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Small, broken drills in aluminum...

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Small, broken drills in aluminum...

Old 02-24-2008, 10:13 PM
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ptulmer
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Default Small, broken drills in aluminum...

How the holy hades do you get them out?! I wanted to run my Toki, but the old wooden adapter was falling apart on me, so I decided to make a nice aluminum one. After going to great pains to make a nice piece, I was drilling the last four holes that were to be tapped 2-56 for holding the engine down and the stupid, cheap*** Chinese drill broke! You probably already realize that the aluminum had galled nicely, clamping the unreachable piece nice and tight. Now what?
Old 02-24-2008, 10:27 PM
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Default RE: Small, broken drills in aluminum...

Patrick, how thick is the aluminum? The bit is most likely not retrievable if buried in thick aluminum. I have tried heating the aluminum to expand it, then pick at the broken bit to work it loose. In the end the only way to salvage the project is to drive out the bit with a punch and re-think your attachment choices. I never try to cut virgin 2-56 threads in anything thick. I think #4 is as low as I'll go, even #6 can be dicey. Only the best cutting tools will do with this tiny hardware.
Old 02-24-2008, 10:32 PM
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Default RE: Small, broken drills in aluminum...

Start again
I have extracted them before by drilling through from the other side (you have to have the hole lined up perfectly, then punch it back out with a very thin pin punch. MAy work depending on how badly galled the ali is.
Old 02-24-2008, 10:34 PM
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Default RE: Small, broken drills in aluminum...

It's thick. Like 3/8" or so. After realizing the tap was too short, I was going to mill it down after drilling. But I wonder what the bit will do to my end mill. Maybe try to mill around it and put the vice grips to work?
Old 02-24-2008, 10:43 PM
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Default RE: Small, broken drills in aluminum...

This is just a plate to test run the engine on? Make a punch out of music wire and blast it out of there!
Old 02-24-2008, 10:46 PM
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Default RE: Small, broken drills in aluminum...

Just use 3 holes, its only a .050 right?...Rog
Old 02-24-2008, 10:56 PM
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Default RE: Small, broken drills in aluminum...

I don't recall off hand what the chemical is, but there is a chemical you can put the parts in that will dissolve the drill bit (or any ferris material) and not hurt the aluminum. May be worth doing a search on the net for it. There was a guy on a Mopar forum who had to extract a broken tap from an aluminum head and it was suggested to do this. He said it worked after soaking for a few days or so.

Hogflyer
Old 02-24-2008, 11:18 PM
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Default RE: Small, broken drills in aluminum...

For this one I put my professional hat on (chemist. biochemist)-what you need is 30% nitric acid, which is passive towards aluminium, but will dissolve the steel drill bit (or broken tap, or broken screw as the case may be) Immerse the plate in 30% nitric (use a plastic bowl or a ceramic or glass dish. Use rubber gloves when handling the stuff. [30% v/v is not especially strong, but stronger than dilute-it works out about 2.25 X dilution of the normal concentrated stuff, which is 67%] There will not be any significant fuming, merely slight bubbling around the site of the hole. The process will take a while-several hours to overnight-since thee is only a small access area for the acid. Eventually the bit will either be completely eaten away, or reduced in size so that it simply falls out.
I've used this trick on both engines and alloy pans on a number of occasions.

Use ONLY nitric acid-you cannot use the other common mineral acids for this process.

'ffkiwi'
Old 02-24-2008, 11:37 PM
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Default RE: Small, broken drills in aluminum...

There's also outfits that'll burn it out with a plasma arc..somehow I'm not sure this particular part is worth that kind of investment though.
Old 02-25-2008, 03:10 AM
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Default RE: Small, broken drills in aluminum...

If it was a gummy aluminium you're pretty much hooped other than drilling from the back side so you can punch it out or the acid trick which were both mentioned above. There's also electro milling but that's pretty pricy to salvage a small bit of aluminium. If you do the acid bit remember your high school chemistry. It's acid into the water. NOT water into the acid. Even so you need to add the acid slowly if it's very strong. You'd probably also want to use distilled water instead of tap stuff to avoid any interaction of the acid with the usual chlorine and flouine in the tap water.

The other option is to toss it and start over. And this time use a better grade of metal or at least use more cutting fluid so it can't gum up.

Hey, at least the new drill bit you need to buy now will be sharp. There's always a silver lining to the storm cloud if you look hard enough.....



Makes you want to reach out and smack me doesn't it?
Old 02-25-2008, 03:24 AM
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Default RE: Small, broken drills in aluminum...

That nitric acid trick sounds just the thing to get a broken screw out of a plastic engine mount. I've been flying with only 3 screws holding down a norvel. It hasn't come off in flight, but I do have to tighten them occasionly.
Old 02-25-2008, 09:17 AM
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Default RE: Small, broken drills in aluminum...

Nitric acid is kind of hard to come by. I remembered that trick from TMBR but couldn't find it or remember what the acid was. Now that ffkiwi has said what the acid was it's easy to remember the "chapter" was labeled "removing small taps from aluminum" and radiator shops use it. That's the frustrating part of those books. Filled with great info in a haphazard fashion. BTW, those books should be renamed. The Machinist Toiletside Reader. That's were all mine were read.

Bruce, I'm ready now to toss all my cheap bits and buy some good ones. Any ideas about what I should be looking for?
Old 02-25-2008, 11:35 AM
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Default RE: Small, broken drills in aluminum...

When drilling the key is to use low speed, plenty of coolant (keep the pressure on to avoid skidding and work hardening on S/S).

I recall breaking a tap in a 1/2" thick stainless steel pipe flange. Obviously it was the last hole of the six. I marked it out again between the original holes after welding up the mistakes.

Works with S/S but when a colleague did the same on an Aluminium component that had to be Anodized the mistake became obvious.

Will your adaptor take double the number of holes?


Best of luck!!




old git - - - - - aka John L

WACO Brotherhood No. 14.

Old 02-25-2008, 12:12 PM
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Default RE: Small, broken drills in aluminum...

now, if you really want to turn this project into another project, you could always build yerself an EDM and use that to remove the tap. Afterwards you would have an EDM to make all sorts of neat things!

cheers, Graham
Old 02-25-2008, 12:16 PM
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Default RE: Small, broken drills in aluminum...

As a private person it is rather hard to get hold of nitric acid, apparently it can also be used to make explosives.... [X(]
Old 02-25-2008, 02:21 PM
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Default RE: Small, broken drills in aluminum...

EDM is what I was trying to think of. That's the one that's very commercil and very expensive.

No real advise on the drills other than buy from a recognized outlet like Enco or similar. Hell, my main set is from the equivalent up here to Grizzly or Harbour Frieght but I try to keep them sharp. I'm still working on ideas for making a drill sharpening jig for drills from 80 up to around 1/4. Sharp drills are the key moreso than brand name I've found.

Sorry Old Git, but for small sizes like we're talking here on this project and in aluminium high speed is what you want to encourage the chips to clear better. But I'll agree on the coolant/cutting fluid recomendation.
Old 02-25-2008, 04:08 PM
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Default RE: Small, broken drills in aluminum...


ORIGINAL: BMatthews
Sorry Old Git, but for small sizes like we're talking here on this project and in aluminium high speed is what you want to encourage the chips to clear better. But I'll agree on the coolant/cutting fluid recomendation.
Bruce, you're quite right, I wasn't paying proper attention. Personally, I can't sharpen small drills any more. (thinks, "not so good with big ones either!")

I have seen a drawing of a Spark Erosion machine for home construction but that becomes rather more like model engineering.



old git - - - - aka John L.
Old 02-25-2008, 08:49 PM
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Default RE: Small, broken drills in aluminum...

When I first saw this thread I immediately thought of Ron Chernich's web site and this bit he wrote about this subject:

How-To Remove Broken Taps ...or... Making and Using a Basic EDM

http://www.modelenginenews.org/meng/edm/index.html

I have read a bit about EDM and have considered starting to sort through my "junk pile" for suitable components and start to collect other suitable bits to build such a device. It isn't happening too quickly mind you. There seems to lots of easy found info on the net, more of a matter of just sitting down and doing it. I guess I just can't think of anything I really need one to make yet so it remains a passing fancy for the moment.

Incidentally for anyone who has never had a look at Ron Chernich's web site, it is well worth spending the several hours just taking a quick look at if you have any interesting in model engineering and model engines in particular.

cheers, Graham

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