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I decided to work on my Bob Shore Eagle for once. I have a very early kit and the drawings had some major issues. I scraped one base casting due to a broken tap. Then the hole layout for the gears were to tight. But I am still moving on with it.
 

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you have a chance of getting a broken tap in aluminum out three ways:
1. alum
2. heat to 400 or so deg and use a tap extractor - the aluminum will expand a lot more than the steel
3. diamond drill point and a high speed drill (dremel, etc) with lots of water for lubriction - just cut the flutes of the tap - it's tedious but it works. I use a 200,000 RPM dental type drill
 
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I have heard that watchmakers make an arc erosion tool to erode tiny taps that have broken in the workpiece. Slow but "clean" for eroding the core of the tap without damaging the thread. The flutes can then be fiddled out.
K2
 
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EDM has been around for 50 0r 60 years. If the tap is 000 or something, the a diamond point is tough, but if it is 4 or larger, you can use diamond just fine. If you have a mill, you can generally use a carbide drill too. I had forgotten that in my prior post. But heat and a tap remover is easiest, try it. Tweezers might work, or long nose pliers if you don't have, or can't get a tap remover, but heat is imperative
 
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I have fiddled out broken taps with fine circlip pliers (smaller than my electrical snipe nosed pliers), but haven't broken bigger taps to have needed to drill them out. I agree that cooking hot helps remove bits from aluminium - But how hot? I use a wipe with a bar of soap, then when it turns black, the aluminium is hot. Any other ideas?
K2
 
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I have fiddled out broken taps with fine circlip pliers (smaller than my electrical snipe nosed pliers), but haven't broken bigger taps to have needed to drill them out. I agree that cooking hot helps remove bits from aluminium - But how hot? I use a wipe with a bar of soap, then when it turns black, the aluminium is hot. Any other ideas?
K2
I just put a heat gun on the aluminum and when it is too hot to touch, proceed. you can use a thermometer if you prefer.
 

karlw144

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Had problems with the drawings too. This is an early run, got it slowed down after some fiddling. Just can’t find the vid.
Karl
 

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arnie

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There is a chemical that attacks hard steel and not aluminum, I can't remember what it's called but I'm sure a little research can be done. It's a simple chemical you could buy at a hobby shop or big toy store.
 

L98fiero

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There is a chemical that attacks hard steel and not aluminum, I can't remember what it's called but I'm sure a little research can be done. It's a simple chemical you could buy at a hobby shop or big toy store.
It's called Alum and it's usually in the canning and spice section of grocery stores. If you have a stainless steel container place the part in a solution of water and alum and heat to boiling, it takes time but the tap will just fall out.
 

Claireb

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you have a chance of getting a broken tap in aluminum out three ways:
1. alum
2. heat to 400 or so deg and use a tap extractor - the aluminum will expand a lot more than the steel
3. diamond drill point and a high speed drill (dremel, etc) with lots of water for lubriction - just cut the flutes of the tap - it's tedious but it works. I use a 200,000 RPM dental type drill
Hi I'm new to site.
I'm trying to sell some books.
Elmers engines etc,could you please point me in the right direction
 
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I tried Alum. It attacked the alloy the main casting was made from. I purchased a new casting and machined it to the original print. The gear spacing was too close. I ended up lapping them in. The other major problem was the head was drawn backwards. So I ended up making two of them also.

Tim
 

cds4byu

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You can also use nitric acid to remove taps from aluminum.
 

Bentwings

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you have a chance of getting a broken tap in aluminum out three ways:
1. alum
2. heat to 400 or so deg and use a tap extractor - the aluminum will expand a lot more than the steel
3. diamond drill point and a high speed drill (dremel, etc) with lots of water for lubriction - just cut the flutes of the tap - it's tedious but it works. I use a 200,000 RPM dental type drill. I don’t remember the exact expansion ratio but about 4 times at least the steel tap will not expand much most home shops could not measure this .
I like the heat you can bleed a little never seize in at the same time

Also I like left hand drills removing a broken 2-56 tap or 2mm tap is tricky as it is if you have a late you might get away carefully measure location and drill from the back side a blind hole is very hard I worked in a primitive by today standards EDM room we had titanium air craft parts with multiple 2.56 and 2 mm taps broken. Heat is not very good here but we used very thing copper wire and carefully made copper tungsten “ heavy metal” electrodes it was a very PIA project . I would have not felt good being responsible for this machining error. I don’t remember what the company charged but it was very significant 20 to 30 broken taps per part . Must have been runaway cnc machine .


Today I drilled a dozen # 10 brass nuts to 1/4-40 ME tap drill size now I’m tapping them Very carefully I can use the cordless drill to run the tap in while normally bass doesn’t need lube I use a drop of tapmatigic . It seems to help although the tap is high quality so it cuts very cleanly. Ultimately I’ll sand or lap them equal and flat for use as precision spacers . I have quite a number of copper washers with just 6mm hole all are within .0005 thickness best as my “ very near calipers can measure .
 
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Chris Murphy

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Nitric acid works quite well-as I can personally testify-BUT (and it is a big BUT)-whilst it does not attack aluminium-it DOES attack other metals-and since very few people are tapping pure aluminium-in practice we are using a variety of aluminium alloys, the acid approach can lead to discolouration due to the trace components of the alloy reacting with the nitric acid. In some cases this may not matter-in other cases it may. In my case I ended up with a discoloured engine pan-(sandcast , low Si alloy-ended up mottled black and grainy) - which didn't trouble me especially, but for some components which might need to have cosmetic appeal -shiny, polished or anodised-you might run into issues.

ChrisM
 

timo_gross

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you have a chance of getting a broken tap in aluminum out three ways:
1. alum
2. heat to 400 or so deg and use a tap extractor - the aluminum will expand a lot more than the steel
3. diamond drill point and a high speed drill (dremel, etc) with lots of water for lubriction - just cut the flutes of the tap - it's tedious but it works. I use a 200,000 RPM dental type drill
4. I give it to the neighbour and he does his magic (spark errosion).
5. Use a small Endmill and mill around the tap (worked once for me) or one of those drills that leave a core. Later plug oversize hole and redrill.
 
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