Friday, October 25, 2013

Tightening the frame and installing Y axis smooth rods (Videos 5 and 6)

Videos 5 and 6 deal with precisely positioning the nuts along the threaded rods and tightening them.

Contrasted with videos 1-4, these two videos are tedious to complete.  You use your digital caliper to precisely measure distances between the vertices so that everything lines up.

Measuring with digital calipers can be tricky.  My digital calipers are Pittsburg 12" model 47261.  This model lets you make a measurement and zero the display at any time with a press of a button.  All measurements after that are an offset to your original measurement.  It measures to within .01 millimeter or .005 inch.

You can measure the distance between the inside of two objects:

or you can measure the distance between the outside of two objects:

You can also make a depth measurement:

It's an "auto-on" caliper which means that it turns on automatically when you slide the jaws.

It also has a locking knob.  When the locking knob is tightened, it prevents the jaws from sliding which is useful if you want to set the calipers to some pre-determined size and susbsequently adjust something until the distance matches the caliper setting.

There is an important pitfall to avoid when measuring for this project: do not measure on any printed part or and nut or washer that is clamping a plastic part.  This doesn't give a correct measurement because the printed part compresses from the tension applied to it by the nut.  Only measure from the actual rods.

A few days passed since I completed video number 4 and one of the interesting things I noticed is that the nuts are not as tight as they were before.  I suspect this is because the vertices have deformed slightly as a result of the pressure applied on them by the nut+washer.  Since the vertices are printed using PLA with a 70% fill there are voids inside them that got compacted.

Around 2:30 into video #6 I also take some issue with the way that bearing for the Y belt is positioned.  The video states that it's important to get the bearing exactly halfway between the verticed.  In the video, a ruler is used to make a rough measurement of the distance between the vertices (234mm).  That number is divided by 2 (117mm) to find the half-way point.  The bearing is adjusted using a ruler also.  I feel the right way is to use the calipers to adjust the bearing until the distance from either side of the bearing to the neighboring vertex is equal.

Around 11:00 into video 6, the four bar clamps for the smooth rods for the Y axis are installed.  Two bar clamps are installed in the front and two in the back.  The distance between the two front clamps and the two rear clamps must be identical to ensure that the rods are perfectly parallel.  Having completed a later assembly video at the time of writing this blog entry and having experienced an issue, I have to state that I disagree with the advice given on the positioning of the Y-axis smooth rods.  The advice in the video is to measure 40 mm from one side to position the first clamp and then measure 139mm from the first clamp to position the second clamp.  What I found in a later video is that the result is that the center of the MDF board did not line up with the bearing for the Y belt.  It was very satisfying to see that the Prusa being assembled in the beginning of video #9 suffers from the same issue.  So my advice is to measure 20mm from either side to position front clamps.  This will center the clamps, the rods and the MDF board.  Then do the same in the back.  Then measure the distance between the two front clamps and compare it to the distance between the two rear clamps.  If they are different, adjust one of the rear clamps until the distance between the two rear clamps matches the distance between the two front clamps.

Thursday, October 24, 2013

Assembling The Frame

The first step in building a Prusa Mendel is assembling the frame.  This is covered in videos 1 through 4.

Building the frame was easy and fun.  In these three videos, you simply follow along.  It was easy enough so that my five year old son helped.

The Prusa Mendel is built on a frame that is composed of threaded rods and printed parts.  It is held together by nuts that you position along the threaded rods.  The printed parts form the vertices/joints that attach one rod to another.  There are six vertices - two triangles linked to each other at each vertex.

Included in the kit are two wooden "measuring" rods that are to be used as guides to establish the correct distance between the vertices.  I found this to be awkward and tedious.  Instead I used my digital caliper.  I was fortunate to have purchased a 12" digital caliper instead of the 6" caliper that was suggested in the introduction video.  The 6" caliper is not large enough to be a substitute for the two wooden "measuring" rods because it's not long enough.

At the beginning of video #4, I am asked to mount the two z-motor mounts and attach two stepper motors them.  There is some confusion about the length of screw to use to attach the stepper motor to the mount - first it says M3 14mm, then M3 10mm and then I believe it says M3 14mm again.  I tried the 14mm screws and they were too long, but the 10mm seemed to work fine.  This sequence of steps requires me to hold the screwdriver upside down to screw in the eight screws that hold the two motors which is really awkward because I can't see the hole in the motor. 

After the end of video #4, I started to question why I'm asked to mount the z motor mounts since they don't appear to be a key component of the frame.  Even more mysterious is why it is necessary to mount the motors at this point.  It seems like this could be delayed until a later time.  The other suggestion I have is to attach the motors to the mounts *before* sliding the mounts onto the threaded rods.  This would have allowed me to place the mounts over the motors which would have left the holes visible and avoided the awkward upside down screwdriver step.

Here is how things look after video #3:

Here is what the Prusa Mendel looks like at the completion of video #4 and the z motors have been added:

Tuesday, October 22, 2013

My Workspace

At this point I reviewed the first of the assembly videos called "Intro" to make sure that I had all of the necessary tools/supplies required during the assembly process. In addition to the required tools, I decided to purchase a digital voltmeter (DVM) that is capable of measuring temperature. I chose the Fluke 179.

Here is what my work-space looks like:

Note that the overhead lamp in the second photo is a vintage Dazor 2134 used by draftspeople in the mid-20th century. The box labelled "PITTSBURGH" is a 12" digital caliper. The assembly tools were purchased from a Home Depot, Ebay and Amazon.

Saturday, October 19, 2013

What the mailman brought...

The Prusa Mendel Kit arrived in a brown cardboard box measuring 20" x 11" x 8", weighing about 20 pounds.  Inside were a number of smaller boxes that contained the actual parts.  The parts in the smaller boxes were grouped by type.  For example, all of the printed parts came in one of the smaller boxes.  The rods came in a cardboard tube.  Everything was neat and organized.

The only suggestion I have for NWRepRap is to pack the outer box in another larger box.  The power supply was slightly damaged because it was positioned right at one of the corners of the outer box which got a bit dented.

Wednesday, October 16, 2013

The maker-apprentice's mentor and tools.

Every apprentice needs a mentor to teach the craft and a set of tools to practice his craft.  I, the maker-apprentice had neither.  So I did my research on the web and here is how I found both.

A Google search for "3-D Printing" returned a huge variety of resources dedicated to 3-D printing.  Probably the most useful site was  After going through this site, it became pretty clear that the primary tools of the maker-apprentice are the 3-D printer and the software.

The choice of printers falls roughly into two categories: buy or build.  Many firms are offering solutions that are supposed to work out of the box.  All you have to do is set up the printer, boot up the software and you're in up and running.

Since I'm a tinkerer and I enjoy building things, I dismissed the idea of buying a ready-made printer out of hand.  For the do-it-yourself type, had information on how to build your own printer.  The bottom of the page stated:

"If you are new to RepRap, you should probably start with a Prusa Mendel (if you want big build volume or Huxley (if you want a small machine). 

BTW a "RepRap" is a machine that can make a significant fraction of its own parts.  In essence the machine can reproduce itself to a large extent.

So I chose to build the Prusa Mendel.  Note that since I made this choice a few months ago, a newer design called the Prusa i3 (iteration 3) has emerged which addresses some of the Prusa Mendel's shortcomings, but introduces quite a few new challenges.

The list of parts and directions for building a Prusa Mendel are available on  The parts can be grouped roughly into these categories:

  • Printed Parts
  • Fastener (includes zip ties)
  • Rod (smooth or threaded)
  • Belt
  • Stepper Motor
  • Springs
  • Electronics + Sensors
  • Bearings
  • Heated Bed
  • Extruder Assembly
The software necessary to design 3-D objects and control a Prusa Mendel is available free.  A very popular choice for 3-D design is Google Sketchup.  There are also tools needed to convert the Google Sketchup files into instructions that can be sent to a Prusa Mendel.

There are two approaches to building a Prusa Mendel: (1) buy all of the parts separately (2) buy a ready-to-assemble kit.  I was pretty intimidated by all of the various parts and tools required.  I'm sure that I would have learned more by buying all of the parts separately, but being new to 3-D printing I was wary of the risks of things simply not working.  So I started looking around for a kit.

The site makes it fairly easy to find all of the vendors selling kits in any given country.  When I was doing this research in January/February 2013, I believe the list had just one vendor selling Prusa Mendel kits in the US which was EasyRepRap.  At the time of writing this blog entry, there are seven vendors listed.  The problem I found with the EasyRepRap kit was that it does not include the printed parts.  This made it necessary to order them separately or find someone to print them for me.  I didn't want to do this because I was afraid that something just wouldn't fit.  So I kept looking.

Luckily I found an outfit called NWRepRap which sells what appeared to be a high quality Prusa Mendel kit with all necessary parts except for the computer to run the design software and the necessary tools.  The NWRepRap web site contained links to a series of videos that show how to assemble the kit step-by-step.  I felt that these videos were a huge selling point because they showed each step of the process very clearly. 

The 25 videos were created by a gentleman that identifies himself as Aaron Dale.  The videos are generally under 10 in length each.  Aaron speaks slowly and clearly with a folksy mid-western accent.   The camera looks down onto Aaron's workbench and records all of the action from above.  You never really see Aaron's face, all you see is two arms working to assemble the kit.  A couple times we see the back of Aaron's head when he leans into the shot.

For some reason Aaron tries to create distance between himself and NWRepRap by saying things like "this kit comes from NWRepRap", but don't be fooled by this - Aaron appears to be running NWRepRap because he has answered all emails that I sent to NWRepRap and signed his name to the note that was included inside the kit.

So having chosen to build instead of buy and to use a kit instead of procuring the individual parts, I placed the order for the kit.  Two weeks later it arrived at my front door...

Monday, October 14, 2013

What is a maker-apprentice?

After several rather busy years helping raise 2 young children, I've been fortunate to have gained a couple hours per week of free time as the children have grown. Instead of spending those precious hours in front of the TV, I decided that a new hobby would be more stimulating and rewarding. Since I'm technically-oriented, I looked into a couple hobbies that would allow me connect computer control with the physical world. Two hobbies that made the list were model railroading and 3-D printing. While I've played with model trains as a child and model railroading seems as popular as ever, I chose 3-D printing because it is growing incredibly fast and looking to disrupt traditional mass manufacturing technology.

What is 3-D printing? According to Wikipedia, 3-D printing is the process of making a three-dimensional solid object of virtually any shape from a digital model.  This is usually done by depositing a melted substance in a controlled fashion.  As the substance solidifies, an object is created  as you can see in this video and many others on YouTube.

One of the dictionary definitions of "maker" is someone who creates, makes or fabricates something.  The 3-D printing community has embraced this term to refer to anyone who is passionate about learning, using and improving 3-D printing technology.  I have to admit that I have not determined the time or place when the 3-D printing community chose the word "maker" to refer to a member of its community, but this usage is pretty universal and consistent - from Meetup announcements to industry web sites.

An "apprentice" as we all know is someone who is starting out and learning a skill or trade or craft.

So a maker-apprentice is someone who is learning 3-D printing.  Having chosen to learn 3-D printing, I have become the "maker-apprentice".  I am entering the world of 3-D printing as a total newbie and I will attempt to document my experiences in this blog for all would-be maker-apprentices to follow.