|Reversing Link HM130: The
reversing link is described in the
Engine Design VI
The critical part of the reversing link is the
slot in which the link block moves. This slot is at a 3.75"
radius. The sides of the slot must be smooth so that the link
block will slide easily as the engine direction is changed.
Rotating the material past an end mill was
selected as the easiest way to make the slot.
The fixture shown in the photo was made to hold
the reversing link while it was being machined. The plate is
1/2" aluminum. The hub was turned to be a snug fit in the
rotary table center hole. The 1/4" pin fits into a mating hole
in the table. This fixture can be removed and later replaced
at essentially the same position on the table.
|This photo shows the fixture in
use. The first step was to locate the center rotary table at
0,0 on the digital readout. The fixture was then attached as
shown and the table rotated such that the long axis of the fixture
was aligned with the left-to-right axis of the milling table.
This angle was noted as the center line of the fixture and later of
the reversing link. While the fixture was in this
position the milling table was moved as required to locate and
center drill two holes where the eccentric links attach to the
reversing link. The fixture was then removed, #3
holes drilled in the fixture and the fixture then used as a template
to make matching holes in the reversing links. The holes
in the fixture were then tapped 1/4"-28 and the holes in the
reversing links enlarged to 1/4".
|The photo above right shows the
stacked reversing links secured to the fixture with a pair of 1/4-28
SHCS. Additional holes were then center drilled
in the reversing links for the link saddle attachment screws.
Holes were also drilled at the four corners of the slot in
the reversing links. These holes were all located using the
X-Y indexing on the mill.
The next step was to drill holes along the
centerline of the slot as a first step to machining the slot.
This was done by rotating the rotary table.
The reversing link shown here has a 2.5" long
slot. As noted in the design section, the slot length was
revised to a length of 2".
|The next step was to machine the
slot using an end mill. The table was rotated under the
end mill. Small cuts --- 1/16" of an inch at a time were
taken. Once the slot was all the way though both reversing
links, the milling table was moved along the left-to-right axis as
necessary to finish the sides of the slot to the correct slot width.
Cast iron left from the piece purchased for cylinder
bushings was used for the revering link. The disks were turned
smooth and to the correct thickness on the lathe
|Photo on the right shows the
The next step was to locate and drill holes at
the four places where there are fillets in the sides of the
The reversing links were then removed from the
fixture. The holes for the saddle attachment screws were
tapped and screws in the holes used to hold the links together.
The sides of the links were then rough cut to shape
on the band saw.
|This photo shows the reversing
links reattached to the fixture. The mill x-y movement and rotary
table rotation were used to finish the sides of the reversing links.
This shows the nearly finished reversing
The rounded edges next to the eccentric
link pins and next to the upper saddle attachment screw were
finished later using the setup shown on the right.
That is a 5C Collet holder which is
attached to the center of the rotary table --- dowel pins from the
holder into mating holes in the rotary table make it easy to remove
and later reattach the collet holder.
A 1/2" diameter rod with a 1/4" -28 thread
hole was put in the collet and the reversing link attached to the rod
with a 1/4" screw as show in the photo on the right. The
rotary table was rotated to make the round sides next to the holes.
I could have used this setup earlier on the link hangers, etc, etc.
|Link Block-HM132 & Block Rear
Engine Design VI):
A couple 1/4"- 28 Holes were drilled and tapped in the fixture along the center line of the reversing link
slot (3.75" radius). The fixture was used to locate mating
holes in the bronze disks shown in the photo. The bottom
disk is the correct
thickness for the link block and the top one the correct thickness for
the block rear plate.
After the disks were reattached, holes were
center drilled for the rear plate attachment screws.
|Next, the disks were rotated
under the end mill making a cut such as to leave sides at a 3.5" radius as
shown being cut here and later at 4" radius cut on the other side.
|This shows the finished sides at
3.5" and 4" radius. The two ends were also finished. At
this point the upper disk (the pair of rear plates) was removed.
|The next step was to trim the
sides that fit inside the revering link slot. These sides are
at a 3.56" and 3.94" radii. The milling cutter was set off the bottom so
as to leave a lip.
|The photo shows test fitting the reversing link
over the link block to make sure everything fits properly before the
link block pair was removed and sawed in half.
The photo above shows the completed link
components with the sleeve bearings installed. The
Link Block Pin-HM133 and the Reversing Link Saddle-HM137 pictured
were fabricated to match the design drawings. Note that a flat
washer and Nyloc nut are used to hold the Reversing Link Saddle in
the Link Hanger. The nut hasn't worked loose yet after an hour
or so operation; if it does work loose a castle nut with cotter pin
might be required. Each
reversing link has a screw in the side to limit the maximum travel
of the block in the slot. Recall that the slot in the
original design was 2.5" long. The slot is 2" long in the
latest design so that screw stop will not be necessary.
|Eccentric Rods-HM141: (See
VIII) The rods are machined from 3/8" X 5/8" bar stock ---
two rods per bar. The first step was to mill out the
area of the yoke.
|The next step was to rough saw off the excess
material along the shafts.
|Next, the mill was used to finish the sides of the
|The holes were center drilled using milling table
indexing as shown on the right. Pilot holes for the
Eccentric Rod were drilled. Recall one side is threaded, the
specific dependent on which eccentric it is used with.
|Next, the bars were sawed in half and the end was
rounded on the belt sander. The rollers and a # 4 screw shown
in the photo was used to as a guide on the belt sander. This
|Eccentric Straps, Inner-HM138,
Outer Upper-H139, Outer Inner-HM140: (See
The photo at the right shows
the finished eccentrics and the parts used to make the straps.
|The steel outer strap was
machined over size and then a section cut out of the middle for the
two bars that will become the tabs. The cuts were
made with a saw and the ends finished on the mill. The bars
were drilled and
tapped for the #6 screws used to hold the two halves together.
The bars were attached to the circular segments with #4 SHCS and then
|The strap tabs were machined as a
single piece and the ends tapered for a pair of tabs as shown in
photo. These two tabs were cut off the ends and the ends
of the reaming piece tapered and cut in half for the other two
straps. Recall that the width of the tabs was
reduced to make it easier to achieve the required rotation between
the inner and out straps. The tabs shown here are the wider
|This photo shows shows machining
a slot in the slide
for the tab.
|The tab was held in place by a #4
screw as shown in the photo. That is flux and a couple
pieces of silver solder rod in the cavity.
|This is the view after the flux
and then the solder has flowed.
|The inner strap was turned to the
correct dimensions and then a slot cut for the tab. The tab
was soldered to the strap using the same technique as for the outer
|The outer strap fits nicely in
the 3-jaw chuck for turning the correct inside diameter. Next,
the recess was turned in the middle of the strap using a boring bar
as shown in the photo.
|The last step was to cut
the slot in the outer strap for the tab on the inner strap as shown
in the photo. The inner and outer straps and the
eccentric were assembled and rough edges removed as necessary until
everything turned smoothly. The inner strap was then cut