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Mach3's DRO pauses intermittently
« on: September 27, 2013, 02:56:46 PM »
Hello - I am relatively new to the world of Mach3 and CNC machines.  I have an older 3-axis router which I am trying to make usable.  I am running Mach3.

I am in the process of making a new table to mount to the existing subtable - a 'simple' matter of drilling a set of holes with counter bores.  I am using G12 to make the counter bores and drill the holes with a 1/4" cutter.

The trouble is that some holes are not coming out round, they are simply 1/4" wide grooves, there is no activity on the Y axis at all.  It was suggested that this was likely to be a problem with the machine getting hung up, so I disassembled the X and Y axis, cleaned them, lubed them, and they both glide nicely when not attached to the screws.  I find no points of hesitation.  I have turned the acceleration down to 1 to further limit the effect of mass/stiff glides.  The screws are acme with Kerk anti-backlash nuts, all clean, lubed, and in apparently good shape.  I have the speed set at 40 because the motors stall at 80.  The feed rate in my drilling program is 30.

There are three things I do not understand:
1) For those holes that are mis-cut, the DRO does not show the Y axis moving - if it was just the steppers missing steps, shouldn't the DRO on the Mach3 screen show the numbers on the Y axis changing, like it does for the X axis?  Why does it not?  On good holes, both axis are shown changing by the DRO.  There is a (related?) issue that occassionally in a traverse the movement will pause, then start again in half a secod or so - and again the DRO also pauses.

2) Not all the holes are misshapen - but it is consistent as to which are.  In particular, the first one is each time (which is nice for testing).

3) I made a test pattern of 25 counterbores (using the same G12 line as for the table) and every one of them is perfect - even when I put it in the same spot on the table.  The only difference is that the test pattern is being cut on the surface of the table, rather than into the table, so the Z axis is in a different spot.

I am not sure where to go next. 

I just ran the driver test - it says I could be running at 65k without trouble.  I am running at 25k.  Nothing else is installed on this machine and it is not networked.  It connects via parallel cable to a Xylotex driver. 

I had some trouble with noise in the control lines which are all shielded cable but do run together with the spindle power.  I am not sure if noise would show up as a pause in the DRO - it seems like it would be more likely to be just skipped steps.

The same holds for trouble with the Xylotex - would those problems show up on the DRO?  There is no feedback, these are very basic steppers.

Any thoughts would be most welcome!



Offline ger21

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Re: Mach3's DRO pauses intermittently
« Reply #1 on: September 27, 2013, 08:12:28 PM »
I'd make sure the g-code is correct. If the Y axis DRO is not changing, and the Y axis is not moving, then the chances are very high that it's a g-code issue.

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Re: Mach3's DRO pauses intermittently
« Reply #2 on: September 28, 2013, 10:09:15 AM »
Right - I should have included the gcode, sorry about that - here it is.

As you can see, I use a subroutine for the actual drill/bore, and the main code does the translation - so it still does not make sense to me that different holes would come out differently - but there is much I do not know!

Code: [Select]
f30 (feed rate)
g20 (inches)
g0 x0 y0 z.25 (zero)
m98 p1234 (call subroutine)
m30 (exit)

o1234 (subroutine 1234 - do most moves on y axis for speed)
g0 x00.8622 y00.8208
m98 p2345
g0 x00.9060 y12.2972
m98 p2345
g0 x00.8748 y23.8758
m98 p2345
g0 x00.8959 y35.4391
m98 p2345
(many more moves trimmed out)
g0 x0 y0

(do the counter bore and drill)
(assume that we are in the right x,y spot, and clear on z)
(assume z=0 is the top of the board)
(feed z to the depth of the counter bore, make a circular pocket at the right diameter)
(feed z to the depth of the drill, make a circular pocket at the right diameter)
(retract z to positive to be clear)
g1 z-.5 (feed to 1/2" deep counterbore)
g12 h.125 i.078125 f10 (assume 1/4" endmill, this makes a 3/8"+ counterbore)
g1 z-.875 (feed to 7/8" deep drill - assuming 1" material, this prevents hitting the steel below the table)
g12 i.015625 f10 (assume 1/4" endmill - this is a 1/4"+ drill)
g0 z.25 (1/4" above board)