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Vicmarc VM120 Bowl Jaws

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Bodger7

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Has anyone got a set of the VM120 485 bowl jaws (effectively very large Cole jaws)? If so could you tell me what clearance is needed between the spindle centre and the lathe bed to use the jaws effectively please? For example, if a 485 mm diameter bowl is held by the jaws what is the resulting diameter of the jaws when the chuck is tightened around it? My lathe has a 26 cm clearance so it seems to me that it would be touch and go.
Thank you.
 

Duncan A

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Diameter of the jaws when fully open is 520mm, with the outermost button mounting hole on 490mm. Obviously the button size and bowl rim profile will have a bearing on the max size you can hold.
Duncan
 

Bodger7

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Thanks Duncan. At 520mm that would be scraping the lathe bed. The 385 jaws sound like a better/safer option.
 

Duncan A

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Jaw diameter is about 490mm when closed so all you'd need to do is accept that you need to keep your bowls slightly smaller, or of a profile that you could grip them internally. Or just use a plywood disc with some router mat and hold the bowl in place with the tailstock.
What lathe do you have? Mine is a Jet 3520 with a nominal 20" working diameter. I can use the Cole jaws opened up to 510mm jaw diameter, 480mm button mounting diameter - I've just measured it.
Duncan
 

Bodger7

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Hi Duncan. My lathe is a Wivamac DB1000. I have checked the handbook and it specifies a maximum diameter of 520mm or 20.5 inches. Those figures confirm my measurements. I would not be concerned with a restriction on the maximum bowl size but as far as I can see there would be a similar restriction on each of the button settings. So if any button setting was used to its maximum, or close to it, the jaws would be open to their maximum and foul the lathe bed. I have just looked at the Vicmarc site and that says about the VM120 "open from 55mm to 110mm". My interpretation of that (which may be wrong) is that the jaws extended to their maximum add an additional 55mm to the diameter (490+55=545). Presumably after opening the jaws to their full extent they will then be contracted to hold the bowl firmly and I was hoping that that contraction would be sufficient to reduce the diameter below 520mm i.e. the compressed buttons adding less than 35mm to the diameter of the bowl. Is the spacing between the button screw holes sufficient to provide the capacity to use the next size up with the jaws more closed rather than opening the jaws to the maximum on the smaller button setting? (I am not sure that I have explained that very well.)
Thanks for your advice on this problem. I would prefer the 485 jaws but might have to settle for the 385's which would still give a maximum bowl size over 15"
 

marcros

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I imagine that these jaws are not cheap so I would drop vicmarc an email asking exactly what you need to know.
 

Duncan A

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The button mounting holes are at 15mm increments (30mm dia increment)
The chuck jaw travel is 55 / 2 = 27.5mm (Vicmarc), 53mm / 2 = 26.5mm (measured on mine).
This gives a decent overlap.
The button mounting holes are tapped M6 so will accept buttons from Record Power jaws, or home made buttons thus giving further flexibility in sizing overlap.
Hope the attached pics help.
Duncan
OpenJaws.jpg

OpenJawD.jpg

ShutJawD.jpg
 

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Duncan A

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Before I acquired the Vicmarc jaws, I was using jaws that I made out of an old HDF tabletop with an Egyptian scene applied to it. Very cultural!
Worked fine.
 

Bodger7

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Thank you all for your replies. Answering some of them as follows:-
1. Lazarus, I have tried making large Cole jaws and they were not very good. I could not achieve the necessary accuracy for drilling the holes in the plates.
2. A vacuum chuck sounds too complicated and expensive to me. I saw one thread that referred to making a vacuum chuck that was used for a while and then sat unused thereafter.
3. Marcros, I did contact Vicmarc and they suggested that it is possible to shave the larger jaws down to reduce the overall diameter when fully expanded. This is not a solution that appeals to me but I am considering it. Vicmarc agree that I could not use the 485 jaws fully extended on my lathe.
4. Duncan, as previously, your reply was particularly helpful. I couldn't really make out all the photo's but the information accompanying them was very useful. If I understand correctly you are able to use the 485 jaws on your lathe with a 20" working diameter but without full expansion using the largest fixings for the buttons. On any smaller settings there is enough overlap to avoid the need for full expansion of the jaws. Have I got that right?
I am still tempted by the larger jaws but may chicken out and go for the 385's. Thank you all again for your positive input.
 

Duncan A

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Bodger, re No.4, yes you've got it right. The jaws movement is greater than the distance between successive rows of button fixings.
Just be aware that the large jaws whirling around near your arms can be a bit offputting if you regularly use them for holding smaller items - better to have a smaller set. The decision is yours, good luck with it.
Duncan
 
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