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10HP motor + rigid ram BP CNC, crazy idea

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  • #16
    I'm going to try an adapter for my mill that holds a spin saw. It does 25,000 rpm variable speed and has a big beefy spindle bearing designed to take side loads. On top of that it is designed to be held by a clamp around the lower spindle bearing. It has a 1/4" built in collet too.
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    • #17
      On the question of air consumption. I looked into air spindles and found that they come in two types - turbine and positive displacement. The turbines will go well beyond 100k rpm, are expensive and use lots of air. The air spindle link I provided is a positive displacement air motor and uses very little air by comparison to a turbine. I don't know the rating, but I would guess of the order of 1 cfm. The downside of these is shorter life and lower max rpm than a turbine. I would compare it to a mini die grinder.

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      • #18
        For me air consumption is not a problem, we have a 15HP rotary screw that put's out something like 58 cfm at 120 psi. I want to be able to use the mills spindle so I can take advantage of the quick change tooling and use multiple tools for complex designs on the CNC. Obviouly each tool requires different RPM and feedrate and I want to control this with G-code.

        At this point I know it can be done, the question is how much will it cost and how long will it take to get it right. Who know I might find it cheaper to redo my mill then sell it for an enclosed machine with a high speed spindle. I'm gonna dig up my other books for the machine and look up the bearing part numbers so I can look for high rpm capable ABEC-7 bearings. The other issue will be cooling and lubrication and these can be addressed, heck if F1 cars can spin 18,000 rpm with a recipcrocating assembly using plain bearings if HAS to be doable with the proper lubrication and heat control using a good ball bearing.

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        • #19
          RSR, Im with you on your last post, if you can keep lube to it and find a way to get rid of the heat (maybe by pumping lube through it) then you shouldnt have a problem with abec-7's...

          There is really no mechanical balance limitations with the rpm that you speak of, like you said its not like the thing has pistons hanging off of it, try double the rpm's of what many of you guys are saying is in the red with con. rods and pistons hanging off of your spindle and your aproaching what a stock honda V-tech shift point is right from the factory, big deal.

          here is where the difference lies --- spindle bearings are pre-loaded, its the pre-load thats the enemy with higher RPM's, double the RPM's and the heat increase is way way over double because if all kinds of factors but ad preload and now it gets serious, find a way to remove this heat and keep fresh lube (and yes maybe thinner lube) and you have the problem solved, will it shorten bearing life? of course it will, if you go by hours of operation the bearing is going through twice as many cycles per second while under the same load, thats one way of looking at it, but the other way is you can achieve close to the same amount of bearing life in how many cycles it will turn before it wears out --- if you supply it with the proper environment to do so...
          To much pre-load --- more heat and wear, not enough preload --- premature bearing failure do to intermittent contact and scuffing.

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          • #20
            Boomer,

            I agree with everything you said. One thing I always need to keep in mind is the cost of my time and the fact that my machining hobby is also a source of income. Let's say I install bearings that last only 25% as long as the originals, the originals are at least 20 years old. Let's say they only last 2 years. On the other hand if I can increase my feedrates as well as improve surface finish I'll be making better parts faster saving time and in the end even if I spend $500-600 on bearings the increased productivity will be well worth it.

            Obviously no one wants to be replacing bearings all the time so I'll definately need to address cooling, lubrication and as you so rightly pointed out (and I overlooked) bearing preloads.

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