What magnets for magnetic cavity cover?

[RonC]

Hi All,

For my current build i would like to use magnets for the cavity cover.

I would like to use 4 magnets.

Does anyone know what would be a good size and strenght of the magnets to hold the cover but also not too hard to get is off?

Any experiences with this?

Thanks!

Ron

 

 

Edited Wednesday at 16:28 by RonC

[itu]

Nd. They are small and powerful. My fretless has 4+4 neodymiums that are Ø 4 mm. You want to open the cavity, use a plectrum: 

 

Edited Wednesday at 19:24 by itu

[velvetkevorkian]

Something like this I would think https://magman.co.uk/product/n52-4mm-x-1mm-disc-magnet-291g-pull-force/

[Matt P]

paging @Andyjr1515 the control cover on my swift is held on with magnets, I'm guessing he could point you to where they were bought from (it works very well on my bass)

 

Matt

[Rich]

13 hours ago, itu said:

Nd. They are small and powerful. My fretless has 4+4 neodymiums that are Ø 4 mm. You want to open the cavity, use a plectrum: 

 

Security! He used the P-word!

 

[itu]

...stolen from a g-word player. 

[SpondonBassed]

7 hours ago, Rich said:

Security! He used the P-word!

 

 

Stand still sir while I open your cavity with a plectrum.

[Andyjr1515]

I can't remember offhand but I'll have a look in the morning

 

[RonC]

On 28/01/2026 at 20:21, itu said:

Nd. They are small and powerful. My fretless has 4+4 neodymiums that are Ø 4 mm. You want to open the cavity, use a plectrum: 

 

 

Thanks! great idea, thats the best way to use a pick!

[RonC]

23 hours ago, Matt P said:

paging @Andyjr1515 the control cover on my swift is held on with magnets, I'm guessing he could point you to where they were bought from (it works very well on my bass)

 

Matt

I've found several websites were to buy them and they're cheap! Most importance is to find the right strenght, so 4 magnets hold the cover steady and it must be easy to open aswell.   

[Richard R]

On 29/01/2026 at 07:00, velvetkevorkian said:

Something like this I would think https://magman.co.uk/product/n52-4mm-x-1mm-disc-magnet-291g-pull-force/

291g pull force per magnet. That seems like quite a lot to lever open with a pl3ctrum as you would presumably need to lift two completely off the back and then use your finger?

 

 

[SpondonBassed]

7 hours ago, Richard R said:

291g pull force per magnet. That seems like quite a lot to lever open with a pl3ctrum as you would presumably need to lift two completely off the back and then use your finger?

 

With four magnets that's more than a kilo.

 

 

 

 

 

 

[Andyjr1515]

I used 3mm dia x 1mm thick magnets with a 0.19kg pull from First4Magnets on my last build.  I've used 5mmx1mm at 0.3kg in the past but that is a bit overkill for a standard size/weight hatch.

Edited 3 hours ago by Andyjr1515

[Andyjr1515]

1 hour ago, SpondonBassed said:

 

With four magnets that's more than a kilo.

 

 

 

 

 

 

Hmmm...not really.  You tend to pull the cover from one side - at the most breaking the pull of two magnets as one half of the hatch lifts up with the other two acting like a hinge.  But, even with that said, they are surprisingly powerful for such teeny things. 👍

[Frank Blank]

My fretless bass has a magnetic cavity cover, it was built by @Jabba_the_gut, he might be able to give you some info.

[Frank Blank]

I was concerned that using fingernails (or indeed a pick) would, over time, possibly damage the cavity cover or body of the bass.

@Jabba_the_gut came up with a solution...

 

 

Edited 1 hour ago by Frank Blank

[Richard R]

Is that a metal insert?

Blimey! Hats off to @Jabba_the_gut