How to clamp or hold a skin on this

[Louise-Paisley]

Anyone got any suggestions as to how I would clamp/ hold a bendy ply skin on the inside curve of this..

This is a design in progress, the bendy ply will be recessed into the inside curve eventually but I have not modelled the recess yet.

I am at a loss as to how to glue the bendy ply liner to the honeycomb, all I can think is maybe vacuum bagging it but I don't have any equipment for that unless a standard hover would generate enough suck to hold it - seems a touch unlikely though LOL

The only other option I can think of is to make a couple of honeycomb inserts that could be wiggled in and then clamped to the outside maybe.

Any suggestions?

 

[Hudson Carpentry]

Battens across and clamped at each end. If the battens are curved slightly on the face that will touch the ply they will provide even clamping pressure.

Thats assuming this isn't a mammoth item.

 

[Louise-Paisley]

Mmmm, why could I not see that! Wood visibility for trees springs to mind :roll:

The only thing that slightly bothers me is the honeycomb will only be thinnish mdf and would it stress the joints too much.. having said that the straight sections will be fitted from the outside in so they will be solid along the outside face so it would try to tighten the joints rather than spread them.

Yes, of course you are right, I was obviously looking for the hard way.

Its not mammoth no, probably about 600mm long, 450mm internal diameter.

 

[Jacob]

Ratchet straps? On foam or something to spread the load? Brace across the inside to stop it folding in?
Looks tricky - I see glue getting everywhere! :roll:

 

[devonwoody]

Use thin veneers and build up a ply in position could perhaps be another way.

But suggestions above should work also.

 

[johnwc812]

Hi,
Just a couple of thoughts:
You say "bendy ply", is this the board that is made specially for bending?
If normal ply (perhaps birch) it will obviously bend better in one direction.
Might be an idea to slightly dampen the ply, work out the best clamping method,
clamp it to the structure without glue and leave for a day to give the ply a bit of curvature before gluing for real.
Looks very interesting.
Cheers John

 

[Grahamshed]

I am wondering if you are going to need a cross baton and clamps for each row of cells to keep it close enough all the way round or whether trapping the two ends will be enough. Calls for a dry run I think.

 

[AndyT]

This totally depends on what is going to happen to the surface of the bendy plywood on this mystery item, but if it is going to be painted or plastered over it might be possible to drill a few holes through the ply, and put woodscrews through them (with washers under the heads) into bits of scrap wood on the back which would bridge across the cells of the honeycomb, applying local pressure where wanted.

If the honeycomb is thick enough, you could just screw or pin into it directly.

 

[Louise-Paisley]

The finished item will be a cat bed.. You should have guessed really LOL

I have yet to model the legs but they will be a similar arc going the other way as part of the 2nd cross section in from each end and the middle cross section so 6 legs in all. I am thinking maybe 12 or 15mm MDF with the legs having another layer glued on each side making the legs 36 or 45mm thick.

I have never used MDF for anything but templates so far so not sure how strong it would be, the honeycomb I was thinking 50mm deep and roughly 50mm squares, does that sound like it would be strong enough made from 12mm MDF? It is likely it will have one or two cats climbing on the top of it which would be 12 or 14kg but spread over most of the area rather than in one lump of course.

The inside I want to recess probably just a 3mm bendy ply, this is to give a nice smooth surface for the cushion (otherwise the ribs will create pressure points if you see what I mean) and also if the cat climbs on top and is half as clumsy as my four it will end up with a foot through the hole so the ply would cap them and make it a bit safer.

The outside will remain open with the edges painted a contrasting colour or edged with something contrasting which will look real nice.

I think battens inside and out clamped together at both ends will be the most sensible option for glueing up, if the inside ones are rounded to roughly the internal curve they should give enough pressure to get a reasonable bond and I can also put a few short screws into the framework as well if necessary but I would sooner not because it would just not look as nice really. I would think also that by fitting the ply into a recess that would help as the recess will also keep the ply in the curve once it is popped in.

It is a bit addictive this woodworking isn't it! a few weeks ago I would never have dreamt of starting anything like this and now I am looking at it and thinking "Oh yeah, that's easy enough, quick template for this, jig for that, lets have a crack at it" It will be a three bedroom cat house next with full electrics and central heating... Mmmm... There's an idea, bound to be someone even dafter than me that would pay for it

 

[AndyT]

Well, that's an original and interesting idea!

I think you could reduce the amount of material in your honeycomb by two thirds or more and still have plenty of strength - unless your cats are really heavy!

If you skin both sides, you could reduce it even further - a honeycomb inside two skins is remarkably lightweight and strong. It's how lots of interior doors are made, with a honeycomb which is little more than

Another simple way of holding the ply in place to glue would be clamps on the edges where you can reach and a bag or two of sand / gravel / compost or whatever else you might have in the shed on the central curved part.

It could be a good job for using impact adhesive, which does not need clamping, just firm pressure with the parts lined up right.

 

[Louise-Paisley]

Thanks Andy

Impact adhesive sounds like a good plan, especially as I have a gallon of the stuff sat waiting for a purpose #-o

I don't want to skin the outside, the honeycomb looks real nice with a contrasting edge and makes the whole thing look much more interesting - visual impact

I also don't want to reduce the honeycomb density for the same reason, but if it would still be strong with only a third of the material then it should be really strong as it is so I am pretty pleased about that.. I do have a tendency to over engineer, I prefer to make things which are stronger than needed rather than cut materials to a minimum and given that these will not be cheap cat beds as sold in most pet stores they need to be a bit less 'Chinese'

I think I will go back to autocad and re-draw it for 12mm sheets.

I love this forum, my very own interactive joinery manual

 

[xy mosian]

How about a balloon? Or tyre inner tubes? Or a smaller diameter cylinder with sausage balloons, ok longish air bags around it? Physio ball?
xy

 

[Sgian Dubh]

Instead of trying to make the ply fit the concavity you create with the torsion box construction, why not laminate two or three sheets of 1.5 mm or bendy ply over a male form made out of something like Celotex insulating board in a vac-bag or bag press if you have one (or something like sandbags flopped over), see what shape you get after any spring back, then cut your MDF torsion box or honeycomb structure to suit? That way you lay the edge of the curved panel on your MDF, draw around it, cut out the MDF parts and assemble, then simply glue the already matching curved panel to the structure. Slainte.

 

[dickm]

Whatever you do, if your cat is anything like our's, it will completely refuse to go anywhere near a dedicated bed. Human's armchairs are SO much more comfortable :evil:

 

[Louise-Paisley]

Whatever you do, if your cat is anything like our's, it will completely refuse to go anywhere near a dedicated bed. Human's armchairs are SO much more comfortable :evil:

LOLOLOLOLOL

Actually my four all use their own beds, until it starts to get colder like now, in which case I end up with four cats asleep on me! Saves on heating bills though as they make great hot water bottles

 

[devonwoody]

I have not seen anyone comment that plywood (I have used anyway) will only bend to one plane. So if you try to make it bowl shaped stand by for some stress. :wink:

 

[Louise-Paisley]

I have not seen anyone comment that plywood (I have used anyway) will only bend to one plane. So if you try to make it bowl shaped stand by for some stress. :wink:

Yes I have already though about that because a bowl shape one/ ones are being considered. Lining those will not be an easy task, I did think maybe making them round outside but faceted inside so the facets could be lined with bendy but it might just be simpler with an open bowl shape to include a polypropylene stiffener in the cushion.

The lining is not essential I don't think and might not be fitted on this one even, the main reason I would prefer to fit it to this is so they don't step through a hole and panic with a leg through it if you see what I mean.

 

[devonwoody]

Dare I mention that those lovely cuddly ******* quite often get visitors, so if those visitors get into any of that lattice work things will get very itchy. :wink: :twisted:

 

[MickCheese]

Could you not just pin it. I have a headless pneumatic pin gun that fires small almost invisible pins or use veneer pins.

Mick

 

[Louise-Paisley]

Dare I mention that those lovely cuddly ******* quite often get visitors, so if those visitors get into any of that lattice work things will get very itchy. :wink: :twisted:

You know what, I have never treated my cats for itchies once, and I have never had a single flea ever.. But then my cats are indoor cats and only go outside on a leash..

Besides which, fleas would not frequent the lattice, fleas live in carpets and soft furnishings and only pop onto the host for a meal and to lay eggs. The hatched larvae fall into carpets and bedding where they eat dust (skin) until they develop into an adult and hop on the nearest warm blooded host to start the cycle again.