Check end mill or slot drill to see if the ends are ground ok lay on a flat surface to see it the cutters are ground correct ie sharp with correct clearance As M G says check to see if the head is square using dti etc .Or slower feed with coolant would help. A good indication if the heads out of square if the cutter trails on the back end when cutting . But you know that already

Nobby

Have you done any milling on your lathe?

See how much difference you get when you have a high stiffness lathe, use the same cutters on the same materials

Any vibration is fatal for milling

Speed isn't always best, sometime backgear is miles better because of heat and vibration issues

I got fed up trying, milling was too much of a wing and a prayer, not a pleasure

So I bought a small shaper

Hi Wolfie ,

Most likely causes :

Blunt cutter .

Excessive cut or feed rate .

Slack in any of column fixing / slides / head / spindle / collet / quill / chuck .

The orbital patterns which you describe seem to suggest either the blunt cutter or the slackness . Most common problem on these milling machines is that the milling spindle is orbiting either due to slackness or poor bearings.

Misaligned slides don't cause the orbital patterns you describe – they just caused crooked work and misaligned successive cuts .

Show me some good pictures of the workpiece and cutter end and describe the sounds made when cutting . With that information it should be possible to analyse problem completely .

This class of problem was discussed fairly extensively in earlier postings . The earlier postings also explained the causes and effects of cutter vibration .

Regards ,

Michael Williams .

Harold,

A very interesting analysis … with much food for thought.

I am intrigued by the suggestion of deliberately misaligning the head:

Effectively this is a work-around for the many forms of backlash and flexure in the system. But presumably this would also require one to always cut in one direction ?

Grateful for your further comment on this point.

MichaelG.

Wolfie,

I think you have a mini-mill.

If so, have you checked to see if the locking nuts at the top of your spindle have worked their way loose?

Just a suggestion.

Ketan at ARC.

Hi There

It is not that difficult with a decent clock.

regards David

Edited By David Clark 1 on 31/07/2012 17:10:11

Its a ten-minute job for me to set my mill to inside a thou over eight inches!

Neil

Edited By ChrisH on 31/07/2012 18:44:19

Sorry Michael for being a little slow in replying, yesterday was a special day out, wife's birthday.

I realise now that I should have quantified the amount I was considering when suggesting that the machine would benefit from the the head being at a minute angle to the tables surface (even that is a debatable comment, more later)

The standard for a new industrial machine is for the permitted error to be no more than 0.025mm over 300mm and I was not expecting a machine to be set greater than this but perhaps approaching the value.

For some reason though, I do not think I have ever seen mentioned the other, and equally important, aspect of a milling machine. That is, how parallel the work table is to its traverse. Again, the standards allow for the table to raise by 0.025mm when being traversed through 300mm. From this it can be seen that even if the spindle is perfectly perpendicular to the tables surface it can still be off perpendicular to the surface of the workpiece being machined.

Perhaps the justification for this features low profile, is that it is one part of the machine that the manufacture finds it easy to better the standard. However, I am not sure about this when the machines come, as most do these days, from the far east.

I am reluctant to go into much more detail here and would suggest the reader visits my website where there are examples of cuts being taken moving left to right and right to left, both with sharp and blunt cutters.

Briefly, Photo 6, with a sharp cutter, shows that for run of the mill tasks traversing either way would most likely be acceptable. What is initially surprising though is that on the left, with the trailing edge of the cutter high, there are still signs of back cutting but very much less than for that on the right. This of course is due to the machines head bouncing up and down and my machine is one of the heavier mill drills so with lighter weight machines the effect is likely to be greater.

Had the machine's spindle been perfectly perpendicular then there would be more evidence of back cutting on the left and less on the right. Of course they would both be the same.

I should add that my machine is just inside the laid down standards left to right and just outside front to back.

For me, both directions would be acceptable for the majority of tasks but where finish is of greater importance, and the workpiece permits it, I have the option of the better finish. This being a better finish than would be achievable with the head perpendicular.

Photo 7 shows again that even with a blunt cutter that on the left is better than that on the right. Had the head been perfectly perpendicular that on the left would have more evidence of back cutting. This showing that in this situation the machine will be more susceptible to the cutter becoming blunt.

Incidentally, the two photographs clearly indicate the burrs that Jason wrote about.

Harold

When milling with an endmill the whole stack up of cutter , chuck , quill , head and column are all twisting away from the cut . In a normal set up most of the deflection occurs in two places – in the cutter/chuck/spindle and separately in the slack of the quill in its housing .

It is the variable effects of this deflection that cause back cutting and excess rib marks in adjacent cuts .

On a quality machine like a Hauser the cut marks are absolutely flat and regular and this is because great pains have been taken to make the whole set up rigid .

Michael Williams