A couple questions about routing driver openings

[truckman]

I built my first pair of speakers 30+ years ago and am currently planning to get back into this hobby. My last speakers, which I'm still using, were covered with woodgrain self-adhesive vinyl and this time I'm hoping to build something that looks and sounds a bit better .

I'm currently in the planning and tool gathering stage and I've been doing quite a bit of reading. I've come up with a couple of questions that I haven't seen any answers for:

• I'm planning on cutting the driver holes before assembling and veneering the cabinets. This will allow the the openings to be chamfered on the back of the baffle, if necessary, and also allows the speaker to be tested before veneering (good for those of us who can be impatient). If the driver recesses are routed using a circle jig before the cutout is completed and before the veneer is applied, how is the veneer trimmed match the edge of the recess? It seems to me that the recess would be too shallow to use a flush trim bit. I've read that some people route all the way through using the circle jig, route the recess using a rabbet bit, and then trim the veneer by using the rabbet bit again. This is supposed to have the advantage of allowing the depth of the recess to be increased if necessary, but it seems to me that the accuracy of the fit around the rim of the driver would depend on the smoothness and accuracy of the cutout.
• The bit of choice for routing the openings seems to be a 1/4" spiral upcut bit. How deep is it realistic to cut with one of these bits? The MLCS #5146 bit (as a typical example) has a cutting length of 1". I don't know how much further up the shank the flutes extend, but I would worry about chip removal problems when routing into a thick baffle, even when only removing a small amount of material per pass. Would a 1/2" bit be a better and stronger choice when routing openings through a double thickness baffle? Assuming the use of a beefy enough router, the only disadvantage would seem to be the generation of twice as much MDF dust.

My current plan is to build a pair of MBOW1s for my office as my first project, and then the Dayton RS WMTW Center & TMWW Mains as my second project.

[PMazz]

If you make a baffle template first, with all driver holes routed to the outside dimension of the drivers (for recessed mounting) you can cut out the rough driver holes to allow for surface mounting of the drivers and use the template (and a shallow pattern cutting bit) after they're veneered to make the recessed lips.

I wouldn't use a 1/4" bit for anything thick. If you decide not to make a template, get the 1/2" bit.

Pete

[dyazdani]

I usually don't cut deeper than 1/4" or so on each pass and have the bit you're talking about. I haven't seen any issues with material removal, but I've only done MDF so a lot of it blows out.

[truckman]

If you make a baffle template first, with all driver holes routed to the outside dimension of the drivers (for recessed mounting) you can cut out the rough driver holes to allow for surface mounting of the drivers and use the template (and a shallow pattern cutting bit) after they're veneered to make the recessed lips.

How do you accurately align the template after veneering? Do you try to align it to the driver holes, or to the cabinet edges? If the latter, doesn't the edge roundover make the alignment more difficult? If you don't align to the holes, don't the holes have to be made larger to make sure there will be clearance all the way around?

Also, is thinning of the template between tightly spaced drivers an issue? It looks like there is just a fuzz more than 1/4" between the rims of the tweeter and the midrange in the TMWW design.

I wouldn't use a 1/4" bit for anything thick. If you decide not to make a template, get the 1/2" bit.

The reason that I ask is that a 1/4" bit is recommended by a number of people in this router bit thread, which is referenced by the tool recommendations reference thread.

[Swerd]

The bit of choice for routing the openings seems to be a 1/4" spiral upcut bit. How deep is it realistic to cut with one of these bits? The MLCS #5146 bit (as a typical example) has a cutting length of 1". I don't know how much further up the shank the flutes extend, but I would worry about chip removal problems when routing into a thick baffle, even when only removing a small amount of material per pass. Would a 1/2" bit be a better and stronger choice when routing openings through a double thickness baffle? Assuming the use of a beefy enough router, the only disadvantage would seem to be the generation of twice as much MDF dust.

If you are going to use a Jasper jig, a 1/4" bit is recommended, but not required. If you use any other size bit, you have to do a little extra arithmetic to before you choose which pin hole to use. The math is not hard, but I have found it is easy to forget to do it at all. So I now have a 1/4" bit. If you don't use a Jasper jig, the choice is yours. Personally, I like the Jasper jigs. They've worked very well in my hands from the very first time I used them.

A spiral up-cut bit is better than a straight bit at chip removal, especially in deep grooves. This becomes an issue as you cut a circle through 3/4" MDF. I find that I need to make 3 passes for 3/4" MDF. I don't think using a larger bit will allow you to do that in fewer passes. A 1/2" bit will make a lot more dust.

If you do not yet have a router, I recommend one that allows you to attach a shop vacuum for even better chip & dust removal. I have a DeWalt 621, but other models now have that feature as well. MDF makes for fine dust that is loaded with the glue used during its manufacture. It can be nasty on your lungs! The best way to avoid breathing that is to use a spiral up cut bit with a shop vac attached to the router.

Finally, spiral up cut bits are made of solid carbide. A 1/4" one costs less than a larger one.

[Martyn]

My first preference would be to do the veneering before cutting the holes for the drivers, but if I were going to veneer later, I think I'd probably use a template as Pete suggests. In this instance it sounds like you might need to make two - one for each driver. Make each template significantly larger than the baffle. This will do two things: first, it will offer better support for your router; and second, it will enable you to screw a couple of battens to the underside so that you can register it against two sides of the cabinet. Ensure that you allow for the thickness of veneer on the sides if necessary. You could also register off other convenient features if you prefer, such as holes for a grill if you will be using one.

[PMazz]

This is the template I made for Jon's M8MTMs. No problem as the recessed area is so minimal. As you can see in the picture, I make the template long enough to accept clamps w/o interfering with the router. Alignment is fairly easy, side to side and along top.

Image not available

If you've ever snapped a 1/4" bit you wouldn't ask.

Pete

[truckman]

If you are going to use a Jasper jig, a 1/4" bit is recommended, but not required. If you use any other size bit, you have to do a little extra arithmetic to before you choose which pin hole to use. The math is not hard, but I have found it is easy to forget to do it at all. So I now have a 1/4" bit. If you don't use a Jasper jig, the choice is yours. Personally, I like the Jasper jigs. They've worked very well in my hands from the very first time I used them.

I'm planning to use a Jasper jig for this. I figure that I can manage to subtract 1/8" from the cut radius for a 1/2" bit. I'll have to do math anyway because the dimensions on the WMTW/TMWW CAD drawings are decimal, and the OW1 dimensions are metric.

A spiral up-cut bit is better than a straight bit at chip removal, especially in deep grooves. This becomes an issue as you cut a circle through 3/4" MDF. I find that I need to make 3 passes for 3/4" MDF. I don't think using a larger bit will allow you to do that in fewer passes. A 1/2" bit will make a lot more dust.

I don't think I'd cut more that 1/4" per pass, even with a 1/2" bit. My concern is that when cutting all the way through a 1-1/2" baffle with a 1/4" bit that the top of the flutes would be below the top of the groove, so that the chips could only be ejected into the groove instead of having the clearance to be ejected all 360 degrees around the bit.

If you do not yet have a router, I recommend one that allows you to attach a shop vacuum for even better chip & dust removal. I have a DeWalt 621, but other models now have that feature as well. MDF makes for fine dust that is loaded with the glue used during its manufacture. It can be nasty on your lungs! The best way to avoid breathing that is to use a spiral up cut bit with a shop vac attached to the router.

The DeWalt 621 is definitely on my short list of potential routers. My current inclination is to buy the new Hitachi M12V2. According to the info that I've read, it is similar to the M12V, but with a dust collection port, an improved plunge mechanism, and controversial styling. If I end up using a router with this much heft, I'm concerned about the danger of breaking one of those brittle carbide bits that sticks way out of the collet to cut all the way through a thick baffle.

Finally, spiral up cut bits are made of solid carbide. A 1/4" one costs less than a larger one.

With what it looks like I'll be spending on tools, I don't think the price difference between a 1/4" spiral upcut bit and a 1/2" bit will matter very much.

[truckman]

My first preference would be to do the veneering before cutting the holes for the drivers, but if I were going to veneer later, I think I'd probably use a template as Pete suggests.

If you assemble and veneer before cutting the driver holes, how do you chamfer the inside edge of the hole in those cases where it is required?

[Martyn]

If you assemble and veneer before cutting the driver holes, how do you chamfer the inside edge of the hole in those cases where it is required?

Ah, if you're going to wrap veneer around the assembled box you have no choice but to cut the holes first.

[dlneubec]

Truckman,

Here is what you might do if you want to use the Jasper Jig. First drill your center point holes all the way through the baffle. The hole will serve as a way to cut from the front and back sides of the baffle.

Now, from the backside, you could use a v-shaped bit (not sure what they are called)and cut a slot with the point of the V at the drivers through cut dimension. Or, you could simply use the 1/4" of 1/2" straight bit and cut a rabbit or shelf, since the whole idea is to open the area up behind the driver so it can breathe. There is nothing magic about it being a chamfer, as far as I know. Perhaps cut the shelf 3/8" deep, leaving 3/8" stock for the driver to be bolted on. Now glue up the baffle to the box.

If you have a way to access from the back of the baffle, say via a port, binding plate opening, etc. you could apply the veneer and then just use a sharp pointer to push through from the back of the veneer at the center points of the holes you drilled for each driver. Then drill the hole through just the veneer at these locations from the front of the baffle and use the Jasper Jig to cut the recesses and then the through holes from the front.

If you have no way to get your hand in the back, you could very carefully measure the location of the center of each hole from the egdes and probably find the holes under the veneer fairly easily. You might even be able to roll something hard and round, like a marble, ball bearing, etc. on the front of the veneer in the area of the through center holes to locate them under the veneer. Once you do, you can drill through the veneer and use the Jasper Jig for the rest.

[dynamowhum]

Dan

Forgive my ignorance but are those your speakers in your avatar? Did you make these or are they commerical. They are stunning.
I am also going to steal most of your baffle procedure. Thanks.

[truckman]

Here is what you might do if you want to use the Jasper Jig. First drill your center point holes all the way through the baffle. The hole will serve as a way to cut from the front and back sides of the baffle.

Now, from the backside, you could use a v-shaped bit (not sure what they are called)and cut a slot with the point of the V at the drivers through cut dimension. Or, you could simply use the 1/4" of 1/2" straight bit and cut a rabbit or shelf, since the whole idea is to open the area up behind the driver so it can breathe. There is nothing magic about it being a chamfer, as far as I know. Perhaps cut the shelf 3/8" deep, leaving 3/8" stock for the driver to be bolted on. Now glue up the baffle to the box.

If you have no way to get your hand in the back, you could very carefully measure the location of the center of each hole from the egdes and probably find the holes under the veneer fairly easily. You might even be able to roll something hard and round, like a marble, ball bearing, etc. on the front of the veneer in the area of the through center holes to locate them under the veneer. Once you do, you can drill through the veneer and use the Jasper Jig for the rest.

I hadn't thought of using a V-groove bit do cut the chamfer. I was thinking about possibly first cutting a clearance slot in the back of the baffle that would be deep and wide enough to provide clearance for the pilot bearing of the chamfer bit, but your idea sounds a lot better. One complication in my case is that I don't have a drill press to get the center hole square with the baffle surface.

I would think that a chamfer or a similar profile would be better from the standpoint of the baffle strength around the driver opening than a rectangular groove that provided the same clearance.

As thin as veneer is, I would think that it should easily be possible to locate the center hole by touch and trim the veneer away from the hole with a sharp knife.

A couple more questions:

• How safe is it to finish the opening after the box is assembled and letting the cutout drop into the box versus completing the cut with the baffle flat on a sacrificial surface?
• When using T-nuts, can they be installed after the box is assembled?

[chasw98]

One complication in my case is that I don't have a drill press to get the center hole square with the baffle surface.

Look into this from Sears. They run about $25.00 and work great for making a perpendicular hole.
http://www.sears.com/sr/javasr/product.do?pid=00967173000&vertical=Sears&BV_UseBV Cookie=Yes

[truckman]

I think I've found a way to build a jig to accurately find the center of the driver opening so that the driver recess can be routed after the driver opening has been cut. This is probably easiest to do with a Jasper jig.

First, cut a circle the same thickness as the baffle and the same diameter as the driver opening. Next, cut away most of the material in the four quadrants so that only the center and four legs remain. Finally, glue (or screw?) thin blocks to the back of each of the legs that extend past the end of the legs. This shape should allow the jig to be inserted through the driver hole at an angle, then straightened so that it sits flush with the baffle.

The jig could be held in place by wedging a piece of scrap between it and the back of the cabinet, possibly with the aid of a jackscrew threaded through the jig.

The center hole in the jig will be concentric with its outer diameter, which will cause the center hole to be concentric with the driver opening, so the driver recess should end up being concentric with the driver opening.

This jig can be reused for different cabinets that use the same driver opening diameter, and it could be adapted to work with a thicker baffle by shimming the blocks on the back of the legs.

[jonathanb3478]

I think I've found a way to build a jig to accurately find the center of the driver opening so that the driver recess can be routed after the driver opening has been cut. This is probably easiest to do with a Jasper jig.

...

My plan for routing the recess after the opening has been cut is to use my jasper jig normally, but on a large piece of MDF. I would then place that on the finished baffle and use my template bit (bearing at the router end, not the tip) to trim through the veneer with that large piece serving as a template. I need to allign it manually before clamping it down, but that is not hard.