Disolving screw with Alum

[Void]

Dragon,

Just putting the part in a solution of Alum and water isn't enough. It may take weeks to dissolve the broken screw.

I did a job very similar to yours a couple of years ago. The solution should be heated to just below simmering. You should dissolve as much alum as possible; keep adding alum until no more will dissolve. You will have to be around to make sure it doesn't dry out. If you have to leave it alone, turn the heat off.

It may take 2-3 days but it will eventually completely remove the broken screw. That doesn't mean you have to nurse it along on a hotplate for 72 hours it just means that that is how long it took mine to dissolve over a weekend.

The alum method is, by far, preferable to the acid methods. Alum is a food additive and is pretty safe to work with. No more precautions need be taken than for boiling an egg. It will not change the part dimensionally. I have no idea what it will do to the anodizing as I haven't had to use it on any anodized parts yet.

I did mine in a large Pyrex beaker. I would recommend something similar or an aluminum pot. For somewhat obvious reasons do not use an iron pot. I don't know that it would affect the efficacy but my guess would be to not use stainless steel either.

-DU-

[vincemulhollon]

I did mine in a large Pyrex beaker. I would recommend something similar or an aluminum pot.

Goodwill or garage sale quartz pyrex stove top pots. Bonus points if it comes with a lid to reduce evaporation. Quartz pyrex bread making pans were once sold, for the bigger jobs.

I had a submersible all glass aquarium heater where the thermostat welded itself on and killed all my fish over a weekend (grrrr). It (the heater, not the fish) had a new life in my ultrasonic cleaner and my alum pot. Eventually I cracked it, but it sure was helpful for awhile. I suppose a GFCI outlet might be a good idea.

Two things to always pick up at garage sales: 50 cent "glass" stovetop pots and 1 dollar aquarium heaters...

[Westline]

For a good heating source try a deep fryer. Heating source and Alu pot all rolled into one. Or well all the models I have seen and the one one I have is Alu ( ask me how I found that out )
Most of then also has a nice lid that will direct most of the steam to condensate and drip back into the pot ( stops drying out)
Or to run it hot but not boiling for a long time a slow cooker or rice cooker would be perfect, low power ( kind of ) and has a ceramic pot build in.

Kobus

[mochinist]

have any 1/16 carbide endmills? if so, put one in your mill, turn your rpms up to 3k or so, use a nice heavy cutting oil, and bring the endmill down slowly, I usually put some pressure on my quill lock so I dont jerk. if you do it right you can see the tap being turned into chips(more like dust) and you go right thru it in a minute or so.


be sure to keep it covered in oil and go slow like I said.

also dont use a drill chuck, use a collet and dont hang the endmill out any more than you need to.

[im#2]

May I add my 2c worth: I have done this with alum and a candle heater and it works! this tap is in aluminum fellows and anything you do under power will sure as hell go off to the side and ruin it-hence the slow easy way. get as much alum disolved as possible and keep it covered with water and hot with the heater and just have patience! it WILL work!

[Dragons_fire]

I ended up drilling out the center of the bolt with a #55 drill bit, and then i threw it in a pot of simmering alum for a couple hours. It didnt seem to do much to the bolt though. Then i realized that my first hole went fairly straight through the bolt, so i just stuck a bigger bit i and drilled it all out. Then i tapped it for a bigger bolt so hopefully the next one doesnt break as easily.

The alum did take the anodizing off though, so be warned if youre planning on trying it.

[Charles P]

I ended up drilling out the center of the bolt with a #55 drill bit, and then i threw it in a pot of simmering alum for a couple hours. It didnt seem to do much to the bolt though. Then i realized that my first hole went fairly straight through the bolt, so i just stuck a bigger bit i and drilled it all out. Then i tapped it for a bigger bolt so hopefully the next one doesnt break as easily.

The alum did take the anodizing off though, so be warned if youre planning on trying it.

In which case if you use a 10% sulphuric acid solution, a lead anode and an old car battery you'll remove the screw and anodise the metal. I used it to remove a broken tap in aluminium recently

Charles

[Circlip]

I ended up drilling out the center of the bolt with a #55 drill bit

Ahh, swopped it back to a bolt then?

English is a very difficult language to understand when you can't read.

Regards Ian.

[gary350]

Ive been reading that its possible to use Alum to disolve a tap thats stuck in an aluminum part.

My mistake. Drill a hole down the center of the broken screw then use a tap extractor. If that does not work then drill the hole larger and larger until only the threads are left. Pick the threads out with a ice pick. You get one end loose pull it out with needle nose plyers it will come out like a coil spring.

[Richard Wilson]

Ahh, swopped it back to a bolt then?

English is a very difficult language to understand when you can't read.

Regards Ian.

The OP always did say it was a screw or bolt. He only mentioned that he'd read that you dissolve out a tap, he didn't say it wasa tap. It was Gary that started talking about removing taps.


Richard