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  1. #21
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    Default Re: bolt frame build

    filled 4 of the t slots completely since those are not used. the last side still needs several hours to dry before i can see how much it did? time consuming process doing this and took me all weekend to get as far as i am with it. waiting for stuff to dry is not my strong suit. i can say the cross beam is getting heavier. i'm not sure how much but taking a guess i would say i have somewhere in the neighborhood of 10 lbs of epoxy granite worked into the extrusion at this point.
    bolt frame build-t-slots-filled-jpg



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    Default Re: bolt frame build

    all this made a big improvement but i still have a little bit of flex. much better than it was but not completely gone. i don't think i can get everything out of it but it's good enough to move forward until i get things under power and can do some test cutting. i think with finishing passes i won't get into the cutting forces needed to move things but it's still to soon to be sure until it's under power and actually cutting material. i think it's within .005 at the extreme side of things right now though. for comparison i put the same kind of forces on my Bridgeport and got .003 so i'm close to where i need to be i think. time will tell i guess



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    Default Re: bolt frame build

    It might be interesting to make quantitative estimates at each stage to see how it is affecting stiffness. If you have an indicator set up to measure deflection, and a fish-scale to apply a reproducible force, you can measure the springiness along any axis, of any component. An assistant might help...

    Paul Rowntree
    Vectric Gadgets, WarpDriver, StandingWave and Topo available at PaulRowntree.weebly.com


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    Default Re: bolt frame build

    Hi - Yes a static deflection measure would be very good. Machines range from less then 5N per 0.001mm to vertical machine centres at over 150N per 0.001mm to super rigid at 500N per 0.001mm. How stiff is yours?? Peter



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    Default Re: bolt frame build

    my ability to get into in depth tests is limited. the best i can do is put an indicator in the spindle and push and pull on parts of the machine. i did put 200lbs on the center of the gantry to see how much flex was there.( the 200lbs was me balancing top of the gantry ) the flex from my weight was about .005 inches at the worst spot being the center of the gantry. all i can say if before the E.G. fill i was looking at .030 to .040 inches of flexing, now it's around .005 so i got some good gains from the E.G. fill. once you start adding parts to mount the milling head and the more those parts stick out the more room for flexing you get as a result. it's like a longer lever to aid in the flexing just by a mechanical advantage.

    when i push and pull on things i'm at the outer most parts of the machine where i can get the best leverage to move the indicator so at the center of the spindle where you get your cutting forces is not going to have the extra advantage. and keep in mind this is only a mini mill spindle with 3/4 HP so material removal rates are not going to be like a commercial VMC. i had this head on a t slot frame in the past but it was far to light by itself and only did ok after i put two double 6" vise on the farme and added 150 to 200 lbs of cast iron vises for extra weight. on that tiny frame i was getting about 1/16 step over at about 28 IPM in aluminum. i think i shout get at least 1/8 step over at 55 to 60 IPM in aluminum on a better frame like this one.

    i think my best test is to finish the drives and get it under power so i can test it by cutting some material. i don't think i can get it any stiffer than what it is right now. i've tossed just about everything i can do at it.

    i can say this for sure the E.G. fill did quite a bit for stiffness and vibration dampening so those are big gains alone. by the time i finish the table top i think it's going to be fine for this spindle at least. extrusion is nice to work with but not really the great for anything bigger than what i am doing with it. i'm probably pushing the limits of the stuff to be honest.



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    Default Re: bolt frame build

    7N per .001mm ? not my area of expertise Peter i can't exactly measure .001mm since it's less than half a .0001 of a inch. but if you do the math based on my crude tests it works out to about 7N per .001mm i know i don't have several tons of cast iron like a VMC so i'm not on the high end.

    i don't happen to have a fish weight scale but if i did that would be a little more precise than what i have been doing.

    i think i good question would be how much cutting force can a little 3/4 HP mini mill head produce?



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    Default Re: bolt frame build

    started on the ball screw mounting for the 8' axis works pretty well with a cordless drill set with the clutch on the lowest setting. not bad at moving a gantry that weighs around 230lbs.
    i still need to make all the stuff on the motor side but i think i have that end figure out as well.

    bolt frame build-0219201817-jpgbolt frame build-0219201817a-jpgbolt frame build-0219201818-jpg



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    Default Re: bolt frame build

    have the 8' axis ball screw hooked up, still need to make another motor mount since i borrowed the one from my gantry to work off of. getting close at least bolt frame build-0222202123-jpgbolt frame build-0222202124-jpg



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    Quote Originally Posted by machinedude View Post
    have the 8' axis ball screw hooked up, still need to make another motor mount since i borrowed the one from my gantry to work off of. getting close at least bolt frame build-0222202123-jpgbolt frame build-0222202124-jpg
    Looking good! That motor driving the ballscrew looks huge. What is it?



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    Default Re: bolt frame build

    it's just some steppers i had laying around for a long time from Automation Direct that never seen any hours so i figured i would find a home for them on this since they are not cheap. i had probably over a $1,100 in electrical stuff close to 15 years ago. they are around 1,200 to 1,300 oz/in motors can remember the exact size but they are bigger for sure. i have 3 of them on all the axis's actually. i have Gekco G201X drives on them.



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    Default Re: bolt frame build

    had a chance to test thing under power. the z axis makes me giggle i thought it was going to be slow since it was a direct drive but it surprised me the cross axis did about as good as i thought and the long axis was not that great because of whip. so i have been working on a solution to that problem to get better results. the central drive makes things tight so any kind of driven nut design would not work well with what i have and another method that requires a linear rail would add more cost to an already over budget build so i came up with a guide / whip dampener that allows the central drive beam to pass under it. did some quick testing today after i did some more work on the entry and exit ramp piece and ran things up and down by hand and everything works really well at that level. so i feel good i am onto a cheap solution that will do some good for the machine.bolt frame build-anti-whip-assembly-jpgbolt frame build-drive-ramp-jpg



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    Default Re: bolt frame build



    been messing around with this for a few weeks and got it to a point where i think everything should work as it should without any issues. i changed a few things but everything works well. the new issue is the gearing on the long axis so i will be changing that to see if i can get some more traverse speed. as of now i can't over 230 IMP but i think i can get more. i just have to wait a few weeks for the new parts to come in since they are coming from over seas. i never thought this would be the fastest machine but i think it can do better so it's a work in progress i guess

    Last edited by machinedude; 03-18-2020 at 08:53 PM.


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    Default Re: bolt frame build

    Quote Originally Posted by machinedude View Post
    my ability to get into in depth tests is limited. the best i can do is put an indicator in the spindle and push and pull on parts of the machine. i did put 200lbs on the center of the gantry to see how much flex was there.( the 200lbs was me balancing top of the gantry ) the flex from my weight was about .005 inches at the worst spot being the center of the gantry. all i can say if before the E.G. fill i was looking at .030 to .040 inches of flexing, now it's around .005 so i got some good gains from the E.G. fill. once you start adding parts to mount the milling head and the more those parts stick out the more room for flexing you get as a result. it's like a longer lever to aid in the flexing just by a mechanical advantage.

    when i push and pull on things i'm at the outer most parts of the machine where i can get the best leverage to move the indicator so at the center of the spindle where you get your cutting forces is not going to have the extra advantage. and keep in mind this is only a mini mill spindle with 3/4 HP so material removal rates are not going to be like a commercial VMC. i had this head on a t slot frame in the past but it was far to light by itself and only did ok after i put two double 6" vise on the farme and added 150 to 200 lbs of cast iron vises for extra weight. on that tiny frame i was getting about 1/16 step over at about 28 IPM in aluminum. i think i shout get at least 1/8 step over at 55 to 60 IPM in aluminum on a better frame like this one.

    i think my best test is to finish the drives and get it under power so i can test it by cutting some material. i don't think i can get it any stiffer than what it is right now. i've tossed just about everything i can do at it.

    i can say this for sure the E.G. fill did quite a bit for stiffness and vibration dampening so those are big gains alone. by the time i finish the table top i think it's going to be fine for this spindle at least. extrusion is nice to work with but not really the great for anything bigger than what i am doing with it. i'm probably pushing the limits of the stuff to be honest.
    What mixture did you use for your E.G. and what epoxy and ratio I'm sure others will be interested in what your mix and supplies you used, it sounds like you made some good gains from using it

    Mactec54


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    Default Re: bolt frame build

    you can get pre made mix and pay through the nose or come up with your own. i used smooth-on epoxy. i will say this if you are doing a large casting don't buy from the smoooth-on site and find which distributor is your best choice and get the 5 gallon bucket instead of gallons because it's cheaper.they don't ofer the 5 gallon size on their site. the slow hardener is more expensive to ship since it's deemed hazardous where as the medium hardener is not. the medium still has a 90 min pot life so it is a good choice too. stay away from the fast hardener all together. the aggregates you use are up to you. believe it or not some common sense goes a long way when working with this stuff. the size of aggregates depend on the size of the space your working with. so without getting into the whole topic keep them small for something like a extrusion fill on 15 series. the key is to get i a tight compact fill more than anything. i used the epoxy pictured which is mineral filled to begin with to make is stronger.

    bolt frame build-screenshot-176-png



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    Default Re: bolt frame build

    HI MD and others - If the aim is to reduce local vibration and to fill voids then a foaming urethane is cheaper then epoxy and much lighter. For instance 26lb/ft3 is 400kg/m3. This will stop your thin walls vibrating easily. But don't aim at filling first time!! Estimate the fill and say do 2/3, let cure then finish with second fill. This stuff is hard to deal with if it overflows!! Peter

    MD you say its 6x stiffer? (0.030" to 0.005") was this checked apples to apples? I can't see gains in this order from EG filling? Peter

    https://www.smooth-on.com/product-line/foam-it/



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    Default Re: bolt frame build

    Quote Originally Posted by peteeng View Post
    HI MD and others - If the aim is to reduce local vibration and to fill voids then a foaming urethane is cheaper then epoxy and much lighter. For instance 26lb/ft3 is 400kg/m3. This will stop your thin walls vibrating easily. But don't aim at filling first time!! Estimate the fill and say do 2/3, let cure then finish with second fill. This stuff is hard to deal with if it overflows!! Peter

    MD you say its 6x stiffer? (0.030" to 0.005") was this checked apples to apples? I can't see gains in this order from EG filling? Peter

    https://www.smooth-on.com/product-line/foam-it/
    Are you saying someone should try the Urethane Foam from your link, it would help with dampening but would not change rigidity of the extrusion very much, where as the EG will do both but adds a lot of weight

    Mactec54


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    Default Re: bolt frame build

    Hi Mactec - Construction extrusions have lots of thin "free ends or edges" these vibrate at all sorts of frequencies. So filling to stop this is effective. I spend some time analyzing these vibs somewhere else here....

    EG is an expensive and heavy solution to stopping this, even a light foam will damp the edge vibs. I think its debatable that EG will increase stiffness significantly. At best its modulus is 30GPa which is half that of aluminium at 69GPa. Its being added to the inside of the extrusion so its geometric inertia is small. Unless an accurate before and after deflection test is done the paper numbers don't add up in the extra rigidity area... Peter

    The easiest and traditional way to stop vibrations is to add mass, EG certainly does this. Its harder to get a heavy object excited then a light one. The issue is: are we dealing with global vibrations or local vibs? With construction extrusions its certainly the local free edges vibrating not the entire gantry resonating at its natural freq. If the entire gantry is vibrating in a global manner then the solution strategy has to change...

    I've attached an image from prior post. All those little edges and cantilevers sing like the birds at the earliest opportunity...

    The gantry or any machine elements potential rigidity is pretty much set once you select its starting geometry and its material. Its outer geometry is its biggest asset in terms of rigidity. Bending Rigidity = material modulus x geometric inertia. Material value is pretty much set. And inertia is a function of its size to the fourth power. So a 1.2x increase in size is a doubling in stiffness. So going from a 100x100 SHS to a 120x120SHS is extremely valuable, whereas filling it is a small step forward. take aluminium>>

    The solid 100x100 is 8,333,000 mm4 and the 100x100x10mm SHS is 60% of that at far less weight I=4,920,000mm4 . The Al tube R=344.400,00 mm4GPa The inside is 80x80 so its inertia is 3.413,000 so its R in EG is 102,400,00 the inside can only contribute 102.4/344.4= 30% more in rigidity. better to go to the 120x120 in the first place at nearly twice as stiff...

    120x120x10 R=626,266.000 mmGPa 8946/4920= 1.82x stiffer plus much less weight then EG solution


    so many numbers Peter

    Attached Thumbnails Attached Thumbnails bolt frame build-free-edges-jpg  
    Last edited by peteeng; 03-19-2020 at 06:45 PM.


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    Default Re: bolt frame build

    Quote Originally Posted by peteeng View Post
    HI MD and others - If the aim is to reduce local vibration and to fill voids then a foaming urethane is cheaper then epoxy and much lighter. For instance 26lb/ft3 is 400kg/m3. This will stop your thin walls vibrating easily. But don't aim at filling first time!! Estimate the fill and say do 2/3, let cure then finish with second fill. This stuff is hard to deal with if it overflows!! Peter

    MD you say its 6x stiffer? (0.030" to 0.005") was this checked apples to apples? I can't see gains in this order from EG filling? Peter

    https://www.smooth-on.com/product-line/foam-it/
    checked with an indicator assembled on the machine before and after the filling so use that as a guide line. i would do it again and not think twice about it,



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    Default Re: bolt frame build

    i honestly think filling most of the t slots on top of the center voids was a big help. what i noticed with the extrusion is a lot of the deflection is more of a twisting kind rather than in a straight line type of deflection. so looking at the cross section of the extrusion by filling the t slots it made the beam more solid across the width of the extrusion,



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    Default Re: bolt frame build

    Hi MD - Construction extrusion is particularly inefficient in torsion vs its envelope. So by tying all those webs together its a big help. Just want to point out that those thinking about doing this sort of thing it maybe easier (and cheaper) and better to use a large std extrusion or steel section for a gantry vs construction extrusion. Choosing things for convenience often does not hold the best solution down the track

    For instance if you place some epoxy on an extrusion and let it cure you will easily be able to flick it off some time in the future. So filled voids will eventually decouple from the structure IMHO. On the other hand foamed PU sticks like the proverbial stuff and will not decouple... These things have to do with surface smoothness and moisture. Extrusions are very smooth (in terms for bonding things to it) and its difficult to prepare inside of voids. PU is moisture tolerant vs epoxy which is not and surfaces have moisture on them creating a barrier to sticking. Having said that many many people do this and are happy and I'm all for people being happy... Peter



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