Parts tray idea

[waynec]

I'm getting ready to cut lots of parts for adirondack chairs, and I have this idea..

Right now, I simply brad 4 1x12 pine board directly to the spoilboard and cut. I pry up the parts, reload, and repeat.

I'm thinking that if I make a moveable spoilboard topper,attach the pine boards to THAT, I can cut the parts and then slide the 'parts tray' off the table with all the cut out parts. Then I can load a second tray, and let the CNC cut parts while I unload the first tray OFF the table.

Has anyone tried this? What do I need to consider as I build the trays. I was thinking to use skate wheels that drop into slots, and then a couple screws to hold the tray onto the spoilboard.

Anyway, any comment would be appreciated before I go investing time and money.

Wayne from White Salmon

[Brady Watson]

Wayne,
Why not use vacuum to hold the parts? A regular old shopvac does more than you think!

-Brady

[andyb]

Wayne,
You must have been reading the January 2006 edition of CabinetMaker. You described in detail what the "Nothing but nesting" article is talking about.

In the article he is using a Thermwood CNC. If you look at the first picture in the article I think he is screwing his material to a spoilboard and then using a rather large vacuum to holddown the spoilboard and the material. The CNC he is using ain't cheap.

Andy B.

[richards]

Wayne,

What you're describing is the 'pallet' system. If you're making many copies of the same part, you can use a vacuum, as Brady suggested. In that case it would be practical to cut a vacuum mask and use Al*star tape (or tape from your favorite vendor). If you're cutting parts that don't allow a standard vacuum mask to be used, you can fasten the material to a 1/2-inch sheet of MDF, slide that pallet sheet onto the table and then use a modest vacuum to hold the pallet sheet in place. When the parts have been cut, slide the pallet sheet off the machine, and slide another pallet sheet on. In that way, the machine is almost always cutting.

[waynec]

Brady
Thanks for the suggestion. It sure would be easier to use a vac, and mine is plumbed for it already. Will that work with long narrow parts like chair back slats? (these are say 36"L x 2-3.5"wide.

Are you suggesting I use a mask and gasket material? That would work well, and I wouldn't have to herc the pallets around, or brad my parts up. Even if I have to take a second to push the parts off the table, it would take no more time than moving pallets on and off. Hmmmm...

I'm cutting 12" pine- its never very flat. Can you recommend a gasket material. I suppose I cut a trench to stuff the gasket into by offsetting a toolpath to the inside of the part, neh?

I'm gonna give it a try this way. Time to learn.

Wayne from White Salmon


Thanks all for the quick responses- this place is SO GREAT!

[Brady Watson]

Wayne,
Depending on just how much cup there is to the part, I would suggest using 1/8" gasketing for 4/4 material. I've had good luck with this combo using the shopvac.

The other alternative is to use carpet tape, although you may have issues with removing reside (easy to remove, but an extra step in the process) and it is an additional cost.

I would proceed with tagging them in with brads & set aside some R&D time to test out the vacuum setup...I think that you will find that it is just the ticket for that size part.

-Brady

[richards]

Everytime I think I have a good understanding of vacuum, I ruin a sheet of material. However, the basic principles are easy to learn. Vacuum works because removing air pressure from underneath a piece of wood allows the atmospheric pressure to hold the wood down. At sea level, you have about fourteen pounds of pressure per square inch. So, if you're trying to cut a piece of wood 36x2 inches, you'll have 72 square inches for surface area or about 1,000 pounds of pressure holding the lumber down - if you have a perfect vacuum pulling about 30-inches of mercury. To get that kind of vacuum you'd probably need something like a GAST vacuum pump, air-tight plenum, good gasketing material and lumber that doesn't leak air. (I've used just such a system to cut hundreds of pockets in 1/2-inch thick cedar fencing and it worked perfectly.) Using a shopvac or Fein will give you a lot less vacuum - probably in the range of around 3-4 pounds of pressure per square inch, perhaps less. Unfortunately, I've misplaced my inches of water/inches of mercury/lbs of vacuum chart that I had when I first started playing with vacuum, but I believe that the 100 inches of water rating of the Fein vacuum is roughly equal to 7 inches of mercury which is roughly equal to 3.5 pounds per square inch. So, your 36x2 inch pieces of lumber would have about 250 pounds of atmospheric pressure holding it down with a good shopvac type vacuum, again assuming that there is no leakage.

As far as gasket material goes, I've stopped using the weather stripping stuff from the local Home Depot in favor of gasketing sold by Al*Star adhesives. It works for me. One of their products is for one-jig use, meaning that once it's taped to the vacuum board/jig, it can't be removed and reused. That's the product that I normally use. They have another product that is meant to be placed into a properly sized groove. I bought some of that, too. It works great, but requires the extra step of grooving your vacuum jig.

One word of caution: once you start using vacuum, you'll be both spoiled and frustrated. What works well with multi-pass cuts may not work with one-pass cuts (as I've learned when trying to cut cabinet panels in one-pass using my Fein vacuum to hold the material in place). Small parts might not have enough surface area to work with anything except the lightest of cuts - and even then they might require tabs to keep the pieces from jumping off the table. Your original idea of using a pallet might still be the best compromise between making a lot of vacuum jigs and getting a lot of production out the door. It all depends on your skill at designing a good vacuum system and the mood of the vacuum gremlins on any particular day.

(Brady, you're a faster typist than I am. Your post beat mine by a few minutes.)

[mikejohn]

Wayne
If you are doing lots of these, think palleting.
It quick, easy, and avoids the dangers of vacuum 'gremlins' and leaks from slightly warped wood.
If you look at the thread Gerald started elsewhere, this even allows a "Van" to operate the Shopbot.
Not sure what you mean by 1 x 12 but I pallet from either end of the table (it could be done side by side also) and the ShopBot can work without stopping for anything, all day long.
And there's no vacuum noise, lower power bills.


............Mike

[waynec]

A question or two about gasketing and templates.
1) Do I use a sheet gasket material, and then cut thru the gasket to allow vacuum to reach the areas I need to hold down? Or do I use a gasket 'cord' that I stuff into a groove in the spoilboard? The sheet idea makes sense to me.
2) Got any good sources for gasket material?
3) Is there a vacuum alternative to the shopvac, but less expensive and less noisy than the Gast monster? For most parts the 250 lbs pressure would be adequate- I nearly always cut in three passes. But I'm wanting to know what sort of upgrade options I have that can increase the hold power without significantly increasing the noise level.

Thanks for the help.
Wayne

[Brady Watson]

Wayne,
1. Yes...although it is easiest to drill holes thru to the vac source because the gasketing doesn't always cut cleanly...and can jamb debris underneath the edge of the gasketing where you did the cut. Rarely do I cut the stuff out anymore...I just drill lots of holes that sit inside the extents of the part to be cut minus @ .015 to play it safe.

2. Yes. AllStar Adhesives

3. If you use gasketing, you can do extremely well with a Fein vac. It will pull about 7" Hg. This is about 2X what your Shopvac pulls. I use a Fein Turbo III for NOTHING other than holding down carbon fiber laminate while cutting. It works extremely well, and the smallest part size to date using this setup is @ 5/8" X 3/4". It's pretty remarkable how well it works...and one of the quietest shopvacs in the world.

My 'skunkwerks' department is currently working on a vacuum hold-down powerplant that will do 16" Hg & 200 CFM and a smaller version that will do 10" Hg & 100 CFM. I am tossing around the idea of offering a kit & plans...there are hard parts needed to make it work that you can't buy off the shelf...It would still be cheaper than anything else on the market by a factor of at least 5X. Again...just an R&D project under development at the moment, which could benefit all of us down the line.

On a side note, it is important to think about the types of materials and size of materials that you are going to cut while using vacuum. A 15hp Cascade would be appropriate for someone cutting out full 4x8 sheets all day, but totally overkill for someone cutting smaller parts unless that vacuum was used efficiently with gasketing and limited vac zones. The other question one has to ask when thinking of using vacuum is, 'How many?' If this is a one off, just use carpet tape. If this is a production item, then it definately pays to earn your wings in vacuum R&D finding out what it takes to hold YOUR parts down. This means designing your vac jig, testing chipload and seeing if vac can hold at 50% material depth, 100% depth etc. You can do full depth passes in many situations...but the time to test it is before you put your expensive stock on the jig! There are others using high Hg (like Gast pumps @ 26"+ HG & 6 CFM) who expect them to hold down entire sheets...boy are they in for a suprise. BUT that setup is ideal for non-porous applications such as plastics and some hardwoods where you don't break thru the back side of the material. So far, the Fein vac is very hard to beat for a general purpose all around vacuum source. I have a Gast too...and the Fein is better suited to the types of materials that I work in. The relatively high CFM is perfect for maintaining good vacuum even if your cutter breaks the seal in many cases. If I could advise you on what to purchase, I would tell you to get a Fein Turbo III until you outgrow it...which may be never.

Sorry for the book..

-Brady