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post #1 of 64 Old 03-27-2015, 07:10 PM - Thread Starter
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Post Clarence's F-20 Build

This is a spin-off from the Most BASS for the $$$ thread.

Since finishing my HT earlier this year, I've been cruising a lot of the DIY subwoofer threads here. I bought 2 of the JBL GTO1514D subwoofer drivers... seemed like an affordable way to get started.

Last year I bought the plans for the THTLP (Tuba Home Theater Low Profile) and was originally going to build that, but it looks like the F-20 might be a little simpler to build. Plus I already had a couple of sheets of 3/4" ply in the garage that I needed to use. The THTLP insists on 1/2" ply, which I didn't already have, so I'd have to buy 3 sheets.

There are already a couple of good F-20 build threads. And since this is my first build, I'm sure they're probably better than I'll do. But the main F-20 thread is a little overwhelming, so this thread is mainly just notes to myself where I can consolidate my thoughts as I step through the build this week.




I'm currently using two 15" subs behind my AT screen, leftovers from the HT I built 10 years ago in our previous house:
  • Definitive Technologies Powerfield 15
    Dimensions 17 1\\2H by 17W by 17D
    Freq. response 18-125hz
    Driver complement One 15" woofer with polymer laminated cone
    Amplifier 200 wattsRMS
    High pass filter 12db/octave selectable (50 or 100 cycles)
    Low pass filter 24 db/octave continuously variable (50 or 100 cycles)
  • Cerwin Vega LW15
    Woofer size 15"
    Nominal (RMS) output power 200 Watt
    Response bandwidth 27 - 150 Hz
    Crossover frequency 40 - 120Hz
    Enclosure material MDF
    Weight 72.3 lbs
They're nothing special. Adequate. But I'm hoping for a little more oomph.


My inuke 3000DSP from ebay arrived today.

I drew a cut list to see if I could use the large scrap piece of ply I already had.

Only needed to buy one sheet.
So I got started.

I'd borrowed my friend's table saw. But I've borrowed it before and struggle with cutting large panels, especially since I'm usually working by myself. I could never cut a straight line with a circular saw... seems like the harder I try, the worse it gets.

So I did some googling on "building a jig to make cuts with a circular saw" and came across this thread. Too long... didn't read. So I just skimmed down to the picture at the bottom captioned "Make your cut" and thought "I can do that!"

I went to Home Depot, got a 16' long piece of 1"x2" finger-jointed pine ($6.44, only used half of it) and a 4x8 sheet of Tempered Hardboard ($13.44, only used 12" of it)... used my air stapler to staple the hardboard to the 1x2. Then ran my circular saw down each side, using the 1x2 as an edge guide. Voila... the blade just made its own cutting guide. I clamped it (using 2 of these $2.99 clamps from HF) to a 4x8 sheet and made my first cut.



OMG. I wish I would've learned this 40 years ago. I've never seen such a straight cut. Since the edge of the jig was cut with the blade of my own circular saw, it cuts exactly where it's clamped... no messing with drawing a line, no worrying about the thickness of the pencil line or the angle that you hold the pencil, no slipping straightedge as you try to draw a long line, no need to guess the width of the blade's cut width (kerf), no need to blow sawdust out of the way so you can see your pencil line as you cut.

Clamp the edge of your jig on your measured marks, place the saw on the jig, slide the saw along the edge of the 1x2. Perfect cut.

You can easily see exactly where the cut line will be by looking at the edge of the jig, so I used 2 folding tables to hold each side of the panel I was cutting. I just needed a gap as little as 1" between the tables. And I could push the saw from anywhere I could reach... no need to see the line, just push along the edge of the 1x2. Oh well... too much rambling over something so simple. Probably obvious to most of you, but maybe there's someone else out there that can't do straight cuts with a circular saw.

I cut 11 panels in about 30 minutes. Used a pencil to check off my cut list and labeled each board as panel 1-11.

Halfway though the cuts, UPS dropped off this box... contents: 15" JBLs, qty: 2.
You can see my fancy "sawdust management system"... a quick blast from the leaf blower after each panel.



Now to go read the next step on how to draw the points on the side panels to play connect-the-dots tomorrow with a jumbo tube of PL.

Gasket tape, speaker terminals, and duratex on the way from PE.

Last edited by Clarence; 03-27-2015 at 10:40 PM.
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post #2 of 64 Old 03-27-2015, 07:26 PM
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Are you building two? That's quite a bit more than "a little more oomph"

That's a lot more oomph!
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post #3 of 64 Old 03-27-2015, 10:51 PM - Thread Starter
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Yeah, one will probably be enough. I'm having a hard time imagining how much oomph one of these subs will give. If one is enough, then I won't need a second one. And if one isn't enough, then I'm not sure I'd want a second one. But the trend around here seems to be: if one is enough, then two is better, and more is more better. I still might try the THTLP with the second JBL.

Here are some other illustrations that I made from the instructions. I'm a visual thinker so labeling the panel names and sketching the measurement points helps me plot tomorrow's steps.

If anyone notices any incorrect interpretation, please speak up before I start gluing.





Quote:
Point 1 is the top of the mouth opening, and is on the left side, 14-15/16” from the lower corner.

Point 2 is the corner of the chamber and the mouth flare, and is 12-11/16” up and 12-3/16” in from the lower right corner.

Point 3 is the corner of the flare near the top right of the cabinet. This point is located 9-1/16” in and 8-13/16” down from the top.

Point 4 is the end of the baffle at the top left of the cabinet, 5-5/8” down from the top and 5-¼” in from the front.

Now, connect point 1 to point 2 to point 3.

Next, we want to draw where the wood panels will be on the side panel. I’ll freely admit it - I cheat. I use a ¾” wide strip of 1/8” thick aluminum. This allows me to lay out both sides of the panel without moving the straightedge. Yes – the plywood is thinner, but the 1/32” is not that big of a deal.

OK, so two panels are in place. Measure in ¾“ from the front, draw in the front panel, then measure in 1-7/8” from the inside of the front panel to locate the horn side of the baffle. Connect this point to point 4, then draw the back side of the baffle. Four down.

Now – measure 19-¼” from the top of the baffle on the inside, then measure 18-½” down from point 3, but on the inside of the panel. Connect these marks, draw in the other side, and the chamber is complete. That’s five, four more to go, and three are super easy.

Using your straightedge, draw in the top, back, and bottom panels, three more down.

The final panel is located 11-¼” in from the top front corner, the panel end is 19-½” from the top edge, and is perpendicular to that edge.
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post #4 of 64 Old 03-27-2015, 11:09 PM
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Sealing that chamber is, as you well know, of utmost importance
I can't pinpoint exactly where in the SUBMAXIMUS thread I posted pictures of my 1 x 3 oak inset set up for the access panel attachment but you might want to take a look,
it is probably overkill but it seems to be absolute
maybe inspire you to come up with something "simpler"


nice pics and layout thinking and visualizing . .

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post #5 of 64 Old 03-28-2015, 12:07 AM
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bracing. :-)

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post #6 of 64 Old 03-28-2015, 12:11 AM
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What driver does the F20 use? Very nice thread, BTW. I am a visual person too.
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post #7 of 64 Old 03-28-2015, 03:59 AM
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I'm pretty sure it was designed for the mfw15, which was a buyout woofer at the time (a sub company went out of business so a whole bunch on the drivers were picked up cheap). several drivers work in the f20, but not all. check the thread. i think there was a post where lilmike was updating drivers that people were using and were proving to work.

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post #8 of 64 Old 03-28-2015, 06:04 AM
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Quote:
Originally Posted by LTD02 View Post
I'm pretty sure it was designed for the mfw15, which was a buyout woofer at the time (a sub company went out of business so a whole bunch on the drivers were picked up cheap). several drivers work in the f20, but not all. check the thread. i think there was a post where lilmike was updating drivers that people were using and were proving to work.
it was designed around the MFW-15 but the Dayton DVC-15 is a near perfect drop in, people have been using it for years
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post #9 of 64 Old 03-28-2015, 08:39 AM - Thread Starter
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Quote:
Originally Posted by asarose247 View Post
Sealing that chamber is, as you well know, of utmost importance
I can't pinpoint exactly where in the SUBMAXIMUS thread I posted pictures of my 1 x 3 oak inset set up for the access panel attachment but you might want to take a look,
it is probably overkill but it seems to be absolute
maybe inspire you to come up with something "simpler"
Found your maximus access panel:
https://www.avsforum.com/forum/155-di...l#post24625403

Love that thread.

I was planning something similar... a 3" picture frame mounted on the inside with gaskets.

Now I'm pondering something even simpler... what if I just mark (pre-drill 1/8" holes only 1/8" deep) the four corners on the exterior of the chamber. Under what circumstances will I need future access to the chamber? Only if I blow the subwoofer driver and need to inspect/replace it, right? When/if that happens, then I drill out the 4 corners, crank out the jigsaw, connect the dots, cut out the panel and mess with resealing it after the repair.

So I just "permanently" install and wire the subwoofer driver in the chamber before I seal on the lid. No access panel. Airtight. Clean.

Stupid plan? (or lazy or short-sighted?)

I love my kreg jig and thought I was going to get laughed at here in my next batch of pictures because I like spacing pocket holes every 6" or so, but it looks like you had 4" spacing. Most threads say the fasteners are just there to hold the panels in place until the PL adhesive expands and dries. I like screwed and glued.

And yes, lots of bracing. Might as well use as many of those panel scraps as possible.
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post #10 of 64 Old 03-28-2015, 09:57 AM
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QED!

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Thanks for driver info.

@Clarence : I think your idea is a good one. Being that the only time you'd have to access the driver chamber is if the driver dies, it wouldn't matter that you'd make a mess cutting out the access panel. Not having to deal with creating an access panel now simplifies construction/speeds things up.

However, I'll quantify my answer by asking "What is the plan for the finish on the F20s? If you are planning on a nice veneer or even a nice Duratex paint job, then I think you should build the access panel now and finish accordingly. Cutting out the access panel would make a mess of the finish. But if the plan for the finish is "Exquisite Flat-Black Rattle Can" then skip the access panel.
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post #12 of 64 Old 03-28-2015, 12:11 PM - Thread Starter
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Quote:
Originally Posted by michaelddd View Post
What is the plan for the finish on the F20s? If you are planning on a nice veneer or even a nice Duratex paint job, then I think you should build the access panel now and finish accordingly. Cutting out the access panel would make a mess of the finish.
I've got a gallon of Duratex on the way from PE. Everything's behind an AT screen, so I don't need them to be beautiful, just black. But the OCD in me wants them to look good.

My main concern with the panel is potential for air leaks, even with double gaskets and 24 screws.

BTW, is there any advantage to putting polyfil in the chamber?

Today's status update: I cut the 3 bevels with the table saw. And I stacked up all of the 18.5" panels next to each other and shaved off maybe 1/16" from a few of the taller ones. They're all within about 1/32" now.

Next I've got to practice cutting circles with my router. I also have a rotozip, but I've snapped bits in drywall just cutting recessed lights, so I doubt it's going to work on 3/4" ply.
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post #13 of 64 Old 03-28-2015, 12:15 PM
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Subbed! I have plans for the exact same build once I'm moved! (New house closes in a month).

Very much looking forward to following your process and findings with the JBL.
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post #14 of 64 Old 03-28-2015, 01:27 PM - Thread Starter
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32 degrees in the garage today.

Measured and marked the panel placement guides:


And I unboxed one of the JBLs:
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post #15 of 64 Old 03-28-2015, 02:06 PM
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You'll most likely need to open the access panel after some of the first spirited bass movies to snug down the driver again. I had to do this with my THT.
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post #16 of 64 Old 03-28-2015, 02:46 PM - Thread Starter
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Yeah, I'm going to include the access panel. My first build is not the time to start tweaking and straying from a proven design.

I just found my router bits. We moved into a new house last year and a few boxes of tools were still unpacked. Unfortunately, I'm not sure if any of the bits will work. None of them say "speaker driver cutout" though. Is there a thread with tips on how to cut out the circle with a plunge router? I'll do a search.

FWIW, my router is a Ryobi RE180PL1 2HP variable speed 1/2" collet. I bought it years ago, used it once, can't even remember on what.
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post #17 of 64 Old 03-28-2015, 02:50 PM
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Without an access panel you would need to mount the driver before attaching the last panel. There is the potential for some glue squeeze out to drip onto the driver.
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post #18 of 64 Old 03-28-2015, 03:17 PM
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Milescraft Router Guide Kit
$40 at Lowes


use a mortising bit,
adjust set-up get to proper/needed mounting diameter on a scrap piece first
feed downward slowly after each circular pass after set-up complete, 3/4 ply maybe 6-9 passes, YMMV
lay the center out
the kit uses a plastic pivot held at the center with a supplied "nail',
I always start the hole first with a punch, then the nail gets started and centers the pivot exactly,
bulls eye
the trick is removing the nail, for re-use
as it is flush to the top of the plastic pivot, you can't just yank on it or do anything to deform/bend the nail or pivot
I use a pair of electricians dykes on a 3/4 ply scrap block to come at it on the same horizontal plane to just get under the head of the nail
and then gently pry straight ,mol, up, maybe from several directions around the pivot
or once its started, a pair of vise grips pulling straight up
nail stays straight-primary/necessary objective


hope that helps

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post #19 of 64 Old 03-28-2015, 03:19 PM
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great looking set of bits,
nice to have when you're inspired . . .

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post #20 of 64 Old 03-28-2015, 04:18 PM
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I'm not the expert by any means but the "Polyfil in driver chamber for horns?" question gets asked often over at the BFM forums and Bill's answer is always "NO." Something about that it's a horn, and the horn path affects the speaker, which affects the chamber and it's all related, etc. Polyfil changes the response of the driver in the chamber, which changes the overall response of the horn. So, no polyfil in driver chamber.

I forgot about having to tighten the driver down again after a few spirited playback sessions. Good catch, superedge 88. So yeah, access panel for you, Sir.
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post #21 of 64 Old 03-30-2015, 06:32 AM - Thread Starter
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After trying to figure out exactly how large the circle should be in the baffle, I finally figured out that it doesn't matter. Since the subwoofer sits completely within the chamber (and not through the baffle hole), the 14" cut specified in the instructions will work for just about every 15" driver. You just need the hole to be larger than the rubber surround (13.75" for my JBL GTO1514) and inside the circle of mounting holes (15.5" for my JBL). So a generic 14" hole works just fine. I was over-complicating it in my mind, thinking the hole had to be perfectly sized and perfectly cut to fit tight. Nope... the driver sits behind the hole (so it can be installed, inspected, adjusted, removed or replaced through the access panel) and the gasket seals it.

So without having to worry about the exact measurement, I felt a lot more confident about trying to use my router.

I found this article on cutting circles with a router. TL;DR... I just looked at picture 3 and then built something quick and easy:


I did a quick practice on a scrap piece and measured to make sure I had a 7" radius. Yep... worked great. So I measured the center of the baffle, made 3 passes with the router, used my sawdust management system (leaf blower) between each pass... voila.



I was all excited about successfully using my router so I got fancy and swapped to a 1/8" round-over bit and polished off the edges...


After routing the 14" baffle circle and marking the mounting holes for the JBL GTO1514D, if I build another one I think I'll use a diameter of 13.75", which is where the foam rubber surround ends and the hard rubber frame gasket begins. This would give me another 1/4" to pre-drill the 8 mounting holes. As it is, they're pretty close to the edge. And it will give more room for gasket tape.

Mike now recommends these inserts instead of hurricane nuts so I ordered those plus these 1-1/4" 10-32 screws (EDIT: I found these screws were a little too short, see post 33) and this tap. According to the product information page, the inserts use a hole size of 0.281 in. (which is 9/32").

I also cut out the access panel. I used the rotozip, since I didn't have a router bit small enough. I tacked trim around the chamber perimeter and used the edges as a guide. It worked ok, but there are a few inches where the rotozip knob was against the edge instead of the bit guard ring so it got a little wavy until I saw what was happening while cutting... easier to describe with a picture. No one will notice but me, especially since it's going to be covered with duratex and behind a AT screen.

I'm going to finish the kreg jig pocket holes on the panels, dry fit (2 kreg screws only, no PL) and fine tune the length of panel 6 and panel 10 (steps 7-4 and 7-8).

We're going to be out of town this week so I'll wait for those inserts and not rush to finish today.
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Last edited by Clarence; 04-05-2015 at 03:42 PM.
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post #22 of 64 Old 03-30-2015, 08:00 AM - Thread Starter
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Quote:
Originally Posted by Clarence View Post
I also cut out the access panel. I used the rotozip, since I didn't have a router bit small enough. I tacked trim around the chamber perimeter and used the edges as a guide. It worked ok, but there are a few inches where the rotozip knob was against the edge instead of the bit guard ring so it got a little wavy until I saw what was happening while cutting... easier to describe with a picture. No one will notice but me, especially since it's going to be covered with duratex and behind a AT screen.
Here's the picture of my cutout access panel and the rotozip I used. I used my brad nailer and tacked a piece of trim alond the chamber perimeter (panels 3/4/5/9), then used that perimeter as an edge for the rotozip to follow. On the left edge you can see where the rotozip knob started bumping against the jig, causing a wavy cut.



And you can see the index holes (i.e., Step 3) where I drilled 2 points on each marked panel though to the other side panel stacked underneath.

Next: build a frame behind it so I can have something to screw the panel into with some gasket tape to seal it.
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post #23 of 64 Old 03-30-2015, 10:27 AM
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Next: build a frame behind it so I can have something to screw the panel into with some gasket tape to seal it.


you can see in the pictures wrt MAX I used 1 x 4 oak trimmed down to 1 x 3 and split the difference building the frame
1 1/2 for attaching the frame to the box and 1 1/2 for access panel attachment
my foam tape was 2" wide. something I found in plumbing in HD


I look at some of those pictures and compared to others posted builds, the word "overkill" comes to mind . .
"Totally"

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post #24 of 64 Old 03-30-2015, 10:44 AM - Thread Starter
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Quote:
Originally Posted by asarose247 View Post
I look at some of those pictures and compared to others posted builds, the word "overkill" comes to mind . .
"Totally"
Yeah, I'm putting half of my pocket joints on the reverse side of the interior panels so critics will only see half of my kreg holes when I post the build pics.

Overkill is where the fun comes from.

Today's overkill: I did a 1/8" round-over bit on the end of the flare panels (i.e., where the horn "folds"... top of panel 3, bottom of panel 8, top of panel 9) and on the bracing panels to "reduce turbulence"... e.g., a tuba doesn't have 90/180 degree bends and edges. Ooh, I see one final edge I can round-over... bottom-right edge of Panel 4... the final bend of the mouth. After testing for air leaks, I'm going to caulk (and finger smooth) the interior edges after the PL dries.
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post #25 of 64 Old 03-30-2015, 11:05 AM
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wrt to the rounding and the edges . .
"someone " sent me a comment about worrying about the "delamination" of the plywood at the ends of the "turns" panels, at least in the baffle area and first fold or 2,
so I applied a light layer of PL to those edges I thought "might" be affected, especially in the high pressure regions


ow beautiful looking work keep the pics flowing

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post #26 of 64 Old 03-30-2015, 01:07 PM
 
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Quote:
Originally Posted by Clarence View Post
Yeah, I'm putting half of my pocket joints on the reverse side of the interior panels so critics will only see half of my kreg holes when I post the build pics.

Overkill is where the fun comes from.

Today's overkill: I did a 1/8" round-over bit on the end of the flare panels (i.e., where the horn "folds"... top of panel 3, bottom of panel 8, top of panel 9) and on the bracing panels to "reduce turbulence"... e.g., a tuba doesn't have 90/180 degree bends and edges. Ooh, I see one final edge I can round-over... bottom-right edge of Panel 4... the final bend of the mouth. After testing for air leaks, I'm going to caulk (and finger smooth) the interior edges after the PL dries.
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post #27 of 64 Old 04-01-2015, 07:50 PM
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Cant wait to see the finished product and hear your impressions.
I already had plans to use my infinity 1262s, but the jbl deal was too good to pass up so I bought two. I may just ditch the infinity's and copy your build.
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post #28 of 64 Old 04-02-2015, 06:58 AM
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Quote:
Originally Posted by Clarence View Post

Mike now recommends these inserts instead of hurricane nuts so I ordered those plus these 1-1/4" 10-32 screws and this tap. According to the product information page, the inserts use a hole size of 0.281 in. (which is 9/32").
y.
Why do you need a tap? The inserts are threaded.

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post #29 of 64 Old 04-02-2015, 07:05 AM
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Lots of folks tap the threads to clean them up.

Why waste $ on more cheap stuff, it's like challenging a dragon with a pocket knife.
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post #30 of 64 Old 04-02-2015, 01:24 PM
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Exactly. If you get PL in the threads and then break the insert loose when you tighten the bolts you will really hate life.
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