- Booting our transition points is the process of installing a shrinkable moulded
sealing boot onto our transition point that when recovered, will provide it with
excellent strain relief as well as sealing the harness sheathing,
further protecting our wires underneath.
Our transition point booting operation will generally fall into one of two categories.
Either all of the harness sections exiting the transition point will be in line with
the main harness trunk, in which case we can use an in line boot of the same sort
used to seal to a connector.
Or we will require a specific moulded boot shape, such as a T section,
where one of the harness sections exits our transition point at a 90 degree angle.
The method of sizing the boots, recovering them onto the harness,
and sealing them, is the same in either case.
There are two commonly available brands of shrinkable moulded shape boots
on the market, being Raychem and Hellermann Tyton.
I find the Raychem products are more commonly used for large transitions and
specific required shapes.
With the Hellermann Tyton products, filling in the smaller end of the scale.
The materials each are made of are compatible however and there's no
problem mixing both brands on a single harness.
If we have a look at a couple of the shrinkable moulded shapes,
it's very apparent that their unrecovered shape is quite different to their
recovered form.
It's very easy to be fooled into thinking you have two large of a size of boot
selected when looking at them in their unrecovered form.
But they are made that way with a very high shrink ratio for a good reason,
and that's to make them as easy as possible to install.
Selecting the correct size and style of shrinkable moulded shape for your
transition point can be a relatively time consuming process and
unfortunately there's no short cut for becoming familiar with the catalog of
available products.
We have linked below to the complete Raychem catalog of shrinkable moulded
shapes.
But I've also provided a list of our most commonly used items and applications.
Once you've found a suitable boot shape, the sizing process is very similar to how
we sized our sheathing.
It's most common to select the largest size boot that will comfortably shrink
to fit all the sections of the harness.
But remember that the diameter measurements you're taking
now include the sheathing as well as the underlying wires.
In the example that we'll show you here, we have three transition point exits,
with one of them at 90 degrees to the main harness trunk.
We have selected a t shaped moulded shape boot of this transition.
Our smallest exiting harness section is the one exiting at 90 degrees,
and has a finished diameter of approximately eight millimetres.
Looking at the Raychem catalog of moulded parts, a 301 A022 is going to be suitable for
our application.
Its maximum recovered exit diameter is 6.9 millimetres so it will recover nicely
into our smallest harness section and its minimum unrecovered exit diameter
is 13.2 millimetres.
Meaning we will be able to install it easily into place.
When installing a shrinkable moulded shape into place, you need to make sure
that you take a good look at the item.
It will have letters embossed into it that let you know which exit point is which.
Looking at our t shaped boot it has exits marked H, J, and K.
Looking at our documentation for this part, we can see that exits K, and J are
in line with one another and exit H is at 90 degrees to them.
It's crucial that these are not mixed up as when the shape is recovered,
for our example it's our ignition harness wiring that we want exiting the transition
point at 90 degrees, not the main harness trunk.
There are boots available that have a pre applied glue lining which will flow
when they're recovered and seal the boot into place.
This will not always be the case however and often you will need to apply separate
sealing epoxy compound.
There are three common compounds used and where you are in the world usually
determines which one you will be able to purchase.
I've found them to be completely interchangeable however and will
happily use any of them.
They are Raychem S1125, Hellermann Tyton V9500,
which is what we're going to use today, and Resintech RT125.
They will all form a nice strong sealed bond between the moulded boot shape,
and the abraded portions of our DR25 sheathing.
As mentioned, we're going to have a look at an example now, which will be installing
a t shaped boot onto our example harness section here.
The first part of this process is actually going to be mixing up our epoxy sealing
compound and getting it into a syringe.
I want it to be easily available and on hand later on when we're undertaking
the recovery process.
To do this, I like to use just an old waste plastic bag that something will
have arrived in and we're simply going to squirt out a small amount of our
epoxy compound onto this and mix it by hand.
Now you can buy these epoxy compounds in different forms.
You can get them in bags that you mix up.
I do find the most economical way though if you are building a few harnesses,
is to buy them in the twin syringe tube and these twin syringe guns are
also not particularly expensive.
I'm going to squeeze out a good amount of our epoxy compound onto the back
of our plastic bag here.
It should be dispensed in even quantities for these compounds which you'll find
this gun is going to do.
With that on there, we'll just release the pressure from that gun,
pop its cap back on and put it to one side out of the way.
Just using my pick here I'm simply going to mix this up much like
you would for any other epoxy compound.
It should be completely back in appearance when the mixing is complete.
You wanna make sure there's no grey streaks through it whatsoever.
The working time on these epoxys is typically around about an hour,
it may vary with the different brands and the temperature that you're
actually working under.
And they fully cure typically after about 24 hours.
So you do have quite a lot of working time.
The syringe I have here is a completely standard syringe available from any
electronics supplier and the tip I've got on the end has a one millimetre bore.
I find that a really good size to actually squeeze enough of the epoxy sealing
compound out easily but also get into those tight spots in our
transition point.
So simply using my pick I'm going to get the epoxy sealing compound,
as much as I can into the back of the syringe here and get it squeezed
down to the tip and then get that all put to one side.
With that to one side, we now want to dispose of this plastic bag
straight away in the bin so we make sure we don't accidentally drop
anything in it and make a mess.
And always remember to wipe off your pick as well before this epoxy
cures, as it is actually quite difficult to remove later.
Next part of the process is actually going to be installing our mouldable shrink
boot onto our harness section here.
Being very careful to look and identify which exits we're after.
So we know our K and our J exits are going to be in line, and our H exit
is going to be the one at 90 degrees.
Now you will notice that in its unrecovered shape, our t boot is actually very very far
from a t shape and we are going to have to bend this harness section around to get
that installed in the right place and then it's going to bend around into its t shape
as we recover it.
So I'm going to get this installed onto our harness section now.
With that shrinkable boot installed onto the harness, we're just going to pop this
in our bench vices here just to lightly support it as I'm going to have to be
working the heat gun back and forth across this section to evenly apply heat.
What that's going to do is it's going to start recovering this boot and this section
is going to start turning around to face out at the 90 degree angle.
We want to get the centre section of the boot as recovered as possible before
we start recovering the exit points.
Now it is possible while we're doing this, those exit points might start shrinking up
as they are still quite close to the centre section we're going to be recovering.
If that happens, what we're going to have to do is stop recovering the centre section,
head to the exit point that has begun to recover, we're going to have to install
our epoxy compound, finish recovering that exit section and then come back
and finish recovering the centre section of the boot.
This becomes less of a concern when you're using larger boots as you can be a little
bit more precise about where you're applying heat with your heat gun
and you can keep it away from those exit point areas.
So I'll get this installed into our vices now, just using our rags again to protect
the harness sections.
Not gonna clamp down particularly tightly on them, I really just want to
be supporting it there so I can easily work with our heat gun.
With that set up in our vices you can see we've got quite a lot of room
to work here which is quite important as we are going to have to be moving
the heat gun around this to evenly apply heat.
If I was building this harness not on camera, chances are I would actually
have this branch facing towards me as it would make it a little bit easier
but you're going to get a much better view if I do it around this way.
The temperature setting for our heat gun will be listed on the packaging
that that moulded boot has come in, and in our instance here we've got a
shrink temp of 220 to 255 degrees celcius.
I find in practice that actually going a little bit above that can give you a
slightly better result.
These boots do take more time than standard heat shrink to fully recover,
and we can speed that process up a little bit.
You want to make sure that if you do go above that temperature,
probably don't stray by more than about 15%, 10% to 15% and ensure that you're
not charring or scorching the boot when you're recovering it.
For our application here I've got my heat gun set to 270 degrees and that's going
to be a good temperature that I'll be able to hopefully easily control and get this
boot shrunk into place.
I've gotten most of the centre of our shrinkable boot recovered and that leg
is bending around to be at 90 degrees much like we wanted it to do.
I've paused at this point because I can see that if I go much further,
these exit points are going to begin to recover down and I wanna make sure
that I get my sealing epoxy compound in there at this point.
So we're actually going to focus on just a single exit leg at a time and I'm going
to start with the most complicated one which is going to be the one where we've
got our four harness sections exiting.
First thing I'm going to do is actually just secure these three smaller harness
sections up with a cable tie to make sure that when we recover this down,
it is going to grip those in a nice tight organised way.
Now we're going to get some epoxy compound in place and because we've
abraded these wires nicely it is going to make a really good bond to them,
and particularly in the middle of the wires here we would be very careful to abrade
in there as well as we are going to seal that with the epoxy compound too.
Got our bead of sealing epoxy in place there.
You really don't need to install too much but if you can, try and get an unbroken
bead around that whole harness section point.
It will flow as you recover this section point and you'll find you actually need
slightly less than you think you will.
When the process is complete you can actually get in there and install
just a little bit more if need be.
Particularly down the centre of that exit point, you want to make sure
that's nicely sealed down there and that can be easier to do after that
boot's fully recovered in place.
I'm now going to turn the heat gun back on and start recovering in this
direction, focusing just on this exit point, making sure that's all gonna seal up
and grab those harness sections nicely.
Now we've got that one transition point recovered and all sealed up,
I've popped a small cable tie on there as it is going to be our last form of
mechanical strain relief, just to ensure that this branch point won't get pulled apart
and affect our seal in here.
With that done, I'm going to undertake exactly the same process on our other
two branch points, sealing them with our epoxy compound and recovering them
into place.
With our mouldable shape recovered into place on our harness, we can do our quick
visual inspections.
What you're looking for here is that everything has recovered nice and
evenly, then you've got a good even bead of that sealing epoxy at each of your
exit points.
Now what you'll often find when you're recovering that boot is that quite a lot
of your sealing epoxy will actually squeeze out.
In that instance you are going to need to clean up that sealing bead and a bit
of isopropyl alcohol sprayed onto a paper towel does a really good job of this.
Now our example harness section here actually turned out to be a little bit of an
interesting one.
We were right on the borderline between two different boot sizes.
And we chose the smaller size boot which has recovered nice and tightly
onto our harness and is giving us really good strain relief but it's quite possible
the larger size might have actually given us a tidier result.
Once you've recovered your sealing boots onto the harness,
the epoxy sealing compound is going to take a full 24 hours to completely
cure so you will want to leave it undisturbed as much as possible
for that time.
Definitely before it sees any rough handling, absolutely before it gets installed
in the vehicle.
Once recovered and cooled, the moulded shape is very rigid,
giving us the strain relief we require.
Once our epoxy has completely cured, it will be bonding the boot and the
sheathing tightly together, sealing away the transition point,
ensuring it will remain reliable for years when in service.
The final part of the process is to put that small cable tie on any exit
containing more than one harness section.
Giving us our final mechanical strain relief.
Now this is just one example of transition booting here.
There are as many examples as you could think of different scenarios,
and we will be showing you several more throughout the worked example
sections of the course.
That was just one of the many modules taken from our course.
You'll start with the basics and build on the knowledge in this course to be able to
do it yourself.
If you're interested in advancing your skills, this is the course for you.
For more information and to purchase this course, click the link to enrol now.