Read this thread:
I have an old Denford CNC Starmill.
I don't have a lot of machining experience as I am only a hobby machinist so I was wondering if there was anyone more experienced on here that might know the cause of the problem I'm experiencing.
I have just machined a flat face on the top of a block of mild steel. If you look at the attached image you will see that the resulting finish is terrible. I used a 10mm cutter and the depth of cut was only about 0.3mm.
You can see that I have ended up with quite visible "rings" from the cutter. They are clearly visible but only just detectable when running a finger across them so in essence are not as bad as they look.
Has anyone seen this before and have an idea what causes it?
Thinking logically I can only imagine that the cause must be some sort of play in the Z axis?
Anyone got any thoughts?
Many thanks in advance.
You got play in the Z axis alright..... In the form of shot spindle bearings.
In the alternative, perhaps your Z axis drive motor is got some noisy signal problems or isn't holding position..
Throw an indicator on the spindle, reading off of a good quality parallel laying flat on and clamped to the table while you're
taking that same cut...you'll only need one pass, not the whole block. If, while the X axis if feeding you get fluctuations in the indicator,
then you know it's the Z axis drive motor.... if it doesn't fluctuate and you get the pattern, then it's bearings.
Thanks both for the responses.
I actually just replaced the spindle bearings and, to cut a really long story short, couldn't get any torque data for how tightly I should secure the retaining collar that clamps them in place.
As such I did the collar up to be in the same position it had been in before I replaced the bearings, I was afraid of ranting the collar up any tighter and damaging the new bearings.
However, I did this test cut (as pictured) which made me think that I must need to do the collar up even tighter. I just thought I'd see on here if anyone else had any other ideas, although that seemed like the logical explanation to me.
As I mentioned I'm not particularly experienced but have been fortunate enough to benefit from the input of others on this forum in the past.
I will re-tighten another turn or two and post back my results.
If you can still tighten it a turn or two it's definitely too loose. Try putting a block of wood or something under the spindle and see if you can move it up and down in the housing. Use an indicator to see it moving.
It looks like too low of RPM and DOC.
You only took around .011 DOC?
What RPM did you run?
How does the cut look at a deeper DOC?
4 flute endmill HSS?
And Yes the Z axis apears to have some slop in it.