Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: spannerman on June 14, 2010, 09:06:41 AM

Title: Z axis G1 moves get shorter with reduced feed rate
Post by: spannerman on June 14, 2010, 09:06:41 AM: I am having this problem.
If feed rate is set below 6"/min then G1 move of Z axis gets shorter.
G0 move is fine
X axis does not exhibit this problem.
I am using ver 3.041 trial version.
Can anyone help?
Title: Re: Z axis G1 moves get shorter with reduced feed rate
Post by: Hood on June 14, 2010, 01:53:04 PM: Is this a stepper or servo system?
Can you swap a drive from Z to X and vice versa and see if the Z still is the problem axis.

Hood
Title: Re: Z axis G1 moves get shorter with reduced feed rate
Post by: spannerman on June 15, 2010, 10:17:57 AM: Hi Hood
this is a stepper system and using Mach 3 turn.
I'll swap the plugs round and see what happens.
It's odd though that the problem only seems to occur on G1 moves but not G0.
For example:-
Z=3
G1Z4 stops short
G1Z3 returns to Z=3
G0Z4 goes to Z=4
G0Z3 returns to Z=3

I'll post again with the result of swapping the axies.
Title: Re: Z axis G1 moves get shorter with reduced feed rate
Post by: Hood on June 16, 2010, 01:26:10 PM: Can you attach your xml and I will see if I can replicate your problem here.
Hood
Title: Re: Z axis G1 moves get shorter with reduced feed rate
Post by: spannerman on June 16, 2010, 03:35:15 PM: Hi Hood
A thought has occurred to me. I originally set this system up with a small desktop PC with separate graphics card and everything worked fine. I replaced the pc with an all-in-one unit with touch screen and integrated graphics and the problem appears to be related to this change. I used the same xml file on both units. I have attached it for your perusal anyway. I will see if i can find another PC that I can use to prove this theory. The only other change was to replace the leadscrew with a trapezoidal one.
Title: Re: Z axis G1 moves get shorter with reduced feed rate
Post by: Hood on June 16, 2010, 04:20:08 PM: Just to clear things a bit, when you command the G1 move to Z4 does the DRO stop short or is it the axis only?
Hood
Title: Re: Z axis G1 moves get shorter with reduced feed rate
Post by: spannerman on June 16, 2010, 07:44:22 PM: The DRO indicates the correct movement but the axis stops short. Also the amount by which it is short increases with a reduced feed rate.
Title: Re: Z axis G1 moves get shorter with reduced feed rate
Post by: ger21 on June 16, 2010, 09:58:05 PM: Sounds like a mechanical issue.
Title: Re: Z axis G1 moves get shorter with reduced feed rate
Post by: RICH on June 16, 2010, 10:38:51 PM: What is "short" amount?
Is it consistant in the amount?

RICH
Title: Re: Z axis G1 moves get shorter with reduced feed rate
Post by: spannerman on June 17, 2010, 03:40:20 PM: Here is a table of results, all commanded movements are 1"
Feed Rate ins/min Actual movement
1 0.45"
2 0.62"
3 0.76"
4 0.84"
5 0.90"
6 1.00"
Title: Re: Z axis G1 moves get shorter with reduced feed rate
Post by: Hood on June 18, 2010, 05:42:47 PM: Sounds like something is tight and the slow speed is causing lost steps.

Hood
Title: Re: Z axis G1 moves get shorter with reduced feed rate
Post by: RICH on June 18, 2010, 08:31:55 PM: Tend to agree with Gerry and Hood that it is mechanicaly related.
RICH
Title: Re: Z axis G1 moves get shorter with reduced feed rate
Post by: stirling on June 19, 2010, 04:45:24 AM: what microstepping value are your drivers set to?

Ian
Title: Re: Z axis G1 moves get shorter with reduced feed rate
Post by: airnocker on June 24, 2010, 04:40:37 PM: Just a thought, did you run "Drive Test" on the 2nd PC after Mach3 installed and rebooted?
Title: Re: Z axis G1 moves get shorter with reduced feed rate
Post by: spannerman on July 06, 2010, 03:38:54 PM: SOLVED!
You guys were quite correct, it was mechanical. I found some tightness in the new leadscrew.
I've cured that and also upped the gear ratio on the Z axis.
Thanks for all your help.