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Post by classicsteve on Apr 12, 2009 12:07:42 GMT
I am thinking of buying a rotary table for my Centec 2A - but prices vary over a wide range. Worm wheel ratios vary too. Centec table width is only 4.25" so maybe a 4" rotary table is all I should consider. Headroom is a bit short so I don't want anything hi-rise !
Anyone got any advice (e.g. what to avoid) ? Is one type more robust than another ? Is there any point in paying extra for indexing when you can rotate it to any angle and lock it ? Are all types suitable for milling while rotating - as milling arcs is usually when I want one of these.
Steve
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Post by AndrewP on Apr 12, 2009 21:58:41 GMT
I've got a 3" Garvin which is a joke, the gear that meshes (sort of) with the worm wasn't fastened to the table when it arrived - it is pinned now but the whole thing is sloppy.
The 6" Soba which probably came from Chronos, on offer with the tailstock and dividing head, is a joy - smooth, precise (to me anyway) and if I can get it under the head on my Sieg X1 then it should be fine on a Centec. The vertical mode fixing slots are 7/8 long at 4 1/2" centres, two holes on centreline for horizontal fixing.
Andy
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steam4ian
Elder Statesman
One good turn deserves another
Posts: 2,069
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Post by steam4ian on Apr 12, 2009 23:01:01 GMT
G'day Steve
I am now the owner of two 4" tables. The first was 36:1, cheap, basic and just OK, cost about AUD200. I bought it on Ebay at what I thought was a reasonable price after having discussed an alternative with an Ozzie tooling supplier.
A few months after receiving the first RT I got a call from the tooling supplier saying they now had the model I originally wanted in stock at a special price; was I interested? There was some oblique implication that I may have ordered the table. At the time I had more money than sense and I am also committed to keeping local sellers profitable within reason. (Means they are there when you need them). So I ordered the RT together with indexing attachments. Overall cost about AUD400.
The second table is a SOBA 90:1 and the quality, although probably not tool room, far exceeds that of the other, smooooooth.
I have an X2 mill and 4" just fits. Remember you may want to put a chuck on it so together with the backing plate you loose a lot of height. I have designed up some jaws to use the slots in the table but they are filed with the round tuit at the moment.
Regards
Ian
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Post by 02jcole on Apr 13, 2009 21:16:30 GMT
I've got a 6" vertex rotary table and there is too much play in the worm drive for maching large radii such as expansion links, the cutter tends to grab the workpiece and chew it up  James. |
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Post by Deleted on Apr 14, 2009 7:22:33 GMT
James. Don't blame the tooling! I have a Vertex rotary table and you may find more satisfactory results if you adopt/try the following: This advice applies to any moving workpiece, whatever the perceived quality of the tooling. 1. Never, ever, climb mill unless you are desperate! Rotate the table against the cutting blade direction. 2. There are two clamps holding the table down: tighten these when milling, but not enough to prevent you turning the actuator. For example, these expansion links were machined quite easily using the approach described above. There was no chatter even though the workpiece was being held 'outboard' of the table. Outside Radius  Inside Radius  |
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Post by classicsteve on Apr 14, 2009 14:42:42 GMT
OK, so it looks like a 90:1 worm is the thing to go for.
Having bimbled around cyberspace I see the main offerings are Vertex and Soba,Shoba,Shobha (all three spellings seen on the Chronos website). It seems these are Indian - the range is Soba engineering tools, made by Shobha Industries.
Although I have a 4" table, I have heard that to get sufficient space to clamp things down, a 6" RT might be better. Though this loses me an inch of headroom if I use it as a vertical table.
And then there is using it properly - it sounds like having table clamps capable of 'half-locked' and that stay at the same level of bite as the table is rotated, could be important. Or should the worm being doing this if correctly adjusted ?
At least it is getting narrowed down. Interesting stuff.
Steve
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Post by Deleted on Apr 14, 2009 15:03:38 GMT
Steve. Just to add a little to my earlier post, if you already have a 4" table, especially if it is Vertex like mine, then you probably have the capability to do 95% of the machining jobs required of a small loco (and some larger ones!). You will probably find the same problems on a 6" version, and lose valuable headroom at the same time. If you look back on this site there have been a number of posts talking about lack of headroom restricting activity.
Worms and wheels need clearance to operate, and lightweight kit needs firm location and workholding, so if you want to do some serious dividing such as gearcutting then I suggest you invest 40 quid in the Vertex dividing discs, when all will be sweetness and light - providing you do the clamps up each time!
Regards
JB
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Post by classicsteve on Apr 14, 2009 16:29:02 GMT
I realised the moment I read it that my note was ambiguous. The 4" table I referred to is the width of the milling table, I don't have a rotary table yet, but I do have a home grown dividing head.
It looks like these rotary table people are trying to put the dividing head people out of business, by being both things at once.
Steve
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Post by classicsteve on Apr 16, 2009 10:35:27 GMT
An interesting story is emerging - it seems that the makers of the cheaper tables (e.g. in India, China, and Taiwan) are all being pushed to lower and lower prices by the big resellers (esp in the US) and as a result the various manufacturers are cutting corners, like dropping back to plain bearings.
This means that new tables might not be as nice and smooth as the ones you already have.
Added to the budget table list now are ArcEuroTrade's 72:1 tables - but again they actually modify them to add better bearings for their CNC fitted tables. Good people there IMHO.
Steve
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