Surging Motion Problem - why?

[geomagnet]

Hello,

I leased a shop with a CNT Motion 5'x10' router table running WinCNC (on Dos). Yes, the machine is about 15 years old and has had better days. Over the past few months I have serviced the machine and got everything working the way it should.

However...when I try to run a low profile 3D project the machine jerks abruptly and erratically. Granted, the machine is not really designed to do 3D milling, but I see no reason why it shouldnt if the feed rates are within capacity.

From what I can see the machine has 2000ipm horizontal motion and 200ipm vertical. So if the code does not exceed 200ipm there shouldn't be a problem right?

Wrong...even at 50ipm the machine complains (I say that figuratively...it just sound aweful).

I don't fully understand the g-code relationship with the controller. From what I have learned the g-code is sent to the controller which turns it into pulses (signal) to send to the motors. I'm also to understand that the controller conditions the instructions so that the machine operates with smooth motion as it passes through the coordinates.

I must be missing something.

I've written diagnostic software to analyze the g-code and it appears that everywhere this machine encounters a transition from flat to slope it comes to an abrupt stop momentarily and then continues (which causes the jerk).

Is there an instruction that will prevent this? I've tried G8 (which errors), and G9 S9 which seems to make no difference.



This images is a representation of the g-code coordinates and slope as it travels the tool path. IF the slope is 0 (flat) its BLUE, anything else is RED. In the real world, this is confirmed as the part is cut with these odd spiked shaped artifacts accompanied by the machine surges.

Can anyone shed some light on this problem and a possible solution. It's really driving me crazy (and can't be good for the machine).

Thanks.
James

[Bubba]

sounds like your running in "Exact Stop" mode. In other words, the machine executes a block and then stops and does the next block. Not sure if WinCnc has either a look ahead function to do "Exact Path" mode or "Constant Velocity" modes.
I can see where this would be quite noticeable at 200IPM.

[geomagnet]

Thanks Art,

The manual says the G9 S[0-9] is a smoothing instruction. However, other sources say G9 is the exact stop instruction. So...I'm dumbfounded. WinCNC support has been helpful in other areas, but defaults to the old "Not our problem" when it comes to g-code. I can understand that as they don't generate the g-code. Of course, they would rather me spend $$$ and upgrade. I'd really like to make some money with this before I start burning through cash.