With dreams of future mass production(!!!) I am going to make a pair of Maccaferri moulds out of layers of MDF so that they can be used with silicone heater pads. Using the UF resin means that I can heat cure the glue lines in a matter of minutes by getting the temperature up to about 70°C. I have used low voltage (24V) silicone heater pads to cure PVA glue lines when edging panels but never before with UF adhesive. You don't need especially high wattage heaters for this and the ones I will be using are only just over 100W (about 0.11W/cm2). The plan is to apply aluminium foil tape to the mould followed by a layer of PTFE glass cloth to make the surface heat reflective and non-stick. The glued up guitar side will then be velcro strapped in place with the heater pad and another caul layer, also with aluminium foil tape/PTFE, on top. Once the mould and lay up is sucked down to vacuum then the heater pad will be powered up. I may build a thermocouple into the mould so that the internal temperature can be monitored but, if not, it will only take a few trials to determine how long it takes for the glue lines to go off. My guess would be no more than 5 minutes.
The slots are simply for weight saving and will be machined 16mm deep in 18mm MDF so that once glued up the mould will still have a very strong internal matrix to make sure is can withstand the almost 9000kg per m2 that it will experience in the vacuum bag.
I think you would need to check with Mark on that and I'm not sure whether he has had a chance to press a front or back yet. I do know that Mark is very keen to get a course of this style of guitar going in the near future.
I have scored the interweb looking for a 3D CAD file of 335 type guitar front/back and I have come up with absolutely nothing that is easily usable so I am now looking at how I can create a file myself. Once I've done this then I can produce a mould and make a few test pressings.
Update: My CNC router vacuum hold down pump has just died so I won't be machining these moulds until Wednesday at the earliest. In the meantime I have laser cut a 11.11% scale version (18mm down to 2mm) to check that the dowel holes all align. When I make the routed version the slots won't go all the way through but this is quite a useful exercise to check everything looks right before committing it to the full size machining. The slots will save something over 40% of the internal layer weight compared to the solid outer layers. If I can find some weirdo with a dolls' house containing a luthier's workshop and I could have a market for these!
Well, what an extraordinarily strange and screwed up world we are all now living in! Firstly, I hope that nobody on here is facing the worst that this crisis has to offer and that we can all, somehow, find a way through to whatever awaits us on the other side of this terrible situation!
We (Bagpress) are still working, as we are a team of only four people and are pretty much isolated from the rest of the world at work and at home. Until the current work runs out (about 10 days max) we will carry on unless forced not to. What happens after that is anybody's guess.
If I do have to implement a shut down then I guess I will still be able to come to the factory, lock the door and get on with some guitar making until the real work starts to come back in again - so there is something of a silver lining even if you have to squint really hard to catch just a glimpse of it!
The heater pads for my Maccaferri mass production line project (!) arrived today and I am hoping to try them out in the next week or so. The full sized moulds have been machined, assembled and given a couple of coats of lacquer, just to make them look pretty, and the next thing to do to them is to apply a layer of heat reflective aluminium foil and then the self-adhesive PFTE glass cloth before adding the Velcro straps. I estimate that I could turn out a pair of perfectly formed sides every 15-20 minutes if I really wanted or needed to.
I also have my fretsaw table to machine and assemble so plenty to do if I find myself with enforced down time.
Keep safe, good luck and hope you are all coping well.
We are in extraordinary times - I guess it must be something like being at war.
I look forward to seeing some progress if you do have to shut down - hope you find time to take some pictures as you go.
Hope you and your team stay safe.
Sod it - make tea!
I am part way through watching Mark's latest (notso) live stream from the workshop and it great to see the guitar we started making together taking shape.
I have now got my heated side moulds up and running and thought I'd give an update. What can I say? They work really well! I applied aluminium tape to the mould and then a layer of PTFE glass cloth and made up a 0.8mm birch ply caul to go on top of the lamination before the heater pad goes on top. There is then another layer of 0.8mm ply with aluminium tape on that goes on top of that. The aluminium tape is just to act a bit like a marathon runners space blanket insomuch as it just helps to bounce some of the heat back into the lamination rather than being absorbed by the mould or lost to the the atmosphere.
I did a few dry runs to check that the velcro straps were pulling the material tight enough to the mould in the right places and then did my first proper trial. I have changed a couple of things for these tests compared to the sides I made with Mark. The first is that I am using the same, or more or less the same, species of veneer all the way through rather than using poplar for the internal layers. In the case of sycamore and massur birch outer layers I have used maple, which is a pretty good match, internally. The other difference is that I am only using one central cross grain player rather than two. This means the sides end up with 80% of the grain running longways rather than 60%.
The resin I have used is the same I used with Mark and, as it has a very long open time at room temperature I had plenty of time to glue up both sides and get them in the press together. The resin will start its accelerated curing at around 40°C so I always made sure that the moulds were cold before strapping the glued up veneers onto them. I then gave them 10 minutes under cold vacuum pressure before turning the heater pads on. This meant that the glue had plenty of time to be properly squished into the grain and the veneers be squeezed hard together before the glue started to go off. After the cold vacuum period the heater pads were left on for 35-40 minutes to ensure everything was fully cooked. I could probably have got away with less but better safe than sorry at this stage. The pads a have a power density of 0.11W/cm2 so each is rated at about 130W and they run at 24V. I bought a great little bench power supply from Amazon (for £60) which is rated at 30V/10A and this is just about perfect, allowing both pads/moulds to be run at the same time.
The results have been fantastic and, apart from getting one of the lay ups the wrong way around (doh!!) I am very pleased with the results with all of the pressings being virtually identical in shape. They all sound and feel very hard and, whilst it is difficult to find a node point on a bent side, they do have very good resonance when tapped in the right place.
As you can see, I have been reasonably busy, but in fact prepping the materials takes considerably longer than the actual pressing with the glue up process for a pair of sides only taking about 15-20 minutes from start to finish.
I now have to make the external assembly mould and the moulds for the laminated linings as the shape of these guitars is very slightly different the Concert model I made before. My plan is to make a two of these as regular steel strings with standard bonded bridges but with the composite tops that I made some months ago. There a few examples of modified cross braced Maccaferris out there so I will have a look and see how others have done it.
In the meantime here are some pics.
I have ordered a similar heat pad for the back mould so when that arrives I can press all of the matching backs. Now, what can I do until then.....?
I have now made the external mould for the guitars and, this will make you laugh (!) I realised that I had pressed all the sides at -4mm all round! Not to worry, the width was pretty much adjusted for in the external mould dimensions but I have now got a Maccaferri variant which I will forever refer to as the 'short bodied' version! If you are interested this is what happens when you forget to check that your CNC router is running the tool outside of the path rather than on it! (8mm cutter, divide by 2 = 4mm offset). The only real issue that I might have had was that this tightened up the radius on the cutaway but in fact the pressings themselves and the laminated lining look absolutely fine so I think I've got away with it!
One thing that always bugged me is how inaccurate side templates supplied always seem to be leaving a considerable amount of additional trimming by hand or blood, sweat and tears on the sanding dish. Time to revisit Rhino me thinks! What I have done is produce a CNC cut domed internal template which can be clamped inside the body and used to guide a trim router to take the sides down very close to their final contour. Pretty easy to do and if I need to do it again it will only take me 5 or 10 minutes to produce the cut file for the router. The results look pretty good considering the jig was machined out of an old 44m thick door blank.
Now to stick the linings on.
Anybody made a motorised sanding dish?
Watched your course on the website today and all I can say is wow.
Absolutely brilliant way of producing a guitar with sustainable resources that can be really spectacular and it sounds as if the wood is also cheaper than "normal" building . Although a bit more money to setup the vacuum kit 🙂 So I may try and get you to do a "test" back & sides to see if I can build one
Can Mark get a course together for the arch top using this method or is that another story?
Thank you for your comments and I'm pleased that you seem to understand some of the advantages that this construction offers. I would never claim that it is better than using solid, but it is certainly an easier process in some respects and does open up the opportunity to use all kinds of materials which just aren't available as solid timber.
I am happy to press you a pair of sides and a back for one of Mark's Bootlegger guitars, as featured on his course, and for which he supplies plans. Let me know what species of wood you are interested in and I'll tell you the cost of the materials.
The archtop is a 'work in progress' project at the moment. I know Mark is keen to have this as an option on his video, and real life, courses but the ball is his court on this at present. In the meantime I have bought the full version of Rhino 3D and I am working through various tutorials which I am hoping will enable me to take the various body sections from a plan and create a 3D model so that I can cut moulds for pressing fronts and backs from constructional veneers. Again, there is a bit of 'watch this space' involved on my part as I am, luckily, still quite busy at work and obviously need to make hay whilst the sun is shining, so to speak.