Ferrules are solid terminators for multi-strand wire. They are used where the wire is connected to a screw or spring clamping terminal. The solid pin of the ferrule provides a much better termination in the screw terminal than bare wires.
Note that applying solder to the end of the wire in order to create a solid pin is not recommended. The contact point with the connector is small and the solder is liable to deform, especially if the connection is heated, and as a result the wire loosens in the connector. Ferrules overcome this problem.
Ferrules also reduce the risk of a stray strand of wire escaping from the screw terminal and shorting against an adjacent connector. When this happens to a fine strand there is a risk of fire occurring before the fuse blows.
Ferrules are typically crimped to the wire in order to ensure a solid connection. A common form of ferrule is a tube which is crimped around the wire to form the solid pin. However this does not work well for very small ferrules.
A suggestion for very small ferrules is to use the pins from a male solder-tail D-type connector, as commonly used for serial data cables. The connector can be disassembled by folding out the tabs of the shield and separating the molding pieces that secure the pins. The pins then fall out.
The pins are exactly 1mm in diameter, and fit small screw and spring-contact connectors very well. The soldered area is about 6mm long and provides a solid connection for the wire. It is not subject to clamping pressure from the screw connector so the soldered joint remains solid. The portion beyond the connection pin can be covered with heatshrink.
When soldering multiple rows of headers to modules it is important to get them properly aligned, or they will not fit the breadboard properly and may break a solder joint when forced. In order to align rows of headers correctly before soldering, insert several rows of pins across the headers. These extra pins will ensure that the headers are parallel and upright, and will also provide a convenient base for holding the assembly during soldering.
A precision 6mm block with wire connection for the height sensor input of a 3018 CNC machine.
The
economy versions of these machines come with a controller that supports
height sensing, but no sensor. The purpose of the sensor is to allow
the operator to define the zero level for the work surface. This can
be done by eye and feel, but a simple sensor that detects the circuit
between the tip of the milling bit and the sensor surface simplifies the
procedure considerably.
The usual approach is to use a small piece of angle aluminium. The problem is that the thickness is not precise, and it can be difficult to get a reliable touch confirmation. The precision 6mm steel block used here sits firmly on the work surface. It happens to have a second hole through the middle which conceals that soldered connection from the securing wire to the flexible connecting wire, and a piece of heatshrink adds a little additional support to the solder joint. A 0.8mm female header connects through to the controller board (there is a matching wire running from the controller to the spindle).
Using a steel block has the added advantage that it can be stored against a magnet that has been screwed or glued to the frame at a convenient point.
Many projects require pieces of prototyping board, either for the actual prototyping or as the finished item, so cutting up pieces of board is a common task. A cut-off disk on a Dremel tool does this, but using it freehand is not always easy, and it's actually bigger than is required. This little project re-purposed a small DC motor (probably from a printer) by combining it with a collet, an arbor and a cut-off disk in a 3D-printed mount to create a miniature table saw that cuts straight edges through protoboard easily. It likely would find other uses that projects require.
The motor is an 18V 1.2A Tamagawa TS3062N1 running at
between 3,000 and 5,000 RPM. It is powered with a laptop plugpack.
The main shaft is plain and takes a collet. The rear shaft is threaded,
and in this case has been mounted with a grinding wheel which can be used
to clean up the edges of the cut. It is mounted using the original
mounting plate at the front: If this plate is missing the printed base
would need to be extended up to the holes adjacent to the shaft, and the
screws would have to be extended slightly to accomodate a thicker support.
The arbor shaft is located in a pair of 8mm ball bearings. The ones selected for this project had a lip on one side which enabled firm mounting in the frame, but the screwed cap is actually firm enough to hold plain bearings easily. The bearing cap could be extended to provide a much larger table surface, but it has not been found necessary as yet. If it was extended then supports would probably required from the base. The screws for the bearing cap were specially selected for the shallowness of the head, to enable a very shallow countersink.
The finished unit has a socket for the pluckpug mounted on the base, and the motor wiring connected to the socket. An on-off switch could be added. A reversing switch is also possible, to allow both left- and right-handed use.
It is
possible to make up IDC cables without the need for a special clamping
tool. This jig is used to clamp the ribbon cable in the connector,
with both the cable and connector located in the jig so that the whole
assembly can be placed in a vice and clamped. The crosswise groove
accommodates the head of the connector, while the lengthwise groove
accommodates the cable. There are four inserts set into the jig so
that a clamp for the cable can be used, but this is often not
necessary. With the connector pushed into its slot, the cable laid
through the connector in the groove, and the cable clamp screwed down (if
required), the whole assembly is then positioned in the vice while being
held by the cable, and the vice tightened down. The completed unit
can be removed from the jig by pushing from the hole in the bottom.
The cable is then folded back over the header and the retaining bar pushed
on (this might also require pressure from the vice, at it is a very tight
fit).
The obvious drawback of the device is that a different jig is required for each size of connector, but they are easy to design and print, and most projects use only one or two widths of cable.
When multi-core ribbon cable is stripped down to the required number of cores the red stripe marking pin one is lost. It can be recovered using a broad-tipped permanent marker pen. With the pen tip pushed gently vertically onto the edge of the cable and then run along the length of the cable, a very neat edge marking can be achieved. The width of the pen tip is sufficient to allow it to overlap slightly around the edge of the ribbon cable, and produce a nice even line down each side.
A 3-pin 90-degree header, with the centre pin removed, makes a simple male-to-male adapter that is sized correctly for the 5mm screw connectors commonly used for power connections. A straight-pin header would also work in the same way. The pin can usually be removed using needle-nosed pliers, but in some cases the header may require gentle heating in order to remove the pin without risk of breaking the strip. The plastic mounting strip can be pushed close into the 90-degree angle to allow maximum length for both sides of the adapter.
For those
who require spectacles for adequate close vision, using laser protective
eyeware can be a problem. This example shows how a cheap
plastic set of lenses from the $2 shop can be inserted at the back of the
protective eyeware in order to provide corrected vision when using
it. The plastic spectacles are best as the bridge can be drilled for
the bolt - metal-framed spectacles would require a small bracket to made
up. The temple pieces are removed by undoing the screws, but they are very
tiny and it might be just as easy to cut through the plastic. The
only difficult part of the construction is drilling the actual shield -
the plastic needs to be well supported immediately behind the drill point
in order avoid strain on the shield while drilling and to minimize any
risk of cracking it. The lens frame is flexible enough to be
bent to the shape of the eyeware and the screw will hold it into shape,
but very gentle heat can be used to make it conform slightly better.
Threaded
inserts are commonly used with 3D-printed parts. They are heated and
pushed into molded holes in the part to provide a secure holding for
screws which is much less prone to wear and slipping than plain threaded
plastic. The simplest way to both heat and place the insert is
with a soldering iron. The iron can be set to temperature
(about 225º C seems to be suitable for PLA). There are many
tutorials available showing the technique. But there are three
important points about the procedure that are often not mentioned in the
instructions.
1. The soldering iron tip should be ground down to the insert diameter. By providing a tip that is the correct diameter for the insert the insert will be heated thoroughly and evenly. Turning the tip in a lathe is the best way to achieve this, but a copper tip can be turned in a drill against a grinding stone if care is taken.
2. A definite shoulder should be left at the correct height along the soldering iron tip for the insert. If the tip tapers and there is not a definite shoulder then there is a risk that the insert will bind with the tip and it will be pulled out of the part as the soldering iron is withdrawn.
3. The insert should be the type that has a short length of shaft at the blind end that can be used for alignment. The hole in the printed part can then be made to the size of this alignment portion. Without this feature it is very difficult to get the insert properly started in the hole, and it will often twist off-centre as it is inserted. On-line sellers often do not realize the importance of this small feature and do not make it clear whether it exists or not. Always check the images carefully when purchasing and return the item as faulty if it doesn't exist.
To assist with aligning the insert and getting it set flush with the surface of the printed part, a nut can be set into the copper tip at the shoulder point. This also assists in getting heat conducted into the insert. This should be removable for those cases where it interferes with surrounding material.
The correct temperature setting for the iron when inserting is usually 5°C to 10°C above the extruder temperature used for the material.
Note that the insert will distort surrounding material to some extent. The inserting may not work correctly where the adjacent wall thickness is not sufficient to absorb the distortion. Infill percentage and wall thickness will affect the amount of distortion that can be accommodated in a particular region.
The 4-port USB assembly fr
om
a junked ATX motherboard can be mounted into a stand-alone case and
powered from a high-current 5V supply to provide a convenient recharging
station. The pins connected to the USB data lines are cut off short
and a small harness fabricated for connecting the four +5V pins and the
four Ground pins together. The supply connection can be to flying
leads, or if the bench power distribution has standardized DC connectors,
to the appropriate socket.
Stepper
motors are configured as 3-, 4-, 5-, 6- or 8-wire. Three and Five
wire steppers are designed for unipolar mode. Four wire steppers are
designed for bipolar mode, while six and eight wire steppers can be either
unipolar or bipolar.
Unipolar is simpler to drive because a simple switching circuit can change the polarity of the magnetic field. For this reason it is very commonly used in small consumer items, such as toys and small printers. Bipolar requires a more complex driving circuit but creates better performance, especially if microstepping is used.
Six wire and eight wire steppers are particularly useful because they can be configured as either unipolar or bipolar. But many 5-wire steppers can also be configured for either mode. This is possible when the connection point for the internal coils is made at a small PCB mounted externally on the motor. By cutting the trace that connects the centre tap of the two coils, a 5-wire (unipolar) stepper can be converted to 4-wire (bipolar).
In this example the trace has been broken at the end of the PCB. The stepper would be driven with a bipolar driver using orange/red and brown/black - yellow is not used. The break could be bridged for use with a unipolar driver.
