Compositions for first crossette experiments

[dangerousamateur]

Hi guys,

 

I have a 3/4 crossette pump that has been lying around for a long time but never made any crossette.

 

Can you suggest me some formulas that work well with crossettes?

Especially focusing on releasing from the pump and not being to harsh on the pump?

 

Both glitter and colored stars.

Maybe with PVB or phenolic resin stars, if you think that can be done.

 

[cmjlab]

Over on FW.com there is a couple conversations and articles on crossettes - all of which recommend SGRS as the binder to prevent cracking and expanding.

 

Many people (myself included for comets) have experienced (When pressing Dextrin bound charcoal comets or crossettes) with excess pressure, they have a tendency to expand and develop cracks when extracting them from the pump or plate. For me it occurs as I'm pushing the comets out of the pump. SGRS helped a lot, but requires a little more water than the Dextrin versions, and some time for the comp to sit and allow the SGRS to activate.

 

I think "JustVisiting" has a bunch of experience with using SGRS (especially in the baggie cut stars method).

 

Charles

[Arthur]

Harsh on the pump always points to flake metals especially titanium. As a starter avoid metals in comps unless the effect is worth the tool damage, for experiments it's not.

[cmjlab]

I agree that metals are responsible for damage to tooling (as I learned with my first 3/4" crossette tooling), but learned that it's most important to determine safe metal mesh sizes to use, based on ensuring the metal can't work it's way up between the ram and wall of tooling. I've learned it can be atomized or sponged metals (any metal), but haven't had an issue with the flake metals. I've never had flake titanium though.

 

For example - a 12 - 20 mesh titanium is okay based on the tolerance of my comet tooling, because it won't fit between the wall and ram. I prob could go 40 mesh, but would be nervous. Then again at 200 - 325 mesh is probably okay, but I'd rather put non metal comp or chipboard disc on top of that before pressing (i.e. Kerr method).

 

Then when pressing stars with a plate, I just wouldn't bother with metal comps in my small plates (1/4" or 3/8") because it'd be a pain in the butt and not worth it.

 

My two cents anyways.

 

Charles

[Arthur]

Something as simple and cheap as tiger tail would be a good start.

[dangerousamateur]

Thank you guys.

 

Unfortunately I only have dextrine and pvb.

So that would make a lot of things very complicated, any of the really cool stuff contains metals.

Even standard colors containing 200mesh mgal require special techniques to save the pump, I expected this to be less problematic

 

I'll stick with tigertail for the beginning. Are there tricks to deal with this expansion thing when only dextrine is available?

[cmjlab]

It may not be an issue for you at all, I see it when over pressing comets, you may not encounter it. If it does expand on you or it isn't consolidating well enough, you can always add a bit more water to help consolidate. It will just take a little longer to dry all the way.

[Arthur]

Pick a base comp, take some choices of binder, try each several times. Make a small batch of comp with each of 2, 4, and 6% of each binder and some that feel damp, some a bit dry and some in between. See how they respond in terms of ease of making a reliable product that dries hard without slumping or fracturing.

 

When you have done all of this you will know what is best for your tooling and method, for most comps.

 

The issue with metal powders is that they can be forced into the narrow gap between the tube and the plunger then the metal grains will either wear away at the tooling or just lock it up permanently. You may be able to make a tool with a piece of cheap plastic tube (plumbing pipe?) as the outer so that a locked tool can be freed by cutting the tube with a knife.

[dangerousamateur]

Speaking of pressing, do you know some proven figures for pressure?

 

A have a new force gauge that should help me a lot

No more guessing, no more "feeling" will be involved.

Edited December 7, 2022 by dangerousamateur

[cmjlab]

Most people on FW.com aim for 2k on the comp, some have pressed at 1500, but the rest of the numbers are from one or two people and different moisture content. Of the people who report issues, it seems to be somewhere between 2500-3k on the comp.l (again this is just for charcoal comps).

 

I do not have a PtoF guage and I just use a 2T Arbor Press. So I can't help you out with personal numbers.

[Arthur]

Force is converted into pressure by dividing by the area of the piston of your tool, and only you know what size that is. I guess if you search YT for a Chinese factory pressing comets/croisettes there will be some using a hammer and some using a power press and probably one showing full automation -powder in pressed croisettes out on a conveyor.

[justvisiting]

For 1" crossette comets, I use 2000lbs on the PtoF gauge. I've used 3000, and that's too much for my comets to crack properly because it's shotless tooling I use. 6% water is the suggested amount for my comp but I found 7% to be better. I think maybe 1500 and a little more moisture might be better. In high charcoal comps, I think the comet cracking is due to the elasticity of the charcoal. I've used both SGRS and dextrin successfully. The guy that swore by SGRS was Shawn Ashbaugh. The faster-burning comps give a tighter timing than slow-burning comps, but I've used only slow-burning comps for a willow crossette effect.

 

People talk about trimming the ends of the comets, but I don't like that method. I like to weigh the comp for each comet carefully and press the comet on a base that looks like a rocket spindle base without the spindle. I press the comets out in one push, and there's no trimming. Folks bicker about whether to weigh and not trim OR to not weigh but have to trim. I don't use 'regular' tooling with the stop holes on the plunger. My tooling has a brass tip that turns freely, which makes removal of the comet easier.

 

I'm no expert and I haven't made crossettes in a while, maybe getting rusty. All the ones I made worked tho'

 

Like Arthur said, it takes a bit of monkeying around to see what works best for you with the comp you have. There's a reason not too many folks make them

[dangerousamateur]

Thanks for the information.

 

I think the comet cracking is due to the elasticity of the charcoal

Do you think there are types of charcoal that one should better avoid? I only have pine, so there is really no choice, but lets see what else I can get...

 

 

I like to weigh the comp for each comet carefully and press the comet on a base that looks like a rocket spindle base without the spindle. I press the comets out in one push, and there's no trimming

So you dump the comp into then pump, attach your base, turn it around and press.

I like the idea of weighing. Production of huge numbers is not my business anyway.

Edited December 8, 2022 by dangerousamateur

[justvisiting]

I can't comment on charcoal types for this particular application because I've only used commercial hardwood airfloat. However, I've made nozzleless rockets with many different kinds of charcoal, and they all seem to have similar elasticity. When the ram goes up, the drift in the rocket rises a bit as the charcoal re-expands. With whistle this does not happen.

 

The base is shaped like a small Walter White hat, and goes up into the comet sleeve about 3/16", with the sleeve resting on the brim of the hat. The weighed comp is added by funnel into the sleeve, and the comet is pressed with the same pressure each time with a couple of seconds of dwell. Then the base is twisted out and the comet is pushed down and out of the sleeve. I made a little jig with a ridge for the sleeve to sit on while the comet is popped out. Since my tip spins, I twist the comet loose by turning it, and then pull the pump back and the comet pops off the tip- usually I used to put a piece of masking tape on the bottom of the sleeve and press the comet, but the comp expands out the end a little and I didn't like it. That's why I got Woody to make me a little base.

 

Sometimes there are issues with the comet not coming off cleanly, and many folks have many ideas on how to handle it. I find that the right combination of moisture and pressure are the best ways to deal with sticking. Also, the comp needs to be moistened evenly by screening a couple of times, and left to 'temper' in a closed container, ideally overnight.

 

That's just how I do it, others may do it differently. I feel that this method makes consistent comets that have consistent timing. I may try to post a pic tomorrow if needed, but I always have a hard time figuring out how to do it.

[dangerousamateur]

The weighed comp is added by funnel into the sleeve, and the comet is pressed with the same pressure each time with a couple of seconds of dwell

 

I think it was mentioned somewhere (with rockets!) that you should NOT dwell.

If I may ask, what is your opinion on that?

 

[justvisiting]

I believe that was Steve Laduke that said you should not dwell on rockets- recently. For decades, his advice was to dwell. I don't remember the details, but he seemed to have a concern about a possible safety issue. I don't recall thinking it was a big deal. I'm not a certified guru, but my opinion is that dwell can be helpful in many cases. It gives air a chance to leave, and give the (rocket) tube a chance to expand on the inside and accept more propellant. It can give better consolidation, especially if you are pressing damp BP propellant at low pressure- which I now do. This would be very advantageous in an end burner. When you dwell when pressing a damp end burner, you can see the dwell compacting the propellant a bit more. When I press a rocket on my arbor press with a torque wrench of the 'clicky' type, I pull down slowly on the wrench to simulate dwell. For years I never used dwell and I made reliable rockets many different ways. If you are pressing a lot of rockets using small increments, the extra time spent dwelling can really add up. I think dwell is one of those 'ask 10 pyros, get 12 different answers' kind of issues.

[dangerousamateur]

I'd rather put non metal comp or chipboard disc on top of that before pressing (i.e. Kerr method).

I cant find anything when I search for "Kerr method".

So you stick the pump into prime and then into the star comp?

That would work with a flat rammer, but also with a crossette tip?

 

 

Would you dare to use willow diadem with your star and crossette pumps?

[justvisiting]

I think the method is called something more like the Siefker method, or maybe Sief-Kur. IIRC, it's a mishmash of the names of two guys.

 

I've pressed comets with -60+325 mesh FeTi in my 1" comet pump by using double-sided tape to 'glue' a plastic disc onto the end of the plunger. The disc was a snug fit in the sleeve, and pushed any metal particles off the wall. It never got stuck after hundreds of comets. The plunger needs to be pushed out the bottom when ejecting the comet because pulling it back will separate the disc. The guys that came up with the method used snug-fitting cardboard discs.

 

I wouldn't use willow diadem for crossettes myself. I think it would burn too long.