How To CNC An Upright

[Mechie3]

Some of you might know me from the 818 forums. For those of you that don't...well, I hang out in the 818 forum. :) Rather than fill up my build thread with my latest part that is completely unrelated to my build I decided to put it here.

Today I finished machining an upright for a Legrand Bmod car. The original part was a cast magnesium piece with minimal post machining. With casting it's very easy to make oblique surfaces. With a 3 Axis CNC it means multiple setups. Some 4 axis, and definitely 5 axis, machines could do it with fewer setups but I don't have access to those. I took pictures of the process to share some insight on what it takes to machine parts. In talking to non-engineers/machinists there's a general misconception that CNCing parts is as easy as putting metal in a vice, uploading a CAD file and hitting go. In reality, you have to sometimes be creative in how you make a part based on the tools you have, the order things must be machined in, and then make a CNC program from the CAD file along with any necessary jigs.

Step 1:
Cut a large piece of aluminum to size, faced off one edge to be a datum, and marked my origin so I had a reference.
http://i.imgur.com/nBBDQsj.jpg

Step 2:
The axle stubs have a 3 degree taper that holds them in place. My taper end mill (bought special for this project) wasn't long enough or big enough in OD so I had to remove material down to the top surface of where the taper started as to not break the end mill. I did this on a manual but could have just as easily programmed it as part of the first CNC setup.
http://i.imgur.com/Mk7llnW.jpg

Step 3:
I machined the taper as well as the two holes for the brake caliper. I don't have a pic of the end of this step, just using my touch off tool to set tool heights at the beginning. You might wonder, "why not machine the whole profile from this angle?" If I did, when I flip it forward 90 degrees to machine the other profile I no long have a square surface to clamp off on or a good way to fixture it. By doing it this way I ensured the brakes would definitely be correct relative to the axis of the hub and it gives me a square surface to work from and the brake caliper mount can be used to fixture the part for the next step.
http://i.imgur.com/2Ar1tOK.jpg

Step 4:
I rotated the part 90degrees towards me and machined the front/back profile.
http://i.imgur.com/7ctcDV7.jpg

Step 5:
Sawing off material is almost always faster than milling it off. That island shown in the previous photo was cut off along with other portions of the base accessible with a saw.
http://i.imgur.com/yJ4OVti.jpg

Step 6:
Back to a manual mill I clamped on the brake caliper mounting ear and machined off the rest of the base. The base existed only to give me a clamping surface. It would have interfered with my jig if I didn't remove it.
http://i.imgur.com/cqtXp1a.jpg

[Mechie3]

Step 7:
I made a jig to hold the half machined part. Because I had machined off my datums for X and Y the corner of the jig was setup to be X and Y so precision in the jig defined precision in the finished part. The part was located by the brake caliper holes and then clamped through the middle. There's a spacer underneath the part to prevent it from flexing while clamped.
http://i.imgur.com/oW8gJBV.jpg

Step 8:
The left/right profile and the through pocket was machined using the jig.
http://i.imgur.com/yTAaHbL.jpg

Step 9:
I setup the next program with an origin that allowed me to flip the part and retain the same X and Y datums. A different height spacer was used but the part was setup the same way in the jig.
http://i.imgur.com/07PPWNW.jpg

Step 10:
I touched off the tools using the ear as a reference as the tools would be touching this already machined surface and I didn't want any tool path mismatch. Touching off on the ear and then compensating for the additional depth meant perfect matching. I machined the back side of the ear and the blind pocket.
http://i.imgur.com/oFGMFWz.jpg

Step 11: The steering arm bracket mounting point needed a square corner instead of a radius. It also wasn't parallel to the surface of the jig. I used a manual mill for this as it was a simple process. I made the hole for the upper control arm bolt at the same time.
http://i.imgur.com/KOSMwjT.jpg

[Mechie3]

Step 12:
The inside wall of the blind pocket was perpendicular to the caliper ear, but not parallel to the upper control arm mounting surface. I rotated the jig 90 degrees and shaved off part of the face so a nut could sit flat. I used a ball end mill to prevent a square corner inside the pocket which could potentially be a place for fractures to start. The two small holes for the steering arm bracket were drilled at the same time.
http://i.imgur.com/5n365gR.jpg

Step 13:
The blind pocket needed slight clearancing to fit the nut. This was due to a change in the control arms made after I machined the pocket.
http://i.imgur.com/7yS7t0S.jpg

Step 14:
A 1/2" hole for the bottom control arm was made on a manual mill as well. This was easy as the hole was parallel to the bottom of the jig plate.
http://i.imgur.com/8OlvpC2.jpg

Step 15:
A bunch of hand deburring and some sanding to remove tool chattering* and it was done. On the right is what I started with.
http://i.imgur.com/U10KYQP.jpg
*Chattering is caused when the tool vibrates and makes small pock marks. It's caused by many factors but is exacerbated when using long tools. Some of the cutters were 4" long. I'm not a machinist (i learned to use CNC's from reading the manual and programming from trial and error) and have little experience with using long cutters. I was able to minimize chatter for the most part and light sanding took out the cosmetic defects.

Step 16:
The original magnesium part next to the aluminum piece. One of the hardest parts in making the CAD model was figuring out what the original designers intended for dimensions to be. The part was cast so it had some decent draft on it along with a poor surface finish. 10 measurements created 10 different dimensions, sometimes as far off as .030"+. Sometimes you just have to use your judgement and do what you think is best. The part could have been made lighter if I had time to analyze it and run some FEA. Instead I just copied it.
http://i.imgur.com/nZjppuA.jpg

[rich grsc]

Sorry, sounds interesting but no pictures.

[skullandbones]

Nice work, Mechie3!

I love watching my friend at his fab shop with non computer driven milling machine. More work is done on the band saw, and lath than the mill. He, too, uses many appliances and jigs to overcome the compound angle issues. I'm sure your computer technology is a wonderful tool to add to the process. Still, there's a lot of stuff people can't appreciate without actually seeing it in real time. Thanks for the pics.

WEK.

[Mechie3]

Sorry, sounds interesting but no pictures.

They take a while to load. Perhaps your location is blocking imgur?

[Buzz Skyline]

Very cool! Thanks for posting it.

[Mike N]

Nice work. Just as a point of reference how many hours do you have into machining that part?

[Mechie3]

Nice work. Just as a point of reference how many hours do you have into machining that part?

Too many. Haha! I tend to be a little conservative on machine feeds especially if I'm only making 1. The taper tool was $80 and the aluminum for this was ~$230 (enough to make 2.5 pieces though) so I didn't want to scrap either. I think total CNC program run time was around 4-5 hours, another hour or two to make the jig, another hour or two to setup all the manual setups, plus quite a few hours worth of measuring and CAD time and CNC programming time.

It was done for a local guy that co-drives a Bmod with a guy that is 5 time national champion (the guy I made this for is multi time runner up in Bmod as well). The co-driver bought his own Legrand this past year but one of the uprights failed his second time out. He said you can't buy new ones so I offered that, if he bought me the tool I needed and material I'd make him one.

[FFR-ADV]

Hi Craig.

Machinists are still critical craftsman particularly for those of us with Bespoke aspirations for our cars.

It takes a lot of engineering / machinist experience to convert a prior cast part into a machined equivalent. Most don't realize the how much skill is involved in choosing setups and reliably holding the emerging part under cutting loads (especially during the final cut when straight features that work in a vice are disappearing. Designing with proper respect for and attempting to minimize the challenge by using their knowledge and growing our first hand knowledge is something all of us in the engineering world owe these critical craftsmen. Thank you for showing part of this world!

Nicely done!