Trying to get higher metal removal rates on the Boss
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  1. #1
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    Default Trying to get higher metal removal rates on the Boss

    The Mill I have is one of those BP Boss mills (R2E3 to be more specific). It runs the Erickson #30 taper spindle and it has no drawbar but rather has the operator engage a spindle brake and using a spanner to unlock the drive dogs so the tool holder can be removed.

    Ok, so I have some hefty chunks of steel that I would like to machine out and the features would require me to use tooling that can get about 1.5" DOC at the bottom of the features. I decided to get some fancy 6 flute carbide roughers in the 3/4" diameter variety and take on the metal with that.

    First thing I noticed and kind of figured would start showing itself; the spindle motor is only 2hp and cutting at 24ipm with a stepover of 0.040 and that full 1.5" DOC was about all the spindle wanted to handle. If I'm assuming a metal removal power consumption of 1hp per cubic inch per minute, then I am around 1.5hp already and if I would assume 80% efficiency of the system, then I am pretty much at the limit.

    So, I may end up making a bunch of these things next year and my machine time would be several hours per unit with the metal removal I am getting. Since I have till the summer to make alterations, I am thinking about modifying the mill with a stronger spindle motor and ditching the vari-speed system. But, before I go and attempt that, I am wondering if the spindle would be fine with the extra metal removal I am asking out of it. Ideally, I am looking for about 3ci/min on mild steel. I would be pretty happy with that. I am just not sure if that spindle is able to handle the extra load or not. I can only imagine that the boss spindles are a little bigger than what's found on the J heads.

    By the way, that 6 flute rougher end mill does not bang at all on the spindle and it cuts beautifully. The only thing I did notice was a bit of a high pitch ring coming from the end mill. I dont know if that was just because it's a brand new tool or the spindle is deflecting a little bit.

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    Buy another mill instead
    Faster better cheaper probably

    Peter

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    What mill would you suggest?

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    At least one with more HP

    Peter

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    roughing end mills with wavy flutes tend to be more efficient at removing higher cubic inches per min per hp. also higher ipt feed even if you need to reduce depth or width of cut is more energy efficient but leaves a rougher surface
    .
    normally you leave .005 to .020" for finish cuts with a cutter better suited for finishing.

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    I used to have a few of these, so I feel your pain. It sounds like your doing quite well. If you're looking for more performance, as Peter suggested you need a better machine.

    I've seen older Amura Sieki go pretty cheap for a decent machine that would kick ass over an older bridgeport.

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    often 1" dia roughing end mill will take what a bridgeport can give
    .
    i often use 1.75 to 4" dia roughing end mills on bigger machines and they easily can need 5 to 10hp, bridgeport cant handle it

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    Only you know what fits your shop and your budget. The bigger the taper the better. once you rough on a horizontal, you won't want to go back to running on a vertical. It is so much easier to flush chips.

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    As far as spindle power capability is concerned figures I found for lower speed applications of 30 taper are Max RPM 6000, Cont torque 18Nm, Peak Torque 80Nm. Which probably comes out at something north of 12 hp. I imagine the figures are very different for something like a Brother or other machines of that ilk wizzing round at warp speed 10 but they sound in the right ballpark for an old Bridgeport.

    Being drive limited a Bridgeport spindle won't be designed to handle that full power but doubling the motor power to 4 hp should be fine. Probably take rather more if it doesn't have a quill, not up to speed with the BOSS Bridgeport configurations.

    If you do dump the Varispeed and use a VFD controlled motor the main issue will be getting an equivalent speed range without running out of low end torque or top end speed. Although you could always fit a (relatively) monster motor.

    Grappling with a similar issue in a different application right now and have concluded that replacing a Reeves drive with a single speed belt from a VFD controlled motor has too many compromises in the torque / speed distribution. Perfectly runnable, but in my case, too much de-rating in the wrong places. Especially as changing the motor for one seriously larger isn't an option. Two speeds via free running fixed belts will do it for me but but I'll need to select high or low range belts.

    Currently looking into the pros and cons of either pulleys free running on the spindle with dog clutches and siding spline collar to select the speed or an intermediate shaft carrying a driven pulley and two free runners using electro-magnetic clutches to select the required output pulley. For me mechanical selection via sliding spline drive means making up the whole unit as a commercial one of the requisite diameter will be silly expensive and still need significant modifications. If I go the electro-magnetic clutch route car air con compressor drives should have enough power capacity for me. Maybe you too.

    Clive
    Last edited by Clive603; 12-09-2019 at 04:54 PM.

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    I wish I was in a position to simply buy my way out of this pickle, but because I only machine as a side gig on the weekends, it would be a bad idea to spend more money. I already dropped a pile of cash for a nice Centroid M400 control upgrade. That was more money than I should have spent, but it turned my mill into something that could seriously run flawless 24/7 and completely eliminate the tinkering games I used to have to play. The reliability put me in a position to do business if I felt inclined and I found a level of confidence in that.

    Perhaps one option I could have would be to pick up a 40 taper mill with a dead control for a couple thousand bucks and cannibalize the Centroid off of my Boss and put it on the bigger mill. Of course, it's never quite that easy, but it would sure beat paying another 15K for another fully functional mill with a known good control.

    Clive, your right about the torque issues with single belt systems. The only real way to combat the inefficiencies would be to install a motor that has about twice the amount of power needed. That way, even at lower RPM, the AC motor would still have enough torque to make it through.

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    Another option which might work to generate more hp at higher speeds is to put on a VFD
    But this will only work if the motor is dual voltage and runs on the high voltage now
    What you basicly do do is connect the motor to the low voltage leads Tell the VFD that the motor is connected to that low voltage Most modern VFD can do that Then at over 60 Hz the VDF can supply a higher voltage to the motor so torque stays the same at higher motorspeeds resulting in more HP But only over 60 Hz

    That way you also do not overtorque your transmissionsystem Only speed it up

    Peter

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    Quote Originally Posted by F14 View Post
    That was more money than I should have spent, but it turned my mill into something that could seriously run flawless 24/7
    If you can do that, then hit the green button in the morning on your way to work and then again before dinner then once before you go to bed. Do the job, make the money, buy a beefier mill with cash.

    Bobw will be long shortly to recommend a Fadal. He makes good sense.

    Perhaps one option I could have would be to pick up a 40 taper mill with a dead control for a couple thousand bucks and cannibalize the Centroid off of my Boss and put it on the bigger mill.
    Disgaree with that idea ... you have a complete machine that makes parts/money right now. You do that and you'll have nothing for an indeterminate amount of time. My two cents - run the Bridgeport as many hours as you can stand until you have enough cash to go bigger.

    btw, gbent recommended a horizontal. I've seen some of those go for cheap, less than the 15,000 you mention. In fact there's a Mazak 500 mm pallets mentioned on this site for $3500. Shipping and fitting it into your garage would be a pain, but if you can fit a Fadal you could fit a Mazak horizontal. And gbent is right, horizontals kick ass.

    The only real way to combat the inefficiencies would be to install a motor that has about twice the amount of power needed. That way, even at lower RPM, the AC motor would still have enough torque to make it through.
    Yeah, and then the rest of that lightweight machine is going to shake, rattle and roll. One thing it ain't gonna do is cut metal very well. They put 2 horsey motors on Bridgeports for a reason.

    If you really need a ram-type vertical for some reason (space ?), ewsley had a Tree that was beefier than Ferdinand. If he still has it that might be an option.

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    The rigid ram bridgeports can take a chip, way, way more than a standard bridgeport. You are running pretty fast for what that vintage iron is going to be able to do with its horsepower.

    What rpm are you running? with the vari speed head you are going to lose torque as the speed increases. It is probably a loss once you get about 1:1 on the pulleys.

    I would be pretty happy running steel at that feed on that machine.

    this is the trade off, money and speed. A real VMC will chew much faster but cost you more. If the time is acceptable, just let it run. Pushing 2hp to do more than 2hp worth of work is pointless

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    And with the upside down head, a new motor is pretty difficult

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    they put a motor hp size that matches the strength and rigidity of the machine. putting higher hp motor aint going to help the whole machine from shaking or vibrating which will damage cutting tools
    .
    1" carb 3flute end mill 200sfpm .005 ipt feed 1018 steel .2 DOC at 1.WOC
    roughly 2.3hp required and 378lbs of cutting force
    ..
    3"dia carb insert mill 6 insert 0.15 depth 3"WOC 600sfpm .006ipt feed
    about 12.4hp at 680lbs of force
    .
    1"dia HSS roughing corncob end mill 1.DOC at 0.1 WOC 75sfpm at .003 ipt
    .5hp at 227lbs....... well within bridgeport hp, cutting force still getting high
    but usually will work if you can hold the part

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    Limiting factor on stiffness in cut for a Bridgeport is the quill. With the quill locked up solid it can safely use more power but you have to pay more attention to what cutter you are using. Big difference between a proper roughing cutter and an ordinary end mill when it comes to cut induced shake rattle's roll. Its not like the OP wants to use oversize facing cutters.

    The conservative "it just works" with no engineering effort range for VFD systems on "any motor" is ± 1/3 rd nameplate speed. Modern VFD with low speed torque boost means power holds up pretty well at the lower end. Unless you are looking for the last fraction of a horse power the low end loss compared to direct drive is rarely noticed. Maximum "any motor" drive speed is generally taken to be double name plate speed as all sort of design parameters run out of range as you go faster so the motor drops out of the constant torque range and becomes inefficient unless its designed to run at higher speeds. As you rarely need full power at high speed on things like milling machines due to cutter sizes its usually OK to run close to double nameplate speed.

    Whatever the OP does he isn't going to get decent torque at lower speeds from replacing the Varispeed with a single belt system unless the motor is way oversize.

    Accepting that two pulleys are needed probably the easiest way is to use a 6 pole, 1,200 rpm motor. Closest match to the normal Varispeed range is with drive ratios of 0.55 and 1.1 giving spindle speeds of 660 and 1320 rpm for speed ranges of 440 to 880 and 880 to 1760 with the VFD varied from 40 hz to 80 hz. Getting to the 3000 rpm normal top end of the Varispeed range needs the VFD to be run up to just over 100 Hz which is still safely conservative. Realistically more sensible drive ratios of 0.5 and 1 will work just fine.

    All pretty practical really, just a matter of fitting things in. Which may be easier with an intermediate shaft sat where the old motor was and the new motor offset enough to make room for belt changes on a suitable bracket. Unpretty but whatever works. Dumping the varidrive will probably win 1/4 hp or so so I think a 3 Hp motor will be usefully better without over stressing things.

    Clive

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    Boss 7 had a 5hp[maybe?] freq drive motor on the same base. Had an inferior taper which tended to chatter more than my R2C3 but would push better

    course Bridgeport disavowed that machine pretty quickly and you will never find a motor, but they do exist

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    and another thing...

    how many cubic inches of material are you removing

    I started thinking about how several hours would be spent at 1.5 cubic inches per minute.

    I have a feeling with 200 ipm rapids, if you are using fancy tool paths from CAD, you are killing yourself, they frequently rely on that rapid back to be faster, and you have no rapid.

    I have run those SEM servos at 300 ipm with the right drives, but that is probably all there is

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    Quote Originally Posted by gustafson View Post
    and another thing...

    how many cubic inches of material are you removing

    I started thinking about how several hours would be spent at 1.5 cubic inches per minute.

    I have a feeling with 200 ipm rapids, if you are using fancy tool paths from CAD, you are killing yourself, they frequently rely on that rapid back to be faster, and you have no rapid.

    I have run those SEM servos at 300 ipm with the right drives, but that is probably all there is
    I generally run the machine at 3000 RPM. What I have done is put the Vari-speed in one position and I have left it there as if it was a single-speed system. My VFD takes care of the rest. I grabbed one of my model airplane propellers and put it in a tool holder and ran my optical tach on it to correctly match the RPM on the control with the true RPM. This way, I could get automatic RPM adjustments running the s-code in the programs and I could be hands-off. I have set the mill to run at a max of 5,000 rpm. It actually runs very smooth up at that speed, but I noticed that its really only good for 1/4" end mills or smaller at that speed. I just loose too much torque up there. Not to mention that when I cut aluminum, I use those Alu-Power end mills and at that RPM, it kicks an aluminum rooster tail that shoots aluminum about three feet outside of the table. Then I have to hit the deck and low crawl.

    The mill uses 750W Estun servos on every axis and it is set to rapid at 300ipm. I do have the accel and decel rates set to where it tries to be gentle on the ball screws and not bang them around with near-instant delta-V. That means that if I am only going to rapid two inches over or so, then I may make it to 200ipm before a decel occurs.

    On aluminum, I have been able to get the mill to give me 6ci/min metal removal, but the spindle will not keep a true 3,000 RPM and will bog down a bit. So, I will generally shoot for 4+ci/min and be happy with that.

    on steel, the best I can hope for is around 1.5ci/min. So, I have stayed away from machining bigger hunks of steel because of that and focused on smaller projects if made of steel.

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    Accel and decel is big, the ball screws will live longer than you will

    There is considerable difference between banging and rapid accel.
    Keep them oiled and crank up the accel. THe limitations will more likely be in the power from your amps[you will get positioning errors]

    I ran my BTC with 300 ipm rapids and pretty sharp accel for a decade with no ballscrew issues.
    I would have to do some research to figure out what the accel rates were, but if you really wanted to know I will do it

    Is your spindle set to 1:1? I would assume 1750 or so would be 1:1 and that would be the best spot, faster less torque. Someone with more experience can pipe in on that

    Again, how much material are you actually removing, to give an idea of where you are losing time


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