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pocketing issues
« on: March 17, 2017, 05:22:13 PM »
I have been trying to do some pocket cuts for inlay work.  Using a 1/8" bit and going 1/4" deep with multiple passes.  It appears that on each pass the cut has moved to the left a mall amount.  So if it takes three passes (cuts) to get to the final depth requested, there are two little shelfs on the right side of the pocket.  No shelf on the left side (or top and bottom) as the last cut at the final depth cuts from the surface to bottom as the bit shifts(?).  So, Any ideas on what is happening and how to go about fixing this issue?
Thanks for the help!
rockaukum

Offline Davek0974

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Re: pocketing issues
« Reply #1 on: March 18, 2017, 04:14:25 AM »
Sounds like you are losing steps on the drive - using stepper motors?

Could be a lose joint also, maybe too fast, too deep, not enough motor current and others.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives
Re: pocketing issues
« Reply #2 on: March 18, 2017, 05:30:29 AM »
Maybe check to see if your spindle is trammed accurately.
Re: pocketing issues
« Reply #3 on: March 18, 2017, 06:21:01 PM »
Hey thanks for the replies,
I will try to answer the questions / solutions posed.
Yes they are the nema stepper motors 23 oz (?).   I have done the pocket at 100 ipm and recently at 40 ipm with the same result, a small shelf on the right side.  I had done the measurement method to determine the steps per and came up with 1366.767132 for the X axis (assuming it is the X axis in question)  the most recent pocket operation was done in two paths, each 1/8" deep. Other than that, I do not know how to check the current for the motors, assuming a loose joint is just a loose connection be it hardware or wire, and Not sure what "trammed" is.  I will be searching that next and figuring on doing a recalculation on the steps per.
Again, Thanks and appreciate the help!
rockaukum
Re: pocketing issues
« Reply #4 on: March 18, 2017, 06:56:43 PM »
Okay, so now I know about tramming.  I will get that done on monday.
rockaukum

Offline Davek0974

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Re: pocketing issues
« Reply #5 on: March 19, 2017, 04:22:04 AM »
Steps per will not be the issue - the will affect every pass the same and just alter the overall finished size.

What motor drives are you using - the current is usually set by little switches on them.

Maybe do a pen test - get some flat board on the table, tape of fix a pen, pencil, marker etc to the head and run the job on paper so its drawing the tool paths.

If you hold the head and push it gently in X & Y is there any movement or wobble?

Is it rack & pinion, belt drive??
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives
Re: pocketing issues
« Reply #6 on: March 19, 2017, 12:00:39 PM »
Dave,
The machine is rack and pinion.  I will try the pen test today and see what that shows.  I did do a recalibration of the steps per yesterday.  This time I started with a small movement of 2".  Then ran the test over the length of each axis.  I came up with only slight adjustments to the steps per.  I have taken a cursory look at the fittings and mounts and it appears to me that all is tight.  Then again....keep in mind that I have no prior knowledge to base this on.
Forgive me for my ignorance with this stuff as I purchased this machine without any prior knowledge to the CNC world.  So with that in mind....
The machine has sainsmart drives.  I have tried to gain information on the interface board but have been spinning my wheels with that.  It appears that the drivers are ST330-V3.
Thanks for the help!
rockaukum
Re: pocketing issues
« Reply #7 on: March 19, 2017, 01:18:18 PM »
All of the above is valuable. If your Z axis is slightly non perpendicular to either the X or Y axis ( not trammed to the bed)you will see exactly what you are referring to, small step like  line on one side of the pocket.

A poor man's way to check is to take a coat hanger, cut it and bend it so that one end can fit in the collett, extend it several inches laterally and then have the other end point to the bed. Lower the Z so that it just touches the bed and then spin it slowly by hand. 180 degrees. If it is not trammed  it will lift or dig in on direction.
Re: pocketing issues
« Reply #8 on: March 20, 2017, 03:57:05 PM »
Today I was able to get my Engineer friend to come over and take a look.  We set up to do the tramming of the router and came to the realization that we should get the table leveled first then set up for the tram.  Going to start on that today (hopefully).  I need to do some welding on the frame first and add a couple cross braces as well.  Once I get that done we will tram the router.  With a quick check we could see it was off just a bit. 
New question now... If I am going to weld on the substructure of the machine (table) should I have to disconnect the motors from the machine,  Disconnect the computer from the machine?  Are there any precautions that I should take to avoid any damage while welding?
Thanks much!
rockaukum

Offline Davek0974

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Re: pocketing issues
« Reply #9 on: March 20, 2017, 04:14:47 PM »
I would disconnect the PC and make sure the weld return lead is fixed close to the area you are welding.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives