General fabrication thread

[Strych9]

I've been doing motorsports fab for quite a while now. My background is in IMSA GTP (BMW Team RLL), NASCAR, SCORE, INDY, as well as specialty welding, pipe welding, and pipefitting. This thread is basically just a place where I can come to contribute what I know about motorsports fab.

I'd like to not discuss welding basics here because that typically dilutes the fabrication process (welding is just a tool at that point), but some of it is inevitable with different alloys.

Whatever you've got, let's talk about it. Suspension components, exhaust, roll cages, intakes, composites, plastics, etc.

Sponsored

 

[rottmore]

https://www.supramkv.com/threads/6-port-supra-b58-big-turbo-options.29770/

 

[Strych9]

https://www.supramkv.com/threads/6-port-supra-b58-big-turbo-options.29770/

Do we need to dive into developing a top mount header? I sure af don't mind spilling the beans lol.

Map the flanges out in CAD (FreeCAD and a quick 2D tutorial can have you spitting files out in a few hours), have them laser cut, measure for a jig, do a lil math, buy the tube and the 90s, then go full on into "Lego minus instructions" method until you have a base model, double check the math, refine it, plan the welds, weld it up. Without a 5k word reply, those are the basic steps. Every one of those is a skill.

316 Stainless is the absolute go to until you're into big budget stuff where you can afford inconel. I personally prefer sch10 pipe or .095" wall tube for a stainless turbo header.

I don't mind prototyping a header, but I will not be making a production run of them. If someone will write the check and bring a donor, I'll do the work and hand the design off.

 

[Strych9]

Would any of you be interested in the process for designing and fabbing a front and rear strut tower brace?

 

[Thraxbert]

I'm a shit welder, but wouldn't mind following along.

 

[razorlab]

People really took you up on your offer, eh?

 

[Strych9]

I haven't forgotten about this thread, I just ended up with 3 fab jobs and didn't have a day off until Christmas Eve.

I'm the manager over the casting mold repair shop at my primary job, manager of chassis development and the fab shop foreman at the second, and I was handling a transfer of the old desert racing team to the new owners for a few months. I didn't want to even think about fabrication, much less get online and talk about it.

Now that I'm freed up, I've got a few projects back on the table.

The first is adapting a downpipe and my exhaust to 3.5". The second is actually finishing my rear strut tower brace (I haven't had a high frequency machine at any of those 3 places in months). The third is that I got a pretty good 3D scanner and I MAY get into laying some CF parts again since I can 3D print molds instead of making plugs.

I'll make a post for each of these just for the nature of the thread itself. I'll also update all of it for whenever I get around to actually doing them. We have a Barrett Jackson built at the hot rod shop that has to be loaded up by the end of next month so I doubt much will happen until then.

 

[razorlab]

The second is actually finishing my rear strut tower brace

What rear strut tower? There isn't one.

Also FYI, the Wagner DP is 3.5", and fits to OEM exhaust with adapter.

 

[Strych9]

Fabbing a downpipe is pretty straightforward.

You can buy the turbo flange online (idr where, but it's like $105 with the gasket). I could machine it, but the hassle of machining it and getting the billet would be more than just buying it. After the flange, I'd make everything out of .080" wall.

Next is the first bend. That's a short radius 4.5" that looks to be around 45°, but I'd buy a 90 and cut it down for safe measure. If you can find one with legs on it (https://www.verociousmotorsports.co...wub0iPk1c2YC5ModJf74qXDWQP0MU-B6Jfm9vM3JgsnqQ) then you'd save a weld and not have to buy the next straight section.

Side note: a pre-bought bend with straight section is called a bend with legs. If you buy just the bend with no legs and weld them on, they're called pup pieces, pup sections, or pups.

If you need a longer leg than what comes with the bend, you'll have to buy the straight run and then add a pup that you cut from that straight run. If you need to add less than maybe 1.5-2" or so to an existing straight run, just fab the entire straight run as one piece.

For example, if you have a 4inch 45° bend with a 3" centerline radius and 6" legs, and you need 9" from center of bend (CoB) to face of pipe (FoP), you'd first calculate the takeout of the 45, then subtract that from the length needed to get the pup length you need to weld in. First, you need to find the takeout for the 45.

The formula for this is as follows:

T.O. = tan(1/2 θ)xR, where

T.O is takeout
θ is the angle of the bend
R is the CLR
CLR is the centerline radius. (Look down at a donut, halfway between the hole and the outside is the CLR)

If you have a 45° bend with a 3" CLR, the formula would be T.O. = tan(22.5)x3 = 1.2426". A short way to do this is that a 45° takeout is 5/12 of the CLR. The short way always works. You just don't always have the luxury of working with an angle that you have the short way memorized for. The formula is super easy after you've used it 4-5 times.

So if you draw a line through the center of the faces of that 3" CLR 45, they will intersect 1.2426" inside from those faces. Doesn't matter if it's a 1/2" tube, 2" tube, whatever. If the CLR is 3", you do the math for 3".

So your takeout for the 45 in the 4inch 45° bend with a 3" CLR and 6" legs is 1.2426". With the 6" legs, you have 7.2426" from CoB to FoP. If you need 9", a 1.7574" pup could work.

There are a lot of thoughts on minimum pup length. If you go by code for general process pipe, the minimum pup length is 1.5x the pipe dia. For high pressure and critical piping, it's 2x or 12" (whichever is greater). For small bore pipe, its 4x or 2". That gets crossed over into fab work often and it needs to be taken with a grain of salt.

The primary reason is HAZ (heat-affected zone) overlap. It is absolutely important, but keeping your weld area cool is the real key. That does not happen in pipe where you may have a piece of 6" sch40 that needs 4 tig passes at 95-220amps, and they're all done back to back. The pipe engineers account for this becuase labor hours are already a nightmare on a $30m job and to tell the welders to keep it cool and eat up the clock is WAY more expnsive than just going up in wall thickness.

If you weld 1" at a time and bounce around, you can get away with a much shorter pup than typically allowable. If you're new to stainless, new to thin wall tube, new to tig, the fit isn't going to be good, etc. then you need to go back to the basics of 1.5x and just keep the heatout of it. (More on that later).

Since we have the flange, bend, and pup sorted, the reducer is next. You can fab one or buy one. I can make them but I'm going to just buy it since I don't need it to do much more than just get from one size to another and I have room to play with. If you want to DIY, buy the sheet and go look on youtube. You can learn it faster there than I can type itor you can read it. It's a handy skill, but buying one is cheap enough.

I personally just try to make it a smooth transition. You can try to calculate pulse timings and non-steady fluid flow, but this is 8-10 from the turbo and if you aren't already doing this math for a day job, you're probably going to miss a step. Just call it turbulent flow, try to make the transition smooth, and call it a day. If we were chasing championships, that would be different. You also wouldn't be reading this if that was the case.

If we're using 4.5" and need to step down to 3", anything that steps down and crosses those two numbers will work. 5x3, 6x3, 6x2, etc. are all fine, just cut off the amount you don't need. They also have a taper associated with them, so they'd be something like 5x3-5L", 6x3x8, etc. We do want a slow taper. 1" reduction per 2" is fine and gives a ~15° taper. The internet says 7° is the golden target and I have seen no evidence for that. Maybe on pie cuts, but pie cuts are for 2 things: ultra-niche situations with no alternative and validation for grown men who pee sitting down.

Next is the flex section. I strongly prefer braided flex couplers. They usually flex 2-4x as much as non-braided. They'll be given by the diameter tube they're meant for and the length of the distance between where the tubes sit inside the coupler. The coupler may be a 4x6 and actually measure 4x6.375, but if you needed a 1' tube with a 6" flex coupler in the middle, you'd cut 6" of tube out and not 6.375".

Next is another reducer. Same as before, except this time you have to consider remaining length before the tight bend at the end of the downpipe. You may not be able to get as much of a slow taper as before, but you can balance the two out for your liking.

Next is the bend, same as before.

Next is the pup, same as before. Now you just have to be concerned with matching ID and OD.

Once you have all of this, you also need bungs and a mounting tab. Aside from that, you need a block of aluminum to make a chill block for the turbo flange. If you have lathe access, now is the time to use it.

I'll get into jigging, mock up, and fab tomorrow. I'm getting pretty tired and this is my last day of vacation.

 

[Strych9]

Turns out I did NOT get around to jigging, mock up, and fab by what I said would be tomorrow. Either way...

I'm fully aware that this is long winded, but there isn't much of a consolidated source of some of this information online.

Jigging can honestly really simple. There isn't really a main idea to it but rather a collection of simple principles:

-The jig can be made in any way you see fit. There is no formal way to jig anything insofar as I've ever seen. Pretty does not mean accurate. Accurate does not mean stiff.

-Keep notes and instructions on paper and keep it in a protective sheath, durable folder, laminate it, etc. and attach it to the jig. Only remove it to keep it to the side when you're using the jig. Attach it when you're done. Don't keep it in a safe spot, don't put it there on that shelf, keep it attached to the jig at all times.

-The jig should be far stronger and stiffer than the part you are trying to replicate. Shoot for triple the wall thickness on all parts of the jig or 10x the overall strength and stiffness of the part.

-You have a few ways to maintain dimensions: mounting points for tabs and brackets, locating points for anything that just has to hold a general piece in place, stops and guides for parts that may or may not have a tab or bracket that you want to just keep aligned, and anything else you can think may help.

-Build the jig as though you won't use it for 10 years. Don't assume you will remember all of the details because you WILL NOT. If you think you are an exception, go right ahead. Imagine you are going to pass this jig off to the dumbest person you have ever met, now imagine they speak your language poorly and as a second language, and that they will lose any instructions that you would like to pass off. It should be simple yet thorough. You should be able to look at the product and the jig and see the general idea of how it works. As an example, I have a jig that I made for a part at my main job. We have to make around 300/mo of these parts. The jig is set up so that no square, tape measure, clamp, nor anything else is needed. Zero tools. Pop the parts in, tack and weld 80%, pull it out and weld it out, repeat. Think Lego's age 3 and up.

-When possible, use countersunk bolts for all mounting points and any jig assembly points. They will self-center and provide a more accurate location. Use every trick in the book for drilling and tapping holes. Annotate the types of bolts that you use, any washers, any spacers, any nuts, etc. in your notes in your folder, preferably with a McMaster-Carr number or MSC number.

-Assume that you will lose all hardware.

-Try to make the part as accessible as possible so that you can weld as much as possible in the jig before removing it.

-If you perfectly fabricate a jig to a part, then reproduce that part perfectly, it will be off after you weld it out. Nobody cares how accurate the jig is. What matters is how accurate the product is. Make your new part with your new jig, compare it to the original part, then adjust the jig so that the new part warps to the original dimensions. This is called working a jig. A finished jig is called a worked jig a working jig.

-Keep your weld sequence in your notes. If you change the weld order up, your part will warp differently. Good luck on working a jig.

-You can almost always sell a jig. I usually sell a jig when I'm done with personal projects as long as the part isn't something I may need to replace (subframes, exhaust, or anything else that may get damaged). Keep a mental tally of your labor hours and material cost. Once you've worked the jig, factor that as well. I'd personally sell a downpipe jig for around $800-1200 or a jig for control arms for $200-$1k depending on the specifics.

So a few notes before getting started. If I took an apprentice and was going to have them build a jig, I would teach them these things:

1. How to drill precision holes. This is one of the areas that I spend the most time on with new fabricators. Drill bit types, materials, purposes, speeds, pressure, chip management, centering, sharpening, cooling, lubrication, etcetera. In the case of building a jig, you need the basics:

An assortment of regular HSS (high speed steel) bits from home depot.

A 5 to 25 pack of 1/8 bits as pilot bits. If it gets dull, toss it.

Stepped drill bit.

Cobalt bits (the material, not the brand) that match the size of hardware you plan to use. They aren't cheap, but they're going to outlast HSS bits when you get into hard materials or drilling through or near a weld.

Whatever bits your taps call for if you intend to tap.

If it's a metric part, BUY METRIC BITS. I buy metric hardware for the actual locations that hold those tabs, brackets, bungs, etc. and I use standard for the jig. I also make sure that the jig hardware is black oxide coated so that I don't get anything mixed up and I use anything but black oxide or stainless for the part. If it's a standard part, I use standard hardware for the part and black oxide metric on the jig.

2. Tapping. This one is and isn't simple. Find the size tap you need, find the thread engagement percentage you need/want, then find the drill bit size needed for it.

Thread engagement is a measure of how much of the full thread height is produced. This may seem like a rabbit hole, but if you just google what size bit you need for a tap, you'll find conflicting information. That conflict is due to varying thread engagement preferences between different manufacturers, different levels of manufacturing precision, and the fact that different materials like different thread engagement percentages. The simple version of it is this: the height difference between the peak and valley (or formally, crest and root) of the threads is potential thread engagement. After a lot of factors, your potential thread engagement of 100% falls to a typical maximum of 75%. Most charts fall between 60% and 75%.

Until you start machining ultra precision parts with ultra precision tooling, just fix your range to 60-75%. 60% is a little loose but almost never breaks taps, and 75% requires really clean threads and you have to take care to keep from breaking the tap. For the purposes of making a first time jig, just get in the 60-70% range. Now that you have that, you can pick a bit that works.

For example, an M10x1.5 tap calls for an 8.5mm if you want 75% engagement. A 9mm gives you around 60% engagement. To stay in that range, you can use these:

8.5mm - 75% engagement
8.6mm
R
8.7mm
11/32
8.8mm
S
8.9mm
9.0mm - 60% engagement

And yes, there are letter drill bits, metric, metric decimal, and number drill bits. I personally have an MSC Hertel chart at several places in my shop that lists 60% on one side and 75% on the other, and I use those two to find my range. You can find pictures of it online but I couldn't find any that had a good enough resolution to actually read well.

You can often find common sizes sold as a tap and bit pair at Home Depot, Lowes, etc. but they're usually in weird places. If not, now you know how to pick the right bit.

You'll also want to buy a countersink chamfer bit. a 5/8" is good for 90% of your purposes.

Now to tap. Locate your mark, use a punch, squirt some tap oil down, drill with a NEW pilot bit, step up to your drill bit that you selected to tap with, put a thin piece of fabric down (old shirt or something), use 2 squirts of oil and hold moderate pressure, drill as straight as possible and use a guide if you want, put about a 1/16"-3/32" chamfer on the hole, clean the hole of all metal shavings or an debris, and start your tap. Take your time to make sure it starts straight. If not, it will wither make it's way in the direction you started it or break. If it gets sideways at the first few threads, just back it out a little and straighten it. Go 180° in, 90° out, repeat. If it's hard (because you HAD to do 75% engagement), go 360° in, 270° out. Use smooth, moderate pressure.

For most purposes, you can honestly just drill a hole, put a flanged nut on the back side, bold it together, and tack the flanged bolt in place.

3. Selecting material. If it has mill-scale, you'll want to clean it all off. If it's rusty, you're going to want to clean it. Even if you weld over it because it's just a jig, the rust can transfer to the part. It doesn't matter if it's stainless, rust can and will transfer if it gets impregnated into the surface. For removing rust, acid works, naval jelly works, grinding and wiping with acetone works. If you use the first two, wash it off and then neutralize it with baking soda or an equivalent, then do your work and coat it with WD-40 or something.

A flap disc (or tiger paw for you pipe guys) doesn't do well with cleaning mill scale or a rusty surface. Furthermore, the rust will stay on it and you'll be transferring it to everything it touches. Use a grinding wheel. Go to the flap disc after you've gotten down to metal. For cutting the material, I'd just use a cutoff wheel.

Also, if there is one time to wear safety glasses, it's with a cutoff wheel. A Metabo spinning at 9000rpm with a new 6.5" cutoff wheel has linear velocity at the edge of about 175mph. If it lets go, you had better hope that rapid disintegration doesn't find it's way to your eye. It's basically a 175mph sand and fiber Frisbee. If you ever see a cutoff wheel that's wet, break it in half and throw it away. If a grinding wheel has gotten wet, it isn't a 175mph sand and fiber Frisbee, it's closer to a grenade.

Anyway... Square tube, square stock, flat stock, and SOME round tube can come in handy. Just go heavy when you start picking. Facebook marketplace or a scrap yard is usually a good place to start. If you don't have luck there, I typically use ShapiroMetalSupply. Calling them sometimes gets better prices depending on the total length you need, plus they can save you money on shipping by doing it on a case by case basis. Ordering 10x 6' sticks will cost more online than if you call and order 60' cut up however you can work with and packed into a smaller tube.

4. Actually making the jig. This part is honestly pretty hard to explain and I don't know how to do it without a hundred case studies. Every jig is different. Every approach is different. In all seriousness, just go to google image search "metal fabrication jig" and you will learn more through skimming through pictures for half an hour than I could explain in a week. Some are entirely made to be a mechanical assembly, some are entirely fabricated, some are entirely machined, some are table mounted, some use a mix of all four methods. If I hired a new or experienced fabricator and wanted to teach them to build a jig, I would tell them everything above and then tell to go to my computer and spend a half an hour on the clock skimming through google images. I was told to do this when I started jig making and I thought it was a "piss off" answer. Now I believe it is the actual best answer.

What I can say is that if you're mig welding, you will have an easier time tacking and fitting things up since you have 2 hands and you'll want 5. I typically turn it all the way up and then turn the wire to the lower end of what that voltage will allow, then I use quick burst tacks when I'm assembling it. They'll fuse in 0.5-3 seconds depending on material thickness. The hotter it is, the faster the puddle forms, the less time you spend putting heat into the part, the less it warps. Welding hotter means welding disproportionately faster and less heat input. Seems counterintuitive, but it is a critical part of all welding that must be understood (google: "calculate heat welding input"). Note: I don't do this for the actual part and I don't do this for welding the jig, but I do weld hot and fast when the situation calls for it. Tacking a jig is one of them.

With that, google search AI will incorrectly summarize the situation. I was going to say to read up on heat vs. travel speed, but I did a google search before suggesting it and the summary is... right-ish. It says that a slower travel speed will lead to distortion (true), a wide bead (sometimes true), and more heat input (right answer, wrong reason). It also says that faster travel speed will give less penetration (sometimes true) and distort less (true). The correct version is that you should adjust the heat and filler to give a good weld for the type of joint you have prepped, then increase travel speed as you can without sacrificing the quality of the weld. If you can travel faster but the puddle isn't moving as fast as you need it to, increase the heat. 200 amps for 30 seconds will be less heat than 300 amps for 15 seconds.

If you're tig welding, you can manipulate how it draws better. Always trail off either with the pedal or by working away from the tack before popping off. If you have it tacked up and need to draw it this way or that way, either cut into it and run another bead or grab some stainless and run a bead. If it's really bad, you can pour water on it (it may crack, don't do this on your part unless you know exactly what you're doing). If it's still bad, cut it out and do a better job of fitting and welding it.

If you end up with porosity and you're feeling lazy, you can lay stainless in it and get it HOT, then shove stainless wire in. Again, this is a practice that works always but is never something I'd do on a part that matters. I've been at a track and had to repair a structural piece that broke and there was no way to get in and get the porosity out. I fed stainless into that single spot, then welded over the rest of it with the right filler. I told them before and after what had to happen and made sure that they were fully aware. It lasted but I was worried the entire time. Again, it always works but it never more than a C- patch.

-----

Part 2: This next bit may seem like more of a side thought than an important note, but it DOES matter and it all needs to be said if you are thinking about venturing into fabrication for anything more than a hobby. If you're just making a jig to copy a single part, none of it is necessary and I'd skip it. Anyway...

You will start your first jig with the intent and enthusiasm of making a jig that Skunkworks would be proud of. That will devolve as you search for scrap material, make your 5th trip to home depot, and behold whatever in the fuck you think it is that you've just made. It happens to everyone. Just know that if you've purchased fabricated aftermarket parts before, their jig probably doesn't look much better than your first one. I know because I've seen what some of those jigs look like at the ultra high end shops and they are rarely nice. It would blow most people's minds to see the difference between the part they're holding and the jig it came off of. A good jig can produce a shit part with a shit fabricator, and a shit jig can produce a good part with a good fabricator.

These are some of the places that I've done work for (either directly or as a sub-contractor) OR that I've been in and seen first hand. This is what I saw of the jigs:

Absolutely perfect:
-Lockheed Martin (didn't work here)

Top tier:
-SpaceX (contract)

Mostly good:
-BMW M Motorsports
-BMW Team RLL
-Rahal (INDY team)
-Dallara
-My second fab shop

Okay:
-LS4 (SCORE team and specialty motorsports fab)

Mostly bad:
-Machine shop in PA where we fabricated nuclear reactor components (NDA)
-Machine shop in PA where we fabricated passenger aircraft parts (NDA)
-NASCAR team (5x championships)
-Houser Racing (multiple championship winning shop)


All bad:
-My first fab shop


Lockheed Martin has the budget, the engineers, and the business relationships with large CNC shops to justify hundred thousand dollar jigs.

The shop where we made outsourced SpaceX parts had good jigs that really only needed a few QOL tweaks. Working there was like running a marathon; pretty cool to say I did it but it wasn't actually cool to do it.

BMW M Motorsports just did what mattered. Nothing more, nothing less.

BMW Team RLL had the same fabricators as Rahal INDY because they were in the same building. When I was there, I took over all BMW fab for the IMSA LMDh effort in 2023. They had ultra high quality fabricators, but they rarely actually needed to jig anything. When they did, they made some solid stuff.

LS4's fab wing was in it's infancy when I got there. The initial jigs were pretty bad. The owner, like me, taught himself to weld and only had about 6 months of experience at the time (he was GOOD for only having that 6 months). The jigs sucked but the parts fit. The customer was happy and they didn't have 100 hours tied up in jigging a $200 part.

Dallara didn't need complex fabricated parts so their jigs were simple, but they were SOLID. They focused almost entirely on carbon fiber manufacturing.

My second fab shop was really just taking what I learned over time and doing better. The jigs were ugly and made of scrap metal, but they were thoroughly worked and the parts fit very well.

The nuclear reactor component fab is the biggest anomaly on the surface. If there is any place where you'd think every item HAS to be perfect, that's one of them and I'd agree. But any experienced fabricator will tell you that the jig is a tool and nothing more. It doesn't matter if it's made of Styrofoam and sticks as long as it spits out a good part. Some of those jigs looked absolutely awful. However, each part that we fabricated then went to get machined. We only had to get in the ballpark. There were a few where we had to fab a part that was perfect, but the general approach there was that the hands made the part good, not the tooling. Though the jigs looked and felt awful, they were thoroughly worked and known to be good.

The passenger aircraft stuff that I subbed for was basically the same as the nuclear fab stuff. Jigs sucked but the result was enough for the next step. There were the few parts that required dead precision but the machine work after welding was the key to the precision.

The NASCAR team had shitty jigs for 3 reasons: designs change constantly, each crew chief builds each setup their own way for each race, and the jig was part of the process and not the whole process. If you make every jig good, you'd need to hire 2 more guys just to keep up. They did have a few really good ones, but the majority were garbage.

Houser Racing was, at one point, one of the best in ATV racing. When the old man and his wife retired, their son took over. As nice of a guy as he is, he is NOT a thoroughbred fabricator. All that aside, the half-assed jigs made parts that almost always fit and never broke. They also won multiple championships. That doesn't mean that the priorities or methods were great because they were NOT.

Again, sorry for the length, but I was hoping to make this a one stop set of instructions to go from "I can lay a decent bead and have some tools" to actually making a functional jig. If you guys have any questions about jig making or anything else, lay them out. I'll reply whenever I get back online.

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