Fixing threads

awb

Member
I had an accident this morning where I wasn't thinking and used my wheel puller where I was pushing against a tapped hole. After taking it off I realized that I pushed in the start of the threads and can't get the bolt back in. Looking at the bolt, the thread size is 5/8-11.

If I buy a 5/8-11 tap on ebay can I fix the hole, or do I need to drill it out and tap a bigger size? All of the threads except the beginning are in good condition.
 
What is the threaded hole used for? If it is pretty deep, and threaded all the way, I would use a 5/8 drill, and remove the few damaged threads (or a
die grinder with a sleeve on the bit to limit depth to the damage. If it holds on a wheel or safety related component, I would drill and tap for
helicoil, or a 3/4" bolt (if it is going to fit). Jim
 
As most taps are tapered on the leading edge to allow easier starting, you can often start them even if the first couple threads are damaged, provided they're not too badly messed up. 5/8-ll is large enough for you to see fairly easily what's going on, and if you try it slowly and make sure to start the tap squarely you stand a good chance of being able to clean them up with little or no loss of clamping pressure.
 
(quoted from post at 16:51:30 09/14/19) What is the threaded hole used for?

The hole fits a bolt with a big washer which keeps things on a rotating shaft. Even though it will only be spinning at a few hundred rpm, I would like to keep the threads strong to avoid things flying off. I will possibly look into helicoil, never used them before.
 
+ 1 just drill the first couple of threads and just try to get the bolt started , don't make things worse
 

Take a bolt that fits , preferably a hardened one , grind the end into a taper and cut a groove parallel to the shaft with a Dremel or some such tool . Centre the bolt into the hole and screw it in , the resistance will drop off once you are past the burred threads .
Works for burred over spark plug threads as well .
 
How thick is a 5/8-11 nut - .400/.444 inches or .65 to .7 bolt diameters? If you can get .7 or more diameters of full thread engagement into steel, you should have plenty of strength left.

Before wiping out all the old threads and completely starting over, I would try grinding out only the damaged thread with a die grinder or Dremel tool and then see how much thread engagement is left. In theory, three full threads on course threads is the minimum needed for a bolt to carry its full rated load (.28 inches for 11 pitch threads), but often the tapped hole is in softer material than the bolt, so more engagement is used in soft materials.
 
If the bolt as is goes in more than one diameter, it will be fine. Pit a smaller bolt in the hole, and use a felt tip to mark the depth. If it is far
deeper than the original bolt extended into the hole, tapping it out after grinding out the damaged threads will also work. As will using thread locker
fluid on the threads. Jim
 
A 5/8" 11 plug tap should work well if the bolt evens looks close to starting. If you buy a tap from ebay make sure you order a plug tap. A lead tap will give you a greater chance of starting a cross thread and the bottom tap will not be much smaller on the end than your bolt.
 
I tried Charles' trick but didn't have much luck with it. I also tried to clean the start of the hole with the dremel but still can't get the bolt in. I'm thinking that I should buy a 5/8-11 plug tap and see if I can't make that work. Here are pictures of the hole


mvphoto42632.jpg


mvphoto42633.jpg
 
the problem with that is if you do not line up with the original threads you will be cutting new threads get a 11/16 or 3/4 drill bit and cut the first couple of threads out
 
It looks like you should be close to getting a bolt started in the tapped hole. Can you use a thread gauge to locate where the threads are still deformed and grind away those irregular spots? A thread chaser or a bolt with the threads relieved might be easier start than a regular bolt.
 
Don?t get a plug tap get a regular tap that is tapered
on the first bit so you can cut into the damaged
threads
 
I agree with the others that say fix it
with a 5/8 tap. You really don't want to
drill oversize and tap new threads in a
John Deere crankshaft if you can keep from
it. I've threaded new holes in a JD
crank, but those cranks are pretty hard. I
kinda cheated though and used a carbide
thread mill, but that's not an option in
your situation :)
 
easy fix, get a taper tap and some cutting oil and just re-tap it. make sure you start straight and make sure its lubed and do a turn and make sure your going straight and keep blowing the cuttings out with air. once it bits into that damaged spot it will screw right in. if you want to clean out all threads to bottom use a bottoming tap. taper tap wont cut to bottom.
 
(quoted from post at 18:42:21 09/14/19) I had an accident this morning where I wasn't thinking and used my wheel puller where I was pushing against a tapped hole. After taking it off I realized that I pushed in the start of the threads and can't get the bolt back in. Looking at the bolt, the thread size is 5/8-11.

If I buy a 5/8-11 tap on ebay can I fix the hole, or do I need to drill it out and tap a bigger size? All of the threads except the beginning are in good condition.

Grizz2 has the right idea, remove the first couple of damaged threads.

If you run a tap into it with the couple of damaged threads still there you risk the tap following the "bad" threads, then tearing into the "good" threads deeper in the hole.

Removing the first 1/8" or 3/16" of damaged threads with a carbide bit in die grinder won't hurt ANYTHING, and will avoid the possibility of hurting the good thread.

Trying to drill them out with a bit in a hand-held drill could result in the bit "grabbing" and taking more than the damaged threads.
 
I have a buddy who owns a machine shop that will check for me on Monday if he has a 5/8-11 tap I could borrow. Today I will clean up the first few threads in preparation for tapping. As Drew mentioned it's hard material and I would like to avoid putting a larger thread in if possible. Thank you everyone for your suggestions
 
Find you one of these. They work great. Web search "NES Internal Thread Repair". Someone like O Reilly s or Autozone may have them in their loaner program.

mvphoto42687.jpg


-Scott
 
Video here. I can NOT post a link for some reason so you ll either have to copy and past or do the web search. The video pops right up there.

https://m.youtube.com/watch?v=yZrdlCtgogY
 
A lead tap is to start a hole where there are no threads. Looking at the picture he might get a lead tap thread to line up and get it started on a thread though. The plug tap does have some taper but has a shallow first couple threads that would start in the hole in the picture I am sure. With the depth of the threads he would also get by with grinding out the first two as well. You never need more threads than the depth of the threads in a nut that fits the bolt. The nuts are designed for maximum holding power. He will be good either way he goes.
 
reading all these ideas on how to fix threads.... man I never knew there was so many taps. LEAD TAP, PLUG TAP. REGULAR TAP, BLUNT TAP, TAPER TAP, BOTTOM TOP. I have tapped a lot of holes in metal from scratch. that is the whole idea of using a taper tap. it is used for starting the threads. then if u need the threads to the bottom u use a bottoming tap. from what I see in this crank there is no need to remove any threads before starting to restore the threads. just have a straight eye and go to it slowly. plus cutting oil is a must. ordinary oil does not work. its as if someone put the brakes on. and a helicoil is not the answer either.
 
A plug tap is your regular taper tap. I buy the three different taps in all sizes for my tool shop. Terminology is the difference in what your seeing.
Example
 
The terminology used in in the shops I worked with 50 some years ago and always used in my shop for 40 years is the lead, plug and bottom tap. I was taught to never use a lead tap in existing holes to keep from cross threading. When ordering replacements over the phone I always ask for a lead tap and received what I wanted. I see in ebay that what I call lead tap a lead tap is referred to as a taper tap.
 
I am going to suggest something no one else has. Using the plug tap, come in from the back. You have good threads to get the tap started and aligned. Then if it cuts into the mangled threads, they will be in line with the deeper threads.

Cliff(VA) now (NC)
 
(quoted from post at 07:56:03 09/16/19) I am going to suggest something no one else has. Using the plug tap, come in from the back. You have good threads to get the tap started and aligned. Then if it cuts into the mangled threads, they will be in line with the deeper threads.

Cliff(VA) now (NC)

It's a "blind hole" in the end of a 2-cylinder John Deere crankshaft.

Nice to hear someone in agreement with me that the "bad threads" likely will casue the tap to be "out of sync" with the "good threads" farther in, though!
 
(quoted from post at 18:50:28 09/22/19) Thats what i was thinking just use a tapered tap .This shouldn't be rocket science

Ditch, NOT to "beat this to death", but it's a bit unusual in that the damaged threads are not just damaged, but squashed down/compacted towards the "good" threads and the natural behavior of a tap will be to grab and follow the "bad threads", making it "out of mesh" (so to speak) as it encounters the "good threads, and try to tear them up vs. the damged threads that need to be cut to match the "good threads" farther into the threaded hole.
 

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