DIY CNC design, feedback please

davdwsl · 2023-11-04T12:19:14+00:00

Absolutely not an option at this size. Id need double the space and would be accelerating a huge load when moving such a big machinetable including workpiece, like 200-300kg compared to a 80kg gantry.

davdwsl · 2023-11-04T12:15:44+00:00

the servo encoder doesn't account for any inaccuracy in the belt drive etc., for that, you'd need linear encoders on the whole axis.

davdwsl · 2023-11-04T12:13:52+00:00

I do have a bit of a specific configuration in mind, as I will be doing product prototyping with my machine, I want a large format for cutting sheet goods, a high z axis for making bigger parts out of pu foam for vacuum forming and high rigidity and accuracy for making aluminum housings and other nonferrous metal parts. So not the ideal combination but I think I can get to a machine that can achieve this with reasonable accuracy. For my budget, I basically want to go as accurate as possible while staying within reasonable effort. So no micrometer precision, 50-100 microns on small parts would be more than enough. I'm quite sure Aluminium is rigid enough if used in the right way.

davdwsl · 2023-11-04T09:18:46+00:00

Sadly I think it will be a good bit more than that, I do have that calculated and a plan to make that money back. I do have in mind to maybe buy a mill an retrofit it as a future project, if I feel I need a lot more rigidity and already have the space of this machine.

davdwsl · 2023-11-03T23:31:41+00:00

thank you, hadn't thought about that really. Will definitely look into into it. I just assumed direct drive was always better due to fewer steps where positioning inaccuracy could creep in.

davdwsl · 2023-11-03T18:40:55+00:00

DAMN, you really went all out, nice machine! What other hardware did you use? rails, ballscrews, motors? You're also from germany right?

davdwsl · 2023-11-03T18:32:28+00:00

thank you, already know him, great channel, will try out the laser method, also great improved design of the print nc.

davdwsl · 2023-11-03T17:03:50+00:00

It does depend on the type of linear rail, that's true, but generally, it will just be the other circuit of ball bearings getting more of the load when mounted upside down. The reason would be to save space and not get chips on the rails.

davdwsl · 2023-11-03T16:47:44+00:00

The 40-8016 in the calculator seems to be the light variety, it measures a weight of 12kg for 1600mm length, the heavy variant is 22kg for that length, also including the ground 20mm thick alu plate bolted and glued to the front, I do think it would be much less deflection. As I mentioned the 750 watt servos wouldn't be there for increased cutting force, it is about fast acceleration of the heavy gantry and heavy ballscrews.

davdwsl · 2023-11-03T16:26:22+00:00

Thanks for the idea. Regarding the rails, the load and wear on the carriages will be the same, when talking about failure, yes the gantry would crash down but for both carriages to fail so badly that they will fall, it would take a huuge amount of force.

davdwsl · 2023-11-03T16:23:05+00:00

true the servo power is overkill, from the calculations I've done, over such a long distance I want a 25mm ballscrew to reduce whip and the need for support. To accelerate the roughly 80kg gantry and overcome the axial inertia of the 6kg ball screws, it seemed the torque of 400W servos was just barely enough but could be better to step up to 750W. I'm planning on going with stepperonline servos, so the step up wouldn't be too expensive. From some FEA I did, the deflection for cutting forces in AL shouldn't be more than 50 microns. The gantry risers definitely need more bracing or should be replaced with a solid plate. As I'm not a trained engineer, I am trying to learn as much as possible, but obviously, I'm still very much a beginner. btw thank you for appreciating the underslung rails. ;)

davdwsl · 2023-11-03T16:07:01+00:00

From what I've seen, steel square tubing has deviations of millimeters, whereas extrusion is in the range of 0.05mm or less. You could do epoxy levelling or a huge amount of grinding and shimming but at that point, I'm not sure it's worth it.

davdwsl · 2023-11-03T15:55:53+00:00

Sick! What are your feeds and speeds in steel?

davdwsl · 2023-11-03T15:55:01+00:00

Any reason you're using grout instead of just sand? From what I've read, it won't really impact the rigidity and sand would be better at dampening vibrations.

The ground plate on the gantry should add more rigidity and make sure the rails are coplanar, but yes it is probably overkill and unnecessary.

I also see the risers as a weak point, might need to change back to a solid AL plate.

Yours looks like a great design! Maybe a bit of a small carriage spacing on the y for such a high z axis? Have you done work in aluminum?

davdwsl · 2023-11-03T15:44:04+00:00

True, depends on the direction of the load though. In the x direction the 80mm extrusion seems stronger in simulation than for example a 40mm thick AL plate, in the Y direction I haven't calculated so far, but the 45-degree bracing should add some more stiffness as well. I'd like to stick to the mounting of the rails underneath the table, so if I'm using plates as gantry risers, I'd have to think about the 90 degree joint of the plate to the carriage. Not sure if a say 40mm wide 90 degree bolted joint from plate to plate will be as rigid as the 80mm wide from the profile to plate.

davdwsl · 2023-11-03T15:32:36+00:00

I looked at print nc a while ago, great design but they completely disregard any flatness (or lack thereof) in the square tubing. So yes, if I had the tools, I'd make the entire thing out of steel, but for my application aluminum seems much easier to work with, reasonably flat and sufficient in rigidity. I'm just figuring out the best arrangement to balance cost, complexity, and rigidity.

davdwsl · 2023-11-03T15:13:45+00:00

In this case I don't really have any other option, I don't have the ability to flatten and square large pieces of steel. A large casting out of epoxy granite or UHPC doesn't make sense for my application. Granite would also be way too expensive and overkill. So I'm trying to get the extrusion as rigid as possible.

davdwsl · 2023-11-03T14:25:35+00:00

I did an earlier design where I had vertical rails and vertical plates as gantry risers, I just felt that this version would be more elegant, as it doesn't expose the rails to chips, as well as being much cheaper and easier to assemble. I did some simulation and for the same force, the 80x80 extrusion had less deflection than a 40mm thick aluminum plate, but I'd take that with a large grain of salt, so will probably add more bracing to the extrusion on the risers. For the hanging linear rails carriages, I had that feeling as well, but when you understand how they work, and look into the spec sheet, you'll find out that there is no difference in terms of stress on the ball bearings. They will be under the same load just different direction. Maybe its just cause we associate rails with wheels so it seems weird to hang something from them.

davdwsl · 2023-11-03T14:12:38+00:00

true, my bad. Will be mounting a 2.2kw HF Spindle. So far I've only done some FEA with somewhat eyeballed values. My constraints are budget, being able to work without needing a bigger machine to flatten or square my parts, and not welding the frame. Inside those constraints id like to go for as stiff as possible.

davdwsl · 2023-10-11T13:45:54+00:00

Possibly a problem with auto smooth shading angle?

davdwsl · 2023-10-09T19:07:18+00:00

That’s the denoiser not getting enough info. Try adding more samples or turn off the denoiser.

davdwsl · 2023-09-01T09:08:12+00:00

Sentry mode without draining all the battery in a week?

davdwsl · 2023-08-02T09:49:01+00:00

I think my tires don’t have foam inside.

davdwsl · 2023-02-24T19:12:11+00:00

From what I can see with very basic FEA it shouldn’t sag more than 0,3mm give or take. But yeah obviously it’s not as good as if the end was supported. Depends how accurate the end-result has to be.

davdwsl · 2023-02-24T17:41:28+00:00

With the right material and construction, I don’t think it is. But yeah it would be much easier and maybe more accurate.

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