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Attachment 19954Attachment 19955
I have used one of these for longer than I care to remember, this is a second edition from 1938 bought from a boot sale. I do not know if anything like this is sold these days but it should be as it is virtually a Zues book in your pocket and very handy when working out of the workshop. If you see one don't pass it up.
BTW I totally agree with Marv that everything should be identified by size and not some reference code.
I used to have all sorts of sliding and circular charts of many various things they used to be used as give away and promotional items for company's advertising.
I always thought they were a great idea maybe because I learned to do my math with a slip stick
Ok, are you going to tell us what it does? It's impossible to tell from the pictures.Quote:
Originally Posted by olderdan
Marv if you click on the image it will open then click again then it will allow you to click one more time to zoom in here is a screen shot of the close up
Attachment 19959
From my observation, this is a thread and clearance hole drill size chart for British Association (BA, BAF), and Whitworth treads (gas piping?). Looks like it gives letter and number drill sizes, as well as fractional, and metric.
You and I would be laughing all the way to the bank as I have one too and would'nt part with it for quids,I also have a Vacuum Oil Co Pty The Pratical Engineers Pocket Book I am not sure of the date as it got wet at some time and where the date would have been is missing I also would not part with it either,it would be nice to know what they would be worth now.
Great to know some one else values the old gear as it it priceless now.
Maybe it's handy for the British branch of the inferial nightmare but it's not exactly simplistic for metric.
Say I want the tap drill for a 10 x 1.5 mm thread. I line up "metric tapping drill" with 10 as is shown in the photograph. The TPI now reads 16.9. How many machinists can do the math needed to convert that to pitch expressed in mm per thread? Well, when you do that you get 1.503... which is close enough. You look at the outer ring and see you need a 0.323" drill. Now, if you're using metric drills you need to convert that to mm since nothing shows on the dial in the millimeter ring. So, you quickly mentally calculate 0.323 x 25.4 and get 8.2 mm which is close to the right value but will produce more than 75% DOT making threading more difficult?
Of course, you could have done the whole thing in your mind with a trivial calculation...
10 - 1.5 = 8.5
Now, maybe someone can explain how you use the chart to find the tap drill for a 10 x 1.25 mm thread.
Another puzzle...The chart shows 8 mm "clearing drill" lining up with 0.323". Does that imply that 8 mm = 0.323" (presumably for small values of 0.323)?
I don't think that a 1938 chart was ever intended to be used for metric (in the UK), other then it had the drill bit size equivalence (if available).
I was just commenting on what my observation was, I think Olderdan does antique motorcycle restorations (I recall some past post, maybe not him), and here these non SAE/SI "standards" are his repair source sizes.
This chart even has the wire gauge sizes, even into the 'ott' nomenclature. We know how useful that system is.
I'm with you Marv, on the simplicity of metric threads.
But any measurement system we have, has no absolute base reference. A millimeter, or inch are just random chosen lengths, and turned into a human standard.
Of course and that's why the oft-heard anti-metric argument that it's "inaccurate" is so stupid. There is no such thing as accuracy of a measurement system; they're all based on some arbitrary standards and their measure is how they express and subdivide those standards.Quote:
Originally Posted by metric_taper
Regardless, 0.323" isn't very close to 8 mm, even if the chart was made up before the inch was set at 25.4 mm.
