Web Goblin cnc has begun

[Web Goblin]

Jonathan,
the setup page on USBCNC for acceleration shows Acc.[AU/S^2]. In this box I have left it set to 50 which is the default setting. I cant remember what this setting means. I think I did ask Gary at Zapp about this a while ago and I have been looking through some old emails trying to find the answer but cant find it so I dont really know what Ive got it set to. I think I will have to email Gary again about it.

Ian

[Jonathan]

Jonathan,
the setup page on USBCNC for acceleration shows Acc.[AU/S^2]. In this box I have left it set to 50 which is the default setting. I cant remember what this setting means.

It sets how fast the speed of the motor can change, which is important since when the machine changes direction one or more axis must accelerate and decelerate, so if the acceleration value is too low the feedrate will reduce significantly every time it changes direction which includes just moving in arcs and circles. In addition to increasing the time taken to cut it causes the chipload to vary on the cutter which, depending on the size of the cutter, could damage or at least increase the rate of wear.

See 3.4.3.2:
http://www.planet-cnc.com/files/CNCUSBController.pdf

Assuming you're using millimetres, the value is probably in mm/s^2 in which case 50mm/s^2 is far too low. You want more like 500-1000mm/s^2, but not too high as it can cause the machine to shake excessively. Keep increasing it until the motor stalls, then back off a bit to be safe.
As 50mm/s^2 is such a small number you will notice a big difference in the time it takes to cut most things, but particularly parts with small moves, such as engraving.

[HankMcSpank]

Jonathan,
the setup page on USBCNC for acceleration shows Acc.[AU/S^2]. In this box I have left it set to 50 which is the default setting. I cant remember what this setting means. I think I did ask Gary at Zapp about this a while ago and I have been looking through some old emails trying to find the answer but cant find it so I dont really know what Ive got it set to.

Hii Ian,

I've just taken delivery of a USB-CNC 9 axis board....not sure if you know, but there's now a proper support forum (it's only opened recently)....

http://forum.planet-cnc.com/index.php

the software author (Andrej) is very responsive to posts on there.

[Web Goblin]

Its USBCNC and not CNCUSB. They are different bits of software.

[Jonathan]

Its USBCNC and not CNCUSB. They are different bits of software.

Fair enough, but this is very basic / universal concept so it shouldn't make a difference.

[Web Goblin]

Jonathan,
You could be right but the manual doesnt specify this. I have emailed Gary at Zapp so he can remind me.

Ian

[Web Goblin]

Jonathan,
I have recieved an email from Gary and he descirbes the App/unit as being made up of mm per step of the motor/ seconds squared.
So it looks like you are correct in what you were saying. I will increase the setting to 500 first of all and see how the machine performs and maybe get higher than this depending on how it is. I have noticed in the newer version of the manual that the setting page does have a value of 950 in the Acc. box so I will see what I can get my machine to run comfortably at.

regards

Ian

[Web Goblin]

Jonathan,
I have altered the acceleration setting to 300 and this seems to be ok. I did try 500 but this wa a bit too abrupt for the machine, it was shuddering a bit at start and stop. I need to email Gary at Zapp to see if it is possible to alter the acceleration and deceleration distances in the software. If this can be changed then I could have a bigger acceleration value.
The new bed for my machine arrived yesterday but this needs a fair bit of work to get it finished to what I have planned. Its 15mm thick aluminium at 1260mm x 910mm. It needs to be cut to 1250mmx900mm then fitted, levelled and drilled and tapped for clamping.


Regards

Ian