Mounting the ND20FB-4

[gorbs]

Re: Mounting the ND20FB-4

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]

Re: Mounting the ND20FB-4

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]

Re: Mounting the ND20FB-4

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]

Re: Mounting the ND20FB-4

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]

Re: Mounting the ND20FB-4

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]

Re: Mounting the ND20FB-4

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.

[jbruner]

Re: Mounting the ND20FB-4

In the past I have used a 1-1/4" paddle bit and a lot of work with a half-round file, but I recently discovered that my homemade circle jig could do it just fine. Here's the jig before I realized I didn't have to use a pivot as large as a screw.



I just cut the head off a nail, smoothed it on top and used it as a pivot. I cut the hole a little undersized so I could taper the hole with my file. Final fitment is so snug no fasteners are needed. Here's the unfinished baffle.



Here's my driver dimensions-
0.470" deep from flange to front edge
1.420" diameter at the flange tapering to
1.389" diameter at the front edge

[mattk]

Re: Mounting the ND20FB-4

I wasn't mounting an ND20, but I did drill a hole for a piece of 1.5" ID PVC, which has an OD just a bit larger than my 1 7/8" hole saw. I didn't have a 1" drum sander around, so I used the mdf plug left from the hole saw, a 1/4" diameter bolt, a couple of washers and a nut, a piece of mounting tape (double sided stuff) and a strip of sandpaper. Mounted it in my drill press, and with the thickness of the mounting tape, the home-made drum was just a hair smaller than the drilled hole, it took less than a minute to get the hole just the right size.