7 replies to this topic

[bigtonyicu]

Hi guys,



I've been thinking of doing color changing starts for a while now and finally decided to get off my butt and make the tools to do them,

I've been rolling start for a few years so that's not a problem, I now need to size my start between the color layers, but I'm not sure how close in diameter they need to be
Would a set of screens ranging in 1/8 of an inch increment (3/8", ½", 5/8", ¾", 7/8", 1") be good enough or should I be making the in 1/16?

Any info would be greatly appreciated.

[Bonny]

The screens should be fine, but hard to see what exacly you are asking. From what I've read you make a (equal size) stars one colour,probably dry them, then roll on a layer of change/relay mix,dry again, and then add the second colour and prime, keeping burn rates in mind so the stars burn out before coming down. And of course chemical compatibility is a must.

[Arthur Brown]

Probably it depends a LOT on the final burn time required and the final star size required. A three inch shell holds few 3/4 stars!

Added.
Grade the size of the stars by passing then down a pair of rails set at a taper. That way the size range can be selected by the place on the taper that the star falls through

Edited by Arthur Brown, 07 May 2008 - 08:57 PM.

[bigtonyicu]

The screens should be fine, but hard to see what exacly you are asking. From what I've read you make a (equal size) stars one colour,probably dry them, then roll on a layer of change/relay mix,dry again, and then add the second colour and prime, keeping burn rates in mind so the stars burn out before coming down. And of course chemical compatibility is a must.

I guess what I'm really asking is how close in diameter must they be to each other. When you roll them they never are exactly 100% the same diameter, so when I separate them... how close of a tolerance do I need for the diameter, so that they change very close to the same time?

I've made a set of 1/8" interval screens (3/8-1”), I'm in the process of rolling a set of test stars (prime/red/dark/green/dragon egg [from out side in]) they should be ready for the red to go on today, so hopefully I should be able to test them for my birth day (May 18th). If the color change happens at a large interval (not synchronized between the different stars) I'll tighten the tolerance on the size at that point.



You should hear back from me shortly on how they turned out.

[Arthur Brown]

The tolerance on the diameter will govern the tolerance on the burn time.

[bigtonyicu]

The tolerance on the diameter will govern the tolerance on the burn time.

so the slower the burn rate the tighter the tolerance, correct?

[Bonny]

so the slower the burn rate the tighter the tolerance, correct?

I think in any case, the tighter the tolerance the better.

[BrightStar]

so the slower the burn rate the tighter the tolerance, correct?

Yes, to hit a given timing, a composition that burns twice as fast allows twice the variation in size, but the star lasts half as long

As an example, imagine making a 2-colour star with Veline rolled stars of 15mm diameter that burn for 4.3s. For simplicity, first assume we have rolled perfectly identical inner colours.

If we wanted the stars to change colour within say 0.5 seconds of each other, the outer diameters can vary by up to (0.5s / 4.3s) * 15mm = 1.74mm, ie +/- 0.87mm tolerance around a given size.

Now in reality, the inner stars are not perfect and we are working with the same tolerance when sizing the inner colour. As the star burns from the outside inwards, the time at which the colour change occurs is dependent on both of the inner and outer diameters. The random variations in each will tend to smooth each other out a bit, so tightening the tolerance by 1/(sqrt 2) rather than 1/2 should be adequate. The inner and total diameters should be therefore be measured to +/-0.87mm / 1.41 = +/- 0.62mm.

Given this, if I wanted 15mm Veline Red to Green stars all changing within a spread of 0.5s at half time of the 4.3s burn I could use:

Inner green star, rolled to diameter 7.5mm +/- 0.6mm
Rolled up with red composition to 15mm +/- 0.6mm

It certainly does make you admire the skill of the Japanese masters!

Edited by BrightStar, 11 May 2008 - 09:24 PM.