cutting table idea

[twelchPTM]

I ran across this thread http://www.talkshopbot.com/forum/showthread.php?t=9185&highlight=vacuum+clamp while perusing the forum and had an idea that i thought I'd toss out there before I tried it....
For one of the exhibits at our museum I wanted to create a wooden surface that would hold pieces that the kids put in place and came up with an interesting solution where I layered 1/8" wood ans a sheet of steel inside of it then used neodium magnets on the pieces. This created a sheet of magnetic plywood. (the funny part is when i tell people its a rare breed of pine grown in volcanic ash rich in iron ferrite) but anyhow suppose my table was a 3/4 ply base, then the 3/4 mdf vacuum plenum, followed by a sheet of 1/16" perferated steel and then the spoilboard. my theory is I could then use mag-clamps anywhere on the table when the vacuum won't work.
Any thoughts?

[myxpykalix]

My gut feeling is that the magnets wouldn't be strong enough to hold.

However there is this device for your tablesaw (sorry i can't remember the name) but it is basically a big strong magnet that holds your material in place to guide it thru blade. Something like that might be too big and bulky:confused:

[adrianm]

Neodium magnets are incredibly strong compared to normal magnets though. I use them a lot in the workshop (but not on the CNC) and ones an inch in diameter and 1/4" thick need a enormous amount of leverage to get off a steel surface.

Not sure how much the spoilboard would reduce that though. Interesting idea but I wouldn't fancy getting the z height wrong!

[jerry_stanek]

It's not the force to pull it up it is the side force on them do they slide easily.

[twelchPTM]

I was looking at Mag-Jig they are a pretty compact design and come with 90 or 150 lb rating, since they are designed to hold thing like fences and featherboards in place I imagine they wouldn't slide to easily. As far as the z-hieght magin of error is concerned that is why I want to bury the steel under the spoilboard, with the exhibit I mentioned before we hace small magnets about the size of a quarter and the hold .5"x3"x16" pieces of wood with 1/4" ply between the magnet and the steel. I don't imagine I would be able to use 3/4" for the spoilboard but 1/2" might work. I think I will mock up a small one and if it works(and I get it done in time) present the design at the upcoming Camp Shopbot here in Philly....

[jerry_stanek]

Yes but they are attached to a metal top not on top of a spoilboard.

[steve_g]

http://www.kjmagnetics.com/largergraph.asp?CI=1&pName=DC2-N52 (http://www.kjmagnetics.com/largergraph.asp?CI=1&pName=DC2-N52)
Here's a chart showing how the magnetic pull force declines with distance... In this case, a 3/4" X 1/8" magnet in contact with a steel plate has a pull force of 12lbs... when separated by about 1/8" the force is down to about 3 lbs of pulling force... that's not even considering a perforated steel plate.

SG

[twelchPTM]

Steve - Thanks for the chart, based on the information I got from that website this particular set-up will definatley not work with a 3/4" spoilboard but 1/2" still has a slight chance.

I'll admit that it sounds sketchy but I have read nothing but good reviews on these mag-jig components.

I appreciate the feedback from everybody, I have a few possible variations in mind and since the general concesus is doubtful and not impossible I think buying one magswitch for testing is a risk i'm willing to take

[twelchPTM]

Well my Magswitch150 came today and it I quickly grabbed my perferated steel and some ULMDF to test my theory and it didn't work. It held down well enough thru the 1/4 material but still slid around.
I'm a little disappointed but I didn't have my hopes to high and the magswitch seems like it will be a useful item to have around the shop.