Jacobson Carbon Fiber Mandolin Prototype

[Dave Greenspoon]

Amazing. Great sounding instrument shown off nicely by some tasteful playing. Loved how the single note articulation sings so sweetly and the chops/double stops want to give a little growl. Any chance this is going to be doable at working-person prices? +1 on the pickup, fwiw.

[Marty Jacobson]

Amazing. Great sounding instrument shown off nicely by some tasteful playing. Loved how the single note articulation sings so sweetly and the chops/double stops want to give a little growl. Any chance this is going to be doable at working-person prices? +1 on the pickup, fwiw.

I tried selling instruments for working-person prices, but the problem is I wasn't rich enough to keep doing it. Most working people I know have fancy new trucks, so I guess it's all about where you put your priorities.

[Dave Greenspoon]

I tried selling instruments for working-person prices, but the problem is I wasn't rich enough to keep doing it. Most working people I know have fancy new trucks, so I guess it's all about where you put your priorities.

Trust me, I totally understand how that plays out. All that said, you really came out with an amazing initial effort. Beautifully done, and incredible sounding. Oh well. Maybe one day CA or Rainsong will realize there is tens and tens of dollars to be made in this niche.

[Ivan Kelsall]

Hi Marty - Very well done indeed !!. I worked in CF composite design & manufacture for over 10 years in the aircraft industry & i know that CF can be a hard material to master - even for simple shapes. It seems that you've got it right first time - maybe a bit of fine tuning (in the manufacture) to eliminate any 'flaws' - terrific work,
Ivan

[bbcee]

Marty, I echo all here - you've made a viable musical instrument from a tricky material (I'm thinking of the first generation of CF guitars-ugh).

The manufacturing process is surprisingly simple. There's a top and there's a back. You put 'em together. You get a mandolin. More luthiers should work with carbon fiber.

I have little experience working with CF, and that wasn't good, as I had zero idea what I was doing. Splinters & dust everywhere! Do you see building something like this in the realm of possibility for us hobby builders?

Will you be posting build logs on your site?

Really exciting to see this being done right!

[J.Albert]

I was wondering how it might sound, but it sounds like, well... a mandolin.

If I hadn't known it was made out of carbon fiber, and had heard only the sound samples, I would have guessed it was just another "wooden" mandolin model, voiced a little differently...

[Marty Jacobson]

I have little experience working with CF, and that wasn't good, as I had zero idea what I was doing. Splinters & dust everywhere! Do you see building something like this in the realm of possibility for us hobby builders?

Will you be posting build logs on your site?

Really exciting to see this being done right!

Yes, I will be doing a full build log including moldmaking and "recipes" for duplicating my results. Not until September or October, though, with what I have going on currently. If you have any questions, feel free to ask.

I think working with carbon fiber is actually more accessible than woodworking, since you really don't need all the special bandsaws, chisels, joiners, planes, etc. which are necessary for woodworking (and the associated skills to use them). The only challenge is making the mold. I think if you had a CNC router and a nice flat 4'x8' table to work on, you could have a complete production carbon fiber guitar & mandolin making shop. Of course making the molds is something you could do by hand, and trimming the parts would be possible using just a cutoff wheel on a Dremel (in much the same way that a car is perfectly functional without power steering or air conditioning). But having a CNC machine to make the molds and then to precisely trim the infused parts makes it a dream to work with. It's precisely the kind of process I envisioned developing when starting lutherie - repeatable parts which are as easy to assemble as making sandwiches.

Of course you need to keep safety in mind - a lab coat, safety glasses, nitrile gloves, and a respirator are necessary for all operations where you are cutting or sanding carbon fiber, so it's also necessary when you are just hanging out in the space where you recently cut carbon fiber due to the dust swirling around in the room, whether you can see it or not. But I treat wood dust as hazardous anyway, so it's not that much of a change from what I ordinarily do.

[tom.gibson]

Is there a significant difference in weight from your other mandolins?

[dan in va]

Now you've really gone and dunnit. There are visions of CF tater bugs dancing in my head.

[Ron McMillan]

Most working people I know have fancy new trucks, so I guess it's all about where you put your priorities.

Unless you can somehow get the banks to support you by offering five-year payment plans, competing with the truck dealerships is going to be an uphill struggle.

[Ivan Kelsall]

With the CF materials we used in the aircraft industry - CF cloth for 'wet lay-up' moulding or CF pre-preg.,the biggest problem was in drilling / cutting it. The stuff's hellishly abrasive & can blunt standard drills / cutting tools in minutes. Also,cut edge & the edges of drilled holes 'feather' so they need sealing with resin to re-consolidate them. Care has to be taken not to apply too much force or de-lamination can occur at the cut edges as well.

In the laying up process,air can get trapped between the layers causing 'voids' ,which over time can expand & cause serious de-lamination. To prevent that,for smaller items,when using 'female' mould tools (where the lay-up is done inside the mould tool),we had rubber ''intensifier'' plugs made from liquid rubber,cast inside the mould tool. The CF was layed-up in the mould / the intensifier was placed inside it & pressure applied to it to consolidate the lay-up. This was usually done by placing the whole thing inside a plastic vacuum bag & pumping the air out while the lay-up cured,if it was 'cold cure' resin. Our pre-preg CF was usually 'hot-cure' material & required an oven,or in the case of very large items,an Autoclave.

I don't know if anything like that is either practical or even affordable for CF mandolin production,but it's one way of avoiding 'voids' & the perils thereof,
Ivan

[Marty Jacobson]

Hi Ivan, I've been doing wet lay-up and vacuum bagging on female molds. When I did it properly using well designed molds, I didn't have any problems. I definitely need to do a mold-conforming reusable latex or silicone vacuum membrane (or "intensifier" as you put it) to get an acceptable final finish on my back/neck/headstock component, which is the only part on which I encountered issues.

PreciseBits makes a nice carbide burr tool, which when used in CNC, leaves a very clean cut on parallel or perpendicular surfaces. And they are quite cheap, only $3 apiece, so if I have to buy one for every mandolin I am fine with that. The benefit of working on mandolins are that they are nice and small, so the tool life issue isn't too much of a dealbreaker.

Interestingly, I just got this email from RobbJack about a drill tip geometry for working with CFRP:

[Glassweb]

Very impressive... the playing, the design of the mandolin, the tone... you've solved the carbon-fiber mandolin puzzle old bean... congrats all the way around!

[Marty Jacobson]

Very impressive... the playing, the design of the mandolin, the tone... you've solved the carbon-fiber mandolin puzzle old bean... congrats all the way around!

Still a long way to go, but thanks for the encouragement!

[Ivan Kelsall]

Hi Marty - It seems like you did a bit of homework before you began - well done,so many folk don't.

Wet lay-up is the way to go in his instance. Pre-preg.is fine for large flat panels. Anything ''with shape'' & it's very messy & difficult to handle. Yank it about too much & the weave can start to get '-un-woven'. As long as the vac-bag goes down nice & evenly inside the female mould,that's fine.The danger is if it starts to wrinkle & causes wrinkles in the inner side of the lay-up. That's one reason why we began to use moulded Silicon rubber intensifier 'plugs'. Added expense but you get a spot on product.

Our drills were made by a German company, ''Klenk'' (now part of another Co.- 'Ceratizit') 100% solid carbide & monstrously expensive,but for cutting high volumes of CF the only ones that would do it. Even then, they were used in rotation - some in use,others being sent back for re-sharpening. They were also 'glass hard'. Drop a 1/2" drill & it would shatter like glass - £150 down the drain !. They were placed back in their foam lined plastic containers after use,& the fitters would go for a long lie down in a dark room,
Ivan

[Marty Jacobson]

Hi Ivan, yes we have that trouble in the college machine shop I manage. Students come in asking for a new cutter for a project and hand it back in destroyed because they let it slide it out if the collet onto the vise while they were unloading it. I basically just supply crappy HSS tooling and if they want to do actual quality work they can buy their own.

[Jeff Hildreth]

Well done Marty, inspirational from a construction and tonal perspective.

Will you pursue this to a viable commercially available unit. ? I hope so.

I'm interested.

[mandroid]

Vacuum bagged the carbon layup at room temperature?

[j. condino]

Cool mandolin....glad you are the one dealing with the CF dust and splinters and not me!

[Ivan Kelsall]

From mandroid - "Vacuum bagged the carbon layup at room temperature ? " Yes - CF can be used with either a cold cure resin or a hot cured resin. Typically, pre-preg. CF is hot cured in an oven (autoclave), which means that for simple shapes,which are also ''structurally simple'',wet lay-up using cold cure Epoxy resing is the most widely used. To warrant the purchase of an autoclave & indeed,pay for the electricity to power it,calls for a lot of expense,something you'd only do if you were into large volume production.

Many components made from 'Glass fiber' are made by using glass cloth impregnated with wet epoxy resin,vac-bagged & allowed to cure at room temp.. The technique is equally applicable to dry CF materials used with wet resin,
Ivan

[dschonbrun]

Nice job, Marty.

Did you wrap CF around a wood neck, or did you use another type of filler?

Thanks,
D

[Marty Jacobson]

The neck is entirely hollow except for the headstock, which has a maple plug and extends about a half inch past the nut. There is also no neck block, no bracing, and no linings. It's a monocoque construction.

[Ron McMillan]

The neck is entirely hollow except for the headstock, which has a maple plug and extends about a half inch past the nut. There is also no neck block, no bracing, and no linings. It's a monocoque construction.

That's interesting. I always assumed the neck on my Mix was solid. Probably not!

[billhay4]

Marty,
How is such a neck made? Is there a mold or form? IF so, how is it removed?
Thanks,
Bill

[Marty Jacobson]

Hi Bill, it's vacuum bagged onto a female mold. Pretty easy to do once you have a mold. The neck and back are all one piece.



My process and mold geometry are not perfect here. As Ivan points out, a better process would be to use a form fitting silicone vacuum bag instead of the flat poly film which resulted in wrinkles in the vertical surfaces. But I wasn't sure the structure would even work so I just went ahead with the prototype.