Collet-style workholding devices, such as collet blocks, offer a number of benefits. Collets automatically center workpieces, an action that reduces setup time by making their center points known locations. Unlike standard vises or three-jaw chucks that provide minimal points of contact with a part, collets provide equal gripping pressure around a part's entire circumference. Expanding collet systems are also available to enable internal gripping of thin-wall parts or delicate materials that might otherwise become distorted using other workholding methods.
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Grouping collet blocks together can enable equipment such as VMCs, HMCs and jig grinders to machine multiple workpieces unattended over long stretches of time. Collet blocks can be oriented horizontally or vertically and can be installed on workholding devices including tombstones, angled fixture plates and rotary trunnion tables. Hardinge, an Elmira, N.Y. manufacturer of machine tools and workholding equipment, offers several collet block models that use standard-sized collets commonly found in many shops, as well as hex-, square- and custom-shaped collets that can hold various non-round workpieces.
The question then becomes: Which style of collet blocks'hydraulically or pneumatically actuated'is most appropriate for a given machining application?
Even though pneumatically actuated collet blocks provide lower clamping force than hydraulic units, many shops prefer to use pneumatic collet blocks because compressed air is often readily available, easy to connect and doesn't require complex plumbing schemes. In fact, a small, individual air compressor will do the job, although filtered air is recommended.
A simple pneumatic arrangement consists of a subplate onto which the collet blocks mount and a control valve(s) for part clamping/unclamping. Depending on application requirements, a single air valve can be used to clamp and unclamp all parts simultaneously or multiple valves can be installed to independently control individual collet blocks or rows of blocks. Select Hardinge collet block models enable users to internally plumb units together using connector bushings. Models that don't use connector bushings must be plumbed externally.
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Hydraulically actuated collet blocks require a hydraulic source, but provide higher clamping forces needed for heavy rotation, tapping, threading or off-center machining work. Hardinge says it offers an inexpensive, air-over-hydraulic pump with accessories for shops that don't have a hydraulic source at the machine. A single two-position, four-way control valve can be used to clamp/unclamp all parts simultaneously. It is also possible to configure multiple valves to control each block or row independently. The control valve(s) mounts on the subplate near the collet blocks and is plumbed to a hydraulic pump located outside the machine.
An optional quick-disconnect system is available for hydraulically actuated collet blocks. This option enables easy preloading of collet blocks with workpieces. Using a quick-disconnect handle with a standard collet block manifold facilitates quick setups because the collet block subplate and pump assemblies are preset and ready to install as needed. However, the collets in a collet block will not maintain their clamped or unclamped position when removed from the manifold unless a check valve is installed in the manifold. In addition, a three-position, four-way control valve mounted outside the machine is required when using the manifold with a check valve to maintain the clamped or unclamped positions with the hydraulic power source disconnected from the subplate. An accumulator is also recommended because it provides a backup reservoir to maintain system pressure if a leak should occur. Accumulators are available in vertical- or horizontal-mount versions and install on the collet block subplate.
Alright... After lots of looking and dinking... I have decided the smartest way for me to do things on my Okuma LC10 is with an air operated chuck of some sort. If I go with air operated 3jaw, I loose some Z work room which isnt good. AS well... they are very spendy from what Im seeing. My max that I need to deal with is 1.625" at the absolute most... and thats even larger than Ill need (really Ill need a max of 1.550") So I started thinking about a 3J or 16C collet chuck and collets. Im not finding an air operated one yet... but the drawtube operated ones were still at .00 or more for my A2-5 spindle...
So, I started thinking... can I build one??? My tolerances are less than most would need, and I seldom work with metal - mostly acrylic plastic - and I have a 6" hyd chuck and 5 collet chuck should I need to deal with harder to cut materials. So I started thinking... that having hardened and ground surfaces might not be a necessity, and all that fun stuff that Im sure the good ones you buy have...
Am I crazy for thinking I could build one on my own? I guess from there... the one thing Im not sure how to handle is applying air at 120-150pis to a rotating mass at up to rpm. Im guessing maybe there are some special bearings? extra seals? I dunno...
Just checking to see if Im completely nuts...
Thanks
Wade
Oh, just so you have a short stat page of what Im needing... Just incase someone has a great idea to share about something I havent thought of trying.
Air Actuated
1.550" min through spindle (use with bar puller)
Fairly short (so it doesnt eat up lots of my Z travel)
RPM capable
A2-5 Spindle mount
size range of material .625" to 1.550"
Tolerances on work piece (ID bore +.005 -.001 and OD shape +/- .020")
Thanks again
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