ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

Postby Robmar » Mon Jun 01, 2015 8:02 pm

Hello VF,

I've been dealing with an inconsistent 'Z' axis ever since we purchased the ShopSabre 4896. I've been on the phone with ShopSabre many different times and no one can seem to figure out what our issue is.

I'm running a 10 tool changer. The problem is that the tool lengths aren't consistent relative to the table surface, or to the other tools. They will vary up to 0.030". Meaning that my cuts are at unpredictable depths every time I cut.

We thought it was a defective tool measuring pad, but now I think the problem must lie somewhere else. For example, I will set the Z0 on the surface of the table. Then, unplug the air - plug it back in - rehome the machine, then when I bring it back down the the exact same spot it will be up to 0.030" off.

The table itself has been resurfaced and is very flat. No one can really pin down the exact problem here but it's destroying my ability to run production. Our machine is about 1 year old with very little use. I've spent a lot of time on the phone with the manufacturer but they seem as stumped as I am.

Not sure where to go from here but I know I need to get this fixed badly. Any help is greatly appreciated. :)

Thank you,
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Re: ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

Postby zeeway » Mon Jun 01, 2015 9:44 pm

Sounds frustrating, for sure. Does Shopsabre have a service man that could check out your machine on your site ? That is clearly the most direct way to get it sorted out.
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Re: ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

Postby darde » Mon Jun 01, 2015 9:57 pm

Check that the ball nut on the z axis is not turning in the holder. If the newer one is the same as mine it is threaded into the aluminum plate. Mine became loose and would turn sometimes. It was very hard to get at and the grease zero woul not allow it to tighten up so I had to lock tight it and no problems since. The other issue could be the coupler at the top or a shim may be neede on the ball screw. Can you lift the z and see if there is any play
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Re: ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

Postby TReischl » Mon Jun 01, 2015 10:03 pm

Robmar wrote:Hello VF,

We thought it was a defective tool measuring pad, but now I think the problem must lie somewhere else. For example, I will set the Z0 on the surface of the table. Then, unplug the air - plug it back in - rehome the machine, then when I bring it back down the the exact same spot it will be up to 0.030" off.


I am curious about why the air is unplugged then plugged back in? But that is just me. . . .

What I do note is that you REHOME the machine after the unplug/plug and after you set Z0. Hope I got that right?

So, when Z homes it is looking for the home switch. On industrial quality machines those switches are usually very precise (which is why most of cheapos do not use them). I am not sure what type of switch SS uses, all they state is that they have limit switches on all three axis. So, what I am saying is that you may have a switch problem.

On my machine, home built, with REALLY cheap limit switches, my axis typically repeat within .004-.005. If I replaced them with expensive ones I could expect way better than that.

Hopefully this will help you out, if nothing else, it is something that you can eliminate.
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Re: ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

Postby Robmar » Tue Jun 02, 2015 12:51 am

zeeway wrote:Sounds frustrating, for sure. Does Shopsabre have a service man that could check out your machine on your site ? That is clearly the most direct way to get it sorted out.


That's what I've wanted to do for a while now. They're about 11 hrs away from our shop here. It just seemed like something that would be very expensive. I'll have to ask about it though. Thank you.

darde wrote:Check that the ball nut on the z axis is not turning in the holder. If the newer one is the same as mine it is threaded into the aluminum plate. Mine became loose and would turn sometimes. It was very hard to get at and the grease zero woul not allow it to tighten up so I had to lock tight it and no problems since. The other issue could be the coupler at the top or a shim may be neede on the ball screw. Can you lift the z and see if there is any play


I'm not very knowledgeable about all of the different parts of the machine, but I think I know what you're talking about. I'll check it out in the morning and probably have a follow up question for you, if you don't mind. Thanks for the input. I will check into this for sure.

TReischl wrote:
Robmar wrote:Hello VF,

We thought it was a defective tool measuring pad, but now I think the problem must lie somewhere else. For example, I will set the Z0 on the surface of the table. Then, unplug the air - plug it back in - rehome the machine, then when I bring it back down the the exact same spot it will be up to 0.030" off.


I am curious about why the air is unplugged then plugged back in? But that is just me. . . .

What I do note is that you REHOME the machine after the unplug/plug and after you set Z0. Hope I got that right?

So, when Z homes it is looking for the home switch. On industrial quality machines those switches are usually very precise (which is why most of cheapos do not use them). I am not sure what type of switch SS uses, all they state is that they have limit switches on all three axis. So, what I am saying is that you may have a switch problem.

On my machine, home built, with REALLY cheap limit switches, my axis typically repeat within .004-.005. If I replaced them with expensive ones I could expect way better than that.

Hopefully this will help you out, if nothing else, it is something that you can eliminate.


My machine shares air supply with a large compressor that is also feeding some thermoforming machines. I unplug the air when I leave the machine for a while to reduce load on the compressor and because we tend to get some water in the line and I don't want any extra to go though the machine. (Our multiple water separators aren't getting the job done.)

Yes, I re-home after I plug the air back in. (It's a requirement with this machine. Not sure if that's the case with other types.) I don't see how it could be the Z limit switch because the tool measurements are off and they are also different relative to each other. If it was an error with the Z switch, since it only hits it once, wouldn't the tools be the same relative to the other tools and different relative to the table all in an equal amount? (I hope that made sense.)

Thanks for your input. That very well could be the issue.
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Re: ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

Postby martin54 » Tue Jun 02, 2015 1:06 am

That's what I've wanted to do for a while now. They're about 11 hrs away from our shop here. It just seemed like something that would be very expensive. I'll have to ask about it though. Thank you.

From what you have said this fault has been with the machine from the very start which means that it should be down to the manufacturer/supplier to sort out the problem & shouldn't cost you a penny. You might even be able to go as far as they supplied a machine that wasn't fit for purpose with the problems it is causing.

Also try doing a search on the forum as this sort of thing has been talked about before, not on your particular make of machine but they all work pretty much the same way. Backlash, binding & anything loose would be the places I would look first.
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Re: ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

Postby fromtheforty » Tue Jun 02, 2015 1:21 am

I've got a Shop Sabre 48-96. I can relate to some of the issues that you have had but I've kind of passed them off as inconsistencies in material. I don't know what type of material you are working with but check it with a micrometer. You might be shocked at how much variation there can be in materials like plywood.

I wouldn't bother disconnecting the air from the machine. Mine uses virtually no air. I can run for hours without my 60 gal compressor kicking in once.

Also, check to make sure that there is no build up of waste in the energy chain. I don't remember how the air is routed thru the machine but I have had my machine shut down from low air pressure because sawdust built up had kinked the air line. That maybe could cause the Z to shift because of changing air pressure.

I really don't know much but maybe it will help!

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Re: ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

Postby Robmar » Tue Jun 02, 2015 2:02 am

martin54 wrote:That's what I've wanted to do for a while now. They're about 11 hrs away from our shop here. It just seemed like something that would be very expensive. I'll have to ask about it though. Thank you.

From what you have said this fault has been with the machine from the very start which means that it should be down to the manufacturer/supplier to sort out the problem & shouldn't cost you a penny. You might even be able to go as far as they supplied a machine that wasn't fit for purpose with the problems it is causing.

Also try doing a search on the forum as this sort of thing has been talked about before, not on your particular make of machine but they all work pretty much the same way. Backlash, binding & anything loose would be the places I would look first.


That's good to hear you say that. I just assumed that's not something they would do for free. But, the machine was a very big investment for us and we've been having this same problem for some time without being able to fix it.

I will look into some of the issues that you mentioned before I bring that up with them. Thank you!

fromtheforty wrote:I've got a Shop Sabre 48-96. I can relate to some of the issues that you have had but I've kind of passed them off as inconsistencies in material. I don't know what type of material you are working with but check it with a micrometer. You might be shocked at how much variation there can be in materials like plywood.

I wouldn't bother disconnecting the air from the machine. Mine uses virtually no air. I can run for hours without my 60 gal compressor kicking in once.

Also, check to make sure that there is no build up of waste in the energy chain. I don't remember how the air is routed thru the machine but I have had my machine shut down from low air pressure because sawdust built up had kinked the air line. That maybe could cause the Z to shift because of changing air pressure.

I really don't know much but maybe it will help!

Geoff


I'm definitely having some issues with material thickness and inconsistencies. I'm using bamboo plywood. Between material thickness and warpage it can become very challenging when paired with the other issues I'm having. But, I'm having the inaccuracy issues while just testing the tools on the CNC table top. I also notice it on my finished parts as well, of course.

The accuracy of the Z axis is just confusing. I can set it at the top of my material (to the 0.001") and have it drill a 0.0625" deep hole in the same place I set the Z. It will always first come out at about 0.04-0.054". Never have been able to get it right on.

Many of my products have small magnets that are mounted flush with the material surface. So, when I have up to 0.03" inaccuracy in my depth, this makes this process extremely frustrating and unpredictable.

What do you mean by the "energy chain?"

Thanks for your reply.
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Re: ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

Postby glenninvb » Tue Jun 02, 2015 2:31 am

Does yours use steppers or is it upgraded to servos...... just thinking, if the air assist Z axis has binding (moisture damage in cylinders) wrong pressure or other mechanical binding you could be losing steps. and would account for inconsistent behavior........ pure speculation of course

Agree with Martin, The manufacture should certainly be able to troubleshoot and repair
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Re: ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

Postby larrybadgett » Tue Jun 02, 2015 11:22 am

I have a ShopSabre and had slack in the x axis ball screw causing similar problems. I'm gathering that you have an air balance z axis which would mean that the z axis basically floats. That being the case you could be zeroing in anywhere within that slack range in the ball screw. Check with machine and air off by prying up and down on the z axis while measuring for any travel with a dial indicator. If you find slack you will need to shim the ball screw bearing to the appropriate amount of slack under the drive motor. Also check that all gantry bolts are tight and not allowing movement. Good luck! If either of these things are happening and ShopSabre did not find the problem the company has changed a lot since I've corresponded with them.
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Re: ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

Postby Robmar » Tue Jun 02, 2015 4:01 pm

darde wrote:Check that the ball nut on the z axis is not turning in the holder. If the newer one is the same as mine it is threaded into the aluminum plate. Mine became loose and would turn sometimes. It was very hard to get at and the grease zero woul not allow it to tighten up so I had to lock tight it and no problems since. The other issue could be the coupler at the top or a shim may be neede on the ball screw. Can you lift the z and see if there is any play


BINGO!

You could be an all-star on ShopSabres support team.

The ball nut on the Z-axis IS turning in the holder, accompanied by a clunking sound. It will usually turn when it hits the top of the Z-axis, but sometimes will turn at the onset of motion. Ben at SS recommended the same fix that you mentioned with the Loctite.

They asked us to go through the process of taking the spindle off, cleaning that up and adding the Loctite, reassembling the machine and trying to get it calibrated, adding the shims back in ourselves.

Honestly, I'm very uncomfortable taking the spindle off myself. I've already spent well over 50+ hours trying to figure out this issue. It's my first time working with a CNC so this depth thing has really made it confusing for me. I've also made many reject parts of expensive material because of the Z-axis inaccuracy.

Is this something that they should come out and fix? Or am I being too dramatic and I should just do it myself? Just seems like a $55,000 dollar machine should do what they say it can out of the box.

Thanks again for the input everyone.
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Re: ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

Postby Leo » Tue Jun 02, 2015 5:15 pm

Robmar wrote:
darde wrote:Check that the ball nut on the z axis is not turning in the holder. If the newer one is the same as mine it is threaded into the aluminum plate. Mine became loose and would turn sometimes. It was very hard to get at and the grease zero woul not allow it to tighten up so I had to lock tight it and no problems since. The other issue could be the coupler at the top or a shim may be neede on the ball screw. Can you lift the z and see if there is any play


BINGO!

You could be an all-star on ShopSabres support team.

The ball nut on the Z-axis IS turning in the holder, accompanied by a clunking sound. It will usually turn when it hits the top of the Z-axis, but sometimes will turn at the onset of motion. Ben at SS recommended the same fix that you mentioned with the Loctite.

They asked us to go through the process of taking the spindle off, cleaning that up and adding the Loctite, reassembling the machine and trying to get it calibrated, adding the shims back in ourselves.

Honestly, I'm very uncomfortable taking the spindle off myself. I've already spent well over 50+ hours trying to figure out this issue. It's my first time working with a CNC so this depth thing has really made it confusing for me. I've also made many reject parts of expensive material because of the Z-axis inaccuracy.

Is this something that they should come out and fix? Or am I being too dramatic and I should just do it myself? Just seems like a $55,000 dollar machine should do what they say it can out of the box.

Thanks again for the input everyone.


As a manufacturing engineer I do this stuff for a living.

At a $55,000 machine I would read the warranty. If it says 1 year -parts and labor, CALL them. Save yourself the time and trouble.
You spent 50 hours trying to solve a problem that you already paid some else to do.

1) You paid for it
2) The vendor saved the time and money by not being there - even though they were paid up front - by you.
3) You lost valuable productive $ earning time - even though you already paid - so you have lost double.

First - READ the warranty.

THEN - call them and tell them you are down and loosing money on their poor workmanship and that they need to get their backside in there and fix the d%&# machine - NOW.

Of course - if the warranty does not cover it - then it is all on you.

Talk to the company owner if you need to.

Next machine purchase - do your due diligence on the support and warranty part of the purchase.
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Re: ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

Postby Robmar » Tue Jun 02, 2015 5:23 pm

Leo,

You're right. We should have done some more research beforehand. We are slightly out of our 1 year warranty window. But, it has taken us months to discover what the actual problem is. It was a user on this forum that turned me onto the actual issue, not their techs.
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Re: ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

Postby Ken Rychlik » Tue Jun 02, 2015 6:07 pm

I have an 08 that I added my own atc to sill with zero depth issues (so far). I do have another machine I service in town that has some depth issues. I will check with this on his. Ben has been very helpful in the past to me.
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Re: ShopSabre 4896 - Persisting 'Z" Axis Accuracy Issue

Postby Robmar » Tue Jun 02, 2015 6:11 pm

We tightened up the nut enough to perform some tests. Even when the nut isn't moving and with a brand new tool measure pad installed, the bits are still up to .010" off from each other.

I'm beyond frustrated and I have no idea how to proceed. I need an accurate machine here and we thought that's what we were buying.
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