pulley ratios on 3 pulley axis

[Jonathan]

Nothing to do with the circumference.
24 teeth, 5mm pitch 1 rev = 24 x5 = 120mm per rev
can't be anything else.

120mm is the circumference at the pitch diameter so it has everything to do with the circumference.

[Jonathan]

Jesus H Christ this is like pulling teeth, we have all the details including what you had for dinner but not what was asked.

HOW MANY STEPS PER ARE YOU SET TO ?

Using EMC2, not mach3 so you don't set the steps per directly... you enter motor steps per rev (so 200 is correct), microsepping (so 16 in this case), pulley ratio (4.5 as discussed) and leadscrew pitch (120mm).

It looks like at the moment you have the leadscrew pitch set to 100mm not 120mm .... so either change that or put the ratio to 5.4 and it'll be fine.

[Swarfing]

Jonathan i tried 5.4 already and it was close but not quite. I will try again tomorrow with the DTI, i think sometimes we can only let the math get us most of the way there then rest is probably a bit of trial and error. i will set out a drawing to draw out markers, I have about 1300 cutting distance which is a large distance to loose on.

[John S]

Ooops my bad didn't read EMC.

Note to self Read all the damn thread...........

[Jonathan]

The difference between 5.35 and 5.4 is less than 1% ... I wouldn't be too surprised if there's that much error in the belt, particularly as it's quite long. I would definately try the DTI, or even attach digital calliper as that gets you 5 significant figures (unless your DTI is digital too). Digital calliper is not perfectly accurate, it will say the tolerances in the instructions. Either way it's better than a ruler which could account for the 1% error.

Note to self Read all the damn thread...........

There was only one post to read when you replied :lol:

[Swarfing]

Here is an example (not my config by the way)

[Swarfing]

my config is set up in metric, it is very straight forward to use

I think John you may have been too long on the dark side (Windoze euphoria)

[Jonathan]

It would be good if they let you set the derivative of acceleration ... that was going to be in the successor to mach3 which never happened. I wonder if EMC2 supports it.
Just out of interest what have you set the acceleration to?

[Swarfing]

only 30 at the mo, still lots of testing the limits as i am confident it runs in the first place. So far i'm pretty pleased with it though

[Jonathan]

30mm/s^2? That's very low ... I've got mine at 2000mm/s^2 on X-axis and it can do more. The moment of inertia of all those pulleys, particularly the 72T ones, will be quite high. That will of course limit the acceleration, but it probably won't be as high as my rotating a ballnut and pulleys.

I'm beginning to think though that high deceleration is actually bad as it causes the Z axis etc to flex very slightly (due to it's kinetic energy...) and 'overshoot'. Would be nice if you could set different values for acceleration and deceleration.