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Harold Hall

 

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Workshop Processes

Ratio

Tables are made in a range of worm wheel ratios so if you have a preference do check the specifications carefully, though tables of 150mm diameter and above  appear to have largely standardised on a ratio of 90:1. Ratios of 60:1 and 40:1 are also available, mostly in the smaller sizes.

 

Above it was mentioned that the dividing plates for your dividing head will likely also fit your rotary table. As most dividing heads have a ratio of 40:1, your 90:1 rotary table will provide a few extra divisions not available with the dividing head.

 

Disengaging the worm wheel

Many rotary tables provide the facility to disengage the worm from the worm wheel enabling the table to be rotated freely. Just how useful this is is debatable, but as the periphery of the table will be calibrated in degree's one could use these for simple tasks rather than counting turns of the hand wheel. Placing say four holes on a PCD would be a typical example.

 

Table locks and end stops

Having positioned your workpiece for the machining to take place, for some tasks the table should be locked rather than relying on the worm wheel engagement to hold it in place. This is because even the slightest backlash may result in the workpiece oscillating with at best a poor surface finish and at worst  a spoilt component or a broken cutter. An example where table locks would be essential is the machining of the large hexagon as seen in Photograph 4. Fortunately, all rotary tables are provided with table locks which is quite the reverse when the provision of end stops is considered.

 

When milling closed slots on the milling machine I always set the table stops to avoid working to dial readings as the cutter is progressively lowered and the cutter moved from end to end. This I would find a very useful provision for similar reasons on a rotary table, unfortunately though, it would appear not to be available, certainly not on the smaller sizes likely to find a place in the home workshop.

 

Using the rotary table.

When carrying out tasks on the milling machine, 99% of the problem is in mounting the workpiece and placing this in the correct position relative to the cutter being used. As I have said on occasions, removing the metal is easy. This is no less the case when using a rotary table.

Rotary Table, using Keats angle to secure workpiece
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