Mounting the ND20FB-4

[brianpowers27]

I need help mounting the ND20FB-4. I saw that Zaph posted in the zdt 3.5 a method which involved a 1 7/16" forstner. The specs on the product page show 1 9/16"... What gives?

http://www.parts-express.com/pe/show...TOKEN=95881282
http://www.zaphaudio.com/ZDT3.5.html

[dthomas]

I need help mounting the ND20FB-4. I saw that Zaph posted in the zdt 3.5 a method which involved a 1 7/16" forstner. The specs on the product page show 1 9/16"... What gives?

http://www.parts-express.com/pe/show...TOKEN=95881282
http://www.zaphaudio.com/ZDT3.5.html

Actually I forget the size of the top of my head but you need a metric hole of about 38 or 39mm. I usually just undersize the hole then use a small drum sander mounted to a cordless drill and expand the hole till it fits.

I have made the hole too big then used silicon to fill the gap with good luck also. Does not take much to hold them in place.

[brianpowers27]

BTW: These are on special starting today. $5 vs $8

[gorbs]

i used half round file for the final fit in my mtm's. i just used the closest wood boring bit in a drill first then filed to fit.

[brianpowers27]

I have tried the drum sander bit before. I got a little overzealous... I always prefer idiot proof methods...

[curt_c]

I need help mounting the ND20FB-4. I saw that Zaph posted in the zdt 3.5 a method which involved a 1 7/16" forstner. The specs on the product page show 1 9/16"... What gives?

http://www.parts-express.com/pe/show...TOKEN=95881282
http://www.zaphaudio.com/ZDT3.5.html

The 1 9/16" measurement probably includes the flange. They are 36 mm in diameter, and the 1 7/16" bit equates to 36.5 mm.

C

[dthomas]

The 1 9/16" measurement probably includes the flange. They are 36 mm in diameter, and the 1 7/16" bit equates to 36.5 mm.

C

Yep I think he is right now I seem to recall using a 1 3/8" forstner bit then using the small drum sander bit to enlarge enough to get the tweeter to fit. It was not too much sanding and went fairly quickly.

[djg]

I used the small Jasper jig to cut the holes for the similar Aura in my ZMB4s. The hole was just a bit big, I used electrical tape to "shim" it out.

[lhwidget]

I used a 1 7/16 forstner bit from Grizzley for an ≈ 1/2" deep hole from the front, and a 2" forstner bit from the back. Just drill from the back until the depth puts the front edge flush with the baffle surface. I used a 1/16" pilot hole through the baffle to line the two bores up.

[MagicO309d]

I used a 1 7/16 forstner bit from Grizzley for an ≈ 1/2" deep hole from the front, and a 2" forstner bit from the back. Just drill from the back until the depth puts the front edge flush with the baffle surface. I used a 1/16" pilot hole through the baffle to line the two bores up.

I'm starting a build with that tweeter too. If I use the recommended 1 7/16 Forstner bit, is sealing or gasketing still needed when mounting the driver to the back of the baffle? (I'm assuming that I can route a nice smooth cut out for the driver's mounting flange.)

[Dirk]

Um, after the speaker is assembled (and presumably glued), how would you get them back out? Affix them to the cabinet with bolts from the front?

[gorbs]

i used a long handle small philips screw driver with some number 4 or 6 wood screws from behind. it was tight but i only used two. next time i will fit them to the baffle before i begin the cabinet construction.

pre drill the holes and remove material for a proper flush face fit. lol say that 3 times fast .

[Dirk]

i used a long handle small philips screw driver with some number 4 or 6 wood screws from behind. it was tight but i only used two. next time i will fit them to the baffle before i begin the cabinet construction.

pre drill the holes and remove material for a proper flush face fit. lol say that 3 times fast .

Yeah, that's the problem I'm envisioning. I was thinking of mounting it in a 4L "sub enclosure" that's made out of a 1/2-round of sonotube. There won't be a whole lot of wiggle room. I wasn't planning on a removable front baffle.

Yep, unless you have a removable front baffle, or access from the back or woofer hole, that tweeter is in there.

Damn. Back to Zaph's comparator.

[brianpowers27]

You could always mount the tweeter with machine screws through the baffle and then wingnuts on the inside.

I mounted the tweeter on my leftovers project this way.

[gorbs]

you know it really can be a compression fit if you get it close enough. i had to push mine out from the front using my index finger on the top then the bottom and kind of wiggling it half way then i pulled it from behind gently and she came right out. i didn't secure it until the painting was done.

[williamrschneider]

Keep in mind also that the body of the tweeter that goes into the baffle is tapered. I'm sure that the taper was necessary to make it removable from the injection molding machine, but that's a bit of a nuisance to deal with.

I measured 1.400" diameter at the very end, and 1.425" diameter at the base of the tweeter.

FWIW, I ordered the 1-7/16" Forstner bit from Grizzly mentioned by John in the ZDT3.5 build, but found that my sample was poorly made (China) with sharpening burrs, It drilled over sized holes when tested on scrap MDF. I used a 35mm Forstner bit that he mentioned for a similar tweeter in his ZBM4 build notes. I believe I got the 35mm Forstner bit from Woodcraft, and it was well made.

Like others have mentioned, I used a small sanding drum to enlarge the hole on the front of the baffle to accept the front of the tweeter, then lifted the drum to sand the back of the through hole more to accommodate the tapered body of the tweeter. It was extremely easy to do.

[lhwidget]

Keep in mind also that the body of the tweeter that goes into the baffle is tapered. I'm sure that the taper was necessary to make it removable from the injection molding machine, but that's a bit of a nuisance to deal with.

I measured 1.400" diameter at the very end, and 1.425" diameter at the base of the tweeter.

FWIW, I ordered the 1-7/16" Forstner bit from Grizzly mentioned by John in the ZDT3.5 build, but found that my sample was poorly made (China) with sharpening burrs, It drilled over sized holes when tested on scrap MDF. I used a 35mm Forstner bit that he mentioned for a similar tweeter in his ZBM4 build notes. I believe I got the 35mm Forstner bit from Woodcraft, and it was well made.

Like others have mentioned, I used a small sanding drum to enlarge the hole on the front of the baffle to accept the front of the tweeter, then lifted the drum to sand the back of the through hole more to accommodate the tapered body of the tweeter. It was extremely easy to do.

When did you get your bit from Grizzly? I got mine in early July 2008 and it was OK. I'm wondering if Grizzly's quality is slipping...

[williamrschneider]

When did you get your bit from Grizzly? I got mine in early July 2008 and it was OK. I'm wondering if Grizzly's quality is slipping...

I got my bit last summer sometime. Perhaps it was an outlier, but I am put off by drifting QC.

When I placed my order with Grizzly, I also bought a pair of inside and outside calipers -not the measuring type of caliper, but transfer calipers. The calipers (also made in China) fell apart after one use. Because the Forstner bit also had problems, I've written off Grizzly and their Chinese vendors as a supplier for my needs.

Dad was right - you get what you pay for.

[brianpowers27]

I got my bit last summer sometime. Perhaps it was an outlier, but I am put off by drifting QC.

When I placed my order with Grizzly, I also bought a pair of inside and outside calipers -not the measuring type of caliper, but transfer calipers. The calipers (also made in China) fell apart after one use. Because the Forstner bit also had problems, I've written off Grizzly and their Chinese vendors as a supplier for my needs.

Dad was right - you get what you pay for.

Indeed...

It costs a ton of money to go from a 98% quality rate to a 99.5% rate!

[williamrschneider]

Indeed...

It costs a ton of money to go from a 98% quality rate to a 99.5% rate!

And it costs even more to go from high-speed steel to carbide. The 35mm Woodcraft carbide bit was better in many ways, but especially performance.

Here's a snap of the two bits in question and some sample holes in some scrap MDF...



The Grizzly bit is chucked up, with the Woodcraft bit beside the hole it made. Check the bottom of the Grizzly hole (left) for roughness and the lip at the rim indicating sharpness problems. Still, both would work.

Both bits are Chinese, but obviously from different manufacturers.