FTIStrap

an overview of (an earlier version of) the FTIStrap

This page describes the "FTIStrap", a RepStrap which is almost completely built from FischerTechnik parts. Constructing an FTIStrap neither needs any special expertise nor any special tools and can usually be completed within a single working day. All parts can either be ordered online or found in many stores in your neighbourhood. After printing the parts for a RepRap the FTIStrap may even be disassembled again and its parts used for other projects.

(please note: because of relatively strict time limits, I plan to document the FTIStrap piece by piece finishing around midth of november)

Introduction

The FTIStrap is a "RepStrap" which almost completely consists of FischerTechnik parts. Stepper motors are used as actuators, the interior of a hot-melt gun forms the extruder and a (removable) glass plate acts as the base to print on. A FischerTechnik "Robo Interface" together with an extension module (both running in "online mode") control the steppers and scan the end stops - they can be connected to an IBM-compatible PC running Windows or Linux or an Apple Macintosh running MacOS X. The FTIStrap is completely "host-controlled" - a small application running on the host can be used to either manually operate the machine or load and interpret a file containing the "G codes" for a RepStrap.

The FTIStrap's main "advantages" are

• it almost completely consists of FischerTechnik parts - including steppers and the driver and interface electronics - which can all be ordered online
• the few remaining parts (hot-melt gun, balsa wood, sand paper, fan, glass plate) can also either be bought online or found in various shops in your neighbourhood
• no special tools are required to build the FTIStrap - although a hacksaw is recommended to cut the balsa wood which covers the hot-melt gun
• no soldering is required - all the electronics you need is already available from FischerTechnik
• when all parts are available, the whole FTIStrap can be easily assembled within a single working day
• as soon as you no longer need the FTIStrap (because you used it to build your own RepRap), it can be disassembled again and its parts used for other projects

The current printing characteristics are

• position accuracy: approx. 0.1 mm in all directions (i.e., approx 256 lpi)
• material thickness in xy direction (i.e. line width): approx 1.0 mm
• material layer thickness (z direction): approx 0.5 mm

The hot-melt gun which is currently used needs cylindrical hot-glue sticks with a diameter of 7mm. The gun melts them at a temperature of approx. 230° celsius which is hold by a thermistor within the gun. The rigidity of the printed objects depends on the thickness of their walls (in relation to their size, of course): one of the first printed test objects, which accidentially got thicker than foreseen, turned out to be really rigid.

Part List

The list of FischerTechnik parts has been automatically generated by the "FischerTechnik Designer" which was used to model the FTIStrap and document its building phases.

(tbd - still waiting for the designer)

Besides the FischerTechnik parts, you will also need

• a Proxxon hot-melt gun (Proxxon no. 28192, or a similar one if you don't mind modifying the extruder casing and its feeder)
• a strip of balsa wood (10mm thick)
• some heat-resistant glue (the author used "Uhu hart" for that purpose)
• a little bit of (rough) sand paper (to cover the cylindrical drives of the hot-glue feeder)
• a glass plate (17.2x12.5 cm*cm, taken from a "frame-less picture frame" which usually costs less than 1€)
• a cheap fan (12x12 cm*cm, 12V)
• some cable straps
• some silicon oil (to reduce friction along the plastic thread rods)
• if need be: a USB-to-Serial converter and/or a serial cable
• if need be: a 12V power adapter for the FischerTechnik interfaces and/or the fan (if you do not want to buy the FischerTechnik PowerBlock)

and, of course, you will need

• hot glue sticks (e.g., Proxxon no. 28194, or similar - depending on your actual hot-melt gun)

The tools you should have:

• a small screw driver (for the Fischertechnik steppers - you may order them together with the other parts)
• a sharp knife (to carve the balsa wood into shape)
• a frame saw (to cut the balsa wood - if need be, you may use the knife for that purpose, but a saw usually gives better results)

Extruder Construction

The extruder consists of nothing but (the interior of) a conventional hot-melt gun which was enclosed by layers of balsa wood and fixed within two FischerTechnik parts (part no. 36297 or similar)

This is the Proxxon hot-melt gun (Proxxon no. 28192) which was actually used - if you prefer another one, you may have to modify the balsa wood casing (and probably the feeder as well).

the Proxxon mini hot-melt gun

If you open the casing, you will see its inner parts

inner parts of the Proxxon mini hot-melt gun

Just take the heater element and remove everything else. Important: do NOT cut-off the silicon guide for the hot-glue sticks (as the author did on this picture) it is really important for the proper functioning of the gun! The author's first gun turned out to be completely useless and he had to buy a second one to continue! The feeder is now by far strong enough to shift the sticks through the guide into the heater element.

heating element and cabling

(tbd)

FTIStrap Assembly

(I've started modelling the FTIStrap with the "FischerTechnik designer". Unfortunately, the "Demo Version" handles up to 10 elements only - this is what you see below - and the "Full Version" is still to be shipped to me...)

the beginning of an FTIStrap model made using the demo version of the "FischerTechnik Designer"

(tbd)

Cabling

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Driver Software

The "FTIStrap Controller Application" provides everything you need. It can be used

• to test and calibrate your set-up
• to move the FTIStrap manually
• to load and evaluate G-Code files

It won't get an award for its user interface but should still be intuitively usable

an early snapshot of the FTIStrap Controller Application

(tbd)

Initial Startup of the FTIStrap

If you have not done so, start the "FTIStrap Controller Application" - it will be used to test and calibrate your set-up.

Check the End Stops

First of all, you should check the proper operation of your end stops - this includes a test of (a part of) your cabling and the proper communication between your PC and the FischerTechnik interface.

(tbd)

Check the Steppers

Now, you are ready to test the proper operation of any steppers - this includes a test of the remaining part of your cabling.

But before, make sure, that none of the end stops is touched by any part of your machine - it is important that the steppers can run free for a few centimeters, at least. Also, do not "load" the feeder with hot-glue sticks yet.

(tbd)

Move into the Origin

Let the driver now move the system into the "origin" (i.e., the smallest possible x-y-z coordinate) Do not forget to place the glass-plate at its foreseen position in the FTIStrap before.

(tbd)

Check easy Movement along all Axes

Using Fischertechnik parts for constructing a 3D printer is not really a professional approach. Thus, it is very likely, that your thread rods are not exactly parallel. Additionally, the plastic parts suffer from more friction than metallic parts would.

For that reason, you should first check for easy movement along all axes and, if need be, align all rods and reduce friction by means of a little bit of silicon oil.

(tbd)

Calibrate the System

and save the current configuration

Check the Hot-Melt Gun (and the Fan)

It is now time to heat up the hot-melt gun and fill it with glue for the first time.

Thus, energize the heating element and wait a few minutes. In the mean time, you may slide a first glue stick into the feeder and - using the Controller Application - move it down until it reaches the silicon guide.

As soon as the heater has reached its target temperature, move the stick down fast for another two centimetres and then slowly further. Watch the casing while doing so and stop as soon as the casing seems to bend away due to the pressure of the feeder - in that case, just wait until the casing bends back and continue. Sooner or later you should see the first drop of hot glue being pressed through the gun's nozzle.

Now, the heater element has been successfully filled with hot-glue.

You should now also check the fan - just to be sure it works.

Check the Base Alignment

It is very likely, that your glass plate is no exactly parallel to the x-y axes. This is checked by printing a large (but thin) grid over the whole glass plate. From the results of that print you get information about where to lift the plate (e.g. by means of one or several layers of adhesive tape) and whether glass plate and rods are straight enough (or whether they bend because the extruder and its feeder are too heavy)

(tbd)

You are now ready to start your first print.

Operation Manual

(tbd)

Tips and Tricks

Quite often, people using hot-glue for printing complain that they were unable to remove their objects from the base plate they printed on - the author never had these problems. The possible reason for successful printing might be:

• a glass-plate is used as the base to print on
• just before printing this glass-plate is wiped with a "multi-purpose anti-static" cleaning cloth which is usally used to clean computer monitors, mobile phones and other devices
• after printing, the object may then be vertically detached from the plate (perpendicular to the base layer) - detach with a bit of care, but it usually gets off easily

(tbd)

Material Recycling

3D printers may also have some nice ecological side-effects: you may use them to "repair" broken devices - and you may reuse the material of failed prints and printed parts which are no longer needed.

The author is currently experimenting with an approach to cast his own hot-glue sticks - more to come...

(tbd)

Software Downloads

The "FTIStrap Controller Application" has been developped with REALbasic on an apple Macintosh running MacOS X - but it may also compiled for Windows XP/Vista and Linux x86.

(tbd)

Modifications and Extensions

The current design is far from being perfect and was often motivated by the parts the author had at home while constructing the system. However, one of the most important advantages of using FischerTechnik was (and is) the ease with which new variants can be built and tested - sometimes, it takes only minutes to realize an idea and see how it works.

For that reason, the FTIStrap is the ideal platform for testing alternatives. Among the supposable modifications and extensions are:

• enhancing the stability of the whole construction
• the integration of different extruders
• provisions for two (or even more) extruders
• any kind of approach to handle overhangs

Additionally, it is quite straightforward to

• control the heating element and/or the fan by the host

Enhancing the Stability of the Construction

Currently, the FTIStrap is built from plastic parts only - an approach which works reasonably well (especially, as the driver software takes care of many shortcomings such as friction and vibrations).

On the other hand, FischerTechnik also offers aluminium bricks which are more rigid than other parts (not only because of the material but also because they combine several connected bricks into a single, longer one). If you just replace plastic components by aluminium bricks (where possible) you will enhance the stability of the construction and reduce vibrations during the print.

As a consequence, you might be able to speed up printing (by modifiying the relevant parameters) or apply other modifications (see below) which require an enhanced stability.

Integration of different Extruders

At the moment, the design of the FTIStrap does not foresee an exchange of the extruder - extruder, feeder and y-axis slider are tightly connected to each other. The installation of another extruder would first require the disassembly of the current one - and then you might even have to modify the slider before mounting a new extruder.

On the other hand, it should not be too difficult to modify the design such that the extruder could be replaced without too much effort. Just take care that the modified construction does not become too heavy for the x-axis thread rods or you will have to modify them as well (e.g., by integration of aluminium bricks instead of plastic parts, see above)

It might be an interesting challenge to integrate the "standard" RepRap extruders into the FTIStrap frame - these are far more advanced than a simple "hot-melt gun". Or to integrate one of the syringe-based extruders preferred by the Fab@Home project. Just keep an eye on the overall weight of your construction.

Provisions for two or more Extruders

Mainly because of the size of the FischerTechnik base plate, the effective printing space of an FTIStrap is smaller than that of a RepRap (or of many other RepStraps). It would therefore be rather difficult to integrate more than a single extruder without reducing the printing space even further.

Overhang Handling

Without additional provisions, an extruder-based 3D printer is unable to print arbitrary overhangs - additionally, all printed objects have to start either on the base plate or (unlikely) on another object. The "Darwin" RepRap design tries to overcome this deficiency by means of another extruder which prints an (easily removable) "filler" to support any parts printed on top of it.

A potential alternative might be the "padding" of unprinted areas with some kind of powder before proceeding to the next layer, where the powder could act as a support for printing.

Future Plans

As usual, the author's activities suffer from his very limited time. For that reason, it is rather unlikely that it will be before 2009 that the FTIStrap will take its next step - the handling of overhangs (in any way). Currently, the author prefers the padding of unprinted areas with powder, but it is completely unclear if such an approach can be successful with hot-glue as print material.

Configuration File Format

The FTIStrap Driver saves several settings (and the results of a calibration run) in a "configuration file" which can be (manually or automatically) loaded prior to the first print after starting the driver. Currently, however, the file contains more information than can be entered through the Controller Application. Thus, it might be necessary to edit the file manually - here is its format:

(tbd)

References

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