Engineering drawing problem – missing dimension?

Been playing around with Fusion 360 and getting to grips with it.

I am currently trying to model a radial engine but I’m a bit stuck with the dimensions on this drawing.

On the plan view, where there is a 150mm distance between 2 curves, the sides run from a 26mm distance to 18mm. How do I work out where the 26mm starts to reduce and “slope” to the 18mm?

87mm from centre- see diagram below. The 26 has extension lines leading to the fold line

The 87mm dimensions is reference only. But because the connecting line between the 72 and 35 radius curves is tangential to both, if you dimension the vertical ends of that line 26 and 18 respectively it fully constrains the profile. You don’t need to know the horizontal position of the curve/tangent intersection.

As irelanst says. Once you set all the tangents and coradials it should all come together. You can then use the 87 dim as a check

Which will probably be something like 87.2342 or something

I think the (87mm) is to indicate the tangent edge where the R72 meets the tapered shaft in the top view. I think that is where the R78 insects the 42 mm thick section as you would need to know that to fully constrain the R78. I’m bored so i will model it and check if I am correct.

yup reference assuming that its tangential to the line.

Isn’t the 18mm dimension the width of the “web” rather than the width of the narrow end of the “slope”?

Web is 12 I think

Thanks for all the advice.

However, I’m none the wiser!

I’m also confused by the “5 PLACES” notation next to the 10mm diameter, when there are only 4 holes?

It’s not a great drawing gobuchul.

In my experience, the most important thing a drawing should do is provide the info so when the part turns up, it’s right. I don’t like the 26 and 18 dimensions. There may be extension lines that are visible on a full size drawing, but the person making it will likely have a small copy. I’d put a note, or a detail view to explain what they are.

And as you say, ‘5 places’ is confusing. Is there another hole not visible in those two drawings?

This is a rendering of the completed assembly. Only 4 holes are required.

The Grabcad page

I’d also put a note (or show on another view) the fact that those holes go into both top and bottom faces, because that’s not clear from the views given. It’s so easy to add views with modern CAD, there’s no excuse for not doing it.

Upper view is a disaster