Question of scale

[johnnyo]

Hello
I recently started playing around with DraftSight and I liked this french twin marine steam engine but thought it rather small. My boiler size is to be around 7" did. and I'd like to see this engine paired up to it with 1" bore/stroke. I first ran the mm dim's by converting to 1/16" to mm. So 10 mm would be 5/8" Then I divided !.0" by the .8125 bore to get a scale factor of 1.231. I plan to draw in this scale to produce the desired scale engine with 1" bores. I noticed that the dim. don't always work out to evan fractions, like the 1.615 for cylinder height I got. If I convert a mm drawing to a 1/16" english version, enlarging itI know, would I not be able to scale it up without running into bastard sizes that may compromise the build later. I may be missing something here, I'm not sure.
Any opinion appreciated, Thanks!
Johnny O

 

[Maryak]

Hi John,

Using 1mm = 1/16" gives a scale of almost 1.6:1

i.e. 1mm = 0.0394
1/16" = 0.0625"

The usual quick and dirty conversion is 1.5mm, (0.0591") = 1/16"

As you say oddball sizes will appear regardless of what ever is used but another quick and dirty is 25mm = 1"

Some things almost match each other e.g. 5/16" = 8mm

I hope I have not misunderstood your question and the above is of some help

Best Regards
Bob

 

[Jasonb]

Its something where you just have to use your own judgement. I would not think that the length of the cylinder at 1.615" is something I would change as its just as easy to machine to that length as it is to 1.625"

However when it comes to things like round shafts it is better to adjust these to stock sizes, who wants to machine a long length of rod to what may work out to 0.238 when 1/4" would do. Same with smaller holes that may need to be drilled or reamed, use standard sizes but once they get big enough to bore then it makes no difference as you will just be working to a decimal.

What you really need to do is look at what does what and see if it can be changed, for example your cylinder height will start to affect piston travel therefore the crank may need altering, piston rod shortening and so it goes on.

J

 

[johnnyo]

Thanks Fellas, I'll hack away at it this week. Should be a good project for getting savy with DraftSight.

 

[Tin Falcon]

I am not sure if i understand what you are trying to do but I think i do so here is what I see.
you have a set of plans you like from france and drawn in metric.

you want to do three things with the drawing

redraw in draftsight

scale up the drawing

convert to imperial dimensions.

as bob said make 1mm = 1/16 and you should be fine and most dimensions will come out even.
you may need to increase the precision on your draftsight to reduce rounding errors.
Hope this helps
Tin