Facing problem with aluminium.

[alexccmeister]

Hi all,

I am trying to facing on an aluminium plate as it has a slight curve to it and I need a flat surface to work on. I am using a 16mm diameter flat endmill (not altogether flat as the center of the endmill is higher than the cutting edge. I am not using a face mill as I haven't got one.

Anyway, after cutting the surface of the aluminium plate has a set of parallel ridges to it along the line of the cut. I can feel the ridges with my finger. This patterns repeat itself over the whole surface. I am guessing either of the two is the problem but I can't be sure.

1. The Z column is not 90 degrees to the table.
2. The flat endmill is not the best tool to use for facing.

I am hoping the second one is true. What could have really caused this problem? My understanding of machining is that if the endmill is turning, even if the table and column isn't trammed properly, I would still get a decent surface as the turning action of the endmill will always cut with the lowest tip of the cutter. Hope someone can help me to explain.

Alex

[Geof]

Originally Posted by alexccmeister Hi all, .....Anyway, after cutting the surface of the aluminium plate has a set of parallel ridges to it along the line of the cut. I can feel the ridges with my finger. This patterns repeat itself over the whole surface. I am guessing either of the two is the problem but I can't be sure. 1. The Z column is not 90 degrees to the table. ...

You did answer your own question, almost. it is actually the axis of rotation of the spindle that is not perpendicular to the plane of travel of the X and Y axes.

If you can feel the ridges from a 16mm end mill the spindle is rather badly out of true.

[Mitsui Seiki]

You need to have the Z axis 90 degrees to the table.If it's not you will never get a flat surface unless you have a 99.9% overlap.

[alexccmeister]

Thanks guys. How do I make sure its true to the vertical? Thanks.

[Mitsui Seiki]

Is it possible for you to post a picture of the machine?Z axis and table.

[joecnc1234]

I had the same problem on one machine I was cutting in x axis I changed to Y axis and it solved the problem. Im guessing the gibs on the side of the spindle are worn out on my machine.
Joe

[Mitsui Seiki]

You got the job done but the problem is still there.You guys need to get your Z axis aligned.

[Geof]

If the spindle axis is out of true to X but is true to Y you will get a different pattern depending which axis you use for facing. If Y is used you get the sharp ridges if X is used you get concave grooves. You can picture the effect if you hold a cutter to the surface at an angle about 20 degrees off vertical and see how it makes contact and what path it makes moving in either direction.

You will notice I say spindle axis. This is because the Z axis may be a true 90 degrees to X and Y but if the axis of rotation is not parallel to the Z axis you will still get the ridges or grooves. However, if the spindle is a true 90 degrees you will get a smooth faced surface even if the Z axis is out of true.

Most machines have the spindle housing and Z axis ways in the same casting so you cannot alter this and just have to trust they are okay. The normal way of aligning the head aligns the spindle axis.

How to check and adjust?

You need a flat surface that is parallel to the X and Y travel and you cannot always trust that the table surface is true. However, your faced surface is true on average; the top of all the ridges or the bottom of all the concave grooves are all level so you can use the faced surface.

You need a good dial gauge mounted on an arm in the spindle so the probe can be rotated around a circle. Unplug the machine before doing this, accidently hitting the switch probably means bye bye dial gauge. With the probe just touching the faced surface rotate the spindle a full turn by hand; don't touch the dial gauge to do this, turn the top pulley so you don't deflect the gauge.

You will see small movements of the needle on the gauge as the probe passes over the ridges/grooves from the facing but the out of true of the axis is shown by a high and a low reading 180 degrees apart.

You will have to figure out how to adjust it.

[alexccmeister]

Hi Mitsui,

Haven't got a shot of the machine as it is. Will try to take a shot tomorrow. I am going to try the technique as described by Geof. Thanks for the help guys.

[alexccmeister]

Ok, I managed to get hold of a couple of dial gauges graduated with 0.01mm mark. There are 100 marks in total make every turn of the dial 1mm. I placed the gauge as per Geof instruction and the tip of the gauge on the table itself and I noticed that when I make 180degree turn of the spindle, there is a difference of 0.05mm on one location. When I run the table along the X axis, I noticed that there is a displacement of about 0.03mm between either end. This seems small and yet make so much difference to the surface being faced. I am just wondering if I ever will get it 100% true as the gauge itself isn't all that accurate as I tap the face, the needle deflected slightly.

Y axis was ok as there isn't much difference in level. So I guess my Z column isn't vertical from the tests performed. Will check it again this evening.

[Geof]

Actually 0.05mm is not that bad for a low cost machine, it could be much worse.

The deflection when you tap the gauge is because you are moving it; this is why I said rotate from the pulley on the spindle so you do not deflect the gauge by touching it while it is being rotated.

Realistically you will never get it perfectly true but with a bit of luck you may be able to get it down to around 0.01mm.

Don't worry about the 0.03mm from end to end on the table. This I what I mentioning about the table not travelling true but .03mm is quite good. It is also difficult to do anything much about this.

[joecnc1234]

You could try moving your leveling screws I think that is whats wrong with my machine I have a matsuura with big ways but I think it setteled since I put it on the ground??
Joe