Centroid Community CNC Support Forum

Hello all.

Has anyone figured out reliable lock up on a stepper driven ratchet and pawl style ATC lathe turret??

I have it set up as an "axis driven turret" with appropriate "move past" and "reverse" parameters set but it still isn't reversing until stall on every tool change.. It will stall on the first too change, then on the next tool change (and all tool changes after for that matter), the reverse move to lock the turret stops right before lock up. it has to be the lost steps shifting turret position vs actual such that it gets more "move past" so "reverse" stops where it stalled on the first TC..

When the machine was making parts with 1 or 2 tools, no problem...
My most recent job needs 6 of the 8 tool positions and the slight difference between the lock up points with each tool makes it so there is no lock up by the end of the program..

Ideally, I'd like to make an edit to the tool change macro to force the motor to stall every time... coding is my weakness so I haven't been able to figure this out.

The next options are all hardware based..
1. Add a sprung element in the driveline for the turret so even if the stepper doesnt stall, theres still some tension in the system forcing the ratchet against the pawl. I can do this but I really dont have time to put my lathe out of service for this.
2. move to a servo W/ brake. its a lot of added expense for something I feel should be fixable some other way.. calling it plan B
3. Buy a better lathe... there isn't enough funding for this yet unfortunately

Can someone end this frustration for me?
Thanks

I've recently done a similar implementation and one many years ago before the wizards were there to help.

Key things to get right to get it to work.

1. Ensure that your turn ratios suit. In other words, ensure that it 'clicks' 8 times on 8 tool moves. I opened mine and manually moved it to see the exact 'measurement' when the pawl would click back in.

2. You can then work out both the amount to go past and reverse. Easier if you can see the rachet / pawl working.

3. To stop a stall / trip, maybe turn the current down so that it just vibrates once it hits the pawl but to help this, get the reverse amount just over the amount needed.

Can you post a report so we can see what you have thus far?

Where are you based? I'm happy to offer some help over WhatsApp - UK timezone ...

Chaz wrote: ↑Mon Apr 28, 2025 9:42 am I've recently done a similar implementation and one many years ago before the wizards were there to help.

Key things to get right to get it to work.

1. Ensure that your turn ratios suit. In other words, ensure that it 'clicks' 8 times on 8 tool moves. I opened mine and manually moved it to see the exact 'measurement' when the pawl would click back in.

2. You can then work out both the amount to go past and reverse. Easier if you can see the rachet / pawl working.

3. To stop a stall / trip, maybe turn the current down so that it just vibrates once it hits the pawl but to help this, get the reverse amount just over the amount needed.

Can you post a report so we can see what you have thus far?

Where are you based? I'm happy to offer some help over WhatsApp - UK timezone ...

Looks like I was on the right reack based on your comments. Items 1 and 2 were prep to set P853 and P854. Item 3 was done way back during the re-control of the machine; the stepper is current limited to about 25% power to keep the reverse from damaging the turret drive train over time.

I really appreciate the offer to talk through the issue via WhatsApp but I think I stumbled on the last piece this morning while examine the homing macro and seeing how it forces axis values to change... its M26 and I feel embarrassed that its been under my nose the whole time.

The new line in the standard cnctch macro is below in Bold Red

;---------------------------------------------------------------------------------
; Axis Driven Turret Section
;---------------------------------------------------------------------------------
N300

;Determine A Axis Position
IF #20101 == 65 THEN #103 = #5021
IF #20102 == 65 THEN #103 = #5022
IF #20103 == 65 THEN #103 = #5023
IF #20104 == 65 THEN #103 = #5024
IF #20105 == 65 THEN #103 = #5025
IF #20206 == 65 THEN #103 = #5026
IF #20107 == 65 THEN #103 = #5027
IF #20108 == 65 THEN #103 = #5028

#101 = #103 % #9161 ;Get Current Turret Location

;Check to ensure turret is not at requested position, if so then skip tool change.
IF [ABS[#4120-#101] < .002] THEN GOTO 1000

;If tool requested is not a valid tool, Skip macro and send message to operator.
IF #4120 < 1 || #4120 > #9161 THEN GOTO 500

;Calculate Requested Position to move Turret to.
IF #101 > #4120 THEN #102 = [#103 + #9161 + #4120 - #101] ELSE #102 = [#103 + #4120 - #101]

G53 A[#102 + #9853] ;Move past tool by P853 Amount
G53 A[#102 - #9854] ;Move back behind toold by P854 Amount
M26 /A L[#4120*#20604] ; Tool number multiplied by encoder counter for A axis or Axis 4

IF #50001 ;Prevent lookahead from parsing past here
G10 P1976 R[#4120] ;Set parameter 976 to tool number

GOTO 1000

N500
M225 #100 "Invalid Tool Number Requested!\nPress Cycle Start to Skip Tool Change.\nPress Cycle Cancel to abort Program"

N1000 ;End of Macro

Great, sounds like you are on the right track.