Suggestions to remove broken drill, and repair some small holes?

Discussion in 'Mistakes, Blunders and Boo Boos' started by Bryanbdp, Apr 7, 2019.

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  1. Apr 7, 2019 #1

    Bryanbdp

    Bryanbdp

    Bryanbdp

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    I have been working on the crankcase for a 9 cylinder radial engine. I turned the major contours on a lathe, then moved over to my new (to me) Syil X4 CNC mill.
    I have had some issues with the posted Gcode from Mastercam. It adds some moves at the beginning and end of my tool paths, I have to figure out how to disable this.

    Anyways, I have two #45 (.082") holes with drills snapped off in them. One was from an unexpected post movement, the other just snapped. If they were larger, I'd know what to do. But these are pretty small, and about 7/16" deep. I thought about heating the casting, then trying to shock them loose. I also thought about using a dab a superglue, and trying to attach to them. Can anyone share methods that have worked?

    Also, I have a few holes that are a bit off. I'd like to fill them and re-machine them. Do you think that aluminum welding/brazing rod would fill the holes? Does that stuff machine OK? Will heating parts of the crankcase permanently distort it, or will it be OK? The crankcase is about 5" in diameter, 6061T6 alloy.

    Any help would be greatly appreciated!
    Thank you,
    Bryan

    cylinder machining.jpg
     
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  2. Apr 7, 2019 #2

    petertha

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    Before everyone comes to your rescue about using alum solution, have a read through of my experience.
    https://www.homemodelenginemachinist.com/threads/broken-tap-in-aluminum-cranckase.26470/
    Now my tap was coated vs bright/HSS and broken off in a blind hole and other issues you can compare & decide on your own. But personally I didn't have a great experience with alum it despite seeing some YouTube vids and other 'authoritative' instances where it did appear to work. If it was slam dunk fix it would be widely documented & I just don't see that.

    I didn't have much luck drilling it out with a carbide although I think that is kind of situational specific. The tap itself is also very hard material & irregular when its sheared off & flutes etc. So kind of difficult for the carbide drill or endmill to center & bite down on it. I was making headway but it was sure slow & carbides are not cheap.

    Of course there is EDM but if you are like 99% of home builders, probably don't have one of those sitting in the corner. But if you have a buddy with the equipment that would be a great solution.

    Personally I would feel better about core drilling the offending drill or tap, thread in an oversize plug with permanent Loctite & re drill/tap the hole. I can envision instances where that may be more or less difficult but its also possible to practice on a representative piece of scrap something until your are comfortable. For example drive a piece of drill but fragment or HSS pin into an undersize hole in some aluminum & pretend that is your investment engine piece.

    Here is an example of a plug. He has done similar fixes in his other engines.
    http://modelicengine.la.coocan.jp/h9090501.htm

    I cant comment on potential heat distortion of TIG-ing material into a hole with no offending tool stuck in there, I am not presently set up for that.
     
  3. Apr 7, 2019 #3

    stevehuckss396

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    Personally I would core it out and put a threaded plug in as well.
     
  4. Apr 8, 2019 #4

    Cogsy

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    Alum can work (I've done it) but it is seriously slow and depending on the material of the bit it may not work for you. I'd go for coring it out and plugging the hole as well. I'd only ever consider using alum again on an expensive casting that I couldn't plug or a cosmetic part with too many hours in it to want to remake.
     
  5. Apr 8, 2019 #5

    lohring

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    EDM will do it if you know a friendly shop that has one.

    Lohring Miller
     
  6. Apr 8, 2019 #6

    werowance

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    I had success on stainless steel removing a tap using ferric chloride (the stuff used to etch ciruit boards) it didn't react with the stainless and the tap was just mush when I went back to it. I used to make circuit boards and back then I could get ferric chloride at radio shack as well as a local electronics place. however I do not know how it would react with aluminum. I know copper and regular steel it will dissolve it. If I have any ferric chloride left at home ill test with aluminum and report back. unless anyone already knows how it reacts to aluminum.
     
  7. Apr 8, 2019 #7

    Bryanbdp

    Bryanbdp

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    Does anyone sell miniature annular cutters or "hollow" drill bits, that I could drill around the bit to remove it?
     
  8. Apr 8, 2019 #8

    mcostello

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    Could You try making Your own coring bit using Aluminum oxide grit. Google drilling a piece of glass with a metal tube using a slurry of Aluminum oxide. Valve grinding compound would work.
     
  9. Apr 8, 2019 #9

    kwoodhands

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    I also have used alum. The first time I broke a 2/56 tap in a 6061 aluminum cylinder. I mixed alum and water and set the cylinder in the glass jar covered with alum. I checked the next day, tap was still visible with no apparent dilution . After 4 more tries in as many days I went online for help.
    As mentioned the alum should be heated to simmering and kept that way until the tap is gone. This time I heated the jar of alum in a small crockpot I use for making hide glue. Left the jar for two days and then found that the tap dissolved and a few raps on a block of wood got the remaining metal out.
    The last time I broke a 1/72 bottom tap in a steam chest. This was a thru hole and it took one day with the heated alum to dissolve the tap.
    mike
     
  10. Apr 9, 2019 #10

    savarin

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  11. Apr 10, 2019 #11

    petertha

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    savarin the spark eroder sounds interesting but unfortunately the links are not working
     
  12. Apr 10, 2019 #12

    savarin

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    Sorry, the links get censored so wont work.
    If enough want it I can do a post here.
    Its not a pretty project as I just wanted something fast that worked.
     
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  13. Apr 10, 2019 #13

    petertha

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    The smallest annular cutters I've seen is 7/16" OD = 0.4375 from these typical suppliers. This is showing set but you can buy individually. Possible downside is standard 0.75" OD shank because they typically fit an R8 or MT arbor holder with a set screw to engage the flat. Maybe grip in a collet? I have the larger ones & they work excellent if you wanted to expand the tool collection. Does not say ID unfortunately. And of course you would have to cut straight through so the inner plug comes out.

    hopefully link wont get corrupted
    https://www.traverscanada.com/annular-cutters/p/26-036-228/
     

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  14. Apr 10, 2019 #14

    RonGinger

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    I have seen annular cutters sold for removing broken wood screws. They are simply a roll pin of the right size with a couple LEFT hand teeth ground into the end. The idea is that by left hand turning you may catch the screw and back it out, but in any case will be cutting a circle around the broken bit. This should be easy make using a dremel cutoff wheel to make the teeth. They do not have to be perfectly formed, freehand is fine.

    Roll pin is also called spring pin. They are hollow rolled springs meant to be driven into a hole to align metal parts. They are made in many sizes and are hard.
     
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  15. Apr 10, 2019 #15

    Ken I

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    I have used Alum several times - it must be a constantly heated supersaturated solution at 100 to 140°C. Get it up to about 120°C by adding Alum - once there the simmering liquid will continue to go up in temperature due to evaporation / concentration. To bring the temperature down you have to add water - lower the temperature to below 100°C (by removing heat) before adding water - real danger of it flashing off on contact - can be dangerous to add water to 140°C supersaturated solution (can be done - very carefully and with protective gear just in case - otherwise not advisable.
    Sparking will be the best - some shops are so intrigued by model engine builders they do it for free or low cost.
    Coring - use one of those diamond tipped glass hole saws (relatively inexpensive - I have a range of them) - use a Plasticine dam to hold coolant - withdraw frequently - particularly with Aluminium. Tedious but it does work.
    Regards, Ken
     
  16. Apr 10, 2019 #16

    mcostello

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    Make sure You get the correct Alum, there are 4 kinds. Has been covered here before.
     
  17. Apr 11, 2019 #17

    Entropy455

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    TIG welding 6061-T6 will temper the base material in the heat affected zone, resulting in "about" a 50% localized reduction in strength of the base material. Tempering 6061-T6 can happen as low as 400 degrees F. (this is why you are not supposed to powder coat high-strength cast aluminum wheels).

    6061-T6 is about 4 times stronger than regular aluminum. Thus the question you need to ask yourself is this - will a localized spot of slightly less-strong aluminum cause you problems? If the answer is no, then machine away the damaged bit, chamfer out the hole, and fill it (TIG weld). Chamfer is required because TIG has essentially zero penetration in aluminum - the arc will wet the surface for adhesion, but you must properly expose the surface to the arc (and for the filler-rod to flow into the hole).
     
  18. Apr 11, 2019 #18

    john_reese

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    Chinese vendors sell diamond tipped core drills in small diameters, 3mm, I think. They are very cheap. You would probably need a continuous flush of coolant through flush cuttings and prevent the aluminum from binding onto the diamonds.
     
  19. Apr 12, 2019 #19

    WOB

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    Once you get the holes cleared,( I used carbide drill), they are easily repaired. I made a full length 6061 plug that was a drive fit in the hole. I coated it with Loctite 609 and drove it into the hole. The next morning I machined the protruding plug top flush with the surrounding metal and you could not see it. I then redrilled and tapped the hole and assembled the engine. The 4-40 screw in that repaired hole took full torque the same as all the others in virgin metal and I never looked back. There is no need for welding.

    WOB
     
  20. Apr 18, 2019 #20

    chrsbrbnk

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    I have made core bits by using a carbide end mill chucked up in a lathe tailstock and feed it into the center of a hs endmill chucked up in a collet in the head stock may turn into the last thing that carbide ever does but if you feed in slowly past the end flutes its a pretty useful method to make raised surfaces for like bolts ect.
     

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