Adding the rungs in the ladder is next. This drawing shows the rungs that will get
added.
The photo on the left shows the second rung set just to
the right of where it will go. The ones
on each end will get added last. The
right photo is a closer view and the vertical pencil line indicates where the
left edge of the rung will go. The two holes
are for the temporary screws that will hold the rung in place providing
clamping force until the glue dries.
After the glue is applied to the back of the rung it is
set in place. Temporary spacers are
added at the top and bottom then a clamp is used to pull the rung down tight to
the already glued on strip at the bottom. Next two screws are run in from the back as shown in the right photo to
pull the rung tight to the bottom skin. Last, the clamps and spacers are removed and any squeezed out glue is
cleaned up. The center bottom photo is a close view of one of the screws.
The washers are to keep the screw from making a divot in the MDF since
their underside is cone shaped. If I had
round head screws the right size the washers would not have been needed since
they have a flat underneath side of the head.
Anyway, when the glue dries the screws get removed.
These front and back photos below show all the rungs
glued in place. Screws were not used on
the end rungs since they could be clamped in place. Once the glue dries the clamps and screws
will be removed.
With the rungs glued in place and all the temporary
screws removed that were holding them in place while the glue dried the last
long strip can be glued on. The top
drawing shows the piece I am talking about and the bottom photo is of it glued
and clamped in place.
After the glue cures the clamps are removed and the
assembly is run through the thickness sander to bring the rungs and long strips
to the same thickness. All the surfaces
and joints were really close with only a few places that were not right. Not for sure why it may have been due to a slightly different thickness in the MDF pieces or maybe a difference in the glue joint thickness. What I do know is the difference between the
high and low point was less than 1/64”.
Cutting the top and gluing it on is next. The size is easy it’s the ladder width plus
½”. The extra ½” is for a ¼” lip on
either side as shown in the top drawing.
The bottom photo shows everything setup and ready for the glue-up to
start. The clamping for this step is a
little involved. I can clamp the front
edge just like when the long strips were glued on. That’s done by using the gray clamps and the
front edge of the bench to provide a flat clamping surface. The far edge and the ladder rungs can’t be
clamped that way as there is no edge to clamp to. I got around that by taking a long caul and
screwing it through the top and into the base assembly to provide the clamping
force. That caul is identified by the
red arrow. Each of the screws in the
caul has a clearance hole just larger than the screw so they move freely. That’s so as they are tightened all the force
goes to pulling the top skin down tight to the long strips. Also, remembering the splitting problem I had during the MDF testing a small pilot hole gets drilled in the
ladder to prevent that when the screws get run in. Not in the photo but a part of the glue-up is
a series of short cauls that are used to apply pressure to the rungs.
One last step before applying the glue and putting
everything together is to put a small chamfer on each of the pilot holes. Often when a screw starts a little bit of
material gets pulled up into a small lip.
That lip can keep the two pieces just slightly apart leaving a gap and
possibly weak joint. In this case it
could also cause the top and bottom to not be exactly parallel. The left photo shows the hand tool used to
make the chamfer and the right is a close view of a chamfered pilot hole.
The actual glue-up and clamping went quicker than
expected once all the cauls were made and a dry run done to make sure it all
went together OK. Doing the layout and
making the cauls took some time but it’s worth it. The photos show the top skin glued on with
all the cauls and clamps in place.
After letting the sled set overnight the clamps were removed
and the sled was run though the thickness sander to take out any
irregularities. The assembly was really
flat and it only took a few very light passes to flatten both the top and bottom skins. When I checked the thickness with a digital
caliper there is less than 1/100” difference between the high and low points
and I am happy with that.
Patching the holes left from the screws that held the
cauls in place with plastic wood is next.
This is what the piece looked like before the surface was sanded.
Using a random orbital sander starting out with 220-grit
paper and working to 400-grit on both top and bottom faces gives me a very
smooth surface. I want that on the
bottom to reduce the friction between it and the platen on the planer. That’s why the 400-grit paper was used, it is
a very fine abrasive and gives a smooth surface. Later on, the sled will get sprayed with
lacquer then wet sanded a with 12,000 grit pad for a glass smooth finish and waxed to minimize friction.
Next Up – Starting Sliding Blocks, Base Plates & Leveling Bars
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