Live centre screw

[Fergie 307]

- I agree that we've 'moved on' somewhat - and yes it's now more about threading in general - and when I awoke this morning I did not expect to be digging into knowledge I gained some 40+ years ago !

As an historical context note - I was for some years head of the Export threading department at Herbert Small Tools, dealing with orders for threading equipment worldwide so being exposed to many 'special' thread forms that most British or American workshops would seldom, if ever, come across.

Ah - No - I don't think I've ever had a discussion on Quora - and I wouldn't have had an opinion about pre "Whitworth" standardisation

You can seldom rely upon the core dia. being the standard root dia. since standard engineering practice is to use a drill to leave something less than full depth to make tapping easier.

As far as measuring the head of an M6 bolt is concerned --- I had assumed he was using a grub screw --- but it could be a Cap Screw, again you would need 'inside knowledge' to determine the 'standard'. I'll bet that you and I could distinguish the difference between a ¼BSF, an M6 and a 0BA grub screw simply by 'feel' and sight but then, we know that the thread forms are quite different.

My previous mention of 2BA (#29) was an error out of context!

Your experience at Herbert's kinds interesting. As you say you can normally look at something and have a pretty good idea what it is by eye. The one time I was truly flummoxed was in restoring an old Churchill mechanical press made in the 1950's. It had a large washer on top of the shaft to retain the wheel. Stupidly I lost the original bolt, only to find that it was a really weird, and very fine thread. I can't remember the details now but it wasn't any standard size. Why they did that I'll never know, but after some head scratching I had to shrug my shoulders and 're drill and tap it to a size I could actually get hold of.

 

[J-G]

re drill and tap it to a size I could actually get hold of.

The pragmatic approach is often the best !

 

[Stigmorgan]

Well, as entertaining as it is watching you two go back and forth this is all wayyyyyyyyy over my head all I know is this, the manufacturer (charnwoods) told me M6x1.5, the hole is 6mm wide, approximately 4 or 5mm deep, I found a bolt in a box of nuts and bolts that was the right diameter for the hole but the thread count looked to be double what was inside the hole, once the package from Phil arrives we will see what fits.

 

[Fergie 307]

Agreed, always amazed me how easily these threads get off topic, and here I am doing it myself
The main thing is for you to get your centre fixed, I hope you managed to find the missing part. Best of luck with it, and do let us know the outcome.

 

[Phill05]

Well within the hour they will be winging there way to Stig.

I see someone has got some money running on this.
" We have come a long way from the original question. My money is on his screw being M6 (x1.0) all along, who would have thought it would have brought about such an interesting discussion.
So what are we saying you are going to donate some cash to the UKW to help keep these threads running on track if you are wrong, maybe I should have put this bit in the Joke thread.

 

[Stigmorgan]

Agreed, always amazed me how easily these threads get off topic, and here I am doing it myself
The main thing is for you to get your centre fixed, I hope you managed to find the missing part. Best of luck with it, and do let us know the outcome.

Thankfully I did, I had heard it drop so knew roughly where it went, I have magnets on my lathe stand to hold my spanners and chuck key so used one of those to sweep the floor.

 

[Fergie 307]

Thankfully I did, I had heard it drop so knew roughly where it went, I have magnets on my lathe stand to hold my spanners and chuck key so used one of those to sweep the floor.

It never ceases to amaze me how far things can travel when you drop them, sometimes I have found myself crawling about on the floor, only to find the thing miles from where I thought it must have gone. Maddening sometimes.

 

[Stigmorgan]

It never ceases to amaze me how far things can travel when you drop them, sometimes I have found myself crawling about on the floor, only to find the thing miles from where I thought it must have gone. Maddening sometimes.

Luckily the floor was still covered in shavings and dust so it didn't bounce far.

 

[Stigmorgan]

@Phill05 an envelope arrived today the finer thread of the two fit perfectly if a little long

Screwed it in until the point was hard to push in then back turned it until the point sprang back freely and finally a tiny dot of superglue to hold it in place
Huge thanks to you sir

 

[Inspector]

So what thread is it exactly, in case another member has the same problem? Maybe Phill knows what he sent and can say.

Pete

 

[Phill05]

Well done Stig, now don't loose it again, let's see some more of the fabulous work you do, well the answer to Pete's question is M6 x 1mm.

 

[Stigmorgan]

Well done Stig, now don't loose it again, let's see some more of the fabulous work you do, well the answer to Pete's question is M6 x 1mm.

I'm actually working on a piece of cherry at the minute but I can't get clean cuts on it for some reason so have spent the last 2 days trying to sand back all the tear out, I've got most of it out, might have to just accept a couple of small marks just won't come out.

 

[Lefley]

Even if @Stigmorgan did have a thread pitch gauge it's unlikely that he could get it in to check the INTERNAL thread at 6mm or ¼" dia. - those gauges are usually used to check external threads - he could posibly take a plasticine cast of the internal thread of course and measure that but it's not easy.

He's already counted the number of thread crests that he can see and adjudged the pitch from the length of the thread which is why he can be confident that it's larger than 1mm but the difference between 1.27mm (20 tpi BSW) and 1.5mm is too close (even at 18%) to determine by eye under the prevailing conditions.

I could certainly separate out a mixed box of ¼"BSW, M6, 2BA, ¼"UNC screws with no difficulty but 'Threads' were my bread & butter for many years - comparing internal threads would be more of a challenge!

Incidentally, your reference to "M6 x 1.5" (in reply #23) is wrong - the 'M' prefix should only be used to indicate the standard coase pitch/dia. combination and 6 x 1.5 is not the standard.

Spray inside with a bit of quick release kitchen spray. Then put in a lump off 5 minute epoxy. When dry take out. Much better then a plasticine mold and then measure that.

 

[J-G]

Spray inside with a bit of quick release kitchen spray. Then put in a lump off 5 minute epoxy. When dry take out. Much better then a plasticine mold and then measure that.

I'll agree that Platicine is not the best but it's certainly the quickest & easiest. If I could trust quick release spray, I might be tempted to use Milliput for such a task.