Vacuum Pump Question

[sodfarmer]

I have a 4' x 4' router. I was wanting to know if anyone has any suggestions on a vacuum pump. What size have they used and any certain models. Thanks

[newlife]

I also have a 4 x 4 table router. My current setup uses two shopvac heads. This seems to work OK, although more vacuum is always better. If I plate off the open portions of the spoilboard it will hold a 6 x 18" piece of flat material as long as I don't push it too hard. Basically it comes down to making sure you block the small pieces in to help keep them from sliding. A vane pump would be nice, but I need to stay. within the hobby budget.

[lgalla]

Hay GrassGrower.
Good question of vacuum.
First I would ask new life for more details on his shopvac system.I admire the guys who get by cheap.
If you cut at 600IPM you probably need at least 10HP of vacuum.If cutting small parts and using perimeter gaskets and zoning a shop vac may be enoughAnother methog would be to cut in 2 or more passes.After the first pass,brad or nail the parts to the spoil board.It works as well as a 20HP vacuum pump.but now you have 2 nails or holes which may not be acceptable.
Check ...www.staradhesives.com for some useful ideas on hold down.
Larry

[newlife]

My vac table is split into 4 quadrants with 1 shop vac head mounted with 2" PVC pipe to supply vacuum to 1/2 of the table which has 1.5" square grids x 1/2"slots. There are ball valves to shut off unused quadrants. I use soft foam rubber strip to seal out the perimeter of the spoilboard. I have trouble pulling down warped ply although flat material holds pretty good as long as it is smooth and clean. This works because I have a limit of about 150 ipm in my control. Not a speed demon but I am a hobbiest and haven't tried to make the system pay for itself yet.

Someone trying to make the mortgage payment would probably want a system that would allow faster feeds. Seems to me it all depends on what you intend to do with your machine.

Newlife

[lgalla]

THANKS for the reply.You are correct.150ipm and a shop vac is OK IF NOT NEEDED for income.Personally I would prefer to watch a 50ipm router than watch the seasion final of LOST for the millionth time.Got to go,the final episode of Boston Legal and desprite house wife's is on,AGAIN!!!!

[sodfarmer]

I have a regenerative blower that I use now. It works pretty good. I planed my spoilboard @ 200" a minute and it held good. I need to modify my grid table, my seal needs to be closer to the edge. What does everyone else use for spoilboard?

[lgalla]

Sorry got the address wrong
http://www.allstaradhesives.com/

[bill south]

Newlife;
How about some more info on the soft rubber seal for the edges of the spoilboard. I have a similar setup with 4 quadrants and valving using a 6.5 Horse Shop Vac. I've also added a 1/4 inch air inbleed to the vacuum header which I hope sill help prevent the shop vac from overheating on long cuts. I don't know if it was needed but it didn't hurt anything and the $100 for the vacuum is a lot to me so I want to protect it.
I also added a vacuum gauge and was surprised that the vacuum was less than 5 inches of vacuum. Thought it would be more. Seems to work OK on MDF cuts at 100 IPM. Thanks for the information.
bill

[newlife]

I currently use 3/8 X 1/2 foam w/ adheasive backing from MCMASTER Carr #8694K13. This is slightly too tall for my grid and holds the spoilboard up off the grid table resulting in a slightly changing spoilboard top surface between clampings. It appears if I had 1/4" high foam, the vacuum wouldn't have to compress the foam as much to get the spoilboard and the grid top to mate and stay stable. As it is if there isn't a good vacuum seal on top of the spoilboard eg too much open space, the spoilboard doesn't get pulled down flat to the grid top, resulting in a uneven work surface. -sigh- lessons learned.

I am considering upgrading to a replacement vacuum head from Grainger to replace both of my existing shop vacs. Grainger Item # 4M944 price (ea.) $178.25 Brand AMETEK LAMB Mfr. Model # 116859-00. This is a 3 stage 240vac unit pulling 115" H2O. I think this should be much higher vacuum than I am currently using but I will need to check with a vacuum gauge before springing for this system.
Any idea on whether this is more than I would get with a regenerative blower?

[Geof]

Rather than spending money on something that only gives you one third of an atmosphere of vacuum look into get a secondhand vacuum pump, or find a junk compressor and convert it into a vacuum pump:

http://www.cnczone.com/forums/showthread.php?p=691162

Shop vacs simply do not have enough suck to hold things down effectively. That one rated at 115 inches of water is quite good for a dust sucking vac but a full vacuum is equivalent to 384 inches of water. To hold things down you really need at least a vacuum equivalent somewhere between 260 and 333 inches of water.

And to put things in the proper terminology you need a vacuum pump that can create a vacuum of between 20 and 26 inches of mercury.

[newlife]

Thanks for the input Geof. Question, can a old air compressor move enough CFM to get a good holddown?
Newlife

[Geof]

Originally Posted by newlife .... can a old air compressor move enough CFM to get a good holddown? Newlife

The answer to this is three more questions:

1, How big is the compressor?

2, What surface area are you holding down?

3, How much leakage do you have?

Answering 1, and 2, is easy, but 3, is almost impossible to answer.

If you have a nice flat surface, good rubber seals, non-porous material and no leaks in the vacuum lines you will probably be able to pull a vacuum of 24 tp 26 inches of mercury with a very small pump capable of only pumping 1 or 2 cubic feet a minute.

Nearly always your leakage is going to be more when the vaccum is low, i.e. when you have just turned the system on, but as the parts snug down against the seals the leakage diminishes. To overcome this initial leakage you may need an enormous pump that can get enough vacuum despite the leakage to start pulling the part down against the seals. This is partly why you see commercial machines with vacuum pumps capable of moving 40 or more cubic feet a minute driven by a 50 hp motor.

I don't think you are in that league so you more or less have to work with what you can get and one advantage of going the old compressor route is that you will probably have a tank that can be used as a vacuum tank. I know some people suggest that compressor tanks are not suitable for vacuum but so far my conversion has worked okay.

The advantage of a tank is that you can pump this down as faras possible with your vacuum pump and then open the valve, a big valve and big lines, to the vacuum table. This gives a strong surge which can overcome the initial leakage and snap the part down on the seals so the pump can continue to handle the leakage from there.