Steering Knuckles

Last semester I had an opportunity to help out the SAE Formula racing team at my school by making some parts for them. To set the scene, every year the team designs and builds a small formula style car from the ground up. This requires an inordinate amount of effort from the team members that culminates in competitions over the summer. For various reasons, I never joined the team but I often work in proximity to them because of my work managing the various CNC machines in my lab on campus.

Finished front knuckle. Large hole diameter is ~3.5 inch

Last spring, in the middle of crunch time for the team making parts, our primary 3-axis mill (Hardinge V1000) had an issue with the tool changer. We don't know what cause the issue but we suspect a crash or similar incident that wasn't reported. It ended up with the ATC timing being off and the machine needing some new parts. While the parts were being shipped, the team had to scramble to get all their parts done on the other available machines. 

In addition to implementing some new policies as a result, we decided to help them team out in our lab and offered to make their steering knuckles (uprights) on our 5-axis. This is the same Okuma 5-axis on loan to us I have referenced in some of my previous posts. Because of the cost of the machine, and the fact we don't own it, the owners requested that I be the only one to use the machine while on loan to us.

Finished rear knuckle. Large hole diameter is ~3.5 inch

Long story short, I offered to make the team's steering knuckles on the 5-axis to save them some time. I made these before the turbines I previously wrote about, and these parts were my first real parts to come off this machine. In total I made 8 parts (2 each front and rear, left and right), with 2 proving parts, 1 each for front and rear. 

The parts started out as big chunks of 7075 aluminum. The blanks were prepped with a simple dovetail for holding in the vise, no other prep needed. Roughing and finishing of more than half the knuckle is possible with the first setup. All critical features and dimensions are completed in the first op, except for the back bearing bore. I had some real fun here with a Sandvik 590 face mill, blasting off extra material like it was nothing. 93 cuin/min and the machine barely noticed, with sustained spindle loads maxing out at 80%. The only down side was spraying all those big chips around the enclosure scratched the plastic window on the door.

Stock before op 1

Stock after op 1

I completed the first op on all parts before second op, mostly because of the fixture I decided to use. The team had shared some pictures and description of how they made these parts in the past on a 3-axis. The basic idea was square up all sides of the stock first, then rough out the top and bottom thirds of the part in 2 ops. With the bores finished, and some other holes established, they could clamp the part through the bore, using some extra holes for rotational alignment, and finish the parts. I opted not to use this method because it required the stock to be squared first, taking a long time. Their method also used extra holes for rotational alignment, which I didn't really trust (I'm an indicator man). The fixture I used ended up saving a lot of time and effort. 

The team's original method of fixturing

Having roughed out 90% of the part from the first op, I flipped the parts over and secured them using an expanding bore clamp. These are fantastic fixturing tools that can get you out of tight spots. Not only do they not require any external clamps, gripping only from the inside a hole or pocket, they also provide full support behind thin walls. They are also good for situations like mine, where you want to clamp in a blind hole. Because of my vise, I couldn't make the full size bearing hole through the whole part. If I did, the part would have fallen off the vise. Instead I drilled a small through hole, only enough to fit in the hex wrench to tighten the bore clamp. The bore clamp located the part in every axis but C, which I indicated in by rotating the C axis of the machine, and setting my work offset. 

My method of fixturing

This worked great. I went a little easier roughing on the second op just to be sure, but there was nothing to worry about. The clamp held strong and didn't rotate. I didn't measure concentricity of the two bearing bores (because there was no tolerance on the drawing), but I skim cut the bore clamp in place, so it should be very good. This clamp worked for all 8 parts, no needing to swap fixtures. It also gives

My method of fixturing with part

Off the machine the parts needed very little finishing, only a small amount of debur. There were some tapped holes for wheel speed sensors that I had drilled, but not tapped in the machine.

All the fixture design and programming was done in Fusion360. Fusion is great for positional 5-axis work, which all most all of these features were. For my thoughts on Fusion's ability for full 5-axis, read my turbine article. One thing that really came in hand with Fusion is the ability to write your own post. I modified the stock Okuma 5-axis post the comes with Fusion to make it work much smoother with our machine. Little extra safety moves here and there, custom tool change cycles added, or even adding multiple tool length offset support I could do fairly easy, and I don't even know Java script the post is written in.

My time to program, set up, and run these 8 parts, including modifying the post processor, was ~85h. This is down from the 200h the team had documented previously making only 4 of theses. Obviously having the 5-axis and a 15k spindle really helped with this. But equally using the right tooling, feeds and speeds, and clever fixturing saved time. This job was a good experience for learning 5-axis programming and operation.

As a thanks, the team put my logo on their car as a sponsor.

8 parts and 2 proving parts on the far left

An Engineer's Spoon

This project came about from a need for a kitchen spoon. Now you would think you could just buy one of those, but where is the fun in that? The bowl is machined 304 stainless steel, with an Osage Orange handle. I was inspired by a limited edition Le Creuset cast iron skillet I came across a few years ago. It was ridiculously expensive, but had a nice aesthetic where the wooden handle blended smoothly with the metal body. Around a year ago I needed a nice kitchen spoon. Growing up with wooden spoons, I gravitated towards that as a choice, but there weren't really any I liked and over time the wood really wears because its never hard enough.

The alternative is stainless but the handles on those aren't comfortable. Remembering the aesthetic of the skillet I liked, I designed a spoon. That spoon was never made. I designed it more as an experiment and didn't really think about how I use spoons when cooking and what manufacturing methods I have available to me. I shelved it and forgot about it for a bit. 

Earlier this year, we finally got our Okuma 5-axis up and running (same machine in the impeller post) and after a busy semester learning a new machine, control, writing a post processor, and making parts (more on those parts to come), I had time on the machine to make a spoon. I dusted off the old CAD model and made a bunch of changes. The bowl was slimmed down to fit the stock I had, the leading edge was thinned out to make scraping the bottom of pots easier, and some of the lines and tangencies were refined. I did all the modeling and programming in Fusion360, and since the first spoon design, they added some more features that helped me refine the look. 

Programming this was a good learning experience for 5 axis work. Stability was a big issue throughout as well as tool access. Off the machine I was quite happy with the finishes. This is due to the superior quality of Okuma, as well as having some really top notch Sandvik tooling. After machining, I just sawed the part off the remaining stock. At this point an interesting issue was presented to me; how do I drill the hole for the handle when there are no reference surfaces, flat or parallel edges or really any way to hold this part? I created an aluminum tool that was machined to be a perfect negative of the bowl. This gave me support over a large area, as well as rotational alignment to clamp it in tall jaws seen below. From there it was easy to indicate the round shank of the spoon and drill the hole. Last was the handle, which I completed over the summer. Very straightforward compared to the bowl. Osage Orange was used because it is very hard, strong, and moisture resistant. Ideal for use in a kitchen without the need for any finishing. Also it matches a kitchen knife handle I made a few years ago.

Having used this spoon for a few months now, I do have some lessons learned. First, weight distribution. The spoon has a heavy metal bowl and a very thin, wooden handle. Its front heavy. If I had thought of this, I could have checked center of gravity in CAD. Spoon still works fine but it takes some getting used to the unique weight distribution. Second, Loctite 380, my favorite adhesive, is not good at bonding to wood in high humidity environments. The joint has come loose over time, but the machined fit is so tight, that once the handle heats up at all in a pot, it swells enough that it won't come off; so no long term issues. Last, I would use a harder material next time. Maybe a 17-4 PH. Something that resists tapping on the edge of a skillet a bit better. 

Now all I need is a fork.....

Liquid Oxidizer Impeller

At my school there is a model rocket group, Launch Initiative. They design, build and fly mid size model rockets. Typically they use purchased solid rocket motors, or hybrid (solid fuel, liquid oxidizer) motors they design and build. While working on some other projects, they are planning for the future and trying to push their engineering skills by designing a hybrid rocket motor with a oxidizer turbo pump.

This project was more of an experiment and test of skills, and this version wasn't intended to fly. Twofold to this project was the design and mathematical modeling of a pump impeller and turbine, and second to manufacture the pumps and impellers. The design was done by one of the Launch Initiative team members; I was only on board for the machining.

This is the second generation of pump impeller, made in aluminum. This machined one is scaled down from its original size to result in a roughly 4 inch (100mm) diameter. This scaling was done primarily for cost; I already had material for this smaller size. It was also done to replicate the size of what a final impeller would be. A flight ready version of this impeller would be out of stainless, and the turbine would be inconel. When I finished machining this impeller, the team had already progressed to the fourth generation of impeller which added splitter fins. 

All programming was done in Fusion360 with a custom post and run on an Okuma Genos M460V-5AX. Absolutely fantastic machine, no complaints with it. There is a real joy in using a machine that does what you tell it to first time, every time. I cannot say the same about Fusion for this type of work; not at all suited to it. I first tried to program the part with simultaneous 5 axis moves, but Fusion couldn't handle it. In the end I had to split all the faces up and do them as positional 5 axis moves. Visually not as good but these impellers would have to be polished before service anyway so this would be functional.

Cycle time on this was around 4 hours a part. This could definitely be cut down by pushing roughing and semi-finishing federates. Using a better CAM package to optimize the tool paths would also help. I have an Esprit license which is the preferred CAM for Okuma machines (they have a partnership and sponsor my school), and the machine simulation models are very accurate. 

Checking clearance inside the machine when testing

Fusion doesn't have machine simulation, so I was a little weary for some of the 5 axis moves. I had improvised a basic simulation that would prevent major crashes, but it was inaccurate for close clearances. There was a risk of crashing the back of the spindle into the table when rotated up at steep angles. This was solved by propping my camera on the trunnion inside the machine. From there I could stream to my smart phone and zoom and watch the clearance in critical areas. I would run the part dry with no stock at a slow speed to I had a hope of being able to react if something goes wrong.

The machining process was quite straightforward. Most of the tooling was Sandvik inserted, solid and drills. I used to be skeptical of the premium price of Sandvik solid carbide tooling. After using them for an extended period of time, I think they are worth the price. The carbide quality is just phenomenal and the cutters just last and last and last. Maybe if were paying for all the cutters out of pocket, I would change my tune but as long as work is buying them (or Sandvik is donating them).

Various stages of machining

In the end, this part was also used as a demo piece for an on-campus creativity festival. I put together a little display with the different stages of of machining seen above, along with the tools used and the chips they produce. This was to show to people who don't know about machining how a part is made. A lot of people thought these impellers were 3D printed and were surprised to find it was cut out of solid.

The project was fun. I think I made 6 of these in the end. I would like to revisit it eventually with a better CAM package. This was only my second 5 axis project and I made it with only 100h of 5 axis machine time under my belt.

Pretty reflections after roughing

One Day Builds: Micro Tripod

    Growing up I had one of the little, flexible "Gorilla" tripods. It worked alright but after a year of light use, some of the ball sockets cracked (made of ABS) and the legs no longer held their shape. The unit was also very bulky given what it could do. This past year at work, I was setting up a coolant manifold on a milling machine and the LocLine I was using reminded me of that old tripod. I had a planned a hiking trip to Vermont coming up and had been thinking about buying or making a tripod to shoot some time lapses.

    I threw together this little tripod in maybe an hour. It's printed on a FormLabs Form 2 in their Durable resin. I had wanted the LocLine to snap into the printed hub, which it does, but the printed material creeps too much over time and the LocLine flops around in the socket; it doesn't stay in position. I solved this by epoxying the first section of LocLine to the printed part. The screw on top is just screwed into the printed part, into printed thread. The short legs work well for most situations, and can always be extended if I feel the need for longer legs. Made of delrin, the LocLine shouldn't see any degradation over time, even if used in the Sun a lot. It's also easy to buy anywhere in the world. As it turns out my phone is much better at taking time lapses than my camera, but luckily the tripod is versatile.

Sterling Engine for Students

    I built 6 of these sterling engines to help a professor to prepare for a class. This professor in the Industrial Engineering department was ramping up for a new class on CAD, CAM, and simulation. Typically the students learn Creo (or OnShape), but if they so choose, they can now take a class to learn SolidWorks modeling, MasterCAM, and SolidWorks simulation. A class project was selected by the professor on the criteria of it needing to be complex enough to last a semester, have moving parts for animation, have a thermal element for simulation, and have some pieces simple enough that a student could program and machine them.

A finished engine. The legs and flywheel are made by the class students.

   
    The idea was the students could progress through the project, modeling and assembling components in CAD, running motion and thermal analysis on the model, and programming and making a few parts. The remaining parts would be made be me and at the end of the year, the students could assemble the engine in real life with their parts and see it run. The parts of the engine the student didn't make would be reused year to year.

    Chosen was the "Vickie" Victorian styled sterling engine designed by Jerry Howell; a beautiful and elegant model engine. This project was really doomed from the start due to the choice of this engine. The plans from Jerry Howell contain no tolerances and the instructions intend a lot of hand fit and finish, creating bespoke parts. This doesn't jive well with the fact that 6 needed to be built, all with interchangeable parts, and several of the parts had to be made by inexperienced students. Add to this some on the fly design changes by the professor that override my better judgement and we ended up with 6, pretty, but non functional model engines.

Detail of the linear guide for the power cylinder.

    I came into this project half way though. The professor and another student worker had already made many of simpler parts of the engine. As I progressed through the remaining parts and sub-assemblies, I ran into fit issues. Going back and measuring the parts the professor and other student had completed, I found every single part was out of tolerance (self imposed +/- 50 um), or in some cases totally missing features. This revelation essentially doubled my workload on the project. While some parts were only off by a small amount or had a bad surface finish, I saw no excuse for missing features, or dimensions off by more than 1 mm. Some parts I reworked or shimmed to fit, most others I totally remade.

    This is what I believe to be one of the larger contributors to the engine not working. The other is on the fly design changes the professor wanted to make the engines easier to build. These included replacing some of the custom fasteners with OTS parts (minimal impact) and replacing some of the weight reduced parts with heavier ones. When I was reading through the assembly plans, a great deal of mention wad given to what components had to be very light weight. Many of those components involved soldered assemblies of machined parts and brass tubes. It was decided to replace the brass tubes with solid steel shafts to simplify. I think this extra weight contributed to the engines not working. 

    In the end, these engines are only good for display. Maybe some student or professor in the future will find these and be able to get them working.

6 completed engines. Note the oxidization on the hot ends from testing.