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Discussion Starter · #1 ·
Hello,

This is my first post so I apologize in advance for my ignorance. I am a timber framer and am going to be enclosing a frame with SIPs, which are Structural Insulated Panels consisting of a sheet of 7/16" OSB, 5 1/2" of EPS Foam and another sheet of 7/16" OSB.

You could call a SIP a "foam sandwich in between 2 sheets of OSB." Typically, the SIP manufacturer cuts the window rough openings into the panels at the factory. The problem is that sometimes they don't get the cuts in the correct location. As a result, I have learned that some folks "field cut" or "site cut" their window openings. Furthermore, I have heard that some pros (framers) actually use their handheld router to cut window openings in the sheathing. One thing about my project is that I only have 2 sizes of windows so I am entertaining the possibility of constructing a template to make the cut using a router. Obviously, I would have to make sure the template is on the same location on the opposite side of the panel but I'm trying to figure out what the sequencing would be using a high quality handheld router with an HSS bit. Would I need a plungeable bit? How much HP would I need on the unit? Should I purchase an acrylic base? How would I approach making a template?

Again, sorry for all the newbie questions. Sadly, I have a rendering but I can't post it because I haven't hit 10 posts yet. Perhaps this thread will have enough action so that I can hit the 10 posts but until then, my question is essentially what is a best practice for cutting a square in a sheet of 7/16" OSB when the sheet is mounted vertically?

The beauty of doing the window RO's once the panels are up is that there is no risk of putting the window behind a knee brace and the position can be fine tuned for the inhabitants of the room and the views afforded by the site. For what it's worth, I do have a "hot knife" tool to cut the OSB and the EPS foam will actually keep the OSB from splintering (I hope). Other folks I know have cut SIPs with a 14" Skil Bar Chain attachment and another fellow suggested a jigsaw against a fence. I turned to this forum because I do think the router (and template) would be the most accurate tool to accomplish this task.

Sorry for the long post and thanks in advance for any recommendations.
 

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John
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Hello and welcome to the router forum.
Any number of companies make aggressive solid carbide bits with a solid pilot. A 2 1/2 H.P. Plunge router with 1/2" shank bits should work. You can plunge it into a window opening and have a perfect cutout in a few seconds.
Cut the OSB with router and electric knife for the foam
You can post from your hard drive till you have 10 posts!
 

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Discussion Starter · #4 ·
Thanks Semipro! I was looking at a couple Porter Cables at the store. I assume that any template I make will be best constructed so that I cut away material on the INSIDE of the template rather than following a path along the OUTSIDE of the template, yes?

Thanks again. This is really helpful info.
 

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Hi JB and welcome. Typically that job is done with a panel bit which has a sharp point on it for plunging. It is quite commonly used in the RV business to cut out openings, going through the metal skin and the sheathing at the same time. The easiest template is to screw some boards to the SIP and follow around the inside with the router. You'd need to calculate the offset just as you would if you were using a skill saw to do it. One way to ensure the inside and outside are at least close is to drill through both sides at all 4 corners. If you are installing a window I'm assuming you still need a frame to set it into so you can do the minor leveling needed at that stage.
 

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Hello,

1... Obviously, I would have to make sure the template is on the same location on the opposite side of the panel
2... but I'm trying to figure out what the sequencing would be using a high quality handheld router with an
3... HSS bit.
4... Would I need a plungeable bit?
5... How much HP would I need on the unit?
6... Should I purchase an acrylic base?
7... How would I approach making a template?
8... what is a best practice for cutting a square in a sheet of 7/16" OSB when the sheet is mounted vertically?
9... and the EPS foam will actually keep the OSB from splintering (I hope).
10. Other folks I know have cut SIPs with a 14" Skil Bar Chain attachment..
11. another fellow suggested a jigsaw against a fence.
12. the router (and template) would be the most accurate tool to accomplish this task.

Sorry for the long post and thanks in advance for any recommendations.
Welcome to the forums N/A...

John and Chuck are right on target... the men w/ the plan...
thought maybe you could use and illustration of the bit...
and more take on this mission...

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1... skip the template.. use a mountable straight guide.. (screwed on 1by or an OSB rip)...
2... why bother w/ a router anyways??? use a 4~6'' circular saw instead...

once the EPS gets inside the motor it's toast not to mention what the melted EPS is gonna do.....
small CS's are light, way better/easier/faster/cheaper/cleaner in free style and a saw blade (demo type) will cut beau coup RO's in at least a tenth of the time compared to the few you'll get from a router bit.. remember, OSB is tough on tooling...

3.... carbide..
4.... yes...
5.... 2+..
6.... no.. acrylic is fragile..
7.... skip the template.. huge waste of material and logistics...
8.... Circular saw and electric carving or hot knife...
9.... nothing will keep OSB from splintering..
10.. that's the speed freak - balls to wall - dam the torpedoes method.. and did you notice nobody ever mentions the bar oil showing up at the most inopportune times later...
11.. A Bosch jigsaw in orbit mode using a Bosch T744D3 progressor blade would be some fast clean accurate cutting... and you'd only need to follow a chalk line here too and w/ a little practice it'll be just like downtown..
https://www.boschtools.com/us/en/boschtools-ocs/t-shank-jig-saw-blades-for-wood-t744d3-35145-p/
12.. not necessarily...
one template per different sized RO that's gonna need man handling... forget that...
don't loose track of the fact that you are in rough mode.. trying now for finish or high level accurate from the git go burns the clock, slows the project, adds expense and can be very wasteful... learning a certain amount of trade off is a must..

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chalk line your RO...
verify...
verify...
verify...
through drill your corners w/ a bell hanger bit... 3/8" X 12" BELL HANGER BIT FOR WOOD | Allied Bolt Products LLC
CS cut your OSB..
cut your EPS w/ a drywall saw or w/ the jigsaw arrangement...

NOTE...
if you ever have to hog out a device pocket in the EPS cut the square/rectangle/round's perimeter w/ your fillet knife and then use a wood spade bit in your drill as a rotary chisel to hog out the pocket...
for cutting the OSB.. nothing beats a jigsaw and it will cut the EPS at the same time...
super fast and accurate w/ a little practice...
 

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When we moved here, the basement included simply stud walls. 3 or 4 of the rooms are sheet-rocked. For the remainder, I used 74- sheets of T-111 plywood.
My method was considerably more simplified: I used a hole saw to make one large hole at each opening, next; I used a bearing-guided template bit and from the exterior side - I followed the "template" (the framed opening). I've done this hundreds of times over the years - I've even used this method for building the cabinets in my office. It is super-fast and efficient, but there will be a lot of mess to clean-up!

Otis Guillebeau from Auburn, Georgia
 

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