Model Engineering threads

Is there a guide at what sizes a bar has to be for engineering thread as well as drill hole sizes something like what is in the Zeus book.

Most of this info is on the net. Have you tried Google ?

Its all out there on the net or in Engineers handbook etc etc. As Chris says GOOGLE is a wonderful thing.

Many people have their own little tricks for jobs they do but when it boils down to it there is a set of published standards that industry uses.

regards

Cheers guys why did I not do that in the first place now I feel such a fool. But then the wife says I am all of the time

Edited By Derek Lane 2 on 26/07/2018 22:38:59

There are also a few apps for your phone / tablet like FSWizard etc .

If you are using metric you just subtract the thread pitch from the thread diameter and that will be the tappiing drill size required ( 6mm dia and 1mm pitch = 6 - 1 = 5 so use a 5 mm drill ) .

Some years ago I created a "crib" card in PDF format for use in my workshop. It contains tapping and clearance drill sizes for Imperial, Metric, B.A., and BSP threads, as well as Imperial-Metric conversion tables. All the tapping drill sizes were computed to give 65% engagement for small taps, and 75% for larger taps as determined in the Model Engineer's Handbook by Tubal Cain.

Unfortunately, PDFs are not allowed in the albums so I have converted them to 300dpi JPGs as follows.

I hope you find them as useful as I do. (They're called Mecrib1a_b_crn in my album called Stuff)

Edited By Gary Wooding on 27/07/2018 08:26:12

Don't feel a fool Derek, no-one is perfect.

One advantage of asking on the forum is you get a range of answers, and the possibility of more information and - if necessary - an exchange of questions and answers.

Gary's crib sheet (thanks Gary!) allows me to draw attention to a potential ambiguity. You asked about 'Model Engineering Threads', and I think that's exactly what you meant, i.e the range of British threads developed for amateur modelling purposes. They're in Gary's Imperial Thread table under 'ME32' and 'ME40'.

May be of interest to others that these special threads exist. I'm not sure how popular or well-known they are. I suspect they're in the 'good idea, very few bother' category. All my models use metric fasteners, but then I shall never win any prizes at an exhibition...

Dave

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The logic underlying these 'constant pitch' series is, I believe, that it's then simple to set-up a screwcutting lathe to produce any size in the series.

MichaelG.

A free app that I use frequently on my IPhone in the workshop is IEngineer useful for cross referencing between imperial and metric.

Dave W

Model Engineer's Handbook by Tubal Cain has the best set of tapping drill hole size charts I've come across for model sized stuff. He uses a thread engagement factor that allows for a slightly larger hole than most charts, which makes it easier to tap with less likelihood of snapping a tap. Yet the threads maintain 95%+ shear strength of full depth threads. It's an inexpensive little book crammed full of useful stuff. Must have for every workshop, IMHO.

Tubal Cain also authored a book on Drills, Taps and Dies which goes into more depth in those specific areas. Both books are available from Tee Publishing.

I think the idea was also to provide fine pitch threads for parts bigger than catered for by BA, but where BSW/BSF/BSP threads are too coarse. The obvious application is boiler fittings and pipework in general. I never use the 40tpi series but I do use 32tpi series for oilers, glands and specials where I need a fine pitch thread.

Andrew

+1 - probably my most refered to book, especially the tapping drill size charts

Andrew

That's the acknowledged source of the data in my crib sheet.

Thank you all for the comments and pointing me in the right direction.

Yes but I should know better being on many forums and also being the moderator one of the sister site to this one

There are only daft answers, very few daft questions! We all had to learn to talk and to walk, and the many other things that we do in life.

All the books mentioned (Zeus Charts, Tubal Cain's "Model Engineer's Handbook, The Amateur's Lathe, The Amateur's Workshop and the Workshop Practice series etc) are useful. Also folk like Chronos, Tracy Tools, and The Tap and Die Company produce charts for tapping giving drill sizes.

Based on my experience, if you are using Model Engineer 40 tpi, (and 32 tpi) threads remember that the thread depth is small (only 0.016" for 40 tpi) so will not drag a Tap or a Die held in a Tailstock along the lathe bed without risk of stripping.

Do use a sliding Tap or Die holder, (My sliding tap holder is a shop made ER25 holder sliding on the arbor for the proprietary sliding Die Holder for the Tailstock).

Good Luck, and don't be afraid to ask advice.

Howard