Fly Cutting again

[Alan RawlinsParticipant @alanrawlins60482]

I have made myself a Fly cutter in which the HSS tool cutter sweeps a diameter of 65mm.

The piece of aluminium I am cutting is 75mm x 20mm The surface finish is extremely good, but by the time the cutter has cut a length of 65mm, the swept diameter of the cutting tool, the tool starts to cut into the aluminium at its starting point, and by the time it has finished cutting the full length of 75mm it has cut 10mm in from its starting point below the surface of the first cut by about 004".

I can only figure out that this is because the tool tip is not exactly parallel to the the face of the aluminium. I used a fine 002" shim to set it correctly but obviously it wasn't set correctly.

How does every one else set up a the work piece to get it exactly parallel to the cutting edge of the tool?

Please forgive the use of metric and imperial sizes as I have a mixture of tools like feeler gauges all being in imperial.

[Alan RawlinsParticipant @alanrawlins60482]

[JasonBModerator @jasonb]

Its either your tool being pushed off the work by the first sweep and the back sweep taking a bit more off as it springs back.

More likely is your mill is out of "tram" basically the head is tilted slightly to one side. Easiest way to see if this is the problem is make the cut in the opposite direction, if it does not cut on the back pass then you need to adjust your mill.

[Bob Brown 1Participant @bobbrown1]

I agree with Jason, larger diameter cutters will show any out of "tram" I like to see both cutting arcs in the finish that way I know the adjustments on the mill are correct. With a large diameter cutter and the mill not aligned you will not get a flat face as it will cut a slight hollow.

Bob

[VicParticipant @vic]

It does indeed sound like the head of your mill is not perpendicular to the table. You need to correct this. Once done a flycutter will produce a "cross hatch" effect on the workpiece. This effect is not actually something I like (the look of) and many of the parts I make are smaller than the radius of my fly cutter. I can therefore in many cases stop cutting before the axis of the fly cutter goes over the trailing edge of the work and this gives a superior finish. I should add that many folks have a problem imagining this and make all kinds of wrong assumptions! Once you experiment though you'll see what I mean.

[Capstan SpeakingParticipant @capstanspeaking95294]

It is very difficult to keep a perfect cut in such circumstances. Flexing and even slight play in the bearings will cause a second cut at the trailing edge.

Actually a tiny difference is not a problem. You could use the lower side to feed in from or carry on the cut so the trailing edge passes right over it.

[Neil WyattModerator @neilwyatt]

A 0.004" difference is excessive, it does sound like the mill is out of tram. If the workpiece was angled it wouldn't make any difference as you are creating a new cut surface.

Neil

[Alan RawlinsParticipant @alanrawlins60482]

Hi everyone, I should have made it clear that I am fly cutting on a lathe>

[John HaineParticipant @johnhaine32865]

A lathe is deliberately made very slightly out of tram, the headstock axis should be angled slightly towards the operator, so a faced end is very slightly concave rather than convex. This might explain what you are finding assuming you are feeding with the cross slide.

[Alan RawlinsParticipant @alanrawlins60482]

Thanks John. I am using the cross slide to feed to the cutter. If my lathe is as you say, can it be sorted or not?

[John HaineParticipant @johnhaine32865]

Which way were you feeding, towards or away from the lathe axis?

If the lathe alignment is causing the issue, normally it can't be changed as it's built in to the structure.

[Alan RawlinsParticipant @alanrawlins60482]

Hi John, I have tried both ways and it does it both ways unfortunately.

[Neil WyattModerator @neilwyatt]

> it does it both ways

Then it may be loose gibs.

Neil

[Alan RawlinsParticipant @alanrawlins60482]

Hi Neil, I will check them again but I did adjust them coincidentally only last week and I thought I may have over tightened them as I couldn't turn the feed handle with one hand, I had to use both hands. This may seam I have over tightened them but I have an arm problem that means I can't turn/twist things like screw drivers as well as I used to do.

Just as after thought, could it be anything to do with the cutting tool? The tool is giving me a great finish on aluminium tho'.

[BazyleParticipant @bazyle]

How deep is the overlapping cut. It may only be tenths and still be visible but can be removed with a quick lapping.

Even with the gibs done up there will be a small clearance and the cross-slide will cant or twist about a vertical axis. If the friction drag is from the tailstock side of the slide it will twist clockwise when feeding in and anticlockwise when feeding out thus giving your problem both ways. To counteract this put a bar along the slide and use a spring or weight to apply a force in the necessary direction.

[JasonBModerator @jasonb]

Posted by Alan Rawlins on 15/06/2015 07:58:23:

Just as after thought, could it be anything to do with the cutting tool? The tool is giving me a great finish on aluminium tho'.

That was the other fault I suggested early on, if the back edge of the tool is not clearing the cut and rubbing it will tend to push the cutting edge away from the work, by the time the overlapping cut happens the tool will have sprung back and take a second slightly deeper cut.

0.004" is too much for the usual machining marks Baz mentions above.

[Ian S CParticipant @iansc]

The way I do it(I'm self taught), is to pass the tool completely across the piece of work, and when finishing bring it back again at the same setting at least once. On todays bit of cast iron the finishing consisted of three passes left to right, then twq passes back and forth, I'll make a mess of it tomorrow.

Ian S C

[Alan RawlinsParticipant @alanrawlins60482]

Hi Ian, do I take it from your comments that you are have same problem that am having

[Ian S CParticipant @iansc]

Probably not, my old mill is fairly beat up, I don't think that I know enough about the machine, I bought it before I started into engineering, I was wood turning at the time, and needed a drill press.

Ian S C

[Author]

Posts