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About Subject: TL120 Focusing 55mm Wide Angle Sekors Project completed.Date: 2008-03-16 20:16:27From: Peter Thomson
Hi All,
I have completed my project at last, and I am VERY pleased
with the outcome. I have full focusing from infinity to 1 meter ( I
doubt if I will use those extremes but they are there! ) I departed
slightly from my plan in several ways. On completing a test piece
with thread, I indeed found that John's suggestion that the thread
alone is strong enough and does not need any "bump" support at the
rear barrel, so this was machined out. This makes the lens mounts
even simpler to machine.
Masking up the shutters was done by cleaning surfaces with alcohol,
then laying a piece of paper on the blades so the tape doesn't stick
to them. I used mylar packaging tape rather than the duct tape here
as it is more flexible and VERY sticky. Three layers were laid down
on the paper and up the insides of the shutter opening, then trimmed
off to the milling depth with an Xacto knife. The rest of the camera
was put in a plastic bag with a hole cut into it, and then fully
taped up with 50mm duct tape. See it all here :-)
http://tech.ph.groups.yahoo.com/group/MF3D-group/photos/browse/734b
The milling you will note looks very off-centre. This was due to the
tendancy of the cutter to cut to the left as well as the fact that I
didn't have a secondary line to gauge the position after cutting to
the marked line. Doesn't matter, it's inside the camera! After a
thorough vacuuming the tape was removed and not one grain of metal
got past, as it shouldn't. The bare metal was painted matt black.
Threading the mounts was done in the standard lathe cutting method,
with a single point tool ground to 58 degrees to yield a 60 degree
thread, and honed to perfect shape with an Arkansas stone. This made
a very sharp cutting tool which yielded a smooth thread in the nylon.
Note: a rake angle higher than that for metal is needed.
In the photo of the block, the lower portion was cut through the
smaller diameter original shape, and hence has torn out. Boring to
the correct diameter is of course most important, just as when
drilling and tapping a hole. I was especially pleased with this part
of the process as I hadn't lathe cut a thread since I was a QANTAS
1st year instrument apprentice back in '68. And it was nowhere near
this fine! I found that there is a variance in the threads of the
lens barrels which require each mount to be match threaded to avoid a
too tight or too sloppy fit. Cuts of 0.01 increments after the
initial 0.19mm depth was cut, with a test fitting in the lathe after
each cut. Most were 0.20 to 0.22 depth.
During this test fitting stage, I found that the method of holding
open the shutter was a problem as I kept pulling the shutter out
of 'B' and the shutter would close. I took the front lens out to see
what I could do about it. I decided to glue the shutter blades open
with Araldite 5 minute epoxy, and also lock the shutter speed ring in
place (on the inside)the same way so it became the ring to grip to
rotate the lens for focusing. This all went very satisfactorily. An
hour 15cm under a 60 watt globe set the epoxy fully hardened.
All unused appendages of the lens were cut off flush with the
Dremel, the aperture lever was also reduced in height. This leaves a
very clean lined set of lenses.
In use (after the photo were done) I found the need to add a 4mm
nylon locking screw at the bottom of the blocks to stop rotation of
the lens when changing aperture.
All in all, a most rewarding project which I can thoroughly
recommend.
Happy 3Ding :) Peter
I have completed my project at last, and I am VERY pleased
with the outcome. I have full focusing from infinity to 1 meter ( I
doubt if I will use those extremes but they are there! ) I departed
slightly from my plan in several ways. On completing a test piece
with thread, I indeed found that John's suggestion that the thread
alone is strong enough and does not need any "bump" support at the
rear barrel, so this was machined out. This makes the lens mounts
even simpler to machine.
Masking up the shutters was done by cleaning surfaces with alcohol,
then laying a piece of paper on the blades so the tape doesn't stick
to them. I used mylar packaging tape rather than the duct tape here
as it is more flexible and VERY sticky. Three layers were laid down
on the paper and up the insides of the shutter opening, then trimmed
off to the milling depth with an Xacto knife. The rest of the camera
was put in a plastic bag with a hole cut into it, and then fully
taped up with 50mm duct tape. See it all here :-)
http://tech.ph.groups.yahoo.com/group/MF3D-group/photos/browse/734b
The milling you will note looks very off-centre. This was due to the
tendancy of the cutter to cut to the left as well as the fact that I
didn't have a secondary line to gauge the position after cutting to
the marked line. Doesn't matter, it's inside the camera! After a
thorough vacuuming the tape was removed and not one grain of metal
got past, as it shouldn't. The bare metal was painted matt black.
Threading the mounts was done in the standard lathe cutting method,
with a single point tool ground to 58 degrees to yield a 60 degree
thread, and honed to perfect shape with an Arkansas stone. This made
a very sharp cutting tool which yielded a smooth thread in the nylon.
Note: a rake angle higher than that for metal is needed.
In the photo of the block, the lower portion was cut through the
smaller diameter original shape, and hence has torn out. Boring to
the correct diameter is of course most important, just as when
drilling and tapping a hole. I was especially pleased with this part
of the process as I hadn't lathe cut a thread since I was a QANTAS
1st year instrument apprentice back in '68. And it was nowhere near
this fine! I found that there is a variance in the threads of the
lens barrels which require each mount to be match threaded to avoid a
too tight or too sloppy fit. Cuts of 0.01 increments after the
initial 0.19mm depth was cut, with a test fitting in the lathe after
each cut. Most were 0.20 to 0.22 depth.
During this test fitting stage, I found that the method of holding
open the shutter was a problem as I kept pulling the shutter out
of 'B' and the shutter would close. I took the front lens out to see
what I could do about it. I decided to glue the shutter blades open
with Araldite 5 minute epoxy, and also lock the shutter speed ring in
place (on the inside)the same way so it became the ring to grip to
rotate the lens for focusing. This all went very satisfactorily. An
hour 15cm under a 60 watt globe set the epoxy fully hardened.
All unused appendages of the lens were cut off flush with the
Dremel, the aperture lever was also reduced in height. This leaves a
very clean lined set of lenses.
In use (after the photo were done) I found the need to add a 4mm
nylon locking screw at the bottom of the blocks to stop rotation of
the lens when changing aperture.
All in all, a most rewarding project which I can thoroughly
recommend.
Happy 3Ding :) Peter