Plan Reading Question

[benjames]

Hello,

I am trying to read a set of plans until I understand them in my head and am a bit confused with the measurements of the crankshaft web. I have attached a picture of the crankshaft web drawing below and a link to the original PDF file on John Tom.

As you can see it mentions no diameter of the steel rod. It does show a radius of 13"/16 which I think is 20.6375mm, so I believe the diameter of the steel rod used would double up to 41.275mm. Is that right?

It does say this in the building notes:
... made up from solid steel stock, the webs are cut with a hacksaw and filed to shape from two 5/16" disks and the shaft and pin cut from drill rod.

I noticed that the " sign was on the second number: 5/16". So does that mean it is a fifth of 16"? A fifth of 16" is 3.2 inches, that would make the diameter 81.28mm, which is obviously wrong.

Any idea what they mean by 5/16" disks? Is my calculation of 20.6375mm for the diameter right?

This is the picture of the web schematic:

This is a link to the plans online:
http://www.john-tom.com/MyPlans/Steam Engines/VerticalValveDesignSteamEngineAll.pdf


Thanks again for your comments.

Ben

 

[stevehuckss396]

13/16 = .8125 so the diameter would be .8125 twice. 1.625 or 1-5/8 1.625 inches = 41.275mm

I would say you are right on the money.

5/16 is .3125 or 7.9375mm

What they mean is a 1-5/8 inch diameter disk, 5/16 thick. Then 1/32 is machined off to form the boss where the shaft goes into it leaving 9/32 thick disks.

 

[Charles Lamont]

As you can see it mentions no diameter of the steel rod. It does show a radius of 13"/16 which I think is 20.6375mm, so I believe the diameter of the steel rod used would double up to 41.275mm. Is that right?

Yes. But 13"/16 is the wrong way to write it ...

It does say this in the building notes:
... made up from solid steel stock, the webs are cut with a hacksaw and filed to shape from two 5/16" disks and the shaft and pin cut from drill rod.

I noticed that the " sign was on the second number: 5/16". So does that mean it is a fifth of 16"? A fifth of 16" is 3.2 inches, that would make the diameter 81.28mm, which is obviously wrong.

Any idea what they mean by 5/16" disks? Is my calculation of 20.6375mm for the diameter right?

No. The crank webs ar to be made of 5/16" thick discs, thats 'five sixteenths of an inch', 0.3125 inch or 8mm, near as dammit.

 

[benjames]

Thanks Steve. The whole 5/16" thing made me overthink that one!

Ben

 

[benjames]

Thanks for replying Charles. It's all becoming a lot clearer! Thm:

 

[stevehuckss396]

Thanks Steve. The whole 5/16" thing made me overthink that one!

Ben

Anytime Ben

 

[stevehuckss396]

Yes. But 13"/16 is the wrong way to write it ...

That may be true but most people who publish plans are not professional draftsmen. Right, wrong, or somewhere in between, as long as there is enough information to figure out what to do, who cares how it's presented. You know what i'm saying?

Cheers

 

[barnesrickw]

Because of the torture of all my drafting teachers/professors, I get wrapped up in the mistakes. Then my ADD kicks in and I forget what I was looking for anyway. But you're right as long as the information is there, what does it matter if someone dimensions to a hidden line. Hey! Is that a squirrel.


Sent from my iPad using Model Engines

 

[charlesfitton]

It took a while to download the plans. but I'll give this a go..

First things first....

(") This sign indicates a dimension in inches. In the Machining world drawings were often done in Decimal inches, or Fractional inches. IE 0.375" which is the same as 3/8". Lots of conversion charts out there, usually free. Metrification came along and just added to the complications... but it's all doo-able with a bit of head scratching and a mug of your favourite bevvie.

When you study the plans , there are usually two views, the other (Front View) is to the left of the bit you cut out and posted (Right Side View). It shows the thickness of the webs as 9/32", with a 1/32" boss (= 10/32", or properly expressed - 5/16" or .3125").

The front view also shows the shaft and crankpin as being 3/8" dia.


Hope this helps.

 

[stevehuckss396]

Hey! Is that a squirrel.

Hahahaaa!! Awesome!


I have published plans and it is not an easy thing to do. God bless the guy's who have the time and energy to do it. Without them we would have nothing to build.