Yellow73SB

I was just wondering if this would work. If I remember correctly it sucks 4cfm. I don't know if thats enough. What do you think. Yes I know about the turbomustangs article.

noonie

Yes it works. You can get vacuum pumps fairly cheaply on ebay. There are different cfm ratings. The air operated ones are pretty fast and inexpensive.

Tommy Samuels

The flow rate is only important for emptying air from the vacuum bag. The important measure is the amount of vacuum it will draw. A decent vacuum pump will pull 26 inHg on a sealed system. This is pretty darn close to -1 atmosphere (29.92 inHg) or 14.7 pounds per square inch.

You can vacuum bag with good results at 15 inHg.

lars

You don't need a real vacuum pump for vacuum forming. I've done vacuum forming using a vacuum cleaner. Much better volume than a little AC vacuum pump... I use the vacuum from my house central vacuum system, which is the same thing as a shop vac.

BB wowbagger

Another "Budget tip" is to use an old refrigerator compressor and use it backwars.

Yellow73SB

I was just wondering because we have one and I didn't feel like making one up

And BTW this is the pump that you use to put vacuum in the a/c before you recharge in case anyone didn't know.

Big2Bird

It will work great.

Yellow73SB

I'm going to try and make some t-tops

Michel B

T tops,,,Very cool !!,,, I hope you post some pics.
If, in your projects you dicide to improve your equipement you can purchase a proper vacume snifer that plugs to your shop compressor. HCS2026-01 - Assembly, from Heatcon industries. This is what we use at work, and bagged properlly you can acheive 20-24 inhg.
Flat layouts are fairly simple and I'm sure you will have nice results, but when you start doing curves you will have to make air passages so that all the bag is vacumed. Use strips of cheap scotch bright for this purpose. If you can find some sort of thin, breathable teflon sheet and applly it directly on the repair, and over this you use some sort of absorbing sheet like fiberglass or even flanel, this will absorb all the extra resin and make a real nice finish. Once its all cured the teflon will come off very easy. Also,,, to save your vacume cleaner from sucking some resin make up a scotch bright filter at the opening.

lars

An AC vacuum pump does not have enough volume to suck down a part as big as a T-Top quickly enough. If you use an AC vacuum pump, you will need to use it in conjunction with a vacuum tank reservoir and a ball valve control system in order to have enough volume and control to do the job.

I used to design, build and operate commercial vacuum forming equipment, and I've done a lot of vacuum forming of aircraft interior parts. You have to have lots of volume and volume control to do the job you intend to do. You also need to build yourself a nice little vacuum table and the vacuum frames for the material and have an oven large enought to heat the material.

BBShark

I'm confused. Vacuum "forming" is as Lars describes above, heating flat sheet of thermoformable material and simultaneously pulling it over a mold and vacuuming the air out from underneath. Carbon fiber is not thermoformable in this manner.

You could vacuum bag a mold with a carbon mat in place and fill the mold with vacuum but you better have a real nice polished mold and a lot of vacuum to pull your resin in.

noonie

You are correct.
The proper way to do this is to use large presses and heated chromed, polished molds and squeeze out any extra resins to create a uniformly dimensioned piece. Extra resin does not create extra strength. Few have the budget resources that GM had.

It can be done by vacuum, but frankly with a good mold and experienced technique you would be better off by hand for all the trouble.

SHAKERATTLEROLL

Go here and look for the info you need. http://www.rcuniverse.com/ With RC Aircraft you need the part you make to not only be light but very strong.

There is lots of info here if you only look for it.

lars

BB is correct. Real "vacuum forming" is typically done using plastic sheets that soften with heat. These are draped over the mold using a frame, sealed against the table surface, and a vacuum pulls the softened material down over the mold until the plastic cools and becomes rigid.

Carbon fiber, when "vacuum formed", is a completely different process. To form carbon fiber, the raw carbon fiber "cloth" is layed into a mold. Resin is added, and the mold is "vacuum bagged." This vacuum bagging process extracts all the air bubbles out of the resin and the matt, and applies pressure to the composite layup. The vacuum bagged resin/fiber/mold assembly is then baked in an oven to cure. You can't heat and "vacuum form" cured carbon fiber sheets, and the layup/molding process is not something I'd want to try to do at home.