MIRAC lathe - 2 – axis tool path movement incorrect

[MEA]

Dear all,
I bought a few weeks ago an old MIRAC lathe. The original PC was broken and the software dongle missing. With a new PC and the MIRAC-Software downloaded from the Denfort Support the lathe was running fine till I made a simple piece where a 2 – axis tool path movement was used.
Depending on the feed rate, I saw an incorrect tool path but the end position was correct!
I did some more tests with the following results:
…
G00 X50 Z-5
G01 Z-0.2
G01 X1 Z0
…
Up to a feed rate of 120 mm/min the tool path is correct. With 130 mm/min the z-axis is not stepping correctly during the x motion. In the example above, there is no z motion until near the end of the x steps. The full z motion is made only during the few last x steps. Depending on the feed range (10-120 and 130-1200) there are two modes for calculating the motion (described in the LCB3 controller manual).
Is a feed of 120 mm/min a known limitation for 2 - axis moving? Is this behavior a bug in the firmware of the controller or the MIRAC Software? Do I make/understand something completely wrong?

Thanks for help.
Daniel

Details of my MIRAC:
Serial No.: EO 3951
Despatch date: Sept. 1991
Export No.: 3951

Controller: LCB3 (Build Level 4)
S/N: 39269

IC U5:
EPROM No 929
PC 03095 LCB3
SKT U5 REV 1.1

IC U4:
SYN-017

[Mr Magoo]

I have seen these sorts of symptoms before.

The old Mirac machine with LCB3 controller did not like interpolating moves that are near-tangental to the X or Z axis.
Your example of X axis moves 25mm (radius) and Z moves 0.2mm is a classic case of this.

Unfortunatly I do not think there is a solution - yes it is a bug in the firmware but the LCB3 controller manufacturer is no longer in business

Try different feedrates, or changing the program slightly may fix the problem (say X moves 25 and Z moves 0.25) but of course this does not produce the profile you want

Moves that are not near-tangental to the X or Z axis should not be afffected

[MEA]

Mr. Magoo,
Thank you for the information. You are right, there is a feed dependency. The above example was helpful for finding the base of the problem.