On 4/10/24 03:37, John Dammeyer wrote:
Hi Marcus,

Here's the problem.

My Alibre CAD/Cam can produce a spiral slot in a disk using X and Y motion.

I looked at alibre, could not get my Iowa farm kid head around it. Far easier for me to write my own gcode.

In linuxcnc, you can trade the axis names around to fit your hdwe.

How far can you tilt your Z? Mine can do a full 90, aka lay the spindle horizontal. Either way IIRC. I can then use X as X, A as A, and a single straight line move to carve the spiral using Z while A is turning N degrees to carve the spiral. So the gcode then becomes a subroutine to do that, and a 2nd loop routine to handle the start of the spiral and possibly a master outer loop to do any incremental cuts to get to the depth needed. Maybe 80 LOC total.

If your head cannot tilt that far, then you''l have to cobble up a C, facing up which I CAN do but its a 90/1 drive and will restrict the speed as It can't turn fast enough. Also has a std stepper motor, push its speed and it stalls. Someday I'll put a good motor on it.

A Warning though, most of the combo gizmos they sell for $300 or so on ebay are belt drive and no-where near strong enough for this. I did use my 90/1 as A when making my tap hats. Used it to drill & tap the 4 grub screw holes. I setup workstations on the length of the go704's table, put a piece of brass rod in the spindle, drilled the hole for the tap, move the brass to a clamp, drilled and tapped for a locking to an r8 collet screw hole, moved the brass to the A chuck and drilled and tapped all 4 grub screws. All in the same gcode file with pauses and automatic tlo offset corrections as the drills were different lengths. Made a regular production line out of it, took longer moving the brass around than the total run time for the machine.




If I tell it to use my 4th axis it's like the video you posted.  Designed
for creating a spiral on something horizontal to say the X axis.

I think I'd have to buy the 5th axis capability in order to be able to have
the rotary table turn while the cutter moves in the X direction as the
spiral is created.

So if I wanted to move the rotary table N degrees while moving X a spiral
would also be created.  I guess I'm having trouble figuring out the math for
the G-Code.

It just one command with prelimiinary. in your case position incut at N degrees

John

-----Original Message-----

From: marcus.bow...@visible.eclipse.co.uk

[mailto:marcus.bow...@visible.eclipse.co.uk]

Sent: April 10, 2024 12:00 AM

To: Enhanced Machine Controller (EMC)

Subject: Re: [Emc-users] Carving a spiral



As I recall, someone on this list posted a note or a link about how to

create a fusee for a clock (essentially a tapered spiral, running from

large diameter to smaller diameter while spiralling - rather like a

tapered woodscrew thread). Is a constant-diameter version of that what

you had in mind?

https://www.youtube.com/watch?v=KAAajypWQyw



Sadly, I can't remember who contributed that note on this list. I do

think there may be a routine somewhere in the LinuxCNC electronic

resources.



Marcus







On 2024-04-10 06:55, John Dammeyer wrote:

A friend and I have been discussing exactly how to write the G-Code to

create a spiral scroll.



His rotary table 90:1 reduction with a 1600 micro-step motor could be

set up

to move N steps for each step of the X axis to create the spiral.  But

that

approach seems clumsy.



Say I wanted to cut a scroll with a 6mm pitch using a 3mm cutter.







Without using G2 or G3 it's really just a triangle isn't it?  Move

rotary

table distance A and move X axis distance A'.  Do it in small enough

increments and you get a spiral.  But I feel like I'm missing something

really simple.







Suggestions?



Thanks



John









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