Thursday, 16 February 2012

Mendel90 finishing touches

I have tweaked a lot of things since building the prototype. The design is fully parametric meaning each part works out how big it should be from basic parameters like the desired build volume, rod diameter, the motor sizes and the layer height used to print it. That means any little modification can change everything slightly, which is why I won't release the files until it is finished. For example, if I increase a screw hole clearance then the brackets might get a bit bigger and that will knock on to moving the holes in the sheets and may increase the sheet size slightly. I also want the drill templates to be accurate so every part that needs a mounting hole had to be modelled, even the cable clips and wire holes.


The cable clips are designed to keep the limit switch wires away from the motor wires to prevent crosstalk. The hole sizes are calculated from the wire size and the number of wires using circle packing rules and so are the holes through the frame for the wires.

The printed holes that need to be accurate sizes are polyholes if they are vertical, truncated teardrops if they are horizontal. I added on half the layer height to all the horizontal teardrops and nut traps to allow for the staircase effect of the layer sampling.

Another change that had a lot of little knock on effects was to allow thin sheets to be used for the vertical parts of the frame, requiring nuts on the back. That necessitated moving the buttresses and fixing blocks to avoid clashes. The net result is that you can specify the thicknesses of the sheets and whether to use nuts. If using nuts it will calculate the the screw length just long enough to work with a Nyloc nut and generates a clearance hole in the sheet. When not using nuts it calculates a screw short enough to not go right through, generates a pilot hole and adds a star washer under the screw. If the sheet is hard it generates machine screws and a hole to be tapped, otherwise it generates a wood screw.

In order to standardise the screw lengths I made all the parts of the brackets that take a screw the same thickness.

I want the BOM to be accurate and remain that way, so the model includes everything apart from the hot end and the electronics. I haven't used any libraries so there are no dependencies apart from OpenScad itself.


I modelled the belt twists and the tension loop to get an accurate assembly diagram and length on the BOM (hopefully I haven't tested that yet). I also modelled the cable strips to get their lengths. The one to the extruder was tricky as it is completely free-form and the ends differ in X, Y and Z. I modelled it as half an ellipse with a shear transform to gets the ends in the right place. It is probably not mathematically accurate but looks about right. Interestingly there isn't a simple formula for the circumference of an ellipse as there is for a circle, only numerical approximations.

I redesigned my fixing blocks to have slotted holes to allow a bit of adjustment. I also changed the hole depth to allow the same screws to be used as elsewhere and cut away some plastic that wasn't adding much to the strength.



RepRap firmware uses a bottom limit switch that needs a fine adjustment. It also needs a coarse adjustment to allow for different nozzle lengths. I found this difficult to accommodate because of limited space at the bottom of the z-axis. This is the design I arrived at after much deliberation: -



The switch is mounted on a lever that is hinged at the bottom by a thin section of plastic and sprung against a screw adjustment by two rubber washers. An extra type of vitamin but I am not impressed by printed springs.


I developed exploded diagrams to make the build instructions. A picture like this with its bill of materials should be self explanatory.

The z-couplings don't need as much clamping strength as the ones I designed for the Prusa (they only need to rotate the screw and not hold the weight of the x-axis) so I was able the make them slimmer, which was necessary to avoid a clash with the z-motor bracket when using NEMA14 motors on the Huxley sized machine.


As you can see two pictures above I also added some pointers on the lead screws. These can be set to face the rods when Z is homed and can then be used to observe if the two motors have got out of step and whether the z-limit switch is repeatable.

This is what the Mendel size machine with 8mm rods looks like with a 6mm acrylic frame and a 10mm base (without the bed).


Note that to make transparency work in OpenScad you have to draw the transparent objects after all the things you might be able see through them.

The hole cut through the gantry is just big enough to make the Y-carriage. I prefer to make my Y carriages from DiBond as I think they are a bit lighter and handle heat better, but acrylic should be OK and it seems a shame to waste such a big bit. I wouldn't recommend it on the MDF version as that is thicker and so even heavier. I have seen people mount PCB beds directly on MDF but I found that even when spaced off and insulated it warps enough to keep throwing the bed out of level.

I offset the Y-axis to allow the ribbon cable for the bed power to be central. That makes it easier to attach the wires to the PCB. I don't think there is any problem with the belt being nearer to the two bearing side, in fact it is probably better.


I had to slim down the back of the Y-idler bracket to prevent a clash with the bar clamp on the Huxley90. The overly long bolt is simply to reduce the number of unique fasteners. Similarly the cable clips could use smaller screws but I kept them the same as the other base screws. On the Mendel90 the base screws are M4 or No6, on Huxley90 they are M3 or No4.

I used a hacked up D connector shell on the prototype with hexagonal posts for locking. To remove those as vitamins and I designed a printed version that uses normal M3 nuts and screws for the locking. It also has a cable clamp optimised for the ribbon cable and its supporting plastic strip.


Again an exploded view makes it clear how the captive parts fit.


I also crudely modelled the tie-wraps because the 10mm bearings require longer ones to be on the BOM.


Modelling the wing nuts showed that one can clash with the X-end if it is oriented in some directions. Fortunately the bolts are captive hex heads so you can rotate the head and try again if the nut happens to stop where you don't want it. I am currently using M4 extruder mounting screws but I see the Prusa2 has moved to M3. I think that would solve the clash with smaller wing nuts but there are a lot of extruders and hot end designs using M4 I think, so I am not sure if I will follow. In any case it is simply a configuration parameter if you are printing your own.

You can see that I added a small part to the belt tensioner. It works a lot better than the Nyloc I had in the design before.

I also added some more nut traps to make assembly easier. Even a pair of "flying" ones inside the X-motor bracket. You can just see one here:


I have done a lot of changes the make things scale correctly for a Huxley sized version. This uses 6mm rods and NEMA14 motors.




I need to make a smaller extruder though as a Wade's is way too big. I plan to do a mini Wade's with a NEMA11 motor for 1.75mm filament. That will make the carriage smaller and reduce the width of the machine.

I also want to make a parametric PCB heater design to allow arbitrary machine sizes.

So as you can see I have put a lot of work into this since Christmas. In fact nearly all my spare time, until 2am a lot of evenings. I get really ticked off when people demand that I release the files before it is finished. Unlike a lot of people I don't put half baked things on Thingiverse, only tried and tested designs.

As all the parts have changed a little bit I am in the process of printing all the Mendel sized 8mm ones to check them. I will then release the design on GitHub. I had wanted to release it with make files to generate all the STLs automatically but it seems the command line option of OpenScad is currently broken so people will have to make their own if they change any of the parameters.





83 comments:

  1. Wow! That's impressive. (As usual.)

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  2. Wow. fine work!
    My one thought on your z end stop was: have you considered getting rid of the current fine adjuster mechanism and putting a 3mm bolt hole in your x axis end piece. Thread a bolt and nuts onto it. I have that on my prusa and it is both simple and it works well.

    Keep up the good work. I would love to build one when the time is right.

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  3. i guess I should clarify, the bolt would be the part that actuated the switch. It would protrude from the bottom of the x axis.

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    1. That would be simpler. Thanks, I will look into it.

      Delete
  4. nophead,

    It is simply astonishing what you've managed to accomplish in openscad. I'm blown away. I don't think anyone anticipated you would take this design to this level of detail before releasing it, and seeing what you've done the delay makes a lot more sense :) This is a beautiful family of bots you've developed.

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  5. If a properly de-obfuscated "nop dot head at gmail dot com" will work for paypal, can I buy you a pint?

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    1. He Chris,

      I switched to ribbon cables myself too on reprap stock electronics, and I figured out in two days, that the
      X-endstop is crosstalking with the x-motor (been in the same ribbon cable).

      Since then I put the X-endstop into its own 0.2mm2 cable (so not ribbon cable), it is not buggy anymore.


      The question is, what would be the most elegant way to solve it? I really would like to stick to ribbon cable for everything, because it is now aesthetically feels a little off.

      Best,
      Laszlo

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    2. Hi Laszlo,
      I have added a couple more wires to the X - cable, which I intend to ground at the controller end and link at the X end to form a shield loop between motor and end-stop wires. I have yet to see if that works but my guess is it will.

      If not the best electronic solution is to use an external pullup followed by a series resistor to the micro's input and a small capacitor to ground. The time constant should be chosen to react fast enough at the homing speed. Not only does that filter noise it also protects the micro against ESD and over-voltage.

      It doesn't affect my firmware because I only look at the sensors during homing and I have a retry loop. My X axis judders while it homes, but it always gets there in the end.

      Delete
  6. That is very impressive, bordering on insane, you sure don't do things by half.
    When you've released it and had a bit of decompress time it would be interesting to hear your views on how the tools could be improved to make this easier next time.

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  7. With your design it would be pretty easy to add a removable box for sound proofing and as a heating chamber. This could be done with plexiglass and made such that you snap in the left and right hand sides and then the front and back followed by the top (in two pieces).

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  8. Love the exploded views, building instructions into the SCAD file itself is clever!

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  9. Beautiful!
    I agree with your comments on half finished items on Thingiverse. There are a lot of designs there that are not completely thought out, or have no documentation, or have not been tested. It is great to get, not only a complete design, but clear explanations of why you have made various engineering decisions. Folks have to know why something is done a certain way if they want to modify it without messing something up.

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  10. This is shaping up to be quite something.

    I'll throw my lot in with the "take as long as you need to make it right" crowd. Don't be rushed by the impatient, you don't owe them anything.

    The decisions guided by sound engineering reasoning that are clearly explained make this project a real stand out, along with the great attention to SCAD detail and parametric design.

    Does your design allow for the use of different sized motors on different axes? I have in mind a Prusa+ sized version on 10mm rods, running NEMA17's on X/Y where speed really matters, but as I want to extrude only 1.75mm PLA i'm thinking of using a lighter motor on the extruder, (NEMA14/11) to cut down weight with a view to getting better X-axis traversal speeds. Possible? Thoughts on the concept in general?

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  11. Yes you can use different sized motors on each axis and different sized rods as well. Each variant of the machine has its own config file that defines everything. Copy one and hack it to make a blend.

    The extruder is the only part not properly parametric at the moment. When I make the small one for the Huxley version that will be fully parametric and you will be able to use it on the larger machines. Selecting it will make the carriage smaller, which will also shorten the X axis and reduce the length of the frame, bring the gantry forward, etc.

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  12. great work nophead!

    just love the cad rendering of the printer.i am just blown by the detail given it.

    i just wanted to know what is the yellow thingy just above the z axis couplers?
    what if the bearings were replaced by gears,which would prevent need of twisting the timing belts.
    it would be great if you add extra stuff like the drill profiles and etc at the backside(just a sugesstion).

    regards,
    gp

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    1. "As you can see two pictures above I also added some pointers on the lead screws. These can be set to face the rods when Z is homed and can then be used to observe if the two motors have got out of step and whether the z-limit switch is repeatable."

      By gears I think you mean a second timing pulley. If you use a pulley you need provide a bearing for it anyway. If it is printed then you have added another source of inaccuracy. If it is metal you have added another expensive hard to find part. I don't think twisting the belt has any downside. You see it in industrial transmission system. If you don't like it you can cut the belt and strap it face to face, see http://hydraraptor.blogspot.com/2011/06/half-belt-hack.html.

      Delete
    2. thanks!

      suppose it's printing something tall(taller than the gap left by the main wooden piece) on the top right corner of the hbp,then wouldn't the main wooden piece knock the print down?

      regards,
      gp

      Delete
    3. The height of the gap is equal to the height of the bed plus the maximum build height plus a little clearance, so the z-axis hits its end stop before it can make an object too tall for the opening.

      The build height is set the same a Mendel in those pictures, i.e. 140mm. It can be set higher, which would make a taller sheet, longer rods and lead screws. If you make it a lot taller it would probably be a good idea to make the Z rods bigger. Again the design will adjust itself to accommodate bigger bearings.

      Delete
  13. I will also email you a beer (or three). We have a micro brewery & future pub right up the road that started up recently. They're building up their own space and make a good product. It seems an appropriate choice for you.
    Perhaps we will assume that the requests for release are from people worried they missed out on the release announcement or are trying to express that they think you have a good idea and can't wait. And ignore those that think you should just do what they say because they want you to.
    Glad to get the update. Reading about the thought you've put into it and why you've made the choices you have is very interesting and instructional.

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  14. Out of curiosity, where do you get your Dibond? And have you considered using it for all of the panel construction? I ask because I can get Dibond and similar products from a local signage supply company, but only in 4x8 sheets. If I'm buying that much, it might be interesting to try using it for all the panel work. Seems like it might require some simple bracing to tie the gussets together at the top-back to eliminate some vibration and flex.

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  15. I got some 500x800 sheets off eBay a long time ago but I think it was a one off sale.

    I found this place that will cut it to size and round corners and drill holes if you want: http://www.cutplasticsheeting.co.uk/dibond-aluminium-composite-sheet/white-dibond-aluminium-composite-sheeting.html. I haven't used them myself but the prices look reasonable for small pieces.

    I have thought about using it for the vertical sheets. That is one of the reasons I added the nuts option, the other being in case I strip a thread in the acrylic or wood, I can just drill it out and use a longer bolt with a nut. Before I moved everything the nuts would have clashed.

    You can add a top sheet over what I have been calling the buttresses (gussets might be more correct) to give more bracing if it is not stuff enough. My guess is you won't need with 3mm DiBond.

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  16. Hello Nophead,
    I'm really a great fan of your blog ! I just bought material to make a printer very "inspired" by your mendel90. My machine will used less printed part, because my current device (extruder on a cnc mill : tmonnot.free.fr/Fraisage/Ninos_Repstrap/Ninos_Repstrat.htm ) is really low...
    I will mill a lot of parts in medium as motor mounts...
    Are your drawing available ? in a cad-file as IGES 3D DXF or anything readable by rhino ...
    It will help me to draw may own machine, and save a lot of time !
    Thanks in advance
    Thierry from the other side of the channel : britanny ;-)

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    1. Hi Thierry,
      Thanks, you have some great looking prints on your blog.

      The only format that will go from OpenScad to another 3D CAD package is STL. I will be selling parts soon. If you wanted to buy just the tall ones that would be no problem.

      Regards, Chris

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    2. OK, I must do the job 100%... but I like that ;-)
      For the prints, I find a great benefit to use a calibration proc├ędure : http://tmonnot.free.fr/Fraisage/Ninos_Repstrap/Reglages_Repstrat.htm
      I use an excel flow calculator made with the help of your formulas from http://hydraraptor.blogspot.com/2011_03_01_archive.html
      Thanks to give us this "scentific approach" of the print job

      THierry

      Delete
  17. Sorry if I am the one bugging you :) I am just excited....

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  18. Well I hope its not too long before the plans are available. Ian who has offered to print the parts for me, is moving to another part of the country for a six month works contract and he may not be able to take his Prusa with him.

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  19. Remember that reason the carriage was modified to mount the extruder parallel to the x axis was to accommodate geared extruders on the Mendel, so that it would fit between the frame triangle supports so we wouldn't loose z height.

    Your design doesn't suffer from this flaw, so you can simply move the mounting holes back to be parallel to the Y axis. By doing this, you can potentially make a shorter x axis as well, to give you more x travel.

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  20. True, I did think long and hard about this, but I like the centre of mass to be between the bars, otherwise I might have gone for a vertical axis, which reduces the printed part sizes. I feel that would allow it to twist as it moves to the middle and the bars flex in opposite direction, displacing the nozzle in the Y direction.

    Also if I turn it 90 degrees clockwise the Z bar clamps and motor brackets get excessively long. If I turn it anti-clockwise it makes it hard to access the idler nuts. Another downside is one of the extruder mount screws clashes with the centre bearing so I would either have had to make the carriage even wider or move the bearing off centre like the Prusa carriage.

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  21. Really nice work Nophead, congratulations. I've been following your project since you first announced. The cool thing about this community is we all give back in some way. There's a few however, like yourself, who contribute in ways that helps to shape our direction and push the innovation. Excited to see what the next big change is going to be to these printers. I'm working on dual extruders for mine, but luckily there's some smart folks already making headway there. Again, nice work and much appreciated.

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  22. Hi Nophead, I just wanted to join the others in congratulating you on an awesome job - thanks so much for sharing your work!
    I read/lurk on a great many 3d-printing blogs and consistently find yours to be the most inventive and well-explained.
    I'm working under what I'm learning is possibly a stupid limitation (I'm hoping to do CNC milling and additive printing on one platform using all OS X-compatible software), but once I'm up and running, I'm excited to make one of these...btw, is there a tip jar anywhere on your site that I'm not finding?
    Thanks again,
    AKA

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  23. Nophead

    Excellent detail and clarity of build, I guess we have come to expect a whole bunch of great work over the years but this surpasses it all so far.

    As always sound work.

    AKA47

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  24. Your work is absolutely amazing. I'm really looking forward to this design.

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  25. One really nice thing I just noticed is that if you box up this design for heat control/to exclude pets, the electronics would be in their own separate chamber, protecting them from exposure to heat or the outside. The attention to detail is extraordinary.

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  26. I have to add my +1 on this is just a awesome job. Sorry for pestering you about releasing but I was hoping to make this for a vacation trip im taking to the phillipines. Had to settle for making a printrbot for them instead but I will make one of these just as soon as I get back.

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  27. Another fan here. Your work is much appreciated!

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  28. A very nice design indeed and so tidy. Do you treat the MDF with anything to harden it and keep it from swelling? I am surprised at you limit switch arrange on the Z, looks at bit tricky to make tiny adjustments, did you consider using a thread for micro adjustments like a mini z-axis, it would get rid of the plastic spring and extra rubber?
    Really nice design, so many choices for my next printer now. My nophead mendel is still holding up well though with just the x-carriage replaced due to a caked extruder from a bad overnight job :)

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    Replies
    1. No I haven't treated the MDF but it would be a good idea to do so.

      I will replace the Z adjuster with a simple screw attached to the X-end and a micro on a fixed bracket.

      Delete
  29. Are you still working on the .scad files? Where can we download them?

    Should I build this or a Prusa for my first RepRap?

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  30. Yes I am still working on the scad files. They will appear here soon: https://github.com/nophead/Mendel90

    I believe this is a better machine but you will need to wait a while for the instructions and full kit to be available, whereas the Prusa is well established.

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  31. Great design.

    How are the y-axis belt clamps accessed?

    Does an access opening need to be cut in the base to allow easy access to them?

    -- Don

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    1. I put the belt on before the Y carriage was installed. I then installed the carriage and then the idler to pull it tight.

      That requires the belt to be about the right length. I haven't checked it yet, but the length on the BOM is calculated from the model so it should be possible to cut it to length and then place it in the the clamps with the amount specified in the model sticking through.

      I will verify this when I make the second prototype and prepare the instructions.

      Delete
  32. Great work. I've been following your progress on the Mendel90 and you blog for a long time with much interest. I *can* wait for you to finish the design, because I appreciate and understand that releasing a half baked design is a sure to lead to disappointment and frustration.
    Do you belong to belong to any 'club' in the North West or can you recommend one, because I'm interested in joining others and discussing ideas.
    Cheers
    Fixer
    PS. If we ever meet, mine is the first round.

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  33. I have been to one in Sheffield a couple of times. http://sheffieldmakers1203-eorg.eventbrite.co.uk/?ebtv=C

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  34. Hi nophead, you wrote:
    "I believe this is a better machine but you will need to wait a while for the instructions and full kit to be available, whereas the Prusa is well established."

    Of course it will take you some time until you will be able to deliver kits.
    Therefore I want to ask you: can anybody else print your parts and sell them or does he need a licence from you?

    Best regards,
    Ron

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  35. Anybody can print them and sell them.

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    Replies
    1. Thank you nophead
      Now there are only two questions left: who will print them as well and who prints a really good quality.
      However, I will still wait for your 10 mm version - the XXL one ;-)

      It is a good idea to use the bed from the cut out of the gantry. But for saving weight do you think it would be enough to make the stands and especially the bed (moving part) from 8 mm MDF?


      Best regards,
      Ron

      Delete
  36. I don't know who else will print them but I certainly will.

    I found that MDF is not a good material for the Y-carriage as it warps due to the heat and atmospheric mositure and the bed does not stay level, so I use Dibond on the MDF version. I use 12mm for all the MDF sheets because they are all cut from the same sheet and they need to be thick enough for wood screws. It don't think it matters much how heavy the machine is unless you want to post it.

    The acrylic version uses thinner sheets because it is a stiffer material and so is more suitable to make the Y-carriage as well, especially as it is a lot more expensive than MDF, so it would be a shame to waste a big bit.

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  37. nophead, could you please tell the lengths of rods for sturdy90 model? I have a short window of opportunity to get those fast and cheap, but need to know the sizes to order..

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  38. A snapshot says they are:
    X 2 off 400mm x 10mm.
    Y 1 off 446mm x 10mm, 1 off 293mm x 10mm
    Z 2 off 281mm x 10mm

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  39. Hi, nophead.
    I have a question about "vitamins list" from thingeverse, about rod`s length
    "1 Rod 8 x 22
    3 Rod 8 x 275
    2 Rod 8 x 382
    1 Rod 8 x 428"
    are all of them right? there is more that six and what could I do with 8x22?

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  40. That is the axle for the idler bearing in the Wades extruder.

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  41. The three that are the same are two Z and the short Y.

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  42. If you attached both Y belt ends to one clamp in the middle of the carriage, you could move the Y Idler and Y Stepper inwards and remove 1 part.

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  43. True but I think it is better mechanically to pull the bed from its ends. It puts less turning force on the bed, so will produce less friction in the bearings and less side to side slop. I don't know how significant it is but I placed the X belt clamps at the ends of the carriage for the same reason.

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    1. One belt anchor and one belt clamp (for the bed) have pads. I guess the padded anchor with unpadded clamp are supposed to the motor side. The other anchor with the padded clamp are for the other side because of the twisted belt?

      Delete
    2. Yes that's right. The belt teeth face down on the motor side and up on the idler side on both the X and Y axes. The clamps have a tooth to engage with the belt teeth on the side where the teeth are and are smooth on the back of the belt.

      Delete
  44. "I also want to make a parametric PCB heater design to allow arbitrary machine sizes."

    I started working on something like that: https://github.com/nrpatel/HeatedBed

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  45. hey nophead, how long do you guess it will take to post the designs on github?

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  46. ETA tomorrow if all goes well. Never used git before!

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    1. I see a lot of printers using cantilever style for the bed, and either get bed going trou YZ(like mosaic) or only Z(like ultimaker)... those printers have very nice printing quality... what do you think of cantilever in a reprap?

      Delete
  47. I would imagine they are difficult to keep level to the required accuracy as that would require enormous stiffness with a cantilever. I can't see how it would contribute to print quality.

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    Replies
    1. hmm, I don't know... I mean, does the 2 motor thing passing each step is COMPLETELY reliable? I mean, most of the printers that are not reprap use cantilever, UP, cubify, mosaic, ultimaker, now the makerbot, etc... is that ONLY to get cheaper as it only needs 1 motor? I don't know... not making a point, just asking

      Delete
    2. I can't see how it saves a motor -- you still need to provide motive force for each independent axis. I *think* the cantilever design is used for its compactness -- without a full set of rails, the printer can be made substantially smaller.

      Delete
  48. hey nophead, I'm trying to choose a new printer for me, I see that the "default" for mendelmax is gt2 pulleys and belts and self-align brass bushings, I read your older post about rods and bushings and you didn't mention those brass bushings... what do you think of gt2 stuff and self-align brass bushings?

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  49. I think bushings are lower friction but will soon wear to give slop, whereas linear ball bearings are preloaded. They also seem to be self aligning to some extent as a single one allows angular play. It would also seem that you need high quality rods to use bushings.

    I haven't tried GT2 belts as they are not available in the UK. I don't have any problems with T5 despite what people say. There isn't any backlash with the pulleys that I use.

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    Replies
    1. ah great, also I forgot to ask, there is also ACME rods for the mendelmax kit, I never saw you mention that... why?

      Delete
  50. Because M8 stainless rods with brass nuts work fine for me. I made some measurements with a digital gauge attached to the z-axis of my Prusa and took measurements every 5mm. The result were accurate to +/- 0.01mm, which is probably better than the scale.

    I don't trade up to more expensive or exotic components unless I see a problem myself with the simple solution.

    ACME would give faster Z movement, but other than the long moves at the beginning and end of a build, the z moves only take a small fraction of a second.

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  51. I see the files have been posted to your github! Fantastic work! One question. I want to use the mendel config file but change the sheet good to MDF. I copied it to my own filename and substituted the MDF12 for the PMMA settings. Is there anything else I have to do to output a MDF mendel? Thanks again! Stuff is already printing for the build!

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    1. That should work. The effect will be to move gantry back a little and change the base and frame screws to No6 wood screws when you build it.

      Delete
  52. I saw the files in github, and I want to use these x ends and x carriage on my prusa, for that the only thing that needs to change is the prusa z motor mount to allow the smooth rod to be the opposite side and near the motor shaft... most of the solutions I'm thinking needs some sort of support, do you think you can make a z motor mount variant for prusa mendel that allows use of your x ends and x carriage?

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    Replies
    1. I have a design as I prototyped the axis on my Prusa. I will post it tomorrow.

      Delete
    2. I have added the prusa-z-motor-bracket.stl to GitHub. It works but it is a bit tricky to fit as the bar has to be inserted from below.

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  53. I noticed one more difference between the mendel and sturdy config. In the mendel config under feature sizes default_wall=3 and thick_wall=4. On the sturdy they are both 4. If I change to MDF in the mendel config does this setting need modification? Thanks again.

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    Replies
    1. No not really. The sturdy version use 10mm rods, bigger screws and thicker walls to make it, well, more sturdy. If you are using 8mm rods and MDF I don't think you want the chunkier parts and screws.

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  54. Hello Chris,

    Let's find here http://tmonnot.free.fr/Fraisage/Ninos_Repstrap/Mendel90.htm the current state of progress from my mendel 90

    I' had redrawn some of the part mainly to avoid M3 screws ( I'd rather M4 )and to gave better ajustment on M8 rods ( i'd better po print a little smaller ant to drill to 8 on a drill press to perfect diameter and perpendicularity

    I manadged to print big PLA parts on my CNC mill repstrap... for the X motor bracket, 13h printing... ;-(

    I wait for my 8 smooth rods. The frame will be 8 mm acrylic

    I will slighly oversized X carriage width and ( +15mm ) to authorized biger extruder body. the carriage body will be dibond made cause I coul'nd managed ABS big prints

    Many thanks for your great great job !!

    regards

    Thierry

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  55. Hi Chris
    I like the design of the Z-axis limit switch bracket, but it does a have a flaw. I printed it at the recommended density, 25%, but recently discovered that no matter how much I tightened the nut, I couldn't get the nozzle to start any higher. The reason was that the rubber washers were a bit stiff and the head of the bolt was just being pulled deeper into the plastic. You can just about see the distorted plastic in the black version here - http://img.photobucket.com/albums/v312/richgain/Mendel90/895ac08d.jpg
    I reprinted the part with 90% infill to make it stronger and also replaced the rubber washer with a softer one and it is now working well.
    Regards
    Richard

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  56. Hi Chris

    here is my Mendel90:

    http://tmonnot.free.fr/Fraisage/Ninos_Repstrap/Images_pieces/Mendel90.jpg

    some slight mods compared to your drawing

    will be connected to my CAM milling sotware "Ninos" with a stepstick board

    Regards

    Thierry

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  57. Hi nop head,
    I was finishing printing all parts of my "personalized" 10 mm acrylic sturdy version, and the last piece I left to print was the x_carriage.stl
    I printed it 2 times (lot of patience) in different flavors of my slicing program (I usa CURA) with 0,25 and 250 degrees (30 mm/s perimeter and infill,) ; 0.20 and 260 degrees (20 mm/s perimeter and infill), infill of 90% in both cases.
    In both times I have the same deffect in the piece...at my 60's it's difficult sometimes to understand a problem or to solve it....
    Can you give me please any clue about.
    You can see a picture of the piece at http://www.juanbe.com.ar/photos/100_2421.JPG
    All the rest of the parts had no problem at all. Only in the x_carriage was the problem.
    Thanks very much
    Regards

    Juan

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  58. De-lamination is normally due to using too low an extrusion temperature or too low width over layer height. Were you able to print the y-bearing holders as they are exactly the same shape?

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    Replies
    1. My layer witdth is 0,5 versus 0,25 or 0,20 height.
      Yes my y-bearings had no problem. It could be that that as the x-carriage is a so big piece, that when the extruder passes again over the underneath layer it takes a lot of time and the underneath layer is already cold ?
      In the y-bearings the extruder passes more frecuently at each point because the piuece is not so big.
      I will raise the temperature a little more...
      What is the maximum temp recommended for ABS ?

      Regards.

      Juan

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    2. I use 250C for natural ABS and 240C for coloured.

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    3. Thanks very much.
      Happy new year !
      Regards

      Juan

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