Just wondering how others are making thier lead bulbs?
And before some smart _ _ _ says with lead ,I’ll make it clear as to what I mean.
I made a model of the bulb using basswood then pressed this into some plaster paris. Did this twice to make 2 halfs.Mold sat for 5 days to ensure it was completely dry.Once it set up I then removed the wood plug and poured the lead. A bit of filing and the two halves were glued together. A bit more sanding and there is the bulb.
Here at Climate Models we have proper aluminum molds made up for our kit keel bulbs.
Some are 1 part, others are 2 part molds.
They are made by a sand-cast method with a CNC milled plug as the master.
The plaster method works OK for one or 2 bulbs at most. Even after drying the plaster for a week it still has moisture content. Be careful, the steam trying to escape from the plaster can send molten lead all over the place.
Peter
Have to agree pouring lead can be very very dangerous. Fumes are one problem another is if the lead boils. Had this happen and splashed the top of my hand. Son of a gun does it ever burn[:-jump]
Yes a plaster mold is only good for a few pours then it is toast. Someone once mentioned using sand to form the mold with but not sure how this is done or even what type of sand a person uses.
For quick, one off bulbs for non racing models I cut up sheet lead to the aproxximate shape of the bulb i want and stick them together bread and butter style. I then fair in the rough shape using epoxy mixed with iron filings. Not as good as a solid lead bulb, but close as you can get without casting and all that hassle, also its dead easy to get the right weight bulb without doing any maths…
I design the bulb I need then make shadows just like a boat. Put rod in through nose and spin with drill and sand with orbital.I cut a pringles can almost in half long ways vertical. Leave metal rings. Pour conc. in the bottom half. Put in foam plug, coat with something I just use vaseline let set up. Put in foam piece for the lead to pour through wedge against side close and tape pour conc through top. Remove from pringles can and let dry two weeks. Heat in oven at 200 for 15 min before pouring. Have no way to attach pictures.
Here at Ludwig Manufacturing we use cast aluminum molds for pre-set weight bulbs, and then there is a 2nd set that has a preset valued nosecone with a hollow tube extension that is glassed to it. There is a piece of all-thread set into the nose cone when it is cast and it works as a spindle which allows you to slide lead donuts over the spindle into the hollow tube and the tail cone screws onto the spindle end which gives you the chance to set the weight of your keel as you see fit. This is immeasurable during testing.
I will echo the warnings above… casting lead is not to be taken lightly. It is absolutely a HAZMAT item, and must be treated accordingly. The slag that we skim off has to be stored in a concrete container and returned to a local foundry for disposition.
Once lead is on you, it is for keeps. Once you breathe it… it stays in you. I hear stories ALL the time from people telling me about “dad melting lead on the stove” right in the family kitchen… and I cannot stress strongly enough to not do anything remotely close to that. Use an approved mask, welders gloves, and leather apron when dealing with this stuff.
Also, I have baked plaster molds in the molding oven at 260 degrees for 3 DAYS, and STILL had moisture in them. Bottom line, plaster is extremely risky.
I am part way thru making my first keel bulb. The method am using is in the US1M construction manual, creating a mold of Plaster of Paris and filling it with lead shot and epoxy resin.
I thinned the epoxy with rubbing alcohol. I found that the Epoxy didn?t cure as it should have. It was a little bendy for a couple of days, but it is hard now. Next time I do it I will preheat the mold in the oven and warm the epoxy with a hair dryer, that should allow the epoxy to flow into all the spaces between the lead shot.
To finish the bulb, I plan to strengthen it by putting an old circuit board, without the components, between the two halves. The tail end is easy to break off, I’ve broken the last inch off each half and had to glue them back on.
Kevin L.
“Oh Drat these computers, they are so naughty and complex… I could pinch them”
I bought my lead bulbs from Great Basin. They charge $25 for their bulbs and their shape is really nice. They come with a slot in them.
The surface is reasonably rough and requires some fairing work to make them smooth enough to use, but it sure is a lot easier than trying to cast it myself.
Yes, I use my metal lathe but it is not that easy.
Because it is a changing curve you have to use the controls simultaneously and it is very easy to screw up.
Lead is diffcult to cut on a lathe,it chatters.
3.It is hard to grab a tapering shape in a chuck.
4.When you get to the last bit,when the ends of the bulb are thin it has the annoying habit of popping out of the lath which bends it severely.
I solved the 3rd and 4th problems by casting a piece of 1/4" brass round stock into the center of the bulb. This stiffens it and also gives you a solid end to grab onto with the chuck. Also as Sails Etc. discovered it adds stiffness to thin bulbs. Apparently long thin bulbs will sag over time.
I do end up with nice bulbs so it is worthwhile. My lath is a combination lathe/milling machine so I can mill the slot and drill the hole quite accurately. It takes the good part of a day to turn old tire weights into a bulb.
Freeze your lead before machining one end, then freeze it again and rechuck to machine the other end. Be very careful of the vapors and chips. Try to recycle as much as you can. Sometimes the cutting tool is too sharp and augers right into the metal. Hone a little dullness into the cutting tool (break the corner). Clyde (machinist in training after 30 years machining)