Measuring and predicting accuracy

# Thread: Measuring and predicting accuracy

1. ## Measuring and predicting accuracy

Hi guys, I have a chinese 6040Z, 2.2kW, I want to measure and predict it's accuracy : for now I found how to measure backlash and linear motion precision and repeat precision. Both under no load. However I presume that when running on a workpiece the machine is much more heavily loaded and the aformentioned results are not extremely useful. If the linear guides bend because of forces on the spindle, the precision on the resultant workpiece will be lower.
Is there a way I can predict the accuracy on the workpiece? the best way I can think of is to measure the deflection of the endmill with a dial when applying a force to it with a dynamometer, at varied forces. Then, before a job, when possible I'd try to predict (with help from software, with endmill geometry, feed, rpm etc as input) the force exerted on the endmill. By using the former results I might be able to predict the deflection I'll be facing with.
Any better way?

2. ## Re: Measuring and predicting accuracy

I think the reason no one answered is that there are so many different factors that could affect accuracy. 6040Z is more like a concept than a spec--a lot depends on how it was put together--though my guess would be that twist between the z-axis and the x-axis is going to be a major source of its error, depending on what you are cutting. As a first pass, one way to resolve that Gordian knot would be to run some benchmarks. Measuring the results would quickly get you some answers about the strengths and weaknesses of your particular machine--al beit on those particular benchmarks--and thereby narrow down the focus as to what things to focus on. So, I propose that as the "better way."

3. ## Re: Measuring and predicting accuracy

hello ricc, white and old thread, but i'll give it a go

for now I found how to measure backlash and linear motion precision and repeat precision
such measurement should vary with axis position among entire travel; deviations should be lower with pretensioned screws, but they still exist

calibration procedure involves a medium value, between rapid and feed, thus there is not a fix4all-value

Both under no load. However I presume that when running on a workpiece the machine is much more heavily loaded and the aformentioned results are not extremely useful. If the linear guides bend because of forces on the spindle
look, for example an okuma machine is rigid in such a way, that when the overtorque is triggered in feed mode, still nothing bent inside the machine; at full rapid, it's non rigid articulations may break or slip, thus avoding costly damage

as for your chinese 6040z, i think you will find it's limit in time, by machining different stuff / kindly

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