82 replies to this topic

[Svimmer]

Yep, that's the one that determines the pull through rate.

i can try with more rubber bands until i get a better fix for it.

 

http://bldr.no/BYM This fuse is also done with rubberbands. 

[Sleipner]

Also, and perhaps a more important factor to the uneven weaving, a wrong speed of the second disc. Looking at the fuse, you see that the second layer has a pattern to it, with about a third "empty" and two thirds "filled". That indicates to me that you need to change the sizes around on the second disc such that it spins ~50% faster.

[Sleipner]

Or use a 50% thicker thread! This is why I'm going for the stepper solution in my design so I can avoid the labour of mechanically changing it depending on thread size and the tuning necessary.

[Sleipner]

i can try with more rubber bands until i get a better fix for it.
 
http://bldr.no/BYM This fuse is also done with rubberbands.

Yes, looks pretty nice, although if you zoom in on the picture there is the same problem with a pattern of denser and less dense areas along the length of fuse. Most likely this pattern is not caused by the stretching of the rubber band but rather a mismatch of disc speed versus pull through rate. I think the guy that made this fuse also needs to speed up the second disc somewhat.

[Svimmer]

Or use a 50% thicker thread! This is why I'm going for the stepper solution in my design so I can avoid the labour of mechanically changing it depending on thread size and the tuning necessary.

 

Could it be that im using polyester thread ? cotton is softer and will be weavin nice or im wrong ? 

[Sleipner]

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.

[Svimmer]

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]

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 by Svimmer, 20 February 2018 - 08:35 AM.

[Sleipner]

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.

 

 

 

[Sleipner]

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]

The machine i made have 12 bobbins on the top and 8 on the bottom.

[Sleipner]

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.

[Svimmer]

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]

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.

[Svimmer]

 

This one burned better.

[Sleipner]

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.amateurp...sign-parameters

[Sleipner]

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..

[Svimmer]

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.

[Svimmer]

http://bldr.no/BZa

 

It was more uneven this time if you ask me.

[Svimmer]

and im not using a die on the plate under maybe that is effecting the weaving ?