Cheshiretaurus

Fantastic, very neat.

Things are moving along now fuselage was closed up last night and filled, This morning I dry assembled the rest with test nose, wings and tail to find the centre of gravity by balancing it at the point where the main wheels will go, found I needed 2.5g of weight in the nose. I've cast a nose with 3g of lead submerged in the resin, hope this is enough as there isn't room to add more later. Nose is now CAd into place and filler added. I'm away with work again for the whole week so this gives plenty of time for it to set ready for me to start sanding when I get back.

Ive given up on casting resin side windows, couldn't get the resin to cure hard enough to polish & the windows had lots of optical distortions so the interior was too obscured to be worthwhile. The easy answer would be just cut them from clear sheet however they are curved, the B window has a complex in it curve too. An Idea came while working on a new mould for the windscreen, Vacuum them! but first I need to make a master, this was created in a similar way that the resin windows would have been done. A piece of acetate was taped over the windows but instead of resin I pushed RTV putty into the apertures. Once set the left & right were stuck to a flat surface and the space between the two filled in with more RTV putty to create a smooth mound with the windows at the top suitable for vacforming. A wooden casting frame was put around and dammed, and a negative cast made from resin. Now I can make as many RTV moulds of the windows as I want in case I trash them while making the vacuum mould. The vac mould was made in the same way as the previous ones this time I used acupuncture needles as suggested by Carlos, one in each corner of the each window, 16 needles. I found grouping the all together with a bit of blutac helped to keep them neat and upright while working and not falling in the way. Pulled several copies this morning from it some better than others but I think I've got a set of usable ones from it going to give them a test fit soon then, I think the plan is going to be to fit them near the end of the build to prevent damage. I can fit them from the inside before the floor goes in, thank you airfix for designing it this way. I can now close up the fuselage and get on with the build! Speaking of which I vacuumed some more spats, this time from 0.75mm card this worked much better. These were cut out, sanded and assembled in the same way for any other vacform part. spent yesterday afternoon carefully cutting out the slots for the wheels For the nose wheel an extra slot was cut for the leg and slither of 0.25mm card inserted for the fin on this spat. The main gear spats have the cut out extending round to the inboard for the leg, still need to do some more research on this to get the right size an shape of the cut out before I do them.

Quick update the etchant I used is back on ebay http://www.ebay.co.uk/itm/500g-Sodium-Persulphate-99-etchant-Top-quality-/220721707800?pt=UK_BOI_Medical_Lab_Equipment_Lab_Supplies_ET&hash=item336409fb18

Measurements from a matchbox Hunter in 1:72 Main wheels 10.2mm x 2.4mm Nose wheel 7.4mm x 2.0mm

Have you got a link to the Amazon ones, the ones I have just looked at on ebay and Amazon are £8-15, bit expensive think it might have something to do with the 'wedding' bit. But its an idea worth investigating to find something else perspex and column sort of shape. Probably wouldn't be beyond any of us to make our own from perspex stock. Good idea, thanks.

Fantastic, very neat, top marks

Another method of getting the interior dimensions & profiles is to tape your fuselage together, tape up all the gaps, windows etc, and fill with plaster of paris or herculite. you might get a few drips and leaks as it sets but after half an hour to an hour you can open up the fuselage and leave your plaster cast to harden for 24 hours, once set you cut it up into slices at various point of interest to find the internal profiles. Obviously this would need to be done before starting your build. I have done this on my airfix cherokee that I am converting from an arrow to a cherokee 140 so bulkheads are in a different place.

Its all been a good education. The bigest hurdle is just collecting all the bits together to make these things. Well worth having a go.

Right, done some hoovering, the fun kind. Taped the moulds to my vacuum tool and sealed up all other gaps. Toaster at the ready and go. Just really test and practice pieces at moment, spats are formed from 0.5mm card and seemed to come out ok but I think next time I make a vacuum mould I'll make smaller air holes, the pip marks left are quite pronounced but these can be sanded so ill stick with this mould and try using 0.75mm card, (1mm card will be too thick and wont leave room for wheels). I've now run out of 0.5mm card so need to order some more today along with some 0.75mm and have another go. As for the windscreen, Ive made a few from 0.5mm PET-G, I'll regard it as a partial success as last time I tried to mould a canopy it just stuck to the resin mould leaving marks on the canopy, I had used less aluminium powder to make that mould but this time I used more I think I've solved that bit. I'm going to make a new master & mould for the windsreen as this one has too many imperfections and no defining line for the edge of the screen making it hard to see where to cut it. Altogether a partial success as I learnt a fair bit more about vacuum forming from it.

Going to try that, just ordered a box of 100 0.25mm needles for next time i make a mould, thanks

Just noticed, have you got the RBF tag on the nose wheel?

Looks good to me. I think it the dogs doo dahs. Nicely done !

Made a start on the side windows filling them with clear resin, I’m on my second attempt as I removed the acetate former from the window too early and left ridges on the surface from it. I tried to polish it out but made an even bigger mess as the resin was not hard enough even after few days. I’ve removed them and started again. However on the plus side I have learnt how to make realistic looking broken windows while removing the old ones. I’m away with work again overnight so that gives them plenty of time to set before I remove the acetate this time. Finally my RTV mould for the spats and windscreen set, took 5 days! Defiantly didn’t put enough catalyst in as they are not as deeper pink as previous ones I have made. All in all, a bad week for casting I think. I’ve made casts from them now and these have become the basis for making the female vacuum forming moulds. I CA’ed the casts to a plastic card backing along with another cast cut out for a second set of main wheel spats then started spraying PVA mould release in a very light layer at a time and leaving it for 10 to 15 mins between layers, I think they got 5 or 6 maybe 7 layers in total this forms a barrier only a few microns thick. The mould release needs to be dusted on lightly at first as it tends to bead and form blobs if too much goes on at once. After a few layers the tendency to bead reduces . Don’t use your expensive airbrush for this, I used a cheap £7 mini spray gun from ebay. I had also made a couple of wooden frames to fit round the cast from 12x4mm batons and glued together with white PVA glue. Sewing pins were gently tapped in at strategic points for the air evacuation points on the mould. The frames were fitted and dammed with plasticine. A mix of 50% aluminium powder and 50% resin was then prepared, this becomes a thick mud so a little acetone was added to thin it into a pourable mix. This was then poured into the frames leaving an air chamber above the resin, given 15 mins to gel then the pins were removed. I gave them about an hour to set then gently prised the plasticard along with the cast masters away, took a little force at times but they both cleanly released, leaving a negative impression of my parts for a female mould. I’ll leave them for a couple of days to set hard before I try to make use of them. In the mean time I have bought a new vacuum cleaner, not sure if the wife picked up on the fact there was no grumbling when it came to getting her a new one! However I need to make an adaptor as the new one doesn’t fit my vacuum tool with the nozzle being the wrong size.

Think I'm going to try putting it in the fridge. Thanks for the replies.

I'm using Easyflo 60 resin, it only has a couple of mins working time, have to work like a one armed paper hanger get into several moulds work any bubbles out, & clean up the mixing beaker. Is there any way of slowing this down and extending the working time, I dont mind a longer demould time as a knock on effect. can the ratios be changed or work a colder temp?

Been working on the interior today, mixed a better match to the red toned down with brown n blue, Tamiya tape seat belts re fitted. Made some seat pockets items from plastic card shapes (usual light aircraft stuff, tech log, first aid kit and fire extinguisher) CA'd to thin backing sheet then masking tape CA'd over the top, when the paint is dry I'll cut them out and stick them to the back of the front seats. Added a little detail to the side walls, once this is dry I think I'm ready to cast the resin windows. Quick summery of today's work Went to Barton a few weeks ago to have look at the real G-PAWL. Apologies for the quality, taken with the phone on a very sunny day lots with of reflections and a greasy fingerprint over the lens.

Spent last couple of hours making the scribing template for the door from 0.002" brass, think the result was worthwhile, hinges I'm going to make from something very thin I think and then CA them on.

Fritag, Definitely frustrating yet satisfying, The insulating tape trick I think is certainly the way to go for complex curves. Beer & short sessions are a must!

Looking good, good work on the no.3 engine, never tried painting checks, seems straight forward just needs planning with the masking I think. What are you going to do for decals?

Little more out of the way, RTV is still not fully set from Saturday but its getting there I'll give it a few more days! not sure what went wrong with it. Been scribing the fuselage today, have a lot to learn about this scribing lark, but found some good tips on BM, thought the simple shape fuselage of the Cherokee would make it a bit easier....nope, but learnt a few things though, tried using electrical tape as to get the lines on the top of the fuselage, seemed to work ok . Still have a long way to go if I ever going match Fritags superb scribing on his chipmunk. Lots of clean ups to do here and there still but will do them as I go along with rest of the assembly. I've painted the upper inside cabin white and window frames in preparation for casing the resin windows hopefully in a few days. Just a few pics, blue-tacked together with the test nose. Mark

Very nice, Have an old ESCI one in the stash, think its the same moulds.

A cheaper alternate to the H&S one is this, might not be as fine but for £7 with postage from the far east I cant complain, this is actually my second one as I damaged the previous one beyond repair by standing on the hose ripping it out while it was in the airbrush holder. I also use it for cleaning my airbrush to purge the brush of any paint or thinners rather than relaying on the venturi effect of the brush. Mark

Bit of progress over the weekend, I'm making RTV moulds to make a resin copy of the masters for vacuforming the windscreen and spats the intention is make female mould for them so going to cast copies of the masters to prevent trashing the real master in the process. The RTV has been setting for nearly 48 hours and is still not fully set, I'm suspecting I didn't put enough catalyst in as I forgot to tare the scale before pouring the RTV into the mixing beaker and had to guess. Anyone know the specific gravity of RTV? Hopefully it should eventually set but It was still tacky when I left for work at 4AM this morning. Ive made a decal sheet for the instrument panel from clear stock to go on the reverse of the panel so have printed it mirror image I've also had a few trial runs on making the resin filled side windows on the fuselage of another arrow kit, I taped a piece of this acetate to the outside and filled from the inside, few for practice sessions to go I think Wings are nearly done, spent Sunday scribing them filling sanding re-scribing. was getting very deep and wide rough scribe lines on areas that had filler e.g. undercarriage bays so those lines were filled back with thin CA and re-scribed with good results. A coat of Halfords rattle can plastic primer was then applied. still more work needed under the wings and walkway this evening. Thanks for looking Mark

Very welcome milktrip, found it very useful for making custom tools & templates as well as parts. Hoping to see some others make some home brew PE on here soon.