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* Pop Rivets and Underframes

* Modify your Sieg C2A Lathe

* Assembling a low cost CNC Router / Laser Etcher

* OpenSCAD and Sample 3D Print Files

* Extended Guide to 3D Printing

Technical

3D Printing.

This has become quite common and in fact is something that I researched before coming to the conclusion -that with the high price and low number of things I would print with it I didn't need one! Most modern commercial kits are based on "Iteration 3 of the J.PRUSA design" or "i3PRUSA". A group of four of use once seriously contemplated buying one between us that would I feel have given the RepRap a suitable market for its use...

These are ideal for the production of several parts for models and can use either ABS plastic or PLA. The main use for them could be the production of casting masters.

The paragraph above was true when I wrote it some months ago. However the market has "crashed" and it is now possible to buy £350 machines for a little over £100...

The three articles below (updated June 2019) detail the construction and use of an i3Prusa RepRap kit, OpenSCAD which is the "Design Software", and CURA which is the "Production Software".

The production cycle for a RepRap system is:

A RepRap compatible machine, there are SEVERAL designs available. A design program that can produce STL files from the raw design, again there are several programs. There are several sources of both STL and GCODE files on the WWW. Chief amoungst these is the site "Thingiverse". A production program that takes the raw STL file and generates the GCODE file for the RepRap to use dependant on the choice of machine, material and user options...

I have documented the ones that have appealed to me and I have found very easy to build and use.

Now that you have some idea of what is possible -the next problem is what do I do first? The basic text files for OpenSCAD will have given you some primitives to work from. You should be able to assemble a station from them -just as I have. The station as printed is 1.8metres long and 50cm wide. The primitives are taken from LMS stations but given the time period... A short survey of the Art Deco style as mostly used by Southern and the Futurist style as adopted by the LNER will give you the working basics.


The Laser Etcher.

I bought my laser etcher at the end of 2018. It came as a Chinese made kit and with "Chinglish" instructions. Fortunately along with it on a "thumb drive" came the software and a short video on how to put it all together. The machine is rated 450nm at 2.5W -which may not sound a lot but is more than enough to cut through 160g/m2 card or 1mm thick ply at one pass.

The bed of the device is A4 -however the cutting area of the device is A5. This means that there is a lot of waste if only using A4 sheets. My normal use of this device is to make templates. Although it does sterling service cutting gaskets... At the moment I am using it to build a 2-NOL from the Locomotive Designs plans.

The standard software for this device is called Laserweb, (current release is 4), The software will take scans in the format of PNG or you can produce drawing in SVG or DXF format for it to use. The software is easy -but I would caution that it does require some practice before you undertake major operations with it. The system can be programmed to accept scans from scanners -but the default setting for the DPI may not be the correct one required for perfect scaling. In the case of my device the scaling is 577 DPI for a 600DPI PNG image.

The main problem using the software relates to the cutting speeds and the laser intensity. 100% laser power can easily cut and set fire to your work at the same time... 10% to 20% and using multiple passes is probably a better bet. The speed of the cut really defines how much time the laser will be in the same place. It is "about right" for cardboard at 200cm and 300cm for wood.

Focussing the laser is a manual operation and has to be done with the laser glasses removed -however the glare can be quite painful. If you wear the glasses then these should block the laser frequency -but this leaves you with the problem of trying to focus something that is now invisible! I have found that a laser focus of 0.1mm is achievable with a few attempts.

The best results are produced with the laser in RASTER mode. This is similar to the old 625line B+W tv as it produces a point with either an on/off state. The laser is driven via a PWM driver and you can set it to produce 256 shades of grey if required. Mostly you will set it to Black only.

I have tried it with "laser plastic" in the hopes of producing my own builders plate and shed code plates. The main problem is the fact that the plastic cannot really cool down fast enough between passes as you are dealing with fonts in the 5pt to 8pt region. Large "poster" scale size fonts in the range 16pt to 24pt will cut with little difficulty.


Assemble a CNC Router and Laser Etcher.

The following PDF file will show how I constructed a 3018 Pro kit CNC Router and laser etcher. This is a "step up" from the simple laser etcher as detailed above and uses a 5.5W laser and a 24V motor. It is however more a semi industrial machine than a domestic one...


CNC GCODE -the common language of 3D printers, Lasers and Routers.

Although the GCODE instructions have been around for several decades -the instruction set is still increasing as new problems need to be addressed in the manufacturing arena. The code is a simple text stream and can be fed into the device by a serial cable (USB or 9pin) or held on a memory store (SD card). The code is very robust and simple to implement. It does however have one serious problem...

If the machine firmware that the code is being "pushed" to, does NOT understand the line of code -IT IGNORES IT. This means that the firmware in your device has to be kept updated. Most machines in the Domestic market use the Arduino chipset. This can be reprogrammed using the Arduino toolkit suite of programs (they are free).

In the case of a RepRap the firmware program is called MARLIN and is updated very rarely, MARLIN can only understand 150 of the GCODES. Current mainstream release of MARLIN is 1.2. Ver 2.0 "may" be available in Q1 2020(?)

In the case of a Router or Laser the firmware is called GRBL (say Gerbil). The current release of GRBL (Jan 2020) is 1.1H. The easiest way to update your GRBL firmware again is to use the Arduino IDE Toolkit.The complete sequence is detailed in the PDF below.


CAD and CAM

Computer Aided Design... I am going to assume that you have some form of mainstream computer in front of you. This can be a MAC, a PC -or a UNIX workstation. There are several OS specific programs for each of the three options that I listed. On the MAC there is TurboCAD. On the PC there are dozens -the market leader is AutoDesk Products, on the UNIX workstation very few are not found with Solidworks.

But instead I am suggesting that you opt for GNU GPL programs that will run on all three systems. This is not to say that they are any better -in some respects they are far worse... But, they all have one overriding plus factor -they are easy to use.

I would recommend LibreCAD as your CAD design system.The current release is 2.0. It is free, but it is a bit of a memory hog! The design menu options are well thought out and the built in library of parts shows its PCB and architecture design origins. The laser cutter shops will accept LibreCAD files in the format DXF rev 2007. This is the default format of LibreCAD.

Computer Aided Manufacture... The manufacture part of it is the difficult one to pin down. The program I recommend is called LaserWeb. Despite its name the machine options that it has include outputs to Mills, Routers, Engravers, Lathes and Lasers. The main problem with using it is that it is a GERMAN program. The words are English but the method of working it is pure DIN standard. When put onto the cutting area the objects automatically set up at 0.0.0 however the position of the object is defined on the cutting screen by its centre. This is perfect for cutting circles -but makes non circular objects a bit of a puzzle. There is an on screen "twiddle box" to edit the positions of each object. Each item on the list maybe cut in any of the various options. The machining list may be grouped and the sum list "rubber stamped" all over the cutting area.


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Page last modified on January 06, 2020, at 07:11 AM