How much powder in the Archetype cable cutter?

So, the instructions for the cable cutter say 0.1 g. I seem to recall that there was a recommendation from Lucas to reduce this, maybe to 0.05? Does anyone know for sure?

Jim

Depends on the POOF of your ematch from what I have found. I tend to find an amount that works (tends to be about up to the first line in whatever centrifuge tube I have) and stick with it.

Ground test.

I've used 0.1g with Q2G2's with no problem so far. FWIW, I wouldn't use any less.

Wayco said:

.1 grams and J-tec ematches, but upgraded the piston to the stainless steel one

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x2 .1 g and upgraded the piston for the same reasons

I've used 0.1 also, and that's probably what I'll use again (if it ain't broke, don't fix it). But I recall getting a note from Lucas specifically recommending using less, or maybe using 0.1 was the "less" amount. I'd still like to know what he recommended if anyone happens to remember.

Jim

The last time I used less than 0.1 it didn't cut the cable completely. I was using Pyrodex, but I don't think that was the reason for failed cut.

JimJarvis50 said:

I've used 0.1 also, and that's probably what I'll use again (if it ain't broke, don't fix it). But I recall getting a note from Lucas specifically recommending using less, or maybe using 0.1 was the "less" amount. I'd still like to know what he recommended if anyone happens to remember.

Jim

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Hey Jim,
I dont want to say you are incorrect but I dont recall ever recommending to lower it below 0.1mL but I have used mine successfully with less. However, you need to have a very good seal to be able to trust using less and even though it might be more damaging to the piston over time using more black powder than absolutely necessary, I do think it is better to wear out the cutter than to wear out the rocket. I did have good success with pyrodex since it didnt seem to be as violent as black powder but 2 or 3F BP would produce similar results compared to 4F. But this was more important back when I was using aluminum pistons as their operational life was limited; the stainless pistons have shown much greater lifespans.
TLDR: Dont risk the cutter not shearing the cable using less than 0.1mL BP. If you do want to try less: ground test, ground test, ground test!!!

lkal32 said:

Hey Jim,
I dont want to say you are incorrect but I dont recall ever recommending to lower it below 0.1mL but I have used mine successfully with less. However, you need to have a very good seal to be able to trust using less and even though it might be more damaging to the piston over time using more black powder than absolutely necessary, I do think it is better to wear out the cutter than to wear out the rocket. I did have good success with pyrodex since it didnt seem to be as violent as black powder but 2 or 3F BP would produce similar results compared to 4F. But this was more important back when I was using aluminum pistons as their operational life was limited; the stainless pistons have shown much greater lifespans.
TLDR: Dont risk the cutter not shearing the cable using less than 0.1mL BP. If you do want to try less: ground test, ground test, ground test!!!

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How does one know if the pistons he ordered are stainless steel? ...
Also, how in the hell does one measure .1mL of BP? Not having scoops...

lkal32 said:

Hey Jim,
I dont want to say you are incorrect but I dont recall ever recommending to lower it below 0.1mL but I have used mine successfully with less. However, you need to have a very good seal to be able to trust using less and even though it might be more damaging to the piston over time using more black powder than absolutely necessary, I do think it is better to wear out the cutter than to wear out the rocket. I did have good success with pyrodex since it didnt seem to be as violent as black powder but 2 or 3F BP would produce similar results compared to 4F. But this was more important back when I was using aluminum pistons as their operational life was limited; the stainless pistons have shown much greater lifespans.
TLDR: Dont risk the cutter not shearing the cable using less than 0.1mL BP. If you do want to try less: ground test, ground test, ground test!!!

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Thanks for responding. I know for sure that I got a note saying to reduce the BP. If you didn't send it, then it must have been a recommendation for the CD3 instead. Those are the only two devices I have used that use a plunger.

Jim

I could be going crazy too, who knows!

I have never once had a successful cut with 0.1g mid air or on the ground, while 0.2g seems massive. I try to use 0.15g when I fill but precision like that is hard to hit.

CzTeacherMan said:

Also, how in the hell does one measure .1mL of BP? Not having scoops...

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Reloading scales are perfect for this.

CzTeacherMan said:

How does one know if the pistons he ordered are stainless steel? ...
Also, how in the hell does one measure .1mL of BP? Not having scoops...

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The piston should be stainless if you ordered within the past two years or so - I dont recall the exact date when I switched the pistons material over to stainless.
If you ordered from me, you should have received a small plastic vial (centrifuge vial). The first marking on the bottom is equivalent to 0.1mL. If you dont have one of these vials, you can order some more here: https://www.ptrocketry.blogspot.com/p/store_28.html (Look in the Accessories drop down box for Powder Measuring Vials)

watermelonman said:

I have never once had a successful cut with 0.1g mid air or on the ground, while 0.2g seems massive. I try to use 0.15g when I fill but precision like that is hard to hit.

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That surprises me. Are you using the supplied zipties? And have you checked the seal around the piston and ematch pass through? If the piston is the older aluminum style, they may have had lower tolerances to develop a seal inside the inner diameter and could allow more gas to pass around it. If the ematch/screw isnt sealed well, you could lose some BP through the hole along with pressurized gas when fired. If you are using a different brand of cable tie, you may have different results than I. (Are you using pyrodex? Also, is your BP fresh?)

lkal32 said:

That surprises me. Are you using the supplied zipties? And have you checked the seal around the piston and ematch pass through? If the piston is the older aluminum style, they may have had lower tolerances to develop a seal inside the inner diameter and could allow more gas to pass around it. If the ematch/screw isnt sealed well, you could lose some BP through the hole along with pressurized gas when fired. If you are using a different brand of cable tie, you may have different results than I. (Are you using pyrodex? Also, is your BP fresh?)

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I wrote you about this a while ago but never heard back. I am using the supplied zips, and I seal the igniter with hot glue the night before. The black powder age is an interesting variable, though. My only real source for it at this point is pulling motor charges from commercial reloads so it could vary. I am definitely not using pyrodex.

I wonder if swapping the pistons would help. Mine must be aluminum. Do you make them available separately? I have four of these but do not use them nearly as much as I would like to after a few bad experiences.

Hey Lucas, I see you have the "series 100" and you say it's the "original". I was wondering if you were planning a larger size, say a "200" series? I would love to see these in a larger size for bigger rockets.

watermelonman said:

I wrote you about this a while ago but never heard back......I wonder if swapping the pistons would help. Mine must be aluminum. Do you make them available separately? I have four of these but do not use them nearly as much as I would like to after a few bad experiences.

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Can you PM me your email address? I don't think there has ever been an email that I haven't responded to unless one made it past me at some time. Do you recall if it was a direct email or a form submission on my website?

The pistons are still available at: https://www.ptrocketry.blogspot.com/p/store_28.html. I do not know if they are still stainless or if they have been switched back to aluminum.

bill2654 said:

Hey Lucas, I see you have the "series 100" and you say it's the "original". I was wondering if you were planning a larger size, say a "200" series? I would love to see these in a larger size for bigger rockets.

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Bill, there is/was a larger cable cutter in the works, but I don't know its current status. I handed off the "business" to someone else, so I am no longer involved with the cutters, aside from trying to offer support to anyone with questions.

I never pushed larger cutters through my lineup since I didn't understand many benefits to them. You can effectively accomplish any similar task with the smaller cutters (by simply chaining together zip ties to accommodate any length) at a lower production cost (as well as mass and size costs in the rockets perspective). The larger cutter also has some loading issues in maintaining solid contact between the BP granules as well as the ematch, which can result in some issues regarding how well it pressurizes. Plus, the larger cable ties become even harder to cut so failure rates rise there as well.

Lucas - thanks for helping answer all these questions - you don't know how much I appreciate it!

I've prototyped a larger cutter with the 0.180" thick zip ties. After a few design changes I've come to much the same conclusion that Lucas did - it weighs more, costs more and getting the spacing right to keep the BP in contact is harder than with the smaller one. That being said I'm going to do a couple flights with it and see how it works in flight.

Edward

I use 1.2 grains of Ramshot TAC smokeless ball powder. TAC being my powder of choice for reloading 5.56, so I have a ton of it laying around. The ematch I use here:

https://www.amazon.com/dp/B00HIDB1QY/?tag=skimlinks_replacement-20

but from a different vendor who happens to be sold out as of the last thread I started announcing the find. Who knew?

I use no O-ring on the charge side, only the cable side and have had 100% functional success with static tests. No hot glue, nothing to seal the ematch to the cap. The coating on the ematch pyro shapes it similar to a bulb, so the charge with ematch is packed very tightly when the cap is screwed on. After I fire them I clean them out with Remoil, Qtips and scrape the carbon out of the bore with a brass or copper pipe cleaner brush (bore brush).

Can't wait to use them in flight!

On this subject, do you have any tips for getting the piston out of the cutter body after a deployment? I have two that are stuck as hell, which renders them basically useless.

I drilled out the front hole about a 1/64" bigger so I could use a small screwdriver to push it out. I'm drawing up plans for a piston with threads cut in the back, so I can put a screw in the back, and twist it to pull it out.

BTW, soak it in WD-40 for the really stubborn pistons.

Good idea drilling out. I may do the same and use a small punch to dislodge the piston. Right now I use a small allen key and tap on it with something.

Would it make sense to use a small bit of oil on the part forward of the piston or would that foul things more?

Will not be using oil in mine. Let us know how it turns out if you decide to.

With the new stainless piston I have not had them get stuck in the body. I've tested it over 20 times on the same model and it can be pushed out each time. The o-ring at the end plus the zip tie give some buffer so it doesn't cut into the cutter body.

I don't know how cutting threads in the back would work. You could get an 8-32 tap in there, but then you will have to take into account the added volume and a place for the black powder to go. In addition to this you would need to be controlled in twisting so you don't spin off the machine screw in the piston.

What cutters do you have that are getting stuck?

Edward

I have a stainless piston cutter. I'll draw up the plan in Solidworks to show you. Easier to explain that way.