magnetic stirrer questions

eli griggs · Dec 17, 2008

I made my first magnetic stirrer tonight out of an old silverware case, scrap plexi, pc fan and 12v 200ma power supply. Two 3/4 inch wide 'super' magnets hot-glued to the center of the fan drive the stir. It works well with a heavy 1 lt., Pyrex measuring cup aboard and polished stainless steel shaft from an old Dremel bit, sans shaping stone, which is a tad more an inch long. My problem is, the steel is not heavy enough to enclose in a slightly longer piece of tubing and still spin well. I tried using a touch of hot glue on each end to enclose it and a small 'O' ring in the middle for better spinning but this isn't working well.

My question is, can I use the stainless steel 'pin' or a mild steel rod, as a stir without it causing problems with my chemistry? What photographic chemicals need to be protected from contact with steel or iron?

I'm mostly working on making some Sodium Metaborate solution, Parodinal and Ansco 130 this week and I'd like to get it done with what I have in hand now, if it can be done without compromising the chemistry.

Eli

Photo Engineer · Dec 17, 2008

Eli;

If stainless is magnetic, it is of such a low grade that it can be corroded by many photographic solutions. This is why stirring bars are often coated in teflon, to both increase "glide" and to protect them.

Higih quality stainless steel is non-magnetic.

PE

Loose Gravel · Dec 17, 2008

You can buy stirrers in many sizes. They are a strong magnet inside of teflon.

eli griggs · Dec 17, 2008

Thanks for the replies. The next time I put in an order to P.Formulary I'll order a proper stir but for now I need something more expedient.

I think I'll try a much smaller Super Magnet in a piece of tubing with hot-glue caps or sandwiched and sealed between some UHMW plastic. Other than that, an old fashioned horseshoe or flooring nail might do for now, again sealed in tube.

Cheers

Photo Engineer · Dec 17, 2008

We used to use glass tubing and put a magnet inside. Then we sealed the ends with a propane torch. Worked fine as long as the glass was sealed and you didn't break it.

PE

Vaughn · Dec 17, 2008

How about some of that liquid handle stuff from the hardware store? It might be a little too grippy.

Vaughn

eli griggs · Dec 17, 2008

I don't think I'd trust any dip-a-handle type product, just because of what chemicals it might bring to the party.

Glass tubes are an idea but the local science hobby shop I use to get lab-ware from closed 2-3 years back and besides, I'm pretty ham-handed at times.

Eli

Larry Bullis · Dec 17, 2008

Why not try some heat shrink tubing? Take your magnet to Radio Shack (if you are in the US), buy the tube, cut off something longer than the magnet (could be oh, say a quarter of an inch longer at each end). Heat it (I use the burner on the gas range; electric would do, or use a hot iron or a torch). I suppose you could fill the open ends with silicone?

I wouldn't think that the handle dip stuff would be a problem at all. We use it on our print tongs so they won't scratch the prints. Works. Haven't seen any problems with it.

Vaughn · Dec 17, 2008

bowzart said:
We use it on our print tongs so they won't scratch the prints. Works. Haven't seen any problems with it.

WOW!!!! That idea is worth the price of admission alone!!!! I got the handle dip stuff, I got many tongs at the university without rubber tips...now I have the answer!!!

Does it work with both the bamboo type and the stainless steel variety?

Thanks!

Vaughn

Photo Engineer · Dec 17, 2008

Shrink tubing leaks! It does not form a seal.

PE

Larry Bullis · Dec 17, 2008

Photo Engineer said:
Shrink tubing leaks! It does not form a seal.

PE

Dang!! Sure could be useful.

Do the walls leak, or is it just that the tubing won't close at the ends?

Larry Bullis · Dec 17, 2008

Vaughn said:
WOW!!!! That idea is worth the price of admission alone!!!! I got the handle dip stuff, I got many tongs at the university without rubber tips...now I have the answer!!!

Does it work with both the bamboo type and the stainless steel variety?

Thanks!

Vaughn

We use it with the stainless ones. The corners will wear off revealing the metal, which will scratch, so they may need redipping from time to time.

The rubber tips on the bamboo ones are much less a problem than the plastic thing that the two sticks fit into; they always fall out, and we haven't found anything yet that will glue wood to that particular plastic. Well hey, I haven't tried the handle dip stuff for that. Hmm, I've been fighting that issue for a long time now. Maybe I'll try some E6000 on it. Have you discovered anything for that?

Larry

Photo Engineer · Dec 17, 2008

bowzart said:
Dang!! Sure could be useful.

Do the walls leak, or is it just that the tubing won't close at the ends?

If you heat shrink tubing it shrinks but does not seal. You can heat it hotter to force a seal but by that time it starts to burn or decompose and forms a rather poor seal. Kinda melted gunk that can stick to the bar or wire or whatever that is inside. It really depends on the shrink tubing I think. I've seen some that does not even shrink properly that is out there.

PE

jeroldharter · Dec 17, 2008

With some luck, you can get a high quality magnetic stirrer on Ebay for $20. I have 2 of them and they work great. I bought several stir bars from an online scientific supply store as well as a magnetic plastic wand to retrieve the stir bar.

Larry Bullis · Dec 17, 2008

jeroldharter said:
With some luck, you can get a high quality magnetic stirrer on Ebay for $20. I have 2 of them and they work great. I bought several stir bars from an online scientific supply store as well as a magnetic plastic wand to retrieve the stir bar.

I got a really great one with heater (more heat than I'll ever need) at a thrift store. I also have an old beater.

I've thought of building a really big one that uses a cow magnet for a stirring bar. It would be useful occasionally, probably not often enough to justify the space it would take up.

L

Bob-D659 · Dec 17, 2008

Other sources for magnetic stirrers are the local farm supply store, they sell teflon coated magnets to keep fence staples from passing thru a cows, sheep etc. they do come in different sizes.

Also the handle dip/liquid electrical tape works well too, just get a piece of a steel or a bolt, attach a small super magnet to one end of it and coat the whole thing with a few coats of the dip.

eli griggs · Dec 17, 2008

Well, I have heat shrink here but I'm leaving that as a last resort. Since my last posting I've found some glass eye-droppers and sealed an one inch section of heavy nail into half a bit, using my handy-dandy Radio Shack Micro Torch; no need to break out the acetylene yet...

My effort wants to turn, but at a lower rpm than my fan does at the moment, which is really frustrating as the hand built multi-unit timer control I'm using has a rheostat on it but I can't get the right combination of switches and plugs right to try it out.

Mostly the tube rattles a high freq. rattle and that just makes me madder. My smallest rare earth magnet is just big enough not to fit these dropper tubes so I may run up to Walgreens 24 hour store and see if they have bigger droppers, but I suspect they're all going to be plastic.

Eli

Vaughn · Dec 17, 2008

Larry...no, I just keep jamming them back in.

Vaughn

Larry Bullis · Dec 17, 2008

eli griggs said:
...
Mostly the tube rattles a high freq. rattle and that just makes me madder.
Eli

Even with the professional units, you have to have the bar in the center and increase the speed from slow. If you just turn it on fast, it just rattles around and I suspect it would break your glass tube.

I got a couple of Labvolt power supply units at an auction. They have continuously variable 0 - 12 DC and 0-120V AC. They work great for variable speed control.

PE -- the tubing from Radio Shack is a mixed bag, for sure. I used to get it at Boeing Surplus. THAT was first rate!

Alas, Bosurp is no more. No more drill bits by the pound. No more great lenses, odd stuff, not so odd stuff, all manner of equipment. I'm sure glad I got my Wing Lynch temperature controller before the doors closed!

eli griggs · Dec 17, 2008

Even with the professional units, you have to have the bar in the center and increase the speed from slow. If you just turn it on fast, it just rattles around and I suspect it would break your glass tube./QUOTE]

If I can't get the timer units' rheostat to work I could try a quick changing out the power supply for a multi-voltage unit, again from Radio Shack, and turn the power up slowly from that.

I think I'll take the dog for a late night walk and pick this up on the morrow.

Cheers

Larry Bullis · Dec 17, 2008

eli griggs said:
If I can't get the timer units' rheostat to work I could try a quick changing out the power supply for a multi-voltage unit, again from Radio Shack, and turn the power up slowly from that.
Cheers

Variacs are very cool! Well, with the little pc - dc 12 v fans, you need a rectifier in there too.

Larry Bullis · Dec 17, 2008

Vaughn said:
Larry...no, I just keep jamming them back in.

Vaughn

I've discovered that it's best to hold onto the sticks and whack the plastic thing straight down hard on a countertop. They still come apart, but it takes a little longer.

Somebody needs to invent a better cheapo tong.

thedarkroomstudios · Dec 18, 2008

Hmm... we got 2 threads going here.

Magnetic Stirrer: Good luck. I do have a couple 30gallon stainless steel units I'll be getting around to listing someday. Doesn't help you now though. I don't know what chem. reaction you'd get but just tossing those nifty nylon furniture glider pads out there as a possible item to attach for better spin?

Bamboozled by Tongs: Drill a small hole through the plastic and bamboo (after whacking on the counter as above) then do quick/cheap makeshift pin out of paper-clip (has worked for me, but then I had a few small cotter pins laying about and they are pretty nice too, or be really official about it and go buy a bolt/rivet/wire... you get the picture.

-Brad

Larry.Manuel · Dec 18, 2008

Some heat-shrink tubing has a sealant layer inside which melts and forms an excellent seal. I used to buy mine from Electrosonic. You may find some info there. Coating a magnet in silicone rubber [aquarium glue] might work, but the [lack of] friction can't compete with Teflon.

totalamateur · Dec 18, 2008

The heathsrink that seals essentially has a coat of hot glue on the inside. I used a ton of heatshrink when I rewired my boat, and since it had to be sealed due to the marine environment, I added shavings of hotglue inside the radio shack heatshrink tubing. The glue melts before the tubing shrinks, so when the tubing does contract, it squeezes the already liquified glue all around whatever you're wrapping. a bit of saliva on the finger tips and some manual manipulation makes sure you got a good tight seal at the ends. HAd to re-wire a connection two years later, due to bilge pump burn out, and the copper was still shinny under my sealed connections, even though it had been resting in an aluminum hull full of salt water for 2 years. Most bare copper disappears in those circumstances.

So , shave of a tad bit of hot glue and shove it into the heatshrink around the metal bar - you'd be better off with a magnet or mild steel (more magnetic) and melt around ....

Just try not to use the high temp melt hot glue, the cheap stuff is best.

magnetic stirrer questions

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