Isogrid Cylinders

Currently on my second Avid machine. I upgraded to a 5x5 with a rotary axis for this specific project, which is machining a 12 inch diameter aluminium cylinder with an isogrid pattern to make lightweight propellant tanks for an amateur built rocket. The cylinders initially weigh 27 lbs and are reduced to 8 lbs.

Smaller cylinder shown on the left is a 6 inch diameter test.

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Very nice! Do you have rocket photos to share?

What’s your final thickness, and Is centering the stock on the rotary straightforward?

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This is incredible. I just checked out your website too, VERY cool stuff.

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@Stephen thanks! The rocket is being built by the Portland State Aerospace Society. mostly on the drawing board, it’s very early in the design process. Here’s some charts from a year or so ago covering the basics.

The raw material is 0.25" thick and we’re targeting a 0.05" skin thickness. The primary issue with the stock isn’t centering but dealing with eccentricity. The wall thickness has a pretty tight tolerance, but the material is out of round by up to 0.02". Pretty small when considering the radius (0.3%), but leads to a large variation in the wall thickness.

To compensate, I’ve developed a general cylindrical auto-leveling process, where I probe the cylinder first, and adjust the g-code to compensate. This allows us to achieve the 0.05" wall thickness with a tolerance of +/- 0.0025".

I’m in the process of cleaning up the scripts and documentation to release the cylindrical auto-leveling tools, so I’ll have a separate post in the future about it.

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Maybe one of the coolest projects I’ve seen on a gantry router in along time.

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Welcome to the forum. People like you make me feel bad about myself! Looks amazing.
ren and stimpy dog GIF

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I plan to build an aluminum chassis for one of my competition rifles and wondered if you could answer a few quick questions. How was the indexing with 27 lbs of aluminum? It looks to be really good. What grade of aluminum was this forged, billet, cast? Do you have the 8.7HP Spindle? That thing is yuuuge and gorgeous!

JH

The indexing worked well. The total mass on the rotary axis was a bit more than 27 lbs as I had to add some sand to deal with vibration and chatter. Probably another 20 lbs or so.

The tube was 6061-T6, I believe it’s extruded.

I’ve only got the 3 Hp spindle. Just had to take it nice and slow. About 80 hours over 10 days.

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Thanks for the information, very helpful! I hope you’ll share a launch, those other projects are wicked cool!
James H

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