How to draw 2:1 Elliptical Head
How to draw 2:1 Elliptical Head
(OP)
Hello folks. I want to see if anyone has a good reference for drawing a 2:1 elliptical head. I always draw them in CAD and get the volume to calculate the weight, but it's kind of a pain. I've got two xeroxs out of old layout books and they offer slightly differently rounded versions of the same approximation. Sometimes that's close enough but other times I'm left having trouble b/c my polylines won't join to make a revolution solid, or I can't make a region out of the shape, etc. That's AutoCAD specific problems as I don't have Solidworks and I still suck at Inventor.
So, good folks of the internet, does anyone have any older style ways to draw these suckers i.e. laying the thing out with arcs and bisecting etc? Or do I stick with my approximations that I've got. I'm not interested in gaining a potential tiny tiny tiny bit better approximation, I just want to find a way that makes the drawing easy.
THANKS!
So, good folks of the internet, does anyone have any older style ways to draw these suckers i.e. laying the thing out with arcs and bisecting etc? Or do I stick with my approximations that I've got. I'm not interested in gaining a potential tiny tiny tiny bit better approximation, I just want to find a way that makes the drawing easy.
THANKS!





RE: How to draw 2:1 Elliptical Head
You can just draw 2:1 ellipse in ACAD, but yeah, can't join the plines.
Regards
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: How to draw 2:1 Elliptical Head
FWIW, you can set the system variable PELLIPSE = 1 and get a polyline approximation instead of a mathematical ellipse in AutoCAD. Or, if you set PELLIPSE = 0 and draw a mathematical ellipse, you can offset it some amount and it degrades to a spline which you can then polyedit into a polyline. Not sure if you knew that, but I hope it helps someone.
RE: How to draw 2:1 Elliptical Head
I figure since a head manufacturer can make a head either "perfectly" elliptical or this shape, this is just as likely to be "right" as a true elliptical shape and simpler to draw.
The problem is that if you offset an ellipse, you don't get a bigger ellipse, and that messes things up.
RE: How to draw 2:1 Elliptical Head
of 0.90D." UG-32
This is only for drawings, not for design, manufacturing and inspections.
Regards
r6155
RE: How to draw 2:1 Elliptical Head
RE: How to draw 2:1 Elliptical Head
RE: How to draw 2:1 Elliptical Head
RE: How to draw 2:1 Elliptical Head
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: How to draw 2:1 Elliptical Head
My example: DP= 1000 psi, ID=60 in L= 0,9ID= 54 in, r=0,17ID= 10,2 in, S= 20000 psi SA 516-70; E=1
Ellip 2:1 tmín= 1,43 in PWHT: not required, only preheat
Torispherical tmín= 1,8 in PWHT: Yes
Hence, ellip 2:1 head is not equivalent to a torispherical with L= 0,9ID and r=0,17ID
They are equivalent only for drawings.
Regards
r6155
RE: How to draw 2:1 Elliptical Head
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: How to draw 2:1 Elliptical Head
[As an aside, in the editions and addenda prior to 2015, this paragraph was sub-paragraph (d). However, in the 2011 Edition paragraph UG-32(b) was deleted, and the UG-32 subparagraphs were subsequently re-numbered for the 2015 Edition. If you look at the 2015 Edition, you will see that it is UG-32(c) now.]
As r6155 rightly points out, the calculated head thickness for the "approximate" torospherical head is higher than the "actual" 2:1 semi-elliptical head. So, the point that I will be bringing up is whether or not that approximation is appropriate. Before I do my presentation there, does anyone here have any thoughts or comments?
RE: How to draw 2:1 Elliptical Head
Regards
r6155
RE: How to draw 2:1 Elliptical Head
RE: How to draw 2:1 Elliptical Head
RE: How to draw 2:1 Elliptical Head
I can help you by giving you a sketch (*dwg format) generated by Solidworks in a dimeter, let's say, 1000 mm. Then you can scale it later on for any diameter will use.
Regards,
M.Salaheldin
Static Equipment Mechanical Design Engineer
RE: How to draw 2:1 Elliptical Head
Whether the thickness calculates the same applying the torospherical equation to the approximated elliptical head is a moot point. A similar discrepancy occurs when applying flange rating equations to 150# flanges, I believe.
TGS4, I think a major consideration would be to check how head producers actually produce heads. If they all produce "true" 2:1 form or all produce 90/17 or whether some do it one way and some the other.
RE: How to draw 2:1 Elliptical Head
If purchase order state ellip 2:1 head the manufacturer shall produce ellip 2:1 , not 0,9D / 0,17D(torispherical)
Regards
r6155
RE: How to draw 2:1 Elliptical Head
RE: How to draw 2:1 Elliptical Head
11042177. If you don't object, I am going to request that your item be covered under my item, as well.RE: How to draw 2:1 Elliptical Head
RE: How to draw 2:1 Elliptical Head
https://www.dropbox.com/s/0to5vjb6vmn95pa/Ellip%20...
Please check as well. Your feedback is most welcome.
Regards,
M.Salaheldin
Static Equipment Mechanical Design Engineer
RE: How to draw 2:1 Elliptical Head
RE: How to draw 2:1 Elliptical Head
Dear Sir,
Thank you for request for interpretation. After review, it appears that a previously issued interpretation may address this:
Interpretation: VIII-1-01-57
Subject: Section VIII, Division 1 (1998 Edition, 2000 Addenda); UG-32(d) and UCS-79
Date Issued: 06/11/2001
File: BC01-288
Question (1): A 2:1 ellipsoidal head is being fabricated from flat plate having a thickness t with a spherical radius of 0.90D and knuckle radius of 0.17D, where D = inside diameter of the head, based on UG-32(d) of Section VIII, Division 1. When applying UCS-79, where there is not an intermediate heat treatment performed during the forming operation, is the original center line radius equal to infinity and the final line radius equal to 0.17D + t/2?
Reply (1): Yes.
Question (2): Does the head described in Question (1), which is manufactured as a flange and dished head, and a head formed having the exact dimensions of a 2:1 ellipsoidal shape both meet the requirements of UG-32(d)?
Reply (2): Yes.
RE: How to draw 2:1 Elliptical Head
https://www.google.com/#q=ellipse+template+set&...
Sometimes its possible to do all the right things and still get bad results
RE: How to draw 2:1 Elliptical Head
https://www.google.com/search?q=ellipse+guides+tem...
Sometimes its possible to do all the right things and still get bad results
RE: How to draw 2:1 Elliptical Head
Thanks for closing the loop on this one!
RE: How to draw 2:1 Elliptical Head
Also, to the OP I would suggest contacting your head supplier to see how they handle 2:1 head manufacture. Then make your CAD model match what they do. We have found considerable differences between the two shapes in the "knuckle" area, which can impact the size and location of clips and other minor details.
RE: How to draw 2:1 Elliptical Head
Thank you pperlich. That was kind of what I was thinking. We rarely use heads in items that we manufacture as our scope ususally is demo of old and installation of new (prefabricated) equipment. That usually involves welding on lifting lugs which brings up the issue you highlighted.