How does one machine a toothed wheel for a film sprocket such as this:

http://www.lavezzi.com/product272.html

That item is a stack of several cylindrical components, with the toothed
portion apparently a slice out of a long toothed stock piece, somewhat like
the sprocket stock you can get to make gearbelt pulleys. Would this
toothed stock just be cut from round stock using axial cuts from a custom
bit, incremented with a spin indexer?

I also have an interesting specimen, a 4-inch diameter metal sprocket that
appears to be an exquisitely fine cast version. Is that possible?

Richard J Kinch wrote:
How does one machine a toothed wheel for a film sprocket such as this:

http://www.lavezzi.com/product272.html

That item is a stack of several cylindrical components, with the toothed
portion apparently a slice out of a long toothed stock piece, somewhat like
the sprocket stock you can get to make gearbelt pulleys. Would this
toothed stock just be cut from round stock using axial cuts from a custom
bit, incremented with a spin indexer?

Production units are probably cut with an internal broach.
To do a one-off or small quantities, you don't need a custom milling
bit--a straight end mill will do it. The tooth sides can be straight,
although curved would be better (circular, no need for involute as on a
geartooth). That's where you'd need a custom cutter, easy enough to make
using a single-bit flycutter.
You just mill the teeth, and the arc between them, in stages on a rotary
indexing table after turning the profile on the lathe.


I also have an interesting specimen, a 4-inch diameter metal sprocket that
appears to be an exquisitely fine cast version. Is that possible?

"exquisitely fine cast" would probably mean investment cast, using a
sacrificial plaster-type mold where the mold cavity is formed with a wax
pattern. Or die-cast, using a metal mold (most likely on a production
item). You can do some pretty exquisite casting with sand, too.

--
Ken Grunke
SW Wisconsin
http://www.token.crwoodturner.com/
Member, Coulee Region Woodturners AAW chapter
http://www.crwoodturner.com/



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

Ken Grunke writes:

Production units are probably cut with an internal broach.

Here are some photos of an 8-tooth 16mm film sprocket (3/4" diameter)

http://www.truetex.com/16mmsc8.jpg
http://www.truetex.com/16mmsc9.jpg

The streaks on the surfaces of the tooth wheel sure look like it was milled
in bulk axially, then sliced off, maybe ground?

Richard J Kinch wrote:

How does one machine a toothed wheel for a film sprocket such as this:

http://www.lavezzi.com/product272.html



Wow, at $51 per for that little sprocket I can see why you're wanting to
make your own.

Guess they're not producing them now at the same volume as they were in
say the 60s, huh?

Jeff



--
Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"My luck is so bad that if I bought a cemetery, people would stop dying."

Jeff Wisnia wrote:
Richard J Kinch wrote:

How does one machine a toothed wheel for a film sprocket such as this:

http://www.lavezzi.com/product272.html



Wow, at $51 per for that little sprocket I can see why you're wanting to
make your own.

Guess they're not producing them now at the same volume as they were in
say the 60s, huh?

I don't think they were cheap then either. I ran
the projectors at the local movie house while I
was in high school (about 68 or 69). The one
cardinal rule was "don't drop the sprockets or
the Cinemascope lenses"

In article , Jim Stewart says...

I don't think they were cheap then either. I ran
the projectors at the local movie house while I
was in high school (about 68 or 69). The one
cardinal rule was "don't drop the sprockets or
the Cinemascope lenses"

Ha ha ha ha.

My mom taught me that if a microscope cost more
than $500 you could carry it with one hand. Above
that, you had to use *two* hands!

I think the cinemascope lenses probably required
about four people to get enough hands.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

jim rozen wrote:

In article , Jim Stewart says...


I don't think they were cheap then either. I ran
the projectors at the local movie house while I
was in high school (about 68 or 69). The one
cardinal rule was "don't drop the sprockets or
the Cinemascope lenses"


Ha ha ha ha.

My mom taught me that if a microscope cost more
than $500 you could carry it with one hand. Above
that, you had to use *two* hands!

I think the cinemascope lenses probably required
about four people to get enough hands.

Same with the Army. I worked on Pershing missiles.
The inertial platform was a "2 man carry" rule
even though it only weighed about 35 pounds. At
least you could share the blame if you dropped it.

jim rozen wrote:


My mom taught me that if a microscope cost more
than $500 you could carry it with one hand. Above
that, you had to use *two* hands!

(Just like a Whopper...)

Make that More or less Jim?

Jeff


Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"If you can smile when things are going wrong, you've thought of someone
to blame it on."

We make similar items all the time. If making only a couple, use a
tapered endmill and do some drawing and calculation first to try and get
an idea of the proper taper and tooth size. After milling on an arbor
(or chuck if the shoulders give you room to grip and keep it true), you
can use a wire brush or similar on a grinder to abrasive machine the
teeth to a more curved profile so they will release properly. Finally,
do your best to polish the tooth faces so that they will not abrade the
film.

There are better ways to get the proper tooth profile but probably not
worth the hassle unless you want to do it as a "learning" project

Koz

Richard J Kinch wrote:

How does one machine a toothed wheel for a film sprocket such as this:

http://www.lavezzi.com/product272.html

That item is a stack of several cylindrical components, with the toothed
portion apparently a slice out of a long toothed stock piece, somewhat like
the sprocket stock you can get to make gearbelt pulleys. Would this
toothed stock just be cut from round stock using axial cuts from a custom
bit, incremented with a spin indexer?

I also have an interesting specimen, a 4-inch diameter metal sprocket that
appears to be an exquisitely fine cast version. Is that possible?

"Jeff Wisnia" wrote in message
...
Richard J Kinch wrote:

How does one machine a toothed wheel for a film sprocket such as this:

http://www.lavezzi.com/product272.html

A short, curious story that relates to this: Back around 1969, Life
magazine's photo department bought about one or two hundred thousand (no
exaggeration) indexed, glass-window plastic slide holders. The relationship
of the sprocket holes to the frame area was fixed; there was a single prong
on the molded slide holders that engaged one sprocket hole, and getting the
full frame in the window depended on the camera having a uniform
relationship between the sprocket drive and the window. Besides having a
*uniform* relationship, it needed a *matching* relationship, one that
matched the relationship in the slides.

No one thought much about this until they discovered that the
department-issue Nikons all had different sprocket-hole relationships. g
They were uniform, but each one was different, and practically none of them
had the *same* relationship. Apparently the sprocket drives on Nikon F's
weren't set in any particular relationship to the gears.

Anyway, they tried to take the slide holders back but it was no-go. Nikon
couldn't, or wouldn't, supply the sprockets that they wanted. So they had
Marty Forscher (Professional Camera Repair, then on 42nd Street) machine new
sprocket wheels for all of their Nikons.

It cost them a significant bundle. I think somebody lost a job over it. g

Ed Huntress