Hot Off the (3D) Press: Suspension Upright 3-D Print

Posted by jjludemann on July 30, 2012

The suspension uprights have gone through a long evolution, but I’m zeroing in on the goal.

First Design: Machined Billet Aluminum

This design uses radial-style brake caliper mounting. Needed to be redesigned when someone ordered the lug-mount calipers and had them delivered all the way from the USA. Probably a Freudian slip as they’re less expensive.

Second Design: Fabricated Steel

Second design was fabricated from steel. Unfortunately, welding will eliminate the temper in the heat-affected zones. The weakening due to this is hard to predict, and can only be eliminated by heat treatment. That would mean days or weeks finding and learning to deal with a heat-treatment supplier.

Mesh used for finite-element analysis of fabricated steel upright.

Finite-element analysis stress plot for fabricated upright. Strong enough, but where are those heat-affected zones?

Third Design: Cast Aluminum

Here’s the final result of literally hundreds of design revisions, ensuring that the upright is strong enough and as light as possible. This design is made possible by the new technology of 3d printing, which will be used to make the master “plug”, from which molds will be made to cast the actual part. Note that the steering arm is not an integral part of the upright, but is modeled together with the upright because the FEA runs much faster this way.

FEA mesh plot for cast upright

FEA stress plot inner

View from outside

Finally, the Master Copy

The upright had to be split into four pieces for 3D printing; split vertically so I can make two mold halves and remove the masters from the molds, and split horizontally to fit the 3D printer. The 3D printer extrudes hot ABS plastic in X-Y layers onto a heated Z-axis stage with 0.3mm resolution. The print is slightly rough and the parting plane is slightly warped, which will have to be corrected with auto body putty, primer, sanding, and paint. The cast aluminum blank will still require several machining steps to cut off the gate and sprue, drill mounting holes, bore the bearing hole and retaining ring slot, and mill the brake caliper mounts. Still far better than trying to machine individual parts (or even a mold pattern) this complex, which would be approximately impossible and semi-infinitely expensive.

One half printed in two colors to highlight the split required to fit it into the 3d printer

Full set of four 3d prints. The cylinder protruding in the upper left is the gate, where molten aluminum will be poured into the finished mold.

Some people get excited by shoe sales. I get excited by this!

Fabricating the Lower A-arms

Posted by jjludemann on June 16, 2012

No, I haven’t just been sitting around the house eating chocolate, but a major malfunction in my main computer leaves me time to update the blog and get caught up on other things I should have done, like taxes. Unlike EVERY OTHER COUNTRY IN THE WORLD (except the Phillipines), even though I haven’t set foot in the USA in over four years, I still have to pay US taxes. The bright side is that California no longer considers me a resident so I don’t have to pay California taxes anymore, which is quite reasonable given that I moved out 11 years ago.

I made the mistake of turning the computer off overnight to help save the planet and all, and the next day it kept dying like someone pulled the plug. Computer shop says I need a new motherboard and graphics card, and oh, by the way, there are no new LGA 1366 motherboards for Intel i7 CPUs in Thailand and the old one will take about a month to fix under warranty. Which is understandable, given that Intel stopped making LGA 1366 i7 CPUs ages ago! Oh wait, they still make them? Or maybe not, from Intel’s website I can’t tell. At least Gigabyte’s warranty will cover their product, or maybe I just haven’t heard what their fine-print objection will be, yet. Azus, on the other hand, says my graphics card is corroded, and corrosion isn’t covered under warranty. Great plan! Make a product that corrodes, then say corrosion isn’t covered. It might be more honest to say “No Warranty”, though. The Azus graphics card was inside a warm computer (which was _almost_ never power-cycled) in an office environment for it’s entire life. Azus is now on my Deferred Vendor List.

Anyway, on to fabricating the lower A-arms, or control arms:

Repeat everything four times. Final result: four lower A-arms

: Starting with the spherical bearing cups, face and cut outside diameter

: Cutting the internal diameter on a bearing cup. This is a press fit, so it has to be cut as perfectly as the tools will allow.

: My boring bar won’t fit into my new quick-change tool holder, so I had to cut it down to fit.

: Boring bar now fits into tool block.

: Cutting the groove for a snap ring. I wasn’t sure I could get the press fit perfect, so I included provisions for a snap ring

: Snap ring in place for a trial fit.

: Using the cutoff tool to cut the part off the stock

: Bearing cup, spherical bearing, snap ring, and ID gauge for cup. I don’t have an internal micrometer, so used my external micrometer to cut a gauge to the precise length for the ID.

: I ground a carbide cutting tool for the boring bar to the correct width to cut the snap ring groove. It took a lot of grinding. Carbide is really hard!

: Starting the rod end receptacles that will be welded to the legs of the A-arms. Face and cut OD on lathe.

: Cut step to fit inside A-arm tube.

: Use center drill for accuracy.

: Drill hole to be tapped for rod end

: Using cutoff tool to part off

: Tap for 3/8-24 left hand threads. A later version of the A-arms may have easy rod-end adjusters, so I’m using left hand threads here, too.

: Cutting a chamfer on the face of the rod-end receptacle. Looks better, is lighter.

: Four finished rod-end receptacles

: Setup for tack welding rod end receptacle into A-arm tube

: Tack welded in place

: Welded all the way around. Holding the tube in a V block makes it easy to turn while welding

: Made 2 aluminum bushings to fit inside the bearing cup and locate it on the jig

: Rod ends are held in jig for welding.

: A-arm jig is made from printed drawing glued to plywood.

: Spherical bearing cup fully welded to one leg of an A-arm

: Both legs of an A-arm fully welded to a bearing cup

: A-arm bearing cup braces marked and cut

: Bearing cup braces in place and welded

: Pushrod mount in place and welded. These pieces were made with the patented (not patented!) technique of printing on sticker paper, cutting with a plasma cutter, grinding to exact shape.

: Spherical bearing is pressed into place on my home made hydraulic press. Custom bushings were made to only push on the correct places, like not the ball.

: Anti-intrusion bar test fitted

: Anti-intrusion bar fully welded. Weld shrinkage is a problem here.

: Welding distorted the bearing cap enough that I had to recut the bore. First, find the center of the hole.

: Next, use a boring head to cut the hole to exact dimension. Very tricky; had to use 1/2 the smallest tick mark on the boring head. Total overlap for press fit is around 0.001″

: Repeat everything four times. Final result: four lower A-arms

Building a Simple Hydraulic Press

Posted by jjludemann on June 16, 2012

I’ll be needing a press to insert the spherical bearings into the control arms and to insert the wheel bearings into the suspension uprights, so I took a couple of hours and built a simple hydraulic press. It’s just a strong steel frame that will give a small 5-ton hydraulic car jack something to push against. It’s taller than it is wide to be able to press items of different sizes by turning the frame on its’ side. Regarding painting, I’m finding that, with modern paints, I don’t need to use primer. I just clean the metal with a wire brush on a variable-speed angle grinder, clean it again with acetone and paper towels, then spray the topcoat on directly. This gives a thin, hard coat that sticks well.

: 4 x 2 x 1/4″ C-channel steel marked for cutting with the plasma cutter

: Plasma cutter makes short work of cutting this thick steel. Each cut would take more than 1/2 hour on a 12″ abrasive cutoff saw, but takes just seconds with the plasma cutter.

: Jigged and clamped, ready for welding

: After welding

: After painting

: Crushed a few things to test it. Can exert some pretty good force.

Fabricating Lower Suspension Clevis Spacers & Washers

Posted by jjludemann on May 10, 2012

Need some spacers to keep the clevises from interfering with some of the frame tubes. Also, custom load-spreading washers that my FEA says are important:

: Starting the lower suspension clevis spacers by facing, turning to size, and drilling aluminum rod.

: Lathe cutting the angled face on spacer

: Using a cutoff tool to cut the part off.

: Long rod to be used for washers is center-drilled for tailstock support

: Aluminum rod is lathe-turned to correct outside diameter.

: Rod is milled flat to half diameter

: Drilling holes for bolts that attach clevises to frame

: Washers are cut to approximate size with angle grinder, then faced at 30 degrees with this setup.

: Eight lower suspension attachment clevis assemblies finished.

: Each assembly consists of these eight parts.

Making Chips… Finally!

Posted by jjludemann on May 10, 2012

Lower suspension attachment clevis assembly drawing

It seems that other people who’ve built cars from scratch attempt to get their cars rolling on the ground as soon as possible, so I figure I’ll do it that way too. With that in mind, it’s time to start fabricating the suspension. First up: lower suspension attachment clevises. I ordered 7075 aircraft aluminum from the United States as part of my big shipment. It’s amazing stuff– stronger than steel but light as aluminum. These assemblies have to be extremely strong, as I calculate that under braking the front one takes a load of over 4400 pounds.

: Start with a solid chunk of 7075 aircraft aluminum, here scribed for cutting slightly oversize

: Blanks are cut to size with thinnest abrasive cutting blade in high-speed angle grinder. I tried using a 12″ cutoff saw, but it couldn’t cut this high-strength aluminum.

: Finished raw blank

: Facing both sides of the blank with carbide-insert face cutter end mill

: Milling holes for bolts to attach to chassis. PDF drawing printed on sticky paper at 1:1 eases the layout and provides a useful double-check against errors.

: Milling the first outside radius on the rotary table.

: Milling the second outside radius

: 45-degree faces are rough cut with the angle grinder, then clevises are supported on V-blocks clamped to the milling machine.

: 45-degree faces milled smooth with face cutter

: Repeat eight times. Ready for slot milling.

: Milling the slots for the rod ends using a ball-end mill.

: Milling holes for the rod-end retaining bolts

: Milling an additional relief for the rod ends. Test assembly showed interference, so I went back to the computer model and, sure enough, there it was. Now I know to use the interference and clearance detection tools.

: Finished lower A-arm clevises. Outside radius on front was also cut on the rotary table / milling machine.

: Lower suspension attachment clevis assembly drawing

Modifying the Lathe Quick-Change Toolpost

Posted by jjludemann on May 10, 2012

So I imported this quick-change tool post for my lathe, which appears to be some kind of standard, but a standard that my lathe just doesn’t happen to abide by. I needed a large (~1 1/2″) hole in the bottom of this solid tool-steel block. I tried drilling it with a carbide-insert drill, but after several minutes had made a cut so shallow it could only be felt by dragging a fingernail across it. After watching a few Youtube videos, though, I decided it must be possible and came up with the setup below, a solid carbide end mill slowly enlarging the hole on a rotary table. The mill left an amazingly high-quality finish.

: New Aloris quick-change lathe tool post mounted upside-down on the rotary table on the milling machine, being cut with a solid carbide end mill.

: Finished hole as cut. Note mirror-like quality from solid-carbide endmill

: Aloris quick-change toolpost in place on lathe after modification, a selection of quick-change toolholders in boxes in background.

Contents: 1 Race Car Kit, some assy. req’d

Posted by jjludemann on May 2, 2012

I’ve been accumulating parts for almost the past two years in a warehouse in Los Angeles as it’s easier to buy things in the US and ship them all the way to Thailand than it is to just buy them in Thailand. Also, I only wanted to navigate Thai customs one time. Finally gave them the go-ahead to ship, and a few weeks later everything arrived at my door. Includes just about everything that I can’t make myself or buy in Thailand: wheels, brake calipers, brake discs, brake pads, master cylinders, Aeroquip tubing and fittings, torsen differential, rear axles, spherical bearings, bearings, rod ends, 2007 Suzuki GSX-R1000 engine, crash padding, radiator, oil cooler, kevlar, vacuum-bagging materials, vacuum pump, Halon fire system, and more. Also, everything I need to fully fit out my machine shop, like a rotary table, angle table, and cutting tools. Better than Christmas!

Some assembly required. May require common household items such as tape, scissors, stapler, lathe, milling machine, and TIG welder.

: Race car kit, somewhat the worse for wear after storage of up to two years and trans-Pacific shipping.

: Some of the parts: centerlock OZ Racing wheels, 13×8″ and 13×10″

: Truck carrying goodies

Redesigning Suspension Components

Posted by jjludemann on April 14, 2012

So I was ready to build the suspension attachment points and decided I’d better do a finite -element analysis. It turns out they needed a lot of tweaking, and in a shin-bone’s-connected-to-the-thigh-bone kind of way, I ended up redesigning just about every suspension part all the way to the lug nuts. Part of this came when the quote on building the upper suspension attachment clevises came in way higher than expected, so I redesigned them so they could be laser-cut, hopefully much cheaper than CNC machining. Don’t have the new quote yet.

Also, I received the huge shipment of parts, supplies, and tools that I’ve been aggregating in LA for almost the past two years, and some idiot in purchasing (me) managed to order the wrong brake calipers. Everything was right except for the mounts, which are the lug style instead of the radial style. At least now I really know the tradeoffs between the two approaches. The upright for lug mount brake calipers is only about 35 grams heavier than the one for radials, and the calipers are $80 cheaper each. Over $1000/pound for that weight savings… Actually, that’s not quite fair as I don’t know the relative weights of the two caliper styles.

Anyway, we have lots of pictures of FEA meshes and results:

: FEA mesh for lower suspension clevis, attachment point for all four lower control arms

: Finite-element analysis results for lower suspension clevis

: FEA plot for front upper suspension attachment bracket that will be welded to the chassis.

: FEA plot for one half of the laser-cut upper front suspension attachment clevis

: FEA plot of one half of the upper rear suspension attachment bracket

: Detail of the FEA mesh for buckling analysis of left front lower A-Arm

: FEA buckling plot for left front lower A-Arm under braking load

: Detail of the FEA mesh for static analysis of left front lower A-Arm

: FEA plot of left front lower control arm under 1600 pounds braking force

: FEA plot for left front lower control arm under 1600 pound right-hand cornering load

: FEA plot of left front lower control arm under 1280-pound left-hand cornering load

: FEA mesh for front axle static cornering analysis

: FEA plot of front axle under cornering load

: FEA mesh for front axle static braking analysis

: FEA plot of front axle under braking load

: FEA mesh for front/rear steering arm

: FEA plot for front/rear steering arm under maximum cornering load

: FEA mesh for front upper control arm attachment bracket, to be welded to chassis

: FEA plot of front upper suspension attachment bracket

: FEA mesh for left front suspension upright static braking analysis

: FEA plot of left front suspension upright under braking load

: FEA mesh for left front suspension upright static cornering analysis

: FEA plot of left front suspension upright under maximum cornering load

: FEA mesh detail of left front suspension upright for snap-ring analysis

: FEA plot of left front suspension upright snap ring slot under cornering load

Building the Frame: Roll Hoop to Tail

Posted by jjludemann on March 8, 2012

: Removed the chassis from the jigs for the first time. Welded the bottoms of all the joints, which brought the chassis back to true & flat

: It’s a commuter car! You can carry it like a briefcase.

: Test fitting the rear beltline tubes. Chassis table has pins to locate these tubes, too.

: Rear subframe beltline welded…

: And into place.

: First parts back from the machinists’. Rear keel jig and the keel itself. Beautiful and accurate! Thanks, Somkuan!

: Rear keel, ready for welding.

: …and welded.

: Welded rear keel jig. Really starting to get the hang of this welding stuff. Yay!

: Bottom perimeter of the engine compartment fabbed and welded.

: Finished rear keel and rear keel jig.

: Engine compartment left side lower tubes

: Engine compartment right lower diagonal

: Bulkhead H right vertical lower tube

: Another example of how my Solidworks fishmouthed tubes fit, this one at the front end of the rear keel.

: Lower diagonal tubes holding the front of the rear keel.

: H-J inner upper diagonal tubes securing the front of the rear keel.

: H-J bottom perimeter tubes in place. These 3 tubes were welded flat on the table then lifted into place. Here you see the bottom of the car start to curve upward to clear the diffuser.

: H-J side diagonals. Here we work our way from front to back to avoid cutting off the ends of the tubes to fit them in from the side.

: J left and right lower verticals

: J to L left and right lower diagonals

: Released from the chassis table again to weld the bottom of all the joints. It’s so much easier this way I don’t even try to weld upside-down anymore.

: J-K inner bottom diagonals hold the rear of the rear keel

: K-L diagonals secure the rear of the rear keel to the beltline. This is the back end of the frame.

: Top frame rails from the main roll hoop to the back of the car are finally in place. Now we can see the complete outline of the frame.

: G-H upper diagonals are curved outwards to allow us to remove the engine from the top. The curve must be in the correct plane.

: From this angle you can see the curve. Removing the engine from the top is a design change based on feedback from the ApexSpeed.com forum. Top rail will be made removable later.

: H bulkhead, upper left vertical. Note that it’s not really vertical, but leans forward and inward.

: Test fitting the G-J upper diagonals. Sometimes it’s necessary to fit a bunch of tubes before welding any in place.

: Now we start welding them in place from front to rear. These are the G-H upper diagonals.

: H, H-J, J upper tubes (6). Skipped a couple of photos…

: It’s almost done. Just a few inner diagonals left.

: J bulkhead, inner diagonal UL-LR. This area of the frame is extremely strong as it has to support the suspension rockers and engine mounts.

: J bulkhead inner diagonals, LL-UR, 2 pieces

: H-J inner diagonals support the rear engine mounts.

Building the Cockpit

Posted by jjludemann on February 7, 2012

Time for a photo update showing how I built the cockpit, tube by tube.

: A complete set of tube drawings for one forumula 1000 cockpit. It’s a lot of work to generate these drawings, but it saves a lot of time in fabrication, and ensures the frame is accurate

: Test fitting the tubes for the cockpit floor

: Now we can see the main roll hoop was fabricated too narrow. The holes on the jigs don’t line up properly with the roll hoop

: Found the hidden stash of angle grinder shields removed by my Thai workers. In Thailand, workers just laugh at safety measures. I’ve even had one quit when I insisted he wear eye protection.