Use of saw dust

[gman]

Those that cast with bottom pour pots, do you add saw dust on top of the melt to help with dross?

 

[Rick]

Almost all of my casting anymore is with the ladle but when I was bottom feeding yes, I kept at least 1/2 inch of sawdust ash on top of the melt to keep air off the melt. Greatly reduces oxidation. Don't add sprues, rejects or ingots to the pot while casting. Just keep the ash on top.
.

 

[JWFilips]

I never use sawdust in my bottom pour nor a pine stick stirrer.

My alloy is smelted clean with 3 applications of pine saw dust and the alloy is ladeled though the pine dust & resutant charcoal
for up to 8 minutes per application once clean those are the only ingots that go into my bottom pour pot ( no sprues)
When the bottom pour is up to temp I scrape the bottom & Sides with a metal tool made from a stainless steel ruler pulling any gunk up the sides and to the top.. I put a piece of beeswax on top and use that as a reductant then skim of anything nasty & then I let a piece of beeswax form a crust of carbon and that rides the alloy down until I get 2/3 empty Then I repeat the scraping add a piece of BW skim and slowly lower more ingots into the melt holding them up so they don't touch the bottom until they melt.
This is just what I do I kind of like clean bullets and no plugged spout in the bottom pour
Jim

 

[Rick]

Jim, that is the correct method of fluxing with sawdust. Using wax will form a layer also but so does the sawdust. Was much written on the CB site about sawdust plugging the bottom of the pot and causing dirt in the bullets. Truth is that it is impossible to get sawdust (or it's ash) to the bottom UNLESS you physically force it under the melt. Flux as Jim said and there will be no such problems.
.

 

[JWFilips]

If one were to use saw dust in a bottom pour....You can get it "into the bottom" of the pot easily if you drop sprews into the melted alloy. Cold spews go right to the bottom carrying the sawdust carbon ...dropping cold ingots likewise into the melt will do the same. What you want do is to lower your ingots into the melt so that they heat up and float.
Also mixing with a pine stick while ok on top is bad news if you go scraping the bottom with it ( carbon will get trapped under the mix.)
When sawdust carbon gets under the melt of a bottom pour it is very troublesome if not impossible to get 100 % of it out from under the mix....Then getting it in to the spout ...bad news You can temporarily fix by using a bent wire into the orfice but you will be draining & cleaning the pot very soon.

When I started casting This was my bane! I drained my pot almost every casting session. Aftewards some of the "great minds" ( many who are here now) thought me right.
"Clean alloy" in the pot only & no need for flux ( sawdust) just a touch of "reductant" to get the oxides & tin back in.
Since I learned what they thought me I'm happy with clean casts & no plugged spouts. Before that it was a nightmare....Which Knowledge helped me out grow..
As always this is what I do, it works for me. Many others do it differently & it works for them.
You just got to find out what works for you.

 

[gman]

I understand now how that carbon was getting under the melt even in my ladle casting pot. Cleaned my pot out and melting to try to get that out so I have clean alloy in my bottom pour. Guess I misunderstood the use of saw dust. That's why I was hesitant to use in my bottom pour. Thanks fellas! Never too old to learn!

 

[quicksylver]

Sawdust or better yet shavings from my jointer is all I use now....I got contractors bags full of the stuff....
never had a plugged spout...don't know where that came from...?

 

[yodogsandman]

I clean up my re-melted COWW with 3 applications of sawdust and then once with a wax or old bullet lube. That's all done in my cast iron "smelting" pot, outside. Those resultant clean ingots go into my bottom pour pot and are melted again when I cast bullets. I'll flux (reduce) again after they're melted with a small amount of wax (or old bullet lube). I'll scrape the sides and bottom and skim any crud off into a metal coffee can. That's it! I do throw my sprues right back in, too. Never a problem with plugging, either. The amount of tin that oxidizes on the melt after the initial reducing is very, very minimal. Certainly not enough to change the alloys' composition by any amount. I mark my ingot ends with spray paint to identify the alloy and that has to be cleaned up and skimmed off before using any alloy from the bottom pour pot, too. I only flux (reduce) once for each casting session when the pot is turned on and the alloy has all melted.

 

[Ian]

If one were to use saw dust in a bottom pour....You can get it "into the bottom" of the pot easily if you drop sprews into the melted alloy.

So very true. Throwing sprues and culls back carry oxide skins to the bottom like you said also, where they get trapped under the melt's surface at the bottom of the pot and migrate to the valve orifice and end up in your bullets. If we reiterate this enough times, perhaps it will reach those it can help.

 

[Rick]

Correct again Jim. I forgot to mention never using a wood stick such as a paint stir stick to scrape the sides and bottom of the pot. Common sense will (should) tell the caster that the stick will char under the melt and by scraping the sides & bottom pieces of charred wood WILL break off. While it is indeed much lighter than lead much of it will not float to the surface because lead is easily dense enough to hold it in suspension. The current flow of the alloy out orifice will then draw it right into the spout and into your bullets.
.

 

[Glen]

I flux with sawdust, and I continuously recycle my sprues back into my SAECO bottom-pour pot. The last time I had to clean out the pour spout was about 10 years ago, and I cast a fair amount, so that's a lot of bullets. A key step that has not been mentioned in the discussion above (at least I didn't see it), is that after I add the sprues to the pot (and through the layer of sawdust and char on top of the melt), is that I give the pot a vigorous stirring -- not only to speed the melting of the sprues (and help insure the thermal homogeneity of the pot), but also to break the dross loose and help float it to the surface. I don't disagree with anything stated above, I'm just saying that there is an easy fix to avoid problems -- stir the pot when you recycle the sprues.

 

[Rick]

I flux with sawdust,

Yep and because of your informative writings I and I'm sure a great many people use nothing but sawdust. I read an article of yours (well before the book) about fluxing with sawdust and why to use it and how/why it works. I tried it and never looked back or used anything else since. Thanks Glen, that day was a huge improvement in my casting knowledge and in the quality of my bullets.
.

 

[Brad]

I use wood shaving for small pet bedding. I have pushed it under the surface but I finish by stirring vigorously in such a manner than a strong up current forms. This brings crud to the surface for removal.
I use a ladle for dross formation is more severe. I don't flux during a session but do add ingots from time to time to keep the pot level as full as possible.

 

[freebullet]

Chain saw dust for mine.

 

[Ian]

Sappy yellow pine sawdust from my compound miter saw. If I don't have any as a by-product it only takes a minute to fill a coffee can cutting up scrap.

 

[JWFilips]

One of the best ways I have found as an indicator that there is "stuff" starting to get trapped in the bottom of the bottom pour pot; that hasn't been brought up to the surface, is from time to time while casting I look at the underside of my cut sprews. It is a faster indicator of trapped particles at a glance then catching sight of them in the bullets. If for some reason I start seeing that I do a good scraping of the bottom and sides with a lot of stirring and pulling the bottom scrapings up the sides to the top. If you let that go too long the next thing that will start happening is the spout will keep dripping.
Since I have started using good clean alloy ingots in my Lee bottom pour I don't find myself getting that "Lee drip-o-matic thing that many folks talk about.
I understand that many folks use sawdust in their casting pots and also stir with a stick and it works well for them. but for me I couldn't get it to work until I switched to metal utensils and only a bean sized piece of beeswax from time to time to reduce oxides

 

[JSH]

Well, I have been casting for a day or so now, danger if I haven't learned something new again.
Here is a question or an issue I have run across.
Will the tin seperate after it has been mixed? I ask because I have weighed out batches of alloy, melted all, stirred, fluxed, stirred more, then go to casting. All is well for this.
Then at a later date I will start off by filling the pot with sprues then stir,flux,stir and cast. The alloy sprues refuse to cast well till I add a bit more tin.
Had this happen on my Lee 20lb pot, then I picked up an RCBS pot, it still happens but doesn't seem as bad. I thought it may be a temp issue, but that doesn't seem to be an issue as I tinkered with it. In the past it seemed if I fluxed that would straighten it out and it worked fine. Not so much anymore.
As to stirring I have a buddy that uses a cordless drill with a length of all thread and a modified fender washer to get a good stir on it. He started using this when he was chasing harder bullets and adding antimony. Of course one want to use a lot of caution here and dang shut don't pull it out while it is spinning.
Jeff

 

[Brad]

Tin doesn't separate out per se. It does oxidize and the oxides will float on the surface given an oatmeal like dross. I haven't ever found a reliable source that showed how rapidly tin is depleted this way, my guess is that it is a reasonably slow process. The dross covers the surface of the melt and prevents oxygen from the air from reacting with the tin remaining in the melt.
I would be willing to bet there is something other than tin causing your troubles. I have cast lots of bullets with alloys having under 1% tin and got good fillout.

Using a drill to stir is a bit excessive. I use a long spoon and stir almost as if bearing eggs. This creates a strong up current that brings crud to the surface. I stir for at least 15 seconds to really make sure the crud is on the surface and ready to be skimmed off.

 

[Rick]

Could be couple of things Jeff. No, it's physically impossible for the Sn to "separate" out but you can deplete the Sn and or Sb by skimming it off as oxides. Second, at what temp are you running your pot? The metallurgy of a Pb/Sn alloy is that the Sn cannot do what you put it in the alloy to do past about 750 degrees. Sn in the alloy reduces the surface tension of the alloy so it fills out the mold better, cast too hot and you have lost that benefit.
.

 

[Rick]

Tin doesn't separate out per se. It does oxidize and the oxides will float on the surface given an oatmeal like dross.

That's not correct brad. The oatmeal look on top of the melt would more than likely be Sb, not tin.
.