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n00bie question - cutting molds
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Author:  nkwak [ Wed Sep 08, 2010 10:52 am ]
Post subject:  n00bie question - cutting molds
This is just my second post and I'm new to building so please bear with me.

I'm attempting to build a medium jumbo based off the OLF plans drawn up by Michael Payne and am in the extreme early stages. Presently I (well actually myself and fellow forum member YJ John) have just gone through the process of cutting the mold and I've already hit a snag. Here's what I did and what the issues were:

1: Tracing the outline: Since the plans are copyrighted I felt it was not ethical to photocopy them and instead tried to trace them on poster board to the best of my ability. IMO they came out pretty close (I triple checked) and moved on to tracing that outline to MDF molds

2: Cutting the molds: I bought some 3/4" MDF from Home Depot and had them cut to 12 10"x24" boards which I in turn glued together in stacks of 3. I traced the outline from my cardboard cut out and using YJ John's rather persnickety band saw I cut the outlines out to the best of my limited ability. We had a lot of issues with the blade coming loose many times though and I think it may have caused the problem I'm having.

The issue:

Going back and laying my finished mold over the the blueprints I see now that the profile of the curves are far from perfect. The outline is close in some places but apparently the tension on the blade caused it to bow making the profile "cupped." In some places there is as much as a 3/8" gap from the outline of the plans to the interior curve of the mold; too much has been cut away. Are they salvageable (i.e. can I make some extensive shims where the spreaders are to go) or should I chalk it up to n00bie error and try try again? FWIW the cutouts have a little "extra" which I can conceivably sand down to the true outline and use in the side bender when the time comes.

FWIW I will post pictures as soon as I am able. In the meantime I am attempting to build a better template (with bracing overlay too) on clear acrylic and am being extra careful that the lines are clearly defined and that the target media and the plans do not shift in the slightest.

Any insights would be greatly appreciated! Thanks! [uncle]
Author:  mhammond [ Wed Sep 08, 2010 11:12 am ]
Post subject:  Re: n00bie question - cutting molds
Neil:
When I'm building a mold, I cut a single mold half (3/4" thickness) of plywood, this is my "master" piece. This piece gets sanded, filled, etc. until its as good as I can get it. I then rough out the other 5 pieces as close as I can. These pieces are then stacked onto the "master" with screws, 2 at a time, and cut to perfect dimension with a router bit that has a bearing attached. Easy, fast, and they come out without even needing sanding to finish.

Good luck,
Mikey
Author:  Edward Taylor [ Wed Sep 08, 2010 11:14 am ]
Post subject:  Re: n00bie question - cutting molds
What Mikey said. Also you can buy some large tracing paper (its not actually called tracing paper it has some other name) and that makes it a lot easier.
Author:  the Padma [ Wed Sep 08, 2010 11:17 am ]
Post subject:  Re: n00bie question - cutting molds
Some AR perfectionists would scrap.
Others more bending would patch with what ever works.....shims, poly filler, bondo, ground up aluminum doors and kids glue. The key here is "what ever works" for you.

blessings
duh Padma
Author:  Pat Hawley [ Wed Sep 08, 2010 11:28 am ]
Post subject:  Re: n00bie question - cutting molds
As a first step, after confirming the dimensions on your plan (in case the paper expanded with humidity, for example) you might consider tracing it onto acrylic to make a template that includes your bracing pattern etc. Drill small holes that you can poke a pencil through to allow you to mark your top to locate the braces. Very handy and worth the few bucks and time to make.

As for making the actual mold, what has already been said above.

Pat
Author:  mhammond [ Wed Sep 08, 2010 12:05 pm ]
Post subject:  Re: n00bie question - cutting molds
Neil:
Just a few further thoughts. There are a few dimensions that are critical, scale length, neck angle, string height, etc. Then there are some that really don't matter. If your lower bout is 3/8" fatter who cares? Maybe it will the very first one of a new, wonderful, Kwak sized, medium, triple O, dread!
Experience will teach you which ones to worry about and which ones don't matter.
Just carry on! :D
Mike
Author:  Barry Daniels [ Wed Sep 08, 2010 12:23 pm ]
Post subject:  Re: n00bie question - cutting molds
Making a photo copy for your own use does not violate copy rights. Only if you offer them for sale.

Trying to fix the form will take more work and achive poorer results than starting over from scratch. Don't use this form because every guitar you build with it will reflect the bumps and hollows. Why start off with these kind of errors?
Author:  Mike OMelia [ Wed Sep 08, 2010 1:17 pm ]
Post subject:  Re: n00bie question - cutting molds
Mikey provided the best advice IMHO. Make a master, use pattern bits to shape the rest.

After I make a photocopy of the drawing (there is NOTHING unethical about that) I place carbon copy paper on the wood, then the plans over the carbon paper, then with a dull pencil, I trace the shape I want. I never use my original plans for this activity.

There are issues regarding center lines, etc you need to pay attention to... but this technique is fast, cheap, and accurate. Remember to save your master templates!

Mike

BTW, this is a great question!
Author:  WaddyThomson [ Wed Sep 08, 2010 1:33 pm ]
Post subject:  Re: n00bie question - cutting molds
Barry is right on. Go to Kinko's or UPS Store. Both have copiers capable of making a full sized copy. Make sure they have had it calibrated recently, and check the measurements carefully. cut it up and write all over it.
Author:  Mike OMelia [ Wed Sep 08, 2010 9:30 pm ]
Post subject:  n00bie question - cutting molds
Btw, when using carbon paper, make sure the black side is facing the wood, not the paper. ;)

The stuff is cheap, I buy it buy the hundred pack at Staples. Draw a center line on the piece to cut. Lay out the carbon paper, overlapping the edges. Tape them to each other and the work piece at the outside edge. Then lay the plan copy over the carbon paper, aligning with the center lines. Trace the shape with a dull pencil. Take up plan and carbon paper. Nice outline laid out for cutting . Now when bandsaw cutting, get close to line but no more. Use relief cuts to minimize blade binding. Use a spindle sander or belt sander (rigid makes a very popular, inexpensive sander for this) to finish up to the lines. You now have a perfect template from which to use router pattern bits to replicate from!

Never use a bandsaw to finish a template shape unless you've been doing it for 20 years and can do it in ur sleep. It will almost always be riddled with errors.
Author:  Mike OMelia [ Wed Sep 08, 2010 9:34 pm ]
Post subject:  n00bie question - cutting molds
If u r confused about pattern bits and router shaping with them, please ask.
Author:  alan stassforth [ Thu Sep 09, 2010 12:37 am ]
Post subject:  Re: n00bie question - cutting molds
i make the template out of 1/4" stock.
easy to sand to perfection.
then use a 1 to 1 router bit, keep steping it down.
be careful.
perfect mold.
at least, good enough.
good for cutting out elec git bods, but positive shape instead of negative.
just go slow with the router. ha!
oh, but first, rough cut about an 1/8" from da line, be it positive or negative, so da router don't have to work so much and want to kick around.
Author:  nkwak [ Thu Sep 09, 2010 12:44 pm ]
Post subject:  Re: n00bie question - cutting molds
Wow! There's lots of good advice here! I think I know what I need to do - and it involves starting over. I'll certainly follow the ideas on making a master perfect and then using a router with a guide to cut the rest.

Several more questions come to mind though:

1 - will a 9" band saw be large enough to cut a 10" x 24" board of plywood. I happen to have one now.

2 - I did 12 boards this size (3 at a time) the first time around. Do I need to do more since I've been advised to do relief cuts? I'm worried that I may have to cut 6 more because doing relief cuts will essentially destroy what I'd intended to use for for the bending forms. Of course, I still need to make the spreaders too so I could use the scrap for that, right?

Other than that I think I know what I need to do. I've made copies of the plans and am about to finish up my plastic template - I just have to carefully cut it out. Then I'll procure some more plywood. Maybe I'll skip MDF this time and go up to birch; I'm starting to think that I may do another build since I'll have done all the setup work - LOL!

Once I have the plywood cut up to the size I need I'll work on the master. I don't have a router or the proper bit just yet though. We'll cross that bridge when we come to it.

Thanks, everyone! I'll let you guys know how it turned out - or if I come up against any other related issues! :?
Author:  nkwak [ Thu Oct 07, 2010 1:01 pm ]
Post subject:  UPDATE - looks like I'm ready to go...
I just wanted to give you guys an update as I am about to embark on the actual guitar building phase of my first project. Thanks to everybody for all your advice.

Image

It's a semi-solid mold for the OLF medium jumbo made with birch plywood and solid pine spacers. The design is a hodge-podge of things but everything seems to measure up according to the plans and it's pretty sturdy. This morning I finished up a set of spacers for the lower bout and need to do another set for the upper bout.

1 thing down, then I figure there's 3 or 4 more things to go (bending forms, trimming the sides, inlaying my rosette and trimming the top and back) and then I can bend the sides and get to work. I'm getting excited! bliss
Author:  SteveCourtright [ Thu Oct 07, 2010 1:10 pm ]
Post subject:  Re: n00bie question - cutting molds
Looking good, Neil! Go for it.
Author:  Darrel Friesen [ Thu Oct 07, 2010 7:46 pm ]
Post subject:  Re: UPDATE - looks like I'm ready to go...
nkwak wrote:
I just wanted to give you guys an update as I am about to embark on the actual guitar building phase of my first project. Thanks to everybody for all your advice.

Image

It's a semi-solid mold for the OLF medium jumbo made with birch plywood and solid pine spacers. The design is a hodge-podge of things but everything seems to measure up according to the plans and it's pretty sturdy. This morning I finished up a set of spacers for the lower bout and need to do another set for the upper bout.

1 thing down, then I figure there's 3 or 4 more things to go (bending forms, trimming the sides, inlaying my rosette and trimming the top and back) and then I can bend the sides and get to work. I'm getting excited! bliss


If your sides need a little tweak here and there to bring them in tight to the mold prior to glueing in your linings, clamping could get a little tricky based on the rectangular shape. Just my thoughts.
Author:  nkwak [ Fri Oct 08, 2010 8:05 am ]
Post subject:  Re: UPDATE - looks like I'm ready to go...
Darrel Friesen wrote:

If your sides need a little tweak here and there to bring them in tight to the mold prior to glueing in your linings, clamping could get a little tricky based on the rectangular shape. Just my thoughts.



Thanks! I didn't understand before why everybody was cutting an outside profile on their molds. Now I know.

Don't worry - I don't feel silly at all! Really. This has been a fascinating learning experience.

FWIW I don't think it's too late to trim from the rectangular shape and if I need an outside surface to clamp against I have LOTS of those .75"x1.5"x3" spacers left.
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