Line Cutter for 50k feet attempt

The Rocketry Forum

Help Support The Rocketry Forum:

TimothyG

Well-Known Member
Joined
Nov 1, 2018
Messages
363
Reaction score
134
Location
Northern Utah
I've purchased, examined and tested four different line cutters for our groups first black Rock project and used what I learned to make a non user friendly high performance cutter. Tested it with zip ties and the wire from used igniters so far with great success. Final weight is just over 3 grams.
20200628_194522.jpg
15933954087513116464920987886443.jpg
 

Speaknoevil

Well-Known Member
Joined
Mar 18, 2018
Messages
1,144
Reaction score
513
Thanks for sharing. Where did you source this one?
 

TimothyG

Well-Known Member
Joined
Nov 1, 2018
Messages
363
Reaction score
134
Location
Northern Utah
I made it myself. Two pieces make it light and small but a pain to reload. Our group is going to crank off 20 or so in the next couple weeks so we can do more testing and then we're hoping to have them ready for our use. Anybody is free to make something similar if they feel the inclination I have no intention of producing them.
 

dhbarr

Amateur Professional
Joined
Jan 30, 2016
Messages
6,320
Reaction score
982
What would you say are the main differences between this version and the ones you sampled?
 

TimothyG

Well-Known Member
Joined
Nov 1, 2018
Messages
363
Reaction score
134
Location
Northern Utah
The ones I sampled are tubes with a plug threaded into place holding the initiator. Mine is a barstock rod drilled out which in turn eliminates the length of threads required as well as the "plug" needed. A more popular design captures the piston on this design the cap is the piston and no O-rings are needed. I basically faced off the rod, drilled through with a hole sized for the wires, drilled to a set depth for my guess at a suitable charge, the parted the piece off with minimal length used. The main housing is 1" on the money and the plug is a plug. If I felt ok with a single use cutter and a projectile being thrown from the cutter I'd make it even simpler but I don't like randomly pointed projectiles on my recovery system.
 

OverTheTop

Well-Known Member
Joined
Jul 10, 2007
Messages
3,692
Reaction score
1,041
Location
Melbourne Australia
Nice. I assume the cap is kept on a string too?

Actually, if you threaded the eMatch wires through the cap too you won't need any extra tether for that part.
 

TimothyG

Well-Known Member
Joined
Nov 1, 2018
Messages
363
Reaction score
134
Location
Northern Utah
Yup strung up with kevlar loop. And that's not a bad idea I think I'll try it out on a smaller flight.
 

TonyL

Lifetime Supporter
TRF Lifetime Supporter
Joined
Nov 13, 2018
Messages
180
Reaction score
90
This is a very nice simple design. I would suggest vacuum testing if you intend to use it for high altitudes, or one could just add the o-ring and seal the wires like some other designs do. Either way a nice compact system.

br/

Tony
 

Cameron Anderson

Well-Known Member
Joined
Sep 14, 2018
Messages
553
Reaction score
178
Location
Reno, NV
Can I ask why you decided to make a cable cutter instead of using one that's already commercially available?
Did the commercial ones not perform to your standard or did you just want the experience of making your own?
 

TimothyG

Well-Known Member
Joined
Nov 1, 2018
Messages
363
Reaction score
134
Location
Northern Utah
I epoxy in my igniters so every firing I chuck up the body and drill out the old ignitor. And these will be used on main so function at high altitude not required. Plus these are smaller in diameter all around making handling components a challenge for even those gifted with dexterity.
 

steveh.jae

Well-Known Member
TRF Supporter
Joined
Feb 23, 2020
Messages
64
Reaction score
17
TimothyG
This is very interesting and given you’re embarking on a 50k’ attempt with your crew I don’t want to trouble you with a bunch of questions ... just one. Where would I go to learn about what it is that you are discussing/describing? Thanks and good luck!
 

Kelly

Usually remembers to get the pointy end up
Joined
Apr 26, 2010
Messages
212
Reaction score
104
Location
Oregon
Where would I go to learn about what it is that you are discussing/describing? Thanks and good luck!
Your question is about a cable cutter? It's used for dual deployment; a cable of some sort keeps the main parachute undeployed until the rocket gets close to the ground, at which point the cable cutter, well, cuts the cable (usually with a blackpowder charge) and deploys the main for final descent.

 

steveh.jae

Well-Known Member
TRF Supporter
Joined
Feb 23, 2020
Messages
64
Reaction score
17
Your question is about a cable cutter? It's used for dual deployment; a cable of some sort keeps the main parachute undeployed until the rocket gets close to the ground, at which point the cable cutter, well, cuts the cable (usually with a blackpowder charge) and deploys the main for final descent.

Kelly, Yes. Thanks. The video was enormously helpful in understanding the process.
 

MClark

Well-Known Member
Joined
Jan 21, 2009
Messages
2,488
Reaction score
498
Location
Glendale, AZ
With the low temperatures at 50,000’ will there be an issue with the zip ties being brittle?
M
 

TimothyG

Well-Known Member
Joined
Nov 1, 2018
Messages
363
Reaction score
134
Location
Northern Utah
There could be. I decided to test out this cutter on wire and zipties. It can very easily cut through a set of igniter wires. Next test will be cutting kevlar cord just to see if it works. But I think I'll limit myself to zipties on the actual flight. I'm not overly concerned about the cold temps enbrittling my zipties as for one they will only be up there for a short period of time and two this is a dust up flight designed to get my friends and I up to speed on larger two stage projects, from a safety perspective and ground prep perspective, so that we can confidently work on a bigger project over the next two years. This flight is a stepping stone.
 

OverTheTop

Well-Known Member
Joined
Jul 10, 2007
Messages
3,692
Reaction score
1,041
Location
Melbourne Australia
Next test will be cutting kevlar cord just to see if it works.
I am betting this would not work. If you have tried to cut Kevlar with anything but the sharpest of sharp scissors you will know why ;). Personally I would probably do the experiment but never fly that way anyway.
 

rocket_troy

Well-Known Member
Joined
Sep 9, 2013
Messages
121
Reaction score
38
I am betting this would not work. If you have tried to cut Kevlar with anything but the sharpest of sharp scissors you will know why
No arguments there :)

You'd likely need to construct your line cutter from a hardenable steel like Silver Steel (Drill Rod in the US?) and ensure the tolerances on the cutting edges are tight, sharp and dag free. That might also mean a final cleanup in the hardened state - which is actually not difficult provided you have the right inserts. I've found that ISCAR IC907 grades are fine for it - well, for turning ODs. As for IDs, that small... maybe a micro carbide boring rod if you actually needed to go that far.
 

rocket_troy

Well-Known Member
Joined
Sep 9, 2013
Messages
121
Reaction score
38
We do a lot with ultra high PE (>9.2 million g/mol MW) and I don't find it terribly difficult to cut. Sure, it's a lot more PITA than your other GP engineering plastics but nothing as challenging to cut as Kevlar or Spectra; although we use engineering grade solid rod material and turn it, so we might be talking apples and oranges.
 

rocket_troy

Well-Known Member
Joined
Sep 9, 2013
Messages
121
Reaction score
38
We do a lot with ultra high PE (>9.2 million g/mol MW) and I don't find it terribly difficult to cut. Sure, it's a lot more PITA than your other GP engineering plastics but nothing as challenging to cut as Kevlar or Spectra; although we use engineering grade solid rod material and turn it, so we might be talking apples and oranges.
Duh, I was talking oranges. Spectra is a form of UHMWPE which *IS* very difficult to cut. Nothing like the engineering grade UHMWPE rod material we deal with at work.
 

TonyL

Lifetime Supporter
TRF Lifetime Supporter
Joined
Nov 13, 2018
Messages
180
Reaction score
90
on Mark's question about cable ties: not all cable ties are equal. The ultra cheap ones are significantly more brittle than the good ones. Thomas and Betts are considered to set the standard for quality and performance at least in auto racing. I did some comparisons by just folding one over on itself several times. The ones from NAPA perform well, as did the orange construction ones from Grainger [neither broke]. I did find that any discount store or Harbor Freight ones I tried tended to snap on the first fold.

br/

Tony
 
Top