[sharob27]

Hey Guys,

I have a CNCRP 4848 with Nema23 motors. Primarily use the machine to cut HDPE and Polycarbonate. The router on it is a PorterCable 7518.

I have recently run into an issue where all of 3 of my axis have started slipping at random times. The z will slip during up travel, the x and y during return to zero or with any speed. The machine then loses its place and damages the workpiece. I've slowed my acceleration down a ton, and don't run any jobs faster than 15IPM...which is tough! Any thoughts? I finally have some jobs for the thing, and I can't complete them!!

I appreciate any help.

Thanks,
Shaun

[nlancaster]

Sounds like the setscrews are not tightened fully. Check the pully setscrews and add some loctite if you don't have it on them already.

[victorofga]

I saw somewhere a post...

user had some impossible acceleration set..

what values you set on the axises? just out of curiosity?

yes I did read you set back a ton... but it doesn't say nothing..

[sharob27]

Attachment 284792
Attachment 284794
Attachment 284796

I have attached my motor tuning settings. The A is the same as the X, Which you guys probably knew Now, as far as checking the set screws, I believe the pulleys came connected to my motors straight from CNCRP, so it's definitely not something I put Loctite on. I'll have to tear it down tomorrow in order to get to them...Unless there's an easy way to get to them...?

Thanks for the help guys.
Shaun

[victorofga]

for me, when I used mach 3

I had set about 120 mm the Z

and 150 X and Y


might be others has different opinion, I would suggest
set all axis to 5 and start to raise till it start to slip..

this way, you could filter out if acceleration were the issue..

if it keeps slipping at 5 , then you need stronger motor on axis slipping..

reason I suggest the 5 because you using rack n pinion, and possible for one motor turn you have larger distance than I had on my router..

I had on all axis 5 mm, less than 1/4 in per motor turn, in inches I had about 5 on Z and 6 on X-Y axises

[sharob27]

Switched all of my settings to what you recommended, seems to be a lot smoother than it was. I've ran for almost 2 hours, 15 minute jobs each time. Z axis finally just slipped again. I'm going to have to check the set screws I believe.

[sharob27]

Just checked the Z axis screws on the zero backlash coupler, and while neither were "loose", they were both able to be tightened. So, I removed them individually and added Loctite, and reefed them down tight! Hopefully this fixes the Z issue. Going to run in a few minutes. Thanks again for the help guys.
Attachment 284892

[LeeWay]

Those motors should not be slipping at all. Especially with such meager settings. What kind of electronics package do you have? I think that is where I would look.

[sharob27]

I didn't think they should be either. When I first built it around Oct-Dec 2013, I had it SCREAMING around the table. So I know it's capable of so much more. I am using the NEMA23 Pre-Wired Kit from CNCRP. 4-Axis Digital Plug and Play Nema 23 System - CRP800-00E-5 | CNCRouterParts

I just ran for about 5 mins again, and the Z slipped again. It's always during uptravel. Usually I am completing a hole, and it slips on its uptravel out of the hole, then it promptly crashes through the workpiece as it's lost is position. The other axes only ever slip during return from zero, so it rarely ruins a workpiece. I'm kind of stumped at this point. Is it possible that my shop's power supply is unreliable and that would be causing an issue? Kind of a N00B with troubleshooting these issues.

Thanks,
Shaun

[LeeWay]

If you have another computer handy, I would try that swap first. I always have back up computers, so that is the easiest to try for me.
You might try a different version of Mach 3 too. Also do you have any other software on the computer besides Windows and Mach 3?

[sharob27]

The only other computer I have for it never worked, as I had to put an aftermarket Rosewill PCI card into it, which I never got to work. So, the only other option as far as that goes is to buy an ethernet smoothstepper for that computer. It ran Windows 7, Mach3, and that was it. The computer I'm using only has Windows XP and Mach3 installed as well, but is a much older HP that had a stock PCI card. The computer could be the issue? Like I said, I'm fairly new to the CNC world, and I haven't had to deal with many issues.

Thanks,
Shaun

[nlancaster]

When I first built it around Oct-Dec 2013, I had it SCREAMING around the table.

If you had it running much faster before. What might have changed?

[victorofga]

shaun

I would suggest either way a stronger motor or screw need to be lower lead..

I believe the initial friction what causing the slips.. that's a very high lead for Z in my opinion...

mightbe just swap to a ballscrew which one has almost no friction...

you have the possible best couplers, they never slip... I mean if diameters are match and bolts normally tightened..

================================================== ==================================

for me similar happened..
I had the impression everything is fine..

til I had a job came up where very much Z movement was involved,

not like a 3d cut, but many tiny pockets... and I noticed the pattern is deepening as machine going along with the part..

after I changed the motor stronger... it stopped..

very possible you had the slip before, but it was so minimal you didn't noticed..

when you just cut trough parts you never notice minor slips..

heres an ebay link

SFU1605 Ball Screw L250MM ballscrew with SFU1605 Single ballnut for CNC | eBay

for this money don't worth to playing around with leadscrew..
leadscrew not cheaper, not more precise..

and leadscrews always has more friction than ballscrews..

[pete1961]

I had the exact same problem with my z-axis. Spoke with CNC router parts and determined a solution to my problem that sounds similar to yours.
My Z-axis would lose steps most of the time while homing or setting up a job and crash into my table or work piece. I lived with it for awhile as it was somewhat random.

I was using a Geckodrive G540 in my system. CNC router parts advised using a smoothstepper to eliminate this problem. It so far has worked perfectly for the last couple of months.

If I remember correctly CNC Router Parts advised the G540 basically can't process fast enough and loses steps.
You can contact them for help, they definitely knew how to fix my problem and my give you some guidance.

[sharob27]

If you had it running much faster before. What might have changed?

To be honest with you, my level of understanding changed, I slowed everything down because I was overheating material, and just learning. When I first put it together, it was more of a "Wow see how fast I can cut stuff!" Then it started slipping, and I dialed it back more. I attributed the slipping to the speed I was running things at, not an issue with the machine. However, now that it is running incredibly slow, and STILL slipping, it's time to deal with it.

[sharob27]

shaun

I would suggest either way a stronger motor or screw need to be lower lead..

I believe the initial friction what causing the slips.. that's a very high lead for Z in my opinion...

mightbe just swap to a ballscrew which one has almost no friction...

you have the possible best couplers, they never slip... I mean if diameters are match and bolts normally tightened..

================================================== ==================================

for me similar happened..
I had the impression everything is fine..

til I had a job came up where very much Z movement was involved,

not like a 3d cut, but many tiny pockets... and I noticed the pattern is deepening as machine going along with the part..

after I changed the motor stronger... it stopped..

very possible you had the slip before, but it was so minimal you didn't noticed..

when you just cut trough parts you never notice minor slips..

heres an ebay link

SFU1605 Ball Screw L250MM ballscrew with SFU1605 Single ballnut for CNC | eBay

for this money don't worth to playing around with leadscrew..
leadscrew not cheaper, not more precise..

and leadscrews always has more friction than ballscrews..

I see, yeah the bulk of my work is numerous tiny pockets in HDPE. So, I get what you're saying about the minor slips. I am going to see what kind of solution CNCRP comes up with before I start modifying everything too much. You said you swapped motors? Any more info...? I appreciate the help and suggestions.

[sharob27]

I had the exact same problem with my z-axis. Spoke with CNC router parts and determined a solution to my problem that sounds similar to yours.
My Z-axis would lose steps most of the time while homing or setting up a job and crash into my table or work piece. I lived with it for awhile as it was somewhat random.

I was using a Geckodrive G540 in my system. CNC router parts advised using a smoothstepper to eliminate this problem. It so far has worked perfectly for the last couple of months.

If I remember correctly CNC Router Parts advised the G540 basically can't process fast enough and loses steps.
You can contact them for help, they definitely knew how to fix my problem and my give you some guidance.

Thanks for the post...yes, this is VERY random. I have no clue its coming, and then the Z makes a weird noise, and bam. I've gotten pretty good at running back around the table to stop it...but, never quick enough to save the workpiece. So do you have the pre-wired Nema 23? I am just curious how the smoothstepper works with the pre-wired kit...or if I have to start modifying everything.

[pete1961]

Call CNC Router parts. Re-iterating, it sounds exactly like my problem.They will offer you a solution. My system is/was G540 Nema 23 although I used many of my own components.
The ethernet smoothstepper I have goes between the G540 and your computer.
Very simple retrofit, Ethernet from computer to smoothstepper, parallel cable from smoothstepper to the G540.

If you talk to them you can mention they helped me about 6 weeks ago. I'm from Illinois, they should remember. If not I can PM you.

[ahren]

Hi all,

Shaun has a system with digital drives (not the G540), and it's a standard system (not a PRO ballscrew like Pete's), so the issue is most likely with the Dumpster ACME nut.

This nut has an external 3/4-16 thread on it (in addition to the 1/2-10 5 start ACME thread inside). This allows the plastic piece to be threaded into the aluminum mount that comes with it and which connects to your high z plate. The nut is held from rotating inside of this aluminum mount by a cross-drilled set screw, as well as a jam nut which jams against the back of the aluminum housing.

It's possible these retaining features have come loose, which can cause the nut to thread in and out of the aluminum body and which will cause lots of strange motion. My suggestion would be:

1) Drive your z axis up and out of the nut so you can get to it.
2) Take the nut apart and examine to make sure the internal threads aren't too worn down. If they are, you might need to replace the nut.
3) Re-tighten both of these retaining features on the nut
4) Spray your screw with a dry teflon lubricant

One other thought -- if you are milling a lot of tiny pockets, make sure your bit is center-cutting, or else make sure you ramp into the cut. Numerous plunges with a bit that doesn't have the blade go all the way across will be tough on any z axis. This probably isn't the case since you have been up and running for a while, but just in case.

It's also possible that you are electronically losing steps, but this is unlikely with the digital drives unless you have recently made changes to your PC. In this case, the Smoothstepper might help, but my guess is that with the age of your machine there are just some mechanical issues that need to be corrected. Shaun, I know you contacted us directly as well -- we can't always respond over the weekend, but we do try to get back to people as quickly as possible.

Best regards,

Ahren
CNCRouterParts

[sharob27]

Thanks Ahren. I understand about the weekends, you guys need a break from work too! No worries. I appreciate all your help with this. I will be doing this tonight. In the mean time, I'll get with you and order what I might need, just in case. No changes to the PC have been made since the initial setup back in 2013...it's not even online!