Z cutting deeper the more time goes by ???

[Mr.Chips]

Vectric VcarvePro 8.5.

I started a V bit text cutting file and after 1.5 hrs it was cutting very deep. I shut it down and told it to go to Z zero (surface of material) but it went 0.080” below the surface.

I lifted up on the router and a didn’t see and play between the delrin nut and the acme thread.

Can you offer some troubleshooting tips.

Thanks

HH

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[rcheli]

Not familiar with that machine but check for pulleys or shaft couplers that may able to slip on the shaft. If mechanically OK, Then I would suspect the Z axis is missing steps. Try slowing the acceleration rate.

[Mr.Chips]

Not familiar with that machine but check for pulleys or shaft couplers that may able to slip on the shaft. If mechanically OK, Then I would suspect the Z axis is missing steps. Try slowing the acceleration rate.

Thanks,
Using Mach3 and Vectric VcarvePro 8.5 have ran this homemade CNC as a hobby machine for 10 years and this is the first time I have had this happen.
I checked the Z stepper connection to flex coupling and flex coupling to Acme shaft, and the acme shaft to the bearing that holds the acme shaft and all were secure.

Set up a dial indicator on the Z axis and did the following. I ran it hundreds of times and Z always returned to Zero.

Any suggestions for troubleshooting?
thanks
HH

F15
X0
Y0
Z0
Z0.5
F70
X0.5
Y0.5
X0
Y0
Z0
F15
Z-0.1
Z0
Z-0.1
Z0

[rcheli]

I would guess that you lost steps on a rapid Z move in the plus direction (up). If it was commanded to go up 1000 steps but only moved 990 and then it was commanded to go back to zero it would end up 10 step too low.

Try something similar to what you did with the G-Code except us a rapid move (G0) in the plus Z direction rather than a feed move and see what happens.

Start with the bit an inch or so above the bed.

G91 Incremental distance mode
G0 Z1 rapid up one inch.
F15 Z-1 Feed back down 1"


Repeat the last two lines a bunch of times

Then G91 set to absolute mode
Then go back to Z0 see where it ends up.

.

[Mr.Chips]

I would guess that you lost steps on a rapid Z move in the plus direction (up). If it was commanded to go up 1000 steps but only moved 990 and then it was commanded to go back to zero it would end up 10 step too low.

Try something similar to what you did with the G-Code except us a rapid move (G0) in the plus Z direction rather than a feed move and see what happens.

Start with the bit an inch or so above the bed.

G91 Incremental distance mode
G0 Z1 rapid up one inch.
F15 Z-1 Feed back down 1"


Repeat the last two lines a bunch of times

Then G91 set to absolute mode
Then go back to Z0 see where it ends up.

.

The Z moves were set to 15, where/how did RApids get in? Are rapids set automatically, where can I find the rapid settings in VcarvePro or MACH3?
Thanks for your comments
HH

[lsces]

The Z moves were set to 15, where/how did Rapids get in? Are rapids set automatically, where can I find the rapid settings in VcarvePro or MACH3?

Rapids and acceleration are set in Mach3 ...
Settings -> Motor Tuning -> select Z axis

Being 10 years old, the motor magnets may be getting a bit weaker, and the z axis may be a bit tight somewhere so lifting is just on the edge. SO try just halving the speed and acceleration values ... and on this screen you have to remember to hit save as well

[ger21]

Check the Z axis for binding. Maybe it just needs cleaning and/or lubrication?

[routalot]

Have you ever changed the acme thread on the Z axis? After ten years of use it must have worn a bit and you would need to check for wear at the height of travel where the loads have been highest.

[Mr.Chips]

Rapids and acceleration are set in Mach3 ...
Settings -> Motor Tuning -> select Z axis

Being 10 years old, the motor magnets may be getting a bit weaker, and the z axis may be a bit tight somewhere so lifting is just on the edge. SO try just halving the speed and acceleration values ... and on this screen you have to remember to hit save as well

Thanks
Didn’t see a “rapids” figure on that screen, maybe it’s called something else there?
Motor tuning is a mystery to me I just came up with these settings and didn’t change them for years, maybe they are not what they should
be.
Here are my motor tuning settings, IN PER MIN
VELOCITY .................70.02
ACCELERATION....... 5
G’s ..............................0.0129509
STEP PULSE .............5
DIR .............................5

Thanks
HH

[Mr.Chips]

Check the Z axis for binding. Maybe it just needs cleaning and/or lubrication?

Gerry,
here are some photos of the Z axis so you know what i'm working with. guess i cant add photos here so i'll post at the end of this thread.
thanks

[Mr.Chips]

Here are the photos of the Z axis. this should help in knowing what i'm working with.
Thanks
HH

[Mr.Chips]

Here are the photos of the Z axis. this should help in knowing what i'm working with.
Thanks
HH

The far right photo shows two button head cap screws in the front , They secure the router assembly to the acme thread/nut. I'll support the Z axis and remove the two screws, this will disconnect the Z assembly from the Acme shaft/drive nut. then drive the Z nut to the topmost position then I can move the Z assembly up and down by hand, looking for binding and such.
We have out of town visitors today so it might be put off till tomorrow.
Thank you all for your comments and assistance.

I have extra acme thread, just would have to turn it down to fit the flex coupling, would have to order a ner 1/2' delrin nut, ill plan this for the near future. Probably replace the delrin nut on the X axis at that time. The two Y axis control shafts are 3/4' ball screws. Yes after ten years i need to check out everything, but it has worked super despite my inadiqate knowledge.

[Mr.Chips]

For your information, here's the right side of the 3/4' ball screw Y axis drive.

[Mr.Chips]

Had some free time and disconnected the Z axis assembly (two button head cap screws) from the acme screw and removed the router. The Z assembly moves up and down the two linear rails using four trucks connecting the assembly to the rails. The assembly moved up and down the rails by hand effortlessly, without and binding or tight spots, it is perfect.

I ran the disconnected nut assembly to the top, middle, and bottom if its travel There wasn't any vertical looseness or free play at any position.

I am satisfied that there is not an issue with any part of the mechanical parts of the Z axis.

So where to now?

I would like to eliminate the TXT file its self. Here is how the TXT file was generated and settings:
The TXT file started out as printed pages in this case Chinese text, (my wife is Chinese, and this was to be a MDF poster for their up coming womens fellowship) I scanned the pages and saved them as .JPG files. I opened a new file in VcarvePro 8.5 (16x20") and imported the files and converted them to vectors. i then used the "curve fit to vectors" utility to smooth out the lines, i was told this enables the cutter to travel more smoothly. I used 60 degree V bit utility, with settings of: Pas depth 0.050", Feedrate 35 IPM and plunge rate of 5.0 IPM. I recall the run time was 2 hr 45 min. Roughly 2 hours into the cut the Z started cutting deeper, I then stopped the run and checked the Z Zero point and it was 0.080" lower than the surface of the material, when the file started the Zero point was set to the surface of the material.

In years past I have ran 16x20" MDF cut posters like this without an incident.

I can attach the file if you would like to look at it and possibly see if possibly there might be code in there that would have caused the problem

With this information so far does anyone have any suggestions?

Thank You all for your kind suggestions.

[GME]

I'm a late comer to the party. I had exactly the same thing happen to me. It turned out to be a slipping flex connection to the screw. I first thought it was a problem with my cut file, but it happened with different files. Rule that out. So, I started looking at the mechanical. I messed with just about everything. It all looked and felt good. I was sure everything was tight, but nothing, other than a loose connection, explained what was going on. A slipping connection to the lead screw made the most sense. I recalled that a couple of years earlier, I tried a product called Vibra-tite as a thread locker vs.the tried and true Locktite. I removed the two cap head fixing screws, cleaned out the gunky Vibra-tite from screws and connector, used blue Locktite and reinstalled the screws. I tightened the screws down so tight I ended up camming out the head on one of the screws. I know it was slippage, because tightening down the screws solved the problem.

I zero through cuts to the spoilboard and never cut into the spoilboard. One day, I noticed a very shallow cut into the spoilboard, but since I was only a couple of thousands, I didn't think too much about it. Sometimes it would make a light cut into the board, sometimes not. Then, one day I was cutting some wood brackets for my dust collection system and the bit dove deep and caused a mess. I thought it was the cut file, so created a new one and ran it. Same problem, different area on the part. That led me on my quest to track down and fix the problem.

Gary

[Mr.Chips]

I'm a late comer to the party. I had exactly the same thing happen to me. It turned out to be a slipping flex connection to the screw. I first thought it was a problem with my cut file, but it happened with different files. Rule that out. So, I started looking at the mechanical. I messed with just about everything. It all looked and felt good. I was sure everything was tight, but nothing, other than a loose connection, explained what was going on. A slipping connection to the lead screw made the most sense. I recalled that a couple of years earlier, I tried a product called Vibra-tite as a thread locker vs.the tried and true Locktite. I removed the two cap head fixing screws, cleaned out the gunky Vibra-tite from screws and connector, used blue Locktite and reinstalled the screws. I tightened the screws down so tight I ended up camming out the head on one of the screws. I know it was slippage, because tightening down the screws solved the problem.

I zero through cuts to the spoilboard and never cut into the spoilboard. One day, I noticed a very shallow cut into the spoilboard, but since I was only a couple of thousands, I didn't think too much about it. Sometimes it would make a light cut into the board, sometimes not. Then, one day I was cutting some wood brackets for my dust collection system and the bit dove deep and caused a mess. I thought it was the cut file, so created a new one and ran it. Same problem, different area on the part. That led me on my quest to track down and fix the problem.

Gary

Thanks for the suggestion Gary but I checked the vertical play of the acme screw when the Z assembly was disconnected from the screw and no vertical play, plus check the second picture I have a bearing below the flex coupling to prevent any vertical movement and both of its locking set screws were tight.
The mystery continues.
I’m gonna run the file again in the morning and see what happens. Thinking of rigging up a dial indicator set at the deepest cut so I can know when it happens if it goes deeper than expected.

[GME]

Thanks for the suggestion Gary but I checked the vertical play of the acme screw when the Z assembly was disconnected from the screw and no vertical play, plus check the second picture I have a bearing below the flex coupling to prevent any vertical movement and both of its locking set screws were tight.
The mystery continues.
I’m gonna run the file again in the morning and see what happens. Thinking of rigging up a dial indicator set at the deepest cut so I can know when it happens if it goes deeper than expected.

My issue had nothing to do with vertical play. I believe my problem had to do with what happened when the Z axis went positive. The coupling was slipping in the positive direction, because the weight of the moving parts require more effort to go up than down. You've probably observed this when turning the acme screw with the stepper removed. Easy to screw it down, but much more effort required to turn it in the up direction. Anyway, because the coupling was slipping, it meant that Z wasn't going up as high as the program commanded. Then, when Z was commanded to go negative, it was already too low, so the bit cut too deep. I don't believe your bearing would prevent the same thing from happening to you. If the coupling slips, it just means the router won't go as high as it should. The weight of the router and related parts translates into less effort required to go negative, so coupling slippage has less, if any, influence on how far negative the router travels.

If your coupling set screws are truly tight enough, I have no other suggestions to offer. I would note that when I was checking things, the coupling was not so loose that I could hold the coupling in one hand and turn the screw with the other. It seemed tight, but clearly wasn't tight enough.

I wish you the best of luck.

Gary

[Mr.Chips]

Thanks Gary
Your reasoning is very sound, after the run I checked, all the Z axis stepper, Coupling, the large bearing and router bit, didn’t find anything loose. I’m going to run the file again this morning and see what happens.
I’ll post results.

[rcheli]

My issue had nothing to do with vertical play. I believe my problem had to do with what happened when the Z axis went positive. The coupling was slipping in the positive direction, because the weight of the moving parts require more effort to go up than down. You've probably observed this when turning the acme screw with the stepper removed. Easy to screw it down, but much more effort required to turn it in the up direction. Anyway, because the coupling was slipping, it meant that Z wasn't going up as high as the program commanded. Then, when Z was commanded to go negative, it was already too low, so the bit cut too deep. I don't believe your bearing would prevent the same thing from happening to you. If the coupling slips, it just means the router won't go as high as it should. The weight of the router and related parts translates into less effort required to go negative, so coupling slippage has less, if any, influence on how far negative the router travels.

If your coupling set screws are truly tight enough, I have no other suggestions to offer. I would note that when I was checking things, the coupling was not so loose that I could hold the coupling in one hand and turn the screw with the other. It seemed tight, but clearly wasn't tight enough.

I wish you the best of luck.

Gary

I believe the issue is what GME said or you are losing steps. In either case there is lost motion in the up direction. If the set screw push directly on the shaft I would put flat spots on the shafts. Then clean the set screw and hole threads with acetone or some other degreaser then use blue Locktite on them. Once it slips or loses steps the machine does accurately know when the bit is in the Z axis.

[Mr.Chips]

Thank you for your suggestions, I ran the file again and the Z zero point from I originally zeroed at the surface only increased 0.010” in depth.

What I did between the first run and the second run:
1. Tightened all the Z axis related set screws, more than I would normally hand tighten, just enough to hear one tick of the S Screw. None of them were moved more than that single tick, none found loose.

2. Changed the pass depth from 0.050” to 0.100”. Cutting MDF with a 60 degree V bit

Don’t think the increase in pass depth had and depth effect, just ran the file about 35 minutes faster.

Summary:
At this time I’m thinking it was related to the set screws.
The lathe turned end of the acme rod does have flats as well as the stepper motor.
However the big flange bearing under the alignment coupler tightens down on the acme rod, no flat spots. I think I should turn the section down and make some flat spots for those set screws to secure to.

Again thank you all for your input and keep me focused.

HH