Sleipner Posted February 19, 2018 Posted February 19, 2018 Could it be that im using polyester thread ? cotton is softer and will be weavin nice or im wrong ? My 2 cents are that this is a speed ratio problem rather than a polyester vs cotton issue. For arguments sake, let's say you have a 1mm diameter thread and you have ten of them on a plate. Assuming you want to achieve perfect coverage, for each revolution of the disc you want to pull the fuse ~10mm(*) downwards. Sure, cotton vs polyester may cause other issues like not settling in the same way due to varying friction, but I really doubt that is the case here. (*) it is actually a little more complicated than that due to the angle the thread has. I'm working on the equations for that. 1
Svimmer Posted February 19, 2018 Author Posted February 19, 2018 My 2 cents are that this is a speed ratio problem rather than a polyester vs cotton issue. For arguments sake, let's say you have a 1mm diameter thread and you have ten of them on a plate. Assuming you want to achieve perfect coverage, for each revolution of the disc you want to pull the fuse ~10mm(*) downwards. Sure, cotton vs polyester may cause other issues like not settling in the same way due to varying friction, but I really doubt that is the case here. (*) it is actually a little more complicated than that due to the angle the thread has. I'm working on the equations for that.Alright il try to speed up the second disc and see whats happens.
Svimmer Posted February 20, 2018 Author Posted February 20, 2018 (edited) Im pretty sure there is many things that will improve the weaving. Both plates spins very bad because the center part off the bearings is really lose sideways so bad bearings. and the hole in the die is 3mm which feeds little to mutch powder. Also the thread leaders on the die is very uneven so going to make a new one with a template i made. Edited February 20, 2018 by Svimmer
Sleipner Posted February 20, 2018 Posted February 20, 2018 Just did some math that can be useful for you. I did the calculations for my project but thought it could be useful for someone else as well. Posted them in the gallery, will see if I can link them here... I needed some math symbols so made them as pics as the forum is no good for math symbols. Let me know if you have any questions. 1
Sleipner Posted February 20, 2018 Posted February 20, 2018 Seems I missed a square in the writeup. The bit of the end result that says "pi^2 * (d_f + d_t)" should be "pi^2 * (d_f + d_t)^2". Will fix it up in the gallery tomorrow... I did some calculations for a 2 layer visco with 0.3mm thread and 10 spools on each disc, and a BP core of 2mm. That gives that the speed ratio between the first and second disc should be of the order of ~5%. (a slightly faster second disc). For thicker threads the difference in speed grows quickly and it is heavily dependent on the number of spools on each plate. The model can give a decent starting point for a design, but since materials behave a bit different from each other there will still be a need for tuning.
Svimmer Posted February 20, 2018 Author Posted February 20, 2018 The machine i made have 12 bobbins on the top and 8 on the bottom.
Sleipner Posted February 20, 2018 Posted February 20, 2018 I'll upload a spreadsheet today or tomorrow with a large number of results for different spool combos, thread sizes and core diameters. Just some loops in the script I have to generate it. 1
Svimmer Posted February 20, 2018 Author Posted February 20, 2018 http://bldr.no/BYT Heres how it looks after changing the bearings. the botom plate is still not 100% tight because the pipe i use is little smaller for some reason. so need to change the pipe so it fits the bearing properly. Also i didnt have anymore of the granulated powder so had problem with getting the powder flowing.
MrB Posted February 21, 2018 Posted February 21, 2018 I THINK a large part of the irregular speed of your burn is due to the fuse not being coated. When a spark lands on, and sets of, a different part of the fuse, it jumps ahead that much. The NC coating on Visco is as much to prevent this, as it is to keep the fuse water resistant. 2
Svimmer Posted February 22, 2018 Author Posted February 22, 2018 https://youtu.be/dl841ZUxl9M This one burned better.
Sleipner Posted February 23, 2018 Posted February 23, 2018 I uploaded a file where I've tabulated the plate rates and fuse collection speed as a function of BP core diameter and number of spools per plate. I assumed a slightly flattened, thin, cotton thread of a type I have and had measured to have a "rectangular" cross section of 0.22mm x 0.15mm. I also assumed a target coverage rate of 80% per layer. It is easy to change the table to cover other dimensions and coverage if someone would like to know. The script producing the table is a simple octave script. Let me know if you need help interpreting the table. https://www.amateurpyro.com/forums/files/go/61e62eb7b943313eb9dfdbf2b8dcda0b/visco-design-parameters
Sleipner Posted February 23, 2018 Posted February 23, 2018 http://bldr.no/BYT Heres how it looks after changing the bearings. the botom plate is still not 100% tight because the pipe i use is little smaller for some reason. so need to change the pipe so it fits the bearing properly. Also i didnt have anymore of the granulated powder so had problem with getting the powder flowing.That's a pretty big improvement. In your next iteration, would you mind having a tape measure in the picture? Just to get a better understanding of the scale so I can use it for some estimates.. 1
Svimmer Posted February 23, 2018 Author Posted February 23, 2018 That's a pretty big improvement. In your next iteration, would you mind having a tape measure in the picture? Just to get a better understanding of the scale so I can use it for some estimates.. Yeah il do that. 1
Svimmer Posted February 23, 2018 Author Posted February 23, 2018 http://bldr.no/BZa It was more uneven this time if you ask me. 1
Svimmer Posted February 23, 2018 Author Posted February 23, 2018 and im not using a die on the plate under maybe that is effecting the weaving ?
Sleipner Posted February 23, 2018 Posted February 23, 2018 and im not using a die on the plate under maybe that is effecting the weaving ?Oh, hadn't noticed that. Yeah, that will definitely affect the weaving. If you have nothing guiding the thread, it will be laid at varying heights depending on where it happens to unroll it from the spool at a particular moment.
Svimmer Posted February 24, 2018 Author Posted February 24, 2018 Oh, hadn't noticed that. Yeah, that will definitely affect the weaving. If you have nothing guiding the thread, it will be laid at varying heights depending on where it happens to unroll it from the spool at a particular moment. Thats the next fix for the machine
Svimmer Posted February 26, 2018 Author Posted February 26, 2018 (edited) http://bldr.no/BZx http://bldr.no/BZy wow i have a long way to go on this machine. have done alot off tests now and cant get the second layer nice. the first layer looks good. The second plate have a die now but the hole through it is 8mm and the pipe is 6mm inside i think that a die with 2.5 or 3mm on the second plate and 2mm on the first plate might do the trick. Edited February 26, 2018 by Svimmer
Simoski Posted February 27, 2018 Posted February 27, 2018 Howsit ( thats how we greet each other in South Africa ) Keep up the good work Sleipner. as for the composition, go with 5grams sugar , 5 grams nitrate for a slow fuse. 2 grams sugar, 5 grams nitrate for a fast fuse... or somewhere there about, less fuel = faster burn ratemore fuel = slower burn rate. I would remove the charcoal so it does not spit fire, or mill it longer, or use balsa or hemp charcoal, for a finer charcoal that is completely consumed. 1
Svimmer Posted February 27, 2018 Author Posted February 27, 2018 Howsit ( thats how we greet each other in South Africa ) Keep up the good work Sleipner. as for the composition, go with 5grams sugar , 5 grams nitrate for a slow fuse. 2 grams sugar, 5 grams nitrate for a fast fuse... or somewhere there about, less fuel = faster burn ratemore fuel = slower burn rate. I would remove the charcoal so it does not spit fire, or mill it longer, or use balsa or hemp charcoal, for a finer charcoal that is completely consumed. Thanks for the tip. That was alot easier to granulate aswell so the powder flows nice.
Svimmer Posted February 27, 2018 Author Posted February 27, 2018 i tried to coat the fuse with styrofoam but that did not work very well.
Sleipner Posted February 27, 2018 Posted February 27, 2018 i tried to coat the fuse with styrofoam but that did not work very well.Nitrocellulose lacquer is usually used to coat visco. If you can't buy it (getting difficult to find depending on where you are), the make shift alternative is to make it yourself from dissolving ping pong balls in acetone). These days it is often used in treating vintage wooden things (guitars etc).
Svimmer Posted February 27, 2018 Author Posted February 27, 2018 http://bldr.no/Ba7 right after coating.
Svimmer Posted February 28, 2018 Author Posted February 28, 2018 (edited) I also have a problem with the threads not collecting the powder as it should. there is coming a pile of powder under the plates. Edit: Could it be that the powder die dosen't have a V enough ? so the powder dosen't get correctly into the threads ? Edited February 28, 2018 by Svimmer
Simoski Posted February 28, 2018 Posted February 28, 2018 I've seen machines spinning at 400 rpm, its probably the number of turns of the thread per cm.
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