[NylonAdmiral]

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.

[djr76]

Read this thread:

http://www.cnczone.com/forums/genera...at-bottom.html

[fizzissist]

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.

[NylonAdmiral]

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.

Thanks again.

[keebler303]

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.

Matt

[Perfect Circle]

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.
:cheers: