Router Circle Jig

[Owen Bartley]

Split from "Need new sub, thought i would build one!

Eric, how did you make your jig? Did you just measure to make the appropriate holes you needed for the cutout, recess, and port opening? I've been tempted to buy one of the nice jigs, but it seems like a lot of people have been getting good results with the homemade kind. Did yours work that well right off the bat, or did you have to make any adjustments?

[Funkmonkey]

Owen Bartley wrote:

Eric, how did you make your jig? Did you just measure to make the appropriate holes you needed for the cutout, recess, and port opening? I've been tempted to buy one of the nice jigs, but it seems like a lot of people have been getting good results with the homemade kind. Did yours work that well right off the bat, or did you have to make any adjustments?

I am not Eric but I can answer your question. I am a professional carpenter and use circle jigs at least once a week (literally) and make them about a dozen times each year. DO NOT waist your money on a pre made one. I mean you are using a router to make something why not make your jig, it is not hard to do.

All you need is some scrap sheet goods (I find that 1/4" or 3/8" works best). Rip a strip of your chosen material (MDF, plexi-glass, delron, luan, it really doesn't matter) to the same width of your existing router base plate. Chop it length wise to at least 6" longer than the radius of the largest circle you intend to cut. Remove the bottom plate from the router and set it on your strip all the way to one end. Use it to locate your holes for the mounting screws (if you use 1/4" material you can reuse the factory screws). You can add a nice touch here by rounding off the end of your strip using the base plate as a template (again). Drill the holes same as the base plate, and countersink them (be careful not to go too deep, the screw head should be just a hair past flush with the surface. If you are using anything thicker than 1/4" you may have to countersink deeper to be able to use the factory screws). Once you have your mounting holes set, put a mortising bit in the router and attach your new jig! ( I usually plunge the bit through to make the center hole for the bit to go through because it makes it easier for me to get an exact measurement, if you do not have a plunge router you can "improvise" with the same result or pre-drill the center hole bigger than your mortise bit and get your measurements directly from the bit itself.)

Now you are ready to cut cricles!

A couple of tips that I have learned the hard way:

-be mindful of which side of the cutting bit you measure from
(for an ID inside dimension, or OD outside dimension you need to measure from opposite sides of the cutter)
-Pre-drill your pivot hole as straight as you can and make sure it not too big, should be tight.
-A nail makes a better pivot than a screw
-if making a ring, cut the outside circle first, then cut the inside
(do it once the other way around and you will understand why, ... unless you are nailed down)
-if you can, nail down the whole sheet you are cutting (center and any rings you are cutting) I use a brad gun for this but double stick(carpet tape) works well if you don't want even the smallest nail hole.
-cut on top of a piece of scrap so that you can cut all the way through without damaging your table top

some of those may sound like common sense, but I have seen guys screw up $100's in materials by not paying attention to those few simple tips.

Good luck and happy building

[Owen Bartley]

Greg, that's awesome, thank you for the step-by-step, and the tips especially. I will definitely give this a try whenever I make my next sub. I wish I'd figured this out when I was making the grille for my rear surround, even though it will be covered by cloth, the ugly wiggly hole is still a little annoyance to me.

[Funkmonkey]

No problem.
One more thing to add when you are cutting only plunge the router bit in a little bit at a time, it may take 5 or 6 passes to get through 3/4" material but your cut will be cleaner and much more precise. Also, the bit will last a lot longer and your router will not strain to make the cut.

If you ever need to cut an ellipse (for a 6"x9" or something) I know of another jig for that, and it uses the same "arm" you use to cut circles, but that one is a bit more complex to learn (though easy when you know how to make it)

[Eric Mathews]

Funkmonkey wrote:

-be mindful of which side of the cutting bit you measure from
(for an ID inside dimension, or OD outside dimension you need to measure from opposite sides of the cutter)

..... ya i did that and had to re-cut my mounting piece for my sub. BTW thats how i made my jig, worked well and wasnt too hard. i also found that cutting one sided, then flipping it over to cut all the way through was not the best way. i found that if i did it that way i would leave a lip or the cuts would be kinda off centered, its hard to explain. so what i did on my last pieces was just cut as deep as it would, then move the bit lower until it cut all the way though. hope that helps!!! Good advice Mr Funkmoney

[eyekode]

Funkmonkey wrote:

I am not Eric but I can answer your question. I am a professional carpenter and use circle jigs at least once a week (literally) and make them about a dozen times each year. DO NOT waist your money on a pre made one. I mean you are using a router to make something why not make your jig, it is not hard to do.

I have a very similar process and it works great for larger circles. Smaller circles are more difficult. Especially problematic is if the radius is a little larger then the radius of your router base. In this case there is no place to put the nail! Any tips for when the nail has to be inside the router base?

[Funkmonkey]

eyekode wrote:

I have a very similar process and it works great for larger circles. Smaller circles are more difficult. Especially problematic is if the radius is a little larger then the radius of your router base. In this case there is no place to put the nail! Any tips for when the nail has to be inside the router base?

Of course... use a hole saw! and then a rabbeting bit if you are going for a flush mount.

Other possibilities would be to:

-use a small laminate trim router (smaller base)

-use a router table and spin the MDF around the pivot rather than the router
(you should affix a piece of scrap across the hole to keep you center when you get all the way through)

-last idea would be to drill the pivot hole in your circle jig and put a nail in your center (just like you do for big circles) but this time do it before you position the jig so the nail sticks up by itself, then clip the head off the nail and slide the jig over the top of the headless nail and you are ready to rock!


Cheers

[Bent]

drill a guide hole in your router base - its's easy.

[eyekode]

Bent wrote:

drill a guide hole in your router base - its's easy.

The problem comes in when the radius you need ends up right in the frame of the router base. Also I would not want to drill in my router base plate. I would be afraid the hole would subsequently scratch other work pieces.

But drilling a "blind" hole in the circle cutting jig, nailing a finish for your pivot and snipping off the head sounds like a pretty good idea. The other thing I have heard of is making a larger circle in a piece of scrap and using a template guide.

[Funkmonkey]

eyekode wrote:

The problem comes in when the radius you need ends up right in the frame of the router base. Also I would not want to drill in my router base plate. I would be afraid the hole would subsequently scratch other work pieces.

But drilling a "blind" hole in the circle cutting jig, nailing a finish for your pivot and snipping off the head sounds like a pretty good idea. The other thing I have heard of is making a larger circle in a piece of scrap and using a template guide.

You could drill right through the metal of the router base, and the base plate to allow a top nail, the hole won't affect anything if it is strategically placed. If you are worried about scratching other projects with the new hole, just buy a new plate, they are easy to find wherever you can get a router and don't cost that much, but it's really a non issue.

The problem with using a template guide is that those guide sets will require you to cut a circle that has a radius of 1/16" - 3/8" bigger than the one you want to end up with. So you are likely to still hit the base when cutting your template...

Another option would be to create a much larger "template" and let the base of the router itself ride the edge. That would give you an offset of two or three inches. Many routers are fairly centered on there base plate but I would recommend marking one spot along the edge of the plate and measure the distance to the cutter to determine the size of your template, and then use that same spot to track along the edge of the template to insure the hole comes out perfectly round.

But all that is much more work than just "blind nailing" your pivot.

On that note I wouldn't be using a small finish nail for the pivot. I usually use an 8d (about 1/8" thick) for that. Smaller nails bend too easily, though a 6d finish would probably be adequate. I certainly wouldn't go any smaller than that.

Happy routing,
Funk

[Bent]

I'd like to hear more about the elliptic jig.

[rodH]

Great thread guys.

I am getting ready to do a sub enclosure. I have a dewalt plunge router and am going to make a jig, seems easy enough.

I actually have a rotozip as well with an adjustable jig, but I am making it out of 1" industrial MDF and a couple test runs I did, the best way I found with the rotozip was to do it multiple depths, but even that gets slightly uneven (not a huge deal, but I am going to build another piece of decorative wood that is going to surround the 2 drivers, and need them to be PERFECT circles and the best/straightest finish possible. My buddy has a dewalt router I am barrowing for the project, it seems to feel more solid and should provide a better cut/hole.

My question is this, some people mention to use a straight or upspiral bit. Which one do you prefer? I am planning on buying one, so I can get either one. The upspiral is about $5 more, but that is no big deal if it works better.

Also, if I am going to cut into 1" MDF and 1" plywood, do I have to have a 1" bit, or do I buy something shorter and just keep dropping it lower with the plunge router? If I am JUST using the bit for this project is the 1/4" bit the way to go?

THANKS!!!

[Bent]

a spiral up-cut bit will help clear the material as it cuts.

[rodH]

Bent wrote:

a spiral up-cut bit will help clear the material as it cuts.

So this is the better way to go?

[solid7]

Funkmonkey wrote:

On that note I wouldn't be using a small finish nail for the pivot. I usually use an 8d (about 1/8" thick) for that. Smaller nails bend too easily, though a 6d finish would probably be adequate. I certainly wouldn't go any smaller than that.

I actually use a 1/4" hardened steel dowel, and make a pilot hole using a 1/4" drill bushing. (as you would use for drilling dowel holes in wood) This has been the most successful method, for me.

Bent wrote:

a spiral up-cut bit will help clear the material as it cuts.

Depends on what you are cutting. For something like MDF, that turns to dust as you cut it, there is no need for chip removal. 30,000 RPM creates enough turbulence to blow the dust right out. If it doesn't, the motor usually blows it out on the next pass. The real problem with spiral bits, is that they hang out too far for the relatively small diameter. They tend to flex more, and leave an angled cut surface, if you try to cut too much, or too fast. Alternately, they can grab some soft materials. If you don't have a nice tight collet in your router, and you hit "grabby" material, you can actually pull those spiral bits right out of the tool, and blow it clean through your workpiece. For me, they are OK for rotozip type tools, but I wouldn't want to use them in a higher horsepower hand tool, like a router, where you can do real damage. (ok to use in a milling machine where you are more likely to break the tool bit than yourself or the tool)

[bobgpsr]

I started out using a cheaper spiral down-cut bit but latter got and switched to a spiral up-cut bit. Was much happier with using it since it made it much easier to monitor the progress with less mess in the way. This was with cutting holes in 13 ply baltic birch plywood.

[solid7]

Stick with standard router bits for wood and MDF. Aside from what I've just mentioned, spiral cutters are high speed steel, where router bits are usually carbide. That means longer tool life for the router bits. Especially if you're cutting MDF - steel shouldn't even be considered, as MDF (or anything else that turns to dust when you cut it) is abrasive, and will eat steel cutters for lunch.

[solid7]

rodH wrote:

I actually have a rotozip as well with an adjustable jig, but I am making it out of 1" industrial MDF and a couple test runs I did, the best way I found with the rotozip was to do it multiple depths, but even that gets slightly uneven

When you machine anything - wood, metal, whatever - you generally make "roughing" passes, and then a very shallow "finish" pass, to take out mismatch from cutter deflection at successive depths of cut. Not a real big deal in wood - you generally can't see the mismatch below the mounting surface. However, if you want to deal with it, you can make a template, and put a couple layers of tape inside the template for your "roughing" pass, and then take it off for a "finish" pass, with the cutter engaging material at full depth - with carbide, of course

[rodH]

So I guess a standard Carbide bit is the way to go, thanks for the input guys!!

[solid7]

Please note: I just caught that you have a rotozip. My replies were relative to a router. I was suggesting that you not use roto bits in a router, and that you definitely use carbide in MDF.

Hope that helps.

[Funkmonkey]

solid7 wrote:

I actually use a 1/4" hardened steel dowel, and make a pilot hole using a 1/4" drill bushing. (as you would use for drilling dowel holes in wood) This has been the most successful method, for me.

That is the ideal, if you can't use a drill press to make the 90º pivot hole. But for most folks all of that is overkill.

One note I would like to make on router-bit selection would be to use one that has a 1/2" shank, the 1/4" shank bits bend easily when they get hot, and your hole could easily become larger than you intended because of the resultant bit wobble.

Great suggestion about doing a rough cut first. I like the tape idea on a template (wish I would have thought of that one ) If you really want to prolong your bit life you could use a jig-saw for the rough cut....

One more note: Roto-zip tools are great for drywall and 1/4" panels. That is what they were designed for. That tool has no business cutting anything that is 3/4" thick. As someone else stated you should always use a router with a solid base for that task. Using the proper tool for a job gives you a much, much cleaner finished product, it makes the job easier, and most importantly it is much safer. I have seen 1/4" spiral bit's and flat cut mortising router bits both crack off at high speed rotation. Luckily one of the spiral bits stayed lodged in the work, but another time the broken bit went flying across the room (the guy was trying to cut 1/2" plywood with it), and the 1/4" shank flat cutter rattled around behind the plastic shield that was on the router. It was lucky that no body got hurt in any of those incidences.

Be careful, and don't cheap-out when considering your tools, it is a dangerous thing to do.

[rodH]

solid7 wrote:

Please note: I just caught that you have a rotozip. My replies were relative to a router. I was suggesting that you not use roto bits in a router, and that you definitely use carbide in MDF.

Hope that helps.

Thanks for the tip.

Ya, I have a rotozip, BUT my buddy let me burrow his DeWalt router, so I am going to go that route. IT just feels so much more solid, in my trial runs you can tell that the tool is doing ALL the work, it just has so much power and RPM. The rotozip bit did bend a tiny bit in my test run. If it is all I had, I would use it, doing many different depths and just plan on using a couple/few bits, but I like the router idea better.

[Funkmonkey]

Bent wrote:

I'd like to hear more about the elliptic jig.

I love this jig!

use the same swing arm, but drill two holes this time.
1st hole = 1/2 minor axis
2nd hole = 1/2 major axis

-put a pin in each hole (I will often use two 1/4" drill bits upside down so that the shaft side is sticking out of the bottom of the swing arm, and they fit the hole perfectly [if you have a comprehensive drill index you should drill the holes an RCH (very thin hair) smaller than the pin to ensure a tight fit)

-make two grooves in a separate piece of ply wood, in the shape of a plus sign (+) (use a table saw and either a dado blade or multiple passes) These grooves will serve as tracks for the two pins to travel along. Track width should allow the pin to slide along it without getting stuck but not be sloppy, and it should be deep enough so that the pin won't jump out very easily.

-stick one pin in each track and slide it around. Each pin should always stay in its own track. You have to be careful not to jump tracks at all four points along the major and minor axis'.

-that's it

try it first with a pencil (instead of a router) to get the feel of it and see how you need to adjust your track length.

Cheers and happy routing,

-Funk