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Thread: ice_2k4 Heavy Machine Build

  1. #1
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    ice_2k4 Heavy Machine Build

    I’ve been working on a new machine now for a while and figured I’d made enough progress to post some pics and information on it. The machine is a gantry design with a work envelope of about 37” x 22” x 15”. The base weight alone is almost 1200lbs, so the whole machine will be quite hefty.

    The base is constructed from high strength grout/cement and a whole lot of rebar reinforcement. I'm hoping the use of the cement grout will dampen out vibrations much better than just a steel base would. Cast into the base are several 5/8” x 11 all-thread posts and a couple of tubes that will allow a steel bars to be inserted and used for lifting. Also, several couplers were cast into the bottom to use some 5/8” x 11 leveling feet. Even though I used high strength non-shrink grout, I am still concerned that the base will “move” over time. Thus, none of the linear bearings mount directly to the base; instead the X axis bearings mount to separate mounts that are attached to the base using the all-thread posts (to allow for future adjustments as necessary).

    Because of construction constraints, the X axis linear bearing mounts were made in two segments (~22.5” long each) so that I could stress relieve them in my kiln after welding. After stress relieving at 122510deg F, the mounting surfaces were sanded as flat as possible (checked with a yardstick). The bearing mount surfaces were then cast using West System Epoxy. Two surface plates were mounted planar to each other and waxed using turtle wax. A small epoxy reservoir was made just slightly larger than the linear bearing mount. A thin layer of epoxy was poured into the reservoir. The bearing mount was placed into the reservoir and pressed down to squeeze out the excess epoxy. The result is an extremely thin layer of epoxy on the bearing mount with a flatness nearly equal to that of the surface plates (taking into account any variation in thickness of the turtle wax, but from what I can tell, this is essentially zero).

    The resulting bearing mounts were then drilled out to match the linear bearings and tapped for m8 x 1.25 threads. At this point, I only have 2 of four linear bearing mounts made, so that’s as far as I’ve gotten. I will say, once I get the machine to a useable state, I plan on remaking the linear bearing mounts so that I don’t have to rely on any epoxy. I plan on being able to mount a grinder to the gantry so I can use it as a surface grinder, as well. It should also be pretty easy to mount a lathe headstock on this thing to use it as an extremely rigid cnc lathe, too.

    I don't have the machine base leveled, but in one of the pics you can see a high precision level sitting on one of the linear bearings. The graduations are .0005" per 10" and there is absolutely no difference in the reading at any point along the bearing (when shown lengthwise or laterally). That pretty much confirms that the rail is perfectly straight and I won't have any issues with setting the machine up precisely. Also, the linear bearings for the X Axis are high precision Hiwin units from Automation-Overstock.com with heavy preload.

    One last thing, I will be powering this thing with a 900watt 4 axis AC servo kit from DMM-Tech.

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    Last edited by ice_2k4; 07-08-2011 at 12:02 AM.


  2. #2
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    Ice,

    Very interesting .. please do post your progress regularly & keep the pictures coming .. a build like this that's well documented should draw many followers.

    What sort of spindle arrangement do you have in mind for the beast?



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    gd.marsh,

    I honestly haven't thought much about a spindle for it yet. A couple of years ago I started designing my own BT30 spindle cartridge, and I think it would be fun to make. I'd have to think a little outside the box, because I don't currently have the tools to do it up proper.

    In my first post I described my rail mounting method of casting an epoxy surface, and now I have some pics of the process.

    Like I said before, I put two surface plates (from Shars.com, the 18x12, .00005" variety) together. I used a couple of Hiwin linear rails clamped to the edges to ensure the surfaces were planar. I was thinking of casting the plates into some EG to have one large surface plate (albeit with a small seam in the middle), but I'm a little leery to commit to it with my surface plates.

    I realize that my building techniques are a bit unorthodox, but I always enjoy trying new methodologies. If the machine performs well, I see no reason why someone couldn't scale it up pretty easily. I'm pretty much using a floor drill press, angle grinder, and welder to make everything, so it doesn't require exotic tools, either. Any comments or critique is appreciated.

    Attached Thumbnails Attached Thumbnails -img_0315-jpg   -img_0316-jpg   -img_0318-jpg  


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    So, it's been a while since I last posted an update. While I'd like to say I've made a ton of progress, I really haven't. I got my servo system from DMM, and I've got it all wired up. I have to say, just getting that first motion from the servos, even though they weren't hooked up to any axes, is very cool.

    I "finalized" the design and made a video of the whole machine. You may notice the base is a bit different than what I have currently built. I first made the base thinking I was going to be using some 30" rails, but I had purchased a couple of longer, higher precision rails and blocks, and I figured, what the heck, might as well use them. So, when I get everything up and running, I plan on doing some mods to make it like the render.

    I have made a bit of progress on the actual gantry beam. I have the thing all welded up, quite poorly, I might add. I got impatient and wanted to see how bad everything would move, so I loaded the gantry up in the kiln before doing some of the heavy grinding I need to do on it. Stress relieving at 1200 deg F doesn't necessarily remove all the stress, so I figure I'll do two runs. After this run, I'll do all the heavy grinding to get all the important surfaces and weld seams nice and smoothed out, then stress relieve it again before final machining/grinding.

    http://www.youtube.com/watch?v=7Muv3Fw7vWI]Concrete Base Mill Design - YouTube

    I should have better pics of the gantry beam after I take it out of the kiln.

    Attached Thumbnails Attached Thumbnails -img_0330-jpg   -img_0332-jpg  


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    well done so far

    Quote Originally Posted by ice_2k4 View Post
    So, it's been a while since I last posted an update. While I'd like to say I've made a ton of progress, I really haven't. I got my servo system from DMM, and I've got it all wired up. I have to say, just getting that first motion from the servos, even though they weren't hooked up to any axes, is very cool.

    I "finalized" the design and made a video of the whole machine. You may notice the base is a bit different than what I have currently built. I first made the base thinking I was going to be using some 30" rails, but I had purchased a couple of longer, higher precision rails and blocks, and I figured, what the heck, might as well use them. So, when I get everything up and running, I plan on doing some mods to make it like the render.

    I have made a bit of progress on the actual gantry beam. I have the thing all welded up, quite poorly, I might add. I got impatient and wanted to see how bad everything would move, so I loaded the gantry up in the kiln before doing some of the heavy grinding I need to do on it. Stress relieving at 1200 deg F doesn't necessarily remove all the stress, so I figure I'll do two runs. After this run, I'll do all the heavy grinding to get all the important surfaces and weld seams nice and smoothed out, then stress relieve it again before final machining/grinding.



    I should have better pics of the gantry beam after I take it out of the kiln.
    Dear ice,
    well done so far. From the design and weight of the base i think you will be able to machine alu easily using this machine. Don't you think putting too much load on the bed (by a bigger metal cut obviously) can damage it?
    And if you are building it for soft machining then it is a giant no doubt (i didn't read anywhere what you are going to machine on it) You are using servos so i guess your aim is at some hot chips.

    It is better to die for something than to live for nothing.


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    Well, I had planned on taking some better pics of the gantry after I pulled it out of the "franken-kiln" but I'm having an issue with the relays that are used to power the coils. Currently I have two relays to control power to the upper and lower kiln sections that are rated at 50 amps each. They should be seeing < 25 amps each, so I didn't think I'd have any issues with them, but yesterday during the heat soak portion of my stress relieving run, I discovered they wouldn't stay on. From the first time they'd switched on, there had always been a lot of arcing between the contacts, so I don't know if they overheated and damaged the coil wire so it doesn't have the magnetic field to keep the relays in contact or what, but I don't like the "danger" with the mechanical relays, so I've ordered a single 75amp SSR relay and heatsink to replace the current ones. I ordered an IDEC RSSAN-75A that turns on at 90VAC between 47 and 80hz so it should work with my Auberins PID (I was an idiot and bout the regular relay output, instead of the dedicated SSR). But long story short, I'm waiting till the new SSR arrives to do more work on the gantry beam.

    Jasminder, I'm not sure I understand your question? Cutting forces would be higher when machining a stronger material, but I don't think machine frame design is predicated on a structural failure of the frame, but instead on the net stiffness of the frame. If you calculated the minimum M.S. of probably any component of a "real" milling machine, it would probably be gigantic, and while I haven't done any "true" stress analysis on my base design (still working on my homebrew Finite Element Analysis code, though I could just run it at work), I'm not terribly concerned about the cutting forces causing any damage (Considering the amount of internal rebar structure and the bed's 1.5" x 1.25" steel bars that will have an aluminum table mounted to them, my engineering gut tells me I'll have plenty of margin).

    Now, if you're talking about the thin epoxy "bed" for the linear bearing mounts, then I agree completely that machining steel is probably out of the question, if I want any kind of accuracy, and want to avoid damaging the epoxy layer. In all honesty, the epoxy rail mount is merely a temporary solution that I wanted to try out. If I can make it work, and can get everything lined up nice and true, I plan on remaking the linear bearing mounts and using the machine to grind the new ones to be nice and planar, so that I don't have to rely on the epoxy layer. For grinding, the cutting forces will be small, and the epoxy layer will hopefully hold up. It's a lot of work, but I'm doing a kind of Gingery type build, and don't want to get anything professionally machined. Kinda a "can it be done" type project.

    If you meant something else with your question, or I'm missing something else that I should be concerned with, please let me know.

    Heh, once I get my Transient FEM code working (Currently trying to come up with a good contact algorithm without just ripping off what LS-Dyna does), maybe I can put together a nice little comparison of the theoretical vs actual performance of the machine, including all the wonderful dynamic analysis, etc. But, for now, I'm just working with pretty much pure intuition and napkin level analysis.



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    Well, I finally received my solid state relay and heat sink. I have my kiln wired up again and it seems to be working, so hopefully I can make some more progress on the gantry this weekend. Below are a couple of pics during the soak portion of the 1st round of stress relieving. The gantry has been sitting in the kiln at ~1225deg F for 45 minutes in the pics. It has a nice orange glow to it, pretty cool in my opinion. Sorry for the blurry pics, but i had to rush so I didn't lose too much heat or burn myself with the hot air escaping the kiln.

    Attached Thumbnails Attached Thumbnails -img_0337-jpg   -img_0338-jpg  


  8. #8
    Very cool! Do you know how much power your kiln draws? I'm trying to design/build my own at the moment.

    CNC mill build thread: http://www.cnczone.com/forums/vertical_mill_lathe_project_log/110305-gantry_mill.html


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    JSheerin,

    Before adding the upper kiln I measured the current right after starting the kiln up and it measured at 27amps I believe. It's on a 50amp breaker, and hasn't tripped it since adding the upper kiln section, so it's gotta be pulling less than 23 amps. I figure the total current between the two is around 45amps. @ 240Volts or so, that's 10.8kW.

    The maximum power it could be is 12kW (50amp limit at 240V), but at the temps I run it to it's a bit lower than that (since the element resistance drops with increasing temperature). I have been following your big build thread and would like to wish you luck. Being a stress engineer, I enjoy seeing designs with a lot of thought put into them (even if I don't show the same, haha).



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    Sorry for bad English, well that is Google.Very nice machine, but many problems.Everything vibrates, hangs in the air, how aligned rails so bolts?The base is solid, but the steel above it changes everything.I think when you do not feel the vibrations of the earth, but the instrument will vibrate.Success Yancho

    Last edited by yancho; 08-27-2011 at 11:06 AM.


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    Very interesting build and great info. I would like to build me oven like this onlu much smaller. Just somethign to heat treat small parts and such. I have some old 220 heaters will elements much like yours. I have no electrical knowlage but would the parts out these heaters work to build small setup (maybe 12"x12"x12").


    I also wanted your thoughts on the Shar's surface plates. I am going to be ordering one soon, are these plates very durable? Some of the Asian plates are very soft and I want one that does not scratch/wear real easy. I am sure I can get better if I pay but thats the hard part. If these will hold up they are priced very good.



    Thanks Jess



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    Yancho, thanks for the input. The X axis (as I'm designating the long axis) is designed as it is because Concrete/Grout has a tendency to move over time, so I needed a way to get some adjustment in the rail mounts, and there was no way I would be able to cast them directly into the grout.

    Aligning the rails will be a very tedious process. I plan on using a precision level (.0005" per graduation per 10", I think) to get the two rail supports to be planar. By casting all-thread supports into the base I can adjust the height of the corners (I'll have to take care to not "pre-stress" the rail mounts so there won't be an inherent tendency for them to move with cyclic loading). With the corners leveled I'll snug up the nuts for the remaining supports. Finally, I'll tighten everything down and re-check the mounts to make sure their upper surfaces are still planar.

    When I have everything aligned, I plan on going back and filling in the "floating" supports with non-shrink grout. This should really help to dampen out vibrations and will increase the stiffness of the rail mounts dramatically.

    The gantry itself has very large principle moments of inertia, so deflection from transverse shear loads should be minimum. When I was first designing the gantry, I overlooked torsional stiffness of the beam, but in that regard, without the EG mix I'm going to fill the tube with, I calculate ~.00018" of deflection at the tool tip, assuming a 100lbf cutting force (I would like to say this is a very crude calculation at this point, actual deflections may vary significantly). Also, the EG in the gantry should help to dampen out vibrations, as well. I am cautiously optimistic that this design will work very well.

    Lucky13, do you have an ohm meter? If you do then you can measure the resistance of the elements and calculate the power output you can expect from the elements for a given voltage by V^2/R (V = voltage, R = resistance).

    I don't know much about kiln design per say (I just added two together making sure I didn't exceed my breaker amperage rating), but I have about 2.2kW/ft^3 of power going into my kiln and it doesn't have any trouble reaching 1200deg F. I would think you'd want to be around this power/volume ratio. So if you are near that, you should be pumping in enough energy to have a good temperature ramp rate (assuming your kiln is insulated well enough).

    I have been pleased with the Shars surface plates, though I don't think I have enough use on them to know about their durability.



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