Vacuum systems

[Harrumff (Unregistered Guest)]

I currently own a PRT and am considering purchasing a complete PRT Alpha with 5hp colombo and vacuum table.

Will the vacuum system adequately hold down solid stock? My main concern is that the solid stock will only cover a small amount of the table compared to a large piece of plywood.

Also, shopbot offers four vacuum systems. Which one is best suited for solid stock?

Thanks.

[hwd_woodworking]

We got the one of the biggest chucking blowers you can get for the vacuum table. The table is great for just about everything. For solid stock you would mask off cetain areas to create more suction at the place you want to hold down. If you are doing something small I will take a piece of scrap (sheet good) and cut out the out side profile of my solid stock and insert it into the mask then run my part files from there. If you are doing alot of pieces you will want to screw down the mask so you won't loose your indexing.
The only problem we ever had would be trying to hold down a really warped piece of plywood but that really of no concern because who wants to use that kind of stock. This maybe a concern for solid stock if you do not surface it flat.

Nate

[dhunt]

Use clamps.

[cip]

David,
Use clamps? What the "H" are you talking about? The question was about vacuum systems and if they would work on solid stock. I have a 15 HP roots vacuum system and it works great on just about anything that i need including solid stock.

[mikejohn]

How rude!
A fellow Shopbotter offers advice and gets this response.
There are many occasions when clamps will work on solid stock when vacuum will not.
I hope David is not too offended.
.............Mike

[cip]

Sorry, no offense intended.

[dhunt]

Settle down guys...

I just love clamps!
They're very effective.

I also think vacuum systems are somewhat over-rated..
- Tech for Tech's sake, most of the time?

[mziegler]

After trying various vacuum system that cause me many headaches, I gave up went to plastic nails. Vacuum is ideal for production runs of one kind of part at a time. Vacuum also great if you got the big iron machine type of big horsepower vacuum pump that use a bleeder board. For one time run, small runs, nesting many parts and for design work type items, for me plastics nails are better. Mark

[tomj]

Plastic nails?

[wayneo]

Mark,
Yeah, PLASTIC NAILS? Where do you get those and a gun to shoot them? I may need to give that a try!

Wayneo

[Brady Watson]

For parts that don't make sense with vacuum, I just use screws. I have found that the self-tapping Kreg pocket hole screws work best. They are square drive and have a pan head. To prevent the bit from contacting the screws, I just setup a drilling file in PartWizard so that I pre-drill the screw holes with plenty of room around them to prevent a collision. In some cases I have only had .02" for clearance...and I have never hit a screw yet.

Vacuum is pretty good if you make yourself an accessory plenum. I have pics of it somewhere on here...You just sit the plenum on the spoilboard and use a shopvac for hold-down. If you use gasketing, this works out well. At the moment I have 2 accessory plenums; One that accomodates 24 X 32" material that I use for a steady customer with interchanging 'masks' for small parts, and another 8' X 10" wide one for long stock like moldings etc. This long jig has held down about 500 lf of hard maple among other things...and this was all done with a shopvac. Search the message board...there are multiple references to my accessory plenum (I think)...you should get the general idea. The other thing that I have not yet done is make vacuum pods, which could be used to hold a variety of materials as well.

-Brady

[mziegler]

Wayne, yes you need an air gun to shoot them. I use the Raptor Nails that Utility Composites sells. The website is http://www.raptornails.com/raptornails.html

[tomj]

Just got done picking my jaw up off of the floor...
Plastic nails....never would have guessed. Thanks for the link Mark!

[hespj]

Mark, how do you un-nail after you've finished cutting?

John

[daniel]

Hey guys, Im building a vac system right now. I hope to use it for some wood toys I'm making. It's a couple of days away from completion, and I'll let you know how it works.

Brady,
I'm confused on some terminology. I'm constructing a system like one I have seen at shopbot.
It consist of what I think you call a "spoilboard", Mine is made of a hardwood called Ipe.
It then has a MDF template that fits into a pocketed out section of the spoilboard. This must be the "plenum".

When I think of "spoilboard" I think of a piece that gets cut into, and is replaced every so often. However, I hope not to ruin the Ipe, I've made mine out of.

I haven't figured out if I'll use my shop vac or my dust collector to power it. I might go to a salvage yard and look for a squirel cage blower.

I'll report back on results!

[Brady Watson]

Daniel,
Your method of machining the grid into the table like ShopBot does is perfectly valid. I just don't process a lot of 4X8 sheets on my machine, so it makes sense for me to just plop an accessory plenum (basically a box with supports to hold the grid above it square with the Z axis) and cut smaller parts that way. Using that method allows me to devote 100% of my vacuum to the task at hand without worrying about losing vacuum over the whole table.

Don't waste your time on the squirrel cage blower...you will be disappointed. Invest in a Fein Turbo III vacuum and you will be able to do *almost* as much as a big vacuum system that sucks thru the entire 4X8 area.

There's lots of info on vacuum here on the board. Do some searching and see what others are using.

-Brady

[daniel]

Thanks for the info Brady,
My system is only 2x4 so I thought a blower might work well. I was just planning on using my shop vac if I didn't use a squirel cage.

[bleeth]

John: Use a wonder bar. Raptor has been around for quite a while now and some cold molded boat builders use it instead of staples so they don't have to pull them out.

Dave

[hespj]

Dave, I have heard of boatbuilders using plastic fastenings and would like to do so myself, but all I have found in the UK are plastic bolts and nuts, no screws or nails, although I've not looked very hard.

I take it a wonder bar is a lever?

[mziegler]

There may be some interest in using plastic nail, so I am starting a new thread. http://www.talkshopbot.com/forum/messages/312/9500.html?1128525502 Mark

[Harrumff (Unregistered Guest)]

Hey guys, thanks for the responses.

I can't use plastic nails because I cut my hardwood pieces down to size before they get CNC'd. Plastic nails only work for me if the pieces are oversized.

This is the routine I would like use in the future:

1.) Lay day full or half sheet of 49x97 MDF.
2.) Run program to cut out 1/4-3/8" deep rectangular recesses to place hardwood parts into. Corners of the recesses must be "extended" to take care of the rounded corders.
3.) Place all parts in recesses, then lock down with vacuum.
4.) Run subsequent program(s) to mill the parts. This includes curves on the edges, slots for panels, mortises, dowel holes, etc.
5.) Repeat all steps, starting at 1 with a fresh piece of MDF. New MDF must be used because whenever the parts get edge treatment, the recesses are destroyed.

[beacon14]

Instead of using up and taking time to cut a full sheet of MDF for each run can you rout an oversized recess and insert a strip of MDF between the part and the edge of the recess everywhere where the edge work would destroy the jig? Then you can pre-rip strips of MDF - in fact, if the vacuum is doing it's job you should only need small blocks of MDF (1" square?) to locate the part until the vacuum is turned on.

[jay_p]

Does anyone have the .sbp file for the 4 zone plenum that they can post or email to me? I have tried to download it for the last two days from the ShopBot site, but I keep getting an "unavailable" message. There is a message on the home page that they are rebuilding the website, so maybe that explains it.

Thanks

Jay

[paco]

7900 (5.6 k)




7901 (11.0 k)

[gene]

does anyone use the 7.5 hp single phase vac that shopbot sells?
My bld only has single phase (what a hastle )
how well does the vac work on a 48 x 96 alpha ?
Thanks for any advise Gene

[elcruisr]

I have an alpha and a prt. for parts cutting on the alpha you may find it to be too small, it's barely enough for the prt with what we do. Our alpha has a 15 hp fpz blower that is really just enough, again, for the parts we cut. Have you considered a rotary phase converter?

In the end your vacuum system will vary depending on the parts you anticipate cutting.

Eric

[dingwall]

Eric, Any idea of the cfm and either water column or " mercury your system's rated for?

[gene]

Scott at shopbot told me it pulls about 145 cfm and 14 " of mercury . I understand the cfm part but what is the mercury or water "s mean ? I assume its another way of measuring pull or holding force. Thank you Gene

[elcruisr]

Sheldon, sorry but I can't get to the model number on my 15 hp pump. It's in a partial sound enclosure to muffle it a bit. My manual has the specs in Italian and I don't speak the language! The folks at Shopbot should have the numbers though...

Gene, a vacuum system needs to maintain a certain level of negative pressure ( Inches of HG or H2O) at a certain flow rate. The higher the numbers the better the hold. In reality the 15 hp blower on a 6 zone 5 by 12 table will hold 8 to 10 inches of HG if all the extra space is masked off. By the time we cut a sheet into say, 20 parts. The vacuum is down to maybe 5 inches on our gauge. We also tab our parts together as a sheet. Without it at 8 to ten inches per second cutting speed you will start pushing things around on the table.

Eric

[dingwall]

Thanks Eric.

Gene, I find " of mercury easiest to understand. 2" of mercury = approximately 1 psi of atmospheric pressure @ sea level.

[sawkerf]

Gene, I have the 6.2 HP pump. I'm not sure if they even sell that one anymore. Mine works suprisingly well. I have a 4 zone 48 x 94 and I use LDF for my spoilboard. There is a big improvement in using LDF over MDF. The cutting strategy also plays a big role in how well it holds. If I could have afforded it I would have gone with a bigger pump, my only regret. Kip

[gene]

Kip,
The restrictions i have is that my shop is single phase. the largest pump they ( shopbot) sells ia a 7.5 hp in a single phase.
I dont think it would be cost effective to buy a bigger pump and a phase converter. (considering the power loss in doing this.
I ordered the pump about two weeks ago so i hope it will do good. ( I also figure the ammount of bits i break hitting screws , so that cost will lower the overall investment, ) Just joking
Thanks Gene

[gus]

If you want to do conversions from one unit to another try this site.
http://www.people.virginia.edu/~rmf8a/convert.html

[ron brown]

Gene,

Depending on what stratigy you use the 7.5HP vacuum pump should be plenty. I will evebntually go up from my $15 setup. I first need a good reason.

Ron