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| awemawson:
I managed to get my hands on a very nice Pratt Burnerd Super Precision MANUAL 200 mm chuck (9210-02005) with a plain back end and face mounting, so I thought if I could get a suitable A2-6 chuck adaptor plate of the 'semi-finished' variety I could turn the required 160 mm register on it and mount it up for those quick and easy one off jobs. I would need to incorporate some way of blanking off the hydraulic open & close lines that emerge at the spindle nose otherwise not only would oil go everywhere, but the PLC wouldn't allow the spindle to turn with no clamping pressure registered. In the event the backplate supplier hadn't got the semi finished backplate but he DID have a fully finished one all ready to go. OK I parted with one of my few remaining limbs and ordered it. When it turned up it fitted the chuck beautifully, a lovely bit of Polish (Bison) machining, but the spindle end, although it had the correct A2-6 taper and bolt holes, it wouldn't actually engage far enough to fit. The original hydraulic chuck had a boss projecting about 9 mm whereas the adaptor boss was only 1.2 mm - argh ! Speaking to Ian at Rotorgrip who supplied the back plate and exchanging pictures it dawned on him that there was a extra shroud surrounding the spindle - removing that all was sweetness and light and it fitted like a glove. I think the shroud, which is a very heavy chunk of turned stainless steel, was probably to eliminate a swarf trap caused by the long original boss. But I still had to stop that hydraulic oil somehow. Investigating the plumbing soon showed me that the two flexible hoses for open and close were routed to the rear of the spindle and fixed by easily removed conical fittings. As it happens I already had the proper male and female 'stop ends' for this range of fittings left over from my long gone JCB 3CX, so blanking them off and tying them up out of the way was easy. OK chuck fitted, tightened down and a few tentative spin ups and downs performed to check it didn't fly off, then a spin test at 2000 rpm and nothing flew off - phew. This chuck will be handy making the collet chuck adaptor, but I need to make a chuck key with a sliding bar as a standard one is fouled by the lathe tin work. |
| rklopp:
Did you have a part in the chuck when you spun it up? Do not spin up a scroll chuck with nothing chucked unless you want yourself or a bystander to eat a jaw sandwich. The scroll’s inertia can activate the jaws on heavy acceleration or braking. I’ve seen it happen. Sent from my iPhone using Tapatalk |
| awemawson:
Also the clamping force decreases markedly as the RPM increases. I've a Pratt Burnerd clamping force meter that measures the squash and I/R transmits it to a second part. I was amazed how great the effect is due to centrifugal outward forces on the jaws. |
| awemawson:
So having acquired all those soft jaws I landed myself with a bit of a storage problem as they were very much in the way in their crate and pretty immovable. I've been trying to find ex factory stores drawer units on the second hand market but it seems that they've gone trendy with prices through the roof. So as something had to be done I bought a pair of brand new five drawer roller cabinets on eBay. Despite being advertised as coming from London they come from Germany :scratch: Anyway they came, I assembled them and have got the jaws at least vaguely sorted and they are now at least moveable as the cabinets are on castors. So now I can get back to sorting out that chuck adaptor ! Have some boring pictures of drawers ! |
| awemawson:
Last night I had a flash of inspiration. If I made an 'insert' in the centre of the adaptor that had the drilling for the hydraulic passageways, not only would it be far easier to make eliminating very long and slender drilled holes, it would mean if I cocked it up I'd only lost a relatively small chunk of steel not the major chunk. It could still seal by squashing O rings against the chuck face and the spindle nose, and could be located by a pin or a set screw. Drawing it up this morning I found to my chagrin that if it was a large enough diameter to encompass the O ring locations, then it clashed with the locator hole on the nose so very sadly was a none starter. Then I thought, OK, eliminate the long drilled holes by milling a deep groove between the ports that need joining, mill another groove around the first to take an O ring laid in in an oval pattern and again sealed by squashing against the spindle nose. I've been kicking that around all afternoon on Autocad, and try as I might cannot generate sufficient clearance using the current hydraulic port size of 6 mm and the current O ring thickness of 2.5 mm cord. I can possibly marginally reduce the port size, it will slow down chuck operation but would work, and I could possibly reduce the O ring cord size and stll get a seal - it's working at about 500 PSI so not enormous by hydraulic standards. I need to go away from it and cogitate as my head is spinning! :coffee: |
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