"Gene Cash" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Mark Olson <(E-Mail Removed)> writes:
>
>> Gene Cash wrote:
>> > (E-Mail Removed) (Scott) writes:
>> >
>> >>Yep. A drill bit made especially for acrylics seems pretty cheap after
>> >>that
>> >>happens once or twice.
>> > I have some from usplastic.com and they work quite well. Worth the
>> > dough.
>> > Use alcohol to lube the drill and keep the plastic from melting and
>> > sticking.
>>
>> Whoa! Don't use alcohol on _acrylic_ plastic. At my workplace, we
>> ruined
>> some very expensive tooling before learing that lesson. Whatever bits
>> you
>> use, keep the speed down to avoid melting.
>
> Thanks! I'll keep that in mind.
>
> -gc
>
> --
> Remember how Senator Glenn's flight was going to do wonders for NASA's
> public
> image and greatly increase public support of spaceflight? Yeah, right.
> -- Henry Spencer SSH

I can't see the rest of this thread, for some reason they've all been
cancelled on this server 'cept this reply and the origonal post.

I've thought of this windscreen thing myself....

I've tried forming things from acrylic sheet heated in the oven. We were
trying to make domed covers for submerged lights in a basement once.

It forms like a sheet of rubber when heated, problem I've encountered is the
surface you stretch it over wrecks the optically nice surface. At one point
we made a male mold from wood, applied lots of layers of Varathane and wet
sanded, polished etc to optical clarity, it still wasn't good enough.

We tried clamping the outer edge on in a fixture and blowing the dome with
compressed air, which worked OK but it was to hard to get consistant
results.

If I could figure a way to not wreck the surface on the mold side, I think I
would try vacuum forming it. Old fridge compressors are supposed to make
good vacuum pumps, although I have never tried this. An old propane tank
would make for a good thing to store up enough vacuum. You'd clamp the cold
plexy in frame over the mold and apply radiant heat somehow to soften
it,then hit it with the vacuum.

The drilling holes thing, it's quite brittle and tends to crack all over the
place when you break thru. Things that seem to work... drill a small pilot
hole thru then drill 1/2 way thru from both sides. Or those brad point wood
drill bits work quite well, or you can grind the cutting edge of the drill
bit to about 90 deg so it scrapes its way thru.

Someone suggested Lexan to me once. But apparenty unless you bake for long
while to drive moisture out it'll get bubbles, and I don't think I want to
try go thru a Lexan windscreen if I run into something anyways.

P.

"Scott" <(E-Mail Removed)> wrote in message
news:4611c82b.184260488@localhost...
> On 02 Apr 2007 20:36:26 -0400, in rec.motorcycles.tech, Gene Cash
> <(E-Mail Removed)> wrote:
>
>>Mark Olson <(E-Mail Removed)> writes:
>>> Whoa! Don't use alcohol on _acrylic_ plastic. At my workplace, we
>>> ruined
>>> some very expensive tooling before learing that lesson. Whatever bits
>>> you
>>> use, keep the speed down to avoid melting.
>>
>>Thanks! I'll keep that in mind.
>
> Me too. I thought isopropanol was safe for acrylic. Water will work,
> though.
>
> I believe alcohols are safe to use with polycarbonate, fwiw.
>
> -Scott
> --
> '73 CB450K
> '82 CB900F (x2)
> '04 FSC600 (SWMBO)
> '01 ZG1000 (SWMBO)

fwiw, my experience with acrylic, which is a sort of self educated
incompetence thing, or plastic in general, because I don't know the proper
methods of machining it ...

There is a problem when the feed is too slow, that's when the heat happens
and everything melts together into a glob.

I keep the air gun on it to get rid of the chips and keep things cool.

In my barn-shod way of doing things, I tend to attack it with a router. If
you don't stop or hesitate, everything seems to go fine....

P.

On 02 Apr 2007 20:36:26 -0400, in rec.motorcycles.tech, Gene Cash
<(E-Mail Removed)> wrote:

>Mark Olson <(E-Mail Removed)> writes:
>> Whoa! Don't use alcohol on _acrylic_ plastic. At my workplace, we ruined
>> some very expensive tooling before learing that lesson. Whatever bits you
>> use, keep the speed down to avoid melting.
>
>Thanks! I'll keep that in mind.

Me too. I thought isopropanol was safe for acrylic. Water will work,
though.

I believe alcohols are safe to use with polycarbonate, fwiw.

-Scott
--
'73 CB450K
'82 CB900F (x2)
'04 FSC600 (SWMBO)
'01 ZG1000 (SWMBO)

"Pete M" <(E-Mail Removed)> writes:

> I can't see the rest of this thread, for some reason they've all been
> cancelled on this server 'cept this reply and the origonal post.

Or it could be that propagation to your server sucks. USENET article
feeds can be iffy.

> The drilling holes thing, it's quite brittle and tends to crack all over the
> place when you break thru. Things that seem to work... drill a small pilot
> hole thru then drill 1/2 way thru from both sides. Or those brad point wood
> drill bits work quite well, or you can grind the cutting edge of the drill
> bit to about 90 deg so it scrapes its way thru.

Drills designed for plastic have much different pilot and cutting angles
to prevent such problems. I found they're worth the money. You only need
a couple and they don't get dull.

Normal bits dig in and make microfractures that cause the cracking.

-gc

--
Remember how Senator Glenn's flight was going to do wonders for NASA's public
image and greatly increase public support of spaceflight? Yeah, right.
-- Henry Spencer SSH