Good idea bad implementation?

[knight_toolworks]

I wanted to put threaded inserts in my base sheet and then drill through the spoilboard so I could access them. That way it would be easy to change sheets and never have to put in threaded inserts again. Well since I don’t know what I am doing yet I did not really have a good set point for home. So after I cut the holes I goofed and got the y off and lost my home. here is the link to the file
http://www.knight-toolworks.com/pictures/hole drilling for fasteners.art
So really right now I can’t replace the bottom sheet so I may just get some brass or aluminum threaded inserts and use them on the spoilboard.
But when I replaced the spolboard and have a good home that is repeatable any downsides of making the base sheet with threaded inserts and drilling access holes through the spoilboard?
here is my file the toolpath generated it horrible all over the place.
also drilling holes in mdf using a 1/4" endmill can I do the full depth of .75? the hole is .31 so most of the material is milled in the first pass.

[myxpykalix]

I couldn't see your pic but if i understand you correctly here is how i did it. I take a 3/4 plywood as first layer, I countersunk my lag bolts thru it and screwed them to the cross supports. I cut my plenum in that plywood. Then i glued my mdf spoilboard to the plenum. You will be resurfacing your mdf and you will be accidentally cutting thru it (take my word for it) and you DO NOT want any metal screws or any type of metal fasteners in your spoilboard. Glue will be sufficient.

Before i was convinced to glue it down I went and bought a bunch of nylon toilet bowl cover bolts and drilled holes thru the spoilboard, countersunk them so even if a bit hit them it wouldn't ruin the bit.
What i discovered was, because i had it set up for a vacumn table the countersink holes allowed too much vacumn to escape rendering my vacumn almost useless.
If you are going to use a vacumn heres a tip. take a tube of silicone caulk and coat the edges of the mdf to seal them. You lose lots of vacumn there too.

You really don't need access holes. You eventually are going to resurface your table till you are about an 1/8" thick on the mdf left. I'm down to about 1/2" at this point. When you get that low resurface it then go get another piece of mdf and glue it on from there.
Are you setting it up for a vacumn table?

[knight_toolworks]

I don't plan on having a normal vaccum. so most of the holding will be fasteners. so I have threaded inserts in bottom boad access holes in the top (these are 5" on center. then I can fasten down through the spoilboard into the underboard. that way I have perdictable fasten spots but there is no metal in the spillboard.

[dray]

I use my spoil board as a pincushion. I use 18g brad nails to hold my material down. I hit one every once in a while and it clips them clean, no marks or abrasions on my bits (so far)

But I know if I was using screws it would definately break bit, ruin the collet and possibly my gantry. I usually cut pretty fast at around 550 inches per minute havent had any problems with slippage yet

[knight_toolworks]

but nails don't work in plastics.
what I was think is on the parts sheet I ahve I would overlay the whole pattern delete the holes I don't want drill them screw it down and I am good to co. that way holes are never in the parts area or in the toolpath.

[handh]

Danny, I would give one word of caution using nails, you don't want to create a spark in your dust collection system if at all possible. The spark can create a fire hazard or a explosion, wood dust is very explosive. Odds are nothing will usually happen but it only takes one time. Just one more thing to think about, like we don't have enough to do.