3D printable Visco fuse machine

[Simoski]

Twitter also fails to render nicely... anyhow, back to the computer aided design

Edited April 30, 2018 by Simoski

[lloyd]

Sim,

I meant both the pulleys' surface finish, and using elastic bands for belts. But we've discussed that, and they don't matter much on a prototype, so long as the elasticity of those bands doesn't throw off some critical motion due to 'oscillations'.

 

Lloyd

[Simoski]

Another test post

Capstan and its half finished housing

 

Edited April 30, 2018 by Simoski

[Simoski]

Sim,

I meant both the pulleys' surface finish, and using elastic bands for belts. But we've discussed that, and they don't matter much on a prototype, so long as the elasticity of those bands doesn't throw off some critical motion due to 'oscillations'.

 

Lloyd

I don't think it will old chap... : )

[Baldor]

What I'm worried about are all those plastic on plastic bearings, like in the capstan. With the surface finish you have shown us and a little load, i fear for their durability. You will be lucky if they only wear. Worst case, the will weld.

[lloyd]

It's a prototype, Baldor! He can sleeve the bearings (if necessary) in a 'production' version.

 

It's the same with my comment about the elastic bands used as belts. I've seen machines driven with elastic belts that underwent motion oscillations -- first taking up the slack, then over-tensioning the belts, then the belts' recovery from that. It can make a mess of 'fixed' ratios.

 

But his is ONLY a prototype! He'll get on. He's already proven he's bright!

 

<grin>

Lloyd

[Simoski]

Its gonna work brothers, I can't really see the machine running for more than a few minutes at a time before the cotton thread runs out.

Anyhow let me send you a photo of where we are

....

 

 

I need to finish wiring up the motor to a 12volt source through a PWM, buy some cotton thread, glue all the uprights into the top spindle. I need to build a thing to hang the tracer threads from... anyway its close now. Problem is I'm going to Malta on holiday next week Monday and its my daughters 9th birthday party this weekend so I'm unlikey to get it done for 2 week : (

Edited May 2, 2018 by Simoski

[lloyd]

Don't FROWN about going to Malta! Obviously, you're going to enjoy the fireworks (not much other reason to be in Malta <grin>).

 

And enjoy that little girl while she's little. They grow up WAY too fast!

 

LLoyd

[Simoski]

8 )

 

I will Sir, guaranteed

[Simoski]

Edited May 2, 2018 by Simoski

[Simoski]

This is turning into one of those grand moments in life...

 

Edited May 4, 2018 by Simoski

[Simoski]

Capstan check, pulleybox check motor check, pulse width modulator check, 12 volt source check, super structure check ,drive shaft check , top spindle check, bottom spindle check, cotton check , fuse guide rollers check.

 

What else is missing besides the guide thread assembly?

 

For the take up drum: How do I build a simple slip clutch out of plastic or magnets or what? Any schematics? Ideas?

 

Can someone grab me a standard NEMA interface schematic please.

[lloyd]

Sim,

A slip clutch is easy.

 

Two disks (usually of dissimilar materials to minimize 'galling') are used. Often the driving disk is metal, and the output disk is made of a fiber composite or plastic. One is permanently-affixed to its shaft -- call that the 'input' shaft.

 

The other 'floats' longitudinally on its shaft (call that the 'output' shaft), but is affixed radially, so it can DRIVE the shaft its on, but also move longitudinally. The way that's done is usually simply to put a cross-pin in the output shaft, and have the pin ride in slots in the output disk -- with the slots deep-enough (longitudinally) to accommodate any axial motion of the output disk. (And that's usually not much, just a few mm.)

 

The floating disc is spring-loaded - usually with an adjustable collet pressing on the spring to alter the spring force - and is just pressed against the input disk.

 

To make it work well, often the input shaft will be solid, and the output shaft will be hollow for a distance long-enough so that the input shaft can ride inside it. That improves rigidity of the whole affair, making it all look like one long shaft with a 'swollen' section where the hollow output shaft accommodates the solid input shaft. Making the bore very close to the size of the input shaft will improve rigidity, and making them of dissimilar metals will help with galling.

 

You'll have to look at several motor manufacturers to get a clear picture of the NEMA interface. Almost every manufacturer has a different set of color-codes on their wires. But the connection arrangement is the same on all of them.

 

Lloyd

Edited May 4, 2018 by lloyd

[Baldor]

I'm thinking more about steeper motors, but I think you will prefer a DC crushed motor. I'm sure Lloids will know more about them than me.

 

One random idea for the final product, not the prototime... Plastic pieces are too thick. I know that with a 3D printer are perfectly possible, but the mould maker in me cringes when i see them. You can save a lot of filament and print time making them hollow, with reinforcing ribs, and lose little or no rigidity. Think about a box with a face removed, and a honeycomb structure inside.

[Simoski]

Guys I'm back from Malta and almost ready to run for the first time.... I have my daughter this weekend and should find enough time to get it going : )

 

Lloyd, Baldor thanks for your input.

 

What is a good fuse composition???

[lloyd]

Sim, 'fuse powder' is the theoretical 'standard'. It ranges downward in KNO3 content from ordinary shooting powder, down to as little as 69% KNO3, but with sulfur being adjusted upward, rather than adjusting the charcoal content. So a typical formula could be 70-15-15.

 

But you cannot go wrong starting with fffffffg (7fg) shooting powder, or its home-made equivalent. Its fine-grained and dense enough to flow well, burns fast-enough to reveal defects in the winding of the fuse, and might just be the appropriate speed for relatively-quick visco.

 

Lloyd

[lloyd]

I could add (in fact SHOULD HAVE added) that Fuse Powder is not rated by grain size, like most powders. It's almost all approximately 7FA grain size (bigger than meal, about -30 mesh, but TIGHTLY sized, so there were very few 'fines'). Instead of rating it by grain size, it's rated by speed.

 

The various grades come in numbering like "111" (which I used a LOT of in my time-fuse manufacturing). The number refers to the number of seconds per yard of burn in their 'rolled core' burn test.

 

In that test, they would settle the powder into a thick-walled copper tube approximately 1/2" i.d., then successively roll it in a rolling mill, until the powder core was about 1/4" (i.d. of the rolled tube), and the powder was effectively compressed into a solid. Then it was burnt and timed for time-per-yard.

 

I've had grades from 90 to 135. Goex and others make various grades for various fuse types.

 

Lloyd

Edited May 16, 2018 by lloyd

[Simoski]

Lloyd old chap.... thanks for the input, so fine powder for a pistol will work, I don't have a 30 mesh handy, I can probably print it though.

Anyway, for waterproof fuse do I need a powder made with sodium chlorate for a very hot burn? Or just a good NC coating?

[lloyd]

No, no chlorates. WaterPROOF fuse is made by dry-spinning a 'full-closure' of threads, then dipping in *usually* hot asphaltum... sometimes a wax that is 'non-penetrating', then over-wrapping with more thread so the fuse can be conveniently handled. Or, as you mention, they'd use a HEAVY application of NC, usually with some sort of plasticizer added to aid in the flexibility of the fuse. The NC type is not waterproof for long, since NC is slowly attacked by water (it swells and is slowly permeated).

 

Most fuses properly coated with NC are at least 'water resistant' for short runs and short periods of time. The M-80s and cherry bombs of old had what was then very ordinary (but US-made) visco, and you could get nearly every one to go off under water.

 

So far as your need to seive-size the powder; if it's commercial shooting powder, it should have a grade number on it.

 

fffffg (5fg) or fffffffg (7fg) will work fine, I think.

 

Lloyd

Edited May 18, 2018 by lloyd

[lloyd]

OH! Sorry!

 

I should have added that 'modern' waterproof fuses (for blasting, etc.) are made with an extruded polyethylene outer layer. It's _absolutely_positively_ waterproof!

 

LLoyd

[Simoski]

Well I spun it up today... what a mess, it took 2 hours to thread it all together and then when it spun up the BP was way too big just clogged up the top spindle and it was almost impossible to pass through. I had to pull the threads hard to get it to go.

 

I've widened out the top and bottom spindle holes and am printing myself a 50 mesh screen.

 

One cannot purchase BP is South Africa, no one manufactures it, the last company stopped in the mid 90's, so I have to sieve out the "fines" from my own BP.

 

I've got a 200 mesh screen and a flour sieve. The latter is obviously of no use. The former might be, I will see what I can come up with in the morning.

 

Lloyd where does one locate asphaltum in this day and age?

[lloyd]

Asphaltum is available in various forms. The 'tar' form (softer, 'plastic' form) often used for built-up roofing is available in (approx.) 25Kg 'barrels' (just a cylindrical lump of tar wrapped with kraft paper).

 

It is usually 'tempered' to the desired degree of cold hardness by the addition of Gilsonite, which is a 'non-tarry' dry form of asphaltum, sold as a powder. It's used to make the material 'hard enough' in hot weather. I used small amounts of it to temper mine for 1/4" military fuse.

 

That is probably also available - like the tarry form - from any competent roofing company who does built-up roofing. But there's only ONE producer of Gilsonite in the world, so far as I know, and they're in the US. So Oz and Africa and Europe might have a substitute for it.

 

LLoyd

[Svimmer]

I just used a filter from a washing machine because that was what i had and that worked great.

[lloyd]

Oh... in case "built-up roofing" is a US term -- it means a roof (often flat) which consists of layers of felt/tar/felt/tar (up to 5 layers of felt), then a layer of white gravel or other stone aggregate bound-on by the last layer of tar, to offer sun resistance.

 

Lloyd

[Arthur]

There is, in the UK, a product called "Slurry Seal", It is an emulsion of bitumen. It is a pourable viscous liquid used for sealing paved surfaces. Simply it's a pourable tar that dries in day time.

 

From recollections of using it to patch runway surfaces, you could pull fuse through it in like a quick match style, and it will dry according to the day temperature.

 

The downside is that I've never seen it in less that 205 litre drums, and it dries permanently to bitumen road topping so it's awfully MESSY and PERMANENT