|
|
#1
05-13-2016, 04:35 PM
|
|||
|
|||
DIY Mega Mold
I was looking at the Kenneth Michael site and you-tube and saw this "Mega Mold" which is seems to be a one-size fits all mold. Have any of you built one (?) and do the slots for the pvc & bolt standards have a bigger slot on the bottom of the mold to keep the 1/4" carridge bolts from turing while you tighten them?
I've built 6 dreadnaughts so far, using sanding dishes and "driving the bus". Also the sanding bar apparatus has to have a solid bushing to rotate on. Any suggestions on what to use for this? I'm currently using a piece of 1/2" iron pipe screwed into a flange for the upright "steering" colum to rotate the dish onto. I think I'd like not to drive the bus so much and this seem the way to go. 
|
|
#2
05-13-2016, 06:00 PM
|
|||
|
|||
|
The use of moveable vertical uprights bolted to slots in a workboard is an idea that I was taught in 1978 by Charles Fox. The "Mega Mold" is a minor variation on the idea. It isn't clear from the video why Kenneth Michael uses a more complex vertical upright comprised of several pieces. Simpler versions have been used by classical guitar makers for probably a century.
In Fox's version, the workboard it cut to a perimeter about 4" larger than the largest guitar shape you intend to make. 1/4" slots are cut from the edges in towards the center. 1" hardwood dowel are cut to a suitable length - a little shorter than the height of the sides - and one end is drilled to accept 1/4" threaded rod. The dowels are then slid into the slots at whatever positions you wish to form a moveable outside mold. Each dowel is attached to the mold from below with a wing nut and washer. The dowels are easy to move and remove since they are inserted in open-ended slots. The "moveable" mold works well, and I use it for a variety of purposes. However, I have found outside molds to be faster and easier for an established shape that is repeated. Although he didn't explicitly state it, what Kenneth Michael is doing in this video - I assume this is the one to which your refer: https://www.youtube.com/watch?v=sy7ieraU-Ns - is to "plane" into the upper bout of the top rim of the guitar a 1.3 degree angle in order to establish the neck angle. His method seems to assume a flat lower bout that "bends" at the waist onto the rims of the upper bout to establish the 1.3 degree neck angle. There are many variations on the geometry of the top - and its curvature - that various luthiers use. What KM shows in one variation. What he shows doesn't address the curvature of non-flat top geometry, should that be one's chosen approach. Were it me making a flat top with an angled upper bout, I'd use a handplane to establish his 1.3 degree plane and finish it off with a flat board with sandpaper on it. I wouldn't bother with the spinning apparatus or the titling workboard and rims, as I would find it unnecessarily cumbersome. Clearly, his method works for him and that is fine. My own preference would be andy one of half a dozen other methods, particularly for preparing the rims to accept the curvature of the back. There are numerous ways you could create the axis and bushings. One option is the flanged pipe you are using in conjunction with a brass or bronze bushing. The bushings are commercially available and easily obtainable. There are different configurations of bushings, in how they attach to the base material. Some have placement for a threaded fastener. If you have trouble finding a bushing to fit the outside diameter of a pipe, switch to a piece of solid metal rod. You could thread one end and insert it into a threaded fitting attached to your mold. Another option for the bushings it to make two rings out of a suitable sheet plastic, such as UHMW, and then use threaded fasteners to attach them to your spinning sanding board. Another option is use a brass, copper or bronze tube who's inside diameter fits your pipe or rod. Press fit it into a suitably sized hole in your sanding board. Another option to consider is that, at least for the top that is flat, there is no reason to have a rotational motion. You could simply move a flat "stick" with sandpaper back and force along a reference surface, eliminating the bushing and rotational motion. Obviously, the curved surface of his rotational "blade" is used for establishing the surface of the rims for the back and he is using the same method for both top and back. Last edited by charles Tauber; 05-13-2016 at 06:08 PM.
|
|
#3
05-13-2016, 06:16 PM
|
|||
|
|||
|
I think though with the "driving the bus" method, (I think of it more as driving without power steering) you have a larger surface area which means more sandpaper (faster and flatter), you can weigh down the disc with barbell plates (faster). If you truly want to keep an area at the same "plane" you'd need some kind of shaft stop collar to keep the sanding stick moving in that same plane, then drop the stop collar down and repeat...
In the video, it looks like bronze bushings or maybe oilite bushings, but I would think you'd need a pretty precise surface other than gas pipe to have precision movement, and possibly larger than 1/2". A cheaper alternative would be to make your own bearings of HDPE, which is self-lubricating. Also known as white chopping board, so readily available. A Forstner bit should give you a relatively accurate hole. I do mine in a similar fashion to Charles, with a hand plane. I have already shaped my mold with a 1 degree slope in the upper bout, so it's pretty easy for me to keep the body clamped in, and go at it with a hand plane, and then sandpaper adhered to a large board. I finally scrape as much of the sanding marks as possible afterwards, and "blend" the angle into the lower bout. But I'd agree with Charles that a planar motion rather than a rotational motion, with a larger surface abrasive, would yield accurate results faster.
|
|
#4
05-13-2016, 10:29 PM
|
|||
|
|||
|
DIY Mega Mold
Thanks for your input, its been helpful already. Since I like to build with the back portion of the top in a 25' radius, I really only want the middle portion of the upper bout to be flat and on the 1.3° plane. So, I guess I'll probably be using a rotating bar for that. It looks like tomorrow I'll literally be "looking into" some of my old lawn mowers in the junk pile or possibly an old steering column from (you guessed it) an old pickup truck out back.
|
|
#5
05-14-2016, 12:08 AM
|
|||
|
|||
|
I'm new to guitar building and recently completed a dreadnaught size kit build from KMG (Kenneth Michael). I also bought the Mega Mold and found it easy and precise. The radius bar does the job in a few minutes. I didn't wear out the sandpaper at all. Flipping it over and using the straight edged side was just as easy and precise. The final geometry of the top leaves you with finished heights that fit the planform of the guitar design. Can't ask for much more than that. Whether an original idea or not, the movable shape feature is well thought out and executed. It's apparent the mold is a product of a CNC set up. I thought it was fairly well priced, probably about the same as it would cost me to build it. Maybe less considering all the different set ups and time it would take without the use of a CNC. My guitar came out very nice. The woods provided were top grade. I did the vast amount of the work. The sides were profiled and bent. The top and back plates were joined and thickness sanded. The neck was pre carved but far from a finished product. I learned a lot using this set up. Enough to start a scratch build without the MM this time. Gives me the opportunity to expand my knowledge and skills. I'm sure I will use this tool again on future builds.
__________________
BradHall _____________________
|
|
#6
05-14-2016, 07:09 AM
|
|||
|
|||
|
Quote:
There are lots of methods to obtain essentially the same result. It makes sense to use whatever works for you.
|
|
#7
05-14-2016, 08:28 AM
|
|||
|
|||
|
As I mentioned, I won't be using the MM on my present build. Two reasons why. Firstly, I am a fortunate recipient of a complete (and then some) set of wood and a OM mold from Joel over on the OLF site. Secondly, I will have the opportunity to use a style of mold most builders employ. I agree with you that there are many ways to do the same job. Some superior to others for a number of reasons. Some merely different. I'm thankful to now have the tools to do a completely different build. I love the learning process and I'm particularly grateful for the help and guidance builders like you and Bruce, and many others, so freely offer. I've spent my life as a woodworker and was surprised to discover how little I knew when it came to luthery. It has already become my next career, although it costs rather than pays.
__________________
BradHall _____________________
|
|
#8
05-14-2016, 01:20 PM
|
|||
|
|||
|
I used the single shaped molds for my first 10 builds and the MM for my last 30+. For me the neck angle match is much easier and better using the MM. I predict you'll be back Brad
__________________
Tim B
|
|
#9
05-14-2016, 05:26 PM
|
|||
|
|||
|
Just to be clear, I have not "left" the MegaMold. I think it is a fine tool for building guitars. I'm anxious to try the solid OM mold, mainly because it's different. If I discover yet another process I'll probably try that next. I'm sure I will learn many new techniques as I progress. That's the fun part for me. It's all good.
__________________
BradHall _____________________
|
|
#10
05-14-2016, 06:18 PM
|
|||
|
|||
|
Quote:
__________________
Taylor 815C '59 Gibson LG2 Washburn J4 jazz box, ebony tailpiece Gold Tone open back banjo Anon. mountain dulcimer Creaky old Framus 5/1 50 About 1/2 of Guitar One completed; currently intimidating me on account of the neck geometry. Stacks of mahogany, spruce, maritime rosewood, western red cedar Expensive sawdust
|
|
#11
05-14-2016, 06:52 PM
|
|||
|
|||
|
started on the rotating thing
Ok , I ran out of nuts and bolts but just need to finish it by building blocks for the ends that hold the sandpaper. I used a piece of plastic "chopping block" material that I foud a couple of years back. Itresembles a plastic rail of some sort. When I get the MegaMold built I'll use this and and hopefully not so much the radius dish. Pardon me if I don't get the pic to load, it's my 1st time to post a pic on this forum.
|
|
#12
05-14-2016, 07:58 PM
|
|||
|
|||
|
Quote:
|
|
#13
05-14-2016, 08:19 PM
|
|||
|
|||
|
Quote:
Quote:
|
|
#14
05-17-2016, 06:14 PM
|
|||
|
|||
|
DIY Mega Mold
So now I that have the base board with the rotating arm built I was asking if the bottom of the work form board with all the slots in it had any recess for the heads of the bolts on the bottom. By looking at the video and pics on the Kenneth Michael site, it appears that they are using 1/4" carridge bolts. Is this right? / Or might they be using the kind of bolts for mounting toilets which are like a wood screw on one end ? Any info would be appreciated.
|
|
#15
05-17-2016, 09:58 PM
|
|||
|
|||
|
Quote:
|
