Venturi Vacuum Hold Downs

[CNYDWW]

I know there are some vacuum pods out there that use compressed air with the venturi setup. I was wondering if anyone has used their own venturi vacuum system on a larger scale?

[Gary Campbell]

Randy...
I have a venturi vac generator. Has a lot of vacuum, 22 inHg, but low volume. I use it for the pucks of my sheet lifter.

You could use that for hold down, but you would need a carefully crafted, totally non porous, non leaking fixture or puck(s). No spoilboard or bleeder. Plastic or metal. Good gaskets. One pin hole will cause these types to lose vacuum. Some are noisy if unmuffled, and many use more air than small compressors put out.

[CNYDWW]

I'm actually planning on using machineable resin cast to make localized pods with a rtv rubber compound for a gasket. This would be a setup for jigs and fixtures and making my own pods in the shape i need is a much better fit for the application then using the generic square pods. I'm basically trying to avoid building a whole vacuum table for a BT48 and masking for curved moldings and the like. Other option would be screws and a substrate attached to the back of the material so i can use the proper cutters. Using a raised panel cutter is going to put a lot of stress on whatever hold down system i use.

[Gary Campbell]

Randy...
Looks like you have a good situation for purpose built jigs. As long as you have the air available you should have no problems.

Very few hold down methods will hold a narrow piece like a molding when using a raised panel cutter. Make sure the bit you use is rated for the rpm and make sure your spindle can handle a bit that size.

[CNYDWW]

Yeah it's still a work in progress. Trying to simplify the process without the long machining time for 3d. Also makes matching patterns on a small shaper or router table easier. The theory is to actually combine the vacuum pods with mechanical hold downs, cut the inside edge, remove the waste prior to using the raised panel bit. Once that's done another radius profile and cut along the back side.

Ps. Bit diameter is going to vary around 3", at less then 1/16" per pass it should be fine even with a PC router. Even if i have to i may run a roughing toolpath before using the large bit.

[Gary Campbell]

Randy...
If you are going to make a matching pattern on a router table, cut out your curved piece and a router template on the Bot. Then run them all on the router table. Simple

Multiple bits, multiple passes, hold down for a narrow curved molding when using a large bit, not so simple.

Coming up with a system that works... priceless

Let us know how it works out. Post pics of the vac hold down

[CNYDWW]

Will do when i get to it. Unfortunately i can't do that kind of routing on a table. Medical issues. I've got a list a mile long of processes to figure out.

[michael_schwartz]

I built a venturi pump from a kit to use with a vacuum bag but I have not used it for hold down yet.

I built the project V2 kit purchased from veneersupplies.com with the larger venturi (not the largest). I need to add a switch and rewire it so I can select continuous operation for hold down.

Certainly pulls down my 5x5 vac bag just fine so I assume it should work ok for hold down given the right circumstances. My pancake compressor was unable to keep up when pulling the bag down, but my 3HP compressor with a 26 gallon tank had no problem.

Took me an evening to build the kit, and get it working. The instructions and parts they provide are very good.

[bleeth]

Michael:
With continuous on your compressor driven vac will work very well for hold down using a puck system for individual parts.

[frank134]

Gary how big of an air compressor do you have? I have a 5 hp with 80 gal tank. Do you think that will be ok for that vac unit?

[Gary Campbell]

Frank...
I have an Ingersol Rand 5hp with a 60 gal tank. I am sure yours will work fine. The air motor on the winch uses way more air than the Vaccon Pump.

[frank134]

Thank gary I got the same so I good. I know what I forgot to ask. Does your unit pick up mfd at all. 4x8 or 5 x10 sheet 3/4" thick. I know it will do plywood.

[Gary Campbell]

Frank...
I have done Trupan (49x97) when I replaced my spoilboard, and noticed it was barely holding after one side was surfaced. MDF flows less than Trupan, so I am guessing it will work