operation cnc

[kingcreaky]

Like that Idea, I noticed on Jonathons this idea was used, but disregarded its main advantage. This way I could buy, say 2m x 1m setup now. make the gantry 2m and the x axis x axis 1m. If its as successful as I hope I can then re-make the x axis longer. Need to think of a cunning way to make the rotating housings... I can worry about that at a later date. Going to start from scratch in sketchup again. this time with my newly quoted 60mm steel box from Adey Steel, and with the new design wide gantry and static screw.

[blackburn mark]

spent most of last night laying awake. I get a bit like this when im 'on one' with something like this.

that's a good sign :)
its interesting and quite easy at the outset of any new design... in my experience though it gets harder the further you get into the nuts and bolts of the job... one small amendment can have a bitch of a knock on effect :(
its frustrating when you want to get building but try to design the knickers out of it before you commit because those amendments and knock on effects can be heart breaking if your half way through a build

having a Y axis that is longer than your X is pretty unconventional for obvious reasons... i can see your logic in expandability, if you will definitely expand if all works well i would keep the faith and go for glory at the outset on the proviso that the consensus was that your design would do what you required

iv not built a machine of that size but there are a few people on here that will give you a good idea if its doable 3m x 3m is quite a large machine... i'm not sure anyone has built one of that size on this forum ?

good luck getting to sleep lol

[Jonathan]

3m x 3m is quite a large machine... i'm not sure anyone has built one of that size on this forum ?

I don't recall any that size here. You can get 3m long rails rails easily, but if you decide to use profile rails then it will be hard to align them over that distance. You're getting into mounting the rails on self levelling epoxy territory. The SBR series rails tolerate a lot more misalignment than the profile rails, so that option would be a lot easier and I'm confident you could make a strong enough machine that size to cut aluminium with them. The gantry clearly needs to be stronger than the current design if it is extended to 3m. You may want to consider placing the Z-axis between two beams with the rails on their inner faces.

With 3x3m you would also need rotating ballnuts on both X and Y. Just in case you've not already found it, there's some ideas about how to mount a rotating nut here. It sounds like you might have a milling machine so as long as you've got a boring head or lathe you can make them.

[WandrinAndy]

... in my experience though it gets harder the further you get into the nuts and bolts of the job... one small amendment can have a bitch of a knock on effect :( Its frustrating when you want to get building but try to design the knickers out of it before you commit because .....

Very true! That is precisely the design phase I have been wading through for the past many weeks, and it's very frustating but, with what I have discovered and had to correct in my little design, I'm very thankful to have found these problems before the build proper!

[kingcreaky]

thanks for the comments gents.

however, although id love to build a machine 3x3. I cant afford too!. Im simply make the biggest I can whilst maintaining my marriage :D

anyway, done a bit more on the design. but those bearings look mighty small for such a large spanning gantry....

might have to have a re-think...

what do you guys think?

[Jonathan]

I don't like the bed being unsupported over a 3m length. You can at the very least mount a piece of steel box section vertically at the back and the front, but the front one would have to be removed when you make the axis longer. A third piece of 3m long box section in the middle wouldn't go amiss either. Also I would make the bed bolt on to the 4 verticals on the other side, again to make it easier to extend the bed in the future. Currently the frame can 'skew' quite easily, since there are no triangles - so add some pieces to make triangles! You can do this in all 3 planes which is a good way of using up the left over box section since no doubt you'll be ordering in 7.5m lengths. Incidentally how much did Adey Steel quote you for the box section, presumably 60x60x3mm? Their pricing seems to be a bit random...

The way you have mounted the ballscrews is good since it allows adjustment of the height via moving the 4 pieces of box section, which is nice and strong. You can make the end mounts fasten to the box section via holes slotted horizontally to get adjustment in the other axis, which will help when aligning the ballscrews.

[irving2008]

Some simple calculations can give you a better feel.

By way of example (and i'm not suggesting this is how to do it necessarily) lets say your gantry is a couple of 60 x 60mm x 3mm 2m long steel box sections joined by 3 bits of 10mm ali plate 200mm x 200mm at each end and the middle. The overall weight is 15.5kg and the deflection in the middle under its own weight, (ignoring the extra stiffness from the ali plates) would be ~0.1mm. A 10Kg spindle/z-package would cause a further 0.1mm sag, for a total of ~0.2mm. The max load on the bearings would be 255N which is nothing for a 25mm SBR. Increasing that to 100 x 60 box section with thicker walls would stiffen it further. Box section has its own issues with resonance but there are ways round that. The Y-rails would add further stiffness. All calcs are approximate and a more thorough analysis could be done.

So its doable... just need to get the detail right...

[Jonathan]

I think if we included the torsional stiffness in the calculation then the results would be a lot worse. Once this 3m gantry is drawn I should be able to do a FE simulation to find how much it twists, rather like the one in this post.

[irving2008]

I think if we included the torsional stiffness in the calculation then the results would be a lot worse. Once this 3m gantry is drawn I should be able to do a FE simulation to find how much it twists, rather like the one in this post.

Don't disagree, my point was to illustrate that the bearing sizes were OK for a gantry of that scale. Of course it will need to be stiffer in torsion and I'd consider plates both side of the box section and some perpendicular as well.