Calibration issues.

[Hatchet Job]

I'm trying to dial in my CNC after changing over to UCCNC.
I'm using the calibration feature in the software and I just can't get the X axis correct.
I've set up a scale on a batten attached to the machine and accurately marked 1200mm on it.
I've performed the calibration multiple times and all seems good.
When I then set the Machine to cut a 120mm square the X axis cut is approx 0.5mm under.
I've checked my drawing and tool settings and all seems good,
Am I missing something??
The only odd thing I've noticed is after moving the X axis 1200mm with the Calibration tool the DRO reads 1200.0034.

[ger21]

My first thought would be deflection somewhere. Try cutting the same part in the opposite direction. What type of machine is this?

[Hatchet Job]

My first thought would be deflection somewhere. Try cutting the same part in the opposite direction. What type of machine is this?

It's a homemade machine, 8x4 bed with a good solid construction so I don't know if it's deflection.
I've set up a story stick across the X axis with 300mm increments marked on it and jogged between them with calibration tool at 300mm/min.
All seems to be spot on but when I cut a 120mm square it's still 0.5mm under on the X axis cut.

[Dazp1976]

Backlash?.
Tool size tiny bit bigger than advertised?.
Spindle runout?.
Tool deflection?.
Machine deflection?.

If it's permanently the same 0.5mm on the machine then you could customise your drawings for that particular MC and make them 0.25mm larger at either end of x axis until you figure it out.

[Pulcik]

I was experiencing something similar once. Calibrated everything as good as I can. Even with magnifying glass . When I cut square in PLY, I was constantly getting 0.2mm less in X direction. Y direction was spot on. I was furious, as I can not nailed it. On measuring tape, the distance was correct. Backlash was compensated right. Code was flawless. But no matter what I was doing to find the cause of that inaccuracy, the X axis was 0.2 mm off.
I was without any clue. It was weird. Then I grab some artificial wood, which is more like plastic, and mill the square again. In was spot on. So I learned that plywood is still quite compressible wood. So, don't use wood for calibration.

[ger21]

It's a homemade machine, 8x4 bed with a good solid construction so I don't know if it's deflection.

Our brand new $180,000 router at work has deflection. Yours does too.

[Hatchet Job]

It's a homemade machine, 8x4 bed with a good solid construction so I don't know if it's deflection.

Our brand new $180,000 router at work has deflection. Yours does too.[/quote

Ah yeah ok I seem what you mean.
It's a 1/2" shank 8mm triple tip cutter, cutting at 5000mm/min so very under stressed.
I can't see it deflecting that much.

[MikeM]

What type of drive is on the X-axis?
If belt driven there could be some stretch in the belt under load.

[Hatchet Job]

What type of drive is on the X-axis?
If belt driven there could be some stretch in the belt under load.

Ahh thanks but it's all rack and pinion and I've backlash compensation all setup.

[Hatchet Job]

Update...

I setup a digital vernier clamped to the machine and performed multiple calibration tests moving 140mm and it's absolutely spot on.
I then did a long 1100mm text cut on the X axis in MDF and it's approx 1.5mm too short.
All I can think of now is it's some kind discrepancy from the material and cutter but 1.5mm seems a lot.