[subnoize]

I was looking in the help files and one part of the tool path menu is missing; the Lead > Radius value

I assume the ramp angle is the angle at which the end mill travels as it cuts in the Z axis on a standard 3 axis mill. The Radius seems to control the swirly motion the end mill does when trying to cut in the Z axis when a ramp isn't practical. That said, the smaller the number the more swirlies it does which is confusing since the swirlies seem to get wider as it travels down.

Can somebody please explain these values?

The secondary question is I am losing steps in the z axis and I need to slow down the z axis. The Z axis feed rate on the tools doesn't seem to help much which is why I need to understand these Lead values and explore how they help cut in the z axis better so the steppers don't lose steps.

What would be some good example values in these fields for a small, week little mill like my X3 conversion? What is the process you would use in MadCAM if your mill is losing steps on the z axis?

Thanks!

[Gregore]

I am surprised you would be moving the mill fast enough to loose steps during a cut and not be breaking cutters, or are you missing steps during rapids?

My thoughts would be one of 2 things either your ways are too tight ( I assume an x3 is a way mill not a linear slide mill ) or your settings in your controller are allowing the rapids to go too fast. I would have this problem with my fourth axis every so often , we have a 80 /1 harmonic drive and it was too much for the stepper at rapid speeds.

One other thought is that if yOur z rates are slower than the x,y rates and they are not missing steps then maybe the z axis is too heavy for the stepper.

I am sure others will have more ideas to add also.

[subnoize]

I'm missing the steps in only the -Z and I can see where the milling starts off at the correct depth but somewhere else as it plunged again it didn't achieve the same depth. The two tool marks side by side are easy to see. Then I come up after going .5" through a .5" thick 6061-T6 bar and I still have 0.012 material left. That would be the amount of missing -Z steps right?

I'm not breaking end mills. A heavy Z axis would result in the "sinking head syndrome" as I lost steps in the +Z. The head would drive further into the negative as it lost positive steps and break the end mill. I know this as I have seen it but not because my head was too heavy but because the pulley was slipping on the shaft.

My gibs on the Z axis are as loose as you can get them.

As to losing steps in rapids I have digital gauges that I calibrate using before every cut. I also drive me CNC like I do my airplanes, if my max is 40 ipm on the Z axis I back it of to 70% to 28 ipm.

I guess what I'm running up against is "what speed my machine can cut in in the Z axis.?" X and Y I could probably double the speed to 20 ipm and it would be fine. I'm just learning what the Z axis speed is, that is all. These stupid speed and feed calculators I paid money for are all 100% wrong. I've had it out with one author of such an app. He claimed that I was using his calculator wrong so I got him on the phone and broke a $30 end mill using his direction. His response what I broke it on purpose, which I promptly fired him and his software.

Its funny when you ask other folk using X3 what their cutting speed is you find about 90% of them can't tell you when the last time they even turn the machine on. Its like they purchased it, converted it and sat there looking at it trying to figure out what to with it.

Anyways, thanks for the ideas Gregore!

[Gregore]

I had a similar problem when cutting flat surfaces . Some how the controller was set for a margin of error that was greater than the step up and down so as The cutter moved across the surface with a .5 mm step over I was getting a slowly ramping up surface where it was to be flat as per the model . I think this error took place when the cutter went up to the safe setting for the step over.

If you need a more accurate explanation of what was happening I can get my friend who fixed it for me to explain more.

[Mauri R]

Subnoize,
What is your current Velocity set for X/Y/Z/A.
What is your current Acceleration for X/Y/Z/A.
What is the size of the Stepper motors for X/Y/Z/A.
I have a converted X3 and have never lost steps on the Z and I do complex 3D jobs mainly in Brass.
You will lose steps if your acceleration is too high depending on the Z Stepper motor type and size.
To ensure we never lost steps we put in a counter weight on the Z to make sure it does not occur.
If you have a Nema 23 270oz on the Z Axis for example and with the counter weight it goes up and down with ease.
Quite a number of things can cause loss of steps Drivers/Steps/Acceleration/Motor Size/Type/GCode/Gibs too tight/Look ahead - being some.
Z loses steps mainly due to heavy 3D operations i.e. running multiple Axis at once and most of the times it will be the Z Axis that suffers.
Since I do not know any of your parameters I cannot give you any definitive answers.
Try lowering the Z Acceleration as a starter.
Regards,
Mauri

[subnoize]

Mauri,

Thanks for responding. My A axis is a Sherline PN 3700. Here is the information you request. I have no balance weight on the Z nor a gas piston. If you can help me find a "safe zone" type settings to make my learn a little easier I would be forever in you debt!


What is your current Velocity set for X/Y/Z/A:

X = 1.3333 in/S
Y = 1.3333 in/S
Z = 0.4 in/S
A = 85 D/S



What is your current Acceleration for X/Y/Z/A:

X = 60 in/S2
Y = 60 in/S2
Z = 60 in/S2
A = 120 d/S2



What is the size of the Stepper motors for X/Y/Z/A:

X = 400 Oz In. Hybrid (3 amp)
Y = 400 Oz In. Hybrid (3 amp)
Z = 1150 Oz In. Hybrid (8 amp)
A = 280 Oz In. Hybrid (3 amps)


Thanks,

John

[Mauri R]

Mauri,

Thanks for responding. My A axis is a Sherline PN 3700. Here is the information you request. I have no balance weight on the Z nor a gas piston. If you can help me find a "safe zone" type settings to make my learn a little easier I would be forever in you debt!


What is your current Velocity set for X/Y/Z/A:

X = 1.3333 in/S
Y = 1.3333 in/S
Z = 0.4 in/S
A = 85 D/S



What is your current Acceleration for X/Y/Z/A:

X = 60 in/S2
Y = 60 in/S2
Z = 60 in/S2
A = 120 d/S2



What is the size of the Stepper motors for X/Y/Z/A:

X = 400 Oz In. Hybrid (3 amp)
Y = 400 Oz In. Hybrid (3 amp)
Z = 1150 Oz In. Hybrid (8 amp)
A = 280 Oz In. Hybrid (3 amps)


Thanks,

John

John,
Your last message stated that you converted an X3 Mill?
If that is so then you have adequate sized stepper motors.
I have Nema 23 270Oz on all drives.
My system is in MM.
X and Y Axis
150 Acceleration
2000 Velocity
Z axis
110 Acceleration
1000 Velocity
A axis 80:1
150 Acceleration
2000 Velocity
I use 2 spindles one max 4000RPM and the other 24000RPM
On brass cutter down to 1/32 ball nose are good at F650 X/Y but keep the Z at 100 with say .2mm Tip 20/30 Degree drop it to X/Y F500 and F80 on Z.
The controller and Micro step drivers also play a part in your problem.
SO start with the acceleration problem first.
Based on you number above you equivalent Acceleration is as follows:-
1500 on XYZ and 3000 on your A axis.
Your Velocity compared to mine is:-
X/Y 2031.95 and Z 609.6 so there is not issue here.
Although you have larger stepper motors than I have on your X3, I still think that if you are loosing steps on the Z, you need to reduce the Acceleration.
Start at a lower level on the Z and work you way up until you loose steps then back off from there.
Your Gibbs should be tight enough so you do not get play (too tight and you will lose steps).
A quick test can be:-
G1Z0 F1000
G1Z10.01
G1Z0
G1Z10.01
G1Z0
G1Z10.01
Etc. So it goes for a while and see if it gives the same Zero result when it stops.
Also
G1Z0F1000
G1Z.001
G1Z0
G1Z.001
Etc. See if goes up and down without loosing steps.
You can change the settings less or more on Z until you get a sweet spot based on you new acceleration value.


We never has issue on our Router Table until we started 3D carving.
With 3D carvings we had the same issues on our Router Table when doing high definition 3D work, our solution was to get specially wound stepper motors (As changing the system to servo motors would cost too much) that did not loose torque at higher speeds and with the inclusion of a smooth stepper and better micro stepper drivers, we never loose steps on Z.

So some Stepper Motors are not made for precision CNC mill work and even though they may be powerful on very low speed can lose it all at higher levels and hence affect the torque to more the machine parts.
Many stepper motors on the market are for agricultural work only, like moving conveyers.
Hope this helps,
Mauri.

[subnoize]

Your last message stated that you converted an X3 Mill?

Yes, my mill is a Grizzly imported X3 with a 4th Axis from Sherline PN 3700.

Your values are way higher than mine! I assume you use a different motor and gear system to drive your spindle as the fastest mine will ever go is 2000 rpm which makes a huge, huge difference.

Last night I backed off the acceleration and didn't see a difference. I don't know if I'm dealing with a dull end mill maybe? I will change that out today. There are so many variables that I see this will take a while. When I do calibration tests where the mill in not under load I see no lost steps. It is for all intent, perfect in that regard. I have a few more variables to use before I pay somebody to take a look.

So, do the Lead variables help or am I making more problems by messing with them?


jb

[subnoize]

Holy Crap!

So the steps only get lost when the machine is hot. About an hour into the cut. The steps only are lost in three places, plunges where the mill does its swirlies BUT!!!! not during the plunge. The plunge gets the correct depth. As the mill moves out of the swirlie motion on a straight path I can see it losing steps along the way.

That made me think so I turned off the power save mode on the driver where once it obtains a position it reduces the power to hold it. Didn't help. I backed off the microstepping from 8 to 2, didn't help. I even went more extreme than Mauri's settings, like way extreme, like very slow. Didn't help.

And as my last cut was wrapping up I suddenly realized that my end mill looked awfully short!

I guess that WD-40 and oil had gotten in my collet and the stupid end mill was slowly slipping upwards!

Grrr! Well, with as many parameters, and buttons and systems with sub-systems as this thing has, sometimes you should just eliminate the hardware first, then look at the software and lastly the electronics.

Lessons learned!

I guess I had better go give some chocolates and flowers to my mom before she thinks I fell of the planet....

Thanks for everyone's input!

jb