Vertical slide

[Gary MagowanParticipant @garymagowan]

I hope someone can help me to solve aproblem i have. I am using a Myford swivelling vertical slide to mill the dovetail on Harold Hall's design for a grinding rest. I have clamped a small angle plate to the slide and clamped the workpiece to the angle plate. everything has been clocked vertical but when I cut the dovetail it is not flat. There is a 10 thou hollow in the middle. Inj order to machine this face I am using the full travel of the slide and at the bottom of the travel is where the eror seems to be maximum. There is no play in the slide and I have checked the vertical sufaces of the slide and workpiece and both are accurate. Has anyone got any suggestions as to what may be the problem?

[Gary MagowanParticipant @garymagowan]

Problem milling a flat surface

[Paul LousickParticipant @paullousick59116]

Hi Gary,

Perhaps your setup of clamping workpiece to angle plate and then to the slide is flexing under load ? Can you post a photo so we can better understand your set-up ?

Paul.

[IanTParticipant @iant]

I have an image in my own mind of how you have set this up Gary – but a photo might help.

I cannot give you a simple "It's this…" answer but clearly if the guide surfaces are linear – then movement in either the cutter or work piece is occurring.

From what you say, I don't think I'd look first at tool deflection. It seems to me most likely that the work is able to move slightly at each end of the work travel, resulting in a deeper cut in the middle of the work. In other words the cutter is unable to apply quite the same force at the ends of the work piece.

I've had something similar happen when milling long work held centrally on the vertical slide. I was able to use adjustable 'hold-ups' (e.g. small screw jacks) at each end which helped considerably. They needed to be reset after each movement of the vertical slide. Whether you can use this in your case – I don't know.

Otherwise – is it possible that there is "rock" in your vertical slide (e.g. the gib isn't tight enough – or you are not locking the slide before the cut?

Regards

IanT

[Nigel McBurney 1Participant @nigelmcburney1]

If everything is square and true ,I assume prior to fitting the angle plate and workpiece,then check the angle plate to ensure that when it is clamped it is not distorting the vertical slide table ,then check the work piece,clamping it tight could also distort the plate / slide. It can be surprising how easy it is to distort any machine table when clamping workpieces which are not flat,the work can be stiffer than the table so the table distorts rather than the work.I would rather use the lathe cross slide to feed the work and the vertical slide for work height adjustment.

[DMBParticipant @dmb]

Hi Gary,
Nobody so far has mentioned on this thread anything about how are you holding the milling cutter? Not in the 3 jaw, I hope. If cutter has a screwed shank it should be screwed into a proper milling chuck. If it has a plain shank with a flat then use one of those alternative “chucks” and do up tight, side screw on the flat. You must also use a drawbar to prevent holder from vibrating loose especially as its almost certainly a Morse Taper.
NOTHING ELSE WILL DO.
No drill chucks, no lathe chucks no matter how many jaws they have.
I am thinking that maybe the cutter is moving a small amount, if its in the 3 jaw and causing your problem.
Rgds.,
John.

[DMBParticipant @dmb]

Nigel,
I am sure that you are aware of the problem with using any lathe to create flat surfaces in that they are manufactured with the cross slides slightly out of square.
Rgds.,
John.

[Ady1Participant @ady1]

I was never very happy with "flat" surfaces on a lathe and bought a shaper

even a well done simple facing job had issues, which were compounded if I tried to say, make a square block, or a "flat plate"

For me lathes do "round stuff" well and shapers do "flat stuff" well

Edited By Ady1 on 06/08/2015 10:21:54

[Gary MagowanParticipant @garymagowan]

Thanks for your replies. I have checked all surfaces and they appear to be true. the cutter is held in a collet using a draw bar. There was less than a thou' runout on the edge of the angle plate, part or slide before machining.

Paul these photos show the setup.

[David Clark 13Participant @davidclark13]

Try without the angle plate. You should be able to turn the vertical slide to mount the plate on the correct angle.

[CirclipParticipant @circlip]

It should also allow you to turn the clamp plates the right way round and lower the back packing.

Regards Ian.

[HopperParticipant @hopper]

+1 on clamp the job directly to the slide table. Seems like a lot of overhang with that angle plate.

[Gary MagowanParticipant @garymagowan]

Thanks everyone for your suggestions. I have, as David Clark suggested, eliminated the angle plate form the setup and although I have ended up with what I originally thought would be a risky setup due to the overhang at the bottom of the slide, this has been successful. maximum depth of cut taken was 9 thou' .

Thanks again for your help.

Regards, Gary

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