Clearly, a Penn 49

[Crow]

How many inches of vacuum do I need to pull?

[sabaman1]

After mixing try pouring into a shallow container such as tupperware lined with aluminum foil, this should help remove most air bubbles then pour from container. Also mix separate batches for each sideplate. Hope this helps.

[jurelometer]

How many inches of vacuum do I need to pull?

I'll tell you how much vacuum, if you tell me what resin you are using


But seriously, I don't know if vacuum will work for all types of resins.  If you are using a two part urethane, then the stuff I have seen  suggests 28 Hg.  I wouldn't be surprised if 25 gets you most of the way there, but that is just a guess.

BTW  - the resin will actually boil when you draw the vacuum, so you have to degas the resin before you pour it, than degas again in the mold,   The resin container has to be  2-3 times the volume of resin to allow room for expansion during degassing, and you might need a larger/longer sprue in you mold to allow for a bit of frothing.   If you want to stick with the same mold design, only degassing the resin before pouring might get you most of the benefit, all the small bubbles from mixing will be gone.

I only do vacuum bagging, and not chambers, so I am not an expert on this, but I have read that homemade glass chambers can fail and you end up with broken glass and resin flying around.  I just did a quick web search and saw this :https://ehs.princeton.edu/laboratory-research/laboratory-safety/laboratory-equipment-and-engineering/pressure-and-vacuum-systems.    You will also need some sort of trap system so that the resin does not backflow into the pump.

One more note:   Sorry about being the safety police, but when I looked into this about two years ago, I couldn't find a water-clear UV resistant two-part urethane that was not scary-toxic from mixing to full cure.   The stuff at the Smooth-On site is listed for Industrial use only (but I think that anyone can order it).  I called around to some other suppliers and the safety recommendations were similar. My apologies if you are well versed on chemical safety, but most of us don't have proper training on fitting respirators, selecting filters, managing ventilation, etc.

-J

[oc1]

I couldn't find a water-clear UV resistant two-part urethane that was not scary-toxic from mixing to full cure. 

Most urethanes do not yellow like epoxy does.  I usually opt for the better adhesion of epoxy so UV and yellowing is always an issue.  The best I've found for UV resistance is Aluzine.  It's 2:1, medium viscosity, either fast or slow setting.  It's expensive and finicky though and needs a low humidity environment as it cures.
-steve

[oc1]

How many inches of vacuum do I need to pull?

A positive displacement pump will approach 30.  A venturi will give you 27 more.  Here's one that will get you 28 for only sixteen bucks.
https://www.harborfreight.com/air-vacuum-pump-with-r134a-and-r12-connectors-96677.html

Most of the benefit (for our purposes) probably comes at a fairly small pressure differential. But, it would be more expensive to maintain 10 inches than to just shoot for 30 inches even though you can never quite get there.
-steve

[jurelometer]

I couldn't find a water-clear UV resistant two-part urethane that was not scary-toxic from mixing to full cure. 

Most urethanes do not yellow like epoxy does.  I usually opt for the better adhesion of epoxy so UV and yellowing is always an issue.  The best I've found for UV resistance is Aluzine.  It's 2:1, medium viscosity, either fast or slow setting.  It's expensive and finicky though and needs a low humidity environment as it cures.
-steve

Don't know about Aluzine, but most laminating epoxies have a pretty high shrink rate, which is not a problem when mixed with fibers or glass cloth, but for casting clear parts there is going to be some warping and shrinking (around 5% shrink by volume I think).  There are epoxy casting resins that don't shrink much.   You might need a thicker part than a 349 sideplate to have a successful epoxy part.  Casting epoxy is usually not elastic enough for thin walled parts, but I could be wrong.  Don't know if it is recommended to vacuum de-gas casting epoxy.

[Crow]

Thanks for all the input, folks !  Here's the stuff I used:
https://www.amazon.com/gp/product/B07BM9LHRB/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

"epoxy resin"
    It does have low...or no..odor, although I used it in a "well ventilated" area, anyway (I didn't get this old by being either stupid, or lucky ! ) . I DO have one of those "cheap" ,air driven, vacuum extractors....and *may* attempt a "try" using it....as I have a couple ideas for a "chamber" (not "see through", though ...unless you're Superman ).  This stuff doesn't seem to "shrink"...although, as the air bubbles came out, it did "settle" deeper into the "sprue"(the fill hole and vent hole)...so, I'm thinking that a longer, larger "funnel" will help with that. I DID "top off" the pour, a couple times, but, I should have "kept topping off" for a longer period...I walked away too quickly, I guess ?!
    As long a period as it takes to "set", I'm thinking on dramatically increasing the time I "stir", as well as allowing more time before I actually "pour"....and if I try the "shallow pan" trick, I'm thinking the "bubble problem" will , for the most part, go away"....or , I'm HOPING it will go away ! After I finish up the molds for the spool halves (hopefully, today) I'll give casting THEM, a try....warmer temps in the shop, and warmer "mix" temperature (put the bottles in a pan of warm water, before I mix), longer stir time, longer "wait to pour" time (in a shallow pan, instead of a "tall cup"), and see what the results are !........Thanks again for your input !

[jurelometer]

Thanks for all the input, folks !  Here's the stuff I used:
https://www.amazon.com/gp/product/B07BM9LHRB/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

"epoxy resin"
    It does have low...or no..odor, although I used it in a "well ventilated" area, anyway (I didn't get this old by being either stupid, or lucky ! ) . I DO have one of those "cheap" ,air driven, vacuum extractors....and *may* attempt a "try" using it....as I have a couple ideas for a "chamber" (not "see through", though ...unless you're Superman ).  This stuff doesn't seem to "shrink"...although, as the air bubbles came out, it did "settle" deeper into the "sprue"(the fill hole and vent hole)...so, I'm thinking that a longer, larger "funnel" will help with that. I DID "top off" the pour, a couple times, but, I should have "kept topping off" for a longer period...I walked away too quickly, I guess ?!
    As long a period as it takes to "set", I'm thinking on dramatically increasing the time I "stir", as well as allowing more time before I actually "pour"....and if I try the "shallow pan" trick, I'm thinking the "bubble problem" will , for the most part, go away"....or , I'm HOPING it will go away ! After I finish up the molds for the spool halves (hopefully, today) I'll give casting THEM, a try....warmer temps in the shop, and warmer "mix" temperature (put the bottles in a pan of warm water, before I mix), longer stir time, longer "wait to pour" time (in a shallow pan, instead of a "tall cup"), and see what the results are !........Thanks again for your input !

Figured you were being safe, but thought I should mention just in case.  A guy at my local shop did himself some lung damage on a single exposure casting some nasty urethane.

Casting epoxy is designed for low shrink.   The issue will be strength for thin walled parts.  For a display piece, this will probqbly not be an issue, just don't use much torque on the screws and tighten evenly. A  coat of clear acrylic will help to slow down the yellowing.

In the photos,  I saw  mini bubbles spread out though the part in addition to the few larger bubbles.   This is probably from the mixing, and what degassing will help with.  Vibration and time will help degas the resin before pouring.  Since it is casting resin, it should be self degassing if you follow the instructions.  They use this stuff for art projects and countertops, so no micro-bubbles is pretty much mandatory for this type of product.

If heat is recommended with pouring, it is probably worthwhile to warm up the mold a bit as well.    The heat should thin the resin.   Pouring from high up with a fine stream can help minimize the air trapped by the resin entering the mold, if you have enough working time. 

Looking at wher the sprue is, there is a long distance for bubbles trapped at the bottom to reach the top.   If the working time is long enough, it might be worthwhile to pour a bit, wait a bit, etc, so that the bubbles at the bottom can work their way to the surface more easily.

With lots of casting resins, the so-called working time is the maximum time it might be possible to pour, but the viscocity can go up before then.  As a rule of thumb I budget my time for half of the listed working time (AKA pot life) for a product that I am not used to.

Exciting!  Keep posting.  I want to learn more about clear resins.

-J

[Crow]

   Yeah, I went back and "refilled" the mold, twice....as the air bubbles left, or more "nooks & crannies" were able to be filled....the level in the funnel went down. I *should* have given it at least one more "refill"....but didn't ! When I "vibrated" the mold....the level went down...dramatically. I refilled, waited,maybe, 10-15 minutes, and refilled, again. I think for my next pour (the spool halves), I'll use a larger "funnel" so the top of the "sprue hole"(and vent hole,as well)has a larger amount of material "on tap". I guess I'll never learn any younger !!
   I knew from the get-go that strength would be an issue....as far as "using" the reel goes....but, it's a "to look at" reel, not a "to fish with". Most of the "high strength" resins are much more "fume prone", and that, along with some other "hazards", made me think they weren't something I wanted ...or needed...to use.

[Fishy247]

This is way too cool. 

[broadway]

Now I have no experience with molds, but when I made a "bottle cap" clear resin table with a friend a few years back we poured about an inch then used a hand torch to bring the tiny bubbles to the surface.  We did the same for the next 2" and it drastically reduced the amount of bubbles (maybe there were 6-8 tiny bubbles that didn't make it all the way to the surface where there were hundreds before the torching) in the end.
Neat project... looking forward to more.
Dom

[Crow]

     Using both the silicone...to make the molds...and the resin...to actually cast the 'object"   are a totally new thing for me, so, any, and all input is appreciated !  I have read about the "torch" trick in my on line "trying to learn" searches. The thing that's complicating the issue...in the way I'm doing it..is the "mold" has to totally "encapsulate" the object. I can't see any other way to do it.Casting "one side" of , say, the head plate, would be much easier to do...but, BOTH sides need to be done at the same time. I'm "hoping" that heating both the resin, and the mold, and being a bit more careful....and slower!...in making the "pour", will get me to an acceptable level .  Mo just sent me a broken plate, so I can salvage the "threaded insert" for the bearing (Thanks, again, Mo !!), so I'd like to try again on the head plate (without "breaking up" the one I've already cast !).....hopefully I'll have time , before we head "south" for the winter !! 

[broadway]

Touche', you're right, can't torch while inside a full mold.
looking forward to this.
Keep it up,
Dom

[jurelometer]

I think it really helps to visualize what is going on at each step to cause the formation of bubbles and how the bubbles are prevented from reaching the surface of the resin. Turbulence is your adversary, especially for smaller bubbles.  Turbulence is occurring when mixing AND pouring.  Once a bubble is in the part, the smaller the bubble, and the greater the distance it has to travel to reach the surface, the more likely that it will remain in the part.

In addition to degassing the resin in the pot, I would avoid the funnel if possible, and pour as small a stream as possible.   in addition to decreasing turbulence,  a very thin steam cannot carry bubbles as we well.

The fact that you had to top off several times means that there was a large amount of air trapped with the current pouring method. This is the air in the mold that is not escaping as the pour is occurring, but rather is having to travel through resin in order to exit.  Controlling the pouring stream should help here as well.


Hopefully, carefully managing temp, mixing and pouring will yield the results you want.  If not, you may need to think about a new mold. Professional mold designers (not me)  use flue, gate and riser design, plus part orientation to allow  the resin to enter the mold without turbulence, and to give the air in the mold the most effective  path  to leave the part as the resin enters.

An additional technique for thinner walled parts  is to use vacuum to draw resin through the part.  You need to design the mold for his purpose.  The basic idea is that a tube goes from the resin pot into the mold. At  the appropriate location in the mold there is an exit port where vacuum is applied.  Not a lot of vacuum that would make unnecessary turbulence,  just enough vacuum to to gently draw the resin through the mold.

Another example:  if the mold was designed to be poured so that the inside of the sideplate was facing up, you could put a series of vents or risers that would allow bubbles to rise above the part.  In addition, by casting the part with a flat orientation, bubbles have less of a distance to travel to escape the part.   This may not be the best strategy for your part.  It is just an example of the thought process that goes into mold design.
Keep us posted!

-J

[Bill B]

What if the mold was tipped on its end, think of a reel sitting on its seat, and the pour flue and vent were at the top, like where you would find a harness lug, and then a vacuum applied?  With a gentle pour to minimize bubbles?  Granted the bubbles would have a long way to travel to the top, but they may collect other smaller bubbles as they rise.....just a thought....Bill