Problem with facemill

[Ageless]

I have been having problems getting a decent finish using a face mill making .05mm finishing cuts.
I was advise to remove the carbide cutters that came with the mill and use HSS instead. This I did however the result was only
marginally better. I was advised to look for a Moiré pattern developing on the surface which is a indication that the Milling machine is trammed correctly.

No Moiré pattern was noticed on a consequence cut so checked the mill for tramming, the mill was off a bit so set it up again and re-cut that test piece that I have been using. No pattern seen when cutting with the material moving from left to right however a very light amount of the Moiré was seen when the material moved from right to left. One further point is that I have now changed to Aluminum versus steel to see if the results where better. I raised three of the cutters up a bit and cut a finish cut with the face mill using only one HSS cutter making contact. The finish was very much better than with four cutters.
I also noticed that the mill seemed to be under more stress when I reached the right side of my 4" machinist vice.
Based on the Moiré pattern being apparent on a right to left cut versus a left to right cut I decided that I might try setting the X-axes
tram off of center to exaggerate the cutting effect on the right side of the mill. I did this two times and each time I increased the amount of offset but basically the same result.
I also checked my vice for for it being level and found that it was .18mm higher on the rights side, this might be the cause of the heavier cutting action on the right side. As a note I removed the vice and checked the bed over the center 8" of the bed and the difference was .005mm. This now appears to be a vice problem being here as well.
My question is what next should I do to improving the finish with a face mill?

Thank you in advance for your assistance.

 

[Blogwitch]

Ageless,

What you are seeing in the moire pattern one way and not the other is because your mill is out of tram.

When going one way, the trailing edge, being slightly lower than the leading takes another minute cut, so cleaning up the rough surface caused by the leading cut. When going the other way, there is no secondary cut because the trailing edge is slightly higher than the leading, so that cut will be fairly rough compared to the other.

Good finish cuts almost always depends on just a few things. A rigid machine, razor sharp tooling (and I mean razor sharp) and your feeds and speeds, plus some lube.

I always use for a good finish either a flycutter or good quality tungsten solid tooling with as many flutes as possible, not replaceable tipped type, they are just too blunt. They are then coupled to fast spindle speed and slow feed. It also goes without saying, keep everything clean and lubed. A lot of bad surface finish is in fact caused by chips being dragged around by the cutter, so just having air blowing the chips away can help.

If cutting ali, try this little experiment. Put a cut on of say 0.1mm, then cut across the surface and see what the result is, then take the cutter back to the beginning, try it again with exactly the same cut, but spray a very fine coating of WD40 onto the surface before taking the cut. There should be a dramatic change in the results.

That is the same thing I show people when they come to my shop and say they don't use lube. They usually change their mind after seeing it. A gallon of WD40 costs me less than 20 squid a year to use on my machines, it would still be worth it if it was treble that cost.

Another thing you mentioned was a choice of cutters. If a solid cutter has ever been used for general cutting of tough non ferrous or any ferrous materials, it should never be used in any attempt to get a good finish on anything, unless it has been resharpened.

If you get things right, the surface finish should be like a mirror, that is usually the best time to see the full moire effect.

Bogs

 

[Ageless]

Hello Bogs, thank you for the reply!
I was hoping to get more information as to why I am not able to get the Moire' pattern when the mill is trammed properly. In my description I mentioned that I re-trammed the mill then did another surface cut, went back a second time and checked the tram and it was right on (X-axis).
I fully understand about how a Moire' pattern is formed and the cutting action that is occurring to eliminate the pattern.
I have a thought that which I will check out later and that is how I am setting up the 4 cutters on my face mill.
Is it possible to shim a milling vice to get it level?

Best Regards

Al

 

[Blogwitch]

Al,

You haven't said what type or size of mill you use. I have mentioned this before, you just might be taking the mill beyond it's designed limits with regards to rigidity for the size and cut you are doing. I wouldn't expect say an X2 to flycut a 6" x 6" face in one hit, whereas a Bridgeport could do it with ease.

It is certainly possible to shim up your vice. I had to do it on the one before this one I use now. This shows the setup I use now.

http://www.homemodelenginemachinist.com/index.php?topic=2641.0

If it was to happen to me again, I would do everything within my power to get the base ground true to the jaws, as shimming is only an interim fix on something as mobile as a vice. It has to be done every time you reposition or remove/replace it.

Bogs

 

[Ageless]

Hello Bogs;
I am sorry that I failed to mention the type of machine I am using, the machine is a ZAY 7045FG/1 milling machine.
If you look at the picture to the right of this post and beside my login name; Ageless, you will see the machine.
The picture does not show the steel stand for the machine or the power feed that it is equipped with.
It is similar to a X3 only bigger (around 800 pounds), if has a square column with a swivel head and a 2-hp motor and
an oil bath transmission.
I hope that this helps, one further question can one shim a milling machine vise to make it level??
My vice is off by .18mm on the top of the fixed jaw when measuring from left to right.

Regards

Al

 

[Ageless]

Hello Bogs;
Boy am I bad I responded with out fully reading your post, sorry about that!
Thank you for helping me with the vice issue.

Regards

Al

 

[Kermit]

Glad you caught it. I was about to post and mention that very fact... :big:

Also check the level of your vise across the bottom of the opening with widened jaws. this is where the workpiece will ultimately be indexed from. The parallels sit on it and the workpiece sits on the parallels etc etc etc. So the top edge of the vise has no affect on the relationship between vise and table. Hope what I'm saying is clear...


Kermit

 

[Blogwitch]

Al,

That is a fairly robust machine, so really, you shouldn't be having major problems with it.

I replied to your query about the vice in my last post.

Kermit has just replied before me, and he mentions the same as I am going to do.

Just one thing you must not do, that is taking a reading off the top of the fixed jaw unless it has been trued up to the base at the inside bottom of the jaws, like I showed in the link mentioned in my last post. The tops of all jaws can be almost in any position unless they are keyed into the main casting, and even then, not until they have been checked like I just mentioned, exactly parallel to the inside base.

I will just mention one thing, don't chase your tail trying to find the perfect position for being flat and level if your vice is out. I very much doubt, unless you subject it to precision grinding, for you to be able to get it within tenths of a thou. On a four inch wide vice, getting it to half a thou (0.0005") (0.01mm) will be plenty good enough for almost all jobs you are ever liable to encounter. That means if you machine a piece 1" (25mm) long in the X axis, the difference from one end to the other will only be approx 0.0001" (0.002mm), in other words, negligible.


Bogs

 

[DickDastardly40]

Hi All,

I hope I'm not missing something here and at risk of showing my ignorance, even if Ageless's vice is not completely flat to the table and if the head is vertical he should still get the 'moire' pattern, but the part will come out slightly tapered.

If your vice is off, try turning it through 90 degrees and see if you still get the same pattern or lack of, to remove this from the fault diagnosis equation. If the vice doesn't fit at 90 deg try, moving the table in Y rather than X to achieve your cut as this direction doesn't care if the head is vertical

Cutting better in one direction than the other suggests to me that you have some flexure somewhere. Is the head tight, is the vice tight, Is the vice rocking on a tiny bit of swarf?

Al

 

[Ageless]

Hello All;

I stumbled upon a possible error that had my tram not correct when in fact it was!
When tramming my milling machine I was using the top of my machinist vice, it had not occurred to me that the top of the vice might not be level as it is a ground surface, Wrong!
The vice is .18mm higher on one end versus the other, to tram the machine I was using a 5” race from a ball bearing and that of course increased the error that existed in the vice.
Anyway, I thought I would tram the mill one more time and use the ground table as the reference point.
When this was finished I machined a new surface on a sample piece and Lo and behold I had a perfect Moiré pattern on the test piece.
This has taught me a couple of things, the first being do not take any short cuts and the second is I can now Tram a mill very easily.

I want to thank everyone for all of there time and effort in trying to assist me with this problem! :bow:

Thanks again.

 

[DickDastardly40]

A quick visual test can be carried out with the vice in position and work in the vice if you think that you have knocked the spindle out of plumb when flycutting for instance:

http://www.homemodelenginemachinist.com/index.php?topic=4039.0

PS this won't work on heads which nod as well as rock.