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Rotary Table Problem

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larry Phelan30/03/2018 15:07:07
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544 forum posts
17 photos

Some time ago,I sought,and was given advice about correcting an error in my rotary table [the center hole appears to be off by about `5 mm ]

The method advised was to press out the MT center and set the table up on my mill and machine the bore true.So far,so good,but due to an ongoing health problem,this had to go on the back burner. Now that the situation is more stable,I would like to get back to it again,but I cannot recall the exact method,and my memory is no help !

Would I be pressing my luck by asking does anyone remember this question or how to go about it? I have since a friend who has a press to remove the center mt bush.

If anyone can assist,I would be more than thankful.

Martin W30/03/2018 15:18:56
921 forum posts
30 photos

Larry

Would this thread be the page ?

Cheers

Martin

Michael Gilligan30/03/2018 15:21:23
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20289 forum posts
1064 photos

Larry

I think this is 'the question in question' : **LINK**

http://www.model-engineer.co.uk/forums/postings.asp?th=125429

MichaelG.

.

Slow off the mark blush

Edited By Michael Gilligan on 30/03/2018 15:22:10

Tim Stevens30/03/2018 15:50:01
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1622 forum posts

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

larry Phelan30/03/2018 17:28:29
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544 forum posts
17 photos

Lucky,lucky me !!!

My thanks to all who remembered. Yes,this was indeed the thread and I now remember the the advice,but to be sure,to be sure,I will print it out this time!.

As the song says "The old grey mare,she aint what she used to be",neither are my old grey cells ! [I know,"Welcome to the club" ]

Regarding the "Cert" for my table,that appeared to be signed off by someone who had had too much Saki for lunch,it looked like a spider had crawled across the page [something like the note you get from your local GP.]

Again,my thanks to everyone for taking the trouble to respond,it,s things like this which restore my faith in people. Long may it last !

Douglas Johnston30/03/2018 18:13:05
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773 forum posts
34 photos

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

Howard Lewis31/03/2018 18:50:13
6305 forum posts
15 photos

My Vertex HV6 has a 2MT bush in the centre of the table, so if yours also has one, hopefully it can be removed.

Once the table is centred under the spindle of the mill, it can be machined to remove any eccentricity in the bore, as described above. In a better world, the table bore will be concentric, and it is the 2MT bush which has the run out.

In both cases a new 2MT bush can be made, and pressed or Loctited into place.

P S Check the supplied chart stating the plates, turns and holes for each division; not all are there, or accurate. I spent nearly a week finding out, and correcting, the hard way! A long job, but time well spent, one of the errors on mine was for 13 divisions, so maybe that's one place for an initial check.

Howard

larry Phelan31/03/2018 20:31:29
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544 forum posts
17 photos

Hi Howard,

Yes I think I am in the same boat,in that I think it is the bush which is the problem [at least I hope so !]

I know what you mean about the so-called "Chart",mine was/is so far out that it,s little more than a joke,you would not want to depend too much on it. How can they send out stuff like this?. I had to go over and over the whole thing to try and make some sense of it,and then,to find that it was running off ! I hate to think what gears it might have produced.

I am now going to attack it,for better or worse,so watch this space,even if the air is blue at times !

Again,my thanks to all,and it,s nice to know that i am not alone in this.

Neil Wyatt31/03/2018 20:38:40
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19076 forum posts
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www.model-engineer.co.uk/news/article/corrected-dividing-tables-for-vertex-hv6-dividing-head/23123

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