McWire (Death March: Do not build!!!)
McWire is a Death March. Do not build one. You have been warned! :D
<sebastienb> Think anyone will complain if I move <sebastienb> http://reprap.org/wiki/McWire_Cartesian_Bot_1_2 <sebastienb> to <sebastienb> http://reprap.org/wiki/McWire_Cartesian_Bot_1_2_(Death_March: Do not build!!!) <chronomex> haha <tesla893> i built a mcwire :( <sebastienb> Page moved.
This is a guide that will help with the decision making and build process of the McWire RepStrap. If you don't have access to printed parts, which as this point in time is most people, you have to bootstrap your reprap using a 3d printer build from standardized or commodity parts. The McWire device is probably the simplest and least expensive device to do that with, it is also considered the current 'official' and possibly best support device to bootstrap with (Unless you count the RepMan.). That being said it has some significant drawbacks.
In the same way that photographers say "The best camera is the one you've got", McWire is currently the best RepStrap we can offer. The other RepStraps are much sexier, but do not exist yet.
Why or Why Not Choose Mcwire
Not sure on whether a McWire is right for you? Hopefully this section can help.
Some Pros About McWire RepStrap
There are some definite advantages of going the McWire route.
Ability to convert to milling CNC - It's possible to switch out different tool heads. The screw-driven axes offer the torque needed for light milling.
Opportunity for cost savings - The free form design offers an opportunity to use things you may already have to build your machine. MDF instead of laser cut plastic? Rubber bands instead of springs? You get the Idea.
Parts or substitutions are easily obtained - Besides the electronics most of the parts can be bought at a local hardware store.
Build Platform Easily Accessible - The build platform is front and center. Not surrounded by a box.
Loose accuracy requirements - The McWire cartesian bot is very forgiving of sloppy workmanship. Because the motion is along extruded aluminum U-channel, if your bed isn't straight or square you'll still be fine. This is a design that's quite forgiving to jury-rigging.
Flexible Parts List - The McWire can usually be built out of whatever you can find locally. You'll need some iron, steel, or sturdy plastic pipe. Threaded might be easier, but you could make it work with glued together pipe too. The bearings can be any size that you can screw down. The lasercut plastic parts are easily cut yourself from MDF, cutting boards, plywood, ODF, whatever. The aluminum U-channel is one part that you might have a hard time finding a replacement for, but you can make pretty much any sized channel work.
Inexpensive - We are working on re-documenting the McWire build using the least expensive, easily available in local hardware stores or online in both the US and Europe to make this a cheap introduction home rapid-prototyping and as a way to make parts for a Mendel or other RepRap that uses primarily RP parts.
No Special Tools or Special Parts - The McWire is designed to be made entirely from parts you can buy from many sources, and using simple tools. No lathe, mill, CNC macine, or welding equipment is needed, although a drill press will be very helpful.
Some Cons About McWire RepStrap
Development Halted Development and official improvement to the McWire has stopped. Because there are a number of faults in the function of the McWire, the RepRap community is currently working to come up with a successor to the McWire. (for more information on that, see this page: Development:McWire_Successor
Slow Speed - The 1/4" - 20 screw drive is slow and this leads to builds that are not as fine or as fast as other machines. In total it will take approximately 200+ hours of print time to complete the printed parts for the mendel. Some people have had some success with using 1/2-16 rod instead.
Not Standardized - No two McWires are built the same. McWire is a concept driven into reality by the individual maker. Your first parts list will not be your final parts list. The design presented on the Seedling website does not offer standardized measurements and may be subject to your printer's whims. Fortuntely, the design is relatively flexible without significant cost in functionality. Put simply: You can mess up pretty bad and still have a working printer.
Some Build and Design Experience Required - You need to be able to work with tools, measure accurately and cut (fairly) straight.
Lack of re-use (additional cost): A few people have had success using the McWire for other purposes such as a CNC milling device with a mounted dremel. In fact that was the original purpose (the McWire is derived from Tom McGuire's original instructables.com concept). Officially and as described here the McWire is not a very good, durable, accurate and reliable CNC device.
Where to Begin
In many ways, the McWire RepStrap (aka "Seedling") can seem like as monumental a task as building a Darwin or Mendel RepRap. Relax. Building your McWire is going to take work, but won't be as overwhelming as it may now seem. The greatest advantage you can give yourself is to Plan Ahead. Think about what you're going to do before you do it, and why. This falls within the same logic line as "Measure twice, cut once." You can save yourself significant time and money if you plan ahead
Beginning with the Cartesian Robot The Cartesian Robot can be a good place to start if you have the tools and materials available to you. Because the cartesian robot is a relatively flexible design, you can make design changes to accommodate your needs and what you have available to you.
Beginning with the Electronics If you can get ahold of the electronics you prefer to use, starting with their construction can be rewarding. You can build and test your electronics without having constructed the cartesian robot.
Beginning with the Toolhead Beginning with the toolhead (typically an extruder) will help you to get going once everything else is done.
There are a number of websites in which builders have documented their experience putting together a McWire build. You may gain significant insight by going over their experiences. Here are the links to some of the sites:
In Most cases, you will need the following tools:
- A Drill Press (A hand-drill can be used, but it is more difficult)
- Drill Bits: 10-24 (#25), 3/16", 5/16"
- A hacksaw (or other saw capable of cutting aluminum)
- A Screw Driver
- A Tape Measure
- A paper printer (for printing out templates)
- Double-sided Tape and paper/Adhesive sheets.
- A pipe wrench (for tightening base)
- A 10-24 screw tap (self-tapping screws are included in the design for this purpose, but it is quite difficult to tap the holes with those.)
An example McMaster Carr Parts List: (imperial)
1x 95462A033 1x 91083A033 1x 90275A714 1x 90494A030 1x 91083A030 1x 90273A581 3x 91034A100 1x 98273A255 2x 8735K111 1x 88805K57 1x 9001K34 3x 4549K606 1x 4549K595 2x 4549K602 3x 44605K115 1x 68095K121 1x 44605K155 2x 44605K105 2x 98847A029
Complete detail for informational purposes:
|1||95462A033||1x Pack Zinc-plated Grade 5 Steel Hex Nut, 1/2"-13 Thread Size, 3/4" Width, 7/16" Height|
|2||91083A033||1x Pack Plain Steel Type A Sae Flat Washer, 1/2" Screw Size, 1-1/16" Od, .07"-.13" Thick|
|3||90275A714||1x Pack Zinc-pltd Stl Flat Head Slotted Machine Screw, 1/2"-13 Thread, 1-1/4" Length|
|4||90494A030||1x Pack Plain Grade 2 Steel Thin Hex Nut, 5/16"-18 Thread Size, 1/2" Width, 3/16" Height|
|5||91083A030||1x Pack Plain Steel Type A Sae Flat Washer, 5/16" Screw Size, 11/16" Od, .05"-.08" Thick|
|6||90273A581||1x Pack Zinc-plated Stl Flat Head Phil Machine Screw, 5/16"-18 Thread, 3/4" Length|
|7||91034A100||3x Each Black-oxide Steel Coupling Nut, 1/4"-20 Thread Size, 5/8" Length, 1/2" Width|
|8||98273A255||1x Pack 410 Ss Type 23 Thread-cutting Screw, 10-24 Thread, 1/2" Length|
|10||735K111||2x Ft. Bar Made Of Teflon(r) Ptfe, Rectangular Bar, 1/8" Thick, 1/2" Wide, 2' Length|
|11||88805K57||1x Each Architectural Aluminum (alloy 6063), 90 Deg Angle, 1/8" Thk, 1-1/2" X 1-1/2" Legs, 8' L|
|13||001K34||1x Each Architectural Aluminum (alloy 6063), U-channel, 1/8" Thk, 3/4" Base X 3/4" Legs, 8' L|
|16||4549K606||3x Each Std-wall Galv Welded Steel Thrd Pipe Nipple, 3/4" Pipe, 12"l,thrded Ends,17/32"l Thread, Sch 40|
|17||4549K595||1x Each Std-wall Galv Welded Steel Thrd Pipe Nipple, 3/4" Sz, 3"l, Thrded Ends,17/32"l Thread, Sch 40|
|18||4549K602||2x Each Std-wall Galv Welded Steel Thrd Pipe Nipple, 3/4" Pipe, 6"l, Thrded Ends,17/32"l Thread, Sch 40|
|19||44605K115||3x Each Low-pressure Blk Malleable Iron Thrd Fitting, 3/4" Pipe Size, 90 Degree Elbow, 150 Psi|
|20||68095K121||1x Each Low-pressure Forged Steel Flange, Threaded, 3/4" Pipe Size X 3-7/8" Od, 150 Psi|
|21||44605K155||1x Each Low-pressure Blk Malleable Iron Thrd Fitting, 3/4" Pipe Size, Tee, 150 Psi|
|22||44605K105||2x Each Cast Iron,125 Psi,3/4" pipe,round Head Cap|
|23||98847A029||2x Each 18-8 Stainless Steel Threaded Rod, 1/4"-20 Thread, 3' Length|
1x Mother Board (or Arduino)
3x Motor Driver boards
1x Extruder Board
1x ATX Power Supply
1x USB Cable
Local Hardware Store
Build and measure as you go. Don't try to drill all holes, cut everything, and have everything semi assembled before putting things in place. Don't rely on the stickers that you can print out as the only measurement, they are guides. Drill holes once you have the bolts that you will put through them. Buy your pipes before cutting the vertical base. The plans show 1/2-inch attachment holes for the vertical base but you may only be able to find 1/2-inch holes on the pipe flange.
The original McWire is built from 3/4-inch water pipe. It has a "C" shaped base consisting two 12-inch pieces of pipe (called nipples by plumbers), connected to two 90 degree elbows then two 6 inch pipes that connect to a "T" with the bottom of the T pointed upwards. The T connects to a third 12-inch piece that goes up to a 3rd 90 degree elbow and a 3-inch piece of pipe that connects to a floor flange. The aluminum "C" channel that becomes the sliders for the X-Y stage bolt across the bottom legs, and the Z axis stage bolts onto the floor flange.
An alternative to water pipe is steel boxed tubing. The advantage of using the boxed tubing is that one length of 1 inch, thin walled box tubing is cheaper than all the pipes and fitting needed for the standard pipe frame. The disadvantage is that you must find a friend (or a friend of a friend) who is a welder to weld the pieces together for you. Once properly welded (you must make sure that the legs are flat and sit securely on a table, and the top bracket is exactly perpendicular to the X-Y table), you have something that is stronger, lighter, and more permanent then the pipe frame.
Another alternative is to build the frame from MDF. Make a bottom plate with an extension in the back for the vertical plate (Z Axis support) and the triangle gussets that keep it vertical
Assembling the Base
The McWire base is made up of lengths of pipe (called "nipples") which screw together. No matter what your starting point in screwing it, the tightening point will always end up the same. Because of this, you will want to assemble your base an tighten it to the point you feel comfortable with it's structure, and then mark the legs for drilling. Make every effort to get the holes vertically faced. If The holes are slightly off vertical, don't worry. The structure of the McWire is forgiving in this regard and you should still be able to connect the x-rails without difficulty.
Tapping the Screw holes in the base
In the McWire base, there are 4 points which you mount the x-rails to. While the self tapping screws are capable of cutting screw threads into the pipe base, this is not an easy task. Alternatively, you can use the following method to tap the holes using a tap:
1) Drill your hole into the pipe using a proper bit. This bit should be one designed to drill metal and of the proper size. These screws are 10-24, so you should have a 10-24 bit, that is, a #25 bit. Drill using cutting oil to ease the work on the bit and make it go smoother.
2) Once you have a clean hole, put some cutting oil into the hole, and place your tap into the hole. Turn it and put a small amount of pressure on to the back of the tap to push it down into the hole. As you turn it you will feel resistance. Every full rotation or so, as you've felt some difficulty turning, back the tap out slowly, and add another drop of cutting oil (or 3-in-1). Screw the tap back in and continue to cut into the hole.
3) Repeat that process until your tap is through the hole. This process is important because your tap is not invincible. It is not difficult to break your tap off in the hole. (The author has done this)
Keep the hole well lubricated and you should be just fine. You can use the self tapping screws for this, but keep in mind that you do need a significant amount of torque to tap the hole, and it can be really difficult with just a screw. If you do choose to tap with the screws use cutting oil. Like the tap, the screws need cutting oil to smooth their movement into the pipe. If you're concerned about the process, drill a hole on the side of the pipe and do a trial run. It might take you some extra time, but you won't damage the base significantly and you'll know better what you're doing when you get to tapping the holes.
The Sleds (or stages) are the platforms that the McWire bot moves around via stepper-motor-driven leadscrew. The official instructions describe these platforms being built out of acrylic, but you can use virtually any material that is flat and not prone to warping. Examples include: MDF, Aluminum Plate, or Steel Plate.
The Sleds use two methods of making sure they travel smoothly and correctly across the rails. The first is PTFE (commonly known as Teflon - but that is a brand name) 'bearings'. These are small strips of PTFE that are screwed to the bottom of the platform. Because PTFE offers very little resistance, it slides easily and allows the entire sled to move.
The second set of bearings are constructed of small arms (made of acrylic, or some other simple material) with common skate bearings attached. These arms pulled tight against the rail via a spring. The rails in turn are pulled against a second set of skate bearings attached to the sled. These bearings are permanently fixed. In this way, the sled will uniformly with the rail, keeping it straight.