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  1. #1
    Join Date
    Feb 2006
    Posts
    120

    a metal cutting Gantry Mill

    I have a new project that I am putting together. you might be interested in it. I have designed it to cut metal, steel and the like. and it is based on aluminum structure. The project got started in the middle of another machine build more as a proof that the building method is suitable. The goal of this machine is to make an accurate one. as accurate as possible using amateur means, and not breaking the bank. I also want it to have a decent work area. Here are the specs:

    Work volume is X 12", Y 6", Z 6"
    Round bar rails, with ball trucks.
    Precision acme screw, (to start with)

    So far I have made the base, which has the x axis rails attached to it. it is made of an aluminum bar 1" x 8" x 14". I milled .030" from the space between the rails to form pads for scraping. I then hand scraped the pads to dead flat. The next step is to mount the rails, and make them true and parallel.

    I will upload pictures of the progress shortly.

  2. #2
    Join Date
    Dec 2007
    Posts
    2134
    I definately want to see this one! Good luck with not breaking the bank though!

    One inch flat bar, good size, I've been getting pricing on some 20mm alu sheet for a couple of similar projects i'm (very slowly) working on, and it's horrendously expensive! I'd hate to think how much 25.4mm would cost here!

    How intense was the hand scraping? I've not had a need to do it myself yet. I'm hoping I can get out easy by beefing up my machine to then machine slots for the rails and fittings in the alu. You've got a big job in front of you. Best of luck!

    Lots of pics please!

    cheers,
    Ian
    It's rumoured that everytime someone buys a TB6560 based board, an engineer cries!

  3. #3
    Join Date
    Feb 2006
    Posts
    120
    Here are some pics, I scraped these to about 5 spots per square inch. Since it’s not a bearing surface this will be enough. I bought the Rails from NXB, and bought the plate from SpeedyMetals. the rails aren’t the best of quality, but NXB is good to work with and the rails are hard, and relatively strait. the aluminum bar had an instrument runout of .010" so it took a bit of scraping to get it flat. I might look into getting my next one ground flat to give me a head start on the scraping. It took me about 4 days to scrape the piece, although the time was diluted with other things like television and a paintball game and work.
    Attached Thumbnails Attached Thumbnails IMG_0053.JPG   IMG_0051.JPG  

  4. #4
    Join Date
    Sep 2010
    Posts
    528
    Looks great so far!

    Where did you find the information about had scraping? I am interested in learning.

    I'm going to watch your build since I am planning on building a milling machine eventually.

  5. #5
    Join Date
    Feb 2006
    Posts
    118
    Please post as many pictures as possible and give us detailed info on the build.
    Would like to know about the hand scraping as well.

    I am looking to build a mill in the very near future so I will be watching your build log and learning from your experiences.

  6. #6
    Join Date
    Dec 2007
    Posts
    2134
    Amazing finish! How much was involved in the process?

    It's really hard to tell but it looks from the photos like the rails sit on a raised portion of the plate? I'm wondering if there's a specific reason for that, as I've been thinking with the machine I'm planning sporadically in my mind, it would be easiest to mill a very shallow and insignificant rebate (0.5-1mm deep) a set distance from each other along the sides so the rails have parallel edges to align to. Or this is not how to do it? I'd be utilising a large mill to do mine so parallel accuracy shouldn't be a problem if machining is considered problematic.

    cheers,
    Ian
    It's rumoured that everytime someone buys a TB6560 based board, an engineer cries!

  7. #7
    Join Date
    Feb 2006
    Posts
    120
    Thanks for the interest.

    I have designed the mill to cater to the scraping process, in that I can take advantage of the inherent accuracy of the process, without complicating my life with the things that a master scraping hand would find trivial, such as aligning “v” ways and the like.

    The portion between the rail pads is milled to a depth of about 1mm. not to form an aligning edge but rather to reduce the area that needs to be scraped. The movement of the 3 axis are defined by flat planes. So in theory if one can produces perfectly flat planes the machine will be accurate. There are a few ways to do this, but hand scraping is so far the best that I have tried. One enterprising individual put a filler epoxy between the base of the machine and its rails and relied on the straightness of the rails and the solidity of the filled gaps between the base and the rails to form the plane. This wouldn’t have worked for me because the rails I purchased have a measurable instrument runout of about .01 inches. This is not acceptable for my machine. The other method that has been used is to put an epoxy putty on the machine base and place the base on a flat granite plate to replicate the flatness of the plate. I find this method acceptable but messy and it lacks the fine control of scraping. It is however much faster.

    the alignment of the rail is accomplished in my case by scraping one edge of the 1 inch plate flat, then while bolting the rail on the pad, I will carefully tweak the rail until it is strait in both the x axis and z axis(which is defined by the scraped pad) if I find that there is too much deviation from strait in the z axis then I will scrape the bottom of the rail as needed until I get the straightness I desire or I give up and call it good. The other rail will be set parallel with gauge blocks to the aligned first rail. It will also be tweaked to be as straight as I can get it. I don’t have allot of time to devote to this project, so I can’t spend allot of time scraping the rails in. but I don’t think it will be all that necessary as everything looks like it’s going to go smooth.

    The rest of the machine will be made out of aluminum too. I have some pencil drawing of it, I want to put it in cad, but I just don’t have time. The construction of the mill is very simple. You have a stationary table, which is also the primary structure of the machine, and then you have a gantry, made of cast aluminum, with 4 scraped surfaces all on the same plane. Two are for the right angle plates that hold the trucks for the rails on the bottom of the table. The other two are for the x axis rails. This is where the accuracy of the machine comes into play. The right angle plates will be hand scraped and will naturally be an accurate right angle. Since the two rail pads are scraped on the same plane it will be easy to maintain the accuracy on the project or at least it will make the tramming of the mill easier. I will have to upload some sketches.
    Ray,
    Life is a choice, death is choice poorly made.

  8. #8
    Join Date
    Aug 2008
    Posts
    1166
    For those asking about hand scraping info, I bought the book and dvd here: Hand Scraping Information and Tools and found it really helpful. I've also only scraped aluminum so far (see http://www.cnczone.com/forums/933700-post107.html). While I was doing it I was wondering if it was actually tougher than cast iron, as I think sometimes I was taking off too much on each layer and making it less flat.

    Ray, looks like a nice mill so far.
    CNC mill build thread: http://www.cnczone.com/forums/vertical_mill_lathe_project_log/110305-gantry_mill.html

  9. #9
    Join Date
    Feb 2006
    Posts
    120
    Here are some preliminary designs. I will probably change a few things before its done.

    As for the scraping thing, I learned originally form an old navy machinist, he used to make me scrape bearings and the like. it was just me and the scraper though, no real teaching other than doing it. I did purchase that DVD and handbook, as well as a scraper from them (the post before this mentions a link), I got my dykem high spot blue from Amazon, and the ink roller from them as well. I have a granite flat plate for my standard. I purchased it from grizzly. It is the 24 x 36" one. I have used plate glass that I lapped together as a flat standard and it worked really well. I will need to make some strait edges which will require some scraping. the best advice I can give you is just pick up a large mill file, grind a slight radius on the end (scrapers are not flat like a chisel) then give it a polished cutting edge with a negative rake, about 10 to 20 deg. then grab a piece of aluminum or cast iron and start scraping it. Make pieces fit together, try making a flat standard by matching three plates together. Nothing beats experience with hand scraping. The hardest part for me was figuring out how to hog material off with a scraper, and then doing the fine scraping. Once you figure that out, scraping is a snap. (Almost)
    Attached Thumbnails Attached Thumbnails SCAN0073.JPG   SCAN0074.JPG  
    Ray,
    Life is a choice, death is choice poorly made.

  10. #10
    Join Date
    Dec 2007
    Posts
    2134
    I'm impressed even more now Ray! I've been looking up scraping on youtube, and it definately is an art form for those with a good "feel" for the work! I see also there are some power scrapers around, do you prefer the feel of doing it by hand or you use them too?

    Two of the links I found very interesting to learn about this process were:
    [ame=http://www.youtube.com/watch?v=esAqz6bCVyQ&feature=related]Scraping in a lathe's top slide (with tapered gib) - YouTube[/ame] [ame=http://www.youtube.com/watch?v=ZTru-KEdaR8&feature=related]The Art of Hand Scraping - Kitamura Machinery Craftmanship - YouTube[/ame]

    cheers,
    Ian
    It's rumoured that everytime someone buys a TB6560 based board, an engineer cries!

  11. #11
    Join Date
    Feb 2006
    Posts
    120
    I have always wanted to use a power scraper, just havent had the chance. I would use it in a heatbeat though. If nothing else but to rough it in. but as I understand it they are capible of fine work too.
    Ray,
    Life is a choice, death is choice poorly made.

  12. #12
    Join Date
    Feb 2006
    Posts
    120
    a quick update

    I have amended the design for the gantry bridge. I am thinking about a rail to rail spacing for the Y axis of 4 inches. This will make the gantry shorter. It sits at 13 lbs of aluminum, I can melt 16 lbs. I am going to do some simulations to determine the relative strengths. That way I don’t over design one part of the machine uselessly. So I had to put it in cad. Here are the cad drawings.
    Attached Thumbnails Attached Thumbnails gantry.jpg   gantry2.jpg   small gantry mill isometric view 1.jpg  
    Ray,
    Life is a choice, death is choice poorly made.

  13. #13
    Join Date
    Feb 2006
    Posts
    120
    Here is a progress report. I will be trying to get to pouring the aluminum tomorrow. I have the fillets in but not shaped yet.
    Attached Thumbnails Attached Thumbnails DSCN2725.JPG   DSCN2724.JPG   DSCN2723.JPG   DSCN2722.JPG  

    DSCN2721.JPG  
    Ray,
    Life is a choice, death is choice poorly made.

  14. #14
    Join Date
    Dec 2006
    Posts
    839
    What can you say about the Grizzley surface plate? Does it hold up without scratching easy? I am needing one but I can't afford a USA built unit. The Asian plates seem to very in quality depending on where you get it.


    On your machine, have you thought about adding a second bracket for the table to run on across the other side of the gantry. This should make it stronger with one set of trucks on each side of the gantry and the table would have equal stress on the gantry when it reached end limits. Less canilevering effect on the gantry.

    Ofcourse this would requair getting two surfaces level & flat to each other which would be harder than the way you are doing it now. But each bracket could be shorter than the one you have now which woudl make them stronger.


    With how your building this machine it may be a moot point anyway with it being so strong to begin with. But making this change could make it stronger. Looks like a interesting build I will be keeping up.


    Jess
    GOD Bless, and prayers for all.

  15. #15
    Join Date
    Feb 2006
    Posts
    120
    Lucky13, the grizzly surface plate comes with an instrument runout map of the surface. it is acceptable for my purposes. so it should conform to the standard tool-room grade that it claims. I have been able to scratch the surface of my plate when I dragged a chip under a part I was scraping. this scratch was due to point contact chipping action, not an indication of the hardness of the plate. it is made of granite, I have had better experiences with a Starrett rose quarts granite plate, but those are way beyond my price range. a friend of mine uses a Starrett plate of the highest quality, I cant remember exactly what it was, just that it was up there, for lapping hydraulic mating surfaces. It was a tragedy of Shakespearean proportions.

    I have read your post regarding the idea of an additional bracket, I am unable to follow what you are suggesting, perhaps you can elaborate. The table is supporting the gantry on both sides of the table. It has four points of contact formed by four trucks in a rectangular pattern of about 6.5 inches by 5.5 inches on center. Admittedly the cantilever relationship of the gantry will amplify the stress on the table by a factor of 1.45 (approximately, as the absolute relationship is not yet set in stone). The table will be supported by a base with attachments to the base located in a position hopefully able to resist bending moments applied to the table. I find that I spend too much time in the theoretical design of the machine and have resolved not to do too much of it on this project. else I will never finish the project. so I am at the point that I just look at it and say "that looks strong enough" an so I welcome anyone’s insight and tricks that might help me to that end, thus I can skip the tedium of finite element analysis, resonance mode analysis, etc. I do have a few projects that I have been working on for years where I have done allot of theoretical design, you might find it in the EDM machine section of this forum. unfortunately the project may never be completed. we will see if I am merely wasting my time with a piece of junk that is unable to cut wood let alone steel, by the end of this project. Its anyone’s guess as there are allot of things that can go wrong. I appreciate your criticism of my design. and as I said earlier, please elaborate on your suggestion so that I can give it the consideration it deserves.
    Ray,
    Life is a choice, death is choice poorly made.

  16. #16
    Join Date
    Feb 2006
    Posts
    120
    I thought I would update this project.

    had a few problems, the first is that I seem to have misplaced a good portion of my sand. about 150 lbs of it. so I plan to remake the flask so as to conserve sand. the second is that my previuos crucable was too small. only 10 pounds of aluminum. I will be needing 16 pounds of aluminum to complete the pour. so I broke out the 40 pounder, and built an extension for my furnace to allow the height of the crucable. the furnace is now done, and I am still in need of my new flask. then I can pour.

    today I will make the flasks.
    Ray,
    Life is a choice, death is choice poorly made.

  17. #17
    Join Date
    Feb 2006
    Posts
    120
    I have not finished the flasks, but I am close here are the pictures
    Attached Thumbnails Attached Thumbnails DSCN2730.JPG   DSCN2731.JPG   DSCN2732.JPG  
    Ray,
    Life is a choice, death is choice poorly made.

  18. #18
    Join Date
    Dec 2007
    Posts
    2134
    All quiet on the Western Front Ray?

    Have you started the castings, I'm curious to see how you are progressing?

    cheers,
    Ian
    It's rumoured that everytime someone buys a TB6560 based board, an engineer cries!

  19. #19
    Join Date
    Feb 2006
    Posts
    120
    my sand isn’t right. it wont release. also I don’t have enough sand. this puts a damper on things. unfortunately the lack of sand makes the coup and drag design more difficult. I have been having problems with my sand deforming under its weight. so I will either need to redesign the casting to release easier or get more sand. I have put the project on the back burner for now. the object for this project was to produce an easy to make (relatively ) CNC machine capable of cutting metal efficiently. my first goal wasn’t not met. but with a redesigned casting or set of castings I should be able to revive the project. unit next time.

    cheers.
    Ray,
    Life is a choice, death is choice poorly made.

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