Hi everyone.

I converted a manual mill to CNC and installed ballscrews, steppers and also encoders, so I can keep the 'manual mode' where the encoders tell Mach3 how far I manually move the table.

My encoders have 1000 ppr and the ballscrews have a 5mm pitch, so the counts per unit should be 800. This is my current setup.

Now, after some testing I discovered the following:

I marked the 400mm on the table and double checked this with movements with the steppers.

To make sure I'm not dealing with any noise coming from the steppers or the drivers, I turned them all off and moved the table manually.
I move the table 400mm and the encoder says I moved 404.125mm (not sure if the decimal portion of the 404.125 is ok, but for sure it was a little over 4mm more than expected).
This means I have over 10% of error, way too high.

Why could this be happening?

Thanks in advance to everyone.

Ballscrews definitely 5mm pitch and not 0.2inch pitch?
Hood

Yes, ballscrews are 5mm pitch.
Automatic movements (with the steppers) seem to be moving the desired distance. At least in this test of 400mm I checked and it's definitely closer to 400 than the 404 the encoders give (measured manually with a tape).

What kernel do you have Mach set to? Encoder input is not that great via the Parallel Port but still should be more accurate than that.
Hood

I 'm using the default 25 kHz.
I just tried with 35 kHz and 45 kHz with no changes. I still get little over 4mms in a table 400mm movement.

25KHz would be the one that would give best results so its not that.
Was thinking maybe encoders were 1024 but that would give you 9.6mm over reading I think so not sure where the issue is.
Hood

Encoders are 1000ppr.

The error is always close to 1% of table displacement, not a constant value.

So if you MDI a move do the encoders show the difference?
Hood

That's right.
I tested it both with MDI movements and manual and in both cases I get the error.
When doing MDI movements, I start with same position indication in DROs and encoders position, after the move both values do not match.

Are you putting the encoder signals in via a breakout board?

Hood