Ways to figure out dimentsions for a transition between 2 body tube sizes

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Sterk03

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Sorry if I'm in the wrong forum but I tried some searches and came up empty. I need to make a transition between 2 body tubes and looking for
how to come up with the measurements to make it out of cardstock with some Ctr rings out of balsa or plywood?
Thanks,

Sterk03
 
I have yet to find a transition template program where it's straight on one side... an eccentric conical transition.

Eccentric Cone.jpg
 
I have yet to find a transition template program where it's straight on one side... an eccentric conical transition.

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I have a book, "Metric Drafting", that has several chapters on pattern development for various manifolds like this. Sorry, the book is in storage, otherwise I'd post the equations.

I've never found equivalent coverage in another drafting book. Maybe there's a pattern development book somewhere.
 
I have yet to find a transition template program where it's straight on one side... an eccentric conical transition.
Over on the Paper Modelers forum, prolific plans maker scissorsandplanes shared formulas for making a pattern for an offset truncated cone. But the formulas only find the corners and midpoints of the pattern. I'm not sure how he gets the curves. He says he uses an Excel file and plots points on curves as a "radar plot" (polar coordinates).
 
Many moons ago I whipped up a tool for work to create concentric and eccentric reducers - generally from stainless steel sheet. It creates a DXF template. Because it was an inhouse thing, I have no idea if it'll work (install correctly) on external computers. So, treat it as a last resort (possible) option.

https://www.propulsionlabs.com.au/Reducer_Template/Template_Helper2.zip

TP
 
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This is an old but tried and true simple method... You need a ruler and a compass... Works for basically any tube sizes. Note does not work that well if the transition is extremely short.. I.E. if this example was only 1/4" tall...errors build up quickly...
Top Horizontal line = diameter of bigger tube.
Bottom line = smaller tube.
Vertical distance is your transition height.
Connect the ends of each line to fond the center point. (Where the circle is...)
Use compass to draw circles at the midpoint of the horizontal lines.
Cut out the curved piece longer than needed, don't forget room for a glue tab... Eyeball it for approx. length...
This example is a 1.5" tall adapter for BT-50 to BT-60... Length along curve about 4.77" Cut out about 5 1/2" along curve, you can trim back to include enough for the glue tab.

Mount smaller tube into larger one with centering rings, making sure the ring where the larger tube is juts out enough to have a spot to glue the transition.
Pre-curve the paper, cardstock or whatever and dry fit it before gluing.

There may be some slight error, try a plain paper one first. Wrap it around and look to see how the ends line up, if square, your golden! If the large diameter part overlaps more than the smaller, then the center point you used needs to move down a little bit. (This changes the ratio of the two curve lengths)

1716911095080.png

Or... 3D Print it...
 
I was going to build a tail cone for a scratch built downscale of the Estes Sprint so I spent a little time deriving the equations. I've seen similar equations on the internet but in slightly different form. Basically the equations tall you the angle and the 2 different radii. You map it out on a piece of paper and cut it.

A few years ago I did a scratch build with 3 side pods around a central core, the side pods were slit so they fit partly onto the central tube. I wanted offset cones on the side pods. I figured out the geometry using equally spaced points around the perimeter of the pods and then calculating the hypotenuse to the offset point of the cone. I mapped this out on a piece of paper, cut it out and did a test fit. Then I made a slight change to the next couple of patterns until it fit the way I wanted and then cut the final cones out of cardstock. Something like this might be possible for the offset cone that someone asked about earlier.
 
Over on the Paper Modelers forum, prolific plans maker scissorsandplanes shared formulas for making a pattern for an offset truncated cone. But the formulas only find the corners and midpoints of the pattern. I'm not sure how he gets the curves. He says he uses an Excel file and plots points on curves as a "radar plot" (polar coordinates).
I joined the forum in order to download that pdf, but never got a member confirmation email, so I can't access it or post anything to the forum.

I found this calculator, which looks like what @lakeroadster was asking about (select "eccentric cone")
 
I joined the forum in order to download that pdf, but never got a member confirmation email, so I can't access it or post anything to the forum.
Might take a couple days to go through. If you'd like, I could ping an admin over there about the status of your user account.
But yep, it's what that calculator produces, nice find. (Hopefully that calculator site is from a real person and not "AI"-generated! A little hard to tell.)
 
Might take a couple days to go through. If you'd like, I could ping an admin over there about the status of your user account.
But yep, it's what that calculator produces, nice find. (Hopefully that calculator site is from a real person and not "AI"-generated! A little hard to tell.)
It was several weeks ago...I tried the "contact us" link to report the issue after a week or so, no reply. I registered under the same username rocketguy101
 
I joined the forum in order to download that pdf, but never got a member confirmation email, so I can't access it or post anything to the forum.

I found this calculator, which looks like what @lakeroadster was asking about (select "eccentric cone")
Well, that's for an eccentric cone where it's straight on one side. I was in need of an eccentric cone that's not straight on any side.​
Eccentric Cone I Need.jpgEccentric Cone.jpg
 
Well, that's for an eccentric cone where it's straight on one side. I was in need of an eccentric cone that's not straight on any side.​
Over powered, but you should be able to use Fusion360's sheet metal tools to create these patterns. Create the 2 tubes, loft the transition, shell it out, make a tiny slit, then convert to sheet metal and unfold, then save the result as a .dxf.
 
Well, that's for an eccentric cone where it's straight on one side. I was in need of an eccentric cone that's not straight on any side.​
I can tell you how I did it-
You know the small diameter and the large diameter, and you know that it is symmetrical so you only have to plot half of it.
You pick points around the perimeter of each tube, maybe 12 points so since it is symmetrical you only have to calculate 6 points. You know the circumference of each tube so you divide each circumference by 12 to get the distance between points. Now you have to calculate the length of the sloping lines connecting each point on the big circle to the corresponding point on the small circle. Actually I'm seeing a complication with this method. I was calculating a cone with a point that was offset. You might have to do this in 2 steps- figure out where the point of this would be if it really was a cone and work the geometry like that- a short cone superimposed on top of a long cone.
Back to the method- once I've calculated the length of one of those lines I draw it on a piece of paper. At the bottom end I draw a line almost perpendicular to it that is the length of the circumference divided by 12. Then I connect the short line and the other end of the long line with a line the length of the second line and so on around the perimeter of the big circle. I cut that out of paper, rolled it to a cone and test fit it then figured out where to trim a little bit.
If someone really wants to do this and needs a better diagram I can try to do that.
 
I can tell you how I did it-
You know the small diameter and the large diameter, and you know that it is symmetrical so you only have to plot half of it.
You pick points around the perimeter of each tube, maybe 12 points so since it is symmetrical you only have to calculate 6 points. You know the circumference of each tube so you divide each circumference by 12 to get the distance between points. Now you have to calculate the length of the sloping lines connecting each point on the big circle to the corresponding point on the small circle. Actually I'm seeing a complication with this method. I was calculating a cone with a point that was offset. You might have to do this in 2 steps- figure out where the point of this would be if it really was a cone and work the geometry like that- a short cone superimposed on top of a long cone.
Back to the method- once I've calculated the length of one of those lines I draw it on a piece of paper. At the bottom end I draw a line almost perpendicular to it that is the length of the circumference divided by 12. Then I connect the short line and the other end of the long line with a line the length of the second line and so on around the perimeter of the big circle. I cut that out of paper, rolled it to a cone and test fit it then figured out where to trim a little bit.
If someone really wants to do this and needs a better diagram I can try to do that.
Thanks.​
This was back in April... I ended going old school: making a paper template... over the rocket.... and transferred it to carboard. Worked great.​

001.JPG 002.JPG003.JPG 004.JPG006.JPG 003.JPG
 
I played around with F360 and it was just generating errors when I tried to unfold the pattern, it would work fine if you wanted to 3D print a transition, but no good if you wanted to make a cardstock transition.
I did find this pattern generator that does seem to create what you're looking for though:
https://www.sheetmetalpatternsonline.com/dialog.php?pattern=0&name=Cylinders and Cones
Yeah flat patterns in CAD can be tricky. I've never used F360 or Autocad, but I've used SolidWorks for many years. Most of my experience is with solids, but have picked up some sheet metal (mainly for rockets LOL). Here is a tutorial I just created for doing this in SWX. Perhaps some carries over to other CAD?

Edit: I meant to mention I tried rolling the flat pattern generated with the points from sheetmetalpatternsonline and couldn't get past the "non linear edge" error message, and I was using one of the straight line edges. Thats when I started playing with the sheet metal loft.
 

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Yeah flat patterns in CAD can be tricky. I've never used F360 or Autocad, but I've used SolidWorks for many years. Most of my experience is with solids, but have picked up some sheet metal (mainly for rockets LOL). Here is a tutorial I just created for doing this in SWX. Perhaps some carries over to other CAD?

Edit: I meant to mention I tried rolling the flat pattern generated with the points from sheetmetalpatternsonline and couldn't get past the "non linear edge" error message, and I was using one of the straight line edges. Thats when I started playing with the sheet metal loft.
Yes, that helped. I was using circles to generate the lofted shape, then cutting the slit, that appears to be the source of the error. I redid my steps with arcs and F360 was finally able to unfold it.

Here's the file if anyone wants to play around with it, you can go to Modify>Change Parameters to change the variables.
 

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  • Eccentric Cardstock Transitions v1.zip
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