ok, first attempt using sketchup 8

[JAZZCNC]

at which point you'll theoretically be doing 18m/min - assuming your motor is still producing sufficient torque at 1800rpm.

Ok first I know people(some) think I have no respect or time for the Law of physics but they'd be wrong.!! . . . I'm realistic not stupid.!!

But none of the calculators allow for, neither can they really, all the other outside factors that DIY building create. They expect, Nah rely on every component being perfect and exact to spec with very little to no physical restrictions.
I don't disagree and can't or wouldn't due to the law of physics that the forces are correct but the forces are not the problem and they can only be realised from what they are connected too and this is where it all goes Pete tong.!!

Your theoretical 18m/min requires the stepper to give usable torque at 1800rpm.!! . . . At 1800rpm stepper motors couldn't pull the skin of rice pudding let alone a 40KG gantry and with only 48V they would struggle get near 1800rpm and have enough torque left to turn the screws with nothing connected.

Couple these things with other build and cheap component issues and the REAL figures are far from the theoretical figures. . . This is all I'm trying to say and get over but If my saying this upsets anyone who's into specs and calc's then I'm afraid it's "Tuff shit" it's true and realistic..!! . . . Ence . . KEEP It REAL.!!

[irving2008]

Ok first I know people(some) think I have no respect or time for the Law of physics but they'd be wrong.!! . . . I'm realistic not stupid.!!

But none of the calculators allow for, neither can they really, all the other outside factors that DIY building create. They expect, Nah rely on every component being perfect and exact to spec with very little to no physical restrictions.
I don't disagree and can't or wouldn't due to the law of physics that the forces are correct but the forces are not the problem and they can only be realised from what they are connected too and this is where it all goes Pete tong.!!

Your theoretical 18m/min requires the stepper to give usable torque at 1800rpm.!! . . . At 1800rpm stepper motors couldn't pull the skin of rice pudding let alone a 40KG gantry and with only 48V they would struggle get near 1800rpm and have enough torque left to turn the screws with nothing connected.

Couple these things with other build and cheap component issues and the REAL figures are far from the theoretical figures. . . This is all I'm trying to say and get over but If my saying this upsets anyone who's into specs and calc's then I'm afraid it's "Tuff shit" it's true and realistic..!! . . . Ence . . KEEP It REAL.!!

Hey, no offence taken Jazz, I am a great fan of the try it and see school... My father was a toolmaker and a marine engineer and couldn't work the physics or maths to save his life... but he still made some great stuff and mostly it worked first time. And yes, I am pefectly aware that a stepper has bugger all torque at 1800rpm if it can get there at all, in fact the point I was making, clearly badly, is that while in theory you'd still be accelerating at the point you'd need to start decelerating in reality you'd be at some lower speed before that and therefore your average over the distance would be less than the theoretical.

IMHO the purpose of the theoretical calculations, recognising they can't model every real-world situation (but can get very close if you can identify all the 'gotchas') is to see if you're in the right ballpark... if the theoretical numbers come out below what you want to achieve then you know there is no point going down that route. On the other hand, if they come out way above then you know its possible, how close you get is then determined by how near to the ideal you can make it - and my experience is that its easy to get within 70%, 85-90% is doable with care, >90% is hard. If they are close you know you've got a marginal design.

[JAZZCNC]

IMHO the purpose of the theoretical calculations, recognising they can't model every real-world situation (but can get very close if you can identify all the 'gotchas') is to see if you're in the right ballpark...

Yep I agree can be ok for a rough ballpark (Thou yours did seem a bit off base.!!) . . . You only have to look to the BIG BOYS in theoretical design and performance like F1 teams and see that even they can't predict and 100% confidently model every outcome.!

Hey, no offence taken Jazz,

Good now give us a hug.!!. .

[deannos]

Would this design be ok, i thought i would use some 100x60 box section as bearing plates. I would have some left over from the gantry and it saves on the Ali plate. The extra height would help with the bed, bit more room to play with. This box section is only 3mm thick, is that ok. I have used 300mm, 2 x 800mm and 1400 SBR20mm rails. The ball screws are 350mm, 2 x 800mm and a 1450mm length.