2 x UM18 20ft^3 build starting .. (almost) - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 81 Old 07-28-2018, 07:00 PM - Thread Starter
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2 x UM18 20ft^3 build starting ..

Opening up a new thread to update as the build progresses.

This is going to be a long lasting build .. with the baby at home and long hours at work it might take a couple of months or more until things get all done. I will update with some pics as I go through it though.

These are going to be placed nearfield behind an HT sofa (2 HT loveseats, one behind each), in a 17x18x8 room. With them being 30 inch deep, they would be almost up against the rear wall too.

Simple sketch of what it roughly would look like (I would do this in SketchUp but I think I mentioned I barely have any time to work on this ? ). Box external size, 30" deep x 60" long x 25" high





Is there an issue with the slot port also not extending to the side walls ? I tried to keep the holes square, so I ended up with either 2 x 5" x 5", or 2 x 4.5" x 4.5" as described below. Just figured might be less chuffing vs something like 7" x 2" or so ..

Before I prepare my cut list and go cutting though, please help me decide between these two options.




I really want to get as low extension possible, but maybe I am pushing things too much and lose too much up higher. For some reason the 14Hz tuned box just looks like a more appropriate option when looking at the SPL curve, and it pretty much has more output down to maybe 12.5 Hz ..

But the lower tuned box, maybe it will be a bit less strain on the amp (less potential clipping ..) based on the apparent amp power - VA (attached). But most importantly, there is just something magical about that 10Hz figure, and the lower tuned box will give me about 7dB more. Is this worth losing 2-3 dB from 12Hz up ? Maybe not much source with 10Hz is out there anyway. And maybe 104dB @ 10Hz is not much to be worth chasing anyway ? (though likely a few dB higher given there will be two subs). Can ~105dB @ 10Hz be felt in any way, or is this simply too low and not worth it ?

I will likely be listening at -25 volume level (~80dB), but planning to use a house curve that would bump up the 10Hz to maybe 30-35 dB hot (there will be a limiter set to prevent blowing up the driver, based on the WinISD cone excursion results, i.e. make sure it does not go more than 22mm).

The idea is, decide which option I like, maybe cut the panels for one box one weekend, start gluing a box another, add bracing the following, etc .. put a weekend in here and there with no time at all, so yeah, it is going to be a long one

SPL


Port Air Velocity


Cone excursion


Amp apparent power VA


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post #2 of 81 Old 07-28-2018, 08:02 PM
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Originally Posted by alextr75 View Post
Opening up a new thread to update as the build progresses.

This is going to be a long lasting build .. with the baby at home and long hours at work it might take a couple of months or more until things get all done. I will update with some pics as I go through it though.

These are going to be placed nearfield behind an HT sofa (2 HT loveseats, one behind each), in a 17x18x8 room. With them being 30 inch deep, they would be almost up against the rear wall too.

Simple sketch of what it roughly would look like (I would do this in SketchUp but I think I mentioned I barely have any time to work on this ? ). Box external size, 30" deep x 60" long x 25" high





Is there an issue with the slot port also not extending to the side walls ? I tried to keep the holes square, so I ended up with either 2 x 5" x 5", or 2 x 4.5" x 4.5" as described below. Just figured might be less chuffing vs something like 7" x 2" or so ..

Before I prepare my cut list and go cutting though, please help me decide between these two options.




I really want to get as low extension possible, but maybe I am pushing things too much and lose too much up higher. For some reason the 14Hz tuned box just looks like a more appropriate option when looking at the SPL curve, and it pretty much has more output down to maybe 12.5 Hz ..

But the lower tuned box, maybe it will be a bit less strain on the amp (less potential clipping ..) based on the apparent amp power - VA (attached). But most importantly, there is just something magical about that 10Hz figure, and the lower tuned box will give me about 7dB more. Is this worth losing 2-3 dB from 12Hz up ? Maybe not much source with 10Hz is out there anyway. And maybe 104dB @ 10Hz is not much to be worth chasing anyway ? (though likely a few dB higher given there will be two subs). Can ~105dB @ 10Hz be felt in any way, or is this simply too low and not worth it ?

I will likely be listening at -25 volume level (~80dB), but planning to use a house curve that would bump up the 10Hz to maybe 30-35 dB hot (there will be a limiter set to prevent blowing up the driver, based on the WinISD cone excursion results, i.e. make sure it does not go more than 22mm).

The idea is, decide which option I like, maybe cut the panels for one box one weekend, start gluing a box another, add bracing the following, etc .. put a weekend in here and there with no time at all, so yeah, it is going to be a long one

30 dB hot is crazy talk, like 1000 times the power. You will definitely notice a 14 hz tuned box in the nearfield. 104 dB @ 10 hz @ 1m outside, so add 6 dB for a co-located box powered the same. That's 110 dB for a pair before room gain.



Based on your dimensions, you have a 26 foot room diagonal, and room gain should start around 42-43 hz. Even if you only ended up with 6 dB per octave room gain, dropping from 43 hz to 11 hz, you will add 12 dB minimum of room gain.

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post #3 of 81 Old 07-28-2018, 08:33 PM - Thread Starter
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30 dB hot is crazy talk, like 1000 times the power.

Haha, it is probably .. but that is why I would also set a limiter, so get as much as I can get, to be able to more closely achieve the equal loudness contour.

Given WinISD shows me 1W needed to get 85dB above 30Hz, 1000W is right in the ballpark of 1000 times the power

EDIT: To clarify, I am not going to be trying to achieve a response like the equal loudness curves, even at the volume level I normally listen to (calibrated 80dB at MLP is probably much more than 80dB at speaker, so +30dB is much more than 110dB (or much more than 1000W, etc ..). Nor will I actually be listening at +30dB, as the limiter would likely kick in before that (unless my volume level is really low), I would just have the DSP setup as such, in order to simply try to get as much as I can from the subs, and hoping that even at signals at 10-15Hz, I do feel something, even if a small rumble ..

My room is not quite rectangular to be honest, the front side (where the projector screen is), sort of breaks into 3 sides really, i.e. side goes to 45, few feet later, another 45 turn, then a few feet before the end another 45 turn, eventually reaching the other side wall at a 45 angle .. (4 x 45 = 180 , check ) .. so not sure how much the simple room gain calculations apply here .. maybe they do, don't really know.

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post #4 of 81 Old 07-29-2018, 09:46 AM
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I can't wait to see how this build progresses. I've been wanting to see someone try to get a really low tun out of a UM18, not just 17.5Hz like the full Marty, even at the expense 20Hz SPL.

I wish you the best of luck!

Based on your references to DSP, limiter, and 1kW I assume you will be using an inuke 6000dsp? Maybe if the build takes long enough the nx6000dsp will be available.

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post #5 of 81 Old 07-29-2018, 10:28 AM
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I can't wait to see how this build progresses. I've been wanting to see someone try to get a really low tun out of a UM18, not just 17.5Hz like the full Marty, even at the expense 20Hz SPL.
The UM18 models pretty much identically to the HT18 below 24Hz, and I built some 31+cf enclosures tuned to 11.5Hz for them. I went with 30cf because I was going vertical and the space would have been wasted otherwise, but 20cf is really the sweet spot for a UM18 tuned super low.

OP: Given the fact that you are building two of these, and that they will be nearfield, I would absolute go for the super low tune. You should end up with plenty of headroom to crank it as loud as you want and it will dig down to 10Hz. The one thing I'd plan for is to minimize chuffing as much as possible, as you'll be moving a ton of air down that low. I'd go with a single port, the biggest square/round port you can manage. Maybe a 6.5"x6.5" square or even better, an 8" round. I have a single 10.25" round port in each of mine and I've never heard them chuff under normal usage. I can make them chuff if I send a 1000W sinewave @ 11 Hz to them, but at that point every window in the house is flexing and the doors upstairs are slamming back and forth within their jambs.

Mine aren't nearfield, and I can only imagine how amazing those will be right behind you. I'm really excited about this build. Please update this thread often as you go.

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post #6 of 81 Old 07-29-2018, 10:47 AM - Thread Starter
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Thanks.

I don't own a router so adding a round ABS / PVC port , or something like Sonotube is not really an option, hence why slot ports.

You mean single port with same cross area (~40 in^2) ? yeah, don't see why a 1 x 6.5" vs 6.5" is a problem.

Is there any downside to going this route besides a bigger hole for kids to throw toys in ? Maybe WinISD should add this spec to their app too (how many toys per week get inside the cabinet)

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post #7 of 81 Old 07-29-2018, 10:55 AM - Thread Starter
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Based on your references to DSP, limiter, and 1kW I assume you will be using an inuke 6000dsp?

Yes, I already own a 6000DSP I'll be using. Granted 2 x 850W with 4 ohm drivers is 2 x 14 amp, way more than what a 15 amp circuit can handle, so I will likely not be getting the most out of this. Even with a 20 circuit amp, I doubt I can safely be driving this with 2 x 850W coming out of a single power outlet / circuit. But I guess it does not hurt to have the head room , and maybe in near future I can consider at least upgrading to a 20amp circuit / breaker for the iNuke to get a bit more out of them.
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post #8 of 81 Old 07-29-2018, 11:12 AM
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Thanks.

I don't own a router so adding a round ABS / PVC port , or something like Sonotube is not really an option, hence why slot ports.

You mean single port with same cross area (~40 in^2) ? yeah, don't see why a 1 x 6.5" vs 6.5" is a problem.

Is there any downside to going this route besides a bigger hole for kids to throw toys in ? Maybe WinISD should add this spec to their app too (how many toys per week get inside the cabinet)
No downside.

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Yes, I already own a 6000DSP I'll be using. Granted 2 x 850W with 4 ohm drivers is 2 x 14 amp, way more than what a 15 amp circuit can handle, so I will likely not be getting the most out of this. Even with a 20 circuit amp, I doubt I can safely be driving this with 2 x 850W coming out of a single power outlet / circuit. But I guess it does not hurt to have the head room , and maybe in near future I can consider at least upgrading to a 20amp circuit / breaker for the iNuke to get a bit more out of them.
A 15A breaker does not limit you to 15A of current. They can pass much more for short periods. My 6000DSP shares a circuit with all my other equipment, and I've never tripped the breaker. It's a non-issue.

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post #9 of 81 Old 07-29-2018, 11:22 AM
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No downside.


A 15A breaker does not limit you to 15A of current. They can pass much more for short periods. My 6000DSP shares a circuit with all my other equipment, and I've never tripped the breaker. It's a non-issue.
Yep, I don't actually have an inuke, but they have been thoroughly tested on this forum. The max output number (around 1000W iirc) is a burst, basically while the capacitors are discharging, not a continuous load seen by the wall outlet. That being said, it never hurts to upgrade, and no one will blame you for upgrading for any reason around here.

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post #10 of 81 Old 07-29-2018, 02:31 PM
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Very interested in this build and your thoughts on how it turns out.
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post #11 of 81 Old 07-29-2018, 02:47 PM
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Dual 5x5 ports are a little undersized in my opinion. I'd go with dual 6x6 if you can. Port might get really long for a low tune though. A single 8x8 is another option.

The 5x5s might be ok if you will only ever use 800w. But that driver can handle more and has more xmax too.

Model with 1600 watts and 28mm xmax and check out the velocity with dual 5x5s.
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Dual 5x5 ports are a little undersized in my opinion. I'd go with dual 6x6 if you can. Port might get really long for a low tune though. A single 8x8 is another option.

The 5x5s might be ok if you will only ever use 800w. But that driver can handle more and has more xmax too.

Model with 1600 watts and 28mm xmax and check out the velocity with dual 5x5s.
Looks like the cutting may need to wait until next weekend with all the good advice here

I was going to go with single 6.5 x 6.5, (42.24 in^2 , 37.72" long). I can try 2 x 6" x 6", but that would be 72 in^2, 68.5" long port. That is not a problem, I can just bend the port (like in the Marty Subs) along the back and bottom wall. But the biggest issue with that is that 1st port resonance falls down to 98 Hz. That is just dangerously low. I have it at 187 Hz currently with a single 6.5" x 6.5"

As far as the 1600W, 28mm xmax, WinISD shows me 22 xmax, and that is what I was trying to stay under ?

I do not even see how an iNuke can drive 2 x 1600W of a single outlet, unless I maybe use two iNukes, one each on a separate circuit.

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post #13 of 81 Old 07-29-2018, 05:28 PM
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Looks like the cutting may need to wait until next weekend with all the good advice here

I was going to go with single 6.5 x 6.5, (42.24 in^2 , 37.72" long). I can try 2 x 6" x 6", but that would be 72 in^2, 68.5" long port. That is not a problem, I can just bend the port (like in the Marty Subs) along the back and bottom wall. But the biggest issue with that is that 1st port resonance falls down to 98 Hz. That is just dangerously low. I have it at 187 Hz currently with a single 6.5" x 6.5"

As far as the 1600W, 28mm xmax, WinISD shows me 22 xmax, and that is what I was trying to stay under ?

I do not even see how an iNuke can drive 2 x 1600W of a single outlet, unless I maybe use two iNuke, one each on a separate circuit.
Yeah, you can't go above the 6.5"x6.5" at that tune without having port resonance go too low.

I think he meant 2x800W. I think you're in good shape with your build as-is.

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post #14 of 81 Old 07-29-2018, 08:45 PM
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... , and maybe in near future I can consider at least upgrading to a 20amp circuit / breaker for the iNuke to get a bit more out of them.
Yes, I had to go with a dedicated 20 amp to prevent blowing the 15 amp that was feeding it for some intense tracks I tried with my iNuke 6k. Unfortunately I also burned out 3 UM 18's doing that with some insane bass tracks like Bass Test 100 Hz to 5 Hz Ultimate Subwoofer Bass Test. I think the amp doesn't constantly draw the same load unless you are running a pure sine wave. Music and movie soundtracks constantly vary the amplifier's output. That is why initially the 15 amp breaker never tripped on movies or normal music, but did trip with the woofer test tracks.

So as @aron7awol says, it really should be a non issue. (Unless you try doing something dumb like I did and really try pushing things to the limit with some insane tracks).
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post #15 of 81 Old 07-29-2018, 09:19 PM - Thread Starter
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Yes, I had to go with a dedicated 20 amp to prevent blowing the 15 amp that was feeding it for some intense tracks I tried with my iNuke 6k. Unfortunately I also burned out 3 UM 18's doing that with some insane bass tracks like Bass Test 100 Hz to 5 Hz Ultimate Subwoofer Bass Test. I think the amp doesn't constantly draw the same load unless you are running a pure sine wave. Music and movie soundtracks constantly vary the amplifier's output. That is why initially the 15 amp breaker never tripped on movies or normal music, but did trip with the woofer test tracks.

So as @aron7awol says, it really should be a non issue. (Unless you try doing something dumb like I did and really try pushing things to the limit with some insane tracks).
Well darn, sorry to hear that. Did you have any limiters set based on WinISD modeling, i.e. see at what power you hit 22 xmax, and set the limiter as shown ?

I guess I better not play any test tracks, lol. I may just run some REW sweeps, lower dB first, try to EQ any huge peaks, and maybe slowly push it up to 105-110dB etc . to see how much of a flat response I can get down to ~ 10-12 Hz .. Doubt I will be playing any sine waves or crazy tracks like that (though it is tempting !)

To update, I only spent time today trying to calibrate my measurements with the straight edge and circular saw, i.e. given a known target size, where to clamp the straight edge in order to get the desired size once the skill saw makes a pass. I did this by cutting testing scrap wood, and with my ****ty DIY skills this took much longer than it probably should have . I guess I could have just measured the skill saw guide width, right up to the edge of the blade .. but alas, maybe I'll just use that as a verification step.

Cutting will likely be next weekend. It also gives me some time for any last minute model changes.
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Well darn, sorry to hear that. Did you have any limiters set based on WinISD modeling, i.e. see at what power you hit 22 xmax, and set the limiter as shown ?

I guess I better not play any test tracks, lol. I may just run some REW sweeps, lower dB first, try to EQ any huge peaks, and maybe slowly push it up to 105-110dB etc . to see how much of a flat response I can get down to ~ 10-12 Hz .. Doubt I will be playing any sine waves or crazy tracks like that (though it is tempting !)

To update, I only spent time today trying to calibrate my measurements with the straight edge and circular saw, i.e. given a known target size, where to clamp the straight edge in order to get the desired size once the skill saw makes a pass. I did this by cutting testing scrap wood, and with my ****ty DIY skills this took much longer than it probably should have . I guess I could have just measured the skill saw guide width, right up to the edge of the blade .. but alas, maybe I'll just use that as a verification step.

Cutting will likely be next weekend. It also gives me some time for any last minute model changes.
No limiters in software because Non DSP. After I burned up one, then yes I used the limiters set by the knobs. Had two LEDs showing so around half(?) power. Still killed two that way. So no, don't run test tracks. It didn't seem like there was crazy output when I turned down the channel gain. So I was suprised when they both went toast. Oh well. Waiting on some Ficar Audio SSD neos as replacements.

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post #17 of 81 Old 07-29-2018, 11:01 PM - Thread Starter
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No limiters in software because Non DSP. After I burned up one, then yes I used the limiters set by the knobs. Had two LEDs showing so around half(?) power. Still killed two that way. So no, don't run test tracks. It didn't seem like there was crazy output when I turned down the channel gain. So I was suprised when they both went toast. Oh well. Waiting on some Ficar Audio SSD neos as replacements.

I hope you did not run ported with no HPF set ? That would not take much power to break xmax.

Sealed a bit harder to break, but given enough power and depending on size of box, I take it they could reach the limits too.
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post #18 of 81 Old 07-30-2018, 07:29 AM
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post #19 of 81 Old 07-30-2018, 10:29 AM - Thread Starter
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Question, how do you clamp port rails when gluing ? I will be putting in a slot port along the back wall (port shares the back wall), so I need to glue about 6.5" tall port rail on that panel. While I can put a clamp where it starts, I won't be able to add any further up its length.

Should I just put some weight on it (though the rail is only 11/16" thick, so not sure how that would work).

Or maybe I need to invest into a small kreg pocket hole jig and screw it to the wall that way (after applying glue of course).

Or would just applying glue, and shooting brad nails through the wall from outside, might be enough ? (no clamps. .)
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post #20 of 81 Old 07-30-2018, 04:51 PM
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Glue and some dumbells is the preferred method around here. I would not use brad nails for fear it'll split the port rail piece. Once the rail is in place, the actual port panel will also hold it in place.
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post #21 of 81 Old 07-30-2018, 05:13 PM - Thread Starter
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Glue and some dumbells is the preferred method around here. I would not use brad nails for fear it'll split the port rail piece. Once the rail is in place, the actual port panel will also hold it in place.

I was actually thinking of putting the port in the corner, so there is only one rail, and the panel just sits on top of it on one side and and is glued sideways to the other wall.

See attached.

I guess having two rails might make things easier ..
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post #22 of 81 Old 07-30-2018, 05:37 PM
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bracing ideas with dowels . .

1 rail may suffice but I'd plunk a few pocket screws where it hits the side, maybe 8" apart.

KISS
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post #23 of 81 Old 07-30-2018, 06:06 PM - Thread Starter
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Thanks for the pocket screws tips fellas, sounds like that is what I'll end up using for the port.

As far as bracing, given the box is 60" tall x 30" deep x 24" wide, 3/4 ply, keeping spacing between adjacent cross braces around 8-12 inches, looks like I may need around 24 braces per box, per my rough calculations. 10 for the front to back, 10 for left to right, and 4 top to bottom. Cutting 48 cross braces for the two boxes in total, and gluing everything in place sure sounds like a lot of fun.

Maybe it will save me a bit of work using asarose247 idea above of using dowels instead. Still, I don't think there is getting away from the 24 pieces per box. Have to say, bracing already starts sounding like the least favorite part of the build...
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post #24 of 81 Old 07-30-2018, 06:34 PM
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Quote:
Originally Posted by alextr75 View Post
Thanks for the pocket screws tips fellas, sounds like that is what I'll end up using for the port.

As far as bracing, given the box is 60" tall x 30" deep x 24" wide, 3/4 ply, keeping spacing between adjacent cross braces around 8-12 inches, looks like I may need around 24 braces per box, per my rough calculations. 10 for the front to back, 10 for left to right, and 4 top to bottom. Cutting 48 cross braces for the two boxes in total, and gluing everything in place sure sounds like a lot of fun.

Maybe it will save me a bit of work using asarose247 idea above of using dowels instead. Still, I don't think there is getting away from the 24 pieces per box. Have to say, bracing already starts sounding like the least favorite part of the build...

A router with a flush trim bit would make life a lot simpler. Once you have one brace completed, rough cut all of the others, then use your completed brace to make them all exact. Any of the windows in the 'copy' braces can be cut slightly smaller with a jigsaw, attach completed brace and trace the cut lines with the router, the bearing will follow the original and make the copy exact.

Ask your doctor if DIY is right for you. Side effects of DIY may include anxiety, elevated blood pressure, lightheadedness, rapid heartbeat, skeletal muscle flaccidity, euphoria, psychological dependence, insomnia, confusion, blurred vision, implusivity, uncontrolled or repeated movements.
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post #25 of 81 Old 07-30-2018, 06:37 PM - Thread Starter
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Wish I had a router in my life .. maybe with the build after this one .. when my wife would likely divorce me .. I may get a router as a companion.
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post #26 of 81 Old 07-31-2018, 11:18 AM - Thread Starter
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Maybe a stupid question, but if adding a dab of some PL glue to the pocket holes, do I add it before putting the screw in, or after the screw is in?

Also, given that the ply I am dealing with is more 11/16" than full 3/4", would the kreg 1-1/4" pocket hole screws still work ? I worry they may poke through on the other side.
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post #27 of 81 Old 07-31-2018, 05:25 PM
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Quote:
Originally Posted by alextr75 View Post
Maybe a stupid question, but if adding a dab of some PL glue to the pocket holes, do I add it before putting the screw in, or after the screw is in?

Also, given that the ply I am dealing with is more 11/16" than full 3/4", would the kreg 1-1/4" pocket hole screws still work ? I worry they may poke through on the other side.

You can put PL in the pocket hole before putting in the screw, and put it over the top of the screw once it is in if you like.



Plywood that measures .721" thick is fine with 1 1/4" screws. If you are using a cordless drill with a clutch, set it between half and 3/4's of it's capacity.

Ask your doctor if DIY is right for you. Side effects of DIY may include anxiety, elevated blood pressure, lightheadedness, rapid heartbeat, skeletal muscle flaccidity, euphoria, psychological dependence, insomnia, confusion, blurred vision, implusivity, uncontrolled or repeated movements.
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post #28 of 81 Old 07-31-2018, 06:20 PM
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I worry they may poke through on the other side.

that's why there is the adjustable depth collar on the bit,

you'll need to run a few trial holes to dial in the adjustment

for my Rigid cordless the setting is a "7" ,

then I use a ratcheting screwdriver with another 6" #2 square bit and tighten the screws up to really snug, by hand . . .

i just really hate the idea of spinning one

but the PL3X is gonna put a good bite on things anyway . .

it is overkill but takes a few seconds and can assure "dero zefects"

hand checked - every one
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post #29 of 81 Old 07-31-2018, 08:48 PM
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I hope you did not run ported with no HPF set ? That would not take much power to break xmax.

Sealed a bit harder to break, but given enough power and depending on size of box, I take it they could reach the limits too.
No, sealed.

If bad sound were Faital, good sound would be almost impossible
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post #30 of 81 Old 08-04-2018, 11:06 PM - Thread Starter
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Regarding cross bracing (that I intend to do from 2" wide plywood strips), do you cut these the same length as the parallel panels to it, or do you make them maybe an 1/8" longer ... and possibly sand of as needed ?

It may end up a lot of sanding with as many braces as I will need .. but probably better than ending up being too short and having tons of unusable braces ?

As far as distance between braces
- on the wider side (27.8" between corners), it would be about 9.2" between braces.
- on the 24" panels (it would be) 8 inches between braces ..
- going bottom to top, along the 60" inch panel (58.6" between corners), it would be about 9.7" between braces.
(obviously due to width of braces, when I say 8" between braces, I mean center to center, edge to edge would be somewhat less. ..)

For a total of about 24 braces
- 10 side to side, 2 on one plane, 5 planes up
- 10 front to back, 2 on one plane, 5 planes up
- 4 top to bottom

If possible getting braces to touch each other when crossing (i.e. side-to-side brace with another front-to-back) and adding some glue to those areas.

Would this suffice ?

It is a long weekend here, so hopefully I get some time either tomorrow or Monday to do some cutting, but need to make sure I get the correct number and length of the braces (where most of the cutting time will be spent on really ..)
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