Mechanical Rigidity Analysis of the Fisher Design

i'm doing a series on mechanical rigidity of 3D printing frames, and came to the conclusion that the Fisher's use of panels is absolutely superb. The typical Kossel is easily susceptible to rotation and shearing, but the addition of those three panels to the Fisher almost *completely* eliminates that. the analysis page is here: [reprap.org]

There is only one potential flaw, and it's this: the top of the open frame hole in each panel face needs bracing, but it can only really be done on the outside as the z-axis mechanisms would otherwise be interfered with. Horizontal Extrusion (or even L-Plate) needs to go on the outside just over the top of each of the open holes in each face, attached in three places each, with each bracing then joined (externally and rigidly) to each other but leaving a gap sufficiently large that each Z-axis travel mechanism can still go through it without interference. Actually... a single flat piece of acrylic could equally well do the job, a quick sketch is attached. Attachment points are shown in green.

Could anyone who has a Fisher say if the panels are actually loose or not? I suspect that they are. Do they wobble about at all (outwards or inwards), and also, what happens if you try to push the top of the Fisher side-to-side when the base is firmly attached to the ground? I would expect the panels to bow and flex (and the top to move about as a result), but it would be nice to have that confirmed.

A specific video demonstrating the concept (which took only minutes to do instead of hours for 3D CAD design and days to weeks to create a first prototype) is here: [youtu.be]

Always looking to improve the quality of 3D printing.



Edited 1 time(s). Last edit at 05/17/2017 01:30PM by lkcl.

at least make a proper model or a 3d model or do a basic fea analysis to prove the point.

Quote
ekaggrat
at least make a proper model or a 3d model or do a basic fea analysis to prove the point.

please submit a purchase order for the work that you would like carried out and i will be happy to do so. my rates are USD $150 per hour, estimated 20-30 hours to do a reasonable design: we can discuss exactly what level of detail you would like, obviously the higher the level of detail, the more i have to charge you. if you would like a ODE engine (https://www.ode.org/ - a physics simulation engine) analysis to be added as well, which would allow an interactive 3D simulaton properly showing the lack of rigidity in the original design, that will be around an extra estimated 40-60 hours. all software and designs produced as per your request will be libre-licensed.

Edited 1 time(s). Last edit at 09/14/2018 06:46AM by lkcl.

Why should anyone answer your questions if you grub for money right away at the mere suggestion of dissent? I see no benefit to the community--Pass. If money is your thing, you should have enough to just buy a Fisher and answer your own questions. Take care.

Edited 1 time(s). Last edit at 10/16/2018 02:57AM by jefbed.

Quote
jefbed
Why should anyone answer your questions if you grub for money right away at the mere suggestion of dissent? I see no benefit to the community--Pass. If money is your thing, you should have enough to just buy a Fisher and answer your own questions. Take care.

the point of the reply that i made, jefbed, is to illustrate that i am providing the design insight and analysis for free to the entire world, and yet i have some complete twat criticising the quality of the drawing, and demanding that i spend *even more* of *my* time, before he might "listen"?

the correct and respectful thing for ekkagrat to have done would have been to say, "hm, that drawing looks hand-drawn, have you *considered* redoing it in a professional / libre CAD package?" that way i have the freedom of choice of what to do, rather than a completely disrespectful PUBLIC DEMAND on my time and resources.

or, even better, "hm, that drawing looks hand-drawn, i didn't like that... so *i* spent *my* time redrawing it, here's a link to the libre-licensed CAD results".

at which point, i can go, "wow, that's fantastic, ekkagrat!" and he's continued and contributed to the spirit of the reprap community.

you see the difference?

neither his response nor yours are appropriate. you should have spotted straight away that i was deliberately illustrating to ekkagrat that he was completely out of line.

both of your answers make me feel completely unwelcome and extremely unlikely to ever want to contribute to this forum and help people to improve the quality of their 3D printers.

i would like to feel in the future that when i post things here it is fully recognised and respected that i am contributing my personal time and resources for community benefit.

@ikcl

sorry for being harsh. but if you were intending to contribute to the design a little more upfront work would help the process. most of the discussions are started with a little base work done. Sure you are welcome to contribute. and a person with a fisher would be in a better place to respond to your query,,

ps: you can easily grab the model from github to play around with . the fisher is a very good design if made out of aluminum or steel . the weak point is the acrylic and plastic joint

Edited 1 time(s). Last edit at 10/16/2018 05:41AM by ekaggrat.

A volatile thought process is what I am observing. A contribution is not a contribution if one should bow down and express tribute for such. It should be freely given whether appreciated or not. Then it will be appreciated. That is the core of open source. Your time is really worth no more than anyone else's time. You insinuated that your time was more valuable, however, than those participating in the discussion. I realize that the response was that to criticism, and I personally have no problem with said drawing. But the nature of the response, veering in the direction of class conflict and self aggrandization, was not appropriate. I would have just said "can you do any better?". It may have just been that your brand of satire rubbed me the wrong way and I'll concede that's what happened.

Quote
jefbed
A volatile thought process is what I am observing. A contribution is not a contribution if one should bow down and express tribute for such. It should be freely given whether appreciated or not. Then it will be appreciated. That is the core of open source. Your time is really worth no more than anyone else's time. You insinuated that your time was more valuable, however, than those participating in the discussion. I realize that the response was that to criticism, and I personally have no problem with said drawing. But the nature of the response, veering in the direction of class conflict and self aggrandization, was not appropriate. I would have just said "can you do any better?". It may have just been that your brand of satire rubbed me the wrong way and I'll concede that's what happened.

yyeah, it's a "trap", for sure, i apologise. i have to admit to having been extremely irritated, i've made massive contributions of time and effort to the software libre world, consistently, for over 25 years now, and in absolutely every case it's been other people that get rich, taking the credit (literally claiming the credit, awards, and donations in one case), spongeing off of my efforts. in another instance, several people got shares sufficient to pay off the mortgage of their house, buy new cars (outright), and so on.

as a direct consequence of people consistently neglecting to compensate me for my efforts, my income's been consistently low, to the point where at some points i would actually have made more money by going "on the dole" (spongeing off the state - something i cannot bring myself to do). at another point i actually had to steal wood from local forests in order to keep the house above SEVEN centigrade, during winter.

so i don't have *time* - or the resources - to put effort into bringing things up to what other people might expect to be a "nice standard". sketches and illustrations like this are quick and easy, they don't take long, and illustrate the point.

the series that i created here - [reprap.org] - was part of a comprehensive analysis of the full range of 3D printing, after i was shocked at quite how many 3D printer designs are mechanically unsound: insufficient use of triangles, lack of recognition of the properties of the materials being used and so on.

Quote
ekaggrat
@ikcl

sorry for being harsh. but if you were intending to contribute to the design a little more upfront work would help the process. most of the discussions are started with a little base work done. Sure you are welcome to contribute. and a person with a fisher would be in a better place to respond to your query,,

ps: you can easily grab the model from github to play around with . the fisher is a very good design if made out of aluminum or steel . the weak point is the acrylic and plastic joint

appreciated, thanks for apologising, ekaggrat. the analysis that i did was a very very rapid examination of the full range of 3D printer designs, based on some exploratory rapid prototyping techniques that i developed when there was a chance, a few years ago, that i might make some money from designing a new type of 3D printer.

in the 3D printing world it is honestly quite shocking to see how mechanically unsound 3D printer designs really are, how little experience in mechanical design people have, and - this is the really unfortunate bit - how that is propagated *particularly* by china cloning.

my friend and i went to huaqiang bay in shenzhen, where, you go up this escalator in one of the enormous shopping-malls, and right in front of you is a 3D printer stall. i took one look at what they were selling, grabbed the bed that was done in an ultimaker-style arrangement and was literally able to waggle it 10-15mm up and down. twin-vertical rod X-gantries are no better: 200+ grams hanging out 40-50mm from the centre of gravity!

these aspects of 3D printer designs are so bad that, as i mentioned in the message above i couldn't possibly leave it there, i felt absolutely compelled to write that wiki page series.

i know where you're coming from: it looks "really bad", right? hand-drawn images, wtf?? who *is* this person, who can possibly make these commentaries yet they haven't actually made a fisher??? don't even have one???

that's the thing: mechanical analysis skills don't have anything to do with the actual final product: the knowledge and analytical skills are completely separate and distinct. plus, it really does take weeks if not months to order the materials, put something together... oh, and *then* find out that it's deeply flawed.

that's why i pioneered the technique of quite literally making the frame from drinking straws, paper, cardboard and tape. it costs practically nothing, and can be done in about 20 minutes flat. you can then go, "hmmmm....", chuck it away, cut it up, and within a couple of days of playing around have a really really clear idea of what the strengths and weaknesses of a given design are, and can compensate for them extremely quickly.

and, due to the flexibility of the materials, any mechanical structural design issues which inappropriately rely on the rigidity of an upright (or a join-point) are massively and obviously amplified, in ways that the *actual* materials used would hide or mask.

even trying to use the priginal plans, from github, would actually not help with that prototyping phase, apart from acting as a topological guide (what to join to what, what the proportions are of each part and so on).

so 3D structural design-wise i really do know what i'm doing: unfortunately what i *haven't* got is the time or the resources to make it "look pretty". i really am going to have to leave that to other people, here, i apologise.

Edited 1 time(s). Last edit at 10/16/2018 08:40AM by lkcl.

Please keep the discussion civil.

On another note: Preliminary analysis does not (and in most cases should not) require FEA or even 3D modelling. That kind of thing should come later, and mostly used to refine designs and find potential overlooked issues. Starting with "popsicle stick" models and such is an excellent way to think through a design. I'm speaking from experience as an aerospace engineer.

---

Help improve the RepRap wiki! Just click "Edit" in the top-right corner of the page and start typing. Anyone can edit the wiki!

@lkcl

I upgraded the Fisher to laser cut 3mm to 5 mm steel plate. [wp.me]
The problem I experinced was the failure of plastic parts that join the steel plates.

Quote

that's why i pioneered the technique of quite literally making the frame from drinking straws, paper, cardboard and tape. it costs practically nothing, and can be done in about 20 minutes flat. you can then go, "hmmmm....", chuck it away, cut it up, and within a couple of days of playing around have a really really clear idea of what the strengths and weaknesses of a given design are, and can compensate for them extremely quickly.

A real model is better than sophisitcated computer simulation. Ingenius people such as Buckminster Fuller developed quite amazing technology by using cheap materials that kids could access. Buckminster Fuller developed a floating building, Cloud Nine. The total mass of structure is lighter than lifting force of heated air trapped inside the structure. When the Sun comes up, heats up the air, it will rise over the ground like a huge Balloon.

I think to understand something, a model or concept, we gotta experince it thorough the whole senses - seeing, hearing, physical sensation by touching and playing with it.

Edited 1 time(s). Last edit at 10/21/2018 08:29PM by janpenguin.

Quote
janpenguin
@lkcl

I upgraded the Fisher to laser cut 3mm to 5 mm steel plate. [wp.me]
The problem I experinced was the failure of plastic parts that join the steel plates.

i would expect that, as the twisting forces that the plates create, even during the motion of the head, would be transferred to shearing effects on the join-points (through the screws holding the uprights).

metal 60 degree brackets (folded plate), attached in 4 places (2 on each plate) and tightened down drastically (M3 won't cut it, M5 might do, M8 is probably overkill, M10 defintiltely is), quantity 6 (3 top, 3 bottom) would create a more rigid triangular shape based on the 3 metal plates, which would stop sideways shearing [which is "nail the base to the floor, then try to push the top sideways"] but not "torquing" about the z-axis [which is "nail the base to the floor, then grab the top, and try to unscrew it like a bottle-top"].

Quote

I think to understand something, a model or concept, we gotta experince it thorough the whole senses - seeing, hearing, physical sensation by touching and playing with it.

fascinating. i didn't realise buckminster had designed buildings.

Edited 1 time(s). Last edit at 10/21/2018 09:02PM by lkcl.