X and Y references on milling table

Joe Pie rather neatly puts X and & reference bars on his rotary table so he can accurately move the part around (adjustable parallels and stuff) and that seems like a good idea.

However, his table has six T slots which makes bolting the reference bars down fairly easy. Mine has four and the slots in no way line up with X and Y on the mill. This appears to be by design, though I have no idea why...

What I thought I could do is to drill and tap a set of M6 holes, effectively making the top of the table into a fixture plate. Possibly also ream for some pins to set X and Y accurately.

The table is an 8 inch and I think the top is probably between 15 and 20mm deep. There are some accurate keys underneath the table so I can be sure of always setting it down accurately on the mill.

Are there any reasons why this is a bad idea or any suggestions for a better approach?

Iain

You could make a sub table with as many holes etc as you like.

Having a table where the 0-360 scale can be moved saves any problems getting the slots or an edge of a part aligned to 0 or 90 (X or y)

That the slots do not align with your mill's long and cross-travels is probably more by chance than design, and while nice to have that symmetry it is not essential.

One option, at cost of some headroom, is to fit the rotary table to a sub-plate made to give that alignment.

Would it be true to say that the rotary table has 360 degree graduations around its perimeter?

Would it also be true to say that there is a fiducial indicator somewhere on the body of the table that registers the passing of these graduations as the table is rotated?

If so, align two of the slots parallel to the X-axis and remove and refix the fiducial indicator such that it reads zero in this position.

I like the idea of a subplate, though it's not something I can do right at the moment.

Sadly, the indications are engraved in the table top and can't be moved relative to it. If I align the T slots X-Y, the 0 degree marker disappears under the table clamp!

Iain

Surely there must be some position where the zero is visible and the slots are aligned with at least one axis. At this point add your own fiducial indicator plate where the zero is, as suggested by DC31k

Martin C

When I'm using the Vertex one with it's fixed 0-360 scale I'll often just put a bit of masking tape where it suits and mark a line against the Zero,