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I am designing a CNC for light aluminum work. I have made 5 examples and cannot figure out which one to use. It's my first build/revision for all 5 of them. I like V5 the most, but it's probably the least strong of them all (Next would be V2).
(File is Sketchup 2017)
Thanks,
-Matt
---Image Order----
- ALL
- V1 (OpenBuilds C-Beam)
- V2 (8020 30-6060 Outer)
- V3 (8020 30-6060 Inner)
- V4 (8020 40-8080 Inner)
- V5 (8020 40-4080 Inner)
To increase rigidity you must decrease torque where linear guides mount to frames. You also need to increase the distance between two sides of structural beams. What this translates to is reducing the total distance between the cutter and the X axis rail as much as possible, it also means the further apart the top extrusion is from the bottom one on either side of the ball screw the better for rigidity. Finally and most obviously, 40mm is better than 30mm or 20mm. You'll need to take a closer look at your drawings to determine which best fits these descriptions, and weigh it against carriage mass and cost.
if u make a cnc to look nice and have no utility , then u can use the most beauty contest components , but if u make a cnc to work with it , u need to make it the most stiffnes u can achieve with stock u have .
I don't think any of them will be much good for aluminium. For wood and plastics, maybe OK. For 3 mm cutters, maybe.
The root of my dislike is the weakness and flex in all those aluminium extrusions. They are just not strong enough.
My 2c
Cheers
Roger
Hi,
aluminum has a Youngs Modulus of 70GPa, steel is 205GPa, even cast iron is 110GPa.
Bang for your buck steel beats aluminum for stiffness hands down.
Craig
Hi Matt - None of them. If you are committed to using aluminium construction extrusions then mount the rails on the side of the extrusion so the column bolts directly to the car, as then the cars bolting face is vertical. Thus means you have reduced the part count considerably (at least 3 parts gone from each side), made it significantly stiffer and simpler. Construction extrusion has a lot of compromises for its apparent convenience. Using std extrusion sections would be much better; cheaper and stiffer.
You are designing the drive system and the structure all at once and your structural design is being compromised by considering the drive system. Since it is your first machine and you are not aware of all the inter relationships of things I suggest you design the structure first. Design the stiffest most rigid and simple structure. Once that's done, then design the drive around that. I also suggest that since you are going to machine plates to build this thing then build the entire machine from thick plate. It will be much more satisfactory then using construction extrusion... machining aluminium effectively is a big ask for a hobby machine and you have a way to go to get there...
Oh and only 5 versions? When you are up to about rev25 you will be close to the money.... Consider making your first one from 16mm formply. You can make this with jigsaws and simple tools. Then once you figure out what you should have done you can convert it all to 16mm aluminium. If you do a really good job with the ply design you can use it to make the aluminium parts... Took me a couple of machines to be able to machine aluminium well. attached is a formply machine and it will machine aluminium... its a test build for a small mill...
Peter
Matt just spotted the starting date in 2017 - did you get this machine built?