Vertical Mill Head Alignment

I had just finished sharpening my largest end mill (20mm) and while taking a test cut across a 12mm square piece of MS I noticed that as the cutter passed across the face of the work in the X plane the trailing edge of the cutter was also taking a cut, this is something I had observed many times before but never given it any thought. Why should it do that ? even if I had made some sort error in the sharpening process surely once the leading edge of the cutter had passed over the work the trailing edge would have nothing to cut - unless the trailing edge was lower than the leading edge.

I was moving the table from right to left so this meant the mill head must be tilted slightly in a clockwise direction. I checked the degree scale at the point where the mill head tilts and it looked to be set on 0deg - my mill an Arboga has a tapered pin that locates the head in the 0deg position, loosening the lock lever I found I could rock the head ever so slightly, even though the pin felt tight I kept tapping it with a plastic mallet until I could feel no more movement in the head.

A quick check by taking a cut confirmed that the head was now much closer to being perpendicular to the table (possibly even perfect) - no matter which direction the feed was in R-L or L-R the trailing edge was no longer taking a cut, this is something I'll have to be aware of in the future. If this something you notice in your own setup maybe it is time to check the vertical alignment of the head.

hi mate .how many teeth does the end mill have? do you mean the trailing edge by the back teeth away from the cutting teeth.
i think if the back teeth are making a small cut this means your head is square to the work piece.
aaron

Hi Guys,

I do a fair bit of fly cutting on the mill and I know that the head tram varies a fraction depending upon how hard I nip the gib screws. I actually built a head tramming tool to set the head accurately, which I can easily do. But the fact that it shifts as above makes it worthless. So the cutter sometimes scratches the trailing edge other times is doesn't.

Attachment 383133
In this picture you can see the two faces of the work that have been fly cut.

Do you tram your mill with a dial gauge or just rely on the zero mark?

With a properly trammed head you will get cutter marks both ways though. Possibly the best way to see if this is an issue or not is to lay a straight edge (steel rule) across a surface you have just cut. If the out of tram is excessive, you will see scallop shapes under the edge. If it seems flat then there is little to worry about.

(If you need a demo on tramming a mill head using a dial gauge then you are welcome to come round)

Michael

Don't rely on the taper pin, use a dial indicator mounted in a Chuck or collet with a maximum diameter or the width of your table, then it will be true.

Below are photos of 200mm plus plate I fly cut some years ago as I don't take many pictures these days, the trailing edge just touching it, which was great as it was true. If I fed in the other direction it was a different matter.
Over time you will learn about your mill and how it behaves.
https://uploads.tapatalk-cdn.com/201...268de23eb8.jpghttps://uploads.tapatalk-cdn.com/201...264ec4fb42.jpghttps://uploads.tapatalk-cdn.com/201...7ea30c8b8e.jpg

Hi Guys.

This is the tramming tool that I built and use.

Attachment 383134
As you can see the head is about a thou out. But that changes if you tighten the gibs.

Here is a pic of my reasoning, looking at the right hand cutter if the head is tilted one way or the other then one side of the cutter will cut deeper than the other. As the table is advanced from right to left the trailing edge of the cutter will be at a lower point than the leading edge. Assuming a good sharp cutter and a light cut to rule out tool and machine spring then once the leading edge passes over the work piece there should be no material left for the trailing edge of the cutter.

I've got a job setup in the mill at present once I'm done I'll check it and post some pics to see how accurately the tapered pin locates the head in the vertical position, the Arboga was made in Sweeden so I'm assuming it was a well made machine, however it is now probably over 50yrs old and had been well used, it will be interesting to see. I did align the head some years back but moved it at the time I rewound the motor to operate on 240V 3Ph.

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BaronJ
As you can see the head is about a thou out. But that changes if you tighten the gibs.

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Not sure why you would need to tighten the gibs - do you mean the gib lock that locks the table there is one for the X and one for the Y direction ? I adjusted the gibs a few years back when I installed my DRO and haven't touched them since, they are not easy to get to
Attachment 383137.

Hi Guys,

My mill is an Optimum BF20. Picture below,

Attachment 383138
The gib locks That I was referring to are the two that lock the head in position when milling. Seen just below the head hight setting handle on the right hand side of the head.

The basic issue with the head being out of tram, is when fly cutting a wide area, the surface is not truly flat !

There will be a scallop in the surface, the deepest point will be in the centre of the cut. Most of the time this is not a problem because the work is not machined over a wide area. For instance a 12 mm slot drill might only cut a scallop a few um deep, where a 75 mm cutter might cut a scallop several thou deep.

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Originally Posted by BaronJ

Hi Guys.

This is the tramming tool that I built and use.

Attachment 383134

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I've always wondered about those. I assume when you first put it up to use, you have to swing it around to check that both dials are reading the same?
I use a Starrett 196 to tram and swing it around, a similar technique to this (The 196 is a rear indicating dial - I use it simply because I don't have to duck around the machine to check readings)
Attachment 383139

Michael

Here are some pics of the alignment of my mill head as set by the tapered pin - distance from the collet chuck to indicator is around 5 inches - the setup is quite touchy but as near as I can make out it is +0.001" on the left and -0.0015" on the right so overall about 0.0025" not sure if this is taken over 5" or 10" but it seems to me that as the two readings are 10" part then it is .0025" out in 10 inches. not sure if this is good or not.

I removed the pin, moved the head slightly, tapped the pin back and checked again it was the same so at least inserting the pin gives me repeatable results. I had a go at getting it perfect and was able to get it to around 0.001" but it was quite touchy and did take a while. The 0.0025 in 10 Inches is probably better than I'm capable of working to - I've seen youtube videos of guys that go to great lengths to tram their mill near perfect using a store bought twin indicator setup then in the next video they are setting up work using a digital protractor.

Attachment 383144
Attachment 383145
Attachment 383146

I always thought that if you want to fly cut and not get cutter marks on the rear then you actually have to set your tram ever so slightly so the head is tilted in the direction of the workpiece to avoid back cutting. Only a very small amount.

As most would know, you can never get your mill "perfectly" trammed, no more than a cross slide on a lathe can cut exactly perpendicular, so with a mill you try to ensure it is tilted in a direction to avoid back cutting (with light cuts) when cutting from a perticular direction; usually in the direction that the numbers on the handwheel increase.

Edit: Also if your table has any appreciable wear, then one it starts to deviate from being balanced in the middle on the saddle, it will tend to droop to one side or the other by a very small amount. This will also affect your tramm.

Of course if you want to machine a reasonable flat surface without back cuts...... get a shaper! :2tsup:

My work here is done.

Simon

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Originally Posted by Michael G

I've always wondered about those. I assume when you first put it up to use, you have to swing it around to check that both dials are reading the same?
I use a Starrett 196 to tram and swing it around, a similar technique to this (The 196 is a rear indicating dial - I use it simply because I don't have to duck around the machine to check readings)
Attachment 383139

Michael

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Hi Michael,

Yes the technique is exactly the same.

I've been criticised by some who have said that both dial gauges have to be the same type and make, and that they have to be at exactly the same hight in the beam. Also that the beam has to be parallel to the mill bed.

I disagree ! As long as both gauges are the same 1 thou reading, and then as long as they are both zeroed at the same point on the mill table, it doesn't matter. This can be checked by rotating the device and rechecking that they both read the same at the other side.

It did surprise me at first that the readings changed when tightening the head gibs.

Hi Familyguy,

If your numbers are correct then I make that around 0.00025 thou (a quarter thou) over ten inches ! Which is excellent.

I can only get near that by tapping my mill head with a mallet and nipping it up.

I believe that is 2.5 thou over 10 inches - that indicator is 0.001" per division. I don't think 1/4 thou over 10 inches is possible on my machine.

Hi Familyguy,

Argh, too many noughts ! :doh:

I shall go stand in the corner for a while... :B