Homespun vacuum forming -having a go

[leccyflyer]

I'm in the middle of restoring and converting a small Beaufighter, built from the RCSA free plan by John Deacon. The model was powered by a pair of OS.10s, but she has a pair of small brushless outrunners in her future.

Anyway, the canopy on the model was a bit agricultural, being rolled from acetate sheet, with a tape joint, so I thought that I'd make a pop bottle canopy, using the similarly sized HVP Modellbau Beaufighter canopy as a pattern, from which I'd made a plaster of Paris male mould. The pop bottle attempts were not 100% successful, say the least,  so I moved on to the idea of putting a little vacuum former together.

A visit to the local charity shop netted a folding wooden frame -intended to be used as a cookbook stand, which was the perfect size for the A4 sheets of PETG on ebay. A few minutes work with the saw and the frame was ready - some bits of scrap timber made the box and a couple of pieces of play made the base and top. Marked out a grid for the holes in the top and used the drill press to perforate that - you could use pre-perforated peg board, but I used what was lying around.

Cut an appropriately sized hole for the vaccum cleaner hose with a Forstner bit and checked it was a snug fit before assembly and then the whole thing is glued and screwed together, to give a reasonably airtight construction.

So, this is what the finished article looks like.

Home-brewed vacformer open for business. Plastic sheet is attached to the frame and warmed with a hot air stripper until soft and saggy.

The perforated bed allows the hot and pliable plastic sheet to be pulled down tight over the mould.

That's the frame closed -plastic sheet attached to the upper part of the hinged frame is brought into contact with the mould(s) which are positioned on the perforated bed.

Here's what the first attempts looked like - not too bad, with a bit of webbing, from placing some of the carved balsa block patterns a bit too close together.

The canopy came out perfect and I'm really happy with the simple addition to the workshop - I'd encourage anyone to have a go, it's not rocket science and it's very satisfying. Almost worth making a plaster of Paris pattern of any new model's cowl/canopy, just in case.....

 

Edited By leccyflyer on 29/07/2014 08:27:51

[Tony Bennett]

i like that.

might have to steal the design. if thats ok.

[leccyflyer]

Please do, feel free - the cookbook stand was £2.50 but isn't completely necessary - in fact a bit of piano hinge on a simple frame would not have the 8mm or so offset that my one has between the perforated bed and the plastic, giving an even better vaccum.

When that vaccum grabs it really does suck the plastic down into the holes though - most impressive.

The only real proble I have found is securing the plastic to the frame - I've used self adhesive heatproof aluminium tape, but that's a bit wasteful. Some kind of clamp arrangement might be better.

[Tony Bennett]

make the top frame loose and use clamps to hold the two parts together trapping the plastic between them, maybe?

[leccyflyer]

Something like that, or countersunk bolts with wingnuts on the top of the frame was my other thought. That would mean punching four holes in the corners of the plastic sheet though.

[Chris Bott - Moderator]

If the top frame is loose, and a bit larger than the vacuum base, the frame can be heated in the oven or under the grill, until it just starts to sag.

Being a little bigger, it can be pulled down so that the plastic sits right down at vacuum base level.

Nice job though Leccy, and you don't get the hot fingers with yours!

[leccyflyer]

More importantly Chris I don;t get the chilling effect that suggesting putting a sheet of plastic in Mrs Leccy's Aga would get........the hot air gun does the job, out in the workshop.

[willhappy]

hi leccyflyer

wow so cool

will

[Martyn K]

Posted by leccyflyer on 29/07/2014 08:44:47:

The only real proble I have found is securing the plastic to the frame - I've used self adhesive heatproof aluminium tape, but that's a bit wasteful. Some kind of clamp arrangement might be better.

I am at a similar stage with mine. I've made an A4 sized vac former. It was suggested on one of the uTube tutorials that the acetate can be clamped and gripped using door seal (available from B&Q). I am going to try that with mine. My first attempt used drawing pins to hold the sheet - I quickly learned the flaw with that idea...

Martyn

[leccyflyer]

The aluminium tape works very well, but, like I said it's a bit wasteful, as it needs to be stripped off after the plastic has cooled. I tried staples, but the wooden frame is too hard for that and would quickly get messed up anyway.

[PatMc]

Nice one Leccy, looks like the basis for a magazine article

Re- holding the plastic; how about another frame above hinged one with the plastic between. The plastic clamped by using countersunk screws through both frames with wing nuts for easy release.

[leccyflyer]

Thanks Pat - that might work. Adding another frame on top might make the offset just too big for the vaccum to work effectively though.

If I were to disassemble the frame and mount the piano hinge directly onto the perforated plate, then put countersunk bolts between the two halves of the frame, with wing nuts on the bolts to clamp the plastic. The sheets that I have used are almost an exact fit for the frame so, unless I cut the corners off, I'd still need to punch a hole in the corners.

[PatMc]

What about hinging both frames at opposite ends, clothes horse fashion, with small latches to hold them together at the same time clamping the plastic between them. The latches I have in mind are either small versions of the ones on most Tx cases or simple swiveling hook & screw type. So long as the clamping action is strong enough the plastic won't need to have holes punched in them.

[Wiltshire Flyer]

Fantastic idea! Will have a go myself nice one!! 👍👍

[Chuck Plains]

Ooo! That works really well! Nicely done Leccy. Another machine to be added to my entirely necessary workshop collection.

[Paul Adams]

A question on method. You fasten the sheet to the frame, do you then close it onto the formers and use the heat gun to soften the sheet sufficiently to close the lid fully down, then switch on the vacuum and continue heating the sheet in areas that are not fully sucked down, or do you heat the whole sheet and when pliable enough lower the frame and switch on the vacuum in one operation?

[Jamie sawyer]

There is tutorials on you tube Paul, the sheet is heated before you apply it to the air suction bed. I'd say practice makes perfect with this to how flexible the plastic sheet needs to be. The one I seen the guy just dropped the frame from a hight of about a foot and it hit the former plug and just stretched over it flawlessly and the hover suction did the rest. It was very interesting to watch how easy it is when you know how.

Well done Leccy flyer

[leccyflyer]

Well, so far I've only done it a few times, but based on what I'd picked up on the internet I figured out the sequence that I thought would work. I set the vacuum cleaner going, then heat the plastic until it has sagged and then tightened up again, at which point it should be soft enough. Then I close the frame, using the handle that I left in place, whilst continuing to play the hot air gun on the plastic. As the frame get close to being closed the plastic is drawn down to the table. I then keep the hot air on for a few seconds more until the plastic is nicely flush, and pulled down into the holes on the table, before removing the heat and letting the plastic cool.

Then I switch off the vacuum cleaner and remove the plastic. That's when the fun starts, in trying to match up the split parts which have to be stuck together. That makes the canopies look easy-peasy.

If, perchance, as happened on the second go, the plastic isn;t quite soft enough, you can open the frame again and reheat the plastic -it will reform into a sheet again, with all trace of the deformation of being pulled partly over the mould gone - giving you a second attempt.

[ROSS MANSELL 1]

It seems that the plastic needs to droop about 12mm (half an inch old money) and then draw down. (According to the experts on various forums