Better finish

[luke11cnc]

I have a little bit of a enigma and the answer is eluding so I'm asking for advice on this problem.




I don't know what is causing the ribbing on the final pass on recess carving I have change speed from 480 mm/min up to 900 mm/min and with different step-overs and different spindle speeds, I've even tried different material and ballnose cutters but still the problem remains.I've also been using a extractor and a air line to keep the cutting path clear.But I think looking at the the ribbing it would seem that the z-axis is dropping, Is this a software problem.James

[blackburn mark]

thats got to be some kind of software bug ?

have you looked at the g-code to see if your machine is being told to drop (if your using trail software it may be designed to drop that mark in untill you buy the full copy ?)

if its not in the code it may also be worth looking at machs compensation fuctions (maybe you have inadvertently added some kind of compensation )

[Jonathan]

Are there several lines on each part, or one line on each? If it's the former then it sounds like the Z-axis loosing position. Perhaps try running the next part with the acceleration and maximum speed settings much lower on Z. If that solves it you can gradually increase the settings.

[luke11cnc]

Yes Jonathan there is several line on each part.
so if I slow the feed rate down and plunge rate down even farther it may give me a better finish.

how low should I go, can you give me a starting point please

I did once run it so slow that my y-axis stalled and the cutter started cutting at the wrong depth and direction (a big cut line running through my work)
I will upload a image of this later if you wish

my step over is set at 5%to 8%


James

[Musht]

Are the lines always lower, which would indicate Z dropping either mechanically by loosing a step or loose screw etc or by software erroneous z-axis drop or by glitch in command, interference on lines, to stepper driver?

Do the lines appear in roughing cut or just finishing pass?

[luke11cnc]

The line appear as a grove (lower) and I've never seen them in the roughing pass always in the finial pas

James

[Jonathan]

Yes Jonathan there is several line on each part.
so if I slow the feed rate down and plunge rate down even farther it may give me a better finish.

how low should I go, can you give me a starting point please

This does sound increasingly like the Z-axis is loosing position. Are you sure pulleys or something else on the Z-axis has not worked loose?
Although changing the plunge rate could solve the problem it's not advisable as the Z-axis is still capable of stalling. If it's too high an acceleration causing the problem then lowing the feed-rate could make no difference. You should go to Config->Motor tuning->Z-axis and reduce the speed and acceleration. I can't say exact values as I do not remember what they are currently set to, so try halving them and see what happens.

[JAZZCNC]

How meny times have you cut this.? If you have cut it a few times did it happen in the same place.? If not then try again and see if it happes in same place.

If it does then I very much doubt it's missed steps due to Accel etc or slipping as I would expect this to be more random and not really repeatable. This would more indicate to me you have a tight spot on the Z axis making it miss steps in the same place.?

If it's random then yes go for lowering the Acceleration.

It could also be electrical noise.!

[luke11cnc]

I will cut two relief carvings today to see what is going on and post them later on today

James

[luke11cnc]

How meny times have you cut this.? If you have cut it a few times did it happen in the same place.? If not then try again and see if it happes in same place.

If it does then I very much doubt it's missed steps due to Accel etc or slipping as I would expect this to be more random and not really repeatable. This would more indicate to me you have a tight spot on the Z axis making it miss steps in the same place.?

If it's random then yes go for lowering the Acceleration.

It could also be electrical noise.!

well the result's are in and after a painful day yesterday It looks like I have a tight spot on my z-axis as the ribbing is more or less in the same place.

I cut my samples with a slower feed rate and spindle speed and with a 5% step-over and a extra finish pass at 90 degrees to the first finish pass
this was all futile as I finished with the same results as all the other times.I will check the machine for lose nut bolts and tighten up my belts and put a little bit of oil on the ball screw and then try again.

A very frustrated, unhappy and discouraged James. I could just cry at this moment

but on a positive flip of the coin I only have until Christmas to get this right, sooner would be better though

James