I finally decided to make a vacuum formed polystyrene cover for the encoder
on the front of the big mill. Seems pretty straight forward. I've got my
first vacuum box finished except for the port to put the vacuum hose in. I
noticed a lot of the DIY guys make a hole for the smaller vacuum hose even
though they have a full size shop vac with the big hose. Is there some
reason for that? Seems to me that the larger port for the larger hose would
evacuate the box faster and form the plastic quicker before it cools. Am I
missing something obvious?

(I have some PETG on the way to play with in case I don't like the way
polystyrene forms or holds up)

If this goes well, I have all kinds of ideas for vacuum forming...

In article ,
"Bob La Londe" wrote:

I finally decided to make a vacuum formed polystyrene cover for the encoder
on the front of the big mill. Seems pretty straight forward. I've got my
first vacuum box finished except for the port to put the vacuum hose in. I
noticed a lot of the DIY guys make a hole for the smaller vacuum hose even
though they have a full size shop vac with the big hose. Is there some
reason for that? Seems to me that the larger port for the larger hose would
evacuate the box faster and form the plastic quicker before it cools. Am I
missing something obvious?

(I have some PETG on the way to play with in case I don't like the way
polystyrene forms or holds up)

If this goes well, I have all kinds of ideas for vacuum forming...



I know little about vacuum forming, suggest running this by the folks
over at:

sci.polymers

There may be other plastics groups as well. Also, I've heard the model
airplane crowd now does a lot of vacuum forming.

As a kid I had one of those Mattel 'Vac-U-Form' things... made stuff
with it for years...

Good luck!

Erik

On Jan 19, 7:39*pm, "Bob La Londe" wrote:
*I
noticed a lot of the DIY guys make a hole for the smaller vacuum hose even
though they have a full size shop vac with the big hose.

I think the reason is that the time is about the same with either
hose. The bigger hose might be faster but not enough faster to be
able to tell the difference.


Dan

"Erik" wrote in message
...
In article ,
"Bob La Londe" wrote:

I finally decided to make a vacuum formed polystyrene cover for the
encoder
on the front of the big mill. Seems pretty straight forward. I've got
my
first vacuum box finished except for the port to put the vacuum hose in.
I
noticed a lot of the DIY guys make a hole for the smaller vacuum hose
even
though they have a full size shop vac with the big hose. Is there some
reason for that? Seems to me that the larger port for the larger hose
would
evacuate the box faster and form the plastic quicker before it cools. Am
I
missing something obvious?

(I have some PETG on the way to play with in case I don't like the way
polystyrene forms or holds up)

If this goes well, I have all kinds of ideas for vacuum forming...



I know little about vacuum forming, suggest running this by the folks
over at:

sci.polymers

There may be other plastics groups as well. Also, I've heard the model
airplane crowd now does a lot of vacuum forming.

As a kid I had one of those Mattel 'Vac-U-Form' things... made stuff
with it for years...

Good luck!

Erik

I went ahead and drilled it to fit my big hose for now. If I do much of it
I know I'll have to make two or three vacuum boxes anyway. It certainly has
plenty of hold for a simple suction test, but not doing any forming. I
couldn't lift a board off the box. I was able to lift a sheet of plastic,
but only because it would bend. I didn't make it particularly perfect
either. I am sure it leaks everywhere. LOL.

I posted over it sci.polymers too, but that group looks like its totally
over run by spam.

On 1/19/2013 19:39, Bob La Londe wrote:
I finally decided to make a vacuum formed polystyrene cover for the
encoder on the front of the big mill. Seems pretty straight forward.
I've got my first vacuum box finished except for the port to put the
vacuum hose in. I noticed a lot of the DIY guys make a hole for the
smaller vacuum hose even though they have a full size shop vac with the
big hose. Is there some reason for that? Seems to me that the larger
port for the larger hose would evacuate the box faster and form the
plastic quicker before it cools. Am I missing something obvious?


Vacuum pump has more vacuum than a shop vac. Should suck down quick
enough, and get better corner forming.




(I have some PETG on the way to play with in case I don't like the way
polystyrene forms or holds up)

If this goes well, I have all kinds of ideas for vacuum forming...





--
Steve Walker
(remove brain when replying)

There are two issues here, ultimate vacuum and pumping speed. A shop vac
(from reading on the Internet, so it must be true :-)) has an ultimate
vacuum of about -5 or 6 psig, or roughly one third of an atmosphere, but it
has a pretty high pumping speed. So when you first turn on the shop vac it
moves lots of air, beginning the evacuation of the box very quickly, and
starts to suck down the softened plastic onto the mandrel very quickly.
However, with no leaks and no matter how long you let it go, it will base
out at about -5 or 6 psig (or 9 or 10 psia), which means the forming force
on the plastic will be 5 or 6 lbs. per square inch of plastic. Adding more
shop vacs in series or parallel helps the ultimate a little, but not much.
Using a standard one or two stage oil vacuum pump gives you much better
ultimate vacuum, down to 1 torr or better which is essentially -14.7 psig or
0 psia. This gives three times the "forming" force, which sounds great, but
the problem is that those pumps (at least affordable, readily available
ones) don't move nearly as much air at the beginning as the shop vac will,
so the plastic has lots of time to cool off and stiffen before it ever gets
formed. So people seem to either live with the shop vac or use a large
storage tank that they pump down with a vacuum pump and then have a large
diameter pipe and valve between tank and vacuum box so the effective pumping
speed is very high at the beginning to really suck down the plastic. I've
also read of hybrid systems using both shop vacs and vacuum pumps, using the
shop vac for the first second or two then switching over to a storage tank.
It all depends on your needs and goals. Not having built mine yet (:-)) I
think starting with a shop vac is the best way to get a simple system up and
running, to get some experience and to see if a better vacuum system is
needed for what you want to do. Then upgrade as needed.

-----
Regards,
Carl Ijames
"Steve Walker" wrote in message
...

On 1/19/2013 19:39, Bob La Londe wrote:
I finally decided to make a vacuum formed polystyrene cover for the
encoder on the front of the big mill. Seems pretty straight forward.
I've got my first vacuum box finished except for the port to put the
vacuum hose in. I noticed a lot of the DIY guys make a hole for the
smaller vacuum hose even though they have a full size shop vac with the
big hose. Is there some reason for that? Seems to me that the larger
port for the larger hose would evacuate the box faster and form the
plastic quicker before it cools. Am I missing something obvious?


Vacuum pump has more vacuum than a shop vac. Should suck down quick
enough, and get better corner forming.




(I have some PETG on the way to play with in case I don't like the way
polystyrene forms or holds up)

If this goes well, I have all kinds of ideas for vacuum forming...





--
Steve Walker
(remove brain when replying)

On Sun, 20 Jan 2013 11:18:59 -0500, Steve Walker
wrote:

On 1/19/2013 19:39, Bob La Londe wrote:
I finally decided to make a vacuum formed polystyrene cover for the
encoder on the front of the big mill. Seems pretty straight forward.
I've got my first vacuum box finished except for the port to put the
vacuum hose in. I noticed a lot of the DIY guys make a hole for the
smaller vacuum hose even though they have a full size shop vac with the
big hose. Is there some reason for that? Seems to me that the larger
port for the larger hose would evacuate the box faster and form the
plastic quicker before it cools. Am I missing something obvious?


Vacuum pump has more vacuum than a shop vac. Should suck down quick
enough, and get better corner forming.


The "average" vacuum pump is WAY too slow. You would want a vacuum
reservoir with a sizeable gate valve to apply the vacuum quichly to
the former box.


(I have some PETG on the way to play with in case I don't like the way
polystyrene forms or holds up)

If this goes well, I have all kinds of ideas for vacuum forming...

On Jan 19, 4:39*pm, "Bob La Londe" wrote:
I finally decided to make a vacuum formed polystyrene cover for the encoder
on the front of the big mill. *Seems pretty straight forward. *I've got my
first vacuum box finished except for the port to put the vacuum hose in. *I
noticed a lot of the DIY guys make a hole for the smaller vacuum hose even
though they have a full size shop vac with the big hose. *Is there some
reason for that? *Seems to me that the larger port for the larger hose would
evacuate the box faster and form the plastic quicker before it cools. *Am I
missing something obvious?

(I have some PETG on the way to play with in case I don't like the way
polystyrene forms or holds up)

If this goes well, I have all kinds of ideas for vacuum forming...

Good vacuum pumps aren't cheap. I remember how expensive the one we
had at Qualcomm was. We used it all the time for holding thin parts on
fixtures we made. It broke in the middle of a job I was doing and I
tried to use a Shop-Vac. Learned a valuable lesson on why a good
vacuum pump is needed.

"Bob La Londe" wrote in message
...
I finally decided to make a vacuum formed polystyrene cover for the
encoder on the front of the big mill. Seems pretty straight forward.
I've got my first vacuum box finished except for the port to put the
vacuum hose in. I noticed a lot of the DIY guys make a hole for the
smaller vacuum hose even though they have a full size shop vac with the
big hose. Is there some reason for that? Seems to me that the larger
port for the larger hose would evacuate the box faster and form the
plastic quicker before it cools. Am I missing something obvious?

(I have some PETG on the way to play with in case I don't like the way
polystyrene forms or holds up)

If this goes well, I have all kinds of ideas for vacuum forming...


Finally got around to the first attempt this evening using Plaskolite
polystyrene.

1st attempt I didn't get the plastic hot enough and let it sag far enough.

2nd attempt was not bad over all. There was just a little too much radius
at the junction between the mold and the table.

3rd attempt we spaced up from the table with popsicle sticks. It formed
very well with the radius below the mold. I had an issue with webbing
because I took the sheet down too fast, and let it vacuum down too quickly,
but I have a feel for it now.

There will be no forth attempt with polystyrene for this project. The
polystyrene is more than hard enough when formed, but its way to brittle. I
have some PETG ordered that should arrive sometimes this week, so I'll give
it a shot when it does.

I do have some ideas for the use of the polystyrene in the future though. I
need to look into its chemical reaction a little more and find out what it
reacts to, and what its stable with.

"Bob La Londe" fired this volley in
:

I had an issue with webbing
because I took the sheet down too fast, and let it vacuum down too
quickly, but I have a feel for it now.


Bob, you just answered your prior question of why the majority don't
bother with the larger hose!

Lloyd

"Bob La Londe" fired this volley in
:

I do have some ideas for the use of the polystyrene in the future
though. I need to look into its chemical reaction a little more and
find out what it reacts to, and what its stable with.


"Reacts with", or "dissolves in"?

Polystyrene is fairly chemical resistant in terms of reactivity, although
it is attacked by aqueous solutions of strong bases and acids and
oxidizers.

It's _soluble_ in many polar and non-polar solvents. No, not very
solvent-resistant at all. Not too UV-resistant, either.

Lloyd

Bob La Londe wrote:
"Bob La Londe" wrote in message
...
I finally decided to make a vacuum formed polystyrene cover for the
encoder on the front of the big mill. Seems pretty straight forward.
I've got my first vacuum box finished except for the port to put the
vacuum hose in. I noticed a lot of the DIY guys make a hole for the
smaller vacuum hose even though they have a full size shop vac with the
big hose. Is there some reason for that? Seems to me that the larger
port for the larger hose would evacuate the box faster and form the
plastic quicker before it cools. Am I missing something obvious?

(I have some PETG on the way to play with in case I don't like the way
polystyrene forms or holds up)

If this goes well, I have all kinds of ideas for vacuum forming...


Finally got around to the first attempt this evening using Plaskolite
polystyrene.

1st attempt I didn't get the plastic hot enough and let it sag far enough.

2nd attempt was not bad over all. There was just a little too much radius
at the junction between the mold and the table.

3rd attempt we spaced up from the table with popsicle sticks. It formed
very well with the radius below the mold. I had an issue with webbing
because I took the sheet down too fast, and let it vacuum down too quickly,
but I have a feel for it now.

There will be no forth attempt with polystyrene for this project. The
polystyrene is more than hard enough when formed, but its way to brittle. I
have some PETG ordered that should arrive sometimes this week, so I'll give
it a shot when it does.

I do have some ideas for the use of the polystyrene in the future though. I
need to look into its chemical reaction a little more and find out what it
reacts to, and what its stable with.

solvents tend to mess up polystyrene. Acetone melts the stuff on contact.