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Harold Hall

Workshop Processes

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Lock the table in both axis as these must not be moved from this point on. From experience, I find it difficult not to instinctively move the table when I should just be rotating the rotary table. My way to avoid this is to remove the hand wheels for both axis as a safety measure.

 

Machining the jaws teeth

Having removed the centre from the spindle fit the milling cutter chuck and with a cutter whose diameter is a little less than half the scroll's pitch. Typically, if the scroll has a pitch of 6mm use a 2.5mm diameter cutter.

 

Fit the two halves of the fence with the inner one against the plug. Fasten the outer fence but leave the inner one just free to slide between outer fence and the plug in the centre of the rotary table. Fit the largest pin in the inner fence and a jaw against that. Using the fence's adjusting facility, set the inner fence so that the grove machined will be in the required place. Fortunately, this position is not critical and a rule dimension will be adequate. Use jaw number one from the chucks normal jaws to provide a value for this dimension.

 

With that done machine the first groove. Unfortunately, with such a small cutter you will probably need to machine to the required depth in two stages, actually this as easy as doing it at one pass. Start with the cutter in a position where it is easiest to fit the jaw, that is with the cutter not in the way, and make the first cut at half the depth of the tooth being made. Lower the cutter to the full depth and make the second cut in the opposite direction. This will leave the cutter in the best place for moving the jaw to the next position. You will need to use the machine's top speed, hopefully in excess of 2000 rpm.

 

With the first grove machined check that the grove made is to requirements and if so remove the pin and move along one pitch on the fence. Reposition the jaw and machine the second groove, repeat until the required number of grooves have been made. With the first jaw's teeth machined remove and fit the second jaw and repeat the process using the middle size pin. Repeat  for the third jaw using the smallest pin,  Photograph 4. This also shows a clamp fitted and resting against the inner fence. The purpose of this it to keep the inner fence against the outer fence when it is being adjusted. This is not shown on Sk. 9.

 

As there is a hole in the centre of the rotary table it would be a disaster if you dropped a pin down this as you would probably have to remove the rotary table to recover it.  This would result in it loosing position. To avoid the possibility make a plug to fit the hole or use a ball of Blue Tack. Advice given from experience I must admit.

Soft Jaws, Making
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