Milling question.

[BK]

Why do I only get a good finish one direction??
I'm using a 3" face mill, the initial cut is good, but I get "secondary" marking from the "back spin" of the mill.
This is moving the table from right to left. 



I thought play in the bearing, but that would do the same both ways.
This is left to right. 



I spun the vice 90 degrees and got these results.






Any ideas?? 

[Bogstandard]

It is purely because the tramming of your mill is out. Nothing to do with bearings, so don't worry.

One way, you will get just one edge cutting, whereas on the reverse cut, both edges will be cutting, first a shallow cut, then the back edge follows along and does another secondary cut.

Hope that explains it OK


Bogs

[Artie]

Gday mate, assuming the tramming..... one issue I found was the trapped or retained swarf on the cutter as it passes over the job on the 'back-spin' causing marking or scuffing.... I use a small jet of compressed air while cutting, makes the world of difference, on aluminium, try a squirt of wd40 as well.

Good luck.

[BK]

Thanks for the quick answers, but a question??, err, how do you adjust the tramming on a fixed head mill??
It goes up and down, and will swing either way, but, no tilt??

[Bogstandard]

What type of mill is it?

If it is a round column mill/drill, then it is a matter of shimming up the clamp base at the bottom of the column to get it spot on. Once done, it should never need to be done again, so it would be pointless to invest either time or money in making or buying a tramming tool. You would use the old method of a DTI on the end of a bent rod.

If it is a combination of a rigid vertical column, but swivelling head, then it would be a combination of shims to get the column truly vertical and so square to the table, and then head adjustment using the swing feature either way, in which case a tramming tool would be desireable but definitely not essential.


Bogs

[BK]

Thanks Bogs, ya round column 12" wide at the base, the bolts are 9" apart, if I use a rod 4-1/2" long I should be able to work out what shims to use under the bolts??? or am I wrong. 

[Stilldrillin]

Bernie.
I lay a piece of 8" square, 4mm glass on the table.

In the drill chuck, I have a dti clock, mounted on an arm. (Piece of bent 1/4" rod will do).

This allows the clock to describe an 8" diameter circle on the glass, showing high/ low areas. 

Simple, when you've done it before.......   

David D

[BK]

Thanks David, the only reason for the 4-1/2" was that it is the spacing on the bolts, and if I halve the reading it should tell me what spacing I need, glass is a good solid medium. 

[Stilldrillin]

Bernie.
Are you saying, "ain't got no clock" ? So, using feelers under the rod?

David D

[BK]

Bernie.
Are you saying, "ain't got no clock" ? So, using feelers under the rod?

David D

No mate, I've got the timepiece, all I'm trying to say is , if I use a 4-1/2" rod (with the "clock" on it), if it reads 0 on one end and .10 on the other, I should need to put .05 under the bolts on 1 side, right or wrong. 

[Stilldrillin]

Thasright! ....... In theory! 

Drinks can/ cooking foil usually works wonders. Good luck! 

David D

[BK]

I did the tramming thingo today, 10 thou out over 10" (on the long thingy  ) I put 5 thou under one side, then checked the other way, another 2 thou (shim brass) I can live with what I have now, about .0015" out each way.
Thanks for the advice.

[Stilldrillin]

Well done Bernie! 

That's my first job, for Monday morning...... 

David D

[Bogstandard]

Sorry I didn't get back to you on the length issue, must have missed it.

There are in fact more reasons to getting the tramming perfect than people realise, and a query from Bernd about why I was machining a part a certain way was explained by this posting.


http://madmodder.net/index.php?topic=2083.msg22206#msg22206


I hope it explains it to you just as well.


John

[BK]

It certainly did Bogs, thanks for the link.