed sections or reffer me to someone who can, at a cost of course. That or I will copy them on a lighter gauge material and forgo the minimal etched detail contained on one section. The base structure should be able to be made to work with forming lighter materials by bonding alone. I might even check to see if GRS have a preformed styrene roof section with the correct curvature. The sections are not simple rectangles, or the same width at either end, in plan view by the way.

Greg, my problem is not the former's lack of structural integrity. It only loses that if I take one end cap off for access. Which I would only need to do if I needed to bolt the battens to grip the material to be bent. My problem, as stated, is I do not have any experience of the process and resulting skills, barring the scant details in the kit's instuctucions that assumes the builder has them. That and the roof sections are unusually thick at 1.6 mm rather than the .5 mm sheet material usually encountered in this application. Been there done that when "engineering" kits for others to build - assuming your customer has the same skill sets you have. Max

 

[Greg Elmassian]

Max, I must have misinterpreted what you said. If you take your form and bind the plywood to it, I gather you can only partially curve it to the form.

Do this under as much tension as you feel prudent, and then start steaming. As you continue, you should be be able to further bind it to conform to your form.

What had you planned to produce the steam? Is there any chance you have a large covered vessel that can have a small amount of water boiling in it. We call these "Dutch Ovens".

Greg

 

[PhilP]

I don't consider 1.6mm to be 'thick' for this. - Though it does depend a little on the width of the article.
I may have missed rough dimensions from earlier in the post?

I would have a couple of old towels, oven mitts, two strips/battens (more than the length of the roof, some tie-wraps (quite wide, in section, by choice).

A recently boiled kettle, pan of water (rolling boil, to produce plenty of steam).
Work on an empty draining board :
Hold the roof section at an angle, and pour the water over the outer surface. - This will (slightly) soften the laminating adhesive, and causes the fibres to swell slightly.
This will allow the top surface to 'sfretch' a little.
Immediately douse the battens with the hot water. - Heat and steam will be difficult to get under them once forming starts.
You now need to work quickly, whilst the material is hot and damp.
Hold it to the former (as best you can) with the battens (not too close to the edge, they will 'walk' towards the edge, is the ties are tightened, and the bend is formed).
Use a number of the tie-wraps, along the item.
Do not try to go all the way at this time, and tighten evenly along the length.
Once this first strapping is secure, you can relax a little.. Then use the Steam from the pan, to 'soften' the item, gently tightening the tie-wraps along the item. - One, or two, clicks at a time.

Once you are happy, you will probably have a warm, damp towel. Fold this over the item, and let it sit for an hour or so..
Remove towel. Item could go in the airing cupboard, for a couple of days..

That is how I would do it.

PhilP.

 

[maxi-model]

I don't consider 1.6mm to be 'thick' for this. - Though it does depend a little on the width of the article.
I may have missed rough dimensions from earlier in the post?

I would have a couple of old towels, oven mitts, two strips/battens (more than the length of the roof, some tie-wraps (quite wide, in section, by choice).

A recently boiled kettle, pan of water (rolling boil, to produce plenty of steam).
Work on an empty draining board :
Hold the roof section at an angle, and pour the water over the outer surface. - This will (slightly) soften the laminating adhesive, and causes the fibres to swell slightly.
This will allow the top surface to 'sfretch' a little.
Immediately douse the battens with the hot water. - Heat and steam will be difficult to get under them once forming starts.
You now need to work quickly, whilst the material is hot and damp.
Hold it to the former (as best you can) with the battens (not too close to the edge, they will 'walk' towards the edge, is the ties are tightened, and the bend is formed).
Use a number of the tie-wraps, along the item.
Do not try to go all the way at this time, and tighten evenly along the length.
Once this first strapping is secure, you can relax a little.. Then use the Steam from the pan, to 'soften' the item, gently tightening the tie-wraps along the item. - One, or two, clicks at a time.

Once you are happy, you will probably have a warm, damp towel. Fold this over the item, and let it sit for an hour or so..
Remove towel. Item could go in the airing cupboard, for a couple of days..

That is how I would do it.

PhilP.

I think this shows I should really get someone else to do it or cut replacements from thinner material. Sounds somewhat involved and somewhat dangerous for a first and probably only attempt But very comprehensive description of the processes Phil, thanks Max

 

[maxi-model]

Max, I must have misinterpreted what you said. If you take your form and bind the plywood to it, I gather you can only partially curve it to the form.

Do this under as much tension as you feel prudent, and then start steaming. As you continue, you should be be able to further bind it to conform to your form.

What had you planned to produce the steam? Is there any chance you have a large covered vessel that can have a small amount of water boiling in it. We call these "Dutch Ovens".

Greg

Large open topped pan. Let's face it if I have to go and buy a whole lot of specialised equipment I will only ever use once think I will have to find a work around - get somebody experienced to do it or remake from thinner ply. Max

 

[Greg Elmassian]

Max, it's really not that complex. What about practicing with a small square of hobby plywood?

Also, maybe you could make the roof of 2 thinner pieces like you just said, but you said earlier in post #7 that you cannot modify the wood as there is some etched detail.

With all the things you have done and shared here, your apparent trepidation is somewhat surprising, and no one is telling you to "buy a whole lot of specialised equipment"...

Not really understanding your resistance after all the complex things you have done in the past, but I'm far away in a different country in a different culture.

Best of luck, I'll stop trying to help, and watch with interest as this develops. I don't feel I can help any more.

 

[Paul M]

Remember, the hardest thing is starting. All you're doing by steaming the wood, is softening the glue holding the layers. Once it's soft, and the wood bent to shape, the glue will re-harden and stick. So any method to soften the glue will do, if you're not happy to use boiling water

 

[Paradise]

An electric iron maybe helpful somehow

 

[trammayo]

I would opt for making a new roof. The etchings only represent what would have been on the roof (I think) so they could be replicated. If they were recessed, then two layers of card/ply/styrene (or whatever) would facilitate that. I once built a steamer in the 1 to 1 world but that was 55 years ago!

I use cardboard for curved rooves, dashes (for trams), etc. All still "as built" after many years use -even though they run outside (not in pouring rain though!).

 

[Homo Habilis]

Have you considered using some type of ratchet strap clamp instead of twine or rubber bands?

 

[maxi-model]

Have you considered using some type of ratchet strap clamp instead of twine or rubber bands?

Yes, that was my first thought. However, as I would need 2/3 of them, even if I use battens at the sides, the cost for this one off never to be repeated job is "prohibitive" (at about £14 or so). Then you need to try and find one that is small in size. There is also the issue of a close woven man made fibre covering a relatively large area of the material to be steamed might also hinder and complicate the process. Again if just makes sense to get another experience person to carry out the task.......and paying if needs be.....or..........

To answer a couple of others' mystification or exhortations due to my seeming reluctance to do it myself, to paraphrase the well know motivational saying - Too much pain, too little gain. You have to draw the line somewhere and recognise when ones endeavours are tantamount to futility or folly. There is a tendency to blinkered vision that can be endemic in hobbies. Lateral thinking is a useful thing. Have stock of sheets of 0.5 mm birch ply, Swan Morton 10A scalpel blades, Titebond 3, a couple of heavy books, big rubber bands and a steady hand, so will fabricate a solution. I have a plan That or get someone else to form the originals

While it may seem odd to say this - The ultimate solution might not always be what the original topic question asked or directly sourced from the advice offered in response. But most certainly inspired by. I know that can infuriate some when confronted by an OP's seeming out and out cussedness and obstinacy. Genuine thanks to all for opening my eyes and getting me to apply my brain to this one. Max