Author Topic: Tinkery 101: Borked Bolt Extraction by Slotting With a Dremel  (Read 196 times)

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Online mnementh

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So... yesterday I needed to fix a borked bolt on an industrial sewing machine (long story); while I was choosing tools for the job, I decided to take a few pics and make a post. Here's the borkage; a m6-0.8 standoff broken below the casting by drop damage. As this was not damaged by cross-threading, there will be a tendency for the borked bit to thread itself into the hole while drilling for an extractor; this can make the job a bit of a PITA in its own right.

Besides, I don't have any of my extractor kits on hand and I didn't feel like tool-shopping right that moment. I know; so NOT like the tool-dwagon we all know and love... err, tolerate.  ;) No, I don't have any left-handed drills (the obvious choice for this scenario) either. But I DO have a Dremel and good assortment of accessories, so let's put a shop towel in place to protect the tender bits of the machine and get to work...


         

1) Choose your Weapons

I have a good assortment of cutoff wheels which would work well if the break were far enough above the casting to allow their use; but these diamond-powdered bits & burrs were available cheap locally, and I have them on hand for other purposes:

https://www.homedepot.ca/product/forney-industries-20-piece-diamond-point-set-with-18-inch-shank/1001204882

https://www.busybeetools.com/products/1-8in-diamond-burr.html

You can find them on banggood.com as well, but for some reason they don't have the one bit we'll be using today in any of their sets.  :wtf:

Along with the cutting tool, we need a screwdriver. This Husky #HD-74501 is my go-to for this kind of work, as the bits are just hard enough to get good bite even in poor conditions, but not so hard they shatter all the time like the similar one from Kobalt. Sadly this model has been discontinued in favor of one with utterly craptacular chromed bits; I've bought several used #HD-74501 from fleaBay and keep the bits as spares. As a backup, I'm grabbing one of my cheap Chinese drivers as well.


      

2) This Hole Boring Business... ;)

Now that the dropcloth is in place, we're going to start cutting a slot in the exposed face of the bolt; working at moderate speed (~2 of 5) so we don't burn up the bit, grind at an angle with the small notching bit and be extra careful not to contact the threads. Once done, it will look a bit egg-shaped; don't worry, the slot is deeper than it looks here.


          
 
3) Screw it! Well, uhh... UN-screw it, ehhh...?

Using my preferred driver, I'll apply as much downward pressure as I can while turning the broken stud out; it turned easily enough until it was just a little above the surface, where it hung up and and the screwdriver slipped. No problem; now that the surface of the stud is above the casting, we can cut more aggressively, making a bigger, deeper slot which can accommodate a full-size 1/4 in screwdriver. :-+ Out she comes!


    

4) NOW we can screw it right!


Now that the borked stud has been removed, we'll take a moment to clean the work area with a brush and rag; then remove the dropcloth and install our replacement standoff. Now we're one step closer to moving this old beast down the road!

I know there are lots of other ways to resolve this problem; many even easier than this solution. This is my take on THIS process is all. It does have SOME advantages:

First, you may already have the required diamond bits on hand for other purposes, so no need to go shopping for an expensive set of extractors TODAY.

Second, it works on even very small bolts; I've successfully removed m2 bolts with this technique!

And lastly; when choosing a technique for this kind of work, you want to consider the potential for Murphy to make you suffer.  :-DD When trying to drill out a stud, especially one like this which you know is going to be loose and turn freely in the hole, it is a LOT likelier that the stud WILL turn down, allowing the drill to skip and either damage the thread or worse, jam up and BREAK in the thread. Or, it could walk JUST enough that you actually drill into the thread without realizing it until you're destroying the threads with an extractor.   :rant:  This is especially true the smaller you get in bolt size. You want to always be thinking of just HOW badly things COULD go wrong, because they WILL too many times out of ten. ;)

Alrighty... enough armchair mechanicking. Go on out there and FIX something!  :-+

mnem
   
« Last Edit: June 29, 2020, 04:20:20 pm by mnementh »
 
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