Router bit question

**Amphiprion** · 14 July 2006, 18:29 Friday

Why the 3/4" large diameter? I would much prefer a 1/2" shank 1/2" diameter 1" cutting length bit for that kind of work. Whether or not it will work for a 2" hole will solely depend on your circle jig, unless I am misunderstanding your question.

**ToddS** · 14 July 2006, 18:31 Friday

Hmmm... I think I read in some post on this or another message board that 3/4" is a good size for that. It's probably a good thing I asked this question before I placed an order.

Yes, you understand my question. I am trying to figure out the best way to make the recess for the tweeter. Someone in another message thread (here or on one of my other boards) talked me into making my own circle jig if that helps at all.

**BobEllis** · 14 July 2006, 19:54 Friday

I use a 3/4" bit for the rabbets, at least when using the RS series. The flange on these drivers is more than 1/2" wide. Using a 1/2" bit requires two different radius cuts. Other drivers have smaller flanges and a 1/2" bit should be enough.

**Amphiprion** · 14 July 2006, 19:54 Friday

Making your own circle jig is fine, but I personally prefer and use the Jasper 200. It's only good down to something like 2.25" or so (not sure). You can get the cheaper, smaller Jasper 400 and it will go down to like 1" diameter circles ($25 at PE I think).

What I do is drill the 1/8" centering pin hole for the jig in the center of the circle to be cut, then set the jig to the outer diameter of the driver flange. Then stick the actual driver flange in the depth gauge of the plunge router to get the depth exact. Pull out the driver, plunge til the depth stop hits, then make your circle cut. Set the circle jig to a slightly smaller diameter and make a cut again at the same depth. This should give you a wide circular recess in the board for the driver flange that is exactly as deep as the driver flange, and its inner diameter should be smaller than the through cut you will make next. Undo the depth stop on the router now so that you can plunge through the thickness of the board for the through cut. Set the jig to the diameter of the through cut, and make the through cut plunging through about 1/3 of the material thickness each time around. This should give you perfectly recessed driver cutouts, within 1/32" of the radius of the driver at most if done properly with the Jasper jig.

Note that the Jasper jigs, which I highly recommend, are calibrated for 1/4" bits. If you use 1/2" bits then you need to make adjustments in where you stick the centering pin in the jig to get a properly sized cut (I think you count four holes down from the 'proper' hole on the jig to get the right size when using a 1/2" bit, but run through the math yourself before doing it).

You may have already known this stuff, but I have lots of free time and someone else might find this useful too. HTH!

**ToddS** · 14 July 2006, 22:40 Friday

I can use all of the pointers that you guys can toss my way. I've never used a router to cut circles before so any and all information is much appreciated.

A friend and I cut all of the flat panels for all 5 of my speakers a few months ago. Now all that I have left to do is make the holes in the front baffles and internal braces and then glue the cabinets together (along with finishing them etc.). I'm pretty anxious to hear what these things sound like.

**seattle_ice** · 15 July 2006, 00:22 Saturday

I have, over the years, used and made many of my own circle/pattern cutting jigs. The ease of use and simplistic workings of the Jasper Jigs are hard to beat, particularly if you are not an experienced woodworker. I would highly suggest one.

Your cuts will end up smoother, and it will be easier to do, if you use a smaller bit than 3/4" for the rabbetts for the drivers and the cutouts. It will take more passes, but is more controllable. And as has already been mentioned, make multiple passes, and be careful when doing the final pass on the cutouts. If the circle cutout is not fastened seperately, your jig will be floating after you make the final cut and you can easily ruin your other cuts. I usually screw a flat piece across the backside to hold the cutout, and just let the bit cut into it slightly.

**noah katz** · 15 July 2006, 04:13 Saturday

The Jasper 300 can at best do 1/8" increments, using 1/2" and 3/8" bits.

I'd expect that a lot of drivers don't come that close, and a 1/16" gap would look pretty bad if you ask me.

Am I missing something?

Thanks

**PMazz** · 15 July 2006, 06:09 Saturday

Circle jig

**BobEllis** · 15 July 2006, 08:44 Saturday

I've used Pete's jig, and it does work quite well. Quick to make and easy use. Thanks for posting it Pete. Benefit #4 is the biggest bonus in my book.

One slight modification I made to make it even easier to use - I mark several radii so I won't have to guess whether I am through the center of the hole. I found I kept forgetting to add 1/2 the bit diameter to the radius I was marking so I made my arc 9.75". With a 1/2" bit I just place my ruler on the radius line, put 10" on the arc and mark my desired cutout radius. Just subtract your bit's radius from 10" and mark there - you could do several arcs for various bits, but materials cost is so low, I have different jigs for different bits.

Just drape the power cord over your shoulder so it doesn't get caught between the jig and the edge of the box as you go around. This is an issue with any circle jig where the jig will hang over the edge of the work.

The only issue I had was caused by my Bosch template collar. Unlike Pete's nice one piece machined unit, Bosch collars have bits of tube press fit into a flat plate. Using a straight bit as shown, the dust buildup inside the guide caused enough heating that the guide disassembled itself. Fortunately Bosch has an adapter to take proper guides like Pete's so I'll buy a set. For today I'll use a larger collar and a spiral upcut bit to clear the dust (painted cabinets this time, you need a straight bit for post veneer cutting).

With painted cabinets I shoot to have the recesses about 3/64" oversize. This leaves a gap of around (another advantage of Pete's jig is you can make any diameter desired) This allows a little room for the paint coating and reduces the chance of chipping.

When the cabinets are veneered I try for 1/32" or less oversize. If I make a veneered cutout exactly the same as the driver diameter sometimes I end up with enough of an interference fit that removing the driver chips the veneer. (yes, I need to work on veneering technique) If you end up with interference, put some 100 grit paper on the convex side of a sanding block and run it around the edge a few times. Using a block helps keep the recess wall straight and smooth. FIngers could easily make an uneven roundover.

A little black paint applied to the recesses' edges with an artist's brush hides the space quite well.

**yousuredo2** · 15 July 2006, 11:53 Saturday

I found a 24 bit set on Overstock.com for $29.99, with less than $3 shipping...
crbide bits, sealed bearings....seems to be a good deal
Link Here

**seattle_ice** · 15 July 2006, 13:12 Saturday

Originally posted by noah katz

The Jasper 300 can at best do 1/8" increments, using 1/2" and 3/8" bits.

I'd expect that a lot of drivers don't come that close, and a 1/16" gap would look pretty bad if you ask me.

Am I missing something?

Thanks

Actually, if you are painting the baffle, you want that 1/16". And 1/16" = 1/32" difference, since it is split equally around the circumference.

I just use a 5/16" or 7/16" straight bit to cut the in between sizes.

**Amphiprion** · 15 July 2006, 13:38 Saturday

There's very little need for the Jasper 300, the model 200 will do over 18" in 1/16" diameter increments (1/32" radially) so you'll never have more than 1/32" gap between frame and cutout if you do it right.

**Dennis H** · 15 July 2006, 13:40 Saturday

The Jasper 300 can at best do 1/8" increments

Right but the 200 and 400 can do 1/16" increments. The 300 is for doing really big circles up to 52". That said, Pete's jig is cheaper and works better.

http://home.flash.net/~jaspera/

**noah katz** · 15 July 2006, 14:01 Saturday

"I just use a 5/16" or 7/16" straight bit to cut the in between sizes."

I didn't know router bits came in 1/16th's; that'll do it.

"Right but the 200 and 400 can do 1/16" increments."

That too, thanks.

**ToddS** · 15 July 2006, 16:07 Saturday

I had thought of picking up a Jasper Jig but I don't believe that it will fit on my inexpensive Firestorm (Black & Decker) router. I was seriously considering a more expensive model but I just couldn't bring myself to pay much more for a tool that I probably won't be using very often.

Pete, thank you for the information about the DIY circle jig and thank you to the rest of you for all of the very useful information.

**topp** · 16 July 2006, 22:35 Sunday

yousuredo2,

That set is 1/4" shank set, I would get a 1/2" set at least. Of course I am assuming your router has a 1/2" shank. Also, you can order direct from Holbren.com and save on shipping. I have ordered there a couple times and Brian seems like a good guy.

Router bit question

Router bit question

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