Okuma LNC8C Lathe - Better Understanding of System/User Parameters

[nathanokkema]

NOTE: Anything I claim to understand in this post could absolutely be incorrect, please bare with me!

I've been hired to set up an Okuma Cadet Lathe and I'm simply trying to achieve max travel on the Z Axis before I move forward but I'm having trouble. I understand the general concept of how these machines work and have limited experience with programming. We seem to have gotten enough travel out of the X Axis but the Z Axis is proving to be more difficult.

Now, I understand that System Parameters (+/- Stroke End Limits) are the outer limits before hitting hard limit switches, but when we move on to setting User Parameters I'm having difficulty with "what's what".

My question is this: What is the difference between "+/- Variable Limit (Prog)" and "+/- Variable Limit (Mach)"? And how do they relate to the System Parameters?

Also, side question: Seeing as these machines use pulse motors, how do the values in the "Actual Position" screen translate to Imperial Units?

Photos attached.

Thanks in advance!

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[Algirdas]

1. Here is Okuma dedicated chat. Sure, it's better to ask there.
2. Can You please be more specific what is the problem with Z axis limits?
3. If I recall correctly, if You command on the soft limits "ADD 0" <return> you will get the selected soft limit = system limit.
4. The difference:
Machine limits = expressed in encoder units directly, you see there some crazy numbers like over 15m written in microns.
System limits = deending where the system "0" ( = origin ) is set these figures gives understanding where is what. These limits are adjusted to hardware limit switches, means absolutelly inaccessible for user.
User limits also controled by variables are limits adjusted to specific work set.
Protection limits ( collission avoidance, also controled by variables ) are set specifically for the work setup and prevent collission.
If he tool offsets are described correctly, the collission avoidance prevents tool - chuck, tool - other turret, tool - steady rest, tool - tailstock collissions.

And the last one. What do you mean saying "pulse motors"?
And what relation can be between motor design ( or any other harware piece ) and use of imperial / metric system?
This is a calculation inside CPU only and nothing else.
By the way, Okuma does really good transition between the measurement systems. You can use both on every segment of shape.

[broby]

Now, I understand that System Parameters (+/- Stroke End Limits) are the outer limits before hitting hard limit switches, but when we move on to setting User Parameters I'm having difficulty with "what's what".

My question is this: What is the difference between "+/- Variable Limit (Prog)" and "+/- Variable Limit (Mach)"? And how do they relate to the System Parameters?

Hello,
The difference between Stroke End Limit and the Variable Limit is that, as you say, the Stroke End Limit is the LIMIT before hitting the stroke END Limit switches.
Where as the Variable Limits are programmable and used to set Operating Limits on where the machine can move to.
ie. if you where using the tailstock, you could program/set the Z+ variable limit to allow the turrent to move to a Z position where the tools will not hit the tailstock when moving at rapid to the tool change postion.
Also, if you have the Tailstock is fully parked and you are doing chuck work, you can set the +Z Limit to prevent the machine from moving further than necessary. This would save you valuable cycle time if doing mass production.
Same can be said for setting Z- limits and setting it so that you avoid hitting chuck jaws.
The difference between Prog and Mach limits is that the Mach numbers are litterally the limit position as per Machine as expressed in system position. i.e. a Large number!
Prog limits are directly related to Zero Set data, you will see this value update when changing the Zero Set value, but the Mach value will remain constant (from memory).
I remember how I would set the "Mach" limit to the same value everytime I wanted to get to the max Z+ limit, that way I didn't have to worry where the Z Zeroset was positioned.
The Mach value was always the same value, unless an encoder change had occured!
Hope this helps.
Cheers
Brian.

[nathanokkema]

So for clarity, the X-Axis travel is good enough for what we want (Actual Positions 957.4265 to 945.4265). But the Z-Axis has only 7.5" worth of travel (Actual Positions 7.42 to -0.08) and it does not reach the chuck face. In fact, at Z-0.08 the tool is still roughly 5.5" away from the face of the chuck.

I hate to do this, but does anything here look out of place?

These are the numbers I have:

USER PARAMETERS
+Variable Limit (PROG) " X957.4265 Z7.4200 "
-Variable Limit (PROG) " X945.4265 Z-0.0800 "
+Variable Limit (MACH) " X964.0000 Z17.5000 "
-Variable Limit (MACH) " X952.0000 Z10.0000 "


SYSTEM PARAMETERS
+Stroke End Limit " X964.0000 Z17.6806 "
-Stroke End Limit " X945.4265 Z3.7616 "
Backlash " X0.0004 Z0.0004 "
PR Zero Offset " X419.9496 Z276.2227 "
+ Stroke Comp. " X-0.0011 Z-0.0009 "
- Stroke Comp. " X0.0000 Z0.0000 "


ZERO POINT
Zero Offset " X6.5735 Z10.0800
Zero Shift " X0.0000 Z0.0000 "

Thanks all in advance!

[Algirdas]

did you try to add zero to limit value in parameters screen?

[broby]

Seems like your machine is doing exactly what you have set it to do.
Move Z between Z-0.0800" to Z7.4800" as these are your SOFT Limits!
Try ADDing a small amount to either of your Z limits and see if that changes your physical motion.
If you are approx 5.5" away from your chuck face, and you are at Z-0.0800" this tells me you have a Z zero point close by.
The VARIABLE limits are yours to play with, Only worry about the PROG limits, the MACH limit values will change by themselves.
Unless you know what you are doing, DO NOT CHANGE the System Parameter +- Limits, these are set to protect from hitting the physical end of the mechanical screws.
If you set the MACH limits on Z to match the System Parameters, this will give you the MAXIMUM movement along Z that your machine can move.
When you move your machine to a position where you don't want to go beyond, either Positive or Negative, then Calculate the new Limit positions there.
From memory, with the machine at the limit position, move the cursor highlight block to the desired limit and press CALC <WRITE>
this should then update the value to match your Z Posn.
if you update your ZEROSET value, the Limit value will change but NOT the actual physical Z point where the machine will stop.
While you are learning, take photos of the values on screen, (So you can go back to the same values) change by small amounts and see what you can then do.
As you obviously don't have someone there to show you, trial and error is your only way to go (along with, hopefully, helpful advice here).
Cheers
Brian.

[Algirdas]

I would like to add a little bit regarding Okuma's "calculation" conception.Let's say the part drawing contains Zerro as marked in the picture. The front face of blank workpiece is 8,5mm ahead. Then, step by step:
1. MDI take the tool with it's offset number lets say T0505,<wrtie>
2. Tool is selectd and at work position after action of the turret. Make sure the rapid positioning speed override control knob is at lowest position
3. Command go to "nowhere" G91G00X0Z0 <enter> this should make no move or move by the distance of tool offset.
4. You should see the distance remaining if the movement to be applied.Turn a little bit the override knob to allow the tool to move if needed.
5. Distance remaining =0, tool selected T05,
6. Start spindle M3S50 <write>. With door open it's the top limit of spindle revolution
7. MDI manual mode on. You will not loose the tool offset and you can move the tool manually with arrows and knob
8. Move the tool tip to touch the face of the blank gently. Make sure you still have T05 active ( with offset)
9. Go to parameters, select the "program zero" and pres CALC 8.5<write>
Now you have the program ( part) zzero set according to the drawing. The same you can set Z offsets of other tools. The CALC 8.5 command on the tool Z offset selected when the tool is touching the shape.
Touching the side shape with known diameter you can set the X offset for every tool. CALC 50 <write> when touching the side shape of round bar with the tool.
It is easier to do than tell.

[broby]

A different point of view on Aldirgas's instructions would be this:
Using your "Z" Zeroset tool (on Z this tool has a Zero (0) Offset)
Rather than using MDI to move your tool into position on the end face of the blank.
Manually index the tool into cutting position and then move to the end face.
On your Zeroset page Calculate the Z position as required.
I have always had my tools on X set with Drills set with a Zero offset, i.e. dial in a blank in the ID Tool Holder and Zero Set X to 0
All tools are then Calculated for their tool offset to achieve target sizing.