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Discussion Starter · #1 ·
I'm going to build MDF boxes for my recessed lights and any electrical boxes that penetrate my HT room. I believe I can cut long pieces of MDF with my circular saw, then cut the long pieces to the proper length with my miter saw (can cut up to 10 inches wide, if I remove the guide, or 8 inches with the guide in place).


How do I hold up the MDF while cutting with the circular saw? I have two saw horses, but would that be enough to guarantee a straight line? Unfortunately, I don't have a bench or table large enough to hold 8x4 sheets of MDF.


Thanks for any responses.
 

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Well I'll be the old granny!


1) Wear a mask, here in Southern California Home Depot refuses to cut MDF as it's listed as a carcinegion. Lowes will cut it so go figure?


2) Be careful about covering light cans. Most have restrictions on that due to heat buildup. They do make fixtures that can be covered with insulation but the base modles must be able to breeth. And even at that MDF is not the same as insulation when it comes to fire rating.


3) Check your local code on covering electrical boxes with MDF as well. Again this could be a fire concern. They do make an approved putty for sound isolation around electrical boxes.


As for cutting strips with a circular saw, how about a rip guide attachment?
 

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I have cut far more mdf without a mask than I should have. My practice was to not breathe while cutting the board and then I would run out of the shop to look for clean air. That gives you about 1.5 minutes for a cut. Pretty dumb when think about it. I also always ran lots of fans in the garage to push the dust out instead of letting it just stay in the air. Man, that's even dumber!


Honestly. Get four 2x4 that you don't care about and place them on the floor so that they support the mdf. Buy an 8' straight edge and clamp it to the mdf - BE SURE that you adjust the straight edge so that the blade cuts the mdf on the correct side.


You can get very reasonable cuts using the straight edge approach. Not perfect but, pretty good for an 8 foot cut.
 

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A way to cut any 4 x 8 board is to use 2 inch foam, the pink stuff found in home depot that is also 4 x 8. Place it on the floor and put your mdf on top of it. Set your circular saw about a 1/4 inch or so deeper than the the mdf and cut. As long as you dont cut deeper than the foam you should not have any problem. Hope this helps you out.
 

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I use scrap 2x4s to elevate 4x8s off the floor. Just make sure you have them set so that you support the panel such that it won't pinch the blade after you get the panel mostly cut through.


-Suntan
 

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Maybe we are all assuming you know but be sure to use a straight edge to guide the saw. Unless you invest in a panel cutting track system you can use anything that is straight and just clamp it to the sheets.
 

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Or make your own straight edge if you are going to have to do lots of cutting. With your own guide you just line up the edge with where you want to cut. You don't have to adjust it to the saw each time as you need to do with store bought guide bar. So I made two guides - one for 4' width cuts and the other for 8' lengths.






If I ever had to build another set of guides, I'd make it it so that i had more clearance for where the clamps attach. Right now the saw doesn't clear the clamp and I have to remove and reattach the clamp when I get to that part of the cut.


My guide to building one of these things in in my theater build thread someplace if you want step by step instructions.
 

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Someone mentioned it, but I'll reiterate: if you have just a handful of long cuts, ask the one of the guys at Home Depot to cut them for you on their rig. It will save a lot of time and be guaranteed to be strait.

I've done this before and they don't care if it is not too busy.
 

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Discussion Starter · #10 ·
Thanks for all of the responses. I previously purchased a generic guide for my saw, but the guide did not fit the saw. I was therefore going to make the guides in a similar manner to what Cathan did (thanks for that, and I'll check out the links). Unfortunately, with the number of boxes of different sizes I have to make, I don't think I could map out all of the cuts to have Home Depot/Lowes make the cuts.


Those are great ideas about how to support the sheets of MDF. Now, if I could only find 2x4s that don't warp! ;-)
 

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Discussion Starter · #11 ·

Quote:
Originally Posted by Glimmie /forum/post/16931312


Well I'll be the old granny!


1) Wear a mask, here in Southern California Home Depot refuses to cut MDF as it's listed as a carcinegion. Lowes will cut it so go figure?


2) Be careful about covering light cans. Most have restrictions on that due to heat buildup. They do make fixtures that can be covered with insulation but the base modles must be able to breeth. And even at that MDF is not the same as insulation when it comes to fire rating.


3) Check your local code on covering electrical boxes with MDF as well. Again this could be a fire concern. They do make an approved putty for sound isolation around electrical boxes.

I purchased insulation contact, airtight recessed lights. I also have a variety of putty, from fire-type to sound insulating type (I use this stuff all the time, even for holes make when perhaps the holes don't need to be filled with putty -- in my house, none of the holes not made by me are puttied).


I have several copies of the National Electrical Code, but I don't believe these types of issues (i.e., surrounding a recessed light or electrical box with MDF) are discussed there. I'll check, though. If these issues aren't discussed in the NEC, where would they be discussed?
 
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