Implementing rotary axis on engraver

[gordonb]

Please be gentle with me, I'm just starting out on the cnc journey and am still struggling with one or two concepts!

Here's the story so far. I was given a non functional commercial rotary engraving machine, a Suregrave Rotation S (top of the range in its day) and I've built a new control system for it based on an AXBB-E. Pleased to say that it works superbly and I had no real problems getting it working. However, the machine is also equipped with a rotary axis, the whole bed assembly can be rotated and the rotary axis brought into play, photo of the machine in its original form should show the basic arrangement, and I'd really like to get this implemented if possible.

I think what I need to do is to find a way of swapping the connection of the stepper motors from the Z axis stepper to the rotary axis stepper, measure the diameter of the workpiece, calculate the steps per unit based on the 200 steps per rev of the stepper, the 90:1 gearbox it's attached to, the microsteps the driver is set for and the circumference of the workpiece. This does seem a touch complicated and if there's a simpler way of doing it I'd love to hear about it! Also it looks like I'd have to physically change over the motor connections before switch on to select the rotary axis. I had hoped I could tell UCCNC to regard the A axis as the Z axis but I can't find a way of doing that as setting the A axis as a slave to the Z axis means that when I deselect the Z axis the A axis is also deselected.

Am I missing something blindingly obvious here? Wouldn't be the first time! Can anyone offer any advice on how to implement the rotary axis in a simpler form? All help and advice gratefully received!

[cncdrive]

UCCNC supports rotary axis on A, B anc C axes.
You can tick in the rotary axis checkbox in the axis configuration for any of these axes.

Then the axis will act as a rotary axis, the axis will be excluded from the feedrate calculation and also there is a rollover on 360 degrees option, if that is selected then the axis will only have 0-360 degrees range and then will rollover on the shorter way when programmed to move that way.

You can use the G93 inverse time feed code and use a CAM software which supports it. I think Vectric supports it and probably many others also.
Then the g-code commanded movements finishes in the defined time, the time is defined by the F keyword, so the feedrate can be correct on the rotary surface even if the diameter changes.
For more info on the G93 please check the users manual.
Also if you using a CAM software check if it supports G93 and rotary axis, if not then find one which does.

[gordonb]

I'm struggling a bit to understand all of your very prompt reply but I'll get there with a bit of reading and thinking! Just one point I'd like clarifying, as far as I understand it the rotary axis effectively replaces the Y axis (not the Z axis as I first posted) so how do I go about telling UCCNC that's what I want to do? Or is that specified in the CAM software? I'm going to be using Vectric Cut2D, I'll have to check it supports G93.

Great support by the way, very, very glad I chose to buy the AXBB!!!!!!!!

[gordonb]

Just checked and found Cut2D Desktop does support G93, below is from the Vectric Help page for Cut2D Desktop

Global File Statements

Statements are items that are either used only once, or have static values throughout the file. Write statement names in upper case letters for clarity.
INVERSE_TIME_MODE="YES"
Rotary: Enables / Disables output of the feedrate F in Inverse Time Feed Mode. In this mode, we're expected to complete a move in one divided by the F number of minutes.
In GCode, this would G93 to switch on, or G94 to switch off and use units mode.

[ger21]

I think what I need to do is to find a way of swapping the connection of the stepper motors from the Z axis stepper to the rotary axis stepper, measure the diameter of the workpiece, calculate the steps per unit based on the 200 steps per rev of the stepper, the 90:1 gearbox it's attached to, the microsteps the driver is set for and the circumference of the workpiece. This does seem a touch complicated and if there's a simpler way of doing it I'd love to hear about it! Also it looks like I'd have to physically change over the motor connections before switch on to select the rotary axis. I had hoped I could tell UCCNC to regard the A axis as the Z axis but I can't find a way of doing that as setting the A axis as a slave to the Z axis means that when I deselect the Z axis the A axis is also deselected.

I would just wire both motors, and use separate profiles for rotary and standard, with the unused motor disabled for that profile. You really don't want to be connecting and disconnecting motors all the time.

[gordonb]

After carefully reading the details on the Vectric help page it's become apparent that Cut2D won't generate code for rotary axes, only V Carve and Aspire will do so, and they are much more expensive However, it looks like I can design in CorelDraw and convert to a rotary job using G-Code Ripper, so all is not lost. I'll get another stepper driver, install that and give it a go.