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Relative motion of cutter to table
« on: November 01, 2011, 11:16:37 PM »

I am a newbie but have managed to put together my first CNC mill. It is running on Mach 3 which I am very impressed with. I have managed to sort out most of the issues thanks to these forums.

I have everything technical working but not having any prior CNC experience I am somewhat confused on the relative motion of my table/ work.

I have viewed all the training videos (more than once) and if my spindle moved instead of my table I am sure that I wouldn't have any problem. In my case, the spindle is fixed and the cutter direction relative to the work is opposite that of the table direction.

Viewed from the front of the mill, when I issue a G0X1 command should the table or the cutting direction of the tool move to the right. same queston for the Y axis.

When I tried to cut the roadrunner sample which is inverted, the only way I could get it to cut was to reference my cutter at the top right. The image appeared upright viewed from the front of the mill.

I understand that the home should be at the bottom left but it this correct for a fixed spindle? I think the home position should be at the top right but this is the opposite of what I understood from the training video.

The key question is are my motors reversed when the table moves to the right for G0X1 and up for G0Y1?

I'm don't think that I have the direction of the motor drives reversed but the real problem is I am not sure where I should establish home position on the mill.

Your help would be appreciated.
Re: Relative motion of cutter to table
« Reply #1 on: November 02, 2011, 12:12:35 AM »
When standing in front of the machine, facing the machine, a positive X will move the tool to the right, or the table to the left.  A positive Y move will move the tool away from you, or the table towards you.  A positive Z move will move the tool up, or the table down.  The home position can be wherever you choose to put it - at any corner, or even in the middle of the travels.  It's completely arbitrary.

Regards,
Ray L.
Regards,
Ray L.
Re: Relative motion of cutter to table
« Reply #2 on: November 02, 2011, 10:03:51 AM »
as far as homing is concerned try to get the "Y" axis to home towards you.

The "Z" axis to home so the tool is as far away from the table as possible.

The "x" at one end of it's travel.

A good guide of tool motion, is to hold your left hand out in front of you and point to the machine with your index finger, then put your thumb up and point your second finger to the right. This is the positive motion of the tool, with your thumb being "Z", your index finger is "Y", and the second finger is "X".
« Last Edit: November 02, 2011, 10:07:55 AM by angel tech »
Re: Relative motion of cutter to table
« Reply #3 on: November 02, 2011, 10:29:19 PM »
Thank you very much for the confirmation of motor directions. It turns out that they are as you said they should be so I just have to work out the homing. Presently I do not have any homing switches. Most people say they are the way to go. My x and y axis go home when I hit go to zero in machine co-ordinates but my Z axis doesn't stop where I expect it to.

I'll add a homing switch on the Z axis on the weekend and see how it works.

Thanks again for all your help.
Re: Relative motion of cutter to table
« Reply #4 on: November 03, 2011, 12:14:47 AM »
Home switches are a convenience, not a requirement.  I've never had them on any of my machines.

Regards,
Ray L.
Regards,
Ray L.

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Re: Relative motion of cutter to table
« Reply #5 on: November 03, 2011, 03:23:45 AM »
Ray, Just curious, do you ever RefAll?
Hood
Re: Relative motion of cutter to table
« Reply #6 on: November 03, 2011, 09:44:39 AM »
Ray, Just curious, do you ever RefAll?
Hood

Hood,

No, not really.  Not sure what that would accomplish, with no reproducible machine zero reference position.  I touch off to the part/vise/fixture.  I will, someday, install homes/limits, but it just hasn't been a priority.  I do have switches on the quill, mostly to protect from damage if it's over-driven, but nothing yet on the other three axes.

Regards,
Ray L.
Regards,
Ray L.

Offline Hood

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Re: Relative motion of cutter to table
« Reply #7 on: November 03, 2011, 10:07:54 AM »
Only reason I was asking is sometimes things go crazy for you, TP also has/had that happening and I seem to recall him recently saying he doesnt use Home switches. Probably a wild shot but just wondering if Machine Coords are massive and maybe rolling over or something when things start going weird.

Hood
Re: Relative motion of cutter to table
« Reply #8 on: November 03, 2011, 10:43:11 AM »
Only reason I was asking is sometimes things go crazy for you, TP also has/had that happening and I seem to recall him recently saying he doesnt use Home switches. Probably a wild shot but just wondering if Machine Coords are massive and maybe rolling over or something when things start going weird.

Hood

Hood,

No, my problem is a confirmed bug in Mach3 with the SmoothStepper.  For reasons we still don't understand they sometimes "sync" when they shouldn't, which means Mach3 updates its position counters with the values it receives from the SmoothStepper.  Unfortunately, these are somehow wrong, and result in the machine zero spontaneously changing mid-program, which should never, never EVER happen.  It's a completely random (though, sadly, not all that rare - happened three times in as many minutes yesterday) occurrence.  Brian, Greg and I have been trying to nail it down for almost two months now, but no joy....  It's become such a problem for me, I'm in the process of switching over to a KFlop right now.

Regards,
Ray L.
Regards,
Ray L.

Offline Hood

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Re: Relative motion of cutter to table
« Reply #9 on: November 03, 2011, 02:33:01 PM »
Heres hoping for your sake its not something in Machs plugin interface that is the issue then. Have never seen any issues myself and I use the SS on all my machines but maybe just dont do the one thing that triggers it.
Hood