[Semus]

Hey guys,

I own the CNCRP Benchtop Pro machine. First, let me just say that I love this machine. Despite the few issues I've had, it's been a great machine. The guys at CNCRP have been absolutely AMAZING to work with. Just superb ;-)

On to my issue...

I have been cutting parts for the last few weeks with this machine. Most parts turn out fine, with minor variations that I would call "acceptable". However, once in awhile I get a part that is longer than it's twin (cut at the same time in the same nest - flipped 180 degrees), or possibly shorter. This really didn't make much sense to me. For the life off me I could not figure out how this could be happening. I've done the usual troubleshooting steps (making sure things are tight - checking straightness with a laser edge finder). Most times, things check out just fine. There has been the odd moment where I would test for straightness and it would be off by quite a bit. Somehow, it always seemed to "fix" itself. Weird, right?

Anyhow, I had some time this afternoon, so I decided to do some more troubleshooting (something still didn't feel right). First off, I homed the machine to make sure things were squared up. I measured the distance between the A-axis metal plate and it's proximity switch, and the Z-Axis metal plate and it's proximity switch (There are metal plates attached to each axis that each prox switch uses to "home" the machine), and found the distances to be the same. No problem there. Then, I moved the gantry to the opposite end of the machine (moved the A and X axes opposite the proximity switches), and here is where I noticed something strange. The distance from the metal plates and the prox switch on each side should have been the same. They were not. In fact, there's a difference of about 1/16". To me, that's a sign that something isn't right.

So, my troubleshooting thus far has led me to the motors. After all, if the motors are not moving at the same rate, obviously the distances from the metal plates to the proximity switches will be different on each side, which is basically what I'm seeing.

I opened up Mach3 to check the motor tuning section. This is where I'm a bit confused and need some guidance. I'm not an expert with this portion of Mach3, and the last thing I want to do is go messing with numbers when I don't know what they do. That said, the first thing I checked on each axis was the "velocity"(in's or mm's per min). I check the velocity for each axis, and each axis had the exact same entry = 250.02 (except for the Z axis = 150 - I think...). Then, I checked the next box called "Acceleration"(in's or mm's per min). I checked the acceleration for each axis, and below are the numbers I found:

Y-Axis = 10
X-Axis = 10
A-Axis = 20
Z-Axis = 20

Again, I'm no expert. So, perhaps someone with more knowledge on the subject can fill me in here. The X and A axes on this machine are basically the same thing (Well...they both control the X axis direction). So, it seems to me that the acceleration of the X and A axis should be the same, right? Or, should they? Once again, I'm not an expert here, so if anyone can tell me why the acceleration should be different, please do. Otherwise, I'll have to assume that this was an incorrect entry, and that these "acceleration" numbers (for the X and A axis) should be the same. I've been running with these numbers since the machine was first set up. I'm starting to think this might be the cause of most of my issues thus far (aside from a few rail issue).

I sent an email to CNCRP, but I figured I would ask this question here too, just in case some of you would like a good laugh at my expense ;-)

[ger21]

If the X and A are slaved, then the acceleration should be set the same.

[Semus]

If the X and A are slaved, then the acceleration should be set the same.

Could you clarify what "slaved" means? I know that word in computing terms, such as master and slave hard drives. I'm assuming it's somewhat similar?

I do know that each motor (A axis and X axis) has it's own connecting wire from the main box.

[Semus]

Ok, I was doing some reading on the CNCRP website and found this, with regard to the proximity switches that I have installed on my machine...

"3 sensors, intended to be used for X-, Y-, and A- on a slave axis for auto-gantry squaring."

I'm assuming this means that they are, in fact, slaved.

[ger21]

Go to Config > Slave axis and see if the A axis is slaved to the X.

What this means is that when the g-code tells the X axis to move, the A moves with it. There are no A axis commands in the g-code.

[Semus]

Go to Config > Slave axis and see if the A axis is slaved to the X.

What this means is that when the g-code tells the X axis to move, the A moves with it. There are no A axis commands in the g-code.

This is exactly what's happening. The A is slaved to the X.

Thanks, Gerry!

I just can't believe I've been running with these numbers for over two months now and didn't even know it. Live and learn, I guess.

[ger21]

I don't know for sure that the A acceleration is used. Did changing it fix the issue?
I do know that if the X and A homing speeds are not the same, then one side will indeed home faster than the other, causing severe racking. But I've never attempted to run the machine with different accel or velocity on the master and slave.

[Semus]

I don't know for sure that the A acceleration is used. Did changing it fix the issue?
I do know that if the X and A homing speeds are not the same, then one side will indeed home faster than the other, causing severe racking. But I've never attempted to run the machine with different accel or velocity on the master and slave.

I think you're right, Gerry. Changing the number had zero affect on this issue.

The distance to the prox switch starts off the same when "homed", but once I move the machine to the opposite end, it's 1/16" off from one side to the other.

[Semus]

Just to verify that the motors are not the issue, I removed them from the machine, placed tape on the shafts and watched the motors move when manually jogging them. They move exactly the same amount no matter which way they turn, so it has to be something mechanical and not electrical.

I'm really at a loss for what to try next...

Could it be that the ball screw is not the same thread pitch as the other? I don't see how that's possible, but I'm just thinking out loud here. Maybe it's something really simple that I'm overlooking.

[ger21]

You have a screw on each side?
Make sure the bearings holding the screws in place are tight, and that the couplers are not slipping.

[Semus]

You have a screw on each side?
Make sure the bearings holding the screws in place are tight, and that the couplers are not slipping.

Yes, there are ball screws on each side (X axis and A axis). The couplers appear to be very tight (no slipping). I doubt the couplers are the problem, and here's my thinking on this... The distance from the prox switch to the metal plate is consistently 1/16" off (from one side to the other) when the machine is moved to the opposite end. Once I move it back, the distance becomes equal again. If the couplers were slipping I would think it would be less consistent. I did check them, though. I confirmed they are tight.

The only way to check the ball screw is to take the machine completely apart. I suppose that's the only choice I have left ;-( I might wait until I hear back from CNCRP. I sent them an email last night. I think these guys are beginning to hate me. They've been fantastic,though. Seriously, a very professional bunch of guys.

[Semus]

Ok, so further checking has revealed a problem.

I checked to make sure that the distance between the switches on both axes were the same when the machine is "Homed". They are not. The distance from the A axis plate to the switch is 0.480. The distance from the X axis plate and it's switch is 0.450. That's a difference of 30 thousandths. That's about 1/32" of an inch. I don't know what sort of tolerances these switches have, but to me this doesn't seem right. Again, this is when the machine is in it's "home" position (Ref All Home in Mach3)

I even switched the switches around. I exchanged the X axis switch with the A axis switch and got the same thing (also had to exchange motors).

Shouldn't the distances to each metal plate be exactly the same? I would think they should be when homed.

I took a look at the ball screws and couldn't find anything wrong with them. The brackets that hold the ball screw to the metal plate seem very tight. I can't physically move either axis using any amount of force. I would need to remove the gantry to be absolutely sure, but I'll wait until that becomes the last option.

EDIT: Here's what really gets me... I mentioned above that I exchanged the switches (moved the A axis switch over to the X axis[along with the motor] and moved the X axis switch over to the A axis[along with the motor]) and I got the same distance variation, on the same side. That's what's bothering me. You'd think that by moving the switches around, the distance variation would move with it, assuming it has anything to do with the switches at all. Still, the switch is what tells the motors to move the gantry a certain distance away from those switches when the machine is homed, so now I'm really confused...

Here is a picture of the switch and the metal plate...

Attachment 261228

[Semus]

Alright, so just to continue passing on some info here...

This is what I have found so far. I decided to test something, and I've had a bit of success with it so far. The variation across the distance of the table is now very minor after performing this test. Before, the distance from the switch on the A or X axis was one amount, and the other side was 1/16"(or more) less than that amount. When I "home" the machine, there's a difference of about 30-40 thousandths between one switch and the metal plate, and the other switch and the metal plate. If you place anything metal in front of the proximity switches, it triggers the switch. So, I decided to attach a washer (about 0.055 thick) on one of the metal plates (on the side that had the least distance between the plate and the switch). With the washer attached (duct taped to the metal plate), the distance between the metal plate and the switches on both sides are almost exactly equal now.

I then moved the machine along the X axis (to the furthest point away from the switches) and measured the distance between each switch and the metal plate. It is now less than 1/32" difference between one side and the other. I'd say it's roughly +- 20 thousandths now. Before I placed the washer on the metal plate, it was around 70-80 thousandths, or more. So, the washer being 0.055 thick actually makes these numbers make sense. The washer being attached makes the metal plate move further away from the switch.

What I still don't understand is why when I reversed the switches, the distance variation didn't reverse with them.

I'm almost positive that these problems are self induced, but if anyone has any ideas to throw out there, I'd be more than happy to listen.

[Semus]

I don't know if anyone will bother to read any of this, but just in case someone does, I'll go ahead and post my findings so far.

I performed an experiment a few minutes ago. I wanted to see if my machine was squared up, so here's what I did to check it. You guys can chime in with any insight as to why this might be the wrong way to check. I'm just winging it at this point, so if I'm doing this incorrectly, just let me know.

I placed a laser pointer inside the router collet, and then put the machine at 0,0 (0,0 being really close to the machine coords - far right corner when looking at the machine head on from the router side). Using the laser pointer, I placed a mark at the 0,0 point. Then, I moved the machine to the X=20, Y=0 position and placed another mark. I then moved the machine to the X=20, Y=-22 position and placed another mark. And finally, I moved the machine to the X=0, Y=-22 position and placed my final mark. The marks basically form a square (or rectangle to be exact). Now, if there is any deviation whatsoever, the distance from the 0,0 position to the X=20, Y=-22 will not be the same as the distance from the X=0, Y=-22 to the X=20, Y=0 position. I even made sure that the distances between each mark was correct, and they were (20" and 22").

My findings show that the distance from corner to corner (diagonally) are the same, at 29.732137 inches (that's as far as my calculator goes, haha). I doubled and triple checked with different measuring tapes, and found the same thing with each one. The point is, I now know that my X axis is a perfect 90 degrees to my Y axis.

I don't know what it was before, and I should have checked it. This thread may not have even been necessary if I had just performed some simple checks in the beginning.

I'm not sure how to leave this, but I'll just say that I'm still learning every single day when it comes to these machines. This is yet another learning experience for me.

EDIT: As to why there was a variance between the X and A axes, I do not know. After I placed the spacer on the metal gantry plate, things just seemed to fall into place. I made a few adjustments to the proximity switch on that side, just to get things back to square again. Other than that, I don't know how or why there were differences. I don't have an answer for that. Human error, perhaps? That's more likely than any other explanation I can come up with at this point.

[ger21]

I was going to tell you to make sure it's square, as that's really the only thing that matters. Sounds like your in good shape now.

[Semus]

I was going to tell you to make sure it's square, as that's really the only thing that matters. Sounds like your in good shape now.

It looks like it, Gerry. I really appreciate the help, even though this was probably my own doing.

[ahren]

Wow, it's pretty amazing how much has been posted on this in 48 hours. I suppose we won't let Cory go on vacation any more

First off, you're right that there is an error in the XML file which we'll get fixed right away. The acceleration should be the same for the slaved axes. This won't impact anything during operation (the slaved axis will use the master axis accel during normal operation), but it will cause the axes to move slightly differently during homing. That being said, the dual-sided homing routine will still correct for this, it's just not the ideal homing sequence as it adds a tiny skew at the beginning of the routine, that then gets corrected out.

In terms of the difference in spacing from one end to the other, we do cut the extrusion for these in multiple lots, so there can be some small variations in the overall extrusion length. Any variation is taken up by the free-end radial bearing, and since homing happens to the motor side, this doesn't have any negative impact on the system, but measuring off of the radial bearing end on two different axes may not yield exactly the same value.

Additionally, the Pepperl sensors we use do have some variation sensor to sensor in terms of sensing distance, especially against aluminum. For this reason we provide threaded holes to adjust them in and out, so it's not surprising that the gap is a little different on both sides. That being said, the sensors are extremely repeatable, which is what really matters for homing. We've tested them under varying conditions, even starting them out in the freezer and then testing repeatability as we put a heat gun on them, and seen variation on a dial indicator of less than 0.0005" over ~80 degree temperature change.

Anyway, your washer solution is fine, and ultimately the squareness of your machine is what matters, but for others reading this thread it's fairly normal for there to be some variation in sensor offset.

Best regards,

Ahren
CNCRouterParts

[Semus]

Wow, it's pretty amazing how much has been posted on this in 48 hours. I suppose we won't let Cory go on vacation any more

First off, you're right that there is an error in the XML file which we'll get fixed right away. The acceleration should be the same for the slaved axes. This won't impact anything during operation (the slaved axis will use the master axis accel during normal operation), but it will cause the axes to move slightly differently during homing. That being said, the dual-sided homing routine will still correct for this, it's just not the ideal homing sequence as it adds a tiny skew at the beginning of the routine, that then gets corrected out.

In terms of the difference in spacing from one end to the other, we do cut the extrusion for these in multiple lots, so there can be some small variations in the overall extrusion length. Any variation is taken up by the free-end radial bearing, and since homing happens to the motor side, this doesn't have any negative impact on the system, but measuring off of the radial bearing end on two different axes may not yield exactly the same value.

Additionally, the Pepperl sensors we use do have some variation sensor to sensor in terms of sensing distance, especially against aluminum. For this reason we provide threaded holes to adjust them in and out, so it's not surprising that the gap is a little different on both sides. That being said, the sensors are extremely repeatable, which is what really matters for homing. We've tested them under varying conditions, even starting them out in the freezer and then testing repeatability as we put a heat gun on them, and seen variation on a dial indicator of less than 0.0005" over ~80 degree temperature change.

Anyway, your washer solution is fine, and ultimately the squareness of your machine is what matters, but for others reading this thread it's fairly normal for there to be some variation in sensor offset.

Best regards,

Ahren
CNCRouterParts

Please tell Cory that I hope he had a great vacation ;-)

With regard to the sensors, I can deal with that. It's not a huge issue since it can be accounted for with spacers (like I did). My one major concern was squareness, and as you've seen by reading this thread, I was able to square the machine just fine. It was probably square the entire time, but due to my own OCD, I was more than likely looking for problems where there weren't any.

These rails on the other hand... They are giving me nightmares.

Let me ask you a question, Ahren. Why did you guys decide to use 4 small brackets for the rails instead of one or two long brackets? It seems to me that longer brackets would keep those rails nice and straight, no? As it stands now, you could possibly have a slight bend in between those little brackets, making it almost impossible to get them straight. Was there some technical reason why you chose to go with four small ones? Weight perhaps? Just curious. I'm having a really hard time with these things...

[ahren]

We use our V-Con clamps individually for Benchtop PRO as they are part of our existing product line, and we make them in large quantities, which is the only way they are cost-effective. We do have an assembly procedure for insuring straightness of the installed rails, and have good success with this, but that certainly doesn't preclude taking a different approach in the future. We're always open to ideas to make our products better!

Best regards,

Ahren
CNCRouterParts

[Semus]

We use our V-Con clamps individually for Benchtop PRO as they are part of our existing product line, and we make them in large quantities, which is the only way they are cost-effective. We do have an assembly procedure for insuring straightness of the installed rails, and have good success with this, but that certainly doesn't preclude taking a different approach in the future. We're always open to ideas to make our products better!

Best regards,

Ahren
CNCRouterParts

As a small business owner, I can certainly understand the concept of "cost effective". We've had our fair share of situations where a different approach was necessary due to cost related issues.

I want to go ahead and admit that a simple phone call to you or your staff would have been better than to vent my frustrations on a forum for all the world to see. That was not one of my better moments. And, even though an apology may not be necessary, I would like to give one anyway.

From the very beginning (from the moment I contacted CNCRP), I was treated as a valuable customer. Through many conversations with Cory and Ahren, I have come to realize that these guys are willing to go the extra mile to make sure their customers are happy. I have had nothing but overwhelmingly positive experiences with their staff, which reassures me that I made the right decision purchasing my machine from them.


Chris