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About Twobad

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    United Kingdom
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    Any type of model really. I go through phases, but at heart I'm an aircraft man.

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  1. I've posted this elsewhere, but it is pertinent to the original question. I started off getting prints done at a commercial print bureau, and eventually decided that I was spending enough to invest in my own 3D printer. I went for a Phrozen Sonic Mini 4k. The pictures going clockwise from top left are: Phrozen 4k at 35um, print bureau at 50um, cheapskate's stamp, another 35um print cleaned too vigorously resulting in some detail being brushed off. The prints are simply text raised vertically and have no slanting components which would suffer from Z-axis resolution. The same STL has been used for the prints.
  2. I'm self taught at the CAD thing, but have always drawn the models full size, either in inches or mm depending on the subject and source material. I do export the STLs at the size I intend to print at though, rather than scale within the slicing software. I find that specific models are required for specific scales anyway, particularly when going smaller. Wall thicknesses are the big bugbear there. What will print at 1:8 will not always work at 1:32. Going in the opposite direction often means that the model would be better broken up into smaller sections for ease of printing, and hollowed out too. Hence, I end up with specific models tailored to each scale, all drawn full scale...
  3. I tend to use a cellulose based etch primer. It's a bit aggressive really but it does cling to most things, even brass.
  4. If you are into fantasy figures then Hero Forge is a must. All are paid for, but they now also offer an STL download option. The site is worth a play with just for fun. https://www.heroforge.com/
  5. There's a real buzz from your first CAD print. Well done. I'm impressed.
  6. If you want detail you need to go for a LCD resin printer, and I'd recommend a "4k" version that can do 35um resolution. My experience is limited as I have only owned 2 3D printers so far. The first was a Da Vinci Mini filament printer. OK as far as it went, but was definitely entry point and old technology really. Not recommended for modellers. My latest printer is a Phrozen Sonic Mini 4K. It's good (35um X-Y resolution) and can do everything that they claim, but printing with it appears to be a bit of a black art. Some people hit the sweet spot from day one and produce print after print successfully. I have gradually homed in on the sweet spot but still suffer random failures of prints. I would estimate I get completely successful prints 60% of the time, and useable prints 80%. I'm using Phrozen's Aqua Grey 4K resin and this is a sample of an good print: And for an indication of the detail you can expect look at the text on this print. Oh, and I've found 3D Jake great to deal with, even post Brexit. They are in Germany but I've had no problems receiving stuff from them. https://www.3djake.uk/
  7. There is a very significant market for Role Playing Game figures and fantasy figures. That is one of the big areas for 3D model sales. However the market, while not mature, is well established and there are some serious players in it. As an example Hero Forge are gaining a good reputation. https://www.heroforge.com/
  8. I've been using Phrozen's Aqua Grey 4k which has given me decent results on their Phrozen Sonic Mini 4k, which prints at 35um resolution. From top left going clockwise: 35um print using Phrozen Aqua Grey 4k on my printer. 50um print from a professional print bureau. Miser's stamp. 35um print cleaned too vigorously before being cured. Bits of fine detail broken off. Another print sample from my system and resin.
  9. A nice model of a lovely little aircraft I'd never even heard of before. Love the Small stuff engine.
  10. I can't claim the credit for that. The print files were prepared using some posh professional software and it did it automatically. At home I use the free Chitubox software which lacks such refinement. There's a Pro version, but it's £120/pa. My home prints look like this.
  11. I had a load of problems with entrapped bubbles in my moulds and resin casts until I bit the bullet and bought a vacuum chamber and pressure tank. They make things so much easier. Basic resin casting is pretty run-of-the-mill for me now, but the cold casting stuff still tests me. You're constantly pushing the boundary of maximising metal content, but trying to keep the mix runny enough to flow in the moulds. Thin webs and small deep recesses need a helping hand with cocktail sticks. Even then I find it almost inevitable that there are tiny bubbles lurking just below the surface on sharp corners. Rubbing with Scotch Brite inevitable uncovers them and there is a need to mix up a tiny batch of cold cast to go around and fill them afterwards. I use a 7 minute pot-life resin for that to give me a little more time to mess about. The repairs are pretty much invisible after filing back flush though.
  12. Sort of both. I've been making models for almost 50 years, but I became medically retired over a decade ago and am housebound now. So I spend a lot of my time model making and designing things in CAD. I love trying new techniques too, so have gradually increased my repertoire over the years.
  13. I really like the way you have displayed that. I'm a quiet fan of the subject too. An unusual aircraft that I've always felt should have done better, the rather public crash stymied it at a crucial time. I work with a chap who was part of the design team for it. One problem he remarked on was that the cockpit suffered quite badly from internal reflections during landing at night. Just at the crucial moment the pilot suddenly couldn't see out properly. He went up on a test flight to experience the problem and said it was fleeting, but quite alarming.
  14. Yeah, I can do a quick precis here. There's a lot of info on my blog, but that would be a bit of a read for many. The basic design is thrashed out in CAD. I still use AutoCAD because I've got a fair bit of experience in it, but were I starting again I'd use Fusion 360. Autodesk do 1 year free licences for non-professional users. AutoCAD allows you to insert pictures into the work space and I usually start by obtaining various drawings of the engine I want to model. These are then scaled to full size and used to trace out the shapes required. Which leads to something like this. I then print that out on my home 3D printer. I have a Phrozen Sonic Mini4K, the 4K meaning that is has a 35um resolution. 3D printing is excellent when it works, which isn't all the time! It's a bit of a black art and I'd estimate about 60% of my prints work, the rest end up in the bin. In fact it feels sometimes like the main output of 3D printing , and resin casting for that matter, is alcohol soaked paper towels. For reference, from top left: 35um 3D print, 50um print, cheapskate's postage stamp, 35um cleaned too vigorously before final curing. Some of the detail has been rubbed off. How the prints emerge from the cleaning tank. The support structures are there to hold the pieces while they are being printed. The print comes out upside down hanging from a build plate immersed in the print resin. A UV light shines through an LCD array and transparent bottom of the resin tank and solidifies the resin in contact with the build plate. Then the build plate is withdrawn slightly and the next layer exposed, and so on. The prints in the photo above probably took about 4 or 5 hours to produce. Larger items like the cylinder block take about 7-8hrs. Parts are printed at an angle as it tends to hide the transitions between layers, especially on flat or nearly flat surfaces. Then it's remove the supports and make silicone moulds from the cleaned up masters. I've tried several types of silicone and mainly use EasyComposites AS40 Addition Cure Silicone RTV. It is pretty thick stuff to pour and impossible to mix without getting a lot of entrapped air, but the big bubbles float to the surface quite quickly and the tiny ones seem to be absorbed during the curing process. I like the stuff because it is transparent so it's possible to see if any bubbles are trapped against the mould master. If there are (and there usually are) then you can help them out with a cocktail stick. You've got about 30 or 40 minutes to do that before the RTV starts to become too thick to play with. I do however, use a degassing vacuum chamber to pull the really large bubbles out quickly before pouring. Dedicated chambers are not cheap (£500+), but if you look around there are much cheaper ones about. You can also help to get rid of air by pouring the silicone from high up enough that it forms a very thin stream on the way into the mould. Mould curing in progress. I use addition cure RTV (also known as platinum cure) because it has very low shrinkage (~0.1%). You can get condensation cure RTVs that are cheaper but they have 3 or 4 times the shrinkage which is enough to cause fitting problems for me. After the moulds have cured (24hrs+) they are ready to use. I use a pressure chamber for my resin casting to crush down any residual bubbles entrapped in the casting resin. This is particularly important when cold casting as the mixture can be quite gloopy. The chamber I have is actually a converted paint spraying vessel. ( http://airtools24.com/pressure_tank_pt8,3,21206,27331 ). I also happened to have a spare air compressor with an 8Bar, 9L tank. That fully pressurized and vented into the pressure pot gives me an almost ideal casting pressure of around 57psi. Being able to charge up the compressor tank before hand also means that it only takes seconds to pressurize the casting vessel, which is useful as the casting resin I use has a 3 minute pot life. The casting resin I use is Xencast P2 Fast Cast, primarily because it is err.. fast. 3 min pot life and demould after about 30 mins. It doesn't need degassing either. To cold cast with this I mix in 60-65% powdered aluminium by weight. In fact I put the aluminium in the mixing pot first, then dig a hole for each part of the resin. Then mix the whole lot up quickly, pour in the mould and then pressurize for 30 mins. More powder in the resin makes it thicker obviously, and I've found that 60-65% leaves it thin enough to flow, but have a good metallic effect. You will find that even with a 3 min pot life the powdered metal starts to settle in the resin and the bottom faces of the moulded part will have a noticeably more metallic finish than the tops, so position your part with this in mind. Brass is especially bad for settling out. I use Lego bricks to make my mould bunds/setups, and also use them to support the moulds during casting to help keep things dimensionally accurate. I use a small piece of plywood to create a lip around the mould to stop resin pouring down the sides. Everything is done on a sheet of glass to keep things level and Pritt Stick used to secure the parts and Lego bricks to the glass. Before pouring the resin mix into the mould dust it liberally with powdered metal to further improve the surface finish. Et voila! The finish is a matt grey fresh from the mould, which has its own attractions. To bring out the full metallic look a quick, and delicate, polish with some fine Scotch Brite is required. I've also found that the handling of the parts during the build process burnishes them up quite nicely and dampens down the fine scratches left by the Scotch Brite. Metal polishes do improve things a bit, but not as much as you'd hope. Astute readers will by now have noticed that these castings are for a Wolseley Viper which is in the build pipeline and may appear here at some point. You can't get a truly polished finish on a cold cast part, but you can get quite a satisfactory metal look. Good enough for people to be surprised how light they are as they expect something heavier when they handle them. it is real metal though and will tarnish. I tend to polish the parts with a wax to try and delay this. I use quite a lot of photoetching to make parts too because I'm not very good at filing things out accurately. Rather than type out a great long speil on that I'll refer you to a post I did some time ago on my blog: Come And See My Etchings Upstairs. The results that you can get from home etching are quite surprising though. This becomes... This... The artwork for the photoetch can also be used to make your own custom decals, which is what I did for the nameplate on the nose of the engine. That was made from some sheet brass with a decal on it. The decals themselves are simply printed out on decal paper using my inkjet printer. Then airbrushed with clear lacquer. When dry they can be used like normal decals. The reason for the decal. My photoetching process isn't good enough for very small details. The top is etched. The bottom printed on an inkjet at 300dpi. I also do a fair bit of DIY plating with nickel, bright nickel and copper, but I'll leave that for now, unless people are interested in it.
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