Opening channels in pitch lap.

Someone suggested using a carpenter's saw to open up the channels in a
pitch lap, as opposed to a box cutter, single edged razor blade, or
what-have-you.

I tried this. It works. And it works very quickly. Took me about 3
minutes to channel (re-channel) my 12.5 inch lap, whereas working with a
single edged razor blade, it usually take half an hour or more.

Just thought I'd pass this along.
(BTW, it was an old rusty ripsaw)

Etok


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Etok wrote:

Someone suggested using a carpenter's saw to open up the channels in a
pitch lap, as opposed to a box cutter, single edged razor blade, or
what-have-you.

I tried this. It works. And it works very quickly. Took me about 3
minutes to channel (re-channel) my 12.5 inch lap, whereas working with a
single edged razor blade, it usually take half an hour or more.

Just thought I'd pass this along.
(BTW, it was an old rusty ripsaw)

Etok

You stirred up an old memory I hadn't thought of in years, and had to go look it up. Look on
page 67 in N. E. Howard's "Standard Handbook for Telescope Making" - it shows a picture of
someone using a carpenter's saw to channel an 8" lap. I remembered trying that, but in
inexperienced hands at the time ( probably 1973) and even following Howard's recommendation to
soap the saw, the saw gave lots of facet chips, especially during the crosscuts. Glad you had
better results. I also found that cooling the lap in the refrigerator (NOT freezer) helped
reduce the tendency to chip. I got pretty handy with the single edged razor blade while working
at an optical shop in summer of 1974, and haven't tried the saw since. I'm about to start
working on a 12.5" f/4.4 hyperboloid (cc=-1.864) for a friend's astrograph, so maybe I'll give
the saw a try again.

Another little shop trick if you didn't already know - after using the lap a while and it gets
charged up with ZOX, Barnesite, whatever you're using, and the facets get that hard glaze on
them, making the polishing drag go way up, take a single edge razor blade and make several small
crosscuts on each facet, 45º to the main channels. Scratch the hell out of it, every facet.
Then press it back in and start running it, and notice how the polishing drag reduces - lots. I
tried the petticoat press, and though it worked well it didn't last as long as the scratches.
Mike

"Steve Taylor" wrote in message
.. .
Mike Jones wrote:

You stirred up an old memory I hadn't thought of in years, and had to go
look it up. Look on
page 67 in N. E. Howard's "Standard Handbook for Telescope Making" - it
shows a picture of
someone using a carpenter's saw to channel an 8" lap. I remembered
trying that, but in
inexperienced hands at the time ( probably 1973) and even following
Howard's recommendation to
soap the saw, the saw gave lots of facet chips, especially during the
crosscuts. Glad you had
better results. I also found that cooling the lap in the refrigerator
(NOT freezer) helped
reduce the tendency to chip. I got pretty handy with the single edged
razor blade while working
at an optical shop in summer of 1974, and haven't tried the saw since.
I'm about to start
working on a 12.5" f/4.4 hyperboloid (cc=-1.864) for a friend's
astrograph, so maybe I'll give
the saw a try again.


Funny, i was only re-reading Howard's book last week. Another tip I
"saw" was to make a hot knife cutter using a soldering iron - high speed
and no chipping at all.

Steve


I have been experimenting with the soldering iron method lately, and I don't
like it. I am concerned that cooking the pitch on either side of the
channel is not a good idea.

Dennis

Mike Jones wrote:

You stirred up an old memory I hadn't thought of in years, and had to go look it up. Look on
page 67 in N. E. Howard's "Standard Handbook for Telescope Making" - it shows a picture of
someone using a carpenter's saw to channel an 8" lap. I remembered trying that, but in
inexperienced hands at the time ( probably 1973) and even following Howard's recommendation to
soap the saw, the saw gave lots of facet chips, especially during the crosscuts. Glad you had
better results. I also found that cooling the lap in the refrigerator (NOT freezer) helped
reduce the tendency to chip. I got pretty handy with the single edged razor blade while working
at an optical shop in summer of 1974, and haven't tried the saw since. I'm about to start
working on a 12.5" f/4.4 hyperboloid (cc=-1.864) for a friend's astrograph, so maybe I'll give
the saw a try again.


Funny, i was only re-reading Howard's book last week. Another tip I
"saw" was to make a hot knife cutter using a soldering iron - high speed
and no chipping at all.

Steve

Dennis Woos wrote:


I have been experimenting with the soldering iron method lately, and I don't
like it. I am concerned that cooking the pitch on either side of the
channel is not a good idea.

I think proper temperature control is vital - the stuff will burn on an
uncontrolled iron.

Steve

Funny, i was only re-reading Howard's book last week. Another tip I
"saw" was to make a hot knife cutter using a soldering iron - high speed
and no chipping at all.

Steve


No chipping but "Stinky"
:^)

Sofjan Mustopoh

I also have found that using a saw lends itself to creating tiny chips,
especially after the lap has been worked for a while and is getting brittle.
My favorite solution is to make a faceting tool out of two pieces of 1/8" x
1" aluminum about a foot long or so held parallel by a couple of pieces of
scrap 1" wood. Soak the lap in hot water for a few minutes and then press
the tool into the pitch to reopen all the channels, and then hot press again
for good contact. It takes about 20 minutes all told (plus the time for the
hot press) and makes super, regular facets with 1/8" channels. Easy peezy.
Only need to do it every couple of sessions.

-Chris

"Mike Jones" wrote in message
...
Etok wrote:

Someone suggested using a carpenter's saw to open up the channels in a
pitch lap, as opposed to a box cutter, single edged razor blade, or
what-have-you.

I tried this. It works. And it works very quickly. Took me about 3
minutes to channel (re-channel) my 12.5 inch lap, whereas working with a
single edged razor blade, it usually take half an hour or more.

Just thought I'd pass this along.
(BTW, it was an old rusty ripsaw)

Etok

You stirred up an old memory I hadn't thought of in years, and had to go
look it up. Look on
page 67 in N. E. Howard's "Standard Handbook for Telescope Making" - it
shows a picture of
someone using a carpenter's saw to channel an 8" lap. I remembered trying
that, but in
inexperienced hands at the time ( probably 1973) and even following
Howard's recommendation to
soap the saw, the saw gave lots of facet chips, especially during the
crosscuts. Glad you had
better results. I also found that cooling the lap in the refrigerator
(NOT freezer) helped
reduce the tendency to chip. I got pretty handy with the single edged
razor blade while working
at an optical shop in summer of 1974, and haven't tried the saw since.
I'm about to start
working on a 12.5" f/4.4 hyperboloid (cc=-1.864) for a friend's
astrograph, so maybe I'll give
the saw a try again.

Another little shop trick if you didn't already know - after using the lap
a while and it gets
charged up with ZOX, Barnesite, whatever you're using, and the facets get
that hard glaze on
them, making the polishing drag go way up, take a single edge razor blade
and make several small
crosscuts on each facet, 45º to the main channels. Scratch the hell out
of it, every facet.
Then press it back in and start running it, and notice how the polishing
drag reduces - lots. I
tried the petticoat press, and though it worked well it didn't last as
long as the scratches.
Mike

On Tue, 14 Oct 2003 17:40:51 +0000, Steve Taylor ...reflected:

Dennis Woos wrote:


I have been experimenting with the soldering iron method lately, and I don't
like it. I am concerned that cooking the pitch on either side of the
channel is not a good idea.

I think proper temperature control is vital - the stuff will burn on an
uncontrolled iron.

Steve

...an Edsyn, or a upper-end Weller?

Alan...who has an Edsyn