LaserCut Mendel Assembly For Complete Beginners

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Revision as of 11:36, 9 May 2011 by RaphaelLuckom (talk | contribs) (Overview)
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Overview

Until this sentence is removed, I have not finished my build and this guide will not describe the whole process.

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, so that they don't get 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 LaserCut Mendel Assembly seems to be the most complete guide, but it's at least a little out of date relative to the current kits; it shows an extruder made of laser cut and glued wood.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.)

Acquisition

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).

Tools

I'm embarrassed to say that when I started I had almost no tools at all. However, that makes me uniquely qualified to describe EVERY tool necessary for the build, because if I needed it I probably had to go get it. Until I remove this sentence, the following list is still a work in progress and probably misses some things:

  1. Multimeter
  2. Meter Stick (so far I've only had to measure small things)
  3. Soldering iron/solder (haven't used yet -May 8)
  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. Razor blades
  6. Hex keys (2.5mm and 3mm)
  7. Silicone Grease (haven't used yet -May 8)
  8. Tape (scotch for holding wires in the tip assembly)
  9. Phillips-head screwdrivers (#1 and #2)
  10. Adjustable wrench (haven't used yet -May 8)
  11. Set of jeweler's files (Ironically, these I already had lying around, even though I didn't have a ruler. 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)
  12. Pliers
  13. Ziploc bags

Organization

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.

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. The conductor is the nichrome wire: the thinner wire in the picture below (the thicker wire is a thermocouple[3], discussed later).

The tip consists of several parts:

These are the parts that came together in a package, and which I think are all for the hot end. Note the cylindrical piece next to the oak block and the long bolt and nut, which don't seem to be on the hot end assembly page

I also notice that the oak block has a drilled hole parallel to the hole the tip is supposed to go into:

the smaller hole on the right doesn't have any purpose I know of. I think the long bolt and nut in the previous image are associated with this somehow.

Note the white cylindrical piece, which doesn't seem to be 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.

Cylindrical piece. Another insulator?


Cylindrical piece. Another insulator?

I also notice that it fits around the outside of the teflon insert in the oak block, and has countersinks that look the same size as the screws that are supposed to attach the hot end to the extruder body:


Cylindrical piece relative to oak block?


Cylindrical piece relative to oak block?

If the cylinder was attached to the oak block that way, it could fit into the hole on the bottom of the extruder:


Cylindrical piece relative to extruder body?


Cylindrical piece relative to extruder body?

This answer doesn't quite satisfy me. First, I can't imagine why a thermal barrier would be necessary there, except perhaps if it's just to fit into an extruder body that was designed for use with a cylindrical tip. Second, the tip assembly page talks about attaching the tip to the extruder body "using the two screws provided. The screws are normally installed at a slight angle." If the cylinder is supposed to be where I think it is, the screws can't be at an angle because they go through the holes in the cylinder. Last, this explanation doesn't shed any light on the purpose of the second hole in the oak block.

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.