Refurbish/rebuild a Bang & Olufsen cx 100 shelf speaker
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Turning a destroyed Bang & Olufsen cx 100 into a new speaker. The only thing that will be left of the old speaker is the aluminum body. New speaker elements and custom oak panels will be made.
There will be experiments with two-sided milling, lasercutting foam and more.
PANG & OLUFSEN CXE Drawing v2.pdfSilly test of the drawing workspace in fusion 360Adobe Portable Document Format - 220.47 kB - 02/25/2019 at 22:17 |
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So since the mechanical parts of the speaker is done (except the crossover filter) finishing the appearance of the speaker is next on the list. I started sanding down the sides of the front and back panels so that it is flush to the sides of the speaker.
I started with a 80 grit paper and went up to a 320 grit paper to finnish it. I might treat the aluminum with some polish.
I used this mirka deros sanding machine for the job. you will not want to go back to regular sanding machine after using this one. it has built in dust collection through the sanding paper/grid and the accompanying vacum turns on and of automatically. its such a joy to use.
quite satisfied with the finnish. Now onto oiling. I am complety new in this field but after some recomandations I decided to use some pigmented hardwax oil.
First part of oiling was masking. I masked of all the parts where i didn't want to get painted.
The oiling went along well, but I did notice that: A: I was completely new at this and B: I used the wrong brush.
Quite happy with the finished color and texture!
Next up is gluing the front panel on and assembling the crossover!
Next on the to do list: Aluminum brackets for the backplate!
The bracket will server to functions: holding the backplate in place and holding the bracket for the crossover filter in place. I have just a little bit of aluminum before so this was an exiting part of the project.
There was some interesting aspects of machining this. first it was finding the right setting and then there where the holes which was going to be tapped. from my research I knew it needed to be 5mm in diameter before i manually tapped the holes. I made the holes using a 5mm drill bit. it was a very effective way of creating the holes.
I had some trouble milling it but that was mainly because of a crappy ebay 6mm endmill. After switching to a 6mm vhf endmill with shc coating bit it ran very nicely.
It turned out quite nice!
tapping holes.
The bracket in use!
It fit nicely and did not need any adjustments. Now all the main mechanical components are finished! Now onto building the crossover filter and sanding the cabinet!
I Milled my second back front panels and my back panels on friday! But the road there was a bit bump and I actually am milling the part again in cherry today. Let me explain:
The second panel got off to a rough start. The material was slightly misaligned (2mm) and since I had one 1mm of clearance I had to scrap the piece.
Before i did this job I talked to a guy about two sided machining. He shared a neat trick with me. By making a pocket in the extra sacrificial material one could make the piece fit exactly in that pocket. All alignment issues should be significantly reduced when combining it with dowels!
This worked very well!
The back plate was made as a one-side job.
Here is the finished back plate with test fitted terminals and screws. Now to the unfortunate thing that happened. When I temporarily mounted the front plate used a block of soft wood and a rubber mallet to fit it snugly in the aluminum cabinet. This worked perfectly for the first front plate. What i did not notice was that the second front plate had a crack down the middle. As I fitted the second front panel in it broke it half. Aand I did not have any material left since I misaligned my second attempt at a front plate. Therefore I am now making new front and back panels of cherry wood. I found out that even cherry wood was much cheaper at my local makerspace that what I paid for the oak at my lumber store. I Also learned a new two-sided milling technique that I am going to use on my back panels.
I worked some more on the bracket today that is going to hold the back plate on.
These back plate holders will be made in aluminum. It is sturdy enough to hold the load and nice material to tap into. This is the screws I am using:
I wanted something golden to make it stand out. These screws are m6 and I intend to tap threads into the brackets. I found this excellent sheet to find out what hole I needed to drill to get the correct thread.
https://littlemachineshop.com/images/gallery/PDF/TapDrillSizes.pdf
as show it states that I need a 5mm hole if the thread pitch is 1mm and 5.25 if the thread pith is 0.75. I used a thread gauge to find the correct pitch.
As I now know it was 1mm thread pitch I made a 5mm hole. then I found a m6x1.0mm tap and got to work.
It went very smoothly and was no problem using the screw.
The more I test such things the less errors I make during the machining. Hopefully.
Experimented a bit in the drawing workspace today. I attached a pdf in the project files. I might release the CAD model when it is finished. but it is a bit messy.
Please note: the pdf drawing is neither serious nor informative. Ill return on Friday with more milling.
Yesterday I started the task of actually making the front plate. Since this requires that I mill on both side of the plate this required yes, you guessed it, two sided milling. Since I have not done that before this was a very exciting experiment. It starts almost like any standard milling.
First I put on the material I am going to cut , but the first plate of material is just a second sacrificial plate. That's because I am going to use wooden dowels to align the oak I am going to cut in so that there is no offset when I turn it around.
I had learnt this dowel technique from a guy at my local makerspace. I have one in each corner outside the piece I am going to cut out of the material. This way the 6mm dowels restricts all the movement horizontally. I first tested (with scrap material) to align it with screws. This proved way be way to unreliable. As the dowels have the same diameter all the way it is a much better candidate.
First side done. Here you can see dowels and screws to restrict movement in all axis.
This was the nerve wracking part. Turning it around and see if it aligned correctly. I had 1 millimeter of margin on each side so precision was key.
It fortunately was within the margins! Next time I will put dowels in the cutouts for the speaker elements so it even more precise.
Temporarily mounted it to the aluminum case with a block of soft wood and a rubber mallet. Looks good!
Mockup with the screws that where available from the makerspace.
I tested the lasercut prototype plates and it worked beautifully!
This was the testrings to make shure the full range elements fit.
Testring for the tweeter. Tight but it should work.
Testplate to make shure the speaker elements fit in their pocket. It looks good!
I decided that I should make some lasercut templates to make shure that the frontplate measurements are correct. Using the project feature in fusion 360 I had some sketches that I lasercut out. Using the lasercutter is ideal for prototyping because it is so much faster to use than the cnc.
The material is 3mm plywood and is more than enough to check that the dimensions are correct.
It fits the aluminum case! I will bring my speaker elements to the makerspace tomorrow to check if they fit. Progress has been made!
Micro update:
The previous days has gone around to a lot of other stuff but i played around with some animations in fusion 360
I will maybe get some time to buy screws for the backplate bracket today.
Today's update is some updates on cadwork. Have remodeled the front plate to be one plate instead of three. Easier to deal with. Also started making the brackets that is going to hold the backplate in place.
Here you can see a detail shot of the brackets
I tried messing around with with depth of field in the rendering, but it just turn into blurry renders. Must experiment a bit more with the center of focus setting and blur setting.
Øystein
When drilling, remember that the drill bit has a tip angle. the tip angle is well, the angle of the tip in degrees. I found out my tip angle at the Würth website. Fusion 360 automatically calculates how deep it needs to go to make shure one drills through the hole. I made a bottom height offset of -2mm anyway since I had an extra sacrificial layer underneath the aluminum stock. 
David Matthew Mooney
Timescale
Myles Eftos