3-Axis CNC Mill Project

**Hobgoblin** · 29-08-2012

Starting to see the error of my ways so far. Taking time out to work on some things. Will update once progress is made.

**Hobgoblin** · 09-09-2012

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.

**Hobgoblin** · 24-09-2012

The eagle eyed among us will of spotted my ball nuts missing for x, thats because im shit at cad and still learning and they have disapeared, so i put them back in.

Thanks.

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**Hobgoblin** · 24-09-2012

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.

Thanks

**Hobgoblin** · 17-10-2012

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?

**Jonathan** · 17-10-2012

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.

**Hobgoblin** · 17-10-2012

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

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**Jonathan** · 17-10-2012

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.

**Hobgoblin** · 17-10-2012

This has helped some what. Aim for 1:1 but leaving the option for 1:2, got it

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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** · 26-10-2012

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.