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Thread: making J bass covers

  1. #1
    Supporting Member StarryNight's Avatar
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    making J bass covers

    I've been seconded to make a few different 5 string J bass pickups. Some are unconventional and I can't source any 5 string J bass covers that are blank. My only option is to construct them out of wood or plastic. Any of you gents have some wisdom to impart on the subject? The bass is a Warmoth product with routes that match the contour of the pickup (i.e. not a rectangle) so my tolerances are going to be pretty tight. If it's going to be wood I suppose I could either build a 5 sided "box" from veneer (maybe laminate a couple sheets together for strength) and glue on the 4 mounting hole 1/2 rounds, or mill the whole thing out of a solid block. If any of you have done this before I'd appreciate some tips. thanks!

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    You could make a simple mold and cast the whole thing in a black potting epoxy or polyester resin. What are the dimensions of the routs? You can buy blank 5 string shells that are 4.062" long, i.e. halfway between the Fender "extended" neck and bridge covers which are 3.95 and 4.125 respectively. There are also 4.5" long covers for sale somewhere because lots of other makers seem to have no problem locating them.

  3. #3
    Supporting Member StarryNight's Avatar
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    ooh, I never thought about casting in resin. I have some aluminum I could mill out for a mold but I'm not sure what I would use as a release agent. I'm also making a few different types of J bass pickups for him (with different magnets and sizes) so I would need a few different molds made up. Not sure if it's worth it. I'm meeting up with the owner on Monday to take measurements. It's a Warmoth 5 string deluxe J bass. the website says pickup sizes that fit are 4" for the neck and 4.125" for the bridge. My google skills must be off as I can't find any blank 5 string j bass covers. I would think the mounting hole spacing would need to be exact as well. Not sure if there is variation there among cover makers.

    I also thought I could purchase standard 5 string covers from Mojotone and mill or sand the tops off and replace with blank plastic that I could drill out as needed.

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    ToneOholic! big_teee's Avatar
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    Quote Originally Posted by StarryNight View Post
    My only option is to construct them out of wood or plastic.
    These might be a good candidate for 3D-printing. The catch is that you have to find someone willing to draw up the pickup cover in a suitable CAD program, and then get access to a 3D printer. If there is a Hackerspace near you, or even a community college, this may not be too difficult. 3D printing is all the rage lately, and even some high-schools have 3D printers. Tinkerine (3D printer manufacturer) is local, in Delta, BC - maybe they might have some leads for you.

    Good luck!

    -Gnobuddy

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    I've had issues with air bubbles and final strength when using casting resins. They really need a filler material to give them strength. My preferred way to make covers is to use GRP and build a simple mould. I've used this plenty of times with excellent results. The advantage of this is it can be made really thin and still have plenty of strength - much stronger than any commercial cover. There's an infinite range of products available. I use paste wax as a release agent and if using a metal mould the cured object can be released in hot water more easily.

    For limited production you can make a solid, dummy cover in wood, plastic or metal (or use an existing cover and fill the holes) and take a female cast off this (you need to lay up the glass on the inside). There are a number of ways to take an impression in rigid or semi-rigid materials. I've used silicone in a potting box to give a peelable mould. Once you have a female impression you can paint on the gel coat and let this go off before layering up glass mat or chopped glass.

  7. #7
    Supporting Member StarryNight's Avatar
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    well Jiminy Crickets! I thought I searched aliexpress but obviously not good enough. Dimensions look pretty good too. Worth a try at least. Thanks Terry!

    Mick, I've been goofing with Fusion360 for a few months now. I could easily draft up a CAD model of these pickup covers. I don't know anyone with a 3D printer but I'm sure I could find someone. Interesting idea! Eventually when I get my CNC machine running I might be able to mill these in house with some decent repeatability. I'm still a month or two away though.

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    Milling would probably be a waste of your time (and your CNC machine's). The finish on most 3D printed parts is not going to cut it. Just email that seventh chord guy in China and see what a 200 or 500 piece order would cost and then you could be everyone's best friend.
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    If you want to try casting, there is a wide range of two-part urethane casting resins available. I used to do a lot of model-making in the film and television industry and we used a few different resins from the Smooth-On company. I had a look recently at the Sculpture Supply Canada website Sculpture Supply Canada - Liquid Plastics and it seems the range of products has widened quite a lot, with some new resins that sound quite promising. We mostly used the SmoothCast 300 series, which give good results and are reasonably strong, certainly much less brittle than polyester. Task4 sounds like it might be a good one to try; it says it is good for cross-sections of .030-.050" and it is tintable, although the curing time is very slow.

    With these types of resins it is important to use the proper silicone mould materials. Tin-catalised silicone is cheaper and gives good results, while platinum-catalised silicone will yield a longer-lasting mould. Mould release is generally not needed and the castings come out with a nice semi-gloss finish. Vacuum-degassing of the silicone, and pressure-casting the resin both go a long way towards getting good results. Nothing too fancy is needed for casting; we just hand-poured and then put the mould in a spray-painting pressure pot, and charged it up to 15psi or so.

    Andy

    P.S. Smooth-On is in New Jersey, so will be available from U.S. suppliers as well
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  10. #10
    Supporting Member StarryNight's Avatar
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    I agree the 3d printing I've seen looks...not so good. As far as milling, I'm looking for any excuse to justify spending my ducats on this build. Don't ruin it for me David! I'm sure the fantasy will wear off soon enough when the machine goes dive bombing into a nice piece of curly maple.

    as appealing as casting is, I would be starting from scratch. making the wood molds to make the silicone molds to make the parts etc. maybe it sounds daunting because I've never done it. I suppose I would need to somehow keep the magnets exposed while casting but still covering the top bobbin with resin...or I guess keep the magnets covered. but that might not work for the types of pickups I'm building.

    seventh chord doesn't seem to have a minimum order (woohoo!) but shipping is between 39-59 days. Although further down it says 5-7 business days upon getting the order. hmm...

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    Quote Originally Posted by StarryNight View Post
    I agree the 3d printing I've seen looks...not so good.
    The Tinkerine 3D printer I saw in action has software-adjustable resolution. You can set it to print finer, at the cost of it taking longer to finish a part.

    But yeah, I agree, the best 3D printed surfaces I've seen don't even match up to the crude plastic toys at the dollar store.

    3D printing is, however, otherwise well suited to the item you have to make - a shape that is complex enough to be a pain to make with conventional hand tools, and also contains no large solid volumes. Who said that pickup covers have to have glossy-smooth surfaces anyway?

    -Gnobuddy
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    A couple of years ago I considered buying a Spinet that needed new quills. This one used nylon rather than porcupine and they were no longer available. I found a guy who had the same problem and he'd drawn them up for 3D printing. He tried every popular 3D printing material from different places and concluded that the strength just wasn't there. I've read this elsewhere - stressed parts don't hold up. Many places use the 3D printing as step in the manufacturing process, not for the final product. Maybe there are some good materials, but not within the reach of the average guy.

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    Quote Originally Posted by Mick Bailey View Post
    A couple of years ago I considered buying a Spinet that needed new quills. This one used nylon rather than porcupine and they were no longer available. I found a guy who had the same problem and he'd drawn them up for 3D printing. He tried every popular 3D printing material from different places and concluded that the strength just wasn't there. I've read this elsewhere - stressed parts don't hold up. Many places use the 3D printing as step in the manufacturing process, not for the final product. Maybe there are some good materials, but not within the reach of the average guy.
    What did you wind up using?

    I'd have a look at nylon guitar or cello or bass strings, match the diameter & cut to length. Beats chasing down the neighborhood porcupine and asking him to give up a few.

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    I didn't buy it in the end - looked like it could turn out to be an expensive indulgence. Thinking back, I think they're called 'plectra' for the quill part. These were fitted into a longer arm ('jack', also broken) that had a felt damper. The problem I saw was that the plectra were formed as part of the hinged tongue, but only in the centre section of the keyboard and had to be replaced as a complete unit. All of the plastic parts were brittle. The top and bottom octaves were different, though and had replaceable plectra. But all needed fixing one way or another. I had a day to make up my mind on whether to buy it or not. Perhaps with more time and creative thinking I would have worked something out.

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    Somewhere on here is a description of Kent Armstrong's process for resin casting potted pickups that was written up by jonson. It may have been in the middle of a different thread but should be findable. I looked for it but no luck yet. From what I remember it was reasonably now tech.

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    Quote Originally Posted by Mick Bailey View Post
    Thinking back, I think they're called 'plectra' for the quill part.
    Interestingly, in British English, a "plectrum" is the thing that we call a "guitar pick" in North America. "Plectra" (or "plectrums") is just the plural of plectrum. A little Googling says the word originates in ancient Greek ("plektron"), which apparently means "thing to strike with".

    I was curious about the durability of 3D printed items, and a little research turned up the fact that the stuff that's used in most affordable 3D printers is called PLA filament. Wikipedia says PLA is "Poly or polylactic acid or polylactide is a biodegradable and bioactive thermoplastic aliphatic polyester derived from renewable resources, such as corn starch, cassava roots, chips or starch, or sugarcane."

    In other words, this stuff (PLA) is actually designed to break down over time - not at all what you want for durable, long-lasting items (like pickup covers or plectra for a musical instrument). PLA is used for exactly the opposite reason, because you want your 3D printed doodads to break down fairly quickly, and not survive for a hundred years in a landfill.

    However, PLA is not the only material widely used for 3D printing. ABS (plastic) is also used, and it is a much more durable material. Finally, it's also possible to 3D print with Nylon, though it requires an all-metal "hot end" for the 3D printer. Nylon is a very durable material.

    I would assume the fumes from ABS and Nylon are toxic, and appropriate precautions should be taken.

    More here: https://www.matterhackers.com/articl...ing-with-nylon

    -Gnobuddy

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    I've had some 3D printed ABS off different machines and it had shear lines - almost like wood grain. Maybe down to how the layers fuse to each other. Larger parts are OK by way of the increased cross-section, but thinner components still don't compare to an injection-moulded product. It has to come down to the process and quality of the machine. In fairness to the 3D process itself, there has to be a difference between a component made on a $1000 machine compared to one costing 10x or 100x the price.

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    Quote Originally Posted by Mick Bailey View Post
    (Ed: 3D printed) components still don't compare to an injection-moulded product.
    Oh, I agree completely. As I wrote earlier in this thread, the 3D printed finish doesn't even match up to the quality of cheap plastic toys at the dollar store.

    That said, personally, I wouldn't care if my pickup covers had fine grain on them, or were slick-smooth. But everyone might not feel the same way.

    -Gnobuddy

  19. #19
    Pickup Maker David Schwab's Avatar
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    Quote Originally Posted by David King View Post
    Somewhere on here is a description of Kent Armstrong's process for resin casting potted pickups that was written up by jonson. It may have been in the middle of a different thread but should be findable. I looked for it but no luck yet. From what I remember it was reasonably now tech.
    I have a few of Kent's rubber molds that he used with Pete Skjold.

    It's not at all a hard thing to do. I make rubber molds when I need to make a pickup in a "non standard" shape.

    Just get a small plastic box, or even a food container. Put your slug (pickup cover) in with the top facing up, and then mix the rubber and pour it in. I use the rubber from Micro-Mark.

    You have to figure out how to suspend the pickup without it touching the bottom of the mold. I use some heavier magnet wire to suspend the pickup. I got that idea by looking at an old Alembic pickup. Then I use MG Chemicals back potting epoxy.

    Here's a mini humbucker and a Yamaha bass pickup both molded and cast in black epoxy. The molds take on the details so well that the mini bucker is as shiny as the metal cover was that I used for the slug!

    glossy_black_mhb.jpgyamaha_nd3.jpg
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  20. #20
    Supporting Member StarryNight's Avatar
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    wow, those look really good! Great info. Thanks David!

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