Larry

Would this thread be the page ?

Cheers

Martin

I guess that you have a separate bush with the taper inside it, and you will need to make a collar to fit around the taper fitting and into the enlarged hole. There is a complication with this problem – aligning the boring head exactly with where the centre of your rotary table ought to be. This is what I would do:

Set up the RT on the vertical mill (having checked that it is trammed properly vertical), and ensure that it is well clamped in place and cannot move relative to the mill table. Fit to the mill a new end-mill cutter of a modest size – perhaps 6mm or 8mm. Position the table so that the cutter is about central in the fore and aft sense (the Y direction) and just clear of the bush hole in the X direction (ie over to one side). Set the cutter a few mm (3mm, perhaps) down into the hole. Lock up every adjustment except the X feed. Start the mill, and slowly wind the rotary table handle so that the movement is towards the cutting edge of the cutter. As you rotate the table, it may start to cut, as it reaches the part which is eccentric towards the centre. At this point it may help to give it a squirt of cutting oil, and to do this again at regular intervals throughout. Unless, of course, you are confident that the rotary table is a fairly soft cast iron, and the cutter is well able to cope dry. Continue steadily rotating the table handle until you are past the original starting point again. With the cutter rotating, move the mill table so that the cutter takes a small cut – perhaps 0.5mm maximum – and lock it. Repeat the same rotation operation, right round and back past the starting point again. Unless your central hole is wildly out, this should cause the cutter to remove metal all the way round the hole and exactly concentric with the table rotation. Now you are well on the way to success. Next you need to lower the cutter to take another cut, again with the cutter rotating as you lower it, lock the head position, and steadily turn the table to take another ring of material out. Continue this process of lowering the head and rotating the table until you break through below it. Finally, clean up the new surface of any minute steps by taking the merest smidgeon of a further cut with the whole length of the cutter in contact. When the rotary table has completed its final turn, you should have a concentric, smooth hole, ready to take the new bush (which you will also have to make, ensuring that the inside and outside of the bush are both turned, bored etc, without moving the bush in the chuck – ie keeping that concentric too). It may be better to do the rotating cutting process until a rather thicker circle of metal has been removed, so that the new bush is strong enough to stand being pressed into place. And perhaps use the same process to skim the inside of the new bush to the size for the taper fitting after it is pressed into place.

Exactly how big a ring of metal each turn removes depends on the size of your mill – it should not cause any shuddering or vibration, so if it does seem to suffer in this way, take smaller slices and take your time.

I am sure that others in our group will have additional helpful comments, and perhaps even their own alternatives.

Regards, Tim

Edited By Tim Stevens on 30/03/2018 15:53:24

The morse taper in the centre of the bush may not be needed and if that is the case there is no reason to have a new bush at all. Just true up the centre of the table and use the new enlarged centre hole to locate any part or chuck etc. I don't think I have ever really used the morse taper on my rotary table. I pulled out the central bush with taper not long after I bought the table and made a few adaptors over the years to locate things.

Doug