elmers engines plans

Hi could anyone tell me what the # (number sign) means on the elmers wobbler plans? e.g. #5-40. I'm a beginner and still trying to decipher old plans like these, i haven't been able to find a solution searching on the web.

the plans i am referring to are for the wobbler http://www.john-tom.com/ElmersEngines/25_26_WobblerBoiler.pdf

It's a thread definition/specification for UNC type threads much as we have Whitworth, BSF, BA etc thread definitions. If you want details then google #5-40 threads and you can get the actual diameter and pitch for each number.

Martin

Just means it's a Number 5 x 40tpi thread. Below 1/4" the various UN threads use a number system much like BA and wood screws.

The US tend to use # where we would put No.as an abreviation for Number, nothing to do with hash tags!

You will find there are other symbols use don his drawings so this may help

Here is a comparison of varoious thread standards. It compares Metric, Unified, BA, Withworth etc. and may help you find what metric screw could replace the Unified.

Thor

Edited By Thor on 07/05/2021 08:08:58

Thanks all, that is very helpful info. You might be surprised that I don’t actually have a lathe/mill yet. My plan is to first model some simple engines in a CAD package (Fusion 360) as an exercise in both learning the CAD software and learning to interpret engineering drawings (especially older ones). I’m finding that a challenge in itself. I have an extensive collection of model engineer magazines inherited from my late father, once I do have some suitable equipment it would be great to go back and have a go at some of the simpler old stuff from the ME back catalog

Getting to know the engine by drawing is a good idea. It will also enable scaling and metrication which may alleviate some of the odd screw sizes. I find most of Elmer's engines to be on the small side so upscaling can be helpful if, like me, poor eyesight and unsteady hands, are an issue. The engine you are looking at has a frame that is just 2.25" long. My last attempt at one of Elmer's was his No.19 Standby Engine, the drawing shown below:-

The final outcome was quite reasonable looking engine that runs quite well.

The details and construction are on my website - Journeyman's Workshop Good luck with the drawing and subsequent build.

John

Your CAD drawings are great Journeyman, it's very clear in terms of measurements. I'm finding it difficult to determine the exact measurements for some parts of elmers drawings. It feels like there are bits missing, for example, the exact position of the air intake / exhaust holes. All i can determine (based on the dimensions provided on the jig) is that they should be 3/8 inch from the hole that atached the cylinder to the frame.

I can't see how far up or down on the frame the holes should be though. There also doesn't appear to be an exact position for the air inlet hole. I must be missing how to read something!

My drawing:

And having done that, it may be easier to convert the American nuts and bolts into Metric equivalents.

Starting out in Model Engineering, I expect many of us were surprised at the number of different thread systems out there. They date back to when nations did their own thing and before, resulting in plans calling for difficult to find nuts and bolts, when similar would do.

In the US, despite the steady advance of metric engineering, the Unified Thread system still dominates and # screw diameter nuts and bolts are easy to buy. Also available elsewhere in world, but tend to be harder to find and more expensive because, outside North America, they're unusual. Although the internet is your friend, I wouldn't recommend American nuts and bolts to anyone other than Americans.

In the UK, industry is almost exclusively metric, but for reasons good and bad, we are stuck with a mob of obsolete and obsolescent Imperial standards as well. BA, BSC, BSF, BSW, UN, and others. Though it's possible to work in any system, it pays to major in either Imperial or Metric. Imperial is good for building models from old plans, mending imperial equipment, and if you went to school before 1970 or inherit a workshop full of wonderful Imperial tools! Otherwise go metric.

The rest of the world is metric and so is the future.

#5 is 1/8" nominal diameter (3.175mm), so either M3 or M3.5 would do. In the American system the # is often left out, so 8-18 is the same as #8-18. The first number is a gauge number, the second is the number of threads per inch. A good reference book is useful; Model Engineer's Handbook, Zeus, Machinery's Handbook etc.

Dave

The problem is that Elmer is using the build instructions and finding that dimension during marking out:-

You will need to do something similar in the drawing using construction lines (Not familiar with Fusion360 so assume it has similar) once you have the centres and the crank offset you can insert the angled lines and finally the ports.

John

Should be possible to plot it

Draw the 3/16" pin 1.25" from the pivot and then a circle 1/2" dia around that. the 1/2" is the pin plus twice the distance of edge of jig to it's ctr line. Then draw a line through teh pivot that is tangental to the 1/2" circle. mark a point 3/8" along the other end of teh line and that's your hole location.

Plot (click for larger image)

And the two dimensions taken off the drawing.

If you do want to make the engine a bit bigger and to metric standards then use the scale of 1/32" on original = 1mm

Edited By JasonB on 07/05/2021 13:26:22