Misprint in Versatile Dividing Head indexing chart (GH Thomas)

[HopperParticipant @hopper]

[HopperParticipant @hopper]

I mentioned this in another thread but thought it might be useful to record this error in Geo H Thomas's book "Workshop Techniques", page 202, 1998 edition.

In the chart giving the settings for drilling 4" VDH plates, the number of turns of the indexing handle is wrong on the 66 hole column. The chart as printed reads 9 turns plus 54 holes, shown as 9/54.

It should read 0/54.

I've checked the math on this and proved it by successfully drilling the 66 hole circle.

Unusual to catch old GHT in an error, but I suspect it is a printer's typesetting error that went undetected by Saint George's posthumous editor.

The error in question is pointed to by the pen. change 9/54 to 0/54 and carry on with the job as per normal, working your way through the micro adjustment graduations as they are shown.

It seems like such a glaring error – 9 compared with the 0 on the next circle etc – but I almost fell for it, thinking it must take multiple passes around the job to get the desired holes but luckily stopped to check the math and it don't work the way it's printed!

Happy drilling.

Edited By Hopper on 28/08/2017 11:04:53

[egaParticipant @ega]

Hopper:

Thank you for pointing this out; I have made a note to check the maths when I am feeling up to it.

In the meantime, I have just visually checked my own plate made to the GHT words and music and the 66 hole circle seems to be OK. I would have remembered if the plunger had not holed out correctly at the end (and, I hope, gone on to find the problem) so I need to follow up on this. Maybe the error is very small.

Would you mind posting your working for the maths check?

[Michael GilliganParticipant @michaelgilligan61133]

Hopper,

You may be relieved to know that the tabulation in the 1983 [Argus Books Limited] "Dividing and Graduating" correctly specifies, on page 99, 0/54

… GHT is safe from turning unneccessarily in his grave.

MichaelG.

[HopperParticipant @hopper]

Ega, I think you probably followed the directions that Michael refers to.

Don't have my scratch pad in front of me but the math goes like this:

For 66 holes, the angle between two holes = 3600/66 = 54.54

54.54 is the angle in tenths of a degree, due to the 3600 in the formula, rather than 360.

So, we use the sector arms to mark out the 54 tenths of a degree. In a 60 hole circle used for indexing in this case, each hole = one tenth of a degree. (One revolution of the handle = 360/60 = 6 degrees. 6 degrees divided by 60 holes = .1 degree.)

Then we use the micro adjustment dial to move the 00.54 tenths of a dergee each time.

So the movement becomes 0 turns of the handle, plus 54 holes in the 60 circle, plus 54 graduations on the micro adjuster. Result, as tested = 66 hole circle perfectly formed.

Alternatively, if you follow the 9/54 misprint, each movement equals an angle of 9 x 6 degrees = 54 degrees, plus the 54/1000ths put on by the micro adjuster. Or 54.054 degrees. If you drill 7 holes to this specification, the seventh hole will fall at the 378.378 degree mark. which is 13.378 degrees past the first hole you drilled. Nowhere near the needed 5.45 degrees between two holes in a 66 circle. It's just totally wrong. Whereas the 0/54 formula is spot on.

I think I got my math right – but I majored in English Lit so don't take it for granted.

[HopperParticipant @hopper]

Michael, interesting that the earlier book got it right – I think GHT was still about in those days so probably proofread it himself. As we used to say in newspapers: "An error was made in the production process".

 

Edited By Hopper on 28/08/2017 12:52:31

[egaParticipant @ega]

Hopper and Michael Gilligan:

Shortly after posting I went back and counted the holes; my "66" circle has 65 holes! I will re-do this on a spare plate and try to figure out what actually happened.

I had the earlier versions of GHT's books and certainly worked from them for some of his dividing devices. Ironically, having treated myself to the revised editions by Tee, I gifted the old ones to a good friend in Christchurch, New Zealand. Newer is not always better and, in fact, having got used to the layout of the original, I have occasionally struggled to find my way in the revised editions.

Most, if not all, of the content appeared in ME first and it will be worth looking to see whether this area was correctly printed in the magazine.

PS Shame one can't "edit" a dividing plate!

Edited By ega on 28/08/2017 14:26:47

Edited By ega on 28/08/2017 14:27:20

Edited By ega on 28/08/2017 14:28:10

[RobboParticipant @robbo]

"Most, if not all, of the content appeared in ME first and it will be worth looking to see whether this area was correctly printed in the magazine" – ega

Here it is: neither 0 nor 9 but a dash.

 

Edited By Robbo on 28/08/2017 21:54:48

[HopperParticipant @hopper]

Robbo, that chart you posted is correct. Thanks for posting that for future readers to refer to.

EGA, count your holes again! Must be one hiding there somewhere. Remember to count the first hole!

[Author]

Posts