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stick · Newbie Joined: 26 Apr 2006 Posts: 11

Hi guys. finally got my table up and running, and did a few runs with some HIPS. The flat surfaces come out great. The outside corners come out great, but the inside corners just don't get vacuumed in. I have seen many of your guys pulls with great inside corner detail. how do you get it? What's the secret!!??
I'm using the 24 x 32 settup with A 6.5 HP vacuum.
Thankyou gentlemen!
stick

AlterEgos · Posted: Sun Jun 18, 2006 10:30 pm Post subject:

Pictures speak volumes so, it might help to see what the problem is. But if I were to hazard a guess, I'd say you need to drill an 1/16" diameter hole at every inside corner all the way through the mold.

That's the main reason I make my molds hollow. Thus, (1) I can drill 1/16" holes with a normal length drill bit and (2) I get better suction from the lack of mass the air has to travel around the mold.

Also, having hollow molds negates having to use a vacuum pump so, a normal 5 hp ShopVac is more than adequate. As you can see, I get great pulls:

Hope this helps. Wink

_________________
-John

ROYAL RED · Newbie Joined: 18 May 2006 Posts: 21

John: That is a great pull.

stick · Newbie Joined: 26 Apr 2006 Posts: 11

[quote="AlterEgos"]Pictures speak volumes so, it might help to see what the problem is. But if I were to hazard a guess, I'd say you need to drill an 1/16" diameter hole at every inside corner all the way through the mold.

That's the main reason I make my molds hollow. Thus, (1) I can drill 1/16" holes with a normal length drill bit and (2) I get better suction from the lack of mass the air has to travel around the mold.

Also, having hollow molds negates having to use a vacuum pump so, a normal 5 hp ShopVac is more than adequate. As you can see, I get great pulls:

Hope this helps. Wink

[/quote]

Wow! Thats perfect!!!! Those are the results I require!!!
When you say hollow mold, what do you mean? Like an enclosed box? or no bottom part against the tabletop? May I see the mold please? Pristine pull Sir! That is perfect...
I drilled the holes and used a heat gun, but the pull was the same. The detail is very good on the flat surfaces, so I think I'm getting enough vacuum, but I have a suspicion that air is slipping through the cracksin the mold, and actually not letting it get a good seal. I think I'll try caulking all the cracks, and sealing up the drill holes, and give that a shot. what do you guys think?

Thankyou!.
robin

jegner · Posted: Tue Jun 20, 2006 9:58 am Post subject:

Well done!

As for the hollow molds, yes, many of mine are no much more than a box with surface detail. Some of my solid mods have risers, and I know Paul slips his molds on thin strips so that air can pass under the mold.

ROYAL RED · Newbie Joined: 18 May 2006 Posts: 21

Post deleted.

AlterEgos · Posted: Tue Jun 20, 2006 8:03 pm Post subject:

I can't really tell what your mold is (the pics look like an abstract painting to me). Take a few steps back and then take the pics.

It would also help to see the mold on your forming surface itself so we can see any problem areas that may be occurring. Sometimes positioning is a key factor, as well.

And a last note, some things just don't form well, no matter what you try. :/

I'll try to post some pics of one of my molds later tonight. Wink

_________________
-John

stick · Newbie Joined: 26 Apr 2006 Posts: 11

Oh this is maddening! here are some pictures of failure. I tried drilling 1 hole in each inside corner, but it had no effect. Ive gone through 2- 4 x 8 sheets already and it's starting to get expensive lol.
I give you guys credit for making something so difficult look incredibly easy!

help! Shocked

thanks
robin

AlterEgos · Posted: Tue Jun 20, 2006 9:31 pm Post subject:

Hmmm... well, it looks like you're getting a pretty good pull. Remember, you aren't going to get exact detail with vacuforming... it's just a fact of the process. Thus, some detail will be lost.

What thickness of styrene are you using? The rule of thumb is: The thinner the styrene, the better detail you'll achieve.

I'm thinking your obvious problem is that the mold is very geometric and has a lot of sharp corners, which aren't really shapes that lend themselves well to vacuforming. In fact, I'd be surprised if you get a better pull that what you're already getting. :/
_________________
-John

stick · Newbie Joined: 26 Apr 2006 Posts: 11

thanks Alterego.
Well I guess It's time to move onto fiberglass then. Rolling Eyes

Ack! can anyone steer me in the direction of a fiberglass forum? lol.
thanks.
robin

jegner · Posted: Wed Jun 21, 2006 6:17 am Post subject:

Show us what your mold looks like. I bet we can come up with something that will work. I'm guessing the edges you are wanting more crisp are the ones on the top, and air flow is just not getting there, before the plastic starts to harden. Also, there are some edges, that might cause lock-down.

A heat gun might also help, and a channel groved into some of the areas to allow air to pull might improve the overall results. One thing to remember, your shop vac powered vac table will only pull about 6 inches of mercury, and a hi-vac with a tank will pull 28 inches of mercury, and will give finer detail.

Thinner plastic as AlterEgos has mentioned will also show better detail, but I tend to think it's more of an air flow issue than plastic thickness.

stick · Newbie Joined: 26 Apr 2006 Posts: 11

here are the pics of the mold. yeah I know it's ugly but I have to keep drilling and filling holes to try to get it to work. so bear with me.

The channel thing sounds promising. I agree I think there is enough vacuum, its just not getting to some areas. I used the heat gun, the plastic started to liquify but not vacuum in so there is just no vacuum there.
Well see what you guys can come up with here.
Thanks again for the help.
robin

jegner · Posted: Wed Jun 21, 2006 9:14 am Post subject:

In the tiny triangles in the back, drill holes, 1/8th dia. into the cavity of the mold.

On the top ridges, take a sharp knife, and score some ridges, and lead them all the way to the base, or to a hole. This will act as a channel. Don't go too deep, as the score will show in the final pull, and try to hide it as best you can in your design.

Also, smooth your mold with a primer coat of sandable primer. Then sand it with some 220 grit paper, do this so that the sand lines lead to the base. These tiny grooves from the sanding will allow the air to flow as well.

AlterEgos · Posted: Wed Jun 21, 2006 12:52 pm Post subject:

What Jim said is right on the money for any hopes of better pulls. My only other thought would be to try making a negative mold of your model and using that to make your pulls.
_________________
-John

stick · Newbie Joined: 26 Apr 2006 Posts: 11

Thanks guys. I'll give the channeling a try. I like the using the sand lines idea as well.
Thanks gentlemen,
have a great day!
robin