by Lester Gilbert
I settled on a design of an adjustable sweep spreader (Adjustable
spreaders v43) that turned out to be rather time-consuming to manufacture,
so I revised it for 3D printing. A
trial design, #51, was printed in PLA Plus from eSun.
I’ve found PLA Plus to be a rather nice filament, recommended by Selwyn
Holland, very easy to print but significantly stronger than PLA, and great for
prototyping. The same design
printed well in ABS, Nylon, n-Vent, and ASA, but did not seem to be
significantly better in strength.
Design #52 (version 4) allowed all threaded holes to be
provided by heat set threaded brass inserts.
The 3D design is illustrated in Figure 2,
where the oversize holes are easily seen.
There are three challenges with heat set inserts.
The first is getting an insert positioned in the right place.
When nice and hot and pushed into plastic, they’ll melt right in wherever
you start and no matter your intended pilot opening to guide them into place.
So some mechanism to position and then hold the insert and its setting
tool is needed.
The second challenge is providing some method of keeping the
insert aligned during insertion. It
is one thing to position the insert correctly at the start, but another to keep
it straight and true while it is being slowly driven into the plastic.
The third challenge is ensuring the correct temperature of the insert before pushing it into place. While the 3D printer extruder might have heated the filament to 220 °C to deposit it, you want a lower temperature for the insert, perhaps 20 °C cooler at around 200 °C in this case. A good temperature is required, of course, so the displaced plastic flows well around the insert and, when it cools, holds it in place, but too high a temperature and the insert could drop right through the item under its own weight. So some temperature control of the setting tool is required.
An important aspect of the iron was that it offered a straightforward method of mounting it in a hobby drill press, as illustrated in Figure 4. An aluminium collar was turned to 20 mm dia to fit the drill press aperture and then attached to a larger collar that secured the iron. Screw holes were drilled and countersunk in the larger collar to match the existing screws that held the iron together. The particular Proxxon drill stand chosen has a simple means of locating a matching small vice, very useful in locating a steady workpiece while pressing the insert home. I had earlier purchased an inexpensive two-heat hobby quilting iron which took tool heads on a 5.5 mm dia rod, and it was very promising. But I found there was no satisfactory way to adapt the body of the iron to the 20 mm press mounting aperture.
Heat set threaded brass inserts come in a variety of styles and lengths, some
illustrated in Figure
The UK isn’t well served yet, but McMaster-Carr is the best supplier in
the USA, otherwise the Lulzbot shop has a small range of the right stuff.
The better inserts have an entry section with a slightly reduced
diameter, allowing the insert to seat square on the hole before being heated and
pressed in, and they also have a cross-hatched knurl to resist both torque and
pull-out. I found an insert without
any reduced entry needed to be started by being held on the heated tip with
needle-nose pliers rather than resting on the plastic item.
The spreader with its various inserts is illustrated in
a production version printed in ASA filament.
ASA is resistant to UV which otherwise degrades most 3D thermoplastics
within a year or so, and this is important for equipment which is going to live
©2023 Lester Gilbert