Creative and Unique Control Cavity Covers?

Discussion in 'Luthier's Corner' started by BassHappy, Jun 5, 2016.

  1. wraub


    Apr 9, 2004
    ennui, az
    Maybe some variant of Dingwall's battery cover, with the magnets and finger holes?

    Atshen likes this.
  2. wraub


    Apr 9, 2004
    ennui, az
    May I ste... appropriate this idea? :)
    BeeTL likes this.
  3. Means2nEnd

    Means2nEnd Supporting Member

    My latest back side... Double ply wenge with magnets for control cavity and separate battery box. Simple, clean, super strong.
    Back 2.jpg Back 4.jpg Back 3.jpg
    BeeTL, Barbaric.Eric, Atshen and 4 others like this.
  4. HaMMerHeD


    May 20, 2005
    It's been done a fair amount before. I vaguely recall our fair @lbridenstine using it on one build. I could be mistaken, but I know I've seen it here in LC before.
    BeeTL likes this.
  5. lbridenstine


    Jun 25, 2012
    *Insert self-promo about how there will be a demo of this in my next build series video... if I ever actually get the guitars and video done*

    I definitely copied this idea from someone here, it may have been Bruce. Thank you for sharing the genius idea!
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  6. Gilmourisgod


    Jun 23, 2014
    Cape Cod MA
    If you have the skills, nothing nicer than a nearly invisible grain matched wood cover.
  7. Hey Gilmour, hey Lisa

    As I mentioned, the grain matching is still absolutely an option. The clamshells on my 3 acoustic models are not glued together yet. It's really a very simple matter of a nice THIN 4" diamond plug cutter and carefully making the 4" hole though the back of the body with a drill press. Then, it's easy enough to fabricate a round retaining ring - around 3.75" or maybe 3.50" and fasten it into the bottom of the body leaving a retaining ledge. You can then have the magnets installed and hold the cover in place from there. The reason that grain matching is not ideal and doesn't solve the problem is that two of the three acoustics have Honduras mahogany backs and while it's genuine, smells like bubble gum and is fantastic light wood, the grain structure is pretty ordinary. Nothing overly special going on. The idea is to dress it up a little and create some flair on what is a more or less a pedestrian back. So I may do the flamed maple back one as a grain matching cover, and do the leather thing on the other two. While I appreciate all the kind comments very much, I have some issues with some of the suggestions. I would want the hole perfectly thin so you can barely notice it is there, and I certainly don't want latches or hinges, or finger pulls or indentations etc on the cover or the back of the body. But that is just me. And the whole idea of having a cavity cover is to avoid having a separate battery box. The battery will be inside the cover which is what I want.

    I found a round leather design that I LOVE and it's 4.25" around, which is fine.

    I am think of shielding the inside of the aluminum plate with copper tape. This tape is 5" wide and will allow me to cut an exact 4.25" disk and stick to the 1/16" thick aluminum disc.

    Screen shot 2016-06-11 at 1.58.26 PM.png

    With piezos I am not sure I will need any shielding but for a couple of bucks it's worth it to me to go ahead and do it, just in case.

    I found a guy who custom cuts 1/16" aluminum discs to size and the price is more than reasonable. He does them on some type of circle cutter, and as below the 3" ones are $2 each. I will wait until I get the leather, make sure it is exactly 4.25" and then ask him to make me four aluminum discs in the proper size. That way I keep my options open on the maple back acoustic, I may prefer the leather design on that one too. As always, when the actual elements are in front of you - it's much easier to make final design decisions.

    Screen shot 2016-06-11 at 2.05.08 PM.png

    Then, I will order 4 of the 5" fridge magnet circles and trim them down to 4.25" or to whatever diameter the leather happens to be.

    Screen shot 2016-06-11 at 2.11.32 PM.png

    So this is the plan:


    I am going to spring for these 3" magnet pullers which pull up to 95 lbs. I think they look nicer than the others and they are cheaper. Since they are $10 bucks each I might spring for two. One for the bench and one in the guitar case.


    I don't know if anyone has recommendations on what brand of tiny magnets I should get to hold the covers on - Lisa, could you let me know what you are using if you see this?

    Someone from an earlier post talked about elegant solutions and being creative and particularly having an innovative, practical and non-abrasive way of getting the cover on and off. While I don't know yet if this will work, I certainly believe it will - and the entire price of finding out - including the leather designs is about $60 bucks in total.

    So, everything has crystallized for me, and as usual, I love this place and I thank all of you for playing along. If it doesn't work or I hit a snag I will figure it out from there. But I think this is going to be the exact solution I was looking for.

    EDIT: I decided to get the 25lb magnet puller which looks the same to try for $4. That should be enough pull, but we will see. I also got a single sheet of 17" X 12" fridge magnet material for $17. They had a minimum order of 10 at Magnet King. Since I would have had to trim them down anyways, I may as well just trace them and cut them out!
    Last edited: Jun 11, 2016
  8. Bruce Johnson

    Bruce Johnson Gold Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier

    What's the fridge magnet sticking to? Are you putting steel plugs down in the body? One simple trick is to put some flat head steel wood screws down into the shelf. The fridge magnet will stick to them. Plus, they have the added benefit that the screws can be turned slightly to fine tune the height of the cover plate in relation to the surface.

    Also, what's the point of the copper shielding tape? The aluminum plate, assuming that it's contacting ground, will provide plenty of shielding by itself, more than the copper tape.

    I suggest that you simplify it by making up a steel disk, and epoxy your leather disk to that. Then set three small magnets down into the body shelf. Any small Alnico rod magnets, epoxied into drilled holes. Your big magnet tool will pull the cover off by attracting the steel disk. The steel also works fine by itself as a shielding plate, although you could add the copper tape on the underside to make it prettier looking.
    Last edited: Jun 11, 2016
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  9. lbridenstine


    Jun 25, 2012
    Rick, I just searched "Neodymium magnets" on amazon and look for 1/4" x 1/16", which is the size that I like to use and pick whichever one is the best deal at the time. Last time I bought them was in 2013 and I got a 100 pack for $12. I'd link it, but that listing is gone now.
    BassHappy likes this.
  10. Hey Bruce

    All great suggestions. and the screw idea is stellar as well to adjust the height. In doing my newbie research, I found that some types of steel are magnetic and some aren't - even in the stainless realm as below.

    Screen shot 2016-06-11 at 6.36.46 PM.png

    Screen shot 2016-06-11 at 6.19.37 PM.png

    On ebay they didn't mention which kind of steel the 4" discs are and they have regular steel and stainless in 1/16" and 1/8". Since I don't have regular access to the shop I figured it would be easiest at $2 bucks each to get the discs pre fab. So is all stainless steel magnetic material? Not according to the above. And would you then use stainless screws in the body opposite the magnets?

    The steel and stainless were both quite a bit more expensive and heavier than the aluminum. I figured it would be better to go with lighter aluminum and use the fridge magnet idea - as I know that aluminum is generally not magnetic. I also figured that I would epoxy the edges of the the fridge magnet to the leather and to the aluminum - and the fridge magnet would connect with the pull magnet through the leather and pull that cover right off. I also have heard (be nice, I am certainly still in the newbie category) that copper is a much better shield material than aluminum. Since the tape is reasonably priced and adhesive backed, I figured I would just slap it on there for good measure like a little insurance policy.

    So thanks for all..
  11. Thanks Lisa!

    Will take a look.
  12. By way of an update, I heard back from the guy making the discs. He wants $3 each for 1/16" X 4.25" in aluminum, but I think he is the same guy doing the stainless steel ones as well. I asked him if the stainless steel he uses is compatible with a magnet and to give me a price on 4 of those. So thanks to Bruce that may mean I could bypass the fridge magnet material altogether. If the stainless works out - I will do as Bruce has suggested, and epoxy the leather right to the stainless disc and then use the copper shielding on the inside. Thanks Bruce!
  13. T_Bone_TL


    Jan 10, 2013
    SW VT
    Copper foil is hardly needed on a stainless steel disc - while it's a "relatively poor conductor" is still a conductor, and you are not trying to ram 900 amps through it. 1/16" stainless conducts roughly as well as 1.4 -1.7 mil copper foil. Your tape appears to be 1 mil when I track down the manufacturer site. Do whatever makes you happy, but I doubt you'll be able to hear a difference in a blind test.
    Last edited: Jun 13, 2016
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  14. Bruce Johnson

    Bruce Johnson Gold Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Yes, I was going to mention that. Copper does have lower resistance than aluminum, steel or stainless, which does make it better for shielding. But that really only matters when you are shielding with thin films like paints or foil tapes. A 1/16" thick plate has such low resistance anyway, that it doesn't matter what metal it's made from. Even stainless will be less than an ohm across the plate. Adding copper foil tape to a metal plate isn't going to add anything practical to the shielding.

    Most stainless sheet/plate stock that's commonly used in industry foe sinks, cabinets, etc., is 18-8, or about equal to 304. Magnetically, it's a little weaker than mild steel, but it will stick fine to magnets. The stainless alloys which are almost non-magnetic are the more exotic and expensive alloys, which are used in chemical plants and aerospace.
    Last edited: Jun 14, 2016
    BeeTL likes this.

  15. Perfect, thanks Bruce. Man, I can't believe how much there is to learn. Even the simplest of tasks seem to have their ins and outs and pitfalls. While I am perfectly willing to learn by trial and error - or I should say trial by fire - anything that can aid in getting it right the first go-round is invaluable. I really appreciate your taking the time with this.

    Just got the email back this morning as below - at least for the moment, the $3 aluminum is looking good. The gentleman doing the inexpensive discs on ebay has stainless, but it is not magnetic as below. Of course, banging out 4-4.25" round stainless magnetic plates is child's play to a guy like you, but I love that I can get these for $3 each - and in the end the fridge magnet should work fine.

    Screen shot 2016-06-14 at 7.38.40 AM.png

    I don't know if Keith mentioned it or not but he has agreed to teach me how to fret the five necks, so I hope to be seeing you. I am doing the barn walk-through soon, and that is a big moving project for me - if that negotiation goes well. So that might be a bit of a distraction/wrench in the works. Plus I have my 40th wedding anniversary coming up August 1st and we haven't even decided yet what we are doing because of the barn project. I have a suspicion that if we get the barn we may throw a little party.

    The necks should be finished in the next couple of weeks, but I will still have to cut out the headstocks and drill the tuner holes. They will be slotted but not fretted. I wish I had the budget to have you and Keith make all five necks from scratch. If these designs work out - I want to go with set necks not bolt on. I am using bolt on now so if these basses aren't as successful as I hope - I can re-use the necks.

    So yes, the plan is to show up out there with the five necks and Keith and I are going to do a marathon fretting session and he is going to teach me the art. It would be great to meet you and of course, lunch is on me for all the work you have done for me. If you are busy we will order out or I can pick up some food locally. My treat. If you want, I am happy to bring the Performer pickups along if you think they can be re-finished with a scratch proof paint or plastic or something. I just hate to see you make up another set of pickups for cosmetic reasons if there is another way.

    I don't think I mentioned it - but I have settled on five different piezo pickups for these basses. Fishman are kind enough to be making me a special under saddle passive pickup, similar to the ones which were in the Martin Acoustic basses for years. Because they use individual pickups on the bar, they needed to make it special according to my 3" saddle coffin size and my exact string spacing.


    The other solid body will be the active Fishman Matrix Natural 1 - it's the same one that is in Rob's "Mouse" models and also the ones Keith is currently dealing with in my Fender Hollows.


    As far as the three acoustics go, one is using a conventional steel German ETS piezo bridge with a tail piece and a Richter preamp.


    Also, Joe at Shadow in Germany has donated a prototype of their new HD passive pickup for me, and I am working on helping him perfect it. Shadow makes pickups for almost every instrument you can imagine, but surprisingly, they don't have an acoustic bass guitar model - but they do have an upright model. He bumped around the guitar model for me and sort of optimized it for bass guitar. He sent along a preamp and a volume/tone control to use. He told me the level is low and in the end he thinks I will need the preamp. I am very disappointed - I have been waiting for this for weeks - and I really wanted to avoid batteries altogether - but hey, the proof will be in the sound.


    For the third acoustic, I have a dual B-Band pickup system also made in Germany - with an under saddle pickup and an adhesive film type pick up as well. It has a volume and blend control.

    B Band.png

    While I was originally just going to test these and use the same set up on all five - I am now thinking - why not go ahead with the installs and make them all different initially? I will try to stay generic on the four under saddle installs so they can be swapped around. Over time I can make adjustments and replace with the ones that test out more to my liking - and swap things around as needed.

    So that is it for the moment, thanks again.
    Last edited: Jun 14, 2016
    BeeTL likes this.
  16. Hey T Bone

    Now that I am going with the aluminum, it takes 10 minutes to cut out the copper tape and slap it on there. If it helps with the shielding, great - if it doesn't it will look much nicer than a scratched up aluminum plate - and it certainly can't hurt anything as far as the shielding goes.

    I am going with my original design and instincts since stainless is not an inexpensive option at this point.

    EDIT: I got the leather for the control covers and I am in luck! They are already laminated really well to thin sturdy wooden discs. Don't need to do stainless or aluminum. Haven't tried it yet because I don't yet have the fridge magnet material. As soon as it comes, I will cut one out to size and see if the magnet puller will work on it alight. If it does, then it's just a circle of the copper tape over the back of the fridge magnet and I am done.
    Last edited: Jun 20, 2016
    BeeTL likes this.
  17. Beej


    Feb 10, 2007
    Vancouver Island
    And stainless-clad refrigerators... :D
  18. JayGunn

    JayGunn Supporting Member

    Jan 24, 2010
    Chapel Hill NC
  19. Means2nEnd likes this.
  20. earlysecond

    earlysecond In Memoriam

    Jan 26, 2016
    Exactly what I did on my last build! Only I have no screws I have Neo magnets and 3 locating pins. If you set the guitar on the edge where the cover rests and spin it, it does pop off. BUT I am not quite done with it either. I used the thinnest blade I have for my bandsaw and really took my time. I only lightly sanded then built both cut edges back up with epoxy glue and hit those areas with a couple extra coats of clear.

    The only caveat is that you must still have a margin on the outside of the guitar to reshape so that it is not undersized. Plus I may be missing something but would there be a way to do this on a guitar without a back. I could see a parital resaw but that could get sticky! I beleive that I will stick the the magnet approach but not always be able to use THE piece of wood which is part of the original back!

    Wait, that guitar above is a neck through. Wings must be chambered and have a back?