URGENT!... How to know No of Turns of Helix using Helix Angle??

[rohitjvbibin]

Hey,

 

Can anyone please tell me how to draw a helix when u know only the helix angle, Base radius and Top radius..Please note that i would like to make the helix angle constant w.r.t the horizontal...Atleast i would like to know the formulae if any for the helix regarding no of turns and helix angle..

Thanks in Advance

 

Rohit

[ReMark]

You know the base and top radius. You know the height or overall length of the helix as well?

[rohitjvbibin]

The exact dimensions are Base Radius: 59.1402mm; Top Radius: 27.8mm; and Length: 100mm....And the Helix Angle should be maintained constant at 20 degrees. I dont know how to find out the no of turns. or pitch. Thanks for ur instant reply Remark...

[ReMark]

So at the end of one turn the helix will rise 21.5253mm right (assuming of course a 20 degree angle of rise). 100 divided by 21.5253 = 4.64569. My wild guesstimate.

[JD Mather]

I'm having a bit of trouble figuring out your design intent.

What is the part? Any more information?

[rohitjvbibin]

I'm having a bit of trouble figuring out your design intent.

What is the part? Any more information?

 

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Mr. JD Mather;

 

Thanks for the attachments(i would like to know the software used to draw that with the angle included as i saw it).

About the part...Its a nozzle of a rocket tapered which dimensions have been posted above. It has a outer shell and an inner shell and the space between them has to be filled with helical channels of rectangular crossection(dimensions given). The number of helical channels are 48 in the array(they should not overlap each other). But that is not the problem.

I cant find any option to include an angle like shown in the diagram. and also to calculate the no of turns from the angle and other data posted above.

I know how to draw the rectangular section and sweep it. But what perplexes me is that while sweeping the face gets perpendicular to the sweep line and not as i want it..

 

Hope i have given enough info....In case anythin else need please post.

[JD Mather]

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Mr. JD Mather;

 

Thanks for the attachments(i would like to know the software used to draw that with the angle included as i saw it).

...Its a nozzle of a rocket ....

 

I think maybe it could be done in AutoCAD (actually I'm pretty sure it can), but I'm also pretty sure I wouldn't even try. I used Autodesk Inventor. If I get a chance I'll model up entire part. Nice thing about a 3D program like Inventor - if I don't get it right on first try it is simple matter of editing parameters.

 

Students can download Inventor Professional for free from http://www.autodesk.com/edcommunity

[SEANT]

It is an interesting problem. Here’s an Excel/AutoCAD way of dealing with the parameters.

 

Unfortunately, It appears that a tapered helix (i.e., larger radius at bottom than top) can not maintain a constant angle w.r.t. horizontal while also maintaining a constant pitch.

 

If that is an absolute requirement, I don’t think it can be done with the helix command.

A spline with the appropriate control point positions would be needed to model the geometry.

Helix.zip

Edited September 17, 2010 by SEANT
Grammar

[SEANT]

As is typical, I’ve pursued an idea beyond what is useful. . . .even to the OP. I do find the puzzles entertaining, though, so that preceding statement isn’t so bothersome.

 

The Excel spreadsheet and DWG from my post above have been modified to demo a tapered, helix like structure (Spline) that maintains a constant 20 degrees incline from a horizontal plane.

 

This new curve (Red) varies quite a bit form my original helix (White).

Helix2.zip

Edited September 18, 2010 by SEANT

[rohitjvbibin]

Thanks for the files.They were very useful. Can u please clear a doubt of mine regarding the second file (Helix2.zip). What is the difference between the early Helix.zip and the new Helix2.zip. I can see an added quantity called resolution. What do u exactly mean by resolution? Every value in the spreadsheet changes when i change the resolution...Awaiting ur response..

 

Rohit-JV-Bibin

[SEANT]

“Resolution” just means the number of divisions I used for that particular setup. I chose 100 (an arbitrary amount) assuming that would be sufficient to keep the spline at the constant 20 degree angle.

Unfortunately, the spreadsheet would require further modification if that “resolution” number needed to change.

[rohitjvbibin]

Ok SEANT. I will go with the given resolution(100). Now i am stuck with another problem. I need to draw a helix over a surface which is a converging and diverging and my restrictions are that I CANNOT SPLIT THEM INTO TWO(Converging Helix + Diverging Helix). I need a single helix path to sweep the element through. I have the dimensions with me. Will provide if necessary. Currently the Converging path(103 mm) has the maximum helix on it and the Diverging path has say 20mm helix on it. I don't want to break up the Helix into two so please help me....

[SEANT]

I having a problem forming a mental picture from that description – do you have a diagram that illustrates the situation?

With regard to the resolution: It can easily be changed, it’s just that it requires more than resetting the number in that particular cell. Is 100 too many divisions or too few?

[rohitjvbibin]

I am sending the link to the 3d drawing.

 

 

http://www.sendspace.com/file/rvn84t

 

It needs two helixes.I have marked vertical blue lines and the helix should be between them. First the convergent and little divergent part needs a continuous helix without the surface breaking when sweeped. Second the next helix is also straight for 90% length and then there is a small Slope as u can see in the given AutoCAD drawing. The constant helix angle is 20 degree for both helixes. Kindly see if u can draw the helixes and also explain to me how to draw it...

 

 

I will tell you in this paragraph how i drew the first helix(using ur excel sheet helix.zip). As u can see i have split it into 5 parts and i drew 5 helixes each one starting where the other had ended. Thus i joined all 5 helixes into a single spline using JOIN command...They got joined but when i sweeped a rectangular crossection it had 5 surfaces which meant it was breaking up at the points where had divided the lines. I am in a fix now...I dono what to do. I do not want different helixes but a single one..Please help me...The cad file will give u all dimensions hence i havent mentioned any..

 

Thanks in advance..

 

Your replies have been truly useful for my project...

 

[SEANT]

Presumably, precision is a driving factor in this project. I see you Units are set to a high precision; and high precision is certainly something I attribute to rocketry.

 

I see that the Helix down by the cone is derived from data returned from the excel spreadsheet in post #8. That helix, though, only has an average slope of 20 Degrees; the angle is less where the cone is widest. It is the reason I modified the spreadsheet in post #9.

 

So, my suggestion on how to proceed would depend on the level of precision required.

 

For instance, the geometry in the attached is fairly close – you would have to determine if it is close enough. A tighter tolerance requirement may necessitate some form of automation (AutoLisp, .NET, etc.).

 

Any spline used for SWEEP/EXTRUDE WITH PATH needs to be at least G1continuous, possibly even G2.

http://en.wikipedia.org/wiki/Non-uniform_rational_B-spline

 

The splines in the attached were derived from the Helix and/or splines from the previously posted spreadsheets, joined to their neighboring splines, divided into equal segments, then a new spline created from the points. The splines are G2 continuous.

splines.dwg

Edited November 4, 2010 by SEANT
grammar

[rohitjvbibin]

Thank You SEANT. The splines sent are of the correct dimensions and can be used for my project. The only problem remaining is that regarding the first spline on the left side, i am not able to sweep at all. The reason is because i notices an awkward bend in the spline which prevented the region from being sweeped. And regarding the second spline, the region sweeps but it gets bend halfway.

 

I have sent u the drawing with one region sweeped but bent. Kindly see if u are able to correct the splines and sweep any regions(rectangle or circle) without getting bend. I would also appreciate if u could tell me the method of how did it in autocad in a simple way. (I am confused upon hearing terms like G2 and other wikipedia stuff).

 

Awaiting for ur next attachment hoping you will correct the bend.

 

http://www.sendspace.com/file/jeq5cl

 

 

RohitjvBibin

[SEANT]

Sorry, I must have inadvertently moved one of the fitpoints prior to uploading. See attached for corrected spline.

 

 

 

Sadly, these types of operations are not simple to do, or explain. What I did for these splines was to use the previously posted spreadsheet to get general splines for the specific sections. I joined the splines together *, created regular intervals with the divide command, and then created a clean spline by snapping to those node points.

 

*(The reference to G0, G1, G2, etc. pertains to splines that are joined together. A clean Sweep/Loft can only be realized if the splines are not kinked at the join point.)

 

Even with a fairly clean spline, however, a sweep operation can be difficult. I’d recommend sweeping with a perpendicular cross section. In the attached I’ve just reoriented the rectangle but you may have to derive what the new perpendicular section would be if the orthogonal section should remain as you have shown.

 

Here is the command sequence for the sweep shown in the attached image:

 

 
Command: sweep

Current wire frame density:  ISOLINES=8, Closed profiles creation mode = Solid

Select objects to sweep or [MOde]: 1 found

Select objects to sweep or [MOde]:

Select sweep path or [Alignment/Base point/Scale/Twist]: b

Specify base point:
Select sweep path or [Alignment/Base point/Scale/Twist]: t

Enter twist angle or allow banking for a non-planar sweep path 
[bank/EXpression]<Bank>: b

splines.dwg

[rohitjvbibin]

The splines are continuous but now a new problem arises.

 

 

 

In the first convergent divergent part (103 mm), when i sweep the section it comes out fine but i noticed that when it reaches halfway it goes below the required place. I am not able to move it above because then the whole helix gets moved.

In the second almost straight part (284 mm), when i sweep the section it too comes out fine but the same way the middle part goes below the required place.

 

I am sending you my whole diagram with both sweeped helixes and the sections on them...

I have written important points in the drawing itself.

 

 

The section on the convergent divergent part is a rectangle of thickness 1mm and height given in the figure.

 

The section on the straight part is a rectangle of 1.2mm thick and height is given too....

 

 

Please note that the sections should not be perpendicular to the sweeped line but in the way i have drawn them in the diagram. The problem with this is that when i sweep them(with Alignment option NO) they remain the same on the starting part but get perpendicular on the other end.

please see if u can correct that too...

 

 

The sections have been drawn a little above and below overlapping on the copper and stainless steel (SS) part. Later on i will subtract and unite them. No neeed to worry about fitting them correctly in between copper and SS shells. I will do that.

 

 

 

So in overall

 

 

1. The sections should be perpendicular to the horizontal not to the sweeped line.

2. The helix channels (both) should passs through the correct path and not below. The corrrect path is in between the copper section and the stainless steel part.

 

 

3. Please find the required dimensions in the autocad file attached below..

 

 

Kindly message me anything is required as i will be frequently checking my mail for your response as i have to submit my work at the earliest and your help is essential in my project..

 

 

http://www.sendspace.com/file/lbslbj

 

 

Thanks in advance

 

 

RohitjvBibin

[SEANT]

I’m afraid I won’t have time to offer more than a couple of suggestions and/or comments.

 

One comment is to repeat that modeling of this type is rather difficult in AutoCAD: Are Solids absolutely necessary to the project?

 

If solids are necessary then perhaps the attached geometry could be used with a Loft operation. You may have to experiment with the various parameters to get useful solids (I’m not certain myself as this is not a common task).

LoftGeom.dwg

[rohitjvbibin]

Thank you SEANT. I will check it again if its a mistake when i transferred the splines to the original drawing. I appreciate and thank u for the time you spent in solving my problem. I will let you know if any positive thing arises in the forthcoming days. Be in touch

 

Thanks again

 

RohitjvBibin