H5 Problem with screwcutting pitch

[Clive66]

When cutting an imperial 14 tpi thread in auto mode I am getting nearer to 16 tpi actually cut.
I get the correct angular reading with 10 revolutions of the chuck and when moving the carriage 10mm I get a reading very close (for example 9.89mm). This could be my Chinese digital dial gauge.
I have recently uploaded the latest firnware but not sure if this is the problem as I have not attempted screw cutting before.
Help would be much appreciated, thanks in advance.

[kachurovskiy]

There's a problem somewhere and we need to isolate it.

1. Try moving left by 1 or 2mm several times with a LEFT button and see with a dial how consistently you're hitting the exact target once backlash is taken out
2. Try setting the pitch to 2mm and make exactly 1 turn of the spindle, see how far the tool moves over several consequent iterations

[Clive66]

Cutting improved by moving the tool further to the right before setting RH stop (ie backlash). I also had the spindle speed set too high and reduced to 125 rpm. When upgrading the firmware I entered the wrong value for the X axis leadscew pitch 2mm (should be 1mm) hence incorrect depth of cut.
I am now getting the correct pitch although the thread ( in aluminium ) could be cleaner.
With the pitch set at 2mm one turn of the z axis leadscrew moves the carriage 1.998 mm
Three turns = 5.979 mm
Is this error within acceptables limits?
Thanks for your reply.

[kachurovskiy]

Yes, that's within the error range of the local wear of the lead screw it seems.

To improve thread quality it helps to understand where the vibration is coming from. I would measure deflection on the tool end and deflection of the part under up-back force and see which is greater.

Sometimes the carbide cutter is lightly chipped and produces imperfections too.

[Clive66]

Problem solved. I also found slight end play on the Z axis leadscrew which was not helping.
Thanks again for the support!