[delco]

I am looking for clues in what is causing this strange harmonic pattern in my machine , it seems to have visual ridges at set intervals , cannot feel then at all.
Flat surfacing was done across the X axis with a 3 flute 12mm endmill , the curved section is machined with 6mm 4 flute bullnose rad 0.5mm with a 0.4mm stepover in the same direction .

I can feel the 0.4mm stepover , wich is fine , just the visual banding is wierd . The band is 2.5mm wide so a cycle is 5mm , same as my ballscrew pitch

[Algirdas]

Prove it is advantage and charge your client extra :-)
joking :-)
what is your static spindle run-out and do you have a sound pattern of your bearings when the spindle was new to compare with the presend sound pattern? Did you check your spindle bearings with diagnostic tool in order to evaluate rising vibrations?
are cutter shank and tool holder throat in good condition?

[MARV]

I would also look at your 3d model. How "tight" are your surfaces? You haven't said what software you use. Is the tool path written from the client's file? Sometimes just "cleaning up" the model surfaces or tightening the tolerance in your tool path can make an improvement.

Another consideration; if your part is in spec, then don't beat your head against the wall. Job complete!

[delco]

Part is in spec , just more for my own reference , just a chinese spindle setup so nothing high end , only happens when travelling in the X axis , using fusion 360 , seems to be in synch with ballscrew pitch - everything new but chinesium .

[routalot]

Two thoughts;it could be a chordal deviation setting in the software or it could be a harmonic vibration of the machine.

[StrawberryBoi]

This strikes me as odd for harmonics unless there is an extremely consistent change in the stiffness of the axis based on the pitch if the ball screw. Maybe the ball screw has a precise out-of-roundness, which is possible especially if ground.

That a harmonic not related to a mechanical change would be so consistent is really unusual to me.

I'd put my money on something in the code or a machine specific interpreter issue.

Have you encountered this on other parts? Did you try varying the SFM to vary harmonic content? Even a 1-2% change in RPM should knock you out of the harmonic if that's what it is.

[Goemon]

I get a pattern like that from rubbing if I take cuts that are too shallow. I also get something similar if I take cuts that are too aggressive with larger end mills, or ones with excess stickout. I.e. chatter.

It's usually worse if I use a high helix end mill for finishing. I'm still learning myself but I've noticed that it happens less if I finish with a flat end like this:

https://www.ebay.com/itm/17413185175...IAAOSwJPxd~N3j

Instead of the ones like this which are better for chip clearance for roughing:

https://www.ebay.com/itm/15300355293...Cclp%3A2334524

[OldSchoolProgrammer]

I am looking for clues in what is causing this strange harmonic pattern in my machine , it seems to have visual ridges at set intervals , cannot feel then at all.
Flat surfacing was done across the X axis with a 3 flute 12mm endmill , the curved section is machined with 6mm 4 flute bullnose rad 0.5mm with a 0.4mm stepover in the same direction .

I can feel the 0.4mm stepover , wich is fine , just the visual banding is wierd . The band is 2.5mm wide so a cycle is 5mm , same as my ballscrew pitch

In my experience on a large number of different machine tool brands, the pattern spacing of a well tuned machine in very good condition is always equal to the ball screw lead, and cutting speed and feed rate do not affect the pattern spacing. The height difference between the lighter and darker bands is on the order of a few millionths of an inch and is simply an artifact of a less than absolutely perfect ball screw. Unless you have a part surface waviness requirement of less than a few millionths of an inch, there's no cause for concern.

[QuinnSjoblom]

is this a home built machine with cheap ballscrews? mine had the same until swapping out to high quality screws that werent warped. The alternating pressure of the warped turning screw on the nut was enough to pick up a visual pattern on the work at the frequency of the screw lead.