LaserCut Mendel Assembly For Complete Beginners

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Revision as of 10:52, 13 May 2011 by RaphaelLuckom (talk | contribs) (Tools)
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Until this sentence is removed, I have not finished my build and this guide will not describe the whole process.

These instructions describe the assembly of a TechZone Mendel kit, which is one of many options to build a RepRap.

I'm almost entirely new to building things. I got a laser cut Mendel kit from TechZone because that seems to be my speed--I can basically manage to put something together from prefab parts, but I don't have access to a shop or a large collection of tools or the skills to use either. I think that's the situation of at least a few people taking on this project, and the best contribution I can make to this wiki is to describe the experience, and the things I learn about process, from the perspective of an absolute beginner. Much of this will probably be obvious to anyone with more experience. Some of it will probably be wrong or misleading--point it out if you see it. I think helping newbies is important, but I also suspect that it can be frustrating for experienced builders to answer the same simple questions over and over. I hope that with this guide I can provide a resource for some of the more basic issues newbies will face that more experienced builders take for granted. I also have an ulterior motive; I hope that I can document things carefully as 'repayment' for people taking the time to answer my questions, to save them the trouble of answering those questions again.

Using This Guide

This guide is structured around tasks in sequence rather than around the design of a reprap, and refers to the complete Mendel kit from TechZone as purchased in May 2011. This guide, and my assembly, began May 7, 2011. If you have found it in an unfinished state, it's probably because my build is still incomplete. I would be delighted to see others adding things to and commenting on anything I've written here; it would be especially helpful to me if, when you do so, you leave a note on the discussion page or in the text letting me know what changed or got added and why.

Other Resources

These are the things I found myself navigating to over and over as I put the kit together (Still in process etc.):

  1. LaserCut Mendel Assembly seems to be the most complete guide, but it's at least a little out of date relative to the current kits; it shows an extruder made of laser cut and glued wood.
  2. The LaserCut Mendel Assembly Blog has more pictures and is sometimes useful in terms of mechanical structure, but seems to describe a hybrid Mendel/Makerbot and the electronic connections look much more complicated than most other builds I've seen.
  3. The TechZone Tip Assembly page.
  4. Gary Hodgson's visual guide to the Wade's Geared Extruder[1]. (WARNING: It is different from the extruder in the kit in important ways, so you can't build from those instructions, but it does provide a good overview of how the extruder works.)


Laser Cut Mendel Kit

This is basically just to say that I've found TechZone's service to be very helpful and responsive. I actually purchased through Ebay because I prefer to use Paypal rather than the Google checkout system TechZone uses (Google already knows the content of my emails and much of my browsing activity via Google Analytics; I see no reason to also tell them about my financial transactions). When I needed to purchase ABS filament, however, Kimberly Andrus at TechZone sent a Paypal invoice for it (thanks!). If I was going to purchase the kit again, I'd probably request an invoice from her because it's more difficult to tell exactly who the seller is when purchasing from Ebay. The seller on Ebay I purchased from was hnd3; that seller IS affiliated with TechZone (as of May 7, 2011).


I've got an idea of making a sort of 'standard tool kit' such that I'll be able to gather the tools I used for this task and lend them out together (or even go with them to help with assembly). That way people who want a printer won't also have to bear the costs of acquiring tools they won't use again. In that spirit I've divided the list of tools below into 'buy-once tools'--things that experience little or negligible wear per use, and which it would make sense to lend--and 'use-once tools and materials'--things that experience complete or considerable wear per use, and which it wouldn't make sense to lend.

Until I remove this sentence, the following list is still a work in progress and probably misses some things:

Buy-once tools

  1. Multimeter
  2. Meter Stick (so far I've only had to measure small things)
  3. Soldering iron
  4. Tabletop vise and spring clamps (I got a tabletop vise because I knew there would be times I would need a stable way to hold things while using both my hands to manipulate them. I was immediately glad I did. It also has a flat surface that I think is meant to be used as an anvil. This is good for things like using a razor blade to strip the insulation off a wire.)
  5. Hex keys (2.5mm and 3mm)
  6. Phillips-head screwdrivers (#1 and #2)
  7. Adjustable wrench (haven't used yet -May 8)
  8. Set of jeweler's files (I'm not sure they're necessary, but they were useful for reaming the Reprapped parts that came with the kit. Without them I think I would've needed something else to do abrasion, like sandpaper or a Dremel tool)
  9. Pliers
  10. Drill (9.6 V)

Use-once tools and materials

  1. Tape (scotch for holding wires in the tip assembly)
  2. Silicone Grease (haven't used yet -May 8)
  3. Ziploc bags
  4. Solder
  5. Razor blades
  6. Sandpaper


The TechZone kit came with several sealed plastic packages of hardware parts. At the beginning of my build, I transferred the contents of each clear plastic sealed bag (NOT including the electronics, which are in pinkish translucent bags and which I don't want to handle until I'm ready to assemble them) to its own ziploc bag. Others have used store-bought parts bins--I wasn't sure which would have compartments of the correct size. The ziploc bags also allow me to store larger parts (such as the laser cut pieces too small to be placed loose in the shipping box and the motors) and to nest subsets of the hardware bags within other bags. If I want to label the bags I can, though I haven't felt the need to do so yet.

The parts arrived in the best configuration for shipping, which (mostly but not always) means that they are not grouped by their position in the assembly of the final machine. My first step for any assembly task is to gather ALL the parts and tools I need for that task, and ONLY those parts and tools, onto my workspace. I have two rules for this:

  1. The workspace must not have anything on it before I start gathering parts for the current task.
  2. If I have placed a part on the workspace that turns out to be unnecessary, I must put it back in the bag it came from immediately.

This strategy allows me to focus on one task at a time and ensures that I won't be distracted or confused by anything unrelated to that task. It also forces me to define each task narrowly and specifically enough that if there's something I don't understand, or if there's a tool I need that I don't have, I'll realize that before I start.

Assembly Tasks In Order

My goal is to document each assembly task with at least two pictures: one picture of the 'initial condition' showing all parts and tools required for the task with the parts in the most disassembled state, and another picture of the 'final condition' showing the assembled parts after the task has been completed. I think I will end up including intermediate pictures for most tasks.

Extruder Tip Assembly

The consensus seems to be that this is the first task to complete, at least partly because it involves glue that takes 24 hours to set. It is already documented well in the TechZone Tip Assembly article, but I'm going to include some notes here because making my own notes helps me understand what's going on. Update: While completing this step I noticed a few things that seemed like they'll become important down the road, either in other assembly steps or during operation. I've tried to note those things in this guide so that when those things come up, or when I have to replace the tip on the working machine, I see what decisions I made in this process and why I made them.

The extruder tip, or "hot end" is the part that melts the plastic. It does so using joule heating[2], the process of running an electric current through a conductor to release heat (This process is really interesting to me; it forced me to remember the chemistry class explanation that temperature is really a measurement of the movement of the atoms that make up a material. When a lot of electrons start moving through a conductive material like nichrome wire, they bump into other particles, accelerating them and raising the material's temperature). The nichrome wire is the loose coil of thinner wire in the picture below (the thicker wire is a thermocouple[3], discussed later).


All the parts of the tip assembly. Note the white cylindrical piece, which isn't yet on the hot end assembly page. It measures 16mm in diameter; the same diameter as some of the PEEK/PTFE thermal barriers I've seen in other models. It's an adapter so that this tip will fit into the Wade's Geared Extruder as shown in the following pictures:



It fits around the outside of the teflon insert in the oak block, and has countersinks for the screws that in the previous design attached the hot end to the extruder body:



Then the adapter fits into the hole on the bottom of the extruder:



The following four pictures show what I think is the correct orientation of the Wade's adapter to the oak block. I'll need to drill sideways through the adapter to attach it to the extruder, and I want to make sure the screws attaching it to the oak block don't get in the way.



This is a rough sketch I made to make sure I understood the relationship between the tip (far right), the extruder (middle), and the x-axis carriage (left). The circles with letters in them denote the places where bolts attach one piece to another (You can see that I'm still learning to name things appropriately; the circles with 'x' and 'y' on the extruder and x-axis carriage should have used different letters to avoid confusion with something related to the axes--they're just the holes used to attach the extruder to the carriage.) Notice that what I've labeled as the 'C' and 'D' bolts go sideways through the adaper; thus, the 'A' and 'B' screws attaching the adapter to the oak block must be aligned out of the way.



Next picture is adding the tip.


Shaping the thermocouple


The first step on the TZ assembly page is to use a multimeter to test the thermocouple wire. A thermocouple is a pair of wires of different metals joined to each other at one end. For a reason I don't quite understand, the fact that the metals are different means that the wires generate electrical current when they're heated. By measuring that current you can calculate the temperature where the wires are connected.

The idea is that there should be very little resistance to the flow of electricity across the thermocouple. I misunderstood what was going on the first time I read the directions; the 'ends' of the thermocouple wire that you're supposed to test are NOT what you'd think of as the 'ends' if you're just looking at it. As noted above, the wires in a thermocouple are *connected at one end*. That means that one end of the wire looks like a metal knot. Don't mess with that end. The other end of the thermocouple should have two wires poking out; a red one and a yellow one. Touch one of the probes of your multimeter to each end with the multimeter set to measure resistance (this is the side of the dial with an omega, which is the symbol for Ohms, which are units of resistance. There are several settings to measure different orders of magnitude of Ohms; you'll probably see notes for 200, 2000, 20k, 200k etc. Because you want to know whether the resistance is above 6 Ohms, use the 200 setting; the lower the number, the more sensitive the setting). Hopefully your multimeter shows less than 6. Mine was around 3. 200 Ohm multimeter setting:


testing the thermocouple:


Stripping insulation off nichrome wire:


"lead" wires taken off motors:


Stripping the insulation from the lead:


The TZ assembly page shows the process of wrapping the nichrome wire around the tip and attaching it to the leads afterward, and notes that some might find it easier to attach the nichrome to the leads first, then wrap it around the tip. That looked like an easier way to do it, so below I've shown the leads and nichrome as I attached them. I did try to solder the connection using the technique shown on the TZ page, but I'm pretty bad at soldering things and I'm not sure I did any good. I tested the resistance of the assembled wire (testing the ends of the leads after they'd been attached to the nichrome) with a multimeter and came up with a resistance of around 7 Ohms. I hope that's within tolerances, but I guess I'll find out when I test it. I also realized after I'd finished that I'd neglected to use something abrasive to remove the ceramic insulation from the ends of the nichrome after stripping the other insulation. If I have problems down the road I'm probably going to start looking at that first.




As I was wrapping the nichrome wire (already attached to leads) around extruder tip, it occurred to me that the way it's wrapped might affect the distribution of heat while the tip is in operation. I found that the threads of the screw made the wrapping slightly irregular--the wraps tended to try to be perpendicular to the threads where they crossed. I also think I put a slightly higher density of wraps toward the base of the tip rather than toward the tip. If that turns out to be a poor decision I want to remember to do it differently next time. The following shows the wrapping:


Wrapping with thermocouple:


Did not have enough hands for picture of the next step, gluing around the nichrome. Finished: