Face mill finish

Hi guys,

I've just bought a Glaze 50mm 90 degree face mill. I've never used a face mill before, so I don't know what finish to expect. As you can see in the photos, the tool marks are showing, but they are very fine and I can't feel them at all with the finger. Using a Scotch grey polishing pad, they completely go... to give you an idea. The "join" line of the step over is completely level around mid way, but I can just feel the tiniest of raised level at the beginning and at the end.

In other words, the narrow band is slightly higher at both 1/4 ends of the piece, but completely level in the middle. It's pretty minute anyway.

My questions are:

-Are the tool marks to be expected, as I say, I can't feel them, so I think that's pretty good, but is it possible to improve, as in...can one get a mirror finish with a 5 insert face mill, or is this as good as it gets?

-How do you explain the slightly raised level at the step over line, and only at the ends? I thought maybe to do with tramming, but then this would only be evident on one end and not both? The piece is only 60 x 60mm.

The feed was constant, 500mm/min at 1700rpm. Many thanks

Edward

Attachment 20577
Attachment 20578

Tool marks are to be expected to some degree but the raised edge is simply because your spindle is out of Tram. Wider the tool the more it will show how far out your spindle tram is. You've most likely not seen this before due to using smaller tooling but soon as you go wide any errors show up.!

Getting a mirror Finish is all about feeds and speeds and material along with whole load of other factors like machine ridgidty, coolant etc only thru trial and error will you find the right combination, if at all.! . . No one can give you magic numbers to achive this.

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Originally Posted by JAZZCNC

Tool marks are to be expected to some degree but the raised edge is simply because your spindle is out of Tram. Wider the tool the more it will show how far out your spindle tram is. You've most likely not seen this before due to using smaller tooling but soon as you go wide any errors show up.!

Getting a mirror Finish is all about feeds and speeds and material along with whole load of other factors like machine ridgidty, coolant etc only thru trial and error will you find the right combination, if at all.! . . No one can give you magic numbers to achive this.

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Thank you, Dean. Off I go to tram that mill then. I am not too worried about the minute toolmarks, as you can't even feel them. But the raised edge is something I have to sort out.


Edward

OK, I've now trammed the column to be perpendicular to the table. I just shimmed it to one side (for the X) and slightly towards the back (for the Y). I am pleased to say that the step over raised edge when using the face mill has completely gone, so the piece is now completely flat. A pleasant achievement.

However, one problem still remains. The Sieg SX2.7 has a fixed head, it can't be rotated, unlike the X3. This means that while you can shim the column to be perpendicular to the table, the spindle may not necessarily be perpendicular as well.

In other words, it doesn't follow that both the spindle AND the column are parallel to each other and in turn that BOTH are perpendicular to the table.

So I did the typical spindle tramming, with an indicator set on a radius of 150mm and lo and behold, when measuring both sides along the X, there was a disparity (even though the column and table are perpendicular).

This probably accounts for the slight face mill circular marks, as the facemill is engaging the piece at an angle as it's not perfectly horizontal to the piece. Since the tool marks are at the trailing half of the face mill circle, this probably gives me a clue as to which way the tool (i.e. the spindle) is tilted.

This poses a new problem....how do I tilt the spindle? I am not sure if it will be possible to shim it, first I have to find out how to take the spindle out, etc...


But before I do so, and find the hard way, is there anyone with knowledge of similar machines who can tell me if there may me some slack in the spindle housing that will allow me to tilt it slightly, or any other suggestions? Or do I just have to live with it?

Edward

So your Z axis is not your spindle? Tricky. How far out is it?

Hi Robin

This is not a router. I should've mentioned that the head is fixed.

The head cannot be tilted or rotated unlike other mills as it's a cast iron block with the dovetails machined into it. So the only thing I can think of is somehow tilting the spindle itself, but it may be tightly enclosed in its housing so that there is no room to shim it to one side.

With a 300cm diameter and the spindle as a centre, I think there is around a mm. tilt on the X. I didn't measure it precisely because I got a shock when I found this and I am still recuperating:)

Edward

Attachment 20588

Let me just try and get my head around this...

If you set the spindle axis of rotation square to the bed you have an X, Y error as you move in the Z axis.

You estimate about 1mm in X, Y over the entire Z travel.

Also the Z axis dovetail slots are cut in the same metal part as the bearing surface that supports the sensitive drilling spindle.

Let me explain:

If I swipe the X axis from extreme to extreme, I have 0 deflection now, the indicator (a bit preloaded) stays on zero throughout. This is because I shimmed the column to be square to the table. That works perfectly and I've never had it so good. I used a very thin aluminium shim, the kind of sheet that you used to get from lithographic plates.

Now for the spindle: I attach the indicator to the spindle by means of one of these annoying articulated bars. So the indicator is touching the table 15cm away from the spindle. Then I swivel the spindle 180 degrees and measure the opposite side of the table. There is a difference of 0.4mm. There should be no difference in an ideal world, the reading should be exactly the same at both ends. I suspect this is due partly to a bit of spindle runout and partly to the spindle not being exactly square to the table.

Because this covers a total distance of 30cm. I don't think it's too bad.

I also did a test with a 10mm bar in the spindle, and measured the Z axis moving it up and down with an indicator just touching along the bar. Depending on how the spindle was turned, I got different readings, from perfect to some deflection, again to be expected due to spindle runout. All this measuring is enough to drive you crazy. The important thing is that the pieces are square using an engineers square and the face mill doesn't leave any ridges, just a few tooling marks which I would rather not have, but they polish off nicely anyway.

I guess I have to live with some imperfections. Next mill will certainly have a possibility to adjust both the column and the head. In hindsight maybe I should've bought a different mill, however, a different mill will have other problems. Nothing is perfect, not for that amount of money anyway.


Edward

I don't understand the first test. It seems to measure bed flatness, it does not depend on the column being vertical to the bed.

The rotating DTI is good, but you want to do North South, East and West to get a vertical.

To compare sensitive quill movement to Z slide movement is trickier. How about putting a bar in a collet, putting your DTI against it from the side and from the front, then comparing quill movement to slide movement. How's that? :fat:

Quote:

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Originally Posted by Robin Hewitt

I don't understand the first test. It seems to measure bed flatness, it does not depend on the column being vertical to the bed.

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The indicator holding prong is actually in the spindle, held inside an 8mm collet. The measuring lever is just touching the table. Therefore any readings of the table are relative to the spindle/head/column assembly. Since the only thing that moves is the swipe east to west of the table, , the reading will change if the table is not horizontal.

Then repeat for north to south travel, using a long parallel across the table to serve as a flat surface for the indicator to slide on.

Doesn't the column bolt down to the base with 4 bolts?
If so you can shim front to back, then shim side to side.

Yes, as I said in post No. 4, that's how I did it, and it's perfect. But aligning the column is not enough, you also need to align the spindle axis.

To give you an example, if you tilt the whole column 20 degrees to the right, your spindle will also tilt 20 degrees to the right because it is attached to the column, but you want to be able to tilt both independently.

And the reason is that column and spindle don't come from factory 100 percent parallel to each other, unfortunately, if they did, then shimming the column would be all that is needed.

If there is no way of adjusting for this parallelism between column and spindle, well, you are buggered basically.

Edward

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Originally Posted by Edward

Yes, as I said in post No. 4, that's how I did it, and it's perfect. But aligning the column is not enough, you also need to align the spindle axis.

To give you an example, if you tilt the whole column 20 degrees to the right, your spindle will also tilt 20 degrees to the right because it is attached to the column, but you want to be able to tilt both independently.

Edward

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You don't tram by measuring the column with a non-angle adjustable head, you tram by measuring the error with a spindle mounted indicator.

Calculate the error in parts which will result, if it's not acceptable strip the head off and scrape the dovetail to correct.

I have a feeling we are talking at cross purposes:)

Forget the word "tram" for a minute.

Basically you align the column first so it is square to the table.

Then, and only then, you align the spindle to the table. In that order. That's provided you can do it. Not possible with a fixed head.

Alternatively, you make sure that column and head run parallel to each other, then you just square them to the table.

I guess modifying the dovetails would do it, if properly done, but that's way beyond my scope.

Edward

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Originally Posted by Edward

Basically you align the column first so it is square to the table.

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Not if you can't independently adjust the orientation of the spindle to the column you don't, you rely on the manufacturer having made the head align to the column, if they didn't you send it back or adjust the fit of the head to the column to correct the error.

Agreed, as I said above:)

Luckily the error is something I can live with.

Edward

Quote:

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Originally Posted by Edward

So the only thing I can think of is somehow tilting the spindle itself, but it may be tightly enclosed in its housing so that there is no room to shim it to one side.]

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You could bore the hole for the spindle assembly slightly over-size and in alignment then sleeve it back to the correct size but scraping or machining the dovetail opposite the gib strips is a far easier way to achieve the required adjustment.

Thank you, re-machining to dovetail on the opposite side to the gibs so that head and column run completely parallel seems like a solution. But it is way beyond my scope, something better left to the experts:)

Next mill will have a head adjustment, that's for sure:)


Edward

Latest news on this subject:)

I came across this video by hossmachine about tramming the head to the column.

I stuck a rod in the spindle and followed his procedure exactly, setting up my indicator like he has done, as I have the same bars. I can't adjust the head like he can, as mine is fixed but I was nevertheless very curious to see how far off my mill head was using this method.

First I jogged to the top of the rod, rotated the spindle by hand and zeroed it to be exactly half way between the maximum plus and minus readings of the runout. Since this was measured at the top of the rod, the runout deflection was quite small.

Then, without touching anything, I simply jogged the Z axis so that the indicator was at the bottom of the rod. I rotated the spindle again and the deflection on either side of zero was exactly the same. I did the same to the Y side of the rod. So I guess this mean I have been worrying about nothing?

Provided this method is good, and I am only going by his video, then I guess I am OK.

Edward

Tramming video by Hoss here:

https://www.youtube.com/watch?v=40Q61UAnOTA

So if your spindle is parallel to your Z axis movement and you have your column square to the bed there will be no error when you check the tram?

Well, in theory you are correct.

Tomorrow I will double check the squareness of the column to the table again. It must be pretty close because when I used the facemill, the stepover raised level was gone completely
whereas before I did the column alignment there was a small raised level on the piece, as can be seen in the very first post.

Earlier I read 0.4mm out of square on a 30cm swipe. I will fine tune this and see what happens.

Edward

EDIT video included:

Forgive the crappy video, but it shows how I measured it. First the top of the rod, hardly any runout, less than 0.01mm. on either side of zero.

Then again at the low end of the rod, notice the equal deflection either side of zero, around plus/minus 0.05mm

https://www.youtube.com/watch?v=V4IKWJDkOSg&feature=youtu.be

Quote:

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Originally Posted by Edward

before I did the column alignment there was a small raised level on the piece, as can be seen in the very first post.

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You keep mentioning column alignment but what were you using to check the angle between the column and table, given that you chose to align that first?

But do you know the Bar is Perfectly round and straight.? If the bar isn't calibrated test bar and the collet high quality then your wasting your time. However I think for machine this size and quality that's good going to get or should expect.!

Edward - your very first adjustment/measurement didn't do what you thought it did. Putting a dial gauge in a collet and winding the table back and forth only tells you that the table is flat. You would get the same result with the column at 45deg, say! The only useful measurement is the turn-round/tramming test where you keep the table still and turn the spindle. However, this only tells you that the spindle is square to the table. The column could be tilted, and the head off-square to the column by an equal and opposite angle, leaving the spindle square to the table and you would not be able to detect this. The test to detect this is to tram the spindle, probably by shimming the column base as you have done and using the spindle turn-round measurements, then with your test bar in a collet and without turning the spindle, clamp dial gauge to table and then run head up and down column, note any variation, then run spindle up and down in head (drilling movement). If these match, head is square to column. If not, then there's no simple fix but at least you can double-check manufacturing accuracy.

Quote:

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Originally Posted by Edward

The indicator holding prong is actually in the spindle, held inside an 8mm collet. The measuring lever is just touching the table. Therefore any readings of the table are relative to the spindle/head/column assembly. Since the only thing that moves is the swipe east to west of the table, , the reading will change if the table is not horizontal.

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Incorrect, what you will get is the error between the plane of the table ways for the moving axis and the table surface, this will remain constant with your indicator mounted on any fixed point on the machine chassis, the column, and if clamped still, the head, are simply extensions from the fixed chassis of the machine.
If there is an angular error between the plane of the table surface and the ways then no amount of jiggling your column, head or spindle angle will "adjust" this away, the only way to correct this is by removing material ;-)