[slumlord]

Yesterday, i found a broken off bolt that held the points eccentric [the out of round piece that opens and closes the points] It is part #7 in the drawing
http://www.hondapowersportsoftroy.c...=Motorcycles&make=Honda&year=1974&fveh=133054

Worst of all, it broke off about an eighth inch inside of the threaded camshaft end!
I needed to drill a perfectly centered hole in that broken bolt to avoid buying a new camshaft. The bolt in question is only 6mm diameter or about 1/4 inch. I made a drill centering jig by finding a tiny socket that was about 6mm outside diameter. I chucked it in my drill and rotated it into a mini-grinder to reduce the OD just enough to fit into the recess. The inside of the socket had about a 3/32nd hole through the center which I used to center the drill bit and keep it from skating across the irregular broken surface. Once the drill bit marked the surface, a center punch was used for good measure. I drilled the small hole deeper and then a bigger one to accommodate the screw extractor.

It worked like a charm. The broken bolt came right out with the camshaft female threads intact.

 

[Unkle Krusty]

Sweet

Well done. Getting the drill started in hard stuff is not easy.
I drilled many in old British casings, but it was aluminium.
Also had friends at air New Zealand in the machine shop. Some good aluminium welders there. Probably long enough ago that no one will get in trouble.

All I did today was remove the two petcocks from the tank on Laramie. Larry had messed up the phillips head screws.

Unkle Crusty*

 

[yahmyxs]

yes yes, finally learning something... get the start hole centered first... I find free handed, that the smaller the drill you start with, the easier it is to get centered. My problem is removing enough screw to get a small easyout in it. 6mm holes are very small!

 

[DianneB]

Using a lefthanded drill bit will often remove the screw before you even have to resort to an extractor. Most industrial suppliers carry them and you only need one or two sizes, not a full set.

 

[Eye_m_no_angel]

That's good thinking Slum, and a great idea!

I would have likely turned a centering adapter of some sort on the lathe, and taken 12 times as long as I needed to get the job done.

 

[Eye_m_no_angel]

Using a lefthanded drill bit will often remove the screw before you even have to resort to an extractor. Most industrial suppliers carry them and you only need one or two sizes, not a full set.

Those are used a lot South of the equator, right?
:wink:

 

[mike721]

My real job is as an industrial mechanic and we keep a small set of left handed bits around here, they get used often enough to justify keeping them. Your right, they very often get the bolt out while your drilling the hole, I think the cutting serts up vibrations that loosen it, that and the heat from the drilling usually do the trick. If not, then your no worse for the attempt, the extractor will go into the hole that was drilled left handed just as well as it goes into a right handed hole
Just don't break an extractor off in the hole, if you do then it gets 'interesting'

Using a lefthanded drill bit will often remove the screw before you even have to resort to an extractor. Most industrial suppliers carry them and you only need one or two sizes, not a full set.

 

[hogcowboy]

Just don't break an extractor off in the hole, if you do then it gets 'interesting'

Been there WAY too many times.

 

[wadenelson]

Just don't break an extractor off in the hole, if you do then it gets 'interesting'

I almost purchased a "Disintegrator" for removal of broken extractors off Craigslist for under $1000. Just didn't have room in the garage for something I'd use once every 5 years.

It utilized a carbide? electrode like you use TIG welding, and a box similar to a welder. Similar to:

http://www.electroarc.com/ac-portable-machines/

With powerful sparks of electricity it would gradually "eat away" the extractor and stripped bolt the same way metal gets removed from ignition points over time. Turned to vapor.

Removing a broken extractor/bolt from a head might take 6-7 hours.

Thought about whether or not I could make a few $ offering it as a service to auto repair shops, etc. Like this guy,

 

[Metaldoc]

The worst part of having a job shop is the endless opportunity of removing broken bolts AFTER someone else has botched the job first. :frown:

 

[hogcowboy]

Actually I don't mind doing it for someone else. I hate doing my own cause I should know better. Know what I mean?

 

[Metaldoc]

Actually I don't mind doing it for someone else. I hate doing my own cause I should know better. Know what I mean?

Yeah, I know what you mean... slapped myself many a time for breaking a tap because I got in a hurry.

The problem with doing it for customers is charging for the amount time it sometimes takes. Just a couple of days ago one came in... an aluminum block with a bolt broken down in the hole. They had tried to drill it and broke the bit off. The bit was half in the broken bolt and half in the block acting like a key locking the bolt so no chance of it turning. THEN they tried to weld onto the broken bolt and were unsuccessful other than in making the end of the bolt HARD. Got it out but it was a bear and took an hour and a half of shop time.

 

[hogcowboy]

Sounds like something my cousins would do. Won't stop until it's nearly impossible. Stuff like that I wouldn't hesitate to charge triple your time. There isn't a glut of people that can salvage what idiots do. I'll work on it for others but only friends. And they know I won't charge but will expect a dinner for me and the wife. It might take me a week too. I just don't rush. I rush when it's my stuff. Stupid fool!!!

 

[OldDeadeye]

Yeah, I know what you mean... slapped myself many a time for breaking a tap because I got in a hurry.

The problem with doing it for customers is charging for the amount time it sometimes takes. Just a couple of days ago one came in... an aluminum block with a bolt broken down in the hole. They had tried to drill it and broke the bit off. The bit was half in the broken bolt and half in the block acting like a key locking the bolt so no chance of it turning. THEN they tried to weld onto the broken bolt and were unsuccessful other than in making the end of the bolt HARD. Got it out but it was a bear and took an hour and a half of shop time.

I get customers wanting phone quotes on extractions. I quote my hourly with a guesstimate as to what I think it will take. In my business, a broken bolt usually means the customer does their own wrenching and you won't be getting much return business from them, so I'm gonna get paid while the vehicle is in the shop.

 

[slumlord]

Yeah, I know what you mean... slapped myself many a time for breaking a tap because I got in a hurry.

The problem with doing it for customers is charging for the amount time it sometimes takes. Just a couple of days ago one came in... an aluminum block with a bolt broken down in the hole. They had tried to drill it and broke the bit off. The bit was half in the broken bolt and half in the block acting like a key locking the bolt so no chance of it turning. THEN they tried to weld onto the broken bolt and were unsuccessful other than in making the end of the bolt HARD. Got it out but it was a bear and took an hour and a half of shop time.

We want details of how the heck you pulled it off.....unless it involves trade secrets.

Now to answer Hogcowboy. Yes ,I know exactly what you mean by 'should have known better'. But I am not talkin' about how that bolt broke off

 

[Unkle Krusty]

Broke it.

We want details of how the heck you pulled it off.....unless it involves trade secrets.

Now to answer Hogcowboy. Yes ,I know exactly what you mean by 'should have known better'. But I am not talkin' about how that bolt broke off

I put a 10mm spanner on one end of the bolt that connects the shift cable to the arm on the gear box on the boat. Other end is 12mm. Gave it a very gentle twist and the bolt broke. That is how I broke it. Nothing could save that bolt.
It happens.

Unkle Crusty*

 

[Metaldoc]

We want details of how the heck you pulled it off.....unless it involves trade secrets.

Not a trade secret, just years of experience and help from the Helper.

The top surface of the broken bolt was an uneven mess from the previous attempts... NO way to get a bit to stay centered and no good way to make a drill guide. Started with a die grinder and fine pointed stone and slowly and patiently ground a centered concave 'dish' in the center of the bolt. At this point the broken drill bit was still undetectable, having been fused with the bolt.

Once the concentric 'dish' was created, I started drilling with a 1/4" carbide bit, not a twist drill but a masonry bit. (The broken bolt was a 5/16 bolt.) Masonry are more rugged and much cheaper. I do sharpen them however which requires a "green" silicon carbide grinding wheel. Maintaining a perpendicular drill angle is critical to drilling straight down the center of the bolt and difficult because it takes a lot pressure. Big chips do NOT result. It is more like powder. I had to get through the weld area as well as the broken bit. IT took several re-sharpenings to get through the hard spot. Then the piece of drill bit became visible and I was able to pull it out with a magnet and carbide scribe to help 'hook' it.

Now there was a tiny cavity where the 3/32 drill bit was which made further drilling an interrupted cut and a prime set up for skewing the drill bit. At this point I wear a magnifying headgear and drill slowly, tilting the drill as necessary to keep it drilling down the middle the bolt. Stop and look closely to make sure of this. When I got past the tiny hole left by the failed attempt, it was almost home free. Drilled on through the bottom of the broken bolt, now using a LH HSS drill bit, which brought out some broken up pieces. Finished up with a tapered tap to clean out remainders of the broken bolt and then a final pass with a bottoming tap.

Sorry for the long winded description but that's how this particular job went. At least it was successful. There are times I have had to over-drill and install threaded inserts.

BTW Slum, my hat is off to you for the way you tackled your situation. :thumbsup:

 

[slumlord]

Not a trade secret, just years of experience and help from the Helper.

The top surface of the broken bolt was an uneven mess from the previous attempts... NO way to get a bit to stay centered and no good way to make a drill guide. Started with a die grinder and fine pointed stone and slowly and patiently ground a centered concave 'dish' in the center of the bolt. At this point the broken drill bit was still undetectable, having been fused with the bolt.

Once the concentric 'dish' was created, I started drilling with a 1/4" carbide bit, not a twist drill but a masonry bit. (The broken bolt was a 5/16 bolt.) Masonry are more rugged and much cheaper. I do sharpen them however which requires a "green" silicon carbide grinding wheel. Maintaining a perpendicular drill angle is critical to drilling straight down the center of the bolt and difficult because it takes a lot pressure. Big chips do NOT result. It is more like powder. I had to get through the weld area as well as the broken bit. IT took several re-sharpenings to get through the hard spot. Then the piece of drill bit became visible and I was able to pull it out with a magnet and carbide scribe to help 'hook' it.

Now there was a tiny cavity where the 3/32 drill bit was which made further drilling an interrupted cut and a prime set up for skewing the drill bit. At this point I wear a magnifying headgear and drill slowly, tilting the drill as necessary to keep it drilling down the middle the bolt. Stop and look closely to make sure of this. When I got past the tiny hole left by the failed attempt, it was almost home free. Drilled on through the bottom of the broken bolt, now using a LH HSS drill bit, which brought out some broken up pieces. Finished up with a tapered tap to clean out remainders of the broken bolt and then a final pass with a bottoming tap.

Sorry for the long winded description but that's how this particular job went. At least it was successful. There are times I have had to over-drill and install threaded inserts.

BTW Slum, my hat is off to you for the way you tackled your situation. :thumbsup:

Wow. Thanks for sharing. Fascinating what a teacher experience can be.

 

[hogcowboy]

I never thought of using a masonry bit. I do use tons of little grinding stones. Do you put a more or less aggressive cutting edge on them? Not a lot of carbide to work with though in the bits I've seen. And with or without hammer mode if that plays a roll?

 

[Critter]

Impressive descriptions, thank you guys for sharing.