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Rep Rap

The Bits in the Box.

The name Rep Rap comes from the Repeatable Rapid Prototype project of the University of Bath. The idea was to produce a machine that was simple and cheap to make that could produce its own parts -or more machines. The modern range of RepRap machines have been produced from the GPL designs of the Czech Josef Prusa. Most machines are now based on the Iteration 3 machine design - Prusa i3

My Prusa I3 RepRap machine arrived as a box with two layers each of foamed plastic. Each assembly was clearly marked and logically arranged in the layers. The instructions came on a CD and were in PDF format. The documentation is however in "Chinglish" but everything was understandable with only one exception. This was the "plug out" for the main PCB -however the RepRap Wiki provided an English wording for it. The kit is made from laser cut 6mm plywood and slots and bolts together with ease. It is a two person job as it often requires a "third hand" to hold the part whilst bolting up. The kit comes complete with all the tools for assembly -a range of Allen keys and a screwdriver. The assembly of the main part took about six hours for two people, wiring and "plugging" it took a further two hours. I would advise you to do the wiring and "plugging" as you progress the assembly as some of the wires require feeding through holes. Careful wiring discipline is essential as the cables move as the bed plate and printer arm move and elevate. Ensure that the cables when installed do not pass through loops of other cables.

 Spaghetti is allowable but Macrame is (K)NOT...

Armour the cables with "spiral wrap" or "spider wrap". The former is easier to apply the latter is far more robust.

There are several "after market" parts that you might consider at this stage. I have bought; An additional five micro switches for movement detection (23p each), a set of five PTFE top bushes for the Z columns to damp down vibration of the screws (10p each), two CNC grade aluminium flexible couplers for the Z axis motors (£2.06p each), and plugs for the additional micro switches (£1.49p for a bag of 50).

The Build....

The first pic shows the contents of two layers of the box. The main upright comes with a special screw fitted on the RHS of the frame. This is a dome head to prevent the Y carriage from bashing into it, the rest of the fixing are M3 caphead allens of 6mm 12mm and 16mm sizes.

After about 2 hours of slotting parts together and tightening up the allens you arrive at the basic frame. The X axis is the heated bed (red square) the Y axis carries the printer head carriage and the two vertical M8 threaded rods fit, with shrink wrap tubes, to the motors.

The next step is "plugging up" the motors and sensors etc. Fortunately the supplied cables are (seemingly) over long but once threaded through the holes in the frame they are correct. At this point I would recommend that you use "spider wrap" to armour the sensor cables as they are somewhat fragile. This is a black nylon tape "tube" rather like an orange net. In that the mesh expands to encompass the cables and snaps back once released.

The "power" cables are best fitted with "spiral wrap". To ensure good working curvature thread a couple of pieces of filament into the spiral wrap. This will take the working strain -rather than the cables.

The next shot is the most difficult part of the construction... The control PCB is PLASTERED with sockets. They all have individual functions but nearly all use the same connector(!) So a short guided tour.

Top LHS is the main DC feed to the PCB. Top centre is the feed to the heated bed. Top RHS is the feed to the Printer heater.

The two ribbon cables are the feeds to the control display panel.

The four small PCBs are the motor drivers. The black green red blue cabled plugs are the feeds to the four motors.

The bottom row is the heater fan and cooler fan.

Orange and Black are the Z axis sensors. Green and Red are the Y axis sensors. Brown and Blue are the X axis sensors.

The next shot shows the RepRap after construction and before the "after market" parts have been installed. You can see the stepper motor that draws the filament through the heater assembly and squirts it out of the brass nozzle below. The heater block has a thermistor to regulate the temperature of the block. This can be set from the control knob on the display. panel.

This shot shows the Y axis motor and the other Z axis motor. The microswitch "stop sensors" are visible on the top of the Z motor and side of the Y carriage. The connection between the Z motor and the M8 threaded bar is by the supplied "shrink fit" flexible coupling. It does work very well -I just don't like it...

Is it hard to build? The answer has to be no. Are the "after market" parts essential? The answer has to be no -but they do fix a few "niggles I have and I think they should be bought. What will it print? It prints Polymerised Lactic Acid (PLA) and Acrylonitrile Butadiene Styrene (ABS), The former is reckoned to be the easier to use and takes CA very easily, whilst ABS is stronger it requires careful setting of temperatures.

The Control Knob.

This is actually the only control on a RepRap and consists of a multi turn switch and with plunger. Turning the knob presents the user with a menu, pressing the knob selects the item on the menu. There are LOTS of menus...

You will have to use the menu options to setup your printer and align all the motors to the stop points. It took me a week of faffing with the thing to get the settings perfect. Now that they are, the only option on the menus I use is "Print from SD card". This afternoon it has printed six stop lamps and one station gate. It is now as boringly functional as the washing machine or tumble drier. Load it up, select the program and go and do other things whilst it works...

Some of the things not noted in the manuals are the height of the print nozzle above the bed and the tape used to cover the bed. The nozzle height is about a playing cards thickness from the bed. This allows the plastic to "pour" onto the bed and not "squirt out" between the nozzle and the cold build. I have found that of the two common filament media PLA is far easier to use then ABS. It has a lower melting point, is very hard and is slightly translucent. This is not really a problem as I always prime my models. So it is not important if they are pink, purple, blue or red... If you are building a large >6cm long print then use "Masking Tape" or "The Blue Tape" (oil protective painters tape) on the glass bed. This will stop the print sliding about on the glass bed whilst it prints!!! If you have a "big" print then rubbing a small amount of "PRITT" across the bed improves adhesion.

The quality that is acceptable is up to the user. My initial test print of a stop lamp was done at coarse resolution 0.5mm layers. It printed in 85 seconds and simply proved the printer worked. It looked like a very rough model of a stop lamp. But I was happy with it. High resolution of 0.1mm layers produced an acceptable print of a stop lamp in 13 minutes but the layer marks are visible, but these will disappear under primer. Ensure that your feed filament has plenty of slack off the reel. The feed motor to the printer head is fine with at least a loop or two off the reel, what it cannot do is to haul around a 1kg reel of filament.

Is a RepRap the perfect modellers tool? I would say that it gets me to 95% of what I want, while I do other things. The final 5% is down to me anyway.

Materials that are printed

Myriad materials are available, such as Acrylonitrile Butadiene Styrene (ABS), Poly Lactic acid (PLA), Poly Carbonate (PC), Poly Amide (PA), Poly Styrene (PS), "Lignin" (a wood fibre & nylon composite), rubber, and chocolate among many others, with different trade-offs between strength and temperature properties. In addition, even the colour of a given thermoplastic material may affect the strength of the printed object. Clear and Green are thought to be the the strongest. Recently a German company demonstrated for the first time the technical possibility of processing granular PEEK into filament form and 3D printing parts from the filament material using this technique.

The type of material that is printed depends on the capacity of your print head. I use a 0.4mm nozzle and I have a 0.2mm and 0.7mm nozzles. After some experimentation I have found that the 0.2mm nozzle requires very high temperatures to keep the feed at a fluid temperature and it does clog easily because of this. The 0.7mm nozzle will produces acceptable replacement parts for my Rep Rap as they wear out and things like brackets and holders etc. The original RepRaps only used PLA printed parts and they have lasted for several years. PLA is actually a plastic known in Roman times and they made theirs from boiled milk and vinegar and they squirted it between joints of hot wood to make a glue, which proves there is nothing new....

Filament feed material is available in two standard sizes 1.75mm dia and 3mm dia. For 1.75mm filament expect to pay about £11 for a 1Kg reel of PLA and about £25 for a 1kg reel of ABS.

Operational checklist and "what to buy next"...

The main thing to check is that the print head is securely fixed. As the nozzle is Brass, the heater block is Aluminium and the feed mounting tube Steel -these expand and contract at differing rates. The only way to be sure is to tighten everything up while it is hot -with the caveat that everything is going to be at a minimum temperature of 200C... The eventual cheat used by me was to drill tap and fit M3 grub screws that held everything tight -whether it wanted to come loose or not.

Make sure that the feed reel has plenty of slack to it and give it the occasional twirl to free more. I have taken to mounting my feed reel on its side and having the feed filament "spiral" off it.

Check frequently on the state of the PTFE feed pipe after the feed motor to the print head. This can split and you will have molten PLA etc oozing out of the top of your print head which when it cools embeds the assembly in plastic! You have to "preheat" the head and then take it apart and scrape out the muck.

The PTFE pipe is available in 1m lengths at 99p per metre. NEW print heads are very cheap, buy a batch of 10 from eBay and then you can swap out the clogged ones very easily. There are micro drills to help unclog the nozzles. I would recommend that for normal work a 0.4mm nozzle is fine and for detail work a 0.2mm nozzle. I have a couple of 0.7mm nozzles for printing brackets and other non visually critical things. The resultant prints from them are not pretty but brackets and hangers do not have to be that aesthetic...

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Page last modified on January 20, 2018, at 02:24 PM