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Home Model Engine Machinist > Building Them > General Engine Discussion > broken tap in aluminum cranckase

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Old 03-04-2017, 04:56 AM   #51
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Just some added FYI on this saga. For kicks I tried over-milling on the stuck tap in junker crankcase. First with Tin coated endmill. It met resistance. I pecked at it for 0.025" or so, but figured maybe it wasn't ground quite correctly for that kind of center cutting. Then I switched to brand new 4.5mm center cutting carbide ball end mill. Almost same result. I need to use these tools so didn't want to bugger them up experimenting. But the tap seems to be tough stuff. One day maybe I'll try a carbide drill.


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Old 03-04-2017, 05:06 AM   #52
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I ended up making a new crankcase. They get better with practice . After trying all kinds of different setup variations & tap types & fluids... this time I offset tap from bottom of hole the proper amount & it everything went smooth & predictable. Concluding that the broken tap arose by a combination slightly shallow hole (drawing interpretation error) and insufficient bottom clearance (my fault).

I'm going turn up some little dedicated (hand) tapping knobs as I have some M2.5 threads into even shallower blind holes in my future. I think I want to do these by hand. But anyway I'm much more confident of my tapping head operation now when the need arises.


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Old 03-16-2017, 11:55 AM   #53
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One way which will succeed is to use a hot sodium hydroxide (Caustic soda and lye are other names) solution. Your crankcase will go into solution, and the tap will be lying in the bottom of the container. As an added bonus there will be copious amounts of hydrogen released as well. The new one looks great by the way
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Old 03-16-2017, 06:04 PM   #54
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I haven't trolled through all the replies here, so forgive me if this idea is already there somewhere.
The basic idea is to weld a steel rod to the tap. I know this is not always possible, but now and again, it is. If the welding is successful, it will almost certainly get the broken tap out.
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Old 03-17-2017, 01:27 PM   #55
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i have had great success with removing broken drills from aluminum with alum powder. i am actually removing a #50 drill now.

here is what i use, mason jar with a bottle of alum in it and water. i have spring water at my house. sort of a double boiler setup because i don't have a pyrex or glass pot and don't want to ruin my wifes good pot. anyway i het on the simmer burner on the stove. you can see the little white dots in the picture, those are actually bubbles that the flash made look white. those bubbles are coming from the hole the drill is in.

the drill is just a cheap black oxide coated drill. when its done the aluminum will look dull gray in color but will rub right off with some fine steel wool or hit it with the buffer for a second. once done ill show what it looks like
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Old 03-26-2017, 08:04 PM   #56
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Default Broken Tap

You're going to be very lucky in getting it out with all these suggestions. I would take it to a shop that has an E.D.M. -- and hopefully they will be sympathetic and do it for free. It's the only way of getting it out without making a mess, and ruining your crankcase and doing more damage. Good luck!
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Old 03-26-2017, 11:47 PM   #57
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The 'mess' is behind me & a new crankcase successfully machined. I learned some important lessons about blind hole tapping. Good thing, radials have a lot of these. I am going to turn myself some knurled style mini tap holders 'knobs' so I can feel the hole & tap progression by hand. I have some even smaller M2.5 & M2.0 ones to do. Stay tuned. Right now I am doing some lathe repairs / upgrades. It coughed a fur ball half way through my crankshaft.

BTW, this fellow is building an homebrew EDM
http://www.****************.com/thre...machine.55621/
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Old 03-27-2017, 08:18 AM   #58
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Peter,

I uploaded a cheap and easy spark eroder to make a few moons ago.

http://www.homemodelenginemachinist....roder-240.html

Instead of making finger turners for your taps, where they can still go in not square, what you really need is a tapping stand.
I made mine from an old cast iron surface plate but almost anything can be used as long as the column is truly vertical to the base.

Just search for tapping stand and look at the images, they will give you enough info to easily make your own.

There are even a few shown on here. This is a basic one, I fitted a small chuck to mine so that it is a lot easier to fit different sized taps.

http://www.homemodelenginemachinist....apper-166.html


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Old 03-27-2017, 08:44 AM   #59
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Greetings John.
Unfortunately, I'm getting precisely nowhere with both projects mentioned..
Cheers

Norman
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Old 03-27-2017, 06:59 PM   #60
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Thanks John, appreciate the plans links.

For this specific part I wanted to preserve the indexing setup on RT & mill. Each of 5 cylinders needs to be facet cut, cylinder skirt bored and the 4 M3 blind tapped holes on a pattern. It was easier to set the XY hole coordinate & then repeat for all 5 facets vs. tapping off the mill or a different tapping fixture. But that looks to be a very useful tool nonetheless.

I have made one finger wheel type tapping knob for a similar size tap (4-40) & it worked quite well. I ground a flat midway on the shank to seat a setscrew in the knob & that allowed the top of tap to extend up into the chuck for centering. I just lightly clamp the jaws so it was free to rotate & slide up & down. One could get fancier with a matching socket that enveloped the shank. There is so little torque required to tap in aluminum it actually goes quite well & I suppose more importantly you can feel by hand.

On the radial I figured let the tapping head do the work & do 20 holes in one tapping operation. Now with an uneventful 'good one' behind me, my entire problem issue was insufficient over-hole depth to accommodate the tap extending further. The instructions are quite clear regarding this, I just made an error on depth.

Hope I don't have to use an EDM but good to have on the project list.


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