BB3 Build - Building a chassis

Thanks for the kind words.  I was trying to make it look non-DIY...  I may be slightly obsessive and love the challenge of trying to get a decent finish. 

I'm not sure if I have the most efficient (and cost effective) manufacturing tools and methods. 🤔😂

The current BB3 case is rather lovely too.

The Trend blades seem to be a decent price too. I will have to check my table saw and make sure I order the correct size. Thanks 

KEEPING A LID ON IT?!

How to attach a lid with no fixings on show?  I needed a straightforward and effective solution to keep the lid securely in place.  I didn't want fixings visible on the top, front, back or sides, so would have to go from underneath.  The top is 4mm thick, so too thin to blind tap holes in its underside.  Instead I opted to bond another 4mm plate to the underside of the lid.  This plate is tapped with 2 x M6 holes which line up with long (81mm) bolts coming up through the base.  



I did some experiments with different bonding adhesives and settled on Everbuild Stixall. This is a flexible adhesive/sealant and was extremely strong when cured. It has the added benefit of adding extra damping to the top plate. As a test I bonded two ally plates together and put a M6 thread into one of them. I then fixed a bolt into one plate and tried to pull the plates apart... The adhesive won! The thread, admittedly only 4mm of engagement, stripped before the adhesive failed. I wasn't too worried about the thread stripping on the chassis as I wouldn't require excessive tightening forces to hold the lid on safely.

Here is an image of the 2 x M6 bolts coming up through the base:



The lid fixing method has the added benefit that it tensions the top and bottom of the chassis together. This reduces vibration and ensures a very solid construction - completely OTT engineering!

Lots of excellent ideas here. Great build thread for a case 

Thanks from me too for sharing 

It's a pleasure and fun to do the thread too. It was much easier to work aluminium than I'd anticipated - I wanted to share in case others may be tempted to DIY with ally too.

(this is the warm up thread... The case is relatively simple compared to the sub and speakers! 😂)

Wouldn't mind building a sub 

THE VALVE WINDOW:

There were quite a few decisions concerning the valve window, for example:

- does it go on one side of the chassis or across the back or front?
- is it raised up on standoffs or flush to the top?
- is is toughened glass or plastic?
- is it clear or tinted?




I'm sorry it's now too late to debate this... As it's now finished.

As you can see, it was decided (with Oli, amongst others) to put the window on the right and to have it flush to the top.

I looked into toughened glass, but it would have been quite expensive (about £70). Strangely more expensive because it was so small. Instead, I chose 5mm thick acrylic! I know, I know, this completely spoils the bulletproof nature of the box! Any decent marksman can now obliterate the window and Oli's wonderful work beneath!!!

Next choice was clear or tinted - these images show glass look acrylic and light tint acrylic:




I preferred light tint as it allowed a good view underneath, but was slightly more subtle and looked pretty slick with the brushed aluminium look.

Here is a quick sketch of how the acrylic was mounted:



The acrylic was cut 20mm wider/longer than the window to give a 10mm underlap all round. I used the table saw to remove acrylic to a 3.8mm depth in a 10mm border all around. This allowed the acrylic to sit a fraction (about 0.2mm) below the top of the aluminium lid. I used the Stixall sealant/adhesive to bond the thin acrylic underlapping lip to the underside of the lid.

This is the finished valve window in place with the PCB underneath:

Yup, looks excellent 

Unfortunately, I don't have pictures of the this process, so hopefully words will suffice... I set the table saw blade to protude about 3.8-4mm and used a digital depth guage to check it. I then used some scrap acrylic to test the depth of the cut. Once this was correct I started to cut the actual window.

The acrylic was 110mm x 256mm (a 10mm underlap on a 90mm x 236mm valve window. For the 10mm underlap border I first set the table saw fence to 107mm and ran the acrylic through lengthways on both sides (with the top of the window facing down onto the table saw top). These first two cuts gave a 3mm wide slither on both sides. I then moved the fence to 104mm and ran both sides through. Then fence at 101mm and both sides through. There was now a 9mm border on both long sides of the acrylic. I required a 10mm border so start moving the fence a tiny amount (0.2mm) and checking the acrylic in the aluminium hole unitl it just fits.

The next step was to cut the 10mm wide slither border on both ends. I made a plywood jig to hold the acrylic at 90 degrees to the fence and once again made a series of 3mm wide cuts to both ends of the window. The fence moving gradually in until the window length was correct.

The width and length of the acrylic (with 10mm underlap) were now correct, but more work was required to get it to fit... The valve window hole in the aluminium had radiused corners (from the 5mm router bit). Therefore I used a needle file to file down and soften the corners on the acrylic window. A little was filed, then it was checked for fit repeatedly until it slotted into the aluminium. This had to be exact, as any obvious gaps would spoil the look of the window.

The 10mm wide (1.2mm thick) acrylic slither was quite delicate, but OK to handle carefully. It was super solid once glued in place on the aluminium.

Hopefully that makes sense. It sounds highly laborious, but wasn't too bad as the table saw it a great bit of kit and the acrylic is very easy to cut. The whole process took about 1 hour.

PCB, TRANSFORMER AND WIRING:

The chassis was pretty much finished, so it was onto wiring and fitting the PCB and transformer.

Oli very kindly sourced the same transformer used for the BB3 and it arrived potted and shielded.  The transformer was placed as far from the PCB as possible and was bolted into M4 threaded holes in the base of the chassis.  The PCB sat on 9mm standoffs - these were chosen so that the valves sit just a few mm under the acrylic window.  



My first iteration had no twists... [My engineering skills are much better than my electronic skills!!!] Oli was very helpful and advised me to improve things by adding twists to the cabling:



I used Neotech copper 24AWG hook up cable for the signal wiring. The power switch LED took a 0V/7V feed from the PCB (Oli advised where).

The keen eyed will also notice a plate in the centre of the base. This is a 2mm aluminium plate which has been bonded on with a flexible sealant - this is to provide additional damping.

Yep, an M4 8mm bolt which goes through both.

Great, you'll love the sound no doubt, it's especially rewarding when you build something yourself. 😀👍

Thanks! I didn't build it that quick, this was all written retrospectively - all finished about 2 weeks ago. It weighs 8kg, so not too bad.