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machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment.

Category: 3D Printing

Video of Casting Small Complex Cannon Parts

This video was taken and edited by my daughter Eleanor.  I was doing an aluminium pour of some parts for the Armstrong RML cannon, explaining the process to her.  I was hardly aware that she was videoing, so the interaction is conversational.

Although the pour was not a success because none of the parts were good enough to use, it does show the process as seen by someone who previously knew nothing about it.

 

 

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There is also a 20 minute video of the whole process which I will add to this post when it is available.

Reader Rob has suggested that the positions of the defects suggests that air entrapment is the cause of the voids and that the fix is to position some vents at the positions at risk.  I will try that with my next pour.  Thanks Rob.

Here is the 22 minute video.  Just as recorded.  Not planned or edited.

 

 

 

 

 

 

 

Second Pour.

One definition of stupidity  is repeating a set of actions and expecting a different outcome.

Well, after my partly successful first molten metal pour, I repeated the same steps, (with some minor corrections), and hoping for a more successful result.

The day was entertaining, with one of my daughters videoing the exercise.  But this was the result…..

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The aluminium melt has not properly filled the cavities at the top (nearest the funnel).  The bottom cavities have filled nicely, with good definition of the printing details.

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The second flask with the same  result.

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My daughter found the exercise very interesting, particularly the pour and the boiling out of the investment material.  But she was a bit disappointed that the end result was not better.

So, I am considering how to change the process.

I believe that I need to increase the filling pressure in the upper half of the flasks.

Possible methods:

  1.  Install a vacuum system for the melt pour
  2. Use a vertical extension for the melt funnel, to increase the height of the column
  3. Increase the diameter of the funnel tube
  4. Increase the number of the funnel tubes
  5. Don’t place tree branches close to the funnel

I had previously considered 1. as recommended on YouTube by several contributors.

The investment powder is a significant cost, so I would prefer to use as much of the volume of the flask as possible, which makes 5. an unattractive proposition.

There are difficulties with instituting 2. but I am thinking about this one.

And possibility 6, is to try bronze or brass, which has a much greater density, and probably less viscosity than aluminium.  I am waiting for some more furnace graphite crucibles to arrive before I can try this one.

Meanwhile I have to 3D print some more PLA parts.

 

A Closer Look at the results of yesterday’s Metal Pour

Yesterday I made some cast aluminium parts for the model 1:10 Armstrong RML cannon. It was the first time I had done lost PLA casting, and seeing the castings emerg from the investment mixture was thrilling.

Today I had a closer look at the parts, band sawed them from the trees, and tidied them up with some belt sanding and filing.

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There were 3 central columns.  In each case the vertical side flanges came out almost perfectly, but the bases contained some voids.

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The undersides of the bases shows that the voids match the internal structure of the original 3D print.  This indicates to me that the fault arises from the 3D print, not from the molten metal pour.  Those columns were among the first 3D printing that I had done, and I remember that the surface layers were only 3 layers thick.  Since then I print substantially thicker surface layers, which I believe are more water tight, and less likely to let the investment material leak into the structure of the print.

Although they look very ordinary, I will fill these voids with JB Weld, then paint them with automotive filler primer, then the final paint coat(s).   If they are still substandard I will start again with new 3D prints,

I also poured 6 wheel forks.  2 were so bad that I have melted them down into ingots for re-use.  The other 4 looked resurrectable.  Unfortunately I had a mishap when bandsawing the parts from the tree.  The tree was flung across the workshop, and one of the forks snapped.  Of course it was the best one.

So 3 of the 6 forks were put into the re-melt, and I did some tidying up on the other 3.

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This lot was remelted into an ingot for future re-use.

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The 3 on the left after some tidying.  Same problem with the voids in one base, but structurally OK and can be fixed.  I scrapped the one on the right.   I might eventually remake them all.

So, although I ended up with 6 use-able parts out of 9 made, and most of those require filling, I am still reasonably happy with this first attempt.  I think that the 3D prints were the weak link in the chain, and with that assessment I will try another casting run in a few days.

Meanwhile, back home I printed a Tyrannosaurus Rex.  I think that it is my best 3D print so far.  It is 250mm long, and the level of detail is excellent, even the vestigial arms are intact.

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About the colour.  No one has any idea what the original T Rex skin colour was.  So even this red is possible (but unlikely).   Nor do the scientists know what noises the T Rex made.  Could have been a reptilian hiss, or a roar, or a porcine grunt.   Whatever, I am glad to never hear it.

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The print took over 24 hours.

Repairing Failed 3D Prints

As a beginner, I have a fair percentage of unsatisfactory prints.

Print breaks free of plate.

Supports fall over.

Overhanging areas insufficiently supported.

Holes appearing due to wrong settings.

etc. etc. etc.

Most of the time I just bin the failure, change the settings or setup, and make another print. And wait another 2, 9, 12 or 24 hours……  Not a huge financial cost, but does involve waiting.  And I am not very good at that.

I used to grow olives and make olive oil.

Sometimes the bottles of oil were sealed with wax.  Melting point 85ºc.

After a failed print of 6 items today, due to inadequate supports of overhanging areas, I wondered if the holes and thin areas could be fixed with the bottle sealing wax.  After all, lost PLA casting is just a descendant of the lost wax method in the metal casting process.

So I found the left over remnants of the bottle sealing wax, and heated up a soldering iron.

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One of the failed prints.  This is a wheel trolley bracket for the model Armstrong cannon.  The moth eaten area was overhanging, and the support had fallen over.  The area was thinned and the holes were not properly formed.   If a brass or bronze casting was made from this, it would have been unusable.

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The 850g slab of bottle sealing wax, and soldering iron.  I do not know if this supplier is still available.  It was not expensive.

The soldering iron is heated, dipped into the wax, and the molten wax carefully dripped onto the deficient area of the print, gradually building it up.

The wax can then be shaped with the soldering iron, or a heated knife, or even a finger or thumb.  I also tried a blade shaver and sharp knife.  I think that my soldering iron, and finger were the best tools.

 

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The repaired area.  It looks unsightly, but of course the wax will all disappear during the casting process, along with the PLA.

I am probably reinventing the wheel with this idea.  Again.  But have not seen it used anywhere else.  So there it is.  I think that it will be useful to me.

PS>. 12 hours later.  I now realise that this is so old hat that I am embarrassed that I posted this.  Reinventing the wheel,… that’s me.

 

 

3D Printing Question

3D printing is really slow.  So slow, that the machine is left unattended to continue the print, overnight in many instances.  The print head is set at 205ºc and the table at 60ºc, and it does bother me that this hot machine is left unattended, unwatched.  I do not know if any fires have resulted, but fires are of some concern, particularly here in Oz.

A substantial component of the printing time is the hidden, internal structure of the object being printed, the “infill”.

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In this photo I set the infill at only 3%, but to compensate for that I increased the wall thickness.  The result was a nicely rigid article, but it was a 24 hour print.

My question.   At this point in the print job could I have paused the printing, and filled the cavities with a substance which set hard.  It would have to be done carefully of course, and keeping the level below the printing edge.  It would also have to be cool or cold, so the PLA did not melt or distort.  It would also need to be able to be poured, or injected.  Plaster of Paris comes to mind.  Car filler bog would be too viscous.

Any suggestions?

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