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Old May 02, 2014, 08:01 AM
RC Newbie with lots of ideas
Chile, Santiago Metropolitan Region, Stgo
Joined Dec 2012
289 Posts
Quote:
Originally Posted by ktm500mx View Post
the hot number with the Brazilian boats right now is 650 grams.
both the little best and the skinny are at that number and doing very well'
Mike

That is my number! Saturday y lead casting day.
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Old May 05, 2014, 12:04 PM
If it floats....sail it!
FoamCrusher's Avatar
Elk Grove, CA
Joined Sep 2002
4,153 Posts
Excellent documentation of your build!

We do not sail RG65's in our area, but we do sail US One Meters. I have built several and right now am building a USOM version of the IOM Goth. The designer, Frank Russell, also has a free RG65 version on his website http://www.frankrusselldesign.com/Plans.htm . Here are some tips from my building experiences:

Put the bulb in a plastic bag in the freezer overnight before drilling or cutting out areas for the fin. It makes the lead harder and easier to machine (less melting at the point of the tool). When you drill holes in the bulb, try using butter (mantequilla) as lubricant. The drill bit will not "catch" as much while drilling. This seems to work better than commercial lubricants. Just be sure to use wash it with a good solvent before painting.

If you can find Ultracal-30 (a US Gypsum product) http://www.ebay.com/sch/i.html?_nkw=...acal-30&crdt=0 use that in place of the Plaster of Paris. Ultracal is a gypsum cement rather than a plaster. It dries much harder so the edges of your mold will not chip or crack and it holds less water as it dries.

It speeds up the drying if you weigh the mold, then bake it at about 250F (~110C) for a few hours and then weigh it again. It will show the loss of weight due to the water that was baked out. Do this again (weigh then bake and weigh again) until there is no change in weight, indicating the water has all either reacted or been baked out. Keep the mold in a sealed plastic bag and one of those little packages of drying material that comes with new electronic devices. (Dried rice also works)

It helps to warm the mold before pouring the lead. You will have fewer blemishes in the surface. I use a two-burner propane camping stove to do my pours. One burner for the lead pot and the other burner for the mold.

Lead has surface tension just like water and will bulge above the top of the mold, making your parts larger in that dimension requiring you to sand (wood rasp) it back flat. If you warm the mold the lead will remain soft like putty for a minute or two after pouring and you can "strike off" the excess with a stick, like you would do when pouring cement in forms. If the lead cools too quickly, a quick pass with propane plumbers torch will soften it just enough. Do not worry about a gap at the edges when the halves are glued, you can fill them with automotive body filler before painting. The less sanding I have to do the better since lead dust is toxic.

Speaking of toxic....Wear a dust mask and disposable gloves when working or handling the part. Also, wash you hands and clothes immediately, washing your shop clothes separately from other clothes, particularly children's clothes.

I sweep the bench and floor rather than vacuuming with a shop vac since it puts less dust in the air.

I hope this helps.
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Last edited by FoamCrusher; May 05, 2014 at 12:07 PM. Reason: Darn automatic speller!
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Old May 05, 2014, 02:30 PM
RC Newbie with lots of ideas
Chile, Santiago Metropolitan Region, Stgo
Joined Dec 2012
289 Posts
FoamCrusher: Thank a lot for all the suggestions.

I do work lead in the open. The stick thing I already discovered myself, rewarming included. Great advice on freezing the lead to work with it! Regarding safety measures, I follow them all, don't worry. Sanding I do with great care over an old towel, so I recover all big particles and store them in a plastic bag. Las saturday I melted those in same pot as before, to reuse all scrap I can.

Last saturday I melted two new halves. Together they weight little more than 650gr. I will bring them down to 600gr.

New fin is a problem: local store is out of carbon fiber rods & profiles. So I do not have what I need!
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Old May 05, 2014, 03:11 PM
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Joined Apr 2002
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Look up your local model helicopter club and enquire if anyone has any suitable blades. A boom strike with a heli will damage one blade leaving one undamaged. Modellers are all the same and tend not to throw spares away even if they are of no use. I have a pair of unused NHP carbon rotors that are almost identical in chord and section to the DF fin.
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Old May 05, 2014, 06:59 PM
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Dick L.'s Avatar
Minnesota, USA
Joined Aug 2002
2,254 Posts
@ FC - thank you for the suggestions for mold material. Originally from Michigan and auto industry I was familiar and used sand casting for my original molds. Haven't had a need since then, but now am faced with needing a couple of "M" bulbs.

Will have to check at big-box lumber stores for that gypsum/cement. Sounds like a perfect replacement for plaster that takes forever to dry out
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Old May 05, 2014, 08:08 PM
If it floats....sail it!
FoamCrusher's Avatar
Elk Grove, CA
Joined Sep 2002
4,153 Posts
Dick:

Just trying to help other builders ...a vanishing part of the hobby IMO

You won't find Ultracal at a big box store. It is a commercial product used for making statuary and molds for production ceramic work.
ULTRACAL® 30 gypsum cement is a traditional tooling gypsum cement, specially formulated for close tolerance tooling.

Low absorption ULTRACAL gypsum cement: Is recommended where extreme accuracy and surface hardness are required (i.e. duplicator molds) Provides the lowest expansion of any rapid-setting gypsum cement; Is ideal for splash-casting molds and models for phenolic, polyester and epoxy resins; Sets 25-35 minutes after machine mixing; Requires 38 parts water by weight per 100 parts plaster.
I found it a local ceramics studio where they hold classes and sell greenware (already fired things like plates and mugs for kids/adults to decorate and do the final glazing and firing. Unfortunately, I had to buy a 50lb bag which I will also use for taking hull plugs and making short run molds, rather than making them out of fiberglass/epoxy.

If I were going to make just a few bulb molds, I would buy it from the guy on eBay. Several internet suppliers will ship a 50lb bag, but the fees are more than the cost of the product.

BTW, most plasters and gypsum cements work better if mixed this way :
Mold Making and Casting Tip: Mixing Hydrocal Plaster (6 min 28 sec)
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Old May 05, 2014, 08:55 PM
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Dick L.'s Avatar
Minnesota, USA
Joined Aug 2002
2,254 Posts
Oh - I was thinking it was a cement product like for casting cove moldings and similar "gingerbread" for old homes. I confused it with "Hydrostone" product.

Also have seen cement with glass fibers, but that didn't give a nice finish. I'm sure I can find some up here in Minneapolis/St. Paul with the universities and their art classes. Thanks again for sharing.
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Old May 06, 2014, 12:02 PM
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Joined Apr 2007
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Hi Dick,

have you thought about this? .... definitely no moisture issues.
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Old May 06, 2014, 12:53 PM
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Dick L.'s Avatar
Minnesota, USA
Joined Aug 2002
2,254 Posts
Thanks, Gio ---- will have to do a bit of homework on this product. Looks interesting - if not for keel bulbs - maybe for some of my other craft projects.

Dick
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Old May 20, 2014, 04:20 PM
RC Newbie with lots of ideas
Chile, Santiago Metropolitan Region, Stgo
Joined Dec 2012
289 Posts
Progress!!!

#1 make the hull watertight - Done. No water comes in now! Perfect.
#2 simplifying the rig - Done. Got rid of the breakback system. Working fine in light winds.
#3 lighter fin - Work in Progress: new lead bulb already casted. New CF sheet already done. Need some CF parts for the reinforcements, now (local store out of stock) .

Sunday was my first race. Came out 8th out of 9 boats. Light winds all day, boat feels heavy in little gusts, I really need my new fin And I already have #4 and #5, which are rig related:

#4 new mylar sails: the current ones are simply too ragged and wrinkled. Mylar on other boats look much more rigid.
#5 more rig simplifications: goes together with #4, meaning using less bowsies and better knots to make everything lighter - less air drag.

Pictures of last sunday here. Mine is the red one with the black sails, sail number 09:

https://plus.google.com/u/0/photos/1...87868411710065

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Old May 20, 2014, 04:51 PM
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Good work Thomas; have a look at the leech of your jib it needs to be tightened to replicate the luff of your main. You have a turbo but is currently switched off. Look at the slot on boat 28 it is like a railway track.
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Old May 25, 2014, 05:58 PM
RC Newbie with lots of ideas
Chile, Santiago Metropolitan Region, Stgo
Joined Dec 2012
289 Posts
Ok, yesterday I won my first informal heat!!! Very happy. Did not winn the day, but happy anyways! Very light wind and only 4 competitors, but proves that with trimming+tactics+some luck this boat can win. Meaning it's not rubbish. Haha. (used the same 800gr fin/bulb)

Current status of my new lighter fin (will be thinner and stronger than the previous one):
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Old May 26, 2014, 08:32 AM
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Joined Jul 2011
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Quote:
Originally Posted by tarmstro View Post
Ok, yesterday I won my first informal heat!!! Very happy. Did not winn the day, but happy anyways! Very light wind and only 4 competitors, but proves that with trimming+tactics+some luck this boat can win. Meaning it's not rubbish. Haha. (used the same 800gr fin/bulb)

Current status of my new lighter fin (will be thinner and stronger than the previous one):
I was told many years ago by a yacht designer friend ''If a boat goes fast just once and never goes fast again do'nt blame the boat''
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Old May 26, 2014, 09:48 AM
RC Newbie with lots of ideas
Chile, Santiago Metropolitan Region, Stgo
Joined Dec 2012
289 Posts
Quote:
Originally Posted by Psychosis View Post
I was told many years ago by a yacht designer friend ''If a boat goes fast just once and never goes fast again don't blame the boat''
Exactly my point. One win proves it's not the boat. So I'm happy with the build. I will finish the new fin/bulb, and then focus 100% on trimming and handling.

New sails maybe as winter project? (july-august for me...)
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Old May 26, 2014, 05:46 PM
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Australia, QLD, Peachester
Joined Dec 2013
96 Posts
I'm another who has enjoyed following your build tarmstro. It's like watching a good documentary on tv.
I've shared your satisfaction from page 1 where it was just an idea on a piece of paper to the beautiful craft in those later pics. Congratulations and thankyou.
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