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Stevie’s 12” FRFR Cab Build Thread (Basschat Cab v3)


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12 hours ago, LukeFRC said:

4x 600mm sash clamps for £16? eBay item 133184878318 

cheap enough it would be daft for me not to buy them. Think I’ve got everything but the screwfix parts now, and there’s a screwfix 400m away! 

Good shout Luke. I tried to make do with the clamps I had and made a slight error. I clearly did not check that the side panel was correctly seated all the way along and have a 2mm curve on one side. The cab is square too and bottom and one painted,  I doubt anyone but me would notice. I did investigate ways of loosening the glue, by heat, to try to reposition it but the glue holding the plywood together is usually only guaranteed to 100 degrees C. I suspect I would have to excesd that to loosen the joint glue, running the risk of plywood De-lamination.

So mine really  is one of a kind, I give you Banana  Cab 
 

EF562086-217C-40F0-89FD-5ACCAE2850E9.jpeg

Edited by Chienmortbb
Spelling and not wanting to upset brexiters.
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36 minutes ago, Chienmortbb said:

Good shout Luke. I tried to make do with the clamps I had and made a slight error. I clearly did not check that the side panel was correctly seated all the way along and have a 2mm curve on one side. The cab is square too and bottom and one painted,  I doubt anyone but me would notice. I did investigate ways of loosening the glue, by heat, to try to reposition it but the glue holding the plywood together is usually only guaranteed to 100 degrees C. I suspect I would have to excesd that to loosen the joint glue, running the risk of plywood De-lamination.

So mine really  is one of a kind, I give you Banana  Cab 
 

EF562086-217C-40F0-89FD-5ACCAE2850E9.jpeg

When I was doing the dry fit I thought that might be a risk of the super tight fit. 

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13 minutes ago, LukeFRC said:

When I was doing the dry fit I thought that might be a risk of the super tight fit. 

Fully agree. Use as many clamps as you can to get an even closed joint. I think 3 clamps per join is ideal or use a piece of scrap wood under the clamp to help spread the clamping force. If you have any,  G cramps can be used from the speaker, port and horn openings as well.

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That's definitely something to watch out for. You can check the fit of the joints visually at each end, but it's difficult to know what's happening in the centre. A steel rule like that one is a good idea. Even better is a steel square. Or you can check the fit against a straight piece of wood.

My number one tip would be to test the fit of the next panel before the glue sets on the piece you're gluing. Maybe even check the fit of the next two panels if you can. The interlocking design means that if one panel is slightly out, you might not be able to fit the other panels.

 

Edited by stevie
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The specification calls for 15.2mm rebates and 15mm plywood. That's not a huge amount of leeway. On the sample I received from the very first CNC company I used (not the current one), the rebates were slightly undersized and I had to take a Stanley knife to open them up. Not funny.

Although I haven't assembled any of the current batch, I expect that taking the roughness off the mating edges with some sandpaper will make things easier.

 

Edited by stevie
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3 hours ago, stevie said:

The specification calls for 15.2mm rebates and 15mm plywood. That's not a huge amount of leeway. On the sample I received from the very first CNC company I used (not the current one), the rebates were slightly undersized and I had to take a Stanley knife to open them up. Not funny.

Although I haven't assembled any of the current batch, I expect that taking the roughness off the mating edges with some sandpaper will make things easier.

 

All good tips. The straight edge is a good test. If the joint is flush top and bottom and there is less than1mm gap at any point, You should be OK. 

I did use clamps from the speaker and port cutouts but in the end it was my failure to check that did for me. The other side is under 0.5mm our top to bottom.

I don’t think you would see it direct from the front, I only noticed it by looking along the side as I undid the clamps. It says something for the design though  that it is still square top and bottom. 

After sleeping on it over night (the thought of living with the error not the cabinet), I am OK with it.

 

Edited by Chienmortbb
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6 hours ago, stevie said:

Thanks for pointing it out @ChienmortbbHopefully, it will stop others making the same mistake.

The glue will have filled the gaps - so I don't think there'll be a problem in practice.

Having thought about this I suggest that during the dry fit, a pencil line is drawn all around the baffle where is meets the sides, top and bottom. That will show up any problems when the dry fit is disassembled and will also have shown the error when I glued it together. 
 
ít is also probably worth doing that with the braces too. 

Edited by Chienmortbb
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I'll post some pics in a while.  Something I learnt on the first joint I glued up is that this is super thirsty ply and needs rather more glue than you might be used to using.  I'm gluing both surfaces, and also giving each face one a coat of pva, leaving for a minute, then giving another coat.  It just soaks straight in.

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12 hours ago, converse320 said:

I'll post some pics in a while.  Something I learnt on the first joint I glued up is that this is super thirsty ply and needs rather more glue than you might be used to using.  I'm gluing both surfaces, and also giving each face one a coat of pva, leaving for a minute, then giving another coat.  It just soaks straight in.

I agree with that. I usually use more glue but followed the instructions on the bottle to the letter. I had virtually no squeeze out and that would worry me if my mistake had not been glued firmly on. 
 

Of course PVA sticks very well to dried PVA so there is no problem coating the wood first. My only worry, and maybe my problem was that it the walls of both the routed channel and the mating board swell that could cause a problem. 

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I have also used a coat of PVA to prime a porous surface before gluing and it does work well. My concern would be that the rebates are fairly tight even when dry fitted. The thickness of a layer of PVA (plus any possible expansion of the wood as mentioned by @Chienmortbb) might make it more difficult to close the joins effectively unless extra clearance was added by sanding first. Looking forward to hearing how @converse320 gets on and seeing the pictures.

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11 minutes ago, stevie said:

You might like to consider spraying the input panel with that paint before gluing it in.

I am not using the kit input panel so that I can keep my options open for fitting a power amplifier inside the cab later. I plan to fit a sheet steel input panel with a gasket and fixed by screws from the inside. It will eventually have a combined XLR TRS input connector, power inlet & switch and a gain control in the panel as well as an extension cab  speakon output - which will come in handy for initial testing with my GK MB500.

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5 minutes ago, basstone said:

I am not using the kit input panel so that I can keep my options open for fitting a power amplifier inside the cab later. I plan to fit a sheet steel input panel with a gasket and fixed by screws from the inside. It will eventually have a combined XLR TRS input connector, power inlet & switch and a gain control in the panel as well as an extension cab  speakon output - which will come in handy for initial testing with my GK MB500.

Of course, I remember you mentioning that. Fascinating project!

Still, it could be an idea for other builders. I sprayed my input panel matt black to contrast with the much rougher dark grey Tuff Cab elsewhere. Unfortunately, I had already glued the input panel on, which made it a lot trickier.

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2 hours ago, basstone said:

I have also used a coat of PVA to prime a porous surface before gluing and it does work well. My concern would be that the rebates are fairly tight even when dry fitted. The thickness of a layer of PVA (plus any possible expansion of the wood as mentioned by @Chienmortbb) might make it more difficult to close the joins effectively unless extra clearance was added by sanding first. Looking forward to hearing how @converse320 gets on and seeing the pictures.

I'm using PVA glue - all I mean is I give it 2 coats of glue on each bit, no need to let it dry first.  They joints go together fine, no sanding of panels needed for me, as long as you have enough clamps.  I'm just trying to avoid dry joins as its very absorbent ply.

Edited by converse320
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