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Had an old thread that wasn't very well named, or focused. Trying to do a new one that's better named and more focused! We'll see. (https://forums.somethingawful.com/showthread.php?threadid=3762097) OK, so this whole thing started out with wanting to do a sustainable roadrace car - IE I'm tired of fixing unibodies. Also wanted competitive class and ... frankly I love 1st gen RX-7s and rotaries and stuff. This all led me to SCCA GT-3, where you can run a full tube chassis, with a given wheel size (15x7 but Hoosier has 10 inch wide tires for that) limited downforce and in the 240-260hp range. Various engine spec lines but relevant ones are streetport 13B with unrestricted intake, bridgeport with 42mm per-cylinder venturis, or peripheral port with a single 38mm venturi before a plenum. This went through various iterations which I'll talk about in the next post. Basically this is going to focus on this thing which is still in the design stage; I'm hoping to come up with a bunch of improvements over conventional cars but at the very least it's fun to build and design.
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Nov 5, 2020 21:41
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OK, where did all this start?    So square tube, based on Wide 5, and so on. Very chonky though and not packing optimized at all. I think it was over 400 pounds which ... isn't great. I was also thinking GT-2 at that point; it's not a great idea because the cost goes up significantly and it would be a major quixote thing trying to chase down what's currently competitive in that class.    Converted everything over to round tube and lost a bunch of weight. This is also when I'm starting to do FEA on revisions.    Working through details including checking a cockpit view  Got a commercially available 3d model of the body - my halfassed one was pretty close! About now is when I'm moving to GT-3 specs.    Narrowed a bunch of stuff down, more revisions... a lot of FEA checking going on in the background.   And that's the last major revision. Another one's in progress though to fit stuff around the revised rear suspension. Next post, custom designed parts!
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Nov 5, 2020 21:54
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OK, so, all the aftermarket stuff for live axles and quick changes and the like are based off of 4x4.5 which was fine in the 90s but sucks now. Basically the only good/light/cheap 15x7 wheels you can get are in 4x100 for Miatas and Civics and stuff. So clearly custom hubs are needed.    First iteration... so basically Wide 5 bearings and cambered snout because rear camber on a live axle is :chefkiss: Sphere on the end of the axle in the cutaway is actually a crown spline to allow angular misalignment.   This is looking better, but the bearings are basically unavailable which is a PITA. "Basically unavailable" for a loving wheel bearing isn't acceptable.  Final version, with brake and wheel stuff thrown in. Back to Wide 5 bearings but everything moved around to fit well!
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Nov 5, 2020 22:01
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Engine stuff... well, the engine bay is tight. And god knows broadening powerband would be nice. So first try at a custom short-runner-for-13B-with-12A-irons intake manifold. And then I got an idea.  So this is copied from a bunch of different things, more directly Yamaha's YCCI intake setup. The velocity stacks are on 4-bar linkages driven by a servo that kicks them up at high RPM. Basically either add 75mm to the intake tract or don't. A few revisions and...   So it all works in CAD; I was printing out a test version but my printer took a crap. Will fix shortly. Now the angle on the manifold was wrong to fit in the chassis so let's fix that.   Now while I was dicking with stuff I went and designed a bellhousing to mate a 13B to a Jerico pattern trans with a Tilton SBC small diameter flywheel. Like so.  And playing with geometry went and banged out a Mumford Link because it lets me do things with the roll center I want.  Next post will be parts coming in.
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Nov 5, 2020 22:07
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So parts coming in, in vaguely chronological order.   Not directly a race car part, but Stuska water brake engine dyno I got here with the help of NitroSpazzz! Still WIP on that but it'll get there.     Trans Am spec centerlock spindle and BBS magnesium wheel center. Intended to reverse engineer but ... it's a loooooot of extra time and effort for no real performance advantage. Cool oh hell yes, but not necessary.  Dry sump tank! I think 3 gallon, but nice and tall and skinny.  Chassis table!     Tilton small diameter SBC flywheel fit to modified RX-8 counterweight.    Quick change rear end  Nice pimpy master cylinders.
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Nov 5, 2020 22:16
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Yeah, it was pointed out to me that the old thread title was... uh... underwhelming. People who followed it followed it but I figured there were probably people who'd be interested who weren't following. So. Text post for a bit. Let's talk about suspension design and philosophy. I've read a _lot_ about suspension design over the last 20 years. The latest version I'm following a lot of guidelines Neil Roberts laid out in Think Fast. His basic treatise is that the main job of everything is not to do anything unexpected and have any weird handling interactions. Some consequences of this are the front roll center at ground level and rear roll center about 2 inches above, long side view swing arm lengths in the front, and most importantly consistent roll center motion with the chassis. See, roll center is an idealization of where force is applied to things, but it works well enough... the moment between roll center and CG determines moment generated and relative moment/stiffness between front and rear determines, for example, handling balance. So if you have the roll center radically move you can have handling balance radically change under acceleration or braking. NFG. Furthermore I figure that a lot of things should be adjustable without affecting other things. I'm in the process of designing front uprights right now, but things like... lower pivot movable vertically by shims to change roll center if desired. Upper pivot connected to the upright via shims (maybe copying Porsche LCA shims for this) so that camber can be changed repeatably without affecting toe or even kingpin inclination. And upper link on the rear suspension (going 3 link) is adjustable vertically to affect anti-squat.  This was a lot of iterations to get here. If everything is made to print, roll center moves with the chassis within a couple thou for the whole suspension travel.  Surprisingly this was only a couple iterations. Roll center moves with chassis within a couple hundredths for most of the suspension travel... a chassis mounted Watts link would do better there, but virtual roll center trumps that. And no, the rear chassis hasn't been altered with Mumford mount points yet. The more basic stuff... I got some guidance from people who've been running the class about what kind of wheel rates the tires in the class like, and back calculated that into ride frequencies so there's targets. Shocks will probably be basic Penskes to start or something - I have weird ideas about trying to make a homebrew controller for off the shelf (Camaro application or something) magneride shocks but there's enough to build first.
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Nov 6, 2020 01:03
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I mean the new thread is all of "today" old. Sway bars you can get away with all sorts of weird locations, and for illustration look up Subarus. What is ideal is the same sort of stuff as is ideal for shocks, having it so that the ratio of wheel travel to sway bar end travel is fairly constant over wheel travel... so links to suspension arms not angled too much, stuff like that... but there's all sorts of ways you can do things where they still work fine and in practice, OEMs seem to mostly put it wherever there's room.
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Nov 6, 2020 01:25
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Well, this is why I check stuff in CAD. Long story short the lovely Mumford link... doesn't fit around the QC axle. Will try to figure it out this weekend, it's far from the first time I have to modify designs to fit.
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Nov 7, 2020 15:30
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Oh hooooooooly poo poo, I came up with a new revision for rear suspension location that uses a linkage that, as far as I know, has never been used for this before, does everything the Mumford does, and clears everything. Pictures to follow after I rebuild it in a "real" version instead of a mocked up version.
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Nov 9, 2020 00:14
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 So it works! It's the same idea as the Mumford link with a virtual pivot point, but with the linkage underslung and pivoting in different planes. This means that I have all the advantages but it's actually possible to package.
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Nov 9, 2020 21:28
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More clarity on how it moves. Single wheel bump:  3 inches up or down from rest position  
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Nov 9, 2020 21:43
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Darchangel posted:So, if I understand right, it's fixed to the chassis at the two bronze bushings that are otherwise unoccupied in the model? Correct - it's constrained in the CAD model as if there were pivots there because while I was figuring stuff out I didn't want to go modify the chassis for it. The Mumford link a few posts back was similarly constrained. The difference is the Mumford had parts going through the QC axle with everything at static ride height, whereas the new thing can handle about 3 inches of compression before something hits, which is more than a purpose built roadrace car will ever see. Fundamentally it works the same way though.
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Nov 10, 2020 00:11
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I mean, it's basically just formula car bellcranks but upside-down and with a linkage instead of springs. Or the linkage is exactly the "roll" element of the Mercedes Project One suspension - if you flipped it upside-down and used a link instead of a coilover. What's novel is just using it for lateral location of a live axle. The thing I like that's not obvious is that it was actually a lot easier to analyze than the Mumford link. The axle-to-bellcrank pivot is 4 inches from the bellcrank-to-chassis pivot because it's a number I pulled out of thin air, and it worked the first time I tried it, and the bellcrank-to-bellcrank pivot location doesn't matter as long as they're mirrored across the chassis pivot. But the cool part of how all this moves is that roll center migration can be tuned by changing the chassis pivot angle - like, if the bellcranks were horizontal the chassis going down (axle going up relative to chassis) would make the roll center move farther away from CG... I could tune it at some other angles to make it move closer to CG under bump. Instead it's at an angle that keeps it almost perfectly the same distance away from CG under bump at any axle location. None of those force vectors matter for using this sort of linkage for springs the way formula cars do, but they totally do for axle location.
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Nov 10, 2020 14:02
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 Maybe a little more clear now what the end goal is.
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Nov 12, 2020 06:49
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kastein posted:Maybe I missed this but I'm curious why you're using a live axle in a full custom chassis like this for track use. I thought most track cars had IRS? I mean as a hillbilly truck builder I love SRA builds, don't get me wrong, I just thought they were passe on pavement builds. Boils down to a couple things. First and importantly, per class, you're not allowed to put IRS in something that didn't come with it and I like 1st gen RX-7s. Secondly, there's a weight penalty for IRS. So basically nobody in the class goes IRS, even things where the body looks like 3rd gen RX-7s or Nissan stuff. But the rules side aside... with as smooth as race tracks are single wheel bumps aren't really an issue, unsprung weight isn't too bad since it's a vey light axle, the ends will be cambered enough for radials to work properly, and live axles have advantages with putting power to the ground efficiently. Normally it's a pain in the rear end to get the roll center down as far as you might like but the Mumford link solves that too.
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Nov 13, 2020 02:14
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Various supporting stuff going on; also holidays and jobhunting and stuff. Whatever. Decided to start playing with the AEM dash designer software.  Standard "race" page - obviously no tach, that's handled by shift lights. Intent is that really, anything on the LCD either lights up a color that can be seen in peripheral vision, or isn't that important. I personally like numbers for a "I'm glancing at this every so often or under pace car conditions"; input appreciated. Most of the layout concepts are cribbed from various IMSA GTLM class cars; probably closest to the Corvette. Oh yeah, the TPMS box with temperatures is an "I'd like this eventually"; the sensors aren't hugely expensive but aren't necessary to get on track.  Alarm page for fun - this would be switched to at "shut the car down" levels of badness, though the text at the bottom is just the generic example warning for setup.
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Nov 30, 2020 19:05
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honda whisperer posted:Agreed the numbers are useless while pushing it but can be handy. I'm trying to figure out a good way, within the context of the software, to do that. The delta in the lower left is PLT; thinking green/yellow background on that because I don't really want to use red for anything other than immediate action (on this screen: "you locked the tires" on the grip bars, or "you way overcooked these things" on the tire temp squares) Also thinking of something useful to do with the graph in the lower right; I stuck an XvY acceleration graph there for now, but that's not really necessary.
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Nov 30, 2020 19:49
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Not important in the grand scheme of things but... startup screen idea!
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Dec 19, 2020 00:26
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 So, the for-real this time final revision. But boy that's a lot of tubes to notch. Looking around I remembered this guy's build: https://imgur.com/a/l7HpO Which... having now dicked with CNC router stuff seems honestly pretty quick and easy to bang out. And would save me so much time. Going to have to get stuff together for that. Other things are taking some time; toy box for the kid for example. I'll post pics of that when it's done too even if it's not really related.
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Jan 2, 2021 17:01
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Cages is a whole bunch of trouble though, with fitting within unibody cars. On the other hand, I've been meaning to do a suspension-and-FEA-optimized Locost, and I could always just make single donor 7 clones for far less than Westfield...
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Jan 2, 2021 18:03
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McTinkerson posted:As someone who's been dreaming of a turbo rotary locost for close to twenty years, I fully support this plan. I mean, it was going to be Miata donor but I mean, I'm me so.
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Jan 2, 2021 18:22
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Well in advance of needing it but I wanted something that spat out CAN streams for testing and it's just too cool... ordered https://trailbrake.com/tire-tpms/ the other day. Not as high of frequency read out as some of the motorsport ones, but something like 15x less expensive than the next least expensive easily-loggable one I was able to find...
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Feb 12, 2021 18:05
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It's my intent to get to there as soon as practically affordable.
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Feb 12, 2021 19:59
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 Proof of concept... so had an FC BBS wheel kicking around, so been working on a work flow to get 3d scans into solidworks. And, well, here we are! No I was not very careful about the spokes. I'm not going to dick with it too far but if you look at the profile stuff, I got it to spit out something I can convert to a 3d sketch and blah blah blah, dimensionally accurate wheel inside barrel to design brake fitment around.
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Feb 27, 2021 22:04
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 And this came! Now to scan
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Mar 6, 2021 18:56
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If I were being careful, I'd incorporate a few different scans to make sure I got al the features so I could reverse engineer properly. Instead I got impatient. Again sort of a rough scan but I got the inside and outside surfaces  And there's the moneyshot!
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Mar 7, 2021 06:14
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NitroSpazzz posted:I might have missed it but what are you using to scan those in? I'm using an Asus Xtion which is one of the Xbox 360 Kinect style sensors, and a software package called Recfusion. There may be better sensors now (Recfusion supports a lot of the Intel Realsense sensors) but why not work with what I have?
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Mar 7, 2021 16:04
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honda whisperer posted:How accurate do you think it is or could be with enough fiddling? Well, that's a really good question. Most honest answer is I have no idea yet. I did a very basic tape measure sanity check and it seemed dead on but, well, tape measure on one dimension. I'm going to try some dimensional test stuff this week I think; getting potentially usable results from this setup is pretty new to me and I just wanted to start off by trying some cooler stuff because OMG it worked and it's cool. 
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Mar 7, 2021 19:30
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 Not an in-depth examination of the question but I mean, the data's all there. 
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Mar 7, 2021 22:41
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Rectal Placenta posted:Are you going to go try and fit splines over all of those points? I use Solidworks daily and that picture made me shudder. Oh heck no. So once I get a good clean scan, my intent is to use the splined 3d scan automatically made at that section (what's in those images) as a guide for a manually created 2d sketch; same sort of way that you'd use a 2d scanned image as a guide. If I had a good point cloud of all sides, I could do sections at various locations to repeat that... like... the section I created is, once turned into a good 2d sketch, revolved, another one perpendicular to that could give guide curves for the spokes and stuff, etc. Or, honestly, looking at that nasty spline and seeing it doesn't interfere with stuff honestly gets me the actual answer I need.
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Mar 8, 2021 15:55
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Oh yeah - for this yeah, what I have looks like it fit my needs already. But there's some other stuff I want to do more complete reverse engineering on to produce patterns for cast parts.
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Mar 8, 2021 19:53
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 La de dah, what have we here?
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Mar 21, 2021 04:38
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I mean yes it'll brap but will it brap enough? Mazdatrix Turbo 2 half bridge pattern template  Scribed onto the RB j-bridge template; notice the later closing. I figure the half bridge template is a bit more radical on the closing since it's the EFI irons where the primary (center) ports are smaller... so I'm pretty sure 12A irons can go that big if you're careful, ergo, gently caress it, moar brap.
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Mar 21, 2021 23:13
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The big question will be "can I go that big without hitting water or breaking side seals" I'm sure it'll be fine.
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Mar 22, 2021 04:05
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Aeka 2.0 posted:I'm going 4mm taller than the pineapple template just fine. I'm using 12A irons though.  To the template worked; not a clean job, just doing a lot of quick metal removal to see if I hit water. Will have to remember to bring a degree wheel and see where that closing edge is now in degrees; I think it's probably enough.
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Mar 22, 2021 22:36
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One of the 12A variants has the biggest port runners on the primaries of anything; no injectors among other things. S4 and S5 T2 end irons actually have the most available meat; IIRC the basic casting was shared with the NA irons with the 6 ports. Even not opened up, I think the secondary runners are quite a bit bigger. I'll take a turbo iron over to the shop tomorrow for a comparison pic. In a world where I was starting from scratch I'd go T2 irons, mill o-ring grooves into a 12A center iron and use T2 housings. But in the world I'm in, I have at least 3 engines worth of 12A irons and GSL-SE rotor housings.
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Mar 23, 2021 01:39
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Port talk! J-bridge roughly carved onto 12A iron; you can kinda see where the main port is kinda feathered in and see an idea where the water jacket is on the other side. More iron might be able to come out, I'll check, but you get the idea.  Bridge template I used for the main port on the J-bridge 12A stuff laid against a streetported T2 iron I got a hold of that was damaged. You can see this has already been ported about to that template, but can kind of get an idea how the port is a lot more vertical near the closing edge.  You can see how from that closing edge you can go basically straight down without risk of hitting water.  From the manifold side - the 12A is on the right and has been lightly worked on from this view - you can see how much bigger the runner is on the 13B T2 iron, though I think there's meat enough to get there.  Template against dead 12A center iron, which actually close about the same place as 12A end irons. You can get an idea how much bigger the port is going to be, timing-wise. I think for what I'm doing 12A irons will be fine, and god knows I have enough of them.
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Mar 24, 2021 23:40
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OK. I figured out how to get a few things figured out which means once I put some time in I can get my bodywork designed up in CAD. Sitting and chewing it over, I have a hypothesis that a CNC'd female mold would be easier to work with than "make plug, pull female molds" especially since I can engineer in parting features in the mold. There's a few different ways to do it, so I need a test piece to figure out what works. Enter test piece. Not that I need NACA ducts desperately or anything but it's cool shaped, kinda complicated but not too bad, needs a 2 part mold, and not too big.  Female cavity generated in CAD  Sliced into 2 inch sections, with alignment features for rods and separated where it'll have to in order for the mold to come apart. First hypothesis on construction is "CNC rout out of pink styrofoam"; so cut slices on the CNC router, glue together, and gelcoat the tooling surfaces. Maybe lay up glass reinforcement too; the whole point of this is figuring out what's necessary. Also to see if the whole mess will stand up to 250F where the prepreg cures at.
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Apr 1, 2021 19:33
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Those holes towards the bottom of the sliced mold are intended to have piece of conduit or rod or something slipped into them for locating. One of the other material hypotheses is gelcoated MDF but for something the size of a car fender that's going to end up heavier and costlier than styrofoam.
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Apr 1, 2021 21:59
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There's a lot of specialized stuff that would be appropriate for this that wouldn't be relevant to stuff sized for body panels - I've done wet layup stuff but haven't worked with prepreg so wanted a place to learn and try some stuff. If I can't get a good vacuum bag seal on this part, I might just leave off the back half of the mold for proof of concept. It's just more interesting than "oh, here's a carbon fiber square" or whatever. Doing a bit of poking around, I'm finding surplus renshape board cut to size advertised at $0.20/in3 which is ... kind of a lot. Making "just use a shitload of MDF" seem pretty attractive.
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Apr 1, 2021 23:31
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