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The Buchka 242 Fake Racecar

Thanks guys!

The support structure is mainly there for thermal reasons. Plastic powder bed printers can keep the entire volume just below the melting point of the material and just add a small amount of heat with a laser to create a meltpool. This is infeasible in a metal printer. The laser has to be significantly more powerful to create the meltpool. This creates large thermal gradients that can either vaporize small unsupported features or simply cause the part to warp.
 
Ah that makes a lot of sense. I didn't even think about the energy required to fuse metal powder together...

What is the part dimension accuracy for a DMS part? Do they have inconsistencies from time to time with the cad model dims and actual printed part?
 
Ah that makes a lot of sense. I didn't even think about the energy required to fuse metal powder together...

What is the part dimension accuracy for a DMS part? Do they have inconsistencies from time to time with the cad model dims and actual printed part?

I'm not totally sure. It's better than you might think. Any critical surfaces get post machined anyway, so I don't worry too much about as-printed tolerances.

The torque tube we gutted ended up having a bent input shaft, so we picked up a new one along with replacement bearings.
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Got the adapter anodized and assembled with the release bearing. Everything seems to fit properly. Also got a chance to test the starter.
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Also getting pretty close on the hardpoint fixture. It's a CMM fixture plate stood up on 80-20 extrusion with 3D printed locating features. We got all the tabs laser cut to near-net shape, so they'll just a little bit of hand fitting before getting welded on.
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Made some progress on the turbo manifolds. The support material has been removed and the parts have been benched to prepare them for tumbling and shot peening. The areas where support material is attached is very rough and needs to be worked over manually. Getting here was about four hours of work.

They're still tarnished and covered in a thin layer of inconel powder. Once they come back from processing they'll be much brighter. After that the pieces can be post machined and welded together.

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Bananas!
I worked at Exotic Metals Forming two years ago, and they made a ton of stuff out of Inconel too.
Like ducting and exhaust nozzles for jet engines. Fun times!
But none of that DMLS stuff. Just lots of different forming techniques, and lots of heat treating!
 
Mega update:

Finished drilling and tapping the ABS sensor brackets doodads
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Also finished up some re-work and small bits on the Xtrac driveline parts. Since the gearbox was originally designed to bolt directly to a bellhousing there are no bearings or support features for a driveshaft yoke. The large plate sits in front of the gearbox and will hold a splined hub pilfered from a C6 corvette torque tube, perfect for the application.

I cocked up the tolerances on a couple of alignment dowel bores so I had to open them up a few thou
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These also recently popped out of the printer. After finish machining it will function as a cable operated reverse lockout. The Xtrac 295 was designed with a reverse gear but fitting it was optional to the indycar teams of the time. It didn't become a common configuration until later seasons when paddle shifting was permitted so the lockout was implemented in software. Since we're running a shift cable we needed a mechanical solution.
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The exhaust manifold parts came back from tumbling and shot peening. They look like really nice investment castings now and after a trip through the vapor blaster they get a really nice matte silver sheen. I machined all the head flanges flat and machining inconel suuuucks. The v-bands on the collectors will require some more fiddling around to clean up but I think we have a good plan for that.
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Spent a few days chipping away at the intake manifold. Metal printing is rad but don't let anyone trick you into thinking the parts come out of the machine anywhere near "done".

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Started by drilling the upper half of the plenum for some -6 ORB ports. I would normally do this type of operation in a mill but I had no good way of indicating the hole axes so I rolled the dice with the pistol drill. Had to visit the bathroom and check wipe a few times during the process. These holes will be capped with port plugs and are tool access points for bolting down the manifold.

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Butt pucker #2 for the day, face milling the throttle body flange. The plenum wall thickness is only 2mm so clamping it down without crushing anything is precarious. I decided to block it from moving at all four corners and I'm convinced this was the only reason it didn't fly off the table and hit me in the face.

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Blended the inside and the peaks of all the ribs with a bonded maroon scotchbrite disc to erase the traces of support material and layer artifacts. Then I drilled and tapped for the throttle body. Next up is glass bead blasting and a trip through the vapor hone to shine it up a bit.



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Chipping away at the intake manifold. I finish machined the head flanges and gave the lower half a test fit.

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Here you can see two of the internal fasteners that the port plugs in the top half will allow access to after the assembly is welded together.

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I've been putting off this job for a long time out of fear for screwing it up but I think it came out ok. The flange machining didn't end up perfect but its well within acceptable bounds.

Next up is to drill and tap a couple more holes, do a last round of blending and deburring, then media blasting, and welding. Really happy to finally see this part come together.

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Did the last bit of machining on this thing. Shown here is a Bosch Motorsport 4 bar MAP/temperature sensor that mounts directly to the plenum.

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The black parts on the upper plenum are blasting masks that we 3d printed from amazon's finest cheapest PLA.

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Karl and I spent a solid 6 hours today getting the parts to this stage. First step was some final hand blending on rough spots with 300 grit paper (layering artifacts, rough bands where the scan field of two lasers overlap, etc), then dry grit blast with aluminum oxide to even out the texture and soften all the hard edges, and ending with wet blasting in a vapor hone cabinet.

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Fuel cell fill plate/surge tank/pump hanger is all done now. The pumps are run of the mill bosch 044's. The surge tank will be fed by four small delphi lift pumps, one in each corner of the cell.

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Tapped all the sensor bosses in the manifold parts and working on a fixture to machine the v-bands. Machining the flanges flat sucked but tapping these holes sucks more. I completely wasted three brand new high quality NPT taps to thread 12 holes.

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Finished the fuel rails. Capped off the front ends and tapped the -6 boss ports for these dry break fittings.

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Pulled the frame off the build table for the first time and got a decent view of what it will look like at ride height-ish. It's way lower than either of us were expecting. Also took the opportunity to weigh the frame. It came in at ~400lbs as shown which is a bit heavier than I would have liked but there's not much to be done about it now.

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In preparation for suspension hardpoints we had to do some table surgery to flatten it out a bit more. Obviously a steel table is preferable for work like this but I think you can get 80% of the way there with wood if you're careful. In hindsight I think engineered lumber is the way to go for a table like this. LSL I-beams and studs are just way more dimensionally stable than regular doug fir.
 
It goes without saying, the ingenuity, fabrication, and craftsmanship skills here are on a completely different level. I can’t imagine what this machine is going to be like behind the wheel!

Great update!
 
It goes without saying, the ingenuity, fabrication, and craftsmanship skills here are on a completely different level. I can?t imagine what this machine is going to be like behind the wheel!

Great update!

Thanks! I can't imagine it either, if my mind wanders in that direction it reminds me of how much work is left and I get depressed. Just eating this elephant one bite at a time.
 
Thanks! I can't imagine it either, if my mind wanders in that direction it reminds me of how much work is left and I get depressed. Just eating this elephant one bite at a time.

You can borrow my Miata again if you need to get behind the wheel of a purebred track beast. I'm sure the driving experience will be identical to the FRC.

I need to make it out to the shop more often - you guys are killing it. Also I hadn't realized how low this thing will be, but it makes sense. Slammed AF.
 
Do you treat the wood build table as a rigid fixture or is primarily to support the chassis and act as a reference plane? I've thought about making a welding table out of engineered lumber, topped with 12 gauge steel because it seems easier to make flat without the warpage that comes with welding.
 
You can borrow my Miata again if you need to get behind the wheel of a purebred track beast. I'm sure the driving experience will be identical to the FRC.

I need to make it out to the shop more often - you guys are killing it. Also I hadn't realized how low this thing will be, but it makes sense. Slammed AF.

I would be honored to try and ruin your track beast again.

Bet it gets air conditioning, cut wool pile carpets, and leather padded touch points on the spaceframe too.

Don't forget the TV's, champagne chiller, and sno-cone maker.

Do you treat the wood build table as a rigid fixture or is primarily to support the chassis and act as a reference plane? I've thought about making a welding table out of engineered lumber, topped with 12 gauge steel because it seems easier to make flat without the warpage that comes with welding.

It's mostly the latter. The table does have more compliance than I would like so as long as you're cognizant of how much weight you're putting on there it should stay flat enough. This table was always a temporary structure and we're nearing the end of its useful life. It'll get scrapped soon and the chassis will sit on jack stands for the remainder of the build.

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Control arm fixture is ready for action. Each counter-bored pocket gets a brass spacer slug that presses into a uniball weld cup, those will then get connected with 4130 tubing. The two rectangular plates in this pic suit the four left hand arms, there's another pair of mirrored plates for the right hand arms.

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Got the first corner's worth of suspension brackets tacked in place. Getting the fixture lined up took a few hours of adjusting and careful measuring. This first corner was pretty time consuming since I was essentially establishing the datum for the other three corners, the remaining tabs should progress pretty quickly. Having the mounting tabs laser cut to near net shape was also a big time saver.

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The steering rack set the fore-aft position of the suspension mounting locations so I took the opportunity to finish up the attachments for it as well. The machined clamp collars that go on the rack were done a while ago so all I had to do here was transfer punch, drill the front bulkhead, and weld in four pieces of tubing the rack bolts to.
 
Got a big box of 3x.035" inconel 625 tubing for the exhaust. Going into this I was intending to make it all stainless but I made a throw away phone call to Woolf Aircraft to see if they had any surplus and I ended up getting everything we needed in inco for 321 stainless prices. Some of the bends are a little wrinkled but it doesn't really matter to me.
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Exhaust manifolds came back from welding. Couldn't be more satisfied with how the welding came out, the guy who did the work is an ace with the TIG. All the joints are welded in one pass and look phenomenal.
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Fit checked the blurbos and everything is looking really good so far. All the clearances are as expected, really excited to build the exhaust and get some plumbing on these things.
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I can certainly understand why you made the comments elsewhere that this is a "motor swap only a mother could love". I'm glad you guys are taking it on.

I've been interested in the additive processes you've used, and chatted about it with some with buddies at work (I'm in manufacturing). I'm curious if you've taken that route out of design requirements, equipment access, a desire to experiment, or some combination of all? Some of those pieces represent some pretty significant amount of machine time! We have started getting more involved with additive inconel processes with some heat exchangers.
 
I can certainly understand why you made the comments elsewhere that this is a "motor swap only a mother could love". I'm glad you guys are taking it on.

I've been interested in the additive processes you've used, and chatted about it with some with buddies at work (I'm in manufacturing). I'm curious if you've taken that route out of design requirements, equipment access, a desire to experiment, or some combination of all? Some of those pieces represent some pretty significant amount of machine time! We have started getting more involved with additive inconel processes with some heat exchangers.

Thanks dude. We're all in on the B8444s sunk cost fallacy at this point.

The additive stuff was initially driven by machine access. We've been fortunate enough to build a relationship with a local shop that does really high end work and the owners are sympathetic to the FRC cause. The headers and intake manifold were definitely tough packaging problems that were a bit easier to solve with the "free" complexity of DMLS. Another big part was the design challenge, I'm heavily accustomed to designing 3+2 machined parts so I had to unlearn a lot of that mindset when designing for printing. I like solving problems and this was a big nut to crack. You really have to think of the end-to-end process in the design phase so you don't paint yourself into a corner.

Feel free to PM me if you want to chat more about it. Additive is not a replacement for machining but it can be extremely cost effective in the right application.

What are the advantages of an inconel exhaust?

Over 321 stainless, not a whole lot. Post-turbine EGT is low enough that it's not really necessary but it will make the exhaust lighter and more durable over time. Especially when you start applying thermal barrier coatings to the outside of the tube that drive the material temperature up.
 
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