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Author Topic: High density ballast.  (Read 1401 times)
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TheLurker
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« on: May 19, 2017, 11:14:28 AM »

I've been away for from the hobby for a little while so forgive me if ask some seemingly daft questions.

To start with.  Ballast.

Background
Like a lot of modellers I used to use lead (Pb) fishing weights from Woolies but the box of (non-toxic) weights I bought recently (Decathlon) don't seem anywhere near as dense as lead and this proved a bit of a problem when trimming a model with a small ballast chamber/tube. I got around it by extending the ballast chamber with an acetate tube, but it was a bit of a bodge.

The Questions
  • What's out there that compares well to lead for density?
  • Any products to avoid completely?

chr$
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billdennis747
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« Reply #1 on: May 19, 2017, 11:51:16 AM »

Use lead. Get an offcut scrap from a roofer
Or De Luxe materials do something called liquid gravity. It's quite dense but is tiny particles so you can get a lot in a small space, then add glue
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Greg Langelius
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« Reply #2 on: May 19, 2017, 02:09:28 PM »

Bismuth shot. https://www.amazon.com/Bismuth-Shot-pound-99-99-Pure/dp/B01F5SB8SO/ref=sr_1_7?ie=UTF8&qid=1495217302&sr=8-7&keywords=bismuth+metal

Bismuth Info: https://en.wikipedia.org/wiki/Bismuth

Greg
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ffkiwi
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« Reply #3 on: May 19, 2017, 03:06:43 PM »

Another material that has application is tungsten putty-which is used by the RC car guys for balancing purposes....presumably to 'tune' the chassis for improved handling. As the name suggests this is a putty like material which is mouldable and filled with powdered tungsten-so remarkably heavy for its size. tungsten has a density of 19.25g/cm3  vs lead at 11.34g/cm3 so even allowing for the fact that not all the material is tungsten in the putty-some is obviously the 'carrier" material-you're still ahead in terms of weight and reduced volume-not to mention that you can mould the material-into any vacant corner ina fuselage or simply use it externally like plasticine or modelling clay. My personal favourite use is on rubber power scale models with exposed engine cylinders-I use it inside the cylinder (especially if they're the Williams Bros moulded pastic ones) to help get the Cg where it should be.

 ChrisM
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mike
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« Reply #4 on: May 19, 2017, 03:53:05 PM »

Tungsten putty isn't so appealing - some actual figures here : -
http://www.flyquiet.co.uk/index.php?topic=4807.msg33349#msg33349

"Densities determined as

Lead                10 gm/cc
Tungsten putty  2.75 gm/cc
Blu Tack            2 gm/cc
Plasticine          1.7 gm/cc

Conclusions
Use lead in small spaces.
(Thin lead sheet (1-2mm) is easy to cut with side-cutters or even strong scissors.  It can be folded tightly with pliers.)
In order of decreasing density, the following are all mouldable with the fingers:-
Tungsten putty - hard to justify with the extra cost. (10x Plasticine)
Blu Tack - easiest to find and has other uses.
Plasticine - for economy and if you have the space - you get a lot for your money (and there are many colours available!)"

More in the rest of the thread at the link.
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TheLurker
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« Reply #5 on: May 20, 2017, 05:25:36 AM »

Thanks for the info. Gents*.

Looks like it will be Pb, if I can find a source - not many roofers hereabouts, or Liquid Gravity.

Quote from: mike
Blu Tack            2 gm/cc
Plasticine          1.7 gm/cc

This has saved me a few pence. I was going to buy some plasticene today as an alternative to the Blu Tack I'm trying (and failing - but that's another story) to trim a small profile rubber model with.

chr$
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*On this sort of forum I think, statistically,  that I'm probably on safe ground calling you Gents. Smiley
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duration
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« Reply #6 on: May 20, 2017, 06:51:07 AM »

Back in the 1970s, a US F1C (FAI Power back then) used depleted uranium for the counterweight on a one-bladed prop! The counterweight was housed inside an oversized spinner.

On a more practical note, I've made turned aluminum and brass nose weights for F1B front ends. These look like oversized wheel collars and fit around the rear bearing housing on Vivchar front ends. To calculate the size I used the specific gravity of the metal (2.64 for aluminum and 8.56 for brass) and then determined the volume need to achieve the desired weigh (typically 4 or 8 grams. Specific gravity is the relationship of the weight of a material to an equal volume of water. By definition, a cubic centimeter of water weighs one gram, so a cc of aluminum weighs 2.64 grams. So all I had to do was calculate the volume I need to get the desired weight (i.e. 1.515cc of aluminum weighs 4 grams).

Louis

PS: The specific gravity of cast lead is 11.35; rolled lead is 11.39. Tungsten is 19.62. Couldn't find info on uranium, depleted or otherwise.
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Mefot
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« Reply #7 on: May 20, 2017, 06:54:40 AM »

Although these days I tend to use plasticine I have in the past used self adhesive wheel balancing weights from the local tyre fitters. The price of a pint to one of the fitters should buy plenty to play with. They can be cut or pared down to any weight you like. I used to trim with plasticine,weigh what I had used and then replace with the appropriate amount of wheel weight. I really should get some more...!!!  Smiley
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flydean1
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« Reply #8 on: May 20, 2017, 09:57:16 PM »

Golf shops use adhesive backed sheet lead.  You can cut with shears easily.  Last roll I bought was from an eBay store.
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TheLurker
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« Reply #9 on: May 30, 2017, 03:37:56 PM »

Well, well, well.  Problem solved.  Nattering (via e-mail) with my uncle the other day.  Turns out he has rather a lot of lead lying around after having the bay window on his house redone a year so back.  At least 1lb of lead is now in the family courier system and will be in my sweaty little mitts within a fortnight. Smiley

That should keep me going until I hop the twig.
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p40qmilj
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« Reply #10 on: May 30, 2017, 05:27:39 PM »

 Grin i use solder for rubber planes

jim Grin
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NeilH
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« Reply #11 on: May 30, 2017, 07:41:40 PM »

When trimming a model, I use modelling clay attached externally.  Once I have the model flying good, I remove the clay, weigh it, and then take a split shot fishing sinker and trim it to the correct weight and attach it internally with epoxy.
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TheLurker
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« Reply #12 on: May 31, 2017, 12:55:09 PM »

When trimming a model, I use modelling clay attached externally.  Once I have the model flying good, I remove the clay, weigh it, and then take a split shot fishing sinker and trim it to the correct weight and attach it internally with epoxy.
More or less the sort of thing I did back in the dim and distant, but all (almost all?) fishing weights sold in the U.K. these days are now made of non-toxic1 metals and don't seem to be anywhere near as dense as lead.  It's not a problem for larger models with lots of ballast space, but it is for smaller stuff.

1 - Too many river birds, especially swans, were being killed by lead poisoning from lost or discarded weights.
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ram
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« Reply #13 on: May 31, 2017, 01:10:21 PM »

Try here:

http://www.sportfish.co.uk/fly-fishing-tackle/fly-tying-materials.html?master_type=6433

and:

http://www.sportfish.co.uk/veniards-lead-wire.html

Rey
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Jez Wilkins
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« Reply #14 on: June 01, 2017, 04:29:48 AM »

The Lurker said
Quote
1 - Too many river birds, especially swans, were being killed by lead poisoning from lost or discarded weights.

Yes, that was the myth that was put about at the time.  The real problem was (and still is) lead shot used by hunters http://www.bbc.co.uk/news/science-environment-34861602.  The difference is easy to distinguish - the lead shot used by anglers/fishermen has a split in the side - 'split shot' - so that you can attach it (squeeze it/bite it) onto your line.  Lead shot used by hunters has no split.

In the U.K., fishing weights can still be lead, if they weigh .06 grams or less, or more than 28.35 grams (lead shot weights from size 14 to size 8 and lead weights over 1 ounce) https://www.gov.uk/freshwater-rod-fishing-rules/tackle-you-can-use.
 
For ballast, I use lead flashing (c. 1.5 mm thick, suitably cut to size, shape and weight and glued into place with slow setting epoxy resin glue).  Purchased from a scrap dealer many moons ago and also used for melting down, to make sea fishing weights.

You need to take suitable precautions in relation to the (toxic) dust produced, when rubbing the oxide off of the surface of the lead, to create a (shiny) 'key' for the glue.  You can prime the lead (with a special primer, suitable for non-ferrous metals) and then paint it, when it is in situ, if having a bare lead surface in a model is a cause of concern for you.

I have tried alternatives (e.g., 'tungsten putty', used for fishing) but have always returned to lead flashing.   
    
Cheers,

Jez Wilkins
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TheLurker
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« Reply #15 on: June 01, 2017, 03:03:08 PM »

Thanks for that. Jez, Ram.

The size limits probably expain why I've only been able to find the relatively low density non-toxic weights because I'd been looking for split shot for the range of diameters and weights. 
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Jez Wilkins
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« Reply #16 on: June 01, 2017, 04:56:38 PM »

Thanks for that. Jez, Ram.

The size limits probably expain why I've only been able to find the relatively low density non-toxic weights because I'd been looking for split shot for the range of diameters and weights.  

No problem Ram.

Size 8 split shot is what I know as 'dust shot'.  Anything smaller than that (10, 11, 12, 13 and 14) I would describe as 'micro shot'.  The largest split shot that I am aware of is SSG (or 'Swan shot') - still only weigh 1.6g each.  So, nowhere near the 1 ounce lower limit for lead.  Therefore, all (U.K.) split shot between 8 and SSG (No.6, No.4, No.1, BB and AAA) will be non-toxic material and not lead.  Caused quite a lot of (fishing) problems when the ban first came in, because the non-toxic alternatives were shinier (i.e., more 'fish scary'), harder (crushed the line more, weakening it) and less dense (hence larger and more noticeable to the fish).  The lack of density/larger size is what prompted your first post - so we have about come a full circle now, haven't we? Smiley

Cheers,

Jez Wilkins          
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