Routing out a circle with a jig - Need advice please!

I used one of my plunge routers with a modified circle guide to cut out my 15" sub-woofer mounting holes in 1" thick MDF. That makes a LOT of fine dust, even with a 1/4" cutting bit. I could have gotten away with using a jig saw and circle guide but then I couldn't post it up here lol. Did it in 4 passes/hole.

For multiple, smaller holes (2-5/8" for the new instrument panel on my project car) I bought a Milwaukee hole saw exactly the right size for $12.

Here are some pics (not exactly tutorial style, I think I was afraid to pull the phone out during the dust storm, even though it was outside lol) hope this helps a bit. Need to remember the difference between the center distance from the guide pin to the router bit is NOT going to be the hole size.....need to add the outer radius of the cutting bit.....

Best bet is to secure the piece you're cutting on a solid surface, maybe with some styrofoam underneath the way the track saw guys do it. That may also reduce the dust since it cannot fall below the work area now and be more likely sucked up by the vac above the table.

Yeah, same question, are you cutting out a circle that you're going to use, or just cutting an opening such as the speaker boxes? If you're cutting a circular piece, you can use a circle cutting jig. You normally would drill a small hole and insert a peg that holds on to the jig. A plunge rounter then makes multiple passes. Since it's a low power router, you will make many light passes and do it without pushing the bit too hard forward.

If you're making some sort of table top, you put the good side down and drill the hole only part way through. Put a tab of tape on the drill bit so you don't penetrate or cause a bump in the middle of the circle's good side.

You do have to work out how to attach the router to the jig. Usually done by taking off the base plate and using it to mark the location of the mounting bolts. Use a punch to mark the center of each mounting hole, it will give you a dimple that will help you drill accurately.

You can use the same small mounting bolds you removed from the base to attach to the jig. If you're using pan head bolts, you can drill slightly oversized holes, then a larger hole part way through so you can position the router on the jig. Here's an over simplified drawing of what I'm saying.

For something like a table top where you're using glued up hardwood, you can use a spiral bit to cut the circle, then put in some sort of roundover or ogee bit to make a nice edge. If it's plywood, you just cut it and use iron on edging.

Once you get started, just take your time. It is really a pretty easy thing to do, just don't try to cut too deep on each pass, usually no deeper than 1/8th inch per pass. The Jig will do most of the work for you. When I do this, I suspend the power cord from something overhead so it stays out of the way. And make sure the center pin is firmly in place. My jig wants a 1/4 inch pin and I often just use an upside down drill bit. If the circle is made of 1/4 ply, I will drill about half an inch deep on the back side.

I am also a fan of using an inch thick piece of insulating foam underneath the workpiece, and clamp the corners down as best I can. You can also use some double sided tape to hold the circle in place. With a couple of strips of tape, if you manage to move it, you're pushing too fast.

Hope this is helpful. These days I cut circles with my band saw, different kind of jig required for that. It's even easier than cutting one with the router. But for cutting a clean circular hole, the router with a spiral bit is the way to go, the band saw won't do that.

Also attached is a picture of four sizes of down spiral router bits. You can use high speed steel for occasional use. Carbide bits are sharper and last longer, but far more susceptible to breaking and heat damage.

Thanks all - the quick responses are greatly appreciated!

I'm cutting the hole out of 3/4" ply so I can put a bucket inside the hole.

Here is the jig I just purchased

I have some sacrificial foam as well as some plywood I can clamp to my bench - that's what I was missing.

I've not used the router before, and have had it for quite awhile.

I tried doing this with a jig saw and home made jig, but the blade on the saw kept bending giving me a beveled cut. Needless to say it wasn't pretty, nor did it work

I'm hoping I can cut out the bevel part with the router and make a clean circle.

Once I have it done, I'll post the results.

Thanks again - your help is greatly appreciated.

newbie2wood said:

Thanks all - the quick responses are greatly appreciated!

I'm cutting the hole out of 3/4" ply so I can put a bucket inside the hole.

Here is the jig I just purchased

I have some sacrificial foam as well as some plywood I can clamp to my bench - that's what I was missing.

I've not used the router before, and have had it for quite awhile.

I tried doing this with a jig saw and home made jig, but the blade on the saw kept bending giving me a beveled cut. Needless to say it wasn't pretty, nor did it work

I'm hoping I can cut out the bevel part with the router and make a clean circle.

Once I have it done, I'll post the results.

Thanks again - your help is greatly appreciated.

Click to expand...

Hi Jessie,


The circle jig is probably the most common jig used for routers,


There are so many on the market and posted in the forum.




I have at least 4 different versions @harrysin has posted a couple you could make yourself, and the one I use the most...


Simples........( a reference to a TV ad in Oz)

make a a torsion grid for the cut table...
size to fit the need...
reusable..
easier clamping...
remember.. the waste center needs clamping/pinning too...

.

Here are pdf's showing how I made circle routing jigs. To hold the rods in the hardwood block on my old one I ground flats on the ends of the rods, drilled 1/4" holes in the top of the block and poured epoxy down the holes.

Jessie if you're going to be doing a bunch of these then I would cut a hole using the jig and router and use it for a template to do the rest. With the template you can use it to mark the holes, then cut out to about 1/8" inside the line with a jigsaw, then using the template and a pattern bit like this: https://www.amazon.ca/Freud-50-102-...=2025&creative=165953&creativeASIN=B0000225XQ or a flush trim bit like this: https://www.amazon.ca/Freud-42-204-...=2025&creative=165953&creativeASIN=B000BV9IPG you use the router to finish the hole to proper size.

The only differences between using a pattern bit or flush trim bit is which side you attach the template to. With a pattern bit the template goes on top of your work and with the flush trim the template goes underneath. The adavantage of using this method is that it will be much easier on router bits (=cheaper) and possibly faster as well, even though you are going through more steps.

UPDATE:

Thanks to the great responses, I was able to accomplish with limited success my first router project: Cut out a circle.

Here's the jig I purchased:


Here's the hole I cut and my lil' monster router:


Here's the hole in the project piece, I clamped the piece to the bench:


And here's the finished project why I needed the hole cut


Thanks for everyone's help, you guys are tops!

More projects to come now that I'm not so afraid of that lil' monster!

Same jig I modified, since it wouldn't cut the 15" dia hole; now the guide plate can be slid in from either end and there are additional pin holes to secure it. I believe any radius within it's length potential can now be cut.

A CnC aluminum pre drilled hole template is in my future; the pin and centre distances are incrementally 1/16 or 1/32 apart from 2" up to 18" IIRC. This allows actually cutting a hole and checking it for clearance/dimension without having to worry about centering the cutter perfectly. Pls see link below and the pics.

https://www.woodcraft.com/products/...004269702d6582000e8d,5b17dc60776f6f5d25002527

DesertRatTom said:

Also attached is a picture of four sizes of down spiral router bits. You can use high speed steel for occasional use. Carbide bits are sharper and last longer, but far more susceptible to breaking and heat damage.

Click to expand...

Just for the record, Tom, the photos you attached are UPcut spiral bits. Here's a photo of a downcut spiral. Note the flutes spiral up to the left rather than the right. The downcut bits leave clean cut edges on top of the board, while an upcut bit can tend to have some tearout along the cut edges.