Is this facing finish normal?

[MiniMillMachinist]

Hi guys, just wondering if I could get some input on this face finish before my machine exits warranty! Doesn't matter whether I'm facing with my 40MM indexable cutter, or a 50MM face mill, with a slow feed I get a distinctive pattern in my face passes which follows the same pitch as the ballscrew (6MM).

I've seen similar results from other machines when facing and both the lead and trailing side of the cutter are making contact with the workpiece, but the pattern does make me question whether it's normal. For what it's worth, I had my machine ball barred a few months ago (my machine has always done this when facing) and the ball bar looked great. I assume this is due to minor twist in the ballscrew affecting the feed ever so slightly, but I'm not entirely sure. Would love to get some input!

PS, please ignore the fact the part was hanging out of the vice - this was just a piece of scrap I used to demonstrate the problem. It exists with all my parts depending on the location on the machine table.

Machine is a Haas Mini Mill

 

[Ox]

Looks good to me.

Perfect tram.


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Think Snow Eh!
Ox

 

[Ox]

I would like to qualify that last post:

"Perfect tram in X"

Y could look like Schidt, and I cannot quantify what fer step you might have between passes in X.

But those marks look normal for a good pass to me.



Edit:

Actually, it does look like there may be a noteable step in Y?
It looks like your last pass was up front (Y-) and that there may be a step (up or down) to the rear pass?
(Purdy sure that's not what your concern was tho)

At first I thought that it was 2 different blocks, and that I was seeing a gap between them, but I don't think that's what it is now.
???


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Think Snow Eh!
Ox

 

[usolutions]

What precicely bothers you?

 

[CarbideBob]

Some of these grooves are deeper than others . This is not a machine problem.

 

[Trevor360]

How big a step is there? Is it mostly cosmetic or is there a large step you can catch a fingernail on? Have you checked the tram of the machine by swinging an indicator like you would on a bridgeport? The Minimill is a very light weldment machine so some of this is to be expected with a big facemill but it is very hard to tell how bad or good this finish is from the photo....

 

[MiniMillMachinist]

Thanks everyone for your input!

I should have clarified about the step in Y — that’s just another pass I took separately at a lower step down, so ignore the noticeable step there!

It was just the pattern of darker/lighter shades of cutter lines I was referring to here. Spindle is within 3 microns over 250MM diameter for tram across X, 10 microns for Y.

Thanks for letting me know it’s normal!

 

[MiniMillMachinist]

Some of these grooves are deeper than others . This is not a machine problem.

Thanks for the info — do you know what causes it?

 

[Ox]

Spindle is within 3 microns over 250MM diameter for tram across X, 10 microns for Y.

And what .... ____ ... on Earth ... ___.... are you using to measure THAT?

3 micron in 10 inches?

I don't think there is anything that good this side of the grave!


Maybe you are cornfusing the "thousandths" with the Micron?





---------------------

Think Snow Eh!
Ox

 

[MiniMillMachinist]

I would like to qualify that last post:

"Perfect tram in X"

Y could look like Schidt, and I cannot quantify what fer step you might have between passes in X.

But those marks look normal for a good pass to me.



Edit:

Actually, it does look like there may be a noteable step in Y?
It looks like your last pass was up front (Y-) and that there may be a step (up or down) to the rear pass?
(Purdy sure that's not what your concern was tho)

At first I thought that it was 2 different blocks, and that I was seeing a gap between them, but I don't think that's what it is now.
???


--------------------

Think Snow Eh!
Ox

Thanks for your reply Ox! I should have clarified — I took a second pass at a lower step down, hence the line you noticed. Really appreciate your insight

 

[MiniMillMachinist]

And what .... ____ ... on Earth ... ___.... are you using to measure THAT?


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Think Snow Eh!
Ox

Just a 2 micron dial indicator in the spindle with a magnetic base — I probe the various points I measure with the Renishaw probe and then compensate for the difference in height between the points when measuring with the mag base/indicator. The probe gave repeatable results on the table so I’m reasonably confident in the results

 

[Ox]

You are awfully green, I git it....
You can believe what you want, it's your story.... Tell it how you see it.


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Think Snow Eh!
Ox

 

[Conrad Hoffman]

I see a light/dark pattern that's probably about 6mm pitch. My guess is even doing a long surface finish measurement, any error you'd see is well within any spec for the machine. Machines aren't perfect, not even a Haas. If you want to machine mirror finishes you need a different tool. OTOH, you can probably hide that stuff by using inserts with the right radius and possibly choosing material with different something. I don't know what that something is because I don't know what the material is. Looks kinda gold- is it brass or bronze?

 

[Ox]

Some of these grooves are deeper than others . This is not a machine problem.

Like Robert said, if you want better, take out all but one insert.


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Think Snow Eh!
Ox

 

[MiniMillMachinist]

You are awfully green, I git it....
You can believe what you want, it's your story.... Tell it how you see it.


--------------------

Think Snow Eh!
Ox

Is there a better way of checking it?

 

[Ox]

A 2/10ths indicator maybe?


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Think Snow Eh!
Ox

 

[MiniMillMachinist]

A 2/10ths indicator maybe?


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Think Snow Eh!
Ox

why would I use an indicator with 2-3 times less resolution?

 

[MiniMillMachinist]

If you’re curious about the indicator — Indicator link

I followed the Haas procedure for checking spindle tram — the spec is 10 microns within 250MM diameter.

Regardless, the point isn’t how well trammed my spindle is — it’s just whether or not the pattern that appears to be consistent with the ballscrew is typical (not the cross hatching, the actual lighter and darker shades) — which it appears to be, so thank you everyone for your feedback!

 

[dcsipo]

Thanks for the info — do you know what causes it?

Does the pattern vary with different feed rates? Try a fly cutter; sometimes, shell mills with varying insert heights may cause issues like that. You can also check if one of your inserts hangs low . Hint, a shell mill with one insert is a fly cutter.

 

[MiniMillMachinist]

Does the pattern vary with different feed rates? Try a fly cutter; sometimes, shell mills with varying insert heights may cause issues like that. You can also check if one of your inserts hangs low . Hint, a shell mill with one insert is a fly cutter.

Hi dcsipo, thanks for the reply — the inserts are all within a few microns according to the renishaw tool setter (I swapped them out and flipped them to get them all as close to perfect as I could). Appreciate the tip on the fly cutter — I’ll give that a go and see how she finishes. Sadly no, the frequency of the lines stays the same. I can only imagine it’s some trick of light due to some microscopic height difference due to the slightest misalignment of the ballscrew or a tiny bend. Can’t be much or I imagine the ball bar would have picked it up!

Funnily enough if I push the cutter harder with a deeper cut the spindle tilt from the cut is enough to knock out the trailing edge of the face mill from the cut, I then don’t get the cross hatched lines and nor do I get the pattern.