G'day
I normally use a vaccuum chuck to hold bowls while finishing off the foot of a bowl ,but sometimes it just won't work ,as in holding an eccentric bowl , where it needs to be held by the edge .
I have a set of 285mm bowl jaws to suit a VM120 chuck and the biggest eccentric bowl I can hold using my home made extensions, is 280mm . See my previous posting on "bowl jaw extensions" 8/12/13.(sorry I don't know how to make the link).
To get the capacity I wanted, I would have to buy another set of jaws at about $140 and for infrequent usage it was not justified and in any case I like making tools.
I bought some 9mm MDF and cut out the largest disc that I could turn between centres then jambed this between my VL120 chuck with bowl jaws fitted and the live centre and trued it up.I then mounted it in reverse with the chuck on a reversing mandril on the tail stock and the live centre on the headstock . I opened the bowl jaws to their full capacity and used a clamp to make sure the relationship between the jaws and the MDF disc did not change . I also put wedges on the bed to make sure it wouldn't rotate . Then using the jaws as a template,I ran a 5mm drill through the 6mm tapped holes that hold the bowl holding mounts . I chose to use only the maximum and minimum adjustment holes . I then screwed 6mm bolts in through the jaws and into the MDF . The MDF is soft enough that the bolts tapped into it .Actually, when I had a few bolts in and I knew nothing was going to move , I removed the chuck from the lathe and drilled the rest of the holes with it on the bench.
I drew a line down the edges of the jaws then removed the disc from the jaws and cut down the extended lines to separate the four MDF jaws .
I drilled out all the locating holes to 6mm and counter sunk them to take new 6mm bolts and refitted the extensions to the original jaws .So each one is held by four bolts.
With the chuck back on the lathe , I marked the positions for the holding mounts ,removed them again and drilled the 6mm mounting holes then refitted them and fitted the mounting posts with nuts and washers on the back.
This now increases my capacity up to 410 mm .
A warning . Although I think this modification is quite safe , I am sure Vicmarc would not approve, so if anyone wants to copy my method they must maketheir own judgement.
Ted
I normally use a vaccuum chuck to hold bowls while finishing off the foot of a bowl ,but sometimes it just won't work ,as in holding an eccentric bowl , where it needs to be held by the edge .
I have a set of 285mm bowl jaws to suit a VM120 chuck and the biggest eccentric bowl I can hold using my home made extensions, is 280mm . See my previous posting on "bowl jaw extensions" 8/12/13.(sorry I don't know how to make the link).
To get the capacity I wanted, I would have to buy another set of jaws at about $140 and for infrequent usage it was not justified and in any case I like making tools.
I bought some 9mm MDF and cut out the largest disc that I could turn between centres then jambed this between my VL120 chuck with bowl jaws fitted and the live centre and trued it up.I then mounted it in reverse with the chuck on a reversing mandril on the tail stock and the live centre on the headstock . I opened the bowl jaws to their full capacity and used a clamp to make sure the relationship between the jaws and the MDF disc did not change . I also put wedges on the bed to make sure it wouldn't rotate . Then using the jaws as a template,I ran a 5mm drill through the 6mm tapped holes that hold the bowl holding mounts . I chose to use only the maximum and minimum adjustment holes . I then screwed 6mm bolts in through the jaws and into the MDF . The MDF is soft enough that the bolts tapped into it .Actually, when I had a few bolts in and I knew nothing was going to move , I removed the chuck from the lathe and drilled the rest of the holes with it on the bench.
I drew a line down the edges of the jaws then removed the disc from the jaws and cut down the extended lines to separate the four MDF jaws .
I drilled out all the locating holes to 6mm and counter sunk them to take new 6mm bolts and refitted the extensions to the original jaws .So each one is held by four bolts.
With the chuck back on the lathe , I marked the positions for the holding mounts ,removed them again and drilled the 6mm mounting holes then refitted them and fitted the mounting posts with nuts and washers on the back.
This now increases my capacity up to 410 mm .
A warning . Although I think this modification is quite safe , I am sure Vicmarc would not approve, so if anyone wants to copy my method they must maketheir own judgement.
Ted
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