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Need Help to Improve Surface Finish

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TomS

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#31
Your comment about untidy wiring got my attention.

Cable dress can be important when it comes to reducing magnetic interference. You have a situation where you have conductors carrying high current to your steppers, and conductors that are relatively high impedance signal lines. Magnetic coupling between them can cause problems (ask me how I know). Shielding in the form of copper braid really doesn't address this kind of interference. Good cable dressing, and keeping high current lines separated as far as practically possible from signal lines, is the way to do it. The cable dresing should minimize the area between your drain lines and signal lines. See my illustrations below

Example 1, bad lead dress (lines far apart)
signal line ---------------------------------------------------------------------------



Drain line ---------------------------------------------------------------------------

Example 2, better lead dress
Signal -----------------------------------------------------------------------------
Drain-----------------------------------------------------------------------------

Example 3, Even better lead dress (this is hard to draw so I won't): make a twisted pair using the signal and drain lines. Induced voltages tend to cancel. I've even seen this approach used in high frequency integrated circuits.

Reason: the larger the spacing between the signal and drain lines, the more magnetic flux can pass through the loop that is formed, producing more induced voltage.

Ideally you'd also route your cables so the high current lines are at right angles to the signal lines but that could be difficult to do.
Sorry, I knew my luck would rub off.

You'll get 'er.
Sorry, I knew my luck would rub off.

You'll get 'er.
This is wierd. I clicked Reply on your post and it brought me to Homebrewed's post. Yeah, I'll get it done just frustrating.

Homebrewed - I like your idea about twisting the drain wire and signal wire. Being that I've got some additional wiring ahead of me tomorrow I'll give it a try.
 

TomS

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#32
My plan for today was to have test data to share. Unfortunately not. I stripped out the unused X and Y Enable - wire and rerouted all of the drain wires. Also added a ground wire from the BoB to the star ground. Ran individual ground wires from the BoB/ESS enclosure and the motor driver enclosure then terminated them at the VFD ground lug. Powered up the system and the Y axis driver fault light is on. Checked all the wiring making sure the termination points were tight then double checked again. Made sure I hadn't crossed a wire and all is good there. Gave up for the day out of utter frustration. Tomorrow I'll swap out the Y driver with the X driver. If the green light comes on then it's the driver. If no green light then it's back to figuring out what changed. Sure would like to be making parts.
I swapped the X and Y driver wires at the BoB. If it was a wiring issue I would have expected the X axis driver fault light to come on. It didn't. The Y axis driver fault light is on so it looks like a bad driver. Looks like I'll be ordering a new driver. The price isn't too bad, about $40 to $45, but it's coming from China. Probably going to take 2 to three weeks to get here.
 

jbolt

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#33
If I recall you used the DQ860MA drivers for the X & Y? Both of mine eventually went bad. There are rectifier diodes on the back of the PBC that kept failing. I went to the KL-11080 from Automation Technologies. It is similar to the DQ2272 I have on the Z axis.
 

homebrewed

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#34
This is wierd. I clicked Reply on your post and it brought me to Homebrewed's post. Yeah, I'll get it done just frustrating.

Homebrewed - I like your idea about twisting the drain wire and signal wire. Being that I've got some additional wiring ahead of me tomorrow I'll give it a try.
I've never heard of it causing a problem like you're describing but it's possible for the different steppers to talk to each other as well. If your wiring configuration for the steppers has changed since your initial build, you might want to take a look at it with this in mind. You wouldn't want to bundle all the stepper cables together because that would be worst-case as far as coupling is concerned. Bundling each stepper's wires together should be OK because the currents should -- more or less -- cancel out (i.e., you've got the same current flowing IN as OUT so the mag fields should cancel). You actually end up with a dipole type of magnetic field, which drops off in intensity much more rapidly than the field from a single wire.

I recall a story one of my electrical engineering professors told long ago. He was contacted by a mining company that was having problems with a new 3-phase electric motor they had gotten. The motor was running as though it had insufficient voltage. The company was testing it before they hauled it into the mine, and he noticed they had coiled and stacked the (very long) wire bundles on top of each other. On a hunch he told them to separate the coils: and the motor began to operate correctly. The problem was the mutual inductance between the phases, exacerbated by their close proximity.
 

spumco

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#35
The problem was the mutual inductance between the phases, exacerbated by their close proximity.

Interesting, and is a parallel to what I was taught in the Navy about extension cords. We were told not to use extension cords or welding cable coiled up but to spread them out to reduce heating. Of course, we didn't want to do that on some big old 00 welding leads when we only needed a couple feet for the job, but you pretty much say Yes, Chief and get on with it. I get my NDE inspectors to do the same thing now when we're doing mag particle inspections running 600 amps through giant cables. You can measure the voltage drop in a 50' cable when it's coiled vs. spread out.

I also was advised by someone here or on CNCZone to twist my VFD conductors inside the conduit to help cancel out noise. Twist the three leads, but do not twist the motor ground with the bundle. Each conductor is looped through an individual ferrite ring right at the VFD end, and then the twist starts. Everything is run inside metallic conduit with ferrite and so far I've had zero VFD noise issues.

Not that that's an issue with Tom's current woes, but I figured I'd mention it anyway since we're swapping electrical pixie stories.
 

TomS

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#36
Received my new driver today and got the mill up and running. I ran a quick test with the mag base mounted to the column and the DTI on the vise jaw as in the previous test. Needle movement was the same as the first test. Tomorrow I'll run the test as jbolt suggested.

I've been doing a lot of reading while waiting for the replacement driver. There are a few settings in CamBam (my CAM software) and the Mach3 post processor that may need to be tweaked. In CamBam there is a arc fit tolerance and auto arc fitting setting. In the Mach3 post processor I found arc center mode which can be absolute or incremental. There is one absolute setting and four different incremental settings. Default is incremental (C-P1). One CamBam user has been using absolute for years without issue so I'm going to give that a try. Then there is arc to line tolerance. The default is .01. I did find a reference that .01 is the default for working in metric. Couldn't find a reference to the default for inch mode but .01 of an inch is much greater than .01 of a millimeter. Looks like I need to make a change.

For info my X and Y power supplies are set at 60 volts output. I've read that higher is better but how high is too high?

I'll post more test results tomorrow.
 

spumco

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#37
Good to hear you're making progress. I had the same problem when I switched from Mach to UCCNC; the default settings are for metric units. My machine profile imported correctly, but all the variables not in my profile caused a few pucker moments until I went through every single thing and set it up for proper units.

As far as the driver supply voltage - it's too high when the smoke comes out :) If you're still using the DQ860MA driver, it's rated to 80 volts. If I recall my internet stepper theory lessons, power is a function of voltage, and torque is a function of current (all else being equal). Increase the voltage, and the power (torque x speed) goes up. The low-speed maximum torque won't change, but the point where it starts dropping off will be at a higher RPM.

The way to increase low speed torque is to raise the max current. The downside to this is motor heating - so just set the driver to the motor rating and be done with it.

(Hopefully someone smarter will chime in and confirm my hillbilly stepper motor hypothesis.)

I suggest you leave them at 60v and get your machine sorted out. Once you have the surface finish problem fixed and you've cleaned up the copper octopus in your enclosure, then you might try bumping the voltage and seeing what feed rates you can achieve in a standard cut before you start losing steps. Increasing the voltage will probably permit you to take more aggressive or faster cuts, assuming your spindle isn't the limiting factor. Again, this assumes your power supplies are capable of maintaining 80v to the drivers at max current draw.

Cant wait to hear how The Jbolt Method (TM) works.

-S
 

TomS

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#38
Good to hear you're making progress. I had the same problem when I switched from Mach to UCCNC; the default settings are for metric units. My machine profile imported correctly, but all the variables not in my profile caused a few pucker moments until I went through every single thing and set it up for proper units.

As far as the driver supply voltage - it's too high when the smoke comes out :) If you're still using the DQ860MA driver, it's rated to 80 volts. If I recall my internet stepper theory lessons, power is a function of voltage, and torque is a function of current (all else being equal). Increase the voltage, and the power (torque x speed) goes up. The low-speed maximum torque won't change, but the point where it starts dropping off will be at a higher RPM.

The way to increase low speed torque is to raise the max current. The downside to this is motor heating - so just set the driver to the motor rating and be done with it.

(Hopefully someone smarter will chime in and confirm my hillbilly stepper motor hypothesis.)

I suggest you leave them at 60v and get your machine sorted out. Once you have the surface finish problem fixed and you've cleaned up the copper octopus in your enclosure, then you might try bumping the voltage and seeing what feed rates you can achieve in a standard cut before you start losing steps. Increasing the voltage will probably permit you to take more aggressive or faster cuts, assuming your spindle isn't the limiting factor. Again, this assumes your power supplies are capable of maintaining 80v to the drivers at max current draw.

Cant wait to hear how The Jbolt Method (TM) works.

-S
I'm taking it a step at a time. I want to specifically identify the root cause so I can pass it along to others. The "copper octopus" is gone. I ran the test today to see if the wiring changes had an effect. They didn't so now it's on to the next test.

Thanks
 

jbolt

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#39
Here is what kept failing on my DQ860MA drivers. Exploding diodes! The diodes are only a couple of bucks and easy enough to fix but after the third one I gave up. Wantai to their credit offered to fix them under warranty but failed to understand that the shipping charges back and forth to China would exceed the replacement cost. They did give me the US spec for a replacement diode.

20150615_191024.png 20150615_191040.png
 

homebrewed

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#40
Here is what kept failing on my DQ860MA drivers. Exploding diodes! The diodes are only a couple of bucks and easy enough to fix but after the third one I gave up. Wantai to their credit offered to fix them under warranty but failed to understand that the shipping charges back and forth to China would exceed the replacement cost. They did give me the US spec for a replacement diode.

View attachment 239887 View attachment 239888
If the diodes are blowing themselves off the board they are severely overstressed! The important parameters are the diode type (speed rating), breakdown voltage and current handling capability. I found a teardown log here: http://blog.bouni.de/blog/2015/02/03/taking-a-dq860ma-stepper-driver-apart/ that provides a link to the diode data sheet. The diodes are "ultra-fast" type with 2 amp/50 amp average/peak, 280/400V RMS/peak ratings. The key to finding a US replacement is the speed -- they MUST be fast-recovery for a PWM application. Of course, you want the current and voltage ratings to be equal to or better than the OEM.

BTW from the same teardown log I note there are some indications that the driver manufacturer may be using counterfeit chips -- the sanded-off surface of the controller IC either says it's counterfeit or the manufacturer did not want their board to be reverse-engineered. If it IS counterfeit, they also may be using diodes that were pulled from other boards. If so, they may or may not be fast-recovery. That could explain the early failure of the diodes.
 

TomS

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#41
If the diodes are blowing themselves off the board they are severely overstressed! The important parameters are the diode type (speed rating), breakdown voltage and current handling capability. I found a teardown log here: http://blog.bouni.de/blog/2015/02/03/taking-a-dq860ma-stepper-driver-apart/ that provides a link to the diode data sheet. The diodes are "ultra-fast" type with 2 amp/50 amp average/peak, 280/400V RMS/peak ratings. The key to finding a US replacement is the speed -- they MUST be fast-recovery for a PWM application. Of course, you want the current and voltage ratings to be equal to or better than the OEM.

BTW from the same teardown log I note there are some indications that the driver manufacturer may be using counterfeit chips -- the sanded-off surface of the controller IC either says it's counterfeit or the manufacturer did not want their board to be reverse-engineered. If it IS counterfeit, they also may be using diodes that were pulled from other boards. If so, they may or may not be fast-recovery. That could explain the early failure of the diodes.
Thanks for the info. Not inclined to try a repair as the cost for a replacement driver is only about $40.
 

TomS

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#42
I ran a multitude of tests this morning. The first test was mounting the DTI as jbolt suggested and running gcode. The DTI needle bounced around quite a bit. I read on another forum that you can run a Fanuc post processor with Mach3. So I tried it. No surface finish change using the standard PP settings. I then set the Fanuc PP Arc Center mode to Absolte and made the same change in Mach3 General Configuration. Again, no change. Made the same change to the Mach3 post processor with no change in surface finish quality. Out of desperation I changed Arc Output from Normal to Convert to Lines. Nada! All these tests were run with Arc Fit Tolerance set at .0004 and Spline to Polyline Tolerance set at .0001. The last test were test cuts made at three different Z heights to see if the faceting lined up. They didn't. See the pictures below.

Still have to run the drain wire disconnected test as jbolt suggested. If that doesn't show anything then I'm leaning towards a motor tuning issue.

20170817_114442_resized.jpg

20170817_114505_resized.jpg
 

homebrewed

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#43
Thanks for the info. Not inclined to try a repair as the cost for a replacement driver is only about $40.
Sometimes it's the down-time that is more important than waiting for a replacement driver. If the driver is that unreliable maybe you should get one or two backups? Depends on whether or not the down-time delays delivery to a customer vs. delaying a personal project.

I suppose your decision to replace or repair also depends on your ability to solder/de-solder surface mount parts without damaging the board or other components. I've done that at work but now, lacking a good stereo-zoom microscope, SMT would be a bit more challenging for these old eyes. I thought I might be able to use a cheap USB microscope but the frame rate is so low it's really difficult to place small components. This is a case of you really DO get what you pay for.
 

TomS

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#44
Sometimes it's the down-time that is more important than waiting for a replacement driver. If the driver is that unreliable maybe you should get one or two backups? Depends on whether or not the down-time delays delivery to a customer vs. delaying a personal project.

I suppose your decision to replace or repair also depends on your ability to solder/de-solder surface mount parts without damaging the board or other components. I've done that at work but now, lacking a good stereo-zoom microscope, SMT would be a bit more challenging for these old eyes. I thought I might be able to use a cheap USB microscope but the frame rate is so low it's really difficult to place small components. This is a case of you really DO get what you pay for.
I hope I didn't come across as flippant. My mill has been running for about three years now so if I have to replace a driver again in three years I'm OK with that. This driver failure was a first for me. Everything else has been running fine.

I'm with you on soldering small electronic components. My eyes aren't what they used to be and I don't have the proper equipment. I'd rather spend my money on tooling for the mill and lathe.
 

jbolt

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#45
My drivers are the ones that kept blowing up diodes, not the OP's. I believe this is the first driver failure for Tom and I have no idea what the failure is. I was just sharing my experience and why I moved away from them. As surface mount components go they are fairly large and easy to replace with a fine tipped variable heat soldering iron. I fixed mine a few time since it only takes a little time to do vs waiting. I'm not suggesting he abandon them but if it is a diode that failed to be aware.

Tom - if you exhaust all options with you current setup you might try reinstalling the old BOB and motion controller. Not fun but it might tell you if it is something in the 126, 107, ESS combo.

Grasping at straws here but I have seen issues (non CNC) with some cheap Ethernet cables. I make sure to use high quality shielded cables, keep them as short as possible and away from power cords.
 

TomS

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#46
My drivers are the ones that kept blowing up diodes, not the OP's. I believe this is the first driver failure for Tom and I have no idea what the failure is. I was just sharing my experience and why I moved away from them. As surface mount components go they are fairly large and easy to replace with a fine tipped variable heat soldering iron. I fixed mine a few time since it only takes a little time to do vs waiting. I'm not suggesting he abandon them but if it is a diode that failed to be aware.

Tom - if you exhaust all options with you current setup you might try reinstalling the old BOB and motion controller. Not fun but it might tell you if it is something in the 126, 107, ESS combo.

Grasping at straws here but I have seen issues (non CNC) with some cheap Ethernet cables. I make sure to use high quality shielded cables, keep them as short as possible and away from power cords.
I understand your logic but I really don't want to reinstall the old breakout board and the UC100. I've changed so much that it would be nearly a complete rewire job. I've got a couple of new things to try first. I'm going to lower the power supply output voltage and see what happens. Read that on Practical Machinist where the lower voltage altered motor resonance and improved the surface finish. I read somewhere else that raising the voltage did the same thing. Who knows? It's an easy thing to do.

I did run the drains disconnected test you suggested. Surface finish didn't change so my assumption is the grounding system is sound.

You bring up a good point about the ethernet cable. It's Cat6 but that's all I know. I'll check into it and make sure it's shielded.
 

jbolt

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#47
I understand your logic but I really don't want to reinstall the old breakout board and the UC100. I've changed so much that it would be nearly a complete rewire job. I've got a couple of new things to try first. I'm going to lower the power supply output voltage and see what happens. Read that on Practical Machinist where the lower voltage altered motor resonance and improved the surface finish. I read somewhere else that raising the voltage did the same thing. Who knows? It's an easy thing to do.

I did run the drains disconnected test you suggested. Surface finish didn't change so my assumption is the grounding system is sound.

You bring up a good point about the ethernet cable. It's Cat6 but that's all I know. I'll check into it and make sure it's shielded.
I totally get not wanting reinstall but it might narrow down the cause of your issue.

When you ran the test as I suggested how much did the Z jump around? Does it jump only when doing arcs or both arcs and straight moves?
 

TomS

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#48
I totally get not wanting reinstall but it might narrow down the cause of your issue.

When you ran the test as I suggested how much did the Z jump around? Does it jump only when doing arcs or both arcs and straight moves?
I'm going from memory here but as I recall the needle jumped about .007" to .010" and only during arc moves. You can hear the motors change sound when cutting arcs. During straight moves they are much quieter.

I tried a test run today with the power supply set at 55 vdc and 65vdc. Didn't make a difference in surface finish. I rerouted my ethernet cable so it was no where near a AC power cable. Again, no change in surface finish. Using a 2 flute 3/8" end mill I ran a 1/4" DOC by .005" WOC at 20 IPM then ran the same scenario at 5 IPM. Something is causing the motors to jump around corners but I don't why. It's got to be a harmonics/resonance issue. Wish I knew what's causing it.
 

spumco

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#49
I'm pretty stumped, too.

Shot in the dark here... Do you have one power supply for all three axis? I'm wondering - you mentioned motor noise changing - if the PS is acting wonky when there's a load from both X/Y at the same time. 'Cause you also mentioned that it's a problem on straight angle cuts, not just arcs, right? Any time you're cutting with both axis moving there's a problem?

Maybe a test doing an X/Z or Y/Z move might result in the same surface finish issue. Do a quickie CAD/CAM of a hill-shaped object and use a bullnose cutter with a parallel 3D contour.
 

TomS

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I'm pretty stumped, too.

Shot in the dark here... Do you have one power supply for all three axis? I'm wondering - you mentioned motor noise changing - if the PS is acting wonky when there's a load from both X/Y at the same time. 'Cause you also mentioned that it's a problem on straight angle cuts, not just arcs, right? Any time you're cutting with both axis moving there's a problem?

Maybe a test doing an X/Z or Y/Z move might result in the same surface finish issue. Do a quickie CAD/CAM of a hill-shaped object and use a bullnose cutter with a parallel 3D contour.
I have a dedicated power supply for each axis drive. Straight line cuts are fine. Surface finish is good. So yes, problem/poor surface finish is on arc and circular cuts.

I'll try a sloped 3D cut and see what happens.
 

homebrewed

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#51
So the Z is jumping around and the sound of the X & Y steppers is different when cutting arcs or angles? What happens when you remove power from, say, the X driver (Y still powered up), and then reverse the situation? There seems to be some odd interaction going on between the axes.

Something else I would suggest would be to write up a table of each hypothesis, experiment and result. Or, since nothing has really solved the problem, at least a list of what you've tried and why. While you may think you've exhausted a particular avenue, you may find some holes in your testing while you are writing up your summary. This has been helpful for me when working on a gnarly problem.

Are you using the sense connections on your power supplies or are they unconnected?
 

TomS

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So the Z is jumping around and the sound of the X & Y steppers is different when cutting arcs or angles? What happens when you remove power from, say, the X driver (Y still powered up), and then reverse the situation? There seems to be some odd interaction going on between the axes.

Something else I would suggest would be to write up a table of each hypothesis, experiment and result. Or, since nothing has really solved the problem, at least a list of what you've tried and why. While you may think you've exhausted a particular avenue, you may find some holes in your testing while you are writing up your summary. This has been helpful for me when working on a gnarly problem.

Are you using the sense connections on your power supplies or are they unconnected?
Power supply sense connections? Here's a picture of the terminal connections on my X and Y power supplies.

Power Supply.jpg
 

TomS

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#53
I'm pretty stumped, too.

Shot in the dark here... Do you have one power supply for all three axis? I'm wondering - you mentioned motor noise changing - if the PS is acting wonky when there's a load from both X/Y at the same time. 'Cause you also mentioned that it's a problem on straight angle cuts, not just arcs, right? Any time you're cutting with both axis moving there's a problem?

Maybe a test doing an X/Z or Y/Z move might result in the same surface finish issue. Do a quickie CAD/CAM of a hill-shaped object and use a bullnose cutter with a parallel 3D contour.

Today I ran a couple of tests in the XZ plane and the YZ plane. Below are pictures of each test done with a two flute 3/8" HSS ball end mill at 3000 rpm, .005" DOC and 010" stepover. As you can see there is virtually no difference in surface finish.

Grasping at straws, between the two tests, I ran a ground wire from my earth ground rod to my enclosure. Guess what? No change. Geez this is frustrating.

But I didn't come away empty handed. During the ZX test the motors emitted a monotone sound. Not so with the ZY test. The Y motor tone changed multiple times during each pass. There may be something there so tomorrow I'll pull the motor and check the ball nut mount and the ball screw AC bearings.

20170819_160953_resized.jpg


20170819_151107_resized.jpg
 

TomS

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#54
I think I found the problem, hopefully. I disassembled the Y axis ball screw bearing block and one of the AC bearings was in failure mode. Spinning it by hand it was rough. The other one was OK. I'm going to replace all four of the bearings on the X and Y axis while I have it apart. I'm praying this is it.
 

homebrewed

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#55
Power supply sense connections? Here's a picture of the terminal connections on my X and Y power supplies.

View attachment 240025
Most high current PSU's have sense terminals, to compensate for voltage drops on the lines. I guess that's one of the things you give up with these types of inexpensive supplies. Or perhaps in this type of application there's not much benefit to be had (PWM stepper driver supply).

Good find with the rough bearing. Hopefully that's the source of your problem. Seems sort of strange for a bearing to go bad in that application. I'd double-check other components in the Y axis to make sure the bearing is not the result of some other problem. Otherwise you could be back in there sooner than you like.
 

TomS

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#56
Most high current PSU's have sense terminals, to compensate for voltage drops on the lines. I guess that's one of the things you give up with these types of inexpensive supplies. Or perhaps in this type of application there's not much benefit to be had (PWM stepper driver supply).

Good find with the rough bearing. Hopefully that's the source of your problem. Seems sort of strange for a bearing to go bad in that application. I'd double-check other components in the Y axis to make sure the bearing is not the result of some other problem. Otherwise you could be back in there sooner than you like.
I've looked things over and didn't see anything else of concern. The ball nut mount is tight to the saddle and the ball screw rotated smoothly. I believe it's the bearings as they are cheap, as in poor quality, asian imports. They came with the bearing blocks. I've got four on order from VXB. Should be here on Wednesday.

Got my fingers crossed.
 

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#58
I hope that solves your problem but it would be an odd coincident that it would happen at the same time you changed the controller. I'll keep my fingers crossed for you.
 

TomS

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#59
I hope that solves your problem but it would be an odd coincident that it would happen at the same time you changed the controller. I'll keep my fingers crossed for you.
Looking back on some jobs prior to changing out the controller there were some surface finish issues starting to appear. They just were not bad enough at that time. Or I wasn't paying attention.

I'm hoping too!
 
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