A Simple Tramming Ring for the Mill.

[Brobdingnagian]

Yep. 0.125"

Then my guess is you have a bend in your lead screw. As the lead screw turns it applies more pressure on to the side of cross slide nut on one half of a revolution than on the other half hence uneven pressure on the cutter.

[pipeclay]

That question you asked and the figure given relate to the lathes leadscrew,not the crosslide screw which is a different pitch.

[Brobdingnagian]

Sorry I should have said cross slide lead screw pitch... I would have thought they would have the same pitch so the dials would be the same????

[Steamwhisperer]

Wouldn't the leadscrew have just as much effect if not more than the crosslide screw??

Phil

[Ueee]

Josh beat me to it, The Mars does that too......i've never investigated as to why, but i'm pretty sure its cross screw is not bent.

[Anorak Bob]

Concerned that more lathe ills await me I set up a couple of indicators to see if I could measure the undulations. I can't. No discernible needle movement on the 1um Millimess. Doubting the Millimess I ran an unused Compac across the face with the same result. So hopefully one of you blokes can enlighten me as to the cause of the rings.

BT

[Stustoys]

Hi BT,
So what was the pitch of yor cross slide screw?(I'm guessing from PC comment the cross slide isnt 0.125" pitch)


Do you have a 1/10th" or 0.001mm DTI?
I find Dial gauges are much less likely to show up this sort of movement unless VERY rigidly mounted.

But lets face it.... its not going to be much.

Stuart

[Steamwhisperer]

Maybe it's harmonic polishing where the tool has the finest of vibrations and so polishes the work harmonically as it is cutting.

Phil

[Brobdingnagian]

If ya can't measure it with those then it's not problem..

You might be able to measure it if you loosen off the gib and gauge the cross slide. Incidentally what is the pitch of the cross slide lead screw?

[Michael G]

There is a cyclic event that is tied up with the cross slide screw. Bent is probably too strong a word - as I discovered with my micrometer, a slight deviation from straightness is enough to be noticeable (I can't pick up any bend by eye). It could also be something like the bearings on the screw are mounted in or something to do with the power feed perhaps like a gear being slightly off centre (or if manual feeding, a not quite constant rotational speed)

However either the cross slide is able to move around on its gibs (so it may be possible to reduce the marks by tightening up the gibs a little so that the carriage can't move 'sideways') or there is spring in the toolpost (if the traverse speed is not constant the load on the tool varies, allowing the tool to dig in more or less).

Michael

[Anorak Bob]

Hi BT,
So what was the pitch of yor cross slide screw?(I'm guessing from PC comment the cross slide isnt 0.125" pitch)


Do you have a 1/10th" or 0.001mm DTI?
I find Dial gauges are much less likely to show up this sort of movement unless VERY rigidly mounted.

But lets face it.... its not going to be much.

Stuart

007 (Large).JPG

No movement with that either Stu. The cross slide screw is 10tpi.

I had a fiddle with an indicator on the leadscrew of both lathes. The '69 ARL leadscrew has roughly .003" TIR about 300mm from the gearbox. The '58 lathe has double that. The indicator reading off the un-screwcut
section of the leadscrew shows 0.0015" on the ARL and double that again on the older machine.


020 (Large).JPG 019 (Large).JPG

The green lathe vibrates. I haven't yet bolted it to the floor.

BT

[Stustoys]

No movement with that either Stu.

So not much then.

Tempted to suggest a smaller dia stylus ball and setting the DTI up for lots of cosine error...... but really, whats the point?

[pipeclay]

The imperial Hercus should have a pitch of .100",on the crosslide screw,and 2mm on a metric machine.

[Brobdingnagian]

Mike,
I blued up my boy's version of a surface plate and the results show a whisker of distortion. There's continuous contact around the inner surface but a couple of non contact areas opposite one another on the outside. Hopefully not enough non contact to cause a problem with the mag chuck. Fingers crossed.

Sorry I got distracted by the concentric rings.

If I align the non contact area the right way so that it has minimal force, and turn down the force way down on the chuck and block it out it should be ok.

-J

[Brobdingnagian]

here a link to the video

The video is of me checking surface ground 150mmx100mmx55mm cast iron block with Mercer type 44 0.0001" dial indicator for parallel.

No special precautions taken, just carefully cleaning and de-burring the part and the chuck before and after grinding. In fact you can see some marks left on the part by me trying to get it off the mag chuck, the flat surface wrings itself to the chuck and is damn hard to get off without sliding. So Bob, it maybe a good idea to put a couple of lifting points on so I can free it without damaging the surface finish.

-Josh