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Bristol Blenheim Mk1V

Long term design project

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Lindsay Todd10/06/2020 13:13:20
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1746 forum posts
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Thought i would update the tale. the moulding of the canopy has been long and tedious one. I have ended up basically building my own vacuum forming table to accommodate A3 size sheets. I also made a glass mould and plaster cast of the canopy as i felt the foam may indeed suffer from the temperature given I need to get quite a large area covered. My bag of herculite must have been older than i though and had turned into a garden ornament that looked remarkably like the inside of a bag of herculite! More acquired and mould and cast made and a few choice words as various sheets of PET 0.5 turned white on me with going over temp before I have finally cracked it rather than cracking up and finally have a completed formed canopy to work with. I can now work back on the frames and mounting and moving forward again. Photos to follow. Linds

Danny Fenton10/06/2020 13:18:31
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Welcome back

I am sure others would also be interested to see your vac forming machine Lindsay, A3 eh, I think we may just be sending stuff to you for forming

Cheers

Danny

Lindsay Todd10/06/2020 13:25:43
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1746 forum posts
1811 photos

Lets not get carried away here Danny, 6 sheets before I got a good one, three heat guns and an infrared heater trying to get the temp even, yes it can be done but it was a challenge. I even started looking around for old eye level gas burner grills to modify but they are like the proverbial rocking horse whats-it when you looking for them.

Linds

Lindsay Todd10/06/2020 13:25:49
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1746 forum posts
1811 photos

Lets not get carried away here Danny, 6 sheets before I got a good one, three heat guns and an infrared heater trying to get the temp even, yes it can be done but it was a challenge. I even started looking around for old eye level gas burner grills to modify but they are like the proverbial rocking horse whats-it when you looking for them.

Linds

Danny Fenton10/06/2020 13:32:25
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9648 forum posts
4458 photos

Sounds interesting if not time consuming, I have seen oven grille elements used.

Cheers

Danny

Lindsay Todd11/06/2020 00:46:05
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1746 forum posts
1811 photos

Plaster (herculite) master pattern sat on my A3 size vacuum bed which is basically a sealed MDF box with hole to plug in my good old Henry vac. Don't ask how long it took to drill the holes.

img_2097.jpg

The sheet is simply fixed with drawing pins and sealed with masking tape to a wooden frame, photo shows the final good part excess material, because it is quite a large form area you inevitably get a bit of waste.

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Success after quite a few trials and fails, going down from 0.6 to 0.4mm material also made a big difference again down to getting the temperature stable over the entire area. about 120 degrees seemed to be the optimum.

img_2094.jpg

New ply frame now going together to support the glazing, then it will have strips across the top surface so i am finally making progress again.

img_2095.jpg

Linds

cymaz11/06/2020 01:01:05
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9272 forum posts
1200 photos

Was the old ply frame unsuited for the new glazing ? I saw a frame a couple of pages back.

Lindsay Todd11/06/2020 08:12:16
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1746 forum posts
1811 photos

Hi Cymaz, the old frame was built into the structure and as this will effectively be a removable section now as i suspect batteries and ballast will need to go up front and the old frame would have needed just as much work to re configure so easier just to start over.

Linds

Danny Fenton11/06/2020 09:16:42
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9648 forum posts
4458 photos

Hi Lindsay, so how did you evenly heat a sheet of A3 I cannot get more than A4 in my oven and hence has limited me.

Your box looks just like mine but bigger, and yes those holes do take a while to drill don't they crook

Cheers

Danny

Lindsay Todd11/06/2020 10:32:33
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1746 forum posts
1811 photos

Hi Danny, quite literally two people, myself and San, two paint heat guns and a further infrared heater, nightmare! you just have to take it steady and carefully, first sheet turned white so quickly through over temp in patches all over the place so you just have to be patient - not really a skill of mine that comes naturally.

Linds

David P Williams11/06/2020 10:38:25
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913 forum posts
318 photos

I keep thinking about making a vac form box. Would something like this be suitable or are there not enough holes? would it be good as a starting point for drilling more holes?

Edited By David P Williams on 11/06/2020 10:38:44

Danny Fenton11/06/2020 12:55:03
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9648 forum posts
4458 photos

I hope you don't mind me leaping in Lindsay?

David I think that board would work fine, but what people often don't consider is some structure inside the vac-box, I am not sure if Lindsay had any structure inside but they can literally be crushed, or at least distorted by the suction.

221112 bt hurricane 5670 (large).jpg

Mine is similar to Lindsay's except with mine only being a max of A4 the plastic sheets will fit under the grille.

Cheers

Danny

Lindsay Todd11/06/2020 13:03:53
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1746 forum posts
1811 photos

Agreed Danny, the timber does look at least a good starting point, i think my holes are 6mm with 6 spacing approx and the box is from 18mm MDF with a few forms inside with large apertures to add strength and as Danny says stop the box getting crushed. I did think about suspending a baffle plate inside to minimise local high suction points but this does not seem to have been a problem.

Linds

David P Williams11/06/2020 13:59:00
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913 forum posts
318 photos

Thanks chaps

Lindsay Todd20/06/2020 23:20:36
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1746 forum posts
1811 photos

finally got a chance to do a bit more on the new canopy, moulding now glued onto the ply frame and trimmed to fit, plastic strips taped over the form so i can mark the position of the frames on the inside of the moulding

500.jpg

Cut strips of self adhesive aluminium tape which was then applied over the moulding, first few sections shown, bit fiddly but goes on easy enough and will have rivets ect applied before being painted. Outer edges obviously still to be done so the timber frame edge will be hidden.

501.jpg

502.jpg

Linds

Danny Fenton20/06/2020 23:30:50
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9648 forum posts
4458 photos

Nice one sir, that should look ace

Cheers

Danny

Lindsay Todd20/06/2020 23:53:03
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1746 forum posts
1811 photos

Thanks Danny, it does feel like i am getting somewhere again

cymaz21/06/2020 05:41:48
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9272 forum posts
1200 photos

Good to see you’re back on it

Lindsay Todd04/07/2020 22:06:43
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1746 forum posts
1811 photos

Finally got another chance to do some more work on the canopy, inevitably the fit had some areas of shrinkage and expansion so a little filler and sanding was required to loose the edges and get a good clean fit, still a little sanding to do but the fit and look is now just so much better for the effort.

img_5522.jpg

img_5523.jpg

good progress and worked so well that i am going to look at some other sections of the canopy as well as the rear gun turret moulding next which originally was planed to be made in two sections but maybe forming in one is worth a go as i already have a plug ready.

I'm not going to embarrass myself by saying more soon but its good progress none the less. Linds

Linds

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