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  1. #41
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    I got some more fea done tonight. The changes I made were to make a lot of my x and y axes solid sections instead of tubes. This helped a lot - the mounting surfaces for the x and y rails no longer deflect as much and the table doesn't end up tilted nearly as much. I also thickened up some of the z axis and added some more bracing, but this did not help much. In fact my stiffness under a z load went down, although my stiffness for an x load went from 153k to 200k lbf/in just looking at the z axis deflection. One of these days I will add the programming to automatically report the displacement of both the cutter and the vise and add them together. I also looked at stress / strain plots and will try adding some material in different locations based on that. The screen shots below are x loading for 1-3, displacement for 1-2, strain for 3, z loading for 4-5, displacement for 4, stress for 5.

    I also realized I need to start thinking about a base for this thing. Currently I have the bottom of the x axis and the frame constrained vertically on some pads. But that is not really how it will function, so there will probably be a lot more deflection between the z axis and the x/y axis than I currently see. To stay within my height limit, this might require me to change things around a bit (again...) as it can only get about 6" taller than it is now and even that is pushing it - doesn't leave much room for a crane above it to do assembly. Thinking about this some more, I might be forced to move away from a gantry design if I want to keep my z travel. Then I'm getting into a more typical mill (which is fine if I can make it hit all my goals).

    Attached Thumbnails Attached Thumbnails Gantry mill-110131_vmc_frame_v1_x-jpg   Gantry mill-110131_vmc_frame_v1_x2-jpg   Gantry mill-110131_vmc_frame_v1_x3vmstrain-jpg   Gantry mill-110131_vmc_frame_v1_z-jpg  

    Gantry mill-110131_vmc_frame_v1_z2vmstress-jpg  
    CNC mill build thread: http://www.cnczone.com/forums/vertical_mill_lathe_project_log/110305-gantry_mill.html


  2. #42
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    Those are some great plots! The strain plots are interesting. They show some hot spots. Maybe some gusseting makes sense in some of these locations? Might be worth an experiment to see what displacement improvements you get by chasing strain hot spots. You will get a feel of whether it is worthwhile in a couple of tries.

    Also, are you including your tool deflection in your stiffness figures? It seems like you are hobbling yourself including tool deflection - your tool is dictated by the process, not the machine (within limits), so why include it in machine design decisions? If your tool is contributing significant deflection, you might consider discounting it...



  3. #43
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    I am currently including some tool deflection, not particularly because I want to, but because it makes a convenient place to apply forces. You're right that I should probably shorten it so it's just a stub and leaves a convenient area... However in general I don't think it is making a vast difference in my stiffness numbers - without the tool I might be at 260k lbf/in instead of 200k in X for example from looking at the deflection plot.

    Honestly, thinking about it over night I don't think this machine design is going to work. The bed and its attachment to the gantry / Z axis is a much bigger issue than I first thought and solving it is very likely going to put me over my max height. So I think if I want to keep the 22" Z, that will push me into a more traditional mill where the Z travels up a vertical column and overhangs the table by half the Y travel (or something like that). That will remove about 22" from the height of the machine which could go directly into the base to stiffen it. However I'm not sure I can make that work with the 25 size linear bearings. I can go bigger but it would just cost more... Additionally it seems as if that style of machine would be less useful with the overhang of the z coming down on top of a part - you couldn't get in to the middle of something as much. I do think some of the work I've done on my current design could adapt really easily to that style of machine though... I would also hope I could make a more compact design this way and use less steel. I think this one is currently going to be pretty pricey to build... It would be roughly $6k of steel based on a quick weight-based estimate and then add a lot of argon and welding rods...

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


  4. #44
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    You should of bought a cnc machine ready to go
    so that way you could get started working and not loose more money while
    time is spent on this.

    Why exactly do you need such a long table?

    Also A VF3 spindle from a haas is a lot of meat right there are you going to be able to power it well with just the the 220 single phase you have in your garage after all it is a 20hp spindle plus the amount of your servo which is what 3 to 5hp?
    This is a huge project that will cost a lot of money more then you might anticipate a rotary converter or a vfd will cost over a 1000 dollars and that's just for the spindle not the servos.

    I say sell your parts and buy a used Matsuura MC-500V or something similar
    if you want to do this right.
    ps you also have to spend time engineering a proper lube system that will effectively lube your bearings constantly.

    Save your self some money and time and buy a pre built ready to go machine



  5. #45
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    I am not a business. No 'work' is being done here. I'm not losing any money by not having a machine. I'm doing it for fun. If I conclude after 5 years of designing that it's impractical I'm out nothing but my time which I can choose to spend as I see fit and whatever money I've spent on parts which I can probably use to build something else or sell. If I decided to buy a mill (which I still might), I wouldn't go buy it tomorrow. I'd probably wait a few more years due to various reasons.

    Yes, I will have to design a lube system (including for the spindle), way covers, an enclosure, a power supply, etc. I'll have to design everything. That's kind of the point...

    No, I will not have 20HP to run the spindle.

    Yes, I do know it will cost a lot. So would buying a used machine, paying for shipping, paying for riggers, paying for service when it breaks if I can't figure out how to fix it myself, etc.

    I don't need a big table - I want one. I have no specific idea of any part that I will make on this (but lots of possibilities). So if I can make something with a bigger cutting envelope, I will. Maybe I'll decide eventually that's not practical for whatever reason. Then I might use different screws than the ones I have now.

    A big machine will not fit in my garage. I could fit something the size of a Haas TM1, mini-mill or VF1 (which I know because they publish full specs on their website including max operating height). Those would come within 3" of my ceiling. However I'm not sure if any of those will fit through my garage door or make it up my driveway. I've thought about buying a used mill, but I would have to go about it backwards - I'd have to find a rigging company and make sure they could get whatever I bought into my garage. Then I could look for a machine.

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


  6. #46
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    Quote Originally Posted by jsheerin View Post
    I am not a business. No 'work' is being done here. I'm not losing any money by not having a machine. I'm doing it for fun. If I conclude after 5 years of designing that it's impractical I'm out nothing but my time which I can choose to spend as I see fit and whatever money I've spent on parts which I can probably use to build something else or sell. If I decided to buy a mill (which I still might), I wouldn't go buy it tomorrow. I'd probably wait a few more years due to various reasons.

    Yes, I will have to design a lube system (including for the spindle), way covers, an enclosure, a power supply, etc. I'll have to design everything. That's kind of the point...

    No, I will not have 20HP to run the spindle.

    Yes, I do know it will cost a lot. So would buying a used machine, paying for shipping, paying for riggers, paying for service when it breaks if I can't figure out how to fix it myself, etc.

    I don't need a big table - I want one. I have no specific idea of any part that I will make on this (but lots of possibilities). So if I can make something with a bigger cutting envelope, I will. Maybe I'll decide eventually that's not practical for whatever reason. Then I might use different screws than the ones I have now.

    A big machine will not fit in my garage. I could fit something the size of a Haas TM1, mini-mill or VF1 (which I know because they publish full specs on their website including max operating height). Those would come within 3" of my ceiling. However I'm not sure if any of those will fit through my garage door or make it up my driveway. I've thought about buying a used mill, but I would have to go about it backwards - I'd have to find a rigging company and make sure they could get whatever I bought into my garage. Then I could look for a machine.
    Well then that's different if it's for personal reasons
    as far as a rigging company it's only around 700 to 800 bucks depending on the company and they do all the work the machine was also 8500 pounds, I had it done in my shop and I couldn't be happier. The cost for my vmc was 5,000 with a 20 ATC and flood coolant built right in and can hold about a .001 to .0002 depending on how I clamp it.
    One thing that you have to consider is what it's going to be used for and I know that you don't have any projects in mind but do you really need high accuracy to hold .001" is good enough for a lot of jobs and even holding that is hard with deflection on tooling. Only reason why I wrote my concerns to you is the fact that I went that route but I have a business so time is money in that case. Ive built several cnc machines from time to time and sell them on ebay, there hobby sized and they are cnc routers but that doesn't mean I haven't looked into the cost of building a big machine. Have you ever tried using a cnc or mill? If not why not try and build something small and see if it's worth going large scale and you get to test the waters with out ruining an expensive spindle.

    Just my two cents



  7. #47
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    I might still buy a machine - your point about it being the faster route to making parts is totally valid and if I can find an old machine in good shape, it would be cheaper. If I had a pole barn with a big door I'd be there in a hot second. But it's a bit trickier with my garage and it's just for my personal use, so I'm not in a big hurry, hence me trying to design something myself.

    I have built another machine - I built a 4'x4'x6" cnc router a few years ago. I spent about $10k on that including good software and then did one custom design / build project with it and paid for it. I've also worked in a machine shop briefly and run a Hurco mill and Okuma lathe along with manual mills and lathes, so I have some experience with cnc and machining although I'm far from an expert.

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


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    Quote Originally Posted by jsheerin View Post
    I might still buy a machine - your point about it being the faster route to making parts is totally valid and if I can find an old machine in good shape, it would be cheaper. If I had a pole barn with a big door I'd be there in a hot second. But it's a bit trickier with my garage and it's just for my personal use, so I'm not in a big hurry, hence me trying to design something myself.

    I have built another machine - I built a 4'x4'x6" cnc router a few years ago. I spent about $10k on that including good software and then did one custom design / build project with it and paid for it. I've also worked in a machine shop briefly and run a Hurco mill and Okuma lathe along with manual mills and lathes, so I have some experience with cnc and machining although I'm far from an expert.
    Well that's good then I wish you luck and
    hopefully everything pans out if you ever need any info or a machined part for your machine don't be afraid to pm.



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    Hi jsheerin, great work there, i have just one question.

    What method are you using to optimize stiffness? By the looks of thing's it seems like you're doing it by feel (changing the design of the machine radicaly etc)
    I sugest you look at the strain energy plots, if the strain energy is the same in every member then you have an optimized stiffness to weight ratio, if not reinforce the more strained members. Also if you are unsure where to add bracing cover the empty spaces with thin shell elements, aplly load, check for maximum strain energy and add bracing to those areas.

    P.S. Sorry for my probably bad english



  10. #50
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    I took some more detailed measurements of the spot in my garage this machine might go and armed with that data, I think my current design might still stand a chance. So I ran an analysis of my current model with the frame only constrained at one of the mounting holes (and with symmetry). This gave me an idea of how much the frame would deflect as it's currently designed - basically without a lot of support in the base. As expected, it twisted around the single tube where the gantry is tied to the x/y axes. However I think I might be able to stiffen this fairly easily since it is not really braced at all at the moment. Stiffness in the Z direction went from 594k to 178k lbf/in. Screenshots below are deflection (first 2) for a Z load and then stress for the same load. Basically all the stress is in that one section of tubing that connects the base to the gantry (once again as expected).

    A note along these lines which I don't think I've mentioned - I found a note a while ago from Mori Seiki that their typical machine's static stiffness is about 228k lbf/in, and their 'high precision' machine's static stiffness is about 685k lbf/in. They specify 'dynamic rigidity' via a primary resonance of between 30-40hz for a standard and 80hz for a high precision machine. I'm currently trying to get a modal analysis to run but not having much luck so far.

    Attached Thumbnails Attached Thumbnails Gantry mill-110131_vmc_frame_v1_no_floor_z-jpg   Gantry mill-110131_vmc_frame_v1_no_floor_z2-jpg   Gantry mill-110131_vmc_frame_v1_no_floor_zvmstress-jpg   Gantry mill-110131_vmc_frame_v1_no_floor_zvmstress2-jpg  

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


  11. #51
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    I got a modal analysis to work on a previous version of my design (smaller model - my computer kept running out of memory on my current model). Plots showing the mode shapes are below for the 2nd and 3rd modes. They're at 23 and 45Hz respectively. I think both of these could be raised fairly easily with what I'm planning on doing to stiffen the frame already which would put me into a good range. The first mode was the frame rotating around the small area where I had it constrained so I didn't include a screen shot of that.

    Attached Thumbnails Attached Thumbnails Gantry mill-110128_vmc_frame_v1_no_floor_m2-jpg   Gantry mill-110128_vmc_frame_v1_no_floor_m3-jpg  
    CNC mill build thread: http://www.cnczone.com/forums/vertical_mill_lathe_project_log/110305-gantry_mill.html


  12. #52
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    Here's a new model. I added some bracing below the x axis to take advantage of my new-found ceiling height and lengthened the x and y axes to take full advantage of my screws. I also made the table bigger for the same reason. In my FEA, I changed to constraining the vise jaw to be fixed instead of the base of the machine and applied the load to a shallow hole in the end of the spindle, getting rid of the tool. So if I put studs in my concrete floor and bolt the frame to it, I will probably make the frame stiffer, but since I don't know how stiff that will be, I'll ignore that for now and just look at how much the spindle deflects relative to the vise. I also finally wrote code to automatically pop out the stiffness calculated from the deflection at a node in the spindle nose. This is especially helpful as the spindle nose isn't necessarily the point of max deflection anymore.

    It's still twisting around the main horizontal beam in the base, but the stress is spread out a bit more now. Z stiffness is 206k lbf/in while X is 179k lbf/in. The first three screen shots are a Z load and the last ones are X loads. I'm thinking about boxing in the lower frame where the stress is highest and adding a diagonal brace from the gantry cross bar down to the front of the X axis. It looks like the entire rear structure support the gantry beam is moving as a unit around the lower horizontal beam, so if I can triangulate that, I'd suspect it would help.

    The primary resonance is 24.8Hz with the X axis still twisting around the main beam that ties it to the gantry legs it looks like. So I will try to stiffen up that portion of the frame some more. I did work out how to get my FEA model smaller so I can run this analysis, so that's most of the progress I made here. Here's a link to a youtube video of the 24.8Hz mode. Unfortunately it came out at 1 second or so long. On my computer I can watch it on repeat so it's easier to see what's going on...
    [nomedia="http://www.youtube.com/watch?v=cJQYJtXCyAM"]YouTube - 110214_frame_v1_24.8Hz.avi[/nomedia]


    Mass is about 7200 lb for this model with about 500 lb of that being spindle, spindle motor, and ball screws.

    Attached Thumbnails Attached Thumbnails Gantry mill-110214_vmc_frame_v1_z1-jpg   Gantry mill-110214_vmc_frame_v1_z2-jpg   Gantry mill-110214_vmc_frame_v1_z3-jpg   Gantry mill-110214_vmc_frame_v1_x1-jpg  

    Gantry mill-110214_vmc_frame_v1_x2-jpg   Gantry mill-110214_vmc_frame_v1_x3-jpg  
    CNC mill build thread: http://www.cnczone.com/forums/vertical_mill_lathe_project_log/110305-gantry_mill.html


  13. #53
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    Mass is about 7200 lb for this model with about 500 lb of that being spindle, spindle motor, and ball screws.
    Now you need a thicker floor. THat much weight in such a small area will cause you problems with deflection and cracking in the concrete floor.

    Most garage floors are 4 inches by specification. Real world thickness is often less.

    A machine shop floor is minimum 6 inches thick. Large machines the floor can be 8 inches or there can be thickened sections. Very large machines even have piers.



  14. #54
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    I checked the spec's on my garage this morning and it is 4" concrete (I thought it was 6" for some reason). The driveway is 5"... Anyway, what would you define as a small area? This thing is around 6'x7' at the moment. If I used 8x 4" diameter pads, that would be ~90psi of compressive force (for a 9k lb weight - adding on some extra for other components), but the issue is whether the subgrade is supporting the slab fully, right? If not and there are voids, then the slab is subjected to bending and can crack?

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


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    Default Thin as in not thick....

    This thing is around 6'x7' at the moment.
    Why I'm saying anything is that I grew up in a family of builders and I mixed hauled and worked with a lot of concrete away back when in the mid to late 80's.

    I don't think things have changed much since then. I finished my folks last house with my Dad five years ago. We did everything from the footings to the roof including the plumbing, heating and electrical work, drywall, flooring etc.

    Well if it is that large an area (6' x 7") you are probably OK.

    Remember things in the building industry are like most other industries. Specs are loosely adhered to. Keep you machine closer to a wall because at the edges you will have the specified thickness. Closer to the middle many concrete guys will dome the back-fill and you end up with about three inches of concrete.

    How old is your place?

    As in has it been up long enough to settle out and show it's true colors?

    if it's older than 4 or five years and has no major cracking your golden.

    Mark



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    It's 7-8 years old and doesn't have any major cracks. It has some small cracks near the doors that spread inward from the doors. The mill would be placed against a wall, so it sounds like I'm probably okay. If not, what would I be looking at - cut out a block of concrete under the machine, dig deeper, put in more rock and then pour a thicker slab?

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


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    Default There is another way

    Drill out an area and drill piers.

    About 8 inches around and 4 to 6 feet deep will be overkill.

    A pier per bearing point.

    Mark



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    Is that something I could do myself with rental equipment, or would that be a 'contract it out' kind of job? Any estimate on price? I'm trying to keep a running total in my head.

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


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    Default Don't worry be happy!

    With the conditions you have explained and the loads you have calculated your fine.

    If you really want to do it you could with a proper hammer/demolition drill.

    But it is a lot of work. It would take you a whole weekend.

    A contractor would charge you a flaming fortune after you explained it a dozen times. Definitely a sweat equity type job. How to pull it off can vary on what type of equipment you have available. If you can rent a cement core drill that will get you a six inch diameter hole your laughing. Some water and a bit of time and you will have 4 holes nice neat and clean through the floor. Drilling the piers will need a post hole auger. They have what are called one man augers up here. They are mounted on short little trailer. When I have to drill piers I use them:

    https://picasaweb.google.com/lh/phot...eat=directlink

    As for mixing cement use a wheel barrow and a hoe or long handled spade.

    If you are not in an area where there is frost in the ground and the soil is not really sandy you can drill a hole and fill it in directly with concrete.

    A pier works in the principle of friction on the sides of the pier and the idea that the deeper down you go in the ground the more compressed the soil is. Therefore the two principles in tandem will get you a lot of load bearing with a little surface area on the top or bottom of the pier.

    Then again you may have taken civil engineering and I am preaching to the choir!

    Mark



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    Nope, I was a mechanical engineer in school, and I've been an acoustical engineer for the last 8 years. I get what you're talking about though. Thanks for all the tips. Hopefully I can reduce the weight a bit by the time I'm done (for cost savings on the steel if nothing else), but we'll see where I end up weight-wise.

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


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