Space Shuttle Launch Pad 39A with Challenger STS-6 (1:144)

[spacerunner]

Hello friends,

only some thoughts to minor changes of the IT.

In consultation with Michael Key we will now omit the inner tube completely, as there would probably be problems with the removal of the support material, which could possibly resist the ultrasonic cleaning. Then one would have to drill out the tube, which seems to me but too risky.

BTW, I did not want to believe it at first, but there was one thing which I have noticed in retrospect on the 3D print, what I have overlooked at the 3D renderings.

The front part of the LO2 PAL Ramp of the 3D model has almost the same width as the back part of the LH2 PAL Ramp, but this is a mistake and does not match the original optics.

The LO2 PAL Ramp is too narrow and therefore needs to be widened, as one can see in these images. And actually, both ramps end up on the stringer top and do not run to the valley as before.


Source: shapeways.com (The Aerospace Place)


Source: NASA
But that can certainly be corrected so that the optics are right again.

[spacerunner]

Hello everybody,

actually I had thought that Michael Key had to make only small changes. But it came different again ...

First, he has omitted the inner tube as well as modified the LO2 PAL Ramp (right) as desired, which looks much better.


Source: shapeways.com (The Aerospace Place)

However, I noticed that he did not modify the LH2 PAL Ramp in the same way, which I took for granted and therefore have not said it again.


Source: shapeways.com (The Aerospace Place)

But about his change of the diameters of the IT to reduce the slightly too large overhang at the rear end (Ør 60,0 mm) I was then quite shocked, because he accordingly must have misunderstood my image with the diameters of the Airfix Intertank and the values measured at the 3D print (red on white ground).

But in hindsight, I must confess that the picture has become rather confusing and misleading.



Because he had now set the front diameter (Øf) of the IT to 57,0 mm and the rear diameter (Ør) to 58,0 mm, so that it is consistent with the front and the rear part of the ET. As a result, there should be no overhang of the IT, neither front nor back, but which in reality is not the case because of the Stringer/Ribs and has never been up for discussion, on the contrary.

Maybe that the rejuvenation of IT by 1 mm seemed to have got mixed up him, which was obviously difficult to implement in modeling.

The bad thing was that he had already uploaded this disimproved Intertank to Shapeways.

After that I have showed him the different diameters of the three ET parts again clearly in the following pictures and explained the differences.

D2 and D3 are the small overhangs of the Airfix IT that need to stay that way.



On this image one can see the connection diameter D2.1, which has to fit into the ET front part (D1.1), and the diameter D4.1 of the heel of the ET rear part, which has to fit into the Intertank,



whose inner diameter D3.1 can be seen here.



Hopefully this should have made it clear that we need the overhangs, so I asked him for the necessary changes in the hope that he could clench his teeth and be able to do it.

Apparently Michael Key has that now understood and has adjusted the LH2 PAL Ramp as well as the rear IT diameter D3 to 59,0 mm and the front diameter 58,0 mm and then uploaded his model again.

And so the Intertank now looks at the Shapeways-Website, whereby he has become even cheaper by the removal of the inner tube with € 69,44.


Source: shapeways.com (The Aerospace Place)
I just ordered it again and hope that all good things come in threes.

[elliott]

Hope so Manfred. Fingers, toes & eyes crossed for ya' ;<)

[spacerunner]

Thanks elliott for your good wishes,

now all the IT has to do is to match with the other two ET parts.

[spacerunner]

Hello folks,
as Shapeways has told today, the new Intertank is on its way to me.

[spacerunner]

Hello everybody,
another subproject are the Ice/Frost Ramps on the LH2 External Tank, and maybe Michael Key can also help me again.

In fact, there are 17 ramps, with the rear three ramps looking slightly different than the front 14.


Source: NASA

And that's how most of the Ramps for the GO2/GH2 Press. Lines look like.


Source: NASA

My ARC friend Bill (niParts) has already modeled a Set of these Ice Ramps in 1:72, but in 1:144 they are much smaller and could possibly be problematic for 3D printing.


Source: shapeways.com (niParts)

In reality, the ramps are 2' x 2' x 1', and accordingly 4 mm x 4 mm x 2 mm for the ET (1:144).

The diameter of the GO2/GH2 Press. Lines is 2'' = Ø 0,35 mm (1:144) and is used as the reference gauge.

The openings in the ramps are slightly larger, approx. Ø 0,5 mm, as one can see on this image.



Possible that the small wall thicknesses for Shapeways pose a problem, but which I do not hope.

[spacerunner]

Hello everybody,

Shapeways' shipping did not take so long, if you have been wondering about the send pause.

The reasons for that I still want to explain before the holidays, but the devil is often in the detail, or better said in this case in the Shapeways' tolerances, which I have not yet known so far.

And if one or the other in the mean time has clicked on the link of the SW website in my Reply #1612, then he will has been surprised. Oops!!!

Outwardly, the second Intertank looks really great,



but already the test fitting of the ET front part was not possible because the connection diameter D2.1 was still slightly larger than that of the first IT, namely instead of 53,5 mm it was now even 54,1 mm. You could have knocked me down with a feather!!!



Instead of getting a little smaller by Michael Key's adjustment for a better matching the Airfix IT-values, the dimensions became in spite of taking shrinkage (0,8%) into account amazingly even a bit larger, which is still mystery to me.

This is shown by the comparison of the dimensions of the two ITs with the Airfix-IT,



whereby I've tried to measure as accurately as possible.









While the larger length is less a problem for the fit of the parts,


the resulting diameters all the more so as the overall IT was printed too large, which can also be seen at the back overhang of the IT, which is just too big for me.



Of course, Michael Key was also very surprised, because according to the SW website, the visible length of the IT (without front connecting ring) should be around 48,9 mm (48,5 mm x 1.008 shrinkage), as it was indicated in his CAD file.

He then removed his shop offer and contacted Shapeways for anew refund, which I've received in the meantime.

While the tolerance for FUD on the SW website is indicated with

Accuracy ± 0,1 - 0,2 mm for every 100 mm,

we have now been told that the actual tolerance of the material is up to 0,4 mm, so one can not guarantee that the IT is perfectly sized, which is inconsistent and in my opinion difficult to accept it.

However, in a sketch by Michael Key with all dimensions of his CAD model without and with shrinkage (0.8%), I discovered a small flaw that may have contributed to the enlarged diameters, which he has now corrected.

With these last changes, he has uploaded the model again, and here it can be found.
Now he will also upload a WSF version, which does not have to consider shrinkage and which will surely become a bit cheaper.

Now I'm curious what kind of egg this time Shapeways will put into the nest me.
Otherwise, I wish you all and thank you for looking in on me.

[elliott]

Still hanging in there with you Manfred although my fingers and toes are beginning to cramp from being crossed for so long. Had to uncross my eyes because I ran into one too many door frames.

[spacerunner]

Thanks elliott, my friend, for your assistance.

Normally it is absolutely a No go!!! It is unacceptable for the customers that SW simply declares new tolerances that are twice as large if the specified limits are not met.

And therefore I will inform SW that I'm expecting their guaranteed FUD accuracy of 0,1 - 0,2 mm for every 100 mm for the proud price of this print, otherwise their talk is only cheap.

[elliott]

A question if I may - What is the "WSF version" you refer to in your post #1617?

As an aside Manfred, you have every right to expect Shapeways to adhere to their indicated tolerance instead of changing horses in midstream and doubling it! Poor way to treat a customer. Is there another company that can do the work for you or are they the only ones?