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  1. #1
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    bolt frame build

    since there has been some collective gathering of the minds on the topic i figured i would share some of my work to date. going into this build I was geared around plasma cutting but i figured why just settle for one process and am in the process of exploring other processes for use on the same table. if possible i would like to be able to have a light duty gantry mill , wood router and plasma with a removable water table for that process but Plasma will be last on the list even though i started with that intention. a light duty gantry mill and wood router will come first and the milling will be my focus of those two.

    first off i will not be using a router for the milling. they simply don't have the low end speeds needed for material other than aluminum. the idea is to have a different head to mounted to the table for the process needed. the table is 5' x 10' with about 50" x 100" of travel and around 8 or 9 " on the Z axis.

    this i s a project for my home shop and a back up retirement plan i guess for reason for building this machine. i'm not in a hurry and this build has been going on since July of this year.

    i have seen first hand how welding can twist a structure and have had to make a few straight by machining them over the years on big boring mills since this is my trade for about 30 years now. so going into my build i knew i wanted to avoid welding for this reason. another reason for bolting this together was the lack of a crane or any other way to move a complete table around by myself. as for equipment i am limited to a Bridgeport mill and a very small lathe at home. So when it comes to designs a lot of it has to do with what you have to work with and working around your limitations.Attachment 433024

    once i finish the table top the table should weigh in around 1,300 lbs so far and the gantry is around 200 lbs after seeing the table come together i could very well do an Epoxy granite there for added vibration dampening and will probably do a t slot top over that probably 1" thick and do some kind of vacuum pod system for it as well.

  2. #2
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    Re: bolt frame build

    Hi MD - excellent will watch this very carefully. You have a single drive under the table? Peter

  3. #3
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    Re: bolt frame build

    yes one ball screw from the center. so the table top has to be rock solid for this reason. i could end up with a mixture of steel, E.G. and aluminum close to 4" thick as a result. the basic frame work is 3/4 x 1 1/2 HR steel the cross braces for the linear rails ended up about 1 1/4 wide after i made the straight in a free state. those are all doweled to the frame to locate them exactly where i wanted them. basically i can bolt it together and it's straight and square with out any indicator work needed. took a long time to machine this way but made the assembly a breeze. i have 8 leveling casters on the legs so i can move the table around as well. they work pretty well.

    as of now i only have one layer of steel going long ways and plan to add another layer to the underside. with one layer i have about .01 inches of flex with me standing on the table in the center at the weakest point. once the second layer if finished i expect that to to get better. anything thing left at that point will go way with the E.G. i believe. once i get to that point this machine should be in the 2,500 lbs range.

    keeping things square is not to hard on a table this size the flatness is the tricky part . right now it is flat within .015 but that should get better once the second layer of steel is added. anything after will get cut flat with the milling head on the work space. so a light skim cut to make it perfect is the game plan but getting most of it out before that step is best.

  4. #4
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    Re: bolt frame build

    just some other pictures from progress along the way.Attachment 433026Attachment 433028Attachment 433030Attachment 433032

    most of the gantry work was geared around plasma so the floating head and magnetic breakaways were my main focus at first. i will be making some changes for milling and routing and adding an extra set of bearings on the cross slid and Z axis. not a big deal just some more work i seem to have created for myself

  5. #5
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    Re: bolt frame build

    Hi MD - I don't think extra bearings will help much but the gantry seems small for machining work? Will be fine for plasma....The thing with square rail is that they are stiff in all directions so what happens is the bearing closest to the load does most of the work so the bottom ones on the Z axis for instance wear before the top ones do etc. With pull downs it's often good to rotate bearings to even the wear. Some people like this idea some don't. The columns are solid especially with the transverse beam (saddle) underneath but then as you say the machine deck has to be stiff as it doesn't have a frame under it....Peter

  6. #6
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    Re: bolt frame build

    Quote Originally Posted by peteeng View Post
    Hi MD - I don't think extra bearings will help much but the gantry seems small for machining work?
    small as in how ? bottom of the cross beam to table or something else? i think it will handle light work. honestly the gantry is compact but it's pretty solid. the Z axis is built from 2" x 6" thick aluminum flat the cross section is 15 series with 5/8 solid flat bolted to it so i would have material to machine bosses for the linear rails to mount. the extrusion will probably get filled with E.G. the weight is not so much an issue i have stepper motors with close to 1,300 oz /in of torque on all three axis. i had the motors and drives sitting around so this was the use fro them i came up with. the side plates are 1- 3/16 thick too.

  7. #7
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    Re: bolt frame build

    Hi MD - What is light work for you? A gantry for that size machine is usually a bit bigger in dimensions (depth and height unless photo makes it look small). The Z looks very solid. The proof will be in the pudding Peter

  8. #8
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    Re: bolt frame build

    Quote Originally Posted by peteeng View Post
    Hi MD - What is light work for you? A gantry for that size machine is usually a bit bigger in dimensions (depth and height unless photo makes it look small). The Z looks very solid. The proof will be in the pudding Peter
    well i have a mini mill spindle already and for $25 worth of materials and some of my time that's what i planned on starting with. nothing fancy just looking for proof of concept at this point. able to cut mild steel and aluminum but not like a VMC. typical hobby style. the travels are more what i am after but not so much on the Z axis, there is a fine line between the sweat spot and too high with gantry machines like this. low profile work holding is what i am thinking. machines like this are best used on sheet and plate material. plus i have another build i am working on that is more VMC style. i built a ATC spindle for the most part for that and it has a BT 30 taper. that build i have servo motors for from DMM that i am using. this size machine will help a lot with that build no doubt and make my life easier sooner or later

  9. #9
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    Re: bolt frame build

    Hi MD - Usually on a machine that big it would use a drive both sides of the long axis. If you hold one side of the gantry and push the other side is there much play? The two drive arrangement is to prevent the gantry walking ie one side progressing and then the other side catching up (its stick slip mechanism) . Cutting steel and aluminium will test this central drive out when the tool is away from table centre. Any particular reason for the central drive? I'm designing a benchtop BT-30 mill at the moment and it will be entirely epoxy composite construction using metal fibres and epoxy. Cheers Peter

  10. #10
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    Re: bolt frame build

    Quote Originally Posted by peteeng View Post
    Hi MD - Usually on a machine that big it would use a drive both sides of the long axis. If you hold one side of the gantry and push the other side is there much play? The two drive arrangement is to prevent the gantry walking ie one side progressing and then the other side catching up (its stick slip mechanism) . Cutting steel and aluminium will test this central drive out when the tool is away from table centre. Any particular reason for the central drive? I'm designing a benchtop BT-30 mill at the moment and it will be entirely epoxy composite construction using metal fibres and epoxy. Cheers Peter
    i just like the central drives for the fact that you have a top and a bottom tied together to make for a more robust gantry. on my uprights i have bosses milled into them to lock and locate the top and bottom cross beams. the bearings are locked in as well the same. when i machined the gantry i held +/- .001 of an inch on everything so i could keep things square from a datum point. so if i have to change direction between the axis i doweled them of the axis i was working from. the gantry is far more precise than the plasma process i started this build for. that's part of the reason for the multi process approach.

    the gantry is solid even the backing plates for the Z axis that the bearings are mounted to is 3/4 thick material. so as far as play i am not seeing any. the biggest down side to a central drive is the table requirements but the steel frame is not an ideal material when you look at vibrations so that's where the E.G comes into play plus it literally makes your table rock solid

    the way i look at it nothing ventured is nothing gained so i just roll over the speed bumps as them come along.i don't see problems i just see solutions i have not figured out yet besides if everyone did things the exact same way this place would get pretty boring pretty fast it's an adventure

  11. #11
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    Re: bolt frame build

    Hi MD - I have found the local stonemason has lots of slabs of granite and that non appearance grade they are happy to sell cheap. They have CNC cutting and polishing equipment. He's at the local cemetery. He does a lot of granite kitchen tops as well. Anyhow maybe you should look yours up. Cost is cheaper then buying the ingredients and doing it yourself at least here... Engineering adventures that's my sort of gig...Peter

  12. #12
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    Re: bolt frame build

    i will say this about E.G. make sure you go with a slow hardner with the longest working time. it takes a good 30 minutes before the air starts to work it's way out during vibrating. my findings were that it has about the same compression strength as concrete. it took about 3000 psi before the structure fails. shrinkage is about .001 inches so very little concern on that part of it. i figured it would take about 9 gallons of epoxy for the needs of this project.

  13. #13
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    Re: bolt frame build

    Hi MD - I use epoxy with a 1hr to 1.5hr gel time depends on temp. I fill moulds dry then fill with resin under vacuum so no air in there !! (very little at least) Yes longest gel time resin you can get is best. 300psi is 20MPa. I'd expect a bit better than that but 20MPa is good for the job. I'm used to working with fibreglass with 500MPa compression strength...Peter

  14. #14
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    Re: bolt frame build

    my materials were not dry when i tested so having dampness probably did not help 3000 psi is more than enough for my needs so if it does better when dry that's a added plus.the frame is doing most of the support in my situation. the epoxy i picked has a working time of 3.5 hours so it works well for the task.

  15. #15
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    Re: bolt frame build

    spent the best part of a month working on the inside of the shop building cleaning up 25 years worth of junk then got sick with the flu the last two weeks but got back to putting some thought into my mini mill experiment and sat down to model some things to get an idea of what it would take to get this idea on the gantry and came up with this.

    Attachment 435166

    i had the mini mill head already and a belt drive kit for this small spindle to to make it work i think it's going to end up looking something like this. the main extension beam to get down to the table is going to be a 2" x 4" section of aluminum flat bar. since i'm not going for excessive gantry height it looks to be pretty short and should be pretty rigid. the idea was something to handle thick sheets of aluminum at the very least and possibly mild steel to some extent if i'm lucky

    this whole project is basically for Sh@ts and giggles to see how it would do and pretty much an experiment. it would have been nice to keep the center line of the spindle closer to the Z axis rails but has to stick out a bit to work with the belt drive kit i have. other than that it looks good enough to start making.

    i have had this spindle on a 15 series t slot frame in the past but that was a long time ago and that build was on a very limited budget and i never was happy with it but i did get get a 1/16 step over at around 28 IPM in aluminum. this spindle can do much better i think on a decent frame. if i can get twice this i would be happy with this little spindle for starters.

    i think the limited range of materials able to be cut has a lot to do with cutting speeds if your frame is heavy enough to try it. this is to satisfy my curiosity mostly and i have never seen one on a gantry before

  16. #16
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    Re: bolt frame build

    one other addition i will try to fit on this thing is a simple and cheap pneumatic manual tool changer. the spindle is pretty simple in design and i have seen some put belleville washers and an air cylinder on these but that's more complex than expensive than i care to get into at the moment. for around $50 i can do close to the same thing and get away from putting that much stress on spindle bearings and or the cast iron housing for the spindle. one other thing is the limit on gantry height i have and a set up like that would require something like a tormach tooling system which would add more tool stick out to what is already a tight fit. So the butterfly impact wrench set up many have done will work better in this case i think.Attachment 435316

    i did pick some push fittings and tubing to run air lines for a few things so i can manage things better since all this stuff is mounted on a moving gantry. so a semi serious attempt at something practical and useful hopefully

  17. #17
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    Re: bolt frame build

    built it. looked at it and was not excited about the outcome since the spindle center line is so far off bearing block on the Z axis. i thought i was stuck with this flaw but after thinking about it some more i can make the front of the spindle housing the rear mounting point and by doing so i should be able to bring things back 3 1/2 or better which will help out quite a bit i think. the drive motor will be out front now but that should not matter as far as cutting goes. This is part of the trouble making something built for something else fit what your building i guess.

    at least this way i can loose the spacer block needed for the belt tension for this drive belt kit. i think it will be worth the extra time reworking parts of this because the gains will be substantial. back to the drawing board

  18. #18
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    Re: bolt frame build

    reworked what i had into this and things look much better, the first configuration weighed about 45 lbs. i think this one will end up around 36 lbs so it's lighter this way anyways. the spindle center line is about 4" from the top of the bearings for the Z axis and is close to half of what it was the first time around. i was able to turn the spacer block from the first configuration into a front cover since the casting was open on this end, the belt drive kit needed some clearance milled out as well so this way is better but was some extra work to get things working. the casting on these mini mill spindles are are pretty limited on space so the mounting was done with 4- 6mm bolts that's about the biggest this casting will allow but should be enough.

    i still need to sort out the mount for the butterfly impact for the draw bar. what i had before is not going to work with the way things are now but should not be to much trouble to fix.

  19. #19
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    Re: bolt frame build

    had time to make some changes and check some stuff out as far as what will work and what needs more attention. mounted every thing and the extrusion cross beam is my weak link. i had the Z axis completely off the machine and had it clamped in a vise on the bridgeport to get an indicator on things to see if i had any flex there and that looks pretty solid. when it's on the extrusion cross beam that's where i get my deflection. so i am trying to fix this issue. the plan is filling the voids with epoxy granite and it's in the process of setting right now. i can say the E.G. does wonders for vibration dampening and that part of it i am really pleased with but the deflection i have to wait until everything is set before i can check that part out.
    Attachment 436328Attachment 436330

  20. #20
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    Re: bolt frame build

    made a few changes on the Z axis and the mounting points on the cross beam of the gantry. i was able to pull my spindle center line back an additional 1.5 inches so at the very least i got some travel back. my thoughts are the further it sticks out the longer the lever is to act as a mechanical advantage to aid in the flexing of the cross beam. did some quick tests off the machine on the bridgeport and think the E.G. made a difference. so the next thing is to take it a step further and fill the t slots i am not using to see if i can gain some more with the E.G. filling.Attachment 436554 things look a bit more balanced now i think. i did a test with an indicator to check the squareness between the Z axis and cross beam axis and only got about .0005 inches of taper over 6.5 inches of travel. so not to bad for keeping things square by locking things into place with bosses and dowel pins to keep the 3 axis square to each other.

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