Trying to sort out the Vacuum mess.......

[daniel]

Hey guys, I have been using my dust collector to power my vacuum table. Its rated at 650 cfm. I'm considering buying a new dust collector just to run the table. Is this the way to go? I've read about others like the Fien III, however they are rated at less cfm as my collector, will they still work? Thanks!

[daniel]

I'm trying to figure out if I need a "vacuum pump" or a good blower motor.
What is the difference?

They both transfer a certian quantity of air from an inlet to an outlet. I imagine that the only difference is that, as the pressure differential between the inlet and the outlet increases the "vacuum pump" is more efficient than the blower.

That being said, most vacuum pumps I find have a small CFM rating. If they can't pull enough air mass to offset for leakage, then the fact they're more efficent means nothing.

Am I right? Should I just buy a good dust collector or blower motor?

[daniel]

Ok I've given this more thought, and I realise that as the pressure difference between the inlet and outlet of my dust collector increases, the CFM it flows decreases rapidly, possibly making it comparable to one of the smaller vacuum pumps I've found. So I'm still unsure about what to go with.

And now a new question. Is a vacuum, like a shopvac or a Fien III, just a mini version of a dust collector? What moves the air? In my dust collector, it is a squirrel cage type blower. What is in a Fien III, a vane type pump or a piston type?

Thanks for any input!

[Brady Watson]

Daniel,
A dust collector is not a good choice for vacuum hold-down. You will be very disappointed with the results...buy a good dust collector for keeping dust at bay...and a good shopvac for vacuum as a vacuum source for around $100. I like the Rigid brand ones with the 2.5" hose. A pretty good deal for the money. I ran one of these for about a year using custom made vacuum jigs. The best the shopvac would pull is about 3.5 inches of mercury (inHg) I recently bought a Fein Turbo III and it pulls a little more than twice that of my shopvac. I use it for vacuum hold-down exclusively and never for anything else that might clog the filter.

Be careful of CFM/Vacuum ratings. Generally speaking, when vacuum is highest, cfm will be lowest and when cfm is highest (open vacuum tube) vac will be lowest. The problem with a dust collector for vacuum hold-down is that it will pull maybe 1" Hg on a good day. The impeller design is meant to accomodate chunks of wood and other debris, so the blade to housing tolerance is very large. This results in the impeller cavatating and not generating a substantial vacuum. A vacuum pump on the other hand has very tight tolerances from the blades of the impeller to the housing....much like the compressor wheel on a turbocharger. This results in a more efficient pump, but not very good for dealing with chunks of wood debris. The dust collector is designed with a purpose in mind...that is to collect dust without clogging a filter.

Initially I asked myself the same questions that you propose here before I got into the vacuum game...Only after some testing with a vacuum gauge did I understand what works and what doesn't.

HTH,
-Brady

[ron brown]

Daniel,

Brady did a pretty good overview of vacuum systems. There is a large difference in how vacuum devices are constructed.

There are basicly three ways vacuum producing devices are built. As Brady stated a dust colector and vacuum motors differ in clearances. A regenerative blower, the next step up(down?) in power and still is using an impeller and close clearances. The regenerative blower will generate about 3 times the pull of a "shopvac" and still has high volume.

The best vacuums (practical for clamping) are positive displacement pumps. Roots type blowers, Vane type pumps and Piston pumps are the three basic types of displacement vacuum pumps. Each is less tollerant of dust and debris than impeller type pumps.

The area of the part being held (size) and the difference between the atmospheric pressure and the "vacuum pressure" is what hold the part. The size of the part becomes "effective size" of the part if there are leaks around the edges as in an un-gasketed setup. The volume of the pump, piping system, leaks, grid channel size and length, permiability of materail, substrate sealing and a few other factors come into effect in determining if the part can be held with a vacuum table.

For most people, once they get a feel for what is going on it all begins to make sense. Others are clueless and build unworkable systems or simply try impossible methods and curse vacuum clamping systems for their own igorance or stupidity - yes, tehre is a difference. There are many varaibles in a vacuum clamping system.

Ron

[jay]

Here is a good site on vacuum systems. It is a large site that takes a bit of poking around to get to the "how to" areas. It is well worth it. Bill Palumbo directed us to this site awhile ago after using some of the parts listed on the site.

http://www.joewoodworker.com/veneering/vacuumclamping.htm?osCsid=fc0663e633bb49f9cd0beaca 781663e5

[gerald_d]

Daniel, the most important issue in selecting a vacuum system is to know what you actually want to hold down onto your table......

[daniel]

Thanks Guys,
I did use a shopvac for holding down my parts before I used the dust collector. I had much better results wit the collector, However that is probably because the shopvac I used was just too small.
So I think tommorrow I will head to home depot and buy a bigger Rigid Brand shopvac and see how it works! Thanks Guys!

[mikejohn]

This is slight
thread drift, but what innovative ideas for hold down has anyone used, where vacuum is innapropriate, clamps inadvisable, and plastic nails unobtainable?
For me, hold down is an ongoing area of invention.
.....................Mike

[Brady Watson]

Outdoor/high-traffic carpet tape...the stuff with the fiberglass mesh in it.

-Brady

[mziegler]

Innovative ideas for hold down

How about placing heavy flat lead weights directly on the part. That could work for large parts. Every tried to cut thick mdf board with ¼ bit? That stuff is so heavy that you do not need to clamp it. Down side is it take awhile to cut it with ¼ bit.

4 by 8 sheets only need a half dozen to dozen screw or plastic nails to hold them in place. Main thing to worry about is the snap off points (end of tool path). By placing the tabs at the right locations and then routing out the tabs you can take care of that problem too.
Mark

[dingwall]

3M Spray 77

I just tried that on some melamine to hold .090" vinyl sheet and it worked great.

[beacon14]

wooden cams which put side pressure on the workpiece, holding it against a rigid fence. The fence and cams can be slightly higher than the workpiece and have slightly beveled faces to help transfer some of that side pressure into downward pressure. I've also used cams alone, arrayed around an irregular shaped workpiece where a fence is impractical.

Hot melt glue (worked great for probing, not sure I'd use it for anything but the lightest cutting).

Masking tape (again, light cutting)

[mziegler]

David, hot melt glue also work good on foam. The glue bond is stronger than the foam. Also it doable to scrap the glue off the spoil board with a chisel. I use this on small to medium sizes of foam.

Also I tried hold a piece of plastic with the hot melt glue. The glue adhere too good to the plastic that I was unable to scrap it off. I soak the glue with paint thinner and then was able to scrap it off.
Mark

[mziegler]

Is there anyone who are cutting out parts with a thin skin in sheet goods and then run the sheet of parts through a belt sander? The sander sands off the skin and this released the parts from the sheet. I read that there are shops doing this and was wondering how big a belt sander is needed to this? (horsepower and type of belts). Would a drum sander work? Mark

[beacon14]

I think almost any wide belt sander would do the job, but most drum sanders don't have the capacity to remove stock rapidly enough to be practical in this application.

[rjguinn@optonline.net]

Mark,
I've been using a Performax 37 X 2 with a 5hp single phase 220v drum motor & a variable speed gear head motor for the the table drive with excellent results. It will handle 37" wide panels X 12" thick using 2 different sandpaper grits with each pass. The sensors enable the table to adjust speed based on resistance, as in the case of uneven thickness material. It can also be used to flatten rough sawn lumber before going to your Shopbot.
Jeff

[mziegler]

Thanks Jeff and Dave. Jeff can the Performax remove the skin in one pass? What sandpaper grits are you using on the two heads? I did a search on Performax Sanders but couldn’t anything about smallest part size that could run through their sander. Would a too small part slip in between the drums or hold down rollers? Mark

[rjguinn@optonline.net]

Mark,
I use 80/120 grit paper. You can go as low as 36 grit.These machines are also known as abrasive planers. The amount they can remove depends upon several factors- grit,type material & feed speed.They require at least a 1200 cfm dedicated dust collector.I think that 6.5" is the smallest part size & wouldn't attempt to remove more than .060" in a single pass.
I also found it difficult to get any info on the larger machine & am waiting for a call back.If I get any contact info, I'll post it.
Jeff

[daniel]

I wanted to update everyone who helped with advise on my Vacuum table. It works GREAT!
I made the grid pattern in a piece of 1.5 inch thick Ipe. The Ipe is pocketed down about .25 inch for the MDF templete. The MDF is 24 inch by 48 inch in area. I did not seal the MDF and I did not use any gasketing. It is running off a Ridgid brand Shop Vac. It holds down small pieces great! Soon I will post a pic of the Grid also. Thanks to those who gave me advise on posting pics!

5396

[charles_o]

Daniel
It appears you have come up with a solution on holding these parts while cutting. I some intresting reading on vacuum theory and application for your next project.

http://www.edcousa.net/vacuum-training.html

http://www.woodweb.com/knowledge_base/Vacuum_application_FAQ.html#considerations

an example of vacuum power

5397
3" Shopbot made pod holding 1/2 sheet of 3/4" bamboo ply (approx. weight=36lbs)

[gene]

Dan,
Im glad you have figured out the vaccum best for your needs. One thing i will suggest not todo is buy a 7.5 hp single phase . I did for 5100.00 and have not seen it run yet, Purchased 10-05-05.
I wired it up and nothing i called the tech support and they said to call an electrican. I have wired several houses shops and numerious blds without a single problem and this guy tells me to call someone else. Would not even try to tell me anything. so much for a warranty. He said he tested it before the unit shipped but this is a lie also. The people at Republic blower were great and very helpful but the people with the control starters suck.. Gene Rhodes

[cncrob]

Hey Daniel Powell,
I was wondering what size Rigid vacuum you got? I was also wondering if you have any pics of your setup yet. Thanks- Robbie