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  1. #61
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    Ok guys, here's where I am at right now. There are lots of loose ends, and things missing in the drawings I attached. Nuts, bolts, certian parts... motors, etc... I'm not done yet by any strech of the imagination. I just wanted to throw this out there, and let you guys tear it apart! Well, I decided on a whim that it would be really nice to try and design this machine around the new "HT" extrusion being offered by 80/20, even though I have never inspected it in person... and I have no idea the cost. I was thinking along the lines of this machine being something of an erector set, that you could buy alot of the parts precut, make a few parts, drill some holes and start bolting things together. Not likely, but I'm trying. So someone said something about a rack and pinion drive system, the green bars in the drawing indicate the gear racks, they are the type that have the pre-drilled holes in them from McMaster (.5 x .5) The trucks that the motors would mount to (two on X and one on Y) are actually designed from 4"x4" aluminum tube that you can find at onlinemetals.com, and the trucks without motor mounts are designed from 4" aluminum angle. I'm not sure what I'm doing with the z-axis yet, that why there are parts missing... Oh and the rails are 2" angle iron... and the red pieces in the drawings are .25" aluminum plate, which as we all know is expensive, so I tried my best to keep it to a minimum. And Yes, I do know that the bolts are pushing into the extrusion on the x axis bearings- I haven't fixed that yet! Thats it for now folks! -Carl

    Attached Thumbnails Attached Thumbnails Mid range design #1-ht-machine-front-jpg   Mid range design #1-ht-machine-profile-jpg   Mid range design #1-ht-machine-right-jpg   Mid range design #1-ht-machine-top-jpg  



  2. #62
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    wow that looks good , i like it

    can see that you got problems with some of the bearings thay sort of run into the frame

    maybe putting the bolt the other way around would give you a little more room
    ie putting the bearing on the bolt first so you have the threaded end at the other side of the carrage

    like the positioning of the rails ,only point that would concern me looking at it is the stability of the Z axis

    Dave



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    ok never posted on here before. wanted to throw out 2 ideas i have been toying with.

    1 drive system. Has anyone ever experimented with a friction drive system. I was somewhat thinking od a rubberized small wheel pulling on smooth steel or aluminum. Just a thought.

    2. I have been working with a similar design to the angle iron also trying to copy shop bot. Using Angle iron on edge to create an upside down V with the truck being on top made out of the oposite angle (right side up V) >< Using small wheels or bearings for it to ride on. this would require gravity to hold the truck on the angle however a rack and pinion drive could be used to hold the system down.

    Perhaps someone can draw what I am thinking.



  4. #64
    Registered anoel's Avatar
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    Couple of obersvations...

    The uprights on the frame should be changed to something that does not need to be cut to length vertically. Getting those pieces to be "Exactly" the same length will be difficult to do at home. (Take a look at ShopBot and EZ Router and their use of the big Channel to support the angle iron.) Using a presized item there would be the way to go. You'd be able to loose the top framing rail also. Looks like a really big footprint for the cutting area as well. Some travel optimization would be good. I'm not convinced that the X axis needs to be driven by two motors and two Racks either. If the thing is as rigid as should be then there should be very little chance of racking and causing binding. There are some really big routers out there that are being driven from one side very effectively.

    Nathan


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    Quote Originally Posted by anoel
    Couple of obersvations...

    The uprights on the frame should be changed to something that does not need to be cut to length vertically. Getting those pieces to be "Exactly" the same length will be difficult to do at home. (Take a look at ShopBot and EZ Router and their use of the big Channel to support the angle iron.) Using a presized item there would be the way to go. You'd be able to loose the top framing rail also. Looks like a really big footprint for the cutting area as well. Some travel optimization would be good. I'm not convinced that the X axis needs to be driven by two motors and two Racks either. If the thing is as rigid as should be then there should be very little chance of racking and causing binding. There are some really big routers out there that are being driven from one side very effectively.
    the uprights i dont see as a problem as it can be corrected in the fixings used , more flex of the x sides i can see as a problem , as drawn i guess i would build it from steel box section welded together rather than extruded aluminium section , could even use unistrut , cutting the bits for a welded version would need to be more accurate as you wont get the adjustabilaty

    as to dual racks , guess the pinion drive could use a simalar method to the usual dual lead screws , ie a sprocket and chain or belt to a single stepper /servo

    the rack idea looks good but i think finding suatable racks may be harder than leadscrews , the other problem is gearing and stepping accuracy
    a leadscrew driven with a 200 steps/rev stepper and a 4 revs per inch lead is going to give you 800 steps inch or 0.00125" per step
    but with a rack and pinion your going to have a verry fast machine but only someting like 0.015" steps (about .25mm) per step ( about 3" per rev of the stepper)
    thats going to be asking a lot to machine out using a router in 1 step from aluminium and if it doesn't miss the step then it may stall the router or worse bend the machine .... but ok for balsa wood i guess
    but 3" per rev at a slow 300rpm = 900 ipm what do you want from it ???
    so some gearing would be needed i guess

    ( based on the fact that with a stepper having a 3/16" shaft(opps 3/8") ,and having a 1" dia pinion would give 3.1415" per rev so also giving odd math or a 0.954929658" dia pinion would be needed to correct it )

    Dave

    Last edited by achiestdragon; 09-21-2005 at 07:05 PM. Reason: correction


  6. #66
    Registered anoel's Avatar
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    Microstepping.... and as small of a pinion gear as possible. And gearing if needed.

    Nathan


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    Carl

    keep up the good work....



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    Hello Everybody

    This is my first post, coming from Western Australia
    Here are some pics of a CNC router that I designed and built.
    I think it fits the description of the kind of things you guys are talking about here.
    I learned heaps from building it, and look forward to building my next.
    Since these pics were taken it now has a beautiful porter-cable spindle (you people in America have it lucky with fixed base routers to use on CNC machines - there are none here)

    Its 2' x 4' (cutting).
    All made from steel and ali tube and angle.
    Does 5mm passes in jarrah (very hard west aussie native timber) at 1200mm / min with no problems, although i hope that increases when I upgrade the steppers (much needed).
    Skate bearings throughout. ACME lead screw. No expensive precision parts

    I am in the tweeking and testing phase at the moment, and trying to find the time to actually build some cool things with it.

    Cheers!

    Attached Thumbnails Attached Thumbnails Mid range design #1-cnc-router-front-jpg   Mid range design #1-cnc-router-side-jpg   Mid range design #1-cnc-router-open-day-2-jpg   Mid range design #1-picture-128-jpg  

    Mid range design #1-picture-023-jpg   Mid range design #1-picture-058-jpg  


  9. #69
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    Hi Tim

    great work...... thanks for the pics



  10. #70
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    Quote Originally Posted by anoel
    Microstepping.... and as small of a pinion gear as possible. And gearing if needed.
    Use microstepping for smoother running motors, but don't count on it increasing resolution. http://www.machinedesign.com/ASP/vie...strSite=MDSite

    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)


  11. #71
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    Timothytitus88,

    Great looking machine. Send us pictures when you cut some projects. Do not forget to start a thread in the project log when you begin building your next machine.

    Jason



  12. #72
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    Carl,

    First: I like the layout of the machine, axis etc..

    I saw your bearing arrangement already a while ago and find it a good concept, the bearings are used at their normal load unlike the 90° mount, heavily loaded and riding on a pipe or round bar.

    But one thing immediatly popped up:
    How are you drilling the 6 holes in one single piece of angle so that everything lines up, no play and correct preload of the six bearings?
    Every attempt I made was just not good enough.
    Or are you using excentric stuff, oversized holes... ?

    Luc.



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    Lucus- Lesson learned for drilling holes that need to line up properly- use a jig. I use a simple jig made of plywood that I clamp to my drill press.
    Also, as for the dual motors on the x-axis, I was thinking along the lines of the shopbot design. It looks like they just drive the machine directly off the motor, with no gearing. (Other than the rack and pinion) Is that possible? Or would I have to go with some sort of gearbox? I was thinking that the two motor design would eliminate any axis twisting, and really take alot of stress off off the motors? Wouldn't the torque of the motors on the x-axis be improved if two motors were used? Just throwing things out there! -Carl



  14. #74
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    Sorry, but I still don't see how you can drill with a 0.1mm precision even with a jig, because approx. 0.1mm is what I think is needed to end up with a rigid bearing arrangment.
    It's probably just me who doesn't understand, too little mechanical knowledge.

    I don't know the details of the shopbot design but have seen several designs using 2 motors, main advantage is no twist and easier to implement than a 2 point drive using one motor and a belt.
    But if one motor looses steps, driver failure, something blocks one side of the chassis etc... this could result in a wrecked chassis.

    Direct drive will work but you have to consider precision, a pinion with 10mm OD will result in a travel of 31.4 mm/turn, at 200 steps/turn = 0.157mm/step. An OD of 15 mm results in 0.2355mm.
    Halfstep would cut this in half, microstepping would theoretically further improve precision but it looks like that is not the case in practice.
    Speed is another issue, driving the steppers at +-250RPM results in 7-8000 mm/min (+300IPM)
    So it will depend on your requirements and pinion size if gearing is required.



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    well quiet here for a while ,

    seem to be stuck waiting for bits to turn up here , but getting close to compleation of my cnc , did a compleate redesign of it , its got phisicaly bigger , had to build a sand for it as its to heavy to lift now ,
    i added a lot of adjustment points so it can be aligned easy without having to grind off and reweld bits
    anyway pic attached
    the cutting aria is 650mm * 350mm * 150mm ( 25.5" * 13.5" * 6" approx) so a bit smaller than what you guys are planning

    Dave

    Attached Thumbnails Attached Thumbnails Mid range design #1-cnck4-jpg  


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    well finished the main work on it , now trying to debug a stepper driver problem
    (works fine driving 1 axis at once but fails to drive 2 at the same time ) think is a power supply problem
    then need to strip it down finish of the edges and paint it then rebuild it

    but has to be better than my first attempts

    whats left to do on it , well the bed wants sorting , need a coolant tray and to sort out the coolant pump etc so i can do aluminium , and some welding of brackets for things to mount on the stand , alignment is easy takes a few hrs to adjust and level the whole machine

    next thing will be to upgrade the m10 threaded bar that i used for the leadscrews with some proper leadscrews

    anyway
    hows the other design comming along there seems to be no updates recently , has it stopped dew to drilling accuracy problems or is work still being done on it ??

    Dave

    Attached Thumbnails Attached Thumbnails Mid range design #1-cnck6b-jpg  


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    Sure has gotten quiet here. What happened?

    Mike...



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    I have tried a similar right angle design a while ago and it never worked. I found out after spending money on Aluminum angles and cam followers that the angle in fact is not at 90 deg and the thickness of the angle is not the same over the length. Leasson leaned.
    Any luck with this approach using better angle?

    Attached Thumbnails Attached Thumbnails Mid range design #1-carriage-rail-r-jpg  


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    Whilst I agree most fervently about the need for larger motors, I'm not sure I agree with your comments about the driver; I'm not familiar with the stepperworld offerings but their website's photos of the motors shows a current requirement of only 1.8 Amps. Now a more powerful motor in the same frame-size is simply longer and does not necessarily draw more current. Beware that the low-current, high-torque jobbies are NOT what you need - they are intended for low-speed only.
    Since the discussion seems to be mainly aimed at routers, I will repeat my remarks in another thread: with a router turning at 25-30,000 RPM, you really need to scurry along so the cutter is cutting and not merely rubbing on the work. To some degree, the wood chips will carry away heat from the cutter. The cutter's life will reduce dramatically if it rubs and heats-up. I know 'cos I am there! My max speed is only 300 mm per min (due to crap motors) and the cuts show signs of rubbing/burning.
    Geoff



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    Default Greatings

    Hello All,

    I just recently got into CNC routing and have little knowlage about it. However I am currently designing and gathering materials to build my own machine. I thought I would post my two cents since it seems you have slowed down. My design may not be large enough to fit into the midrange but I dont since it isnt hardware store I dont know. Being an engineering student it hurts my pride to build one from parts at a hardware store when McMaster sells everything you need almost. I am planning to use 80/20 1" by 1" to build my frame and use acme lead screws and 1/2 inch steel rod as guides. I will later be able to upgrade to precision lead screws or even ball screws someday. Hopefully I will be able to cut things out for people I know and they will throw a few dollars my way to pay for improvements. Steppers motors and a Black and Decker 1 Horsepower, 5amp, 30,000rpm router. Hopefully I am stealing the router from my father, and if im lucky I will get the 80/20 free since im part of a student organization. I will post some design blueprints later this week, and would love for you all to critique it. I am curious if a 1hp router will be able to cut aluminum or not? Anyone know. Also what size torque for the steppes would be good so I can start watching e-bay? 150 ounce inches?

    Joshua Updyke



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