That does look to be cutting only on one side but it depends on the size of the workpiece and fly cutter. I often cut small parts with a large cutter so it only cuts in one direction. What are you using to tram your head?

You only need the tram to be off by a very small amount to get a cut on the trailing edge, If it's very small I would not worry about it, get can similar on my X3 but if you know it's there you can work around it. Either taking advantage of the trailing cut as a fine finish to the leading edges roughing cut or simply cut with the lower edge as the leading one. As Jeff says too much tool stick out does not help. the radius of the cutter marks on your work suggest you were swinging a very large radius with quite a small bodied tool.

One other cause can be a less than sharp cutter and a bit of spindle play or machine flex. If not sharp the tool can get pushed up and ride over the work and the the trailing edge then drops and takes a fine cut.

A lot of people prefer the finish shown in your photo to the double hatch that you get when it is perfectly trammed with its almost holographic look, here is one I prepared earlier.

Edited By JasonB on 24/12/2020 07:22:34

What you have sounds like the spindle bearings need a bit of adjustment. Do the bearings warm up when the machine is run for something like 30 minutes? When you tram the head everything is positioned purely by gravity. When you are cutting there is a side force on the spindle that will affect the tram if the bearings are loose. I am assuming you are tramming using something mounted in/on the spindle. With your indicator mounted see what happens if you apply side forces to the spindle. Some very small indicator movement will just be flex in the metal of the machinery, large indicator movement will show the need for bearing adjustment or that the clamping of the spindle is not effective.

Martin C

Photographing shiny metal surfaces is hard! You might try drawing an obvious line across the work with a dark felt-tip. The camera should be able to auto-focus on a sharply contrasting line drawn across the otherwise bland confusing surface. Another approach is to vary the angle between lighting and camera until the camera 'gets it'.

Back to the question, the problem may be your materials are smearing. Ordinary mild-steel doesn't machine to a good finish particularly well – it tends to tear and smear. Many aluminium alloys are even worse – soft. Could be you don't have a problem at all; the cutter removes metal to create a flat surface and then hides it's tool marks by rubbing the ridges into the valleys. Maybe!

Dave

(Particularly if you fly cut this piece on both sides) if you cannot measure any significant difference in thickness across the width, how do you propose improving anything? (Running a dial gauge across the y axis of the part would show even less)

To get the diffraction effects shown on JB’s pic demonstrates flatness to low tenths of a thou, I would guess (of course that part might be off a lot, on thickness, from end to end, but I doubt that🙂 ).

Pleeese stick to one system of units.🙂 I don’t mind which (I favour SI units – and powers to base 10 of those units – as they are so much more universal these days). Mixed units can make my head ache just sorting which is appropriate at the time or throughout the thread.

For most things a thou, over 3 inches, will not be noticed by many. Only precision kit needs better. The biggest problem is likely squaring stock with the mill.

I hope I can now get far better finishes than even JB’s pic shows – I can now take off tenths of a thou if minded to do so – but I might only surface grind when I want a more pleasing finish – not closer dims – or the same dims for a set of parts.

Just no point in going crazy on dimensions when not needed. Experience will improve your understanding of your particular machine so practice is the name of the game. Most on here do not have tool-room quality machines but many can make perfectly satisfactory working models with what they have.

I also know there is an awful lot I don’t know about surface grinding – but I will not let that bug me too much.