• Cutting Circles - Plywood - Router?
    5 replies, posted
I need some help with some plywood.The Plywood i am using is 12mm thick I want to cut a Circle for a drive unit to be mounted in I need the main circle to have a diameter of 170 mm or 6 5/8 inches, adn the be 5 mm deep then i need a lip 9mm wide lip around the edge, so it has an internal diameter of 152mm, what is 7mm deep a poorly drawn diagram: [IMG]http://i264.photobucket.com/albums/ii191/Warlord_1011/HiFi/Speakercutout1.jpg[/IMG] does anyone have any ideas? I have a router, with a series of tips, but i as i don't have any paper work for them i don't know how to identify them, nor what sort of finish they give, as i want a vertical edge. due to the fact it is plywood i am not that keen on using a coping saw as all my blades shred it to hell and it leaves a nasty finish. [editline]8th March 2011[/editline] Or would it be easier for me to cut a 170mm hole in a piece only 5mm deep, then mount that on a thicker board what has a hole with a 158mm diameter?
Somebody with more experience might prove me wrong, but from what I understand a jigsaw is the tool you're looking to use for a hole of this size. It might give you a bit of a rough edge, but you should be able to smooth it out with sandpaper or attach an edge liner.
I had thought of that, but if i started the hole, then spiraled outwards?, or perhaps if i tried using the jigsaw and then tidying up the edges with a rabbet bit for the router?
Since you're working with small thicknesses, it would seem to be most wise to draw a circle for the inner on a sheet, remove it roughly with the jigsaw and then sand it to the circle, glue to the background plate and do the same for the outer side. Considering that the piece is a bit small, it would be most wise to do it that way. You'll have more control with a jigsaw (which you can easily use upside down so you can see even clearer) than with a router, as those are usually heavier.
The best way that comes to my mind for your design would be to use a dremel, cutting out using a guide-shape (a ring a specific diameter larger than your intended shape that you can simply push the tool guide against while it goes around to ensure a smooth circle made from a substance that's easier to cut, eg. foamcore) for the inner circle, then as to the lip, that would require a depth gauge, effectively turning the dremel in to a mini router -a regular size router is far too big for this sort of work and too large a bit will gnarl up plywood like nobody's business A point to consider is that plywood is not manufactured to be suitable for partial cuts, as the structure of the layup will give a possibility of pieces of the wood in between the layers of ply breaking up as you dremel/rout your way through. If the depth of the lip is not an extremely important consideration, a much much easier and likely stronger solution would be to cut your 170mm dia. hole out of your main bit of wood, then attach another piece aligned beneath it with a 158mm hole; no need for edge finishing beyond sanding it, and if you use a good join between the pieces of wood then much stronger too
Prob answered, and sorry for bumping, but drill a 3in diameter whole or so and then put the jigsaw blade inside the whole and begin cutting, thats the easiest way to do it :D
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