On 3 August 2024 at 20:57 samuel heywood Said:

If your mill is out of tram in both axis’ it will still render a flat plane, however this plane will not be parallel to the reference plane

Wrong, it will leave a curved surface on the X-axis. Think about what would happen if you tilt the head over at 45 degrees and then run an endmill across the workpiece. It will leave a curved groove. Same thing happend with a flycutter and the head slightly out of tram; just that the curve is imperceptible.

Andrew

If you flip the part, the error will not change because your part is still lying on the same parallels.

To reduce the tramming error, you can use a smaller fly cutter.

To reduce the bending error you can use a smaller fly cutter and take shallower cuts.

To compensate for tramming errors, you can make parallels from mild steel and mill them flat in the position they are used. That will compensate tramming errors and errors from your vice. It will not compensate for deflection during facing/milling.

I think all lathes are (or should be) set up to face concave, the more you pay the less concave, but concave is preferable to convex.

On 3 August 2024 at 20:57 samuel heywood Said:

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Firstly, whilst i regularly  throw caution to the wind and climb mill using endmills, the little x1 really doesn’t seem to like climb milling with a flycutter, conventional milling seems to be the way to go.

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Why throw caution to the wind by climb milling?  Unless the mill is powerful and heavy enough to take the strain there’s no advantage in climb milling, which thrashes most hobby machines for no benefit, maybe flexing the machine enough to tilt the cut.  The exception is that a single very light climb cut right at the end often improves the surface finish.

Apologies if it’s me, because stomach ache is destroying any limited ability to think I might have had,  but does a fly-cutter ‘climb-cut’?  My gut feel is that they cut conventionally.

Dave

My mill seems to be trammed as good as I can get it, so I mounted a lazer switched on, to shine to the roof focussed to  inside the hole of a small washer. I hope this will help if I tilt the head again. One could add markings for degrees chosen & trammed.

A mill that is in tram should give a very slight back cut but it should not be so deep that it removes the cutting marks from the leading cut. You should end up with an almost holographic effect where the (((( shaped leading cut and the )))) trailing cut cross each other.

One I prepared earlier on the X3

1/2 a degree sounds quite a lot. You probably only need a thou or two over a foot to tilt the head enough to stop the back cut and any more will increase the amount the surface becomes concave.

A quick bit of cad gives quite a dip. Say the flycutter is swinging 8″ dia which would be about right for a 6″ wide head then at 1/2deg you would get 0.010″ dip in the middle. Would certainly cure the back cutting as the trailing edge would be about half a mil above the work.

Texture is really a product of feed rate and shape of the tool, think of it like threading, if you feed fast then the Vees are more noticable than a fine thread and then reduce it even more you get turning cuts rather than threads.

I found with flycutters, the greater the mass of the fly cutter, the smoother the cut becomes. Some have made flywheels for their spindles to assist in this more constant load cutting. Vernier mills come to mind. The lighter the rigidity of the machine the finer the radius needs to be on the tool to reduce tool deflection. If the tool has too high a rake, it can sometimes actually pull the cutter into the surface a small amount. The advantages of fly cutting is to use a larger area than the size normal mill cutter can make and with less cutting forces.

When you have a mill like BP clone, I worked at a place and we placed another table ontop of the existing tabled. The knee was brought to the correct height and locked solid. The X axis was locked solid too. The Y axis had the gib adjusted firmly but could be moved. The part was moved on the bolt on table that used linear rails for it’s smoothness. It worked remarkably well. We were able to do work that previously needed a fixed bed mill like a Deckle with it’s axis all hanging off the back of the bed.  With the bigger plates being bored , DTI were set up and then the height was corrected with essentially a large bottle jack. I made the alloy wheel tooling on that set up for what was then the Ford alloy wheel plant in Auckland.  Learnt alot about how much things can flex and move, and the lighter the  cutting forces are, the better the end result will be.

You can balance the fly cutter by having provision for two cutters opposite each other that are the same dimensions, but have one a small amount lower than the other. It gives you an option of just changing the height and you have another edge ready to go. If taking cuts deeper than 0.1 , the second cutter will effectively rough the height to that 0.1 or what ever the difference is you choose.  Two were vertical opposite each other, and the other two were on a shallow 30 deg to cover a wider area. Mild steel worked very well for the holder. The first one I made a bit light and used a chunk of high tensile steel and it had a ring happening sometimes.  2nd one was MS and heavier.

The fly cutter itself is easy enough, I have a commercial version that uses the round RPMT inserts that produces a really good surface finish in most materials. It’s also very cheap to operate since the insert can be slightly rotated as the edge dulls or possibly chips. Neils clever work around to remove that table rocking within it’s own clearances due to gravity obviously worked out well.

This is also one area where those with both a vertical and horizontal spindle machine have a clear advantage since that inevitable table rock really doesn’t matter as long as the whole surface is being fly cut. Fixturing something like an automotive engine head so it’s exactly vertical and true to that horizontal spindle would be more difficult. But I still think that given the fairly reasonable costs and the time involved to set it all up and do one or two automotive heads on something with even a horizontal spindle. It just makes more sense to have a professional with the right equipment and the required experience to do it properly. In a commercial situation where the effort and costs can be justified over many many parts, then what he was doing clearly made it worthwhile.