johnsmachines

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. I read every comment and respond to most.

Tag: PLA casting

Spur Gears -1

The model Armstrong cannon has 7 gears, 2 of which are bevel gears, and 5 spur gears, including one quadrant gear.

4 of the original spur gears. These position the carriage on the chassis for loading and firing. There is also a decoupling mechanism on the second shaft. (Portland cannon)

The spur gears will be machined and cut from bronze, brass or steel. I have a set of module 1 cutters, which are close in 1:10 scale to the originals which are close to module 10.

The bevel gears I have made by casting them in bronze, teeth and all, and they are pretty darned good. Not perfect, but they will be hidden from sight in the gear case. They seem to mesh pretty well, but, if they are not up to the job of elevating the barrel I will cut some replacements.

The biggest gear is a spur gear, and it has a brake drum as part of the casting. It is a bit more complicated than a simple cut spur gear. Apart from the brake drum, the gear teeth have flanges at each end of the teeth, which will make them difficult to cut, unless I add the flanges later. I guess that the original was cast, teeth and all.

From below, the biggest gear with the brake drum on the left of the picture. The brake band is a steel band. (Port Fairy cannon)

I have decided to cast this gear also.

You can see the flanges more clearly in this photo. (Port Fairy cannon)
So I have 3D printed casting blanks with teeth and flanges (left) and without teeth and flanges (right). I will cast both, then decide which to use. 58mm diameter, 25mm wide. The prints are colourless PLA. I have had problems with plate adhesion with this PLA.
The bevel gear case. Cast bronze. Some more finishing required.
The cast bevel gears. Since this pic I have machined bores and improved the finish. PLA blanks.
And can you guess what this fingernail size piece is? It will cast in bronze.

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.

IMG_8520

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.

IMG_8522

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.

 

IMG_8521

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.