Brady Vac Updates?

[john_l]

Regarding the vac hold down system in this thread... http://www.talkshopbot.com/forum/messages/28/22456.html

Is there anyone besides me still running this setup? Other than replacing the trupan every few months and blowing the dust out of the boxes (rarely), mine has been running as strong as when new (July 2007). I wish I had put an hour meter on mine.

[loriny]

I use a steup like that daily. Works well except if my material is extremely twisted. I replaced a motor a couple months ago. Couldn't imagine being without it.
Lorin

[magic]

Q.

Lets say that I have a sheet of 3 mil PVC and cut 400 parts with a 3/16 bit. (typical job for me)

With a Vacuum - In practice a sacrificial piece of Styrofoam will be sandwiched between the material and the table.

Does any one have an opinion as to weather a vacuum set-up would hold everything? If so... how many motors (one motor per zone) and how many zones would I require?

[john_l]

There are vacuum setups that will hold that. But mine would not. Using vacuum, I just had a job to cut 300 ornaments out of 1/8" acrylic and was starting to have pieces come loose.

There are several ways to do it.. My solution was to spray a very light mist of the temporary contact cement (super77?)on a sacrificial sheet that the vacuum would hold onto. Once cut.. the pieces popped right off.

My acrylic had a factory applied protective paper face so cleanup wasnt an issue. Unfaced pvc might require a cleanup test or you could cover the side you wish to spray with a high tack paper transfer tape.

Downcut bits will help keep small parts on the table too.

[erik_f]

A good way to estimate for me is to convert hg to psi and then figure out how much psi will actully be on each part. Make sure to estimate your total curf loss.

[magic]

Wouldn't that be by trial and error since I have not installed the system yet?

How about a crazy set-up where I can direct all the vacuums to any of the zones (in parallel ) or to individual zones.

It would be a snake pit under the table.

[Brady Watson]

"My solution was to spray a very light mist of the temporary contact cement (super77?)on a sacrificial sheet that the vacuum would hold onto. Once cut.. the pieces popped right off. "

John,
This is how I hold very small parts for production. In most cases, .060 styrene or Sintra are perfect. In some cases, .125" material will work better if you need additional 'onion skin' strength when moving the finished product off of the machine. As long as you don't puncture the bottom laminate, you'll have full vacuum for your small parts without the need for constructing exotic fixtures - or the frustration that comes with parts that move.

Running the sheets through a laminator is best, but careful work with a J roller will do. You may wish to experiement with 3M Repositionable Adhesive 75 where residue is an issue. Transfer tape also works with the caveat of adhesive smearing on the edges of parts and more variations in Z than thinner adhesives.

-B

[fredtoo]

Brady, can you expand a bit on this?

"Running the sheets through a laminator is best, but careful work with a J roller will do."

[Brady Watson]

Running your material to be cut, transfer tape (or contact cement) + sacrificial backer (PVC/styrene) thru a laminator will yeild a bubble-free and void free lamination. Not much more to say about that.

-B

[john_l]

Brady, I fully agree. And thanks for the nudge reminding me of the option to leave an onion skin, especially with a sheet that already has a protective skin on it. Makes perfect sense. Honestly, if I had done that with all those ornaments I probably wouldn't have even needed the spray adhesive in my particular situation.

As you stated, you do loose some control on sheet thickness with the transfer tape method but it's still usable in many situations. I wanted to mention though, for applying transfer tape there is a tool available that works quickly and lays it on very smooth. It can be seen here... http://www.bigsqueegee.com/ I actually made my own out of some PVC before I knew this was even available, but mine works the exact same way.

[john_l]

Glad to hear both Lorin and I are still holding down with the central vacuum systems. Anyone else still running them?