What to buy

[T. McCaw (Unregistered Guest)]

Thanks guys keep it coming. Vacuume stong enough to suck z axis.spindle with hyper drive.
Question... If holding down small parts is an issue would it be better to have a smaller table then lets say a 4 x 8.

Tom

[richards]

Tom

Get the biggest table that you need and use a zone system to more easily regulate the vacuum to smaller portions of the table (shopbot supplies a 4-zone file with their software).

If I understand vacuum properly, it's the pressure of the atmosphere that creates the hold-down (somewhere around 12-14 lbs per square inch). The vacuum pump simply removes air (suction) to let the atmosphere press down on the part. A big vacuum pump will keep that suction even though some air is slipping around the part (hence the listing of CFM in the vacuum's specifications). A very small pump, 1/2 or 3/4 hp, can hold just as well as a very large pump if you use a vacuum mask and the proper gasketing to prevent air from slipping around the part. Since it is the atmosphere that is holding the part down, if you use a small pump or a large pump to generate the 25+ inches of mercury, the hold-down pressure is the same. Of course a large pump will suck the part down quicker and allow you to cut without resorting to a vacuum mask, in many cases.

If I had my choice, I would use a big vacuum and forget about a vacuum mask, but I work with what I have and hope to buy what I want as time goes by.

Now, back to the table size issue. Most of my work could probably be cut on a 24x48 inch table, but that means that I would have to cut all panels to rough size before sliding the material onto the table. My Alpha is the 120-60 model so that I can easily cut 48x96 material as well as 60x60 baltic birch ply. The extra 24 inches on the x-axis has proven to be real handy as a 'landing zone' for the y-carriage. By using the 'landing zone', I have full access to the entire table top when I change sheets of material.

[T.McCaw (Unregistered Guest)]

Thanks Mike. A vacuum mask would not work here. Runs are small and always different. We too could probably route everything on a 4 x4. At the moment we have a 12' panel saw ... cut lage sheets down...even recut on tablesaw. route by table mounted routers and jigs. We get some of our jigs cut by laser up the road and some parts if need be.

Tom

[ron brown]

The thought of vacuum and vacuum leaks needs to be addressed. If one had "Super-Scuker 2010" vacuum pump, comming into existance about the time a practical tele-transporter comes in effect, the same hold-down problems will exist. The "air slipping around the part" will cause the parts not to be held down properly. Small parts will loose at least 1/2 the thickness of the spoilboard around the perimeter area when they are cut through. It could be less if thin bits were being used.

A true "pin-hole" causes a 28" 4 CFM vacuum pump to go to about 15" of vacuum. This was measured at the pump. In the areas around the pinhole the vacuum was noticably less than that.

I commend Mike on chosing the larger table. On my first ShopBot controlled machines, I had a 4' wide "Y". I cursed it every time I had to cut a sheet of 5' X 5' plywood to fit the machine. I had a 62" Y axis on my last one. I'll build the next one out to at least 64". If I have room, I'll have 16' or more of "X". I'd like to use 24' material for the table and have a 22+' X.

But, if money were no object... and I didn't have to make a living, life would be a bit different.

Ron

[superior]

I once heard the search for a good vacuum system was like the search for the "Holy Grail", and as time slips by, that holds forth more and more.
I have two pals that own/use multicam equipment, one a 4'x10', the other a 5' x 10', both costing well over $65,000. Now the the gist of this post: I have seen/used both systems several times. Both systems have the approved/furnished HUGE vac systems. Both run on 240 volt hookup, etc. Just for funnies, I have cut 4" x 4" pices of plex, aluminum and masonite. These were placed on the table (MDF) and the vac turned on. None of the pieces moved so much as a hair...I cut numbers, letters, and geometric shapes onto and THROUGH them. Again, no movement what so ever. Multicam lists their vac systems at about $5500.00, as I recall. After the trials and tribulations of trying to cut some small stuff for Christmas ornaments, I think that is a bargain.
I am no engineer, probably can't spell it correctly. I just wanted to pass this along to all my bot' buddies for what it is worth. I currently use a five zone table, with both a Sears shop vac and a dust collection system. Still can't hold small stuff down.
I feel as though I am in about the same position as most other botters on this issue.
Looking forward to your feed-back.
Doug

[T.McCaw (Unregistered Guest)]

On a visit to a shop I worked in a long time ago they had purchased a cnc machine and I got to see in in action .They would mask the bottom of a sheet of styrofoam (they actual had a machine that would mask a 4 x 8 panel all in one shot.Kind of like a paint roller machine)on to the bed the styrofaom went. The router did not cut through the tape. The operator would slide the cut sheet out of the way, put another sheet on and then pick apart and bag up the words required for the deli section the produce section and so on. I bet you this machine paid for itself in no time. It was fast and quiet. What make no idea.

Tom