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  1. #21
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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    Quote Originally Posted by wmgeorge View Post
    Are you about ready for the first cut Gary? Curious as to how it does.
    Thanks for asking, Bill. Not too far off. I need to update my build with some discussion and photos. Right now I working on hard stops and sensor flags. Then, it's on to making up a spoilboard. I am going to replace some of my cabling to my steppers and have to rewire plugs for P&F sensors. I want better wire (Igus) to my steppers and I used XLR connectors for everything, including my proximity sensors. P&F sensor wires come with aviation connectors.

    Gary




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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    There are many issues with building a machine that is accurate and true to the axes (Square and flat). Industrial machines are built using lasers and master squares for alignment and flatness. Even large, heavy cast iron machines exhibit twist along an axis which has to be taken out with "leveling" the machine.

    For accuracy, the ball screw is what will control positioning and accuracy. The cheap ball screws we use on hobby machines are rolled threads, not ground. They are very economical for a reason, they are NOT accurate like you would find on an industrial CNC machine. I would not trust the accuracy of a rolled ball screw to anything less than .003" / foot of length.

    Using an old Tool Maker rule that I believe still applies today...

    If you need +- .002" you better have an accuracy in your 'tool' that is 10% of that amount or better. Tool in this case is the machine and thus, if you want to hold +-.002" you better have a positional accuracy of +-.0002".

    Chris D



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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    Hi, when you said you had the facilities of a workshop with machines etc, I assume you also have a decent sized marking off table to erect the machine on...….a sheet of steel welded to a bench is not suitable, but it's as good as some need it in the end.

    I would say that if you just went and dived in and did your utmost all along the line and paid attention to the fitting and calibrating of the various axes...…..something good will no doubt eventuate and you'll learn a lot along the way......especially your shortcomings and how to overcome them to make it work.

    We all had to learn by mistakes and rectifications and the courage to accept that we're not experts in all fields.

    I would hate to think that you are one of those pedantic nit pickers that think that if it looks good on a drawing it will automatically be good when you eventually cut the metal, having in the mean time.....many years etc...….agonised over higher spec tolerances you will never achieve and even higher product specs you may never afford so that it will never get built.

    You are not the best engineer on the Planet or the most skilled craftsman that ever there was when it comes to working metal.....once you accept these facts you will be at peace with yourself and proud of you achievements.

    Anything made can be corrected if it shows up a fault or two...…...trust me, we have all been down that path.

    I would think that as the longest journey starts with the first step.....propose a concept design sketch to see what it is you want to get with and you will no doubt get many suggestions as to the practicality of it.

    If it's just wood and ally parts you settle on then at least that bit is not too hard to achieve compared to steel items.

    BTW......…..better cancel the kid's inheritance 'cos you are gonna need every penny from now onwards...….have you thought of a maximum budget you can handle?
    Ian.



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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    Hi JLF - You are right to think about how to measure the parts or the machine to establish its accuracy, precision and repeatability. These days this is resolved using lasers and co-ordinate measuring machines. And Chris D says aim at 1/10th the required figure to ensure you get there. (0.001" = 0.0254mm and your workshop machines should be able to get 0.01mm"??) The other addage is to build a machine of a certain accuracy you need to build all the parts on a machine that is more accurate then what you are building. As you have a machine shop this seems to be the case?... So learn up on lasers and CMM's I think you are going to need them from day dot. Peter



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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    Thanks everyone. I'm aware of the journey to DIY CNC. I rebuild machine tools as a hobby. I have well over 2000 hours in hand scraping slides and vee ways in flatness and geometry. I'm not an over analyzing engineer by a long shot. But I do try to get a lot of info from people that have been down the road. If someone tells me they built a machine with 80/20 extrusions and laid out with a steel rule and scribed lines, checked the geometry with a carpenters square and triangulation, and the end result was 0.005" accuracy and repeatability... then that gives me a very good starting point in my design process. Personally I'm inclined to go with welded steel tubing because I have the capability to work with it and have access to reasonably priced materials. (ie. cheap).



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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    Quote Originally Posted by peteeng View Post
    Hi JLF - You are right to think about how to measure the parts or the machine to establish its accuracy, precision and repeatability. These days this is resolved using lasers and co-ordinate measuring machines. And Chris D says aim at 1/10th the required figure to ensure you get there. (0.001" = 0.0254mm and your workshop machines should be able to get 0.01mm"??) The other addage is to build a machine of a certain accuracy you need to build all the parts on a machine that is more accurate then what you are building. As you have a machine shop this seems to be the case?... So learn up on lasers and CMM's I think you are going to need them from day dot. Peter
    Very true.

    Follows an old adage....

    A rough carpenter uses a square carpenters pencil
    A finish carpenter uses a sharpened point pencil
    A cabinet maker uses a knife
    A fine furniture maker uses a sharp razor blade.



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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    Hi, it all comes down to your design layout preference...…..perhaps a quick sketch of a typical layout would give more food for thought as to what direction you want to pursue.
    Ian.



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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    If you are involved in the machining industry you should know there is a big difference between repeatability and precision. Most routers are terrible with respect to precision. A well designed machine can often repeat well though.

    Quote Originally Posted by JFL4066 View Post
    Thank you everyone for your replies. You proved my suspicions. I'm a mechanical engineer in the automotive industry. Specifically block and head machining lines with 120 4 axis and 5 axis CNC machines. So I'm used to holding contours, holes, surfaces within microns. I also work with skilled trades in the maintenance of these machines.
    Most routers are used in entirely different manner. You should not expect a router to come anywhere near similar performance. A good portion of my CNC experience comes from the machining of optical parts at volume and frankly it is a different beast than common router usage.
    Any way, I'm looking to build a 48" x 48" CNC router. I already have a manual vertical mill. From everyone's experience what can I expect from 1. a better than average kit.
    Well you won’t get results anywhere near what your CNC kills are doing. Further I consider most kits to be poor values. If you have access to machine shop equipment you can do far better going the DIY route.

    I’m not sure your expectations are in line with what can be had in low end CNC routers. It almost sounds like you want the results that might come from a bridge mill.
    2.Sub $5000.00 machine? If I machine a contour like an arc how much variation of the profile will I get on average. If I drill a pattern of holes, how much variation in true position of each hole to part datum? In wood and in aluminum.
    That can vary from absolutely worthless to maybe +- 0.005”. Maybe may be a stretch too. If you have any concern about true position routers, at least low end DIY machines, are not where you want to be.
    I'm assuming wood tolerances are usually +/- 0.015" (1/64") I'd like to know what everyone really sees in their machines when they compare CAD drawing to actual part.
    There is no way to give a useful answer here, mainly because of the wide variability of builds and designs.



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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    Hi JFL - I'm designing a router at present in this forum look up Maximus. It discusses many of these issues and goes through the calcs to achieve various accuracies (your a numbers man). I'm a mech eng and design machinery for my bread and butter. So have a look thru that, may give you an insight into where your going. Also note that I'm probably well over the 200 hours into so far so quite a slog and not at the finish yet. Peter



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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    Wizard - I know exactly what you are saying. The reason I posted this thread was to get input from varied approaches to DIY and if the actual machined parts are within what they anticipated.

    Check this guy out MadVac CNC - home made 4'x8' cnc precision gantry router

    He is cutting shallow aluminum mold halves to within 0.0005". Which is hard to believe, but his machine building process is sound.

    Peter - I will check it out. Thanks



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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    A half a thou...…..



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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    He is cutting shallow aluminum mold halves to within 0.0005". Which is hard to believe, but his machine building process is sound.
    I don't think it actually says that anywhere, and I think he's basing those numbers off the specs of the ballscrews.

    He built that machine over 15 years ago (maybe 20), and what he did back then still works well today.

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    Hi Gerry - He does quote this spec on the first page.

    Hi JFL - Another point that has not been discussed. You want to do timber and aluminium. If its the occasional Al part then you will be fine cleaning up the mess from the coolant. But if the ratio moves to mainly Al then you will never want to put a timber part on the machine due to all the oil and swarf on it. Really need a mill and a router. As mentioned before a small mill retro to CNC is best and then have your 4x4 for timber great combo. Then the stiffness and accuracy requirements are much more relaxed for timber. Why build an Uber machine for aluminium then spend its life cutting timber? Peter



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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    That's his design objective.

    I dug in a little further where he claims to have dowel holes within .0005.
    I guess this is due to the precision ground ballscrews he used.

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    …...and a temperature controlled environment to control expansion and contraction etc etc......pull the other one.

    Pardon me if I'm Uber sceptical, but .0005" is way up in the clouds.... and building it even in a highly equipped workshop then moving it to a home garage ……..no way can you do that.

    As someone said, if you want to fly to the stars you first have to get off the ground.
    Ian.



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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    Anything is possible with time and patience I guess. Mad Vac definitely had both. Precision ball screws sure, but he's using what looks like an off the shelf Bosch router. Spindle run-out under load would be high. Sure you can take light speed and feeds, but it would take 200 hours to cut the molds. Then again time and patience. LOL.



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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    Lets see some actual concepts you would like to browse on....you must have an agenda for what you mainly wish to achieve.

    I'll set the ball rolling by posting a pic of a build that I started a year or so back when I wanted to get into CNC and almost gave up on the CNC mill order I placed.

    I got as far as loosely assembling it when the said CNC shipping date became a reality......it was designed specifically to cut steel.....table size 300mm X 250mm. and 200mm high work piece.
    Ian.

    Attached Thumbnails Attached Thumbnails How is everyone building a DIY CNC router system that maintains cutting tolerances?-dscf1501-jpg  


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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    Quote Originally Posted by handlewanker View Post
    Lets see some actual concepts you would like to browse on....you must have an agenda for what you mainly wish to achieve.

    I'll set the ball rolling by posting a pic of a build that I started a year or so back when I wanted to get into CNC and almost gave up on the CNC mill order I placed.

    I got as far as loosely assembling it when the said CNC shipping date became a reality......it was designed specifically to cut steel.....table size 300mm X 250mm. and 200mm high work piece.
    Ian.
    Now we're talking...

    Looks like a fixed gantry moving table design?

    On you tube 'This Old Tony' made a nice one. I believe his is around 36" x 36" there about. With a Z travel around 6" - 8".

    I would like to go 48 x 48" with a moving gantry - less space used. Has anyone built a vertical mounted one. Interested in their thoughts.



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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    No real agenda. I work equally time-wise in metal and wood. So I would design a CNC for aluminum. Most of the stuff will be plates and panels with holes. I could use the CNC for hole layout and spotting. 48" x 48" would allow for nesting which would save a lot of setup time and fixturing. I also could use it for scribe layout on sheet metal.



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    Default Re: How is everyone building a DIY CNC router system that maintains cutting tolerance

    One big advantage of a moving table design is that you can have a central ball screw whereas the moving gantry even with a central ball screw under the table and on the crossmember can have the gantry slew if the cut is to one side of the job....that can never happen with the moving table due to the table lin bearing layout.

    That is apart from the more rigid fixed gantry of the former one.

    True you need more length to cover the table with a moving table but you can make the table wider than longer to compensate somewhat as the fixed gantry can be made quite massive.

    Here's a pic of my favourite design type, a machine made in Hindustan......note the tool changer rack behind......this would be so good with ISO 30 etc.
    Ian.

    Attached Thumbnails Attached Thumbnails How is everyone building a DIY CNC router system that maintains cutting tolerances?-toolcrafter-fixed-gantry-router-jpg  


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How is everyone building a DIY CNC router system that maintains cutting tolerances?

How is everyone building a DIY CNC router system that maintains cutting tolerances?