combining vacuum pumps

[AllgäuSki]

I was trying to build a vacuum holddown system, but my pump just doesnt move enough air. I know that most of you use a shopvac for the holddown system, but also when just pressing it feels like hours til the air gets sucked out of the hose-
Therefore my question: would a combination of two vacuum pumps be a reasonable solution to make my vacuum-setup stronger?

I'm not talking about the amount of vacuum (i know that -1bar or at my altitude more like -700mBar is the absolute maximum that i can get), i am talking about "suckability"! (nice word, isn't it)

by the way: found the time to turn an old barn into a shop. I will soon be posting a journal and keeping you up to date on my progress.

Cheers!

[twizzstyle]

You're looking for flow rate, CFM. I don't think even two (or three?) vacuum pumps will work for a hold-down. I've never used a vacuum hold down system, but I'd think you need a lot of CFMs, and vacuum pumps like you said are slow.

For your layup it will help a little, but is it worth the cost of buying another vacuum pump? Unless you are running up to the limits of your epoxy curing times, I'd just be patient and let it suck down, you can also try to push the bag down as flat as you can before sealing it up so there's less for it to suck.

[deepskis]

Hi AllgäuSki!
What does yor setup look like? Pictures?

I use a vacuum table and suck from underneath. I put a breather fabric under my mould and make sure there are no air leaks. When its good I reach 0.95 atm within a minute.

[falls]

You can use vacuum pump for vacuum hold-down. In fact it works really well (CNC tables use a vacuum pump for their hold-down). BUT you need a perfect seal for it to work well. Usually this means using vacuum tape (closed cell foam tape) on your jigs.
For using vacuum to hold down p tex on a jig its much easier to use a shopvac or normal vacc that keeps moving a lot of air so any leaks don't matter too much.

Vacuum hold down jigs
http://www.joewoodworker.com/veneering/ ... amping.htm
http://www.joewoodworker.com/veneering/ ... matrix.htm
Vacuum tape (different to the double sided stuff you use in vacc bagging)
http://www.veneersupplies.com/products/ ... -x-18.html

I think you could use this tape effectively for routing core blanks using a template with tape around the periphery rather than using clamps.
I think the original skevik skis video looked like they used vacc tape on their ptex hold down templates.
http://vimeo.com/6523899

I had a really good site about creating custom hold down jigs for a CNC where you are repetitively cutting the same shape. I've lost it, but will try and find it.

Sorry a bit off topic.

The others are right that it is CFM that governs pull down time. That any any leaks.