Saturday, 14 March 2015

The dilemma- Lead screw or threaded rods

my previous 3d printer that i had built used threaded rods for the linear motion along the z axis, while this seemed to work fine there was a particular point upto which we could get accurate. No matter what we did after that the z axis accuracy seemed to be at that particular state. The individual layers were still visible and our printer could be easily distinguishable from a professional printer. We worked hard and toiled day and night calibrating it but to no avail. 

the problem was that we happened to be using threaded rods. Threaded rods were never meant to be used for linear motion, they have designed for exclusively for fastening objects together, hence their threads don't have a very good finish and have a lot of friction with the nut, they also have a very low efficiency in terms of transferring power. Hence you will need to get a powerful motor to carry a relatively smaller load.

Lead screws on the other hand were designed to transfer load along the linear direction, they are popularly seen on lathe machines. They have an efficiency varying from 30% to 90% and hence make it a better option over threaded rods, they are also better at handling tensile and compression loads, since they are made of a slightly different material.

Threaded are way cheaper than lead screws and very easily available in most hardware stores unlike lead screws, but lead screws though more expensive have better accuracy and precision. If you could afford it I would definitely recommend lead screws.

Also read up more about this here:


                                                                                          

Thursday, 10 July 2014

Building your very own 3d printer !

The first step.


Building your own 3d printer seems to be an amazing project but could also be a bit confusing in the beginning. The aim of this guide is to give you a basic idea about the procedure and for those of you who live in Chennai procurement details are also provided. 

So getting back to the first step which is construction of the frame. The frame is the part that acts as the support and carries the loads of the motors,rods, bearings etc. It needs to be rigid and you have to make sure it doesn't bend at any point during loading. I have worked with two different materials, one was Acrylic and the other was sheet metal you can choose what material to go for based on cost and availability. Make sure you design it properly to avoid any sort of bending that may take place due to the loads. Those of you who know how to use  advanced CAD software's can design the frames using the help of these software's  and for those of you don't you guys can just download google sketchup and design it there. Sketch up is a relatively easy software and is free to download and has many tutorials on youtube. While designing your frame you will have to keep in mind that accommodations for joints, motors and bearings must be given. In the beginning its better to use pre-existing designs of the more famous desktop printers with maybe a few modifications of your own. The following is a list of basic materials you will need. Some of the frame design will depend on the specifications of the parts you are purchasing.

A picture of my design on the Catia software
  1. Linear bearings : Linear bearings help for smooth movement along the given axis. Since we have three axis's we will require three sets of these. There are various types of linear bearings like smooth rods with bush bearings ( ex : LM8UU ) or rail with block bearings these are the two I have worked with. Stability of the rail with block is much higher but comes out a bit more expensive as well.  

                           
  2. Stepper motors :  Steppers are used to create the X Y Z movement. Their positioning is very important and there are also various ways to transfer the motion. You can use a rack and pinon set up, Screw rods or Timing belt and pulleys. I have used the timing belt and pulleys cause of their relative ease and also since I have never worked with rack and pinon before. For the Z axis alone we use screw rods cause it can carry the load on its threads. Positioning plays a major role in the design so make sure you have decide this before you start the frame design. Most 3d printers use the nema 17 stepper motor, so in case you are new to this you can stick to buying the nema 17.                                                                                             
  3. Joints for the frame : Since the frame is made of acrylic you might have to make the frame by joining the various sides of  the acrylic. The acrylic can be laser cut to any shape you want, but remember that the machining can only be done from the top. You will need to keep in mind the exact location of the joints on each piece so that they are aligned at the time of fixing. This is done only for acrylic.
A piece of my frame drawn in 2d on Sketch up.
So these are the basics for you to start of on you CAD model. While working with the CAD software the most important thing is the shape of the frame and placement of steppers. I generally make sure the placement of the motors and bearings are perfect and don't add the joints. After am happy with the 3d visualization I then start drawing each piece of the acrylic on 2d using sketch up which is an open source software. On sketch up I add the details of the joints along with the other details from my CAD drawing. Once that is done it can exported to .svg format and this file can be used for laser cutting. To convert your 2d diagram to .svg, requires a pluggin that can be downladed for free as well.                                                                                      
A close up of the joint ( this gives you an idea of how to design the joints )

 If you are new to CAD then I suggest you make your printer with acrylic frames as its a lot easier for you to design and you are likely to make lesser mistakes. Also try using this software called tinkercad.

Below is list of parts that needs to be bought. Incase you don't understand the need for a part you can leave a comment below

List of parts and specs
1)      Acrylic frames  :  12 sq feet area , 6mm thickness for improved stability, laser cutting process for close tolerances in dimensions
2)      A2 stainless steel rods : for support.
3)      Acme screw rod + nut : length of the rod 255mm , 10 mm dia 3 mm pitch , 
4)      Stepper motors : Nema 17 stepper motors , No. of motors 5., Procurement based on calculation and price
5)      Bearings : Ball bearings arranged in a cylinder : LM8UU this has two types cylinder type and flange type : Ball bearings arranged in a block : MGN12C
6)      Extrusion Mechanism: Mk8 nextruder mechanism ,
7)      Motor to shaft coupler : 5mm to 8 mm dia coupler , Procurement based on shaft dia’s
8)      GT2 pulley + GT2 timing belt : pitch of 2mm , belt width of 6mm, Procurement based on research done by other 3d printing projects
9)      Fastners : dimension yet to be decided
10)   Electronics : Arduino mega board + RAMPS 1.4 shield + 5 stepper stick
11)   Power source: 12V, 20 A , Procurement based on Arduino board requirements
12)   Limit switches

Most of the electronic parts were purchased from http://diy-india.com/store/ the advantage of using diy india is that they are located here in Chennai, they still charge for shipping though.

The hardware parts such as the bearings smooth rods and screw rods were purchased at Parrys. The street names are Thambu chetty, lingi chetty etc. They have tons of shops that sell bearings. make sure you visit at least five shops before you purchase anything.


Sunday, 29 June 2014

What is 3d printing ?



A lot has been going on in the news about 3d printing but to really understand its awsomeness one must understand its working. 3d printing is a layman's term to Additive manufacturing which is what it was originally called when this tech first came out in the 1980's!. Yes 3d printing has been around for a long time and is growing at a rapid pace of late due to its commercialization. So getting back to its working, there are about three basic steps involved. 
  1. Creating a CAD model.
CAD stands for Computer Aided Design. This is the digital model that can be made through various software's,  some are free and the advanced software's come at a price. Using the various tools available inside the software you can create a virtual design of the object.

    2. Converting to .stl

Once you have created your digital model you need to convert it into an STL file format. This file will contain the basic geometry of your model.

     3. Upload and print 

Once your done converting to .stl you will need to upload it on to another software that will interface with the machine and will be able to tell the printer the X Y Z co-ordinates that it has to move in. This also cuts or slices the object into layers. Greater the number of layers better the quality but the time taken will be more.


From the information given to the 3d printer the nozzle of the printer moves around extruding material in the molten state layer by layer, each layer being of about 0.1 mm thickness and hence the term Add-itive manufacturing was created cause we are adding material and building an object from ground up. It is similar to making things using lego blocks. The major advantage of this method over conventional manufacturing is that a lot of material is saved. In conventional methods we start with a block of material and slowly remove the pieces that are not required like how a sculptor works. Hence we can clearly see a lot of  that time and money is saved.