building molds

any info for building molds for a sportfish hull.


thanks sean

 

What type of information are you looking for?

 

wood for mold and any pointers that would lead me into the right direction..

thanks much sean

 

wood for mold and any pointers that would lead me into the right direction..

thanks much sean

 

Hi Sean,

I have been building a lot of plugs. My customers are using a chopper gun to build up a mold over the plugs. I will check to see just what materials they are using.

If it helps here is a brief run down of the plug construction, if you are making a male mold then this would work for you.

1) I design the boat using MaxSurf and export the frames and stringers into AutoCAD. I use a maximum frame spacing of 18" and have stingers every 12". This helps keep hollows to a minimum

2) In AutoCAD I add rabbets in the frames and stringers so they will fit together properly. Make the on the outboard edge of the frames and on the inboard edge of the stringers. Basically you are making a 3D puzzle. I lay out the pieces in 4 x 8 sheets. For pieces that are larger I break them into smaller sections with numbers on each side of the joint. This way when you assemble the pieces you will have two pieces with a "1" on each identifying the joint between them. The next joint is labeled 2 and so on.

3) I get 3/4" birch plywood from China for the frames and stringers, think its 11 plys. My prices range from $20 - $27 per sheet depending on quantity. My local sign company has a 3 axis router and cuts the frames out for a reasonable price. I give them the wood and a DXF file with the pieces to be cut. Note that splines in AutoCAD do not get read by several CNC machines. If you save the AutoCAD file to a version 12 DXF any splines will be converted to polylines which will work fine. Note that a 1/4" dia double helix router bit helps keep both sides of the wood from tearing. No matter what you will end up sanding the edges.

4) I make up a rectangular jig using 2" x 2" x 1/4" angles matching the frame spacing. The frames bolt to this so it is critical that this jig is welded up true, square, and level. Secure the frame to the floor where you will build the tool making sure that it is still level.

5) I assemble the frames and stringers adding doublers at joints. My habit is to design the frames so that the waterline is level when they are inserted (bolted) into the metal jig. I make the stringers parallel to the waterline. Tilebond glue works well.

6) Bolt the frames onto the metal jig. You may have to use some temporary supports to keep them rigid. Once the frames are all installed on the frame I install the centerline stringer and work outboard port and stbd at the same time. Tilebond glue all of the joints but dry fit first! When you were making all those rabbets and got frustrated this is where it will show up! I use Wurth self tapping screws to hold everything together until the glue cures.

7) Strip plank the hull. You have several choices for materials here depending on the shape you have to match. Luan ain't what it used to be, much of it is delaminated before you buy it. I recently built a hatch for a jet boat with two molded humps like the old racing cars used to have. I made these highly curved surfaces by pouring 4-lbs density foam over the stringers and frames and fairing it with a batten and 40-grit sand paper. Seal this with an epoxy wood laminating resin, I use one from Composite Polymer Design CoPoxy 100.

8) Once the hull is covered fair it as best you can. If you have any notable humps and hollows use west system and micro-balloons, 407 balloons are the easiest to fair and still offer some structural support. Mix the epoxy completely and then add the micro-balloons. You are still shaping here so 40-grit sandpaper is all you need.

9) After you are happy with the hull fiberglass it with Epoxical resin. I mix up a putty of silica with Epoxical and cover the hull with that before applying the fiberglass. It holds great but it sands like a rock. Epoxical has a 4-hr pot life so you have time to work on large surfaces. Hold onto your wallet!

10) You now have some choices if you are making a male mold. To keep the fiberglass from printing through you will need to cover the mold with something like West System with 407 micro-balloons which will level to some degree and is pretty easy to sand. Vertical surfaces are best faired with Ultra Fair which will not sag.

11) For a truly fair surface you will sand with 80-grit in a diagonal pattern following the part. Apply Awl Grip 545 primer to the part and sand again with 80-grit looking for highs and lows. Putty as necessary and repeat. Once everything looks fair then prime the part again and sand with 120-grit. When you burn through the primer in spots check to see if you need to putty or if another coat of primer will be enough to fair the part. You will continue doing this until you no longer sand through the primer. Once you have made it to this stage you are polishing the tool so take it to whatever grit you are comfortable with.

Just in case anyone is paying close attention, I am writing this without vetting it so ye be warned. I noticed that there really is no book or bible for building molds and everyone seems to have their own ideas.

I hope this helps.

Roger

 

Not to derail the thread, but man how this caused me problems in the past. If you export lines to .dxf, save as polylines. Then you have to go through each piece and ensure it's closed. Takes some time but man does it save you some headaches and cost.

Sounds like a simple enough idea but that did not occur to me. Hopefully someone can learn from my experience.

 

Roger,
Where in SC Are you from. I used to live down that way near Santee. What type of boats to you generally do?

Regards
Ken

 

We have several kind of boat mould designs to be easy build by Yourself using laser cut parts. We can supply You files to cut the parts; You buy the plywood and cut it with a laser cut machine in any laser cut service (cheap!) and assembly it easily as a puzzle, fairing the inside a little (bcs of laser cut precision), and You will have a direct female mould ready to build boats as a traditional mould but without necessity to build an expensive and loose plug. See pictures. We can even design for You a completely new boat design, digitalizing Your design and making files for the laser cut mould. System is also for deck and interior (and many others) moulds.
More info at www.3dwmoulds.com

 

Are you wanting to build an original design? I assk because there are a lot of molds already built. Do you need help with this project? E-mail me at aqualityfg@bellsouth.net