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  1. #1
    Rich's Avatar
    Lives in Warrington, United Kingdom. Last Activity: 08-04-2015 Has been a member for 5-6 years. Has a total post count of 30. Received thanks 1 times, giving thanks to others 0 times.
    Hi all,

    I thought I’d better introduce my build and thank all those that have contributed to this forum, it’s helped my a lot already.

    I should own up to the fact that I have started my build. I was having trouble getting my head around the challenge, so started mocking up an idea with bits of sheet material I had hanging around.

    The design started in sketchup, I will post it up on the site once I have found a host.

    I’m quite a practical person, but I know my limits, especially when poking a stick into an electrical circuit. If I could borrow from your collective experience, that would be great.

    Here’s the outline, photo’s to follow.

    The machine will be used for profile cutting sheet materials using a drag knife or a small router. It’s for personal use, so no more than 10 operating hours a week. The cutting area is 1600mm x 800mm, with 100mm clearance between the gantry and the cutting table. The main material to be cut is natural wood nothing too hard – mostly European species, circa 1600 on the janka hardness scale. I will be aiming at a feedrate of 8m/min.

    My target resolutions are 0.1mm the X and Y axis and 0.05mm on the Z-axis. The Z-axis is the priority. I appreciate they are not considered particularly tight by the standards found in this forum.

    Although I had read and viewed as much as I could before starting, the technical stuff takes a while to sink in, so the machine was designed with http://www.cncroutersource.com/ as the main reference point. It’s a great resource for beginners like me, although I have made a mistake with the position of the gantry over the X-axis carriages. If the machine works, I will correct this.

    Frame
    The frame has been built using dexion bought from the local scrap yard. The frame sits over and will attach to a woodworking bench while the machine operates, borrowing mass and stability. The table is made from mdf, its a torsion box. Dexion is being used internally and externally to create the structure. The mdf used isn’t the moisture resistant type.

    To hold work down, I’m thinking t-nuts for two thirds of the table, one third vacuum.

    Gantry
    The gantry has been constructed, it is 10kg and when I give it a shove, it runs three quarters the length of the X axis. Its dimensions are 1200 x 50 x 150mm. Made from two lengths of aluminium box section 50 x 50 x 3mm, they have been spaced by and bolted to an extruded aluminium I- beam, 50 x 25 x 2mm. The design flowed from what was available from the scrapyard at the time, bearing in mind the designs I’d studied online; 3mm is a little light for creating stable joints in aluminium, steps have been taken within the design and will be taken within the final assembly.

    The ends of the gantry are connected to aluminium plate, which make up one face of a torsion box that connects to the carriage running on the X-axis.

    Z-Axis
    The Z-axis is a box wrapped around and over the Y-axis, think ‘Joe’s CNC’. Drive is at the rear, which I appreciate is sub optimal. I’m assuming this will introduce additional wear and could lead to binding. The front and rear plates of the box are made from 6mm aluminium plate. The box is 170 x 89 x 230mm.

    A Tr 12 x 3 trapezoidal screw made from steel C45, with a derilin antl-backlash device will provide motion to the Z-axis carriage. Tr 12 is much more than I need, but is defined by the backlash device. The screw will be fixed and supported. The spindle will be supported at each end by 6mm aluminium angle. I've looked a micro-leadscrews, but dismissed this option.

    The Z-axis will be belt driven, no reduction. I will be using 2 x 15 tooth T5 pinions, providing the 6 tooth engagement required and a polyurethane timing belt, 280mm long. The requiring a centre distance will be102.5mm.

    Linear Rails
    At the time, and without the benefit of the information contained within this forum, cheap linear motion was the main stumbling block. I went with Makerslide, which might be considered unfortunate:

    http://www.mycncuk.com/threads/6569-...ght=makerslide

    The Makerslide has been mounted horizontally on two dexion rails that make up each X-axis. The rail has been mounted in parallel on the each vertical face of the aluminium box section that make up the Y-axis. The Z-axis consists of four sections of Makerslide, two sections working as rail attached to a carriage made from 6mm aluminium plate, two sections acting as structure for the router/knife.

    The X and Y axis solidly resist the forces and moments of inertia described by cncroutersource when tested firmly by hand:

    http://www.cncroutersource.com/do-it...NC-router.html
    http://www.cncroutersource.com/build...nc-router.html

    The Z-axis needs a little more work to make it completely solid. I will create a pattern, against which I can tighten and lock off the v-wheels on the carriage.

    If I keep the rails clean, then hopefully the main issue will be wear.

    Visiting the scrapyard the other day I pulled out a section of V-track (US Patent), 2 meters or so long, made of carbon steel. They may well become part of the design, dependent on the rate of any wear.

    Motion
    The intention is to drive the X and Y axis using reinforced timing belts, per Mike Everman

    http://bell-everman.com/products/lin...elt-linear-sbl
    http://www.cnczone.com/forums/linear...-ever-say.html

    The belt to be used is Brecoflex T5 10mm steel reinforced belt. The system requires reduction, circa 3:1, over above. The gearing for the X-axis will be boxed in within the ends of the gantry protecting the exposed belt from debris, I have some work to do to find the parts at ‘beltingonline’, to make the gearing fit.

    http://www.cnczone.com/forums/linear...er-say-14.html
    http://www.cnczone.com/forums/linear...er-say-20.html

    Per the above thread, the gap between the upper belt and the rollers must be held at 0.05 -0.1mm. and the belt must be seated within a channel preventing it track laterally. Resolving these two points has not been too problematic. I have a few more hours on the X-axis before it is finished, I will be using four UHMWPE pads to reduce the reliance on bearing.

    In the real world the end result can looks something like this:
    http://www.youtube.com/watch?v=SpIuQ...KmL6gQvVQ-GvWw
    http://www.youtube.com/watch?v=T9QU3YQe-Sc

    Does anyone here have experience of the Bell - Everman approach?

    Drive
    This feels tricky. The recommended approach is 3Nm, Nema 23, low inductance motors, ideally run at 65-70Vdc on 75-80vdc drives.

    The motors I have in mind are: www.cnc4you.co.uk/index.php?route=product/product&path=83_84&product_id=364 . For what I have in mind, I suspect it is preferable to set up the wiring in series i.e. high torque/low speed.

    I’m still considering what steppers to use. I understand, 1/8th micro-stepping should be sufficient for my needs. I still have a little time in hand before I need to raise the funds.

    Power supplies, the options are between regulated and unregulated supplies. It looks like unregulated supplies are better suited to deal with fluctuating loads. More reading required on this so I can gather the right parts.

    Control
    BOB. I’m currently looking at the OPPB V3. A four axis controller offering the required 25KHz step frequency and 10A (80% total) load requirements, if wired in parrallel. Running 60Vdc means I would lose some functionality. It is built with MACH 3 in mind. More reading required.

    Mach 3, I’ve used the product briefly in the past. It has a forum for support not provided by the manual.

    So, even without the addition of photographs, it might sounds like there are a lot of weaknesses in the choices I have made to –date. At this stage, I’m not overly concerned, as it takes time to build the skills and insight required. The hope being, when it come to building v.2, I will have all the parts and skills required to build a much stronger machine.

    Thanks in advance for any comments!
    Rich
    Last edited by Rich; 25-10-2014 at 11:40 PM.

  2. #2
    Rich's Avatar
    Lives in Warrington, United Kingdom. Last Activity: 08-04-2015 Has been a member for 5-6 years. Has a total post count of 30. Received thanks 1 times, giving thanks to others 0 times.
    Table design using dexion and images of the build so far.

    The front plate of the z-axis is currently made from 2 x 3mm aluminium plate. The final build will separate these two plates, increasing stiffness and absorbing vibration., I will use sheet ply and a vibration dampening material.
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    Last edited by Rich; 27-10-2014 at 05:04 PM.

  3. #3
    If this version 1 will suite your requirements why build version 2 ?
    If you think it might not suite your requirements then go straight to verison 2 now. After reading your post I would go straight to version 2.
    Last edited by EddyCurrent; 26-10-2014 at 09:18 PM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  4. #4
    Rich's Avatar
    Lives in Warrington, United Kingdom. Last Activity: 08-04-2015 Has been a member for 5-6 years. Has a total post count of 30. Received thanks 1 times, giving thanks to others 0 times.
    Thanks Eddy. I did give that issue some thought. I decided to factor in my own in-experience and concluded that I would carry on building this slightly fragile machine first. I may need to cut plate aluminium in the future, hence the need for v.2.

    Spent last evening reading the support offered by Gecko: http://www.geckodrive.com/support/st...or-basics.html . It offered a very helpful understanding of why unregulated supplies are preferrable i.e. motors behaving as alternators. On a three axis machine, using 4 x 3.1Nm motors (CNC4YOU) in parrellel, the numbers appear to be 11.088 amps and 57.25 volts. The numbers on power requirements will need double checking, they seemed low.

    Anti-backlah Nuts
    Is this a good buy: http://www.damencnc.com/en/component...--spindles/101

    I was originally looking for something that worked with a Tr10 x 3, but I have been unable to find a workable solution, other than the MDL-2-TR 10x2D Special Nut, sold by Merchant Dice:

    http://www.ebay.co.uk/itm/CNC-Z-Axis...item483f9663e7
    Last edited by Rich; 27-10-2014 at 01:17 PM.

  5. #5
    Igus do these, I expect them to be top quality coming from them

    http://www.igus.co.uk/wpck/2371/dryl...zgewindemutter


    Quote Originally Posted by Rich View Post
    On a four axis machine, using 3.1Nm motors (CNC4YOU) in parrellel, . . .
    Did you mean a 3 axis machine with 4 motors ?
    Last edited by EddyCurrent; 27-10-2014 at 11:34 AM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  6. #6
    Rich's Avatar
    Lives in Warrington, United Kingdom. Last Activity: 08-04-2015 Has been a member for 5-6 years. Has a total post count of 30. Received thanks 1 times, giving thanks to others 0 times.
    Lol - yes, I'll edit. Thanks for the link!

  7. #7
    Rich's Avatar
    Lives in Warrington, United Kingdom. Last Activity: 08-04-2015 Has been a member for 5-6 years. Has a total post count of 30. Received thanks 1 times, giving thanks to others 0 times.
    Spent last week tidying up the gantry, fitting flange bearing and reading, mostly about stepper motors:

    http://homepage.cs.uiowa.edu/~jones/step/an907a.pdf
    https://www.mpja.com/download/18304ms.pdf
    http://www.haydonkerk.com/Portals/0/...uators_101.pdf
    http://www.selene.co/Blog/2011/08/se...motor-winding/
    http://www.micromo.com/microstepping...-and-realities

    The aim was to understand how the choice of motor i.e. chopper motors, effects the design of the circuit. Without the depth of knowledge to fully understand everything I have read, there where a number of points I need to carried forward:

    (1) Motors can be driven at between 10-24 times there specified voltage. Increasing the multiplier will increase the stiffness of the motor.
    (2) A motor is most effective when is it operating within the 'slew' range of the speed torque curve.
    (3) Micro-stepping increasing the machines efficiency at the expense of the available holding torque.

    The last point is important as it helps limit my expectation of micro-stepping i.e. it won't make up for accuracy lost within the design or the build ) I would imagine this last point is reflected in the 'motorcalcs' spreadsheet, which includes a significant safety factor?

  8. #8
    Quote Originally Posted by Rich View Post
    The last point is important as it helps limit my expectation of micro-stepping i.e. it won't make up for accuracy lost within the design or the build ) I would imagine this last point is reflected in the 'motorcalcs' spreadsheet, which includes a significant safety factor?
    From what I've read, 1/8 microstep seems to be the most popular and is a good starting point, that's what I use anyway and it's working fine.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  9. #9
    Rich's Avatar
    Lives in Warrington, United Kingdom. Last Activity: 08-04-2015 Has been a member for 5-6 years. Has a total post count of 30. Received thanks 1 times, giving thanks to others 0 times.
    Thanks Eddy, that helps with my working out.

    At 8 microsteps the resolution using a pinion with a pitch diameter of 23.87mm is 0.0149mm, and that is good enough for me ) But the holding torque is reduced to 19.5% peak value, per the linked paper. However, with a gear ratio 2.8, holding torque is increased to 54.6% peak value. It seems to follow when the gear ratio is include that 4 microsteps provide a resolution of 0.0106mm, with no loss of holding torque.

  10. #10
    Quote Originally Posted by Rich View Post
    At 8 microsteps the resolution using a pinion with a pitch diameter of 23.87mm is 0.0149mm, and that is good enough for me )
    Nope you forgot the to include mr Pie.!! . . . .23.87*pi=74.989 /1600=0.0468

    Also you shouldn't really think of Micro stepping in terms of increasing resolution. It has more affect making motors smoother.
    If you need resolution then best to achive it by lowering the pitch.

    Regards voltage then you can easily run those motors above the guide given on Gecko site. They easily run at 68Vdc without any trouble and the extra voltage gives that bit more torque and speed.
    The amp you'll require will depend slightly on the type of PSU used. With Unregulated toroidal supply you'll only need aprox 60%-70% of total rated motor amps. IE: 4 x 4.2a=16.8 / 65%=10.92A
    Last edited by JAZZCNC; 03-11-2014 at 11:21 PM.

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