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10HP motor + rigid ram BP CNC, crazy idea

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  • rsr911
    replied
    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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  • A.K. Boomer
    replied
    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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  • rsr911
    replied
    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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  • Bruce Griffing
    replied
    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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  • Evan
    replied
    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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  • snakebit95
    replied
    Originally posted by Bruce Griffing
    If you need higher speed than your mill will provide, but need it only now and then, you might consider one of these. I use it for drilling PC boards.

    http://www.macrotechnologies.com/hig...r_spindles.htm
    Bruce,
    I have looked at the air spindles in the past, and they always have extremely high CFM air requirements. I looked on the website you posted, but could not find any volume requirements. They only list a pressure range. Do you have any idea how much air these spindles use?

    Just to let you know, I also have a Boss 6 machine in the retrofit stage and would like to have a high-speed spindle option too; without toasting the stock bearings.

    Thanks,
    Wayne

    Leave a comment:


  • rsr911
    replied
    Originally posted by Timleech
    I have a VFD on my Boss Series I, it'll go to about 25% above normal top speed, after that the spindle gets warm pretty fast.

    Tim

    Thanks Tim, I assumed that would be the case with stock bearings. It also ties into what the spindle reconditioner told me as 5000 is about 25% more than my machines 4200 rpm max. My plan would involve good high speed bearings and extra lubrication.

    I've often wondered about wood routers, 15,000 or so rpm. I guess the motor's fan keeps the bearings cool.

    As for the air spindle that was recommended by the spindle conditioner but defeats my purpose of wanting to control spindle speed directly with G-code or Mach 3. I've got a month or two before I'll have enough inventory to take the mill apart so I'll see what's available for bearings at that time.

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  • Bruce Griffing
    replied
    If you need higher speed than your mill will provide, but need it only now and then, you might consider one of these. I use it for drilling PC boards.

    http://www.macrotechnologies.com/hig...r_spindles.htm

    Leave a comment:


  • Timleech
    replied
    I have a VFD on my Boss Series I, it'll go to about 25% above normal top speed, after that the spindle gets warm pretty fast.

    Tim

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  • rsr911
    replied
    I heard back from a spindle reconditioner today, the bearings in my head are good for about 5000rpm. An upgrade to higher RPM capable bearings is possible and spindle precision balancing is recommended. According to the recondioner my head should have an ABEC-7 lower bearing on the bottom and a regular bearing up top. Both would need to be replaced with high RPM ABEC-7 bearings and oiling might need to be addressed. As expected the increased speed would bring increased wear.

    I think I'll pursue this a little farther before giving up. As I'll need to disassemble the head to ditch the reeve's drive anyaway I figure I can check bearing availability at that time.

    Now to get all these parts done so I can tear the mill apart.......

    Leave a comment:


  • rsr911
    replied
    Thanks Rich,

    Like I said the 10hp is just a motor I have lying around that I could fit to the mill with some work. You did touch on what I figure the key problem is and that is heat. I also have assumed the existing bearings won't take the higher rpm but I won't know unless I get part numbers off of them or if someone here knows the part numbers. A polyvee or cog belt is definately in the plans as I don't much care for the guesswork of the reeves drive and I want to directly control spindle rpm with software a speed increase would just be a nice added bonus. I'm leary of adding an increaser in that I think it will put more lateral strain on the spindle as well as be less rigid, as it is I prefer to run most of my programs in the upper 2" of Z travel which is the quill on the bridgys. I know this is doable it's just a question of how much cost as at some point I'd have to ask myself if it wouldn't be better long term to just save for a mill with the features I want. For example I've got a rather specific wheel I'd like to reproduce in sizes never originally available like 17" and 18". The current mill makes this impossible unless I had a CNC rotary table so I could index into the work envelope.

    My biggest problem is time as my shop is located at work and I have a family that wants me at home. I just finished a fixture for one of the items I make that makes 4 sets of parts rather than one, the run time is 3 hours so I can go home for dinner and come back later to cleanup. I'm also constantly coming up with other items that I can make and sell so faster cycle times would be great. Heck I've even considered another Boss 5 so I could double production but that requres more space which I won't have until I move the shop into the building next door to the current building and that's at least a year away.

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  • Rich Carlstedt
    replied
    I don't disagree with your thoughts on dumping the Reeves drive.
    The mill will be much quieter with a direct drive, or poly V drive.
    The 10 HP may be over kill since VFD's increase torque through a motor feedback mechanism that add power when the motor runs below a freqency setting. I think what you are saying is that you want to run a 3 to 1 increase in pulley size, but that would still give you the effective torque of a 3 HP motor at the spindle. don't forget the Reevs drive takes about 2 Hp away from the spindle now, so you gain that.
    Rich

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  • Rich Carlstedt
    replied
    John is right, Its a bad idea, because your bearings will not hold up to the higher RPM.
    You do not look at precision grade (ie 7) as a means of determining RPM.
    In plain English, All bearings have a life. This life is DIRECTLY related to speed, no ifs, and,s or buts. The faster you turn, the shorter the life.
    The bearing "ways" can only survive so many cycles. the faster, the shorter the life, but it is not linear !
    The speed rating is based on surface feet per minite that the bearing can turn and is in many bearing handbooks.
    The grade 7 bearings (2mm207DUL) in my CNC headstock are rated for 3,000 rpm,even though the mill can do 4,000. The 4,000 is in Red..signifying that this speed reduces my bearing life.
    Lubrication makes heat.. when a bearing is going to run fast, you need to "lighten" the lubrication...believe it or not. High speed spindles are many times lubed with a oil spray mist. The grease in your bearing will overheat the bearing in short order if you try to run over the 3 or 4 k max.
    Check the speed rating of your bearings before engaging in such a venture.
    Or, do what John suggested as the easy way.

    I find it interesting...Was just at the International Machine Tool Show in Chicago last week...among many things, I saw more "Spindle Rebuilders" there , then in my whole earlier life..you can imagine that all this is the result from the High Speed work that the new mills are doing.. adding to maintenace too!

    There are high speed bearings out there.. but you just don't drop them in,
    especially at the prices they charge.
    Rich

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  • rsr911
    replied
    Originally posted by John Stevenson
    Christian,
    I personally think it's a bad idea and that the spindle just isn't built for this type of work....
    .....So far i have only used the 4:1 head but it's been very good and certainly speeded the jobs up.

    .
    In your opinion why is it a bad idea? If it's bearings that should be easy enough to address or is it spindle balance? Lubrication could also be addressed. I am looking for reasons both for or against the idea but I need to know those reasons. Perhaps there is an issue I'm totally overlooking. My problem with an increaser is the lack of torque I'll have if I eliminate or lock the reeves drive and control speed with a VFD, this would be exaggerated with an increaser. I'm not limited to using the 10hp motor I have, there is room in the budget for a smaller motor if you think it's too much hp for the spindle. My next step is to contact spindle reconditioners for there professional advice. My thing is the mill is in fantastic shape with perfect ways and a flawless table, now if I could get an enclosed VMC in similar mechanical condition with at least a 20x20 XY work envelop on the cheap then this machine would be for sale in a heartbeat. Since those type machines usually command more money than I'm willing to spend I figure it's cheaper to modify what I have. My spindle runs dead smooth at it's 4200rpm max.

    Things I'd change on the Boss 5 besides the controls update?
    1) spindle speed
    2) servos rather than steppers
    3) larger XY
    4) more rigidity
    5) enclosed work area

    I'm actually working on enclosing the work area and I think I have a pretty good design, now I just need to buy a sheet metal brake so I can build the enclosure. Of course everything I'd change could be found on a good Mazak if I had the money. My current temptation is to strip and repaint the mill, install the controls, update the spindle drive and eventually sell the machine if a good VMC comes along.

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  • John Stevenson
    replied
    Christian,
    I personally think it's a bad idea and that the spindle just isn't built for this type of work.

    I have two CNC mills, a Bridgy MDI with a fixed head, variable speed and a QC30 spindle limited to 3,000 rpm
    The other is a Beaver mill, INT40 taper and a top speed of 4,000.

    Both are too slow for small cutters, I managed to get a couple of speed increasers off Ebay. One is a INT45 [ yes weird ] with a DIN collet chuck built in and it's 6:1 ratio.
    I was going to machine the taper down to a 40 and fit it to the beaver but then a INT40 speed came up on Ebay with a Clarkson chuck at 4:1 which fitted straight on.

    I aim to make a new shank for the 6:1 head to fit the Bridgy and then both machines will have roughly the same top speed.
    I paid آ£135 for the 6:1 head in like new condition and آ£45 for the 4:1 in reasonable condition.

    So far i have only used the 4:1 head but it's been very good and certainly speeded the jobs up.

    .

    Leave a comment:

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