Thread: 3-Axis CNC Mill Project
http://videobam.com/FeuSv <-- link to video
Ive knocked this up in solid works, there is now 200 gantry plates, and the gantry profile is now 425 long not 600.
Any advice, input welcome and required lol thanks
Last edited by Hobgoblin; 06-09-2012 at 09:24 PM.
Big thanks for Jazzcnc's input in my project, I'll be referencing his ideas as i get further into the project, so far the guy has gone far far out of his way to lead me on the right path.
This far now, this was supposed to be a re draw. But I think ill be going for a re re draw just to be sure all my parts right.
If I am driving my X axis with two 16mm diameter x 10mm pitch screws via a belt and pulleys, do i use a 1:1 ratio? so the pullys on the screws and motor each have for example, 40 teeth?Hobgoblin.
Yes, for the vast majority of things 1:1 is the best choice to get good speed and acceleration with 10mm pitch screws. There may be occasions when you need to use 1:2 (e.g. motor 15:screw 10), but it would need to be something very detailed to warrant that. Also there's no need to use such a large pulley, it will only increase the inertia of the system and reduce your acceleration as a result. 30T is a good choice since then you can use 1:2, in addition to 1:1, without having to use very small pulley.
See now i just feel really thick. I had in mind 5mm pitch, 15mm belt. Ive already been having a lift with this from jazz and it has helped me to be in the right direction but i still dont fully understand this aspect of the machine im building. Not that im ignoring his advice i just thought id throw the Q on here and see what comes of it. Your last sentence went straight over my head jonathan, sorry .Hobgoblin.
If you use a 30T pulley on the ballscrew then you can put a 30T pulley on the motor to get 1:1, or use a 15T pulley on the motor (which is unlikely to be needed much if at all, but it's good to have the option) to get 1:2 ratio. It's best not to use smaller than a 15T pulley since the belt will wear quicker and you may not have enough teetth engaged with the pulley if it is too small.
The moment of inertia of a cylinder (which is essentially what the pulley is) is proportional to its squared, so a small increase in the pulley diameter will cause a relatively big increase of the inertia. The torque required from the motor is proportional to the inertia, so you want to minimise it if possible - hence use the smaller pulley, 30T instead of 40T.
This has helped some what. Aim for 1:1 but leaving the option for 1:2, got it .
I'm up to working with Chai to finalise a parts list at the moment, Then its save up time. Hopefully I can get my china bits before xmas.Hobgoblin.
Before xmas for my order of bits now looks unrealistic. Other more important things have had my pocket money, new helmet for the bike being the biggest.
Anyway, I have now got all the extrusion I need. I was 1 piece of 20x80 x 600 missing for my new design to work. And My side, vertical, pieces of 20x80 were 600 high, have now been re cut down to 425 high.
I have a fair bit to get on with though.
Photos to come.Hobgoblin.
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