& Shaft Construction I
Nelson Riedel, Nelson@NelsonsLocomotive.com
9/29/2009, last updated
The cast iron used to make the Universals is great to
machine but dirty. Bronze is about the same strength as the
cast iron and can be substituted if one wants to avoid the black dust.
The first steps to fabricating the
HM304 Round Shaft Us and the HM305 Square Shaft Us were to square the
material and then finish the shaft ends.
|I purchased 1" X 2" and 1.5" X 2" rectangular cast
iron bars from McMaster-Carr. The rods are rough sawed and at
least 1/8" oversize. The 1" X 2" bar is slightly small
to make the 1.125" diameter end of the round shaft U. I made
that end ~ 1.09" diameter.
The first step was to saw the lengths of bar
two Us plus a margin for a saw cut.
Note the 2.125" dimension on the bar sold as
|The sides were smoothed and squared on the lathe as
shown in this photo. The two bars here will make 4 Us.
This operation was repeated for all the
required round and square shaft Us.
|Once the sides have been turned smooth (and made
nearly perfectly square) the bars were cut in half and the ends
turned to make them square. The bar was also made
length in this step.
|The neat thing with working with rectangles is that
it is easy to locate the holes for the pins and shafts. The
photo shows mounting the block so that the holes for the pins
could be drilled (undersize) and then bored to size.
|The shaft ends of all the Us were
finished next starting with sawing off the excess material on
the shaft end. Sorry that this photo is a bit out of focus.
|This a the shaft end of a square
shaft U. The inside had been drilled and then bored to
5/8" diameter. The outside was turned to
1.275" diameter. Material at the base of the shaft part
was left so that a fillet could be machined there later.
|This is a round shaft U.
The inside was drilled and bored 5/8" The end was turned to ~
1.1" OD and a fillet turned where the shaft end meets the U end.
Recall that this was 1" thick bar stock that was in fact a little
thicker then 1.25". The shaft OD could be made a bit smaller
A 3/16" wide broach was then used to cut a
3/16" X 3/32" key slot in the shaft end of these round shaft Us.
That finished the shaft ends.
|The last step was to drill the
yoke end 1" diameter to remove excess material.
Those are 1/4" holes located at the inside corners of yoke.
These holes help with a sawing operation later.
Making the Square Hole: The big challenge
was to turn the round hole into a square hole. I looked up
square broaches and found the cheapest ones cost ~ $250 and they didn't
produce a square hole ---- the sides bulged slightly because the pilot
drill is 21/32".
I could easily square up the 5/8" diameter round
hole on the mill but there would be fillets the radius of the end mill
in the corners. The smallest diameter end mill that would be
strong enough to take reasonable depth cuts is about 1/4". I
have a 3/32" key slot broach that did the Shay wheels and gears and also
the Heisler wheels and gears and is still reasonably sharp. I
decided to try to use it to remove the 1/8" radius fillets in the
corners after the sides were finished with a 1/4" end mill.
|The sleeve shown on the right was
made from 5/8" square bar stock. A 3/16" tension pin will be
inserted in the hole to keep the sleeve from sliding through the
|This shows the "hole squaring"
tools. Normally one shim is used to broach a 3/32" deep key slot.
I had to make the brass shim that was used together with the standard shim to
make a third pass.
|The milling vise was rotated 45
degrees so that the sides of the square shaft ends could be milled
flat as shown in the photo.
|Note that material was left in
the corner where the shaft end meets the U end.
|This shows plunging an end mill
into the corner to make the fillet.
|This square shaft end looks
pretty good. It was further smoothed using a 1/2" diameter
sanding drum in the rotary tool.
This shows the finished shaft ends of
all the Us ---- note that I made an extra of each type --- in case I
ruined one in the fabrication process.
The description of finishing the Us and
fabricating the other universal parts are described in the
Construction II page.