View Full Version : Who don't make mistakes ?

John Stevenson
01-23-2009, 03:36 PM
OK we all make them, anyone who says they don't is only lying to themselves.

So converting some Rotabs to stepper drive and they need a combined nut, thrust and Oldham coupling to save space, Simple bit really. Milled the Oldham coupling bit on the end and start to centre drill then drill and tap for the nut part.


Crunch, centre drill pops it's clogs off, take it out the chuck, bang it on the vise, will the damn bit fall out [ no they never do ] so right seeing as it was the damn centre drills fault it can be responsible for getting itself out.

Stuff it in a temporary holder so as not to burn my tiny, dainty pinkies and grind it up free hand as such.





Basically it's a trepanning tool of fixed radius when held in the tailstock chuck. The radius has to be larger than the broken bit and seeing as part of it is on the tool that's the bit you have to grind past.

Back in the 3 jaw chuck with the part, modified centre drill in the tailstock chuck and feed in slow with lube and you will get the broken bit standing up on an island.

I was going to take a picture of it but as I took it out the chuck the broken bit fell out and disappeared into the black hole, known all over the internet as Johns Floor


Not a new idea, God knows how many decades old ? but still a time saver and I though on topic for a home shop forum.

Liger Zero
01-23-2009, 03:44 PM
Proof that other people do 'asplode drill bits! HA HA! I AM VINDICATED! MAHAHAHAHAHAHA! :D

*bookmarks thread*

Humor aside, nice way to save a busted bit.

Now my question is what exactly is a "trepanning tool" and why would I need one? :o

...all I come up with is trepanation which is the art of drilling holes in the skull. My lathe at home isn't quite big enough to swing a normal sized adult and I'm not sure how to get around the neck-snapping issue. Mount 'em in the tail-stock? Or is there a fixture I need to make?

01-23-2009, 03:46 PM
Hey John, good trick. I know you won't believe this but I never break centerdrills, but if I ever do I will remember this. Yes, I do use them every day but always have enough speed and coolant and make sure tailstock is dead nuts centered and be very gentle. Peter. ( Is Man U going to end up on top? ):D

01-23-2009, 03:47 PM
Thanks for an excellent idea and pictures to match.

Does your QC department allow chatter marks on the bottom of a hole like that? If mine did, I'd get myself a beer and in a little while QC would quit whining.

01-23-2009, 03:52 PM
Now, that gem is going to save a bit of stock and a few scribers from destruction:)

01-23-2009, 03:52 PM
Now my question is what exactly is a "trepanning tool" and why would I need one? :o

...all I come up with is trepanation which is the art of drilling holes in the skull. My lathe at home isn't quite big enough to swing a normal sized adult and I'm not sure how to get around the neck-snapping issue. Mount 'em in the tail-stock? Or is there a fixture I need to make?

A trepan is a tool for cutting large discs from sheet metal. Very handy tool and surprisingly accurate I've found. Easy to make.

Here's one: http://www.enuii.org/risley/training_school/Trepanning_tool_s.jpg

01-23-2009, 03:58 PM
John, just noticed that you're out of the virgin business? Were you disqualified when you hit 61? :)

John Stevenson
01-23-2009, 04:07 PM
No I posted before, it was the lack of them that forced me out of business.
The last known sighting was in 1924 on the Cadbury's chocolate firms outing going to Blackpool

Tiffiepedia fails to publish the results of the return trip.


01-23-2009, 04:14 PM
Thats a great idea. But why not use a carbide center drill or some type of carbide cutter to remove it? If a carbide center drill was used then the hole would not be oversized.

01-23-2009, 04:28 PM
Who don't make mistakes ?

who DOESN'T make mistakes, or was that they humour bit :D

the mistake isn't busting the centre drill, its using a centre drill when you're not drilling a centre.....I have never busted the pip off a centre drill while using a spot drill :)

using a centre drill to start a hole instead of a spot drill maybe the most common shop error; there are good practical reasons for not doing so.....yet everywhere you turn people start holes that way

good creative corrective action though!

Forrest Addy
01-23-2009, 04:32 PM
I don't make mistakse. What's the prbmleo?

01-23-2009, 04:48 PM
I don't make mistakes either. I'm perfect.

Thanks for sharing John. I hate broken center drills.

01-23-2009, 04:56 PM
I thought I made once, but I was mistaken...................

Jim Caudill
01-23-2009, 05:37 PM
Here's some other "ready made" trepanning bits for those of you that have led a sheltered life ;-)

Mark Hockett
01-23-2009, 07:46 PM
I have to agree with Mcgyver, I only use center drills when spotting for a lathe center. I use spot drills for locating holes, center drills are too fragile. And with a 90 degree spot drill I can do a 45 degree chamfer at the at the top of the hole in the same drilling operation.

Steve Steven
01-23-2009, 08:25 PM
I was taught a similiar trick by my mentor. Take the broken center drill, get a Dremel tool with a cutting disc in it, and cut vertically down into the remains of the flutes and cut out the center to a depth deep enough to get to the bottom of the broken part. Be sure that the cut leaves a sharp edge with relief to cut on the vertical part.

This will leave you with a two-flute cutter that will cut a tapered hole around the broken part, that you can break off at the bottom.

Just another way to do the same job.


Limy Sami
01-23-2009, 08:46 PM
''Who don't make mistakes ?''

Those who've never made anything, and those who can walk on water.

01-23-2009, 09:05 PM
Yeah i only make mistakes it seems LOL Mike (PS NICE ASSES)

01-23-2009, 10:33 PM
It is not a mistake if you can fix it . Its just a F--K up then.

01-24-2009, 12:23 AM
The difference between an amateur and a professional is that the pro knows how to cover/fix his mistakes.

Montezuma, IA

Weston Bye
01-24-2009, 06:38 AM
Good machinists make very few mistakes. The best machinists seem to make none at all, because they are artists at retrieval and salvage, and are quiet about it.

An excellent example of the art of retrieval and salvage. Thanks for the tip, John.

01-24-2009, 07:07 AM
You were bound to screw up John. Now if you'd been making the bits to convert ROTARY TABLES, wouldn't have been a problem.

:D :D :D :D

01-24-2009, 07:18 AM
I think knowing what to do when it hits the fan is called experience which is what is normally found on the forum.
The likes of Sir John and others who take the time to pass on their experience so we can all know about the little tricks of the trade make our learning process that mush easier.
Now if this is all what a pro would do is a matter of debate in that do they not make mistakes or are they careful not to do the very thing which will cause an action to break something.
A case in point was something I was doing for my wifes Maritiime museum in that I was producing some key rings using inert bullets which intailed drilling a cross hole in the copper clad lead bullet so as to insert a triangular insert to take the key chain and ring. Duly made a jig so as to drill in the right place each time, drilled a few started to get over confident ping broken drill, get another drill add more lubricant drill some more , added more confidence then ping another bites the dust. Decide the drills not strong enough buy some carbide drills, try again, ping not as strong as the HSS drills. So I think the moral is carbide is not tough, drilling through copper and then lead is not easy but it has certainly changed my view on carbide its not the be all and end all.


John Stevenson
01-24-2009, 08:35 AM
As many of you know a lot of my work is repair work and so being worn out is a mistake, - you shouldn't have used it :)

I don't mind sharing because that is where I got most of my information from, working with true professionals who wanted to pass on their skills.

What is hard to share though is experience, that has to be learnt by all. You may have two broken studs in a part but use two different methods to remove each because of how they are situated.

I try to steer clear of carbide tooling on broken parts because it's not the be all and end all, mostly the part you are removing / repairing is hard, has broken uneven and carbide being a powder is very friable. That broken slug, although it had about 10 minutes machining on the other end would have at least chipped an expensive carbide tool, at best broken it, so a $30 tool for a $2 slug ? no contest.
In fact it was borderline to throw it anyway but I had the centre drill already done and thought the series of pictures was worth more.

I must admit I need to get out of the habit of using centre drills for jobs such as this but I have then mounted in holders that are easy to use.

More on this in a later post either today or tomorrow, Gert's Ebay work calls...............


Frank Ford
01-24-2009, 12:07 PM
Mistakes? I don't make mistakes.

If I screw up while I'm working by myself, it's a "learning experience."

If I screw up in front of others, it's a "teaching opportunity.

01-24-2009, 03:55 PM
holy cripes. All I had to do was a cut a silly plate to length today. I'm redoing the column mount on the cnc boring mill project. First had to cut the hardened "way" off the bed which right off the bat got me cranky. I have a pretty good abrasive chop saw, but man this stuff is hard and it was taking forever to cut. Tripped the breaker a few times but finally removed what I needed to.

On to the plate that would tie in the bed better and give more support to the column mount. Had just enough steel plate on hand, cut it to length and made it look purdy with the belt sander. Get ready to drill and notice I cut it short by 1".
That's it, call it day...

John Stevenson
01-24-2009, 04:12 PM
Following on from what Mac and mark said about spotting drills which is very relevant, I have decided to start a new thread called Tailstock mounted drills.

All the ground work is done I just need to get some pic's and write it up so look out for it later tonight.

There WAS a reason I was using centre drills :D