Face mill finish

[Edward]

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.

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

[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

[Robin Hewitt]

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

[Edward]

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

[Robin Hewitt]

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.

[Edward]

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

[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.

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?

[magicniner]

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.]

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.

[Edward]

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

[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: