What type of Hiwin!

Hallo,
I need to know what model of Hiwin linear rail I can use in my corexy!
I know that the perfect way is to calculate all the specific loads, speeds etc but I need a medium quality item with a good ratio price/quality!
on hiwin.com i see 3/4 options, what you suggest?
regards

...and this?
[www.robotdigg.com]
are these a cheap type?
are they a valid product and what is the difference with an Hiwin original?

Edited 1 time(s). Last edit at 04/02/2015 02:51AM by mdcompositi.

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mdcompositi
Hallo,
I need to know what model of Hiwin linear rail I can use in my corexy!
I know that the perfect way is to calculate all the specific loads, speeds etc but I need a medium quality item with a good ratio price/quality!
on hiwin.com i see 3/4 options, what you suggest?
regards

Sorry, here's no awnser at your question but to do calculations. There's no half way because there's no reference point. And there's no price/quality ratio because how could we know the print quality you expect and the money you're ready to spend on it ? How should we estimate a component for a machine we know nothing about ? When we recommend a good component, anyway people will buy a component that fits their budget, explaining it will be "good enough".

I understand you don't want to calculate anything. I desagree, but it's your machine, your money and you will have from day to day to worry about this machine, not me So, you should awnser that question buy yourself, and the point will be the money you're ready to spend on it, because with no calculation, there's no way to know. And a system that works subjectively well on another machine means nothing on yours. There's no secret, better components will be more expensive. Do your budget allow you to buy expensive components ? Whatever, select any linear system that fits your budget, it will certainly be good enough. If you can't make up your mind between 6 types /brands, roll a dice, it works !

Edited 1 time(s). Last edit at 04/02/2015 04:12AM by Zavashier.

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Collective intelligence emerges when a group of people work together effectively. Prusa i3 Folger (A lot of the parts are wrong, boring !)

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Zavashier

Quote
mdcompositi
Hallo,
I need to know what model of Hiwin linear rail I can use in my corexy!
I know that the perfect way is to calculate all the specific loads, speeds etc but I need a medium quality item with a good ratio price/quality!
on hiwin.com i see 3/4 options, what you suggest?
regards

Sorry, here's no awnser at your question but to do calculations. There's no half way because there's no reference point. And there's no price/quality ratio because how could we know the print quality you expect and the money you're ready to spend on it ? How should we estimate a component for a machine we know nothing about ? When we recommend a good component, anyway people will buy a component that fits their budget, explaining it will be "good enough".

I understand you don't want to calculate anything. I desagree, but it's your machine, your money and you will have from day to day to worry about this machine, not me So, you should awnser that question buy yourself, and the point will be the money you're ready to spend on it, because with no calculation, there's no way to know. And a system that works subjectively well on another machine means nothing on yours. There's no secret, better components will be more expensive. Do your budget allow you to buy expensive components ? Whatever, select any linear system that fits your budget, it will certainly be good enough. If you can't make up your mind between 6 types /brands, roll a dice, it works !

Thank you for reply!
I assume that my request is too generic but I've open this topic to find a way!
you find attached my system realized from laser cutted sheet that I've designed from cad
I say this because in this way we can assume that mechanics is good positioned!
I've used 3 of this [www.robotdigg.com] , two on the sides and the third on gantry.
System works good, smooth and without jerk with 400 of feedrate and 7000 for accelerations (I think also with 500 and 9000)
The only issue is some noise that I think is due to resonance of components and also due to the temporary "wood case" on wich is placed!!
I'd like to calculate my system cosidering loads, speeds and other but I like to know what are methods, what are parameters I have to consider, what are typical variables and sizes for a corexy!
for example in hiwin catalogues you can find all formules and parameters to choose a linear rail but in my case(china made mgn) I haven't nothing, only dimensions!
these rails is cheap and works good (I don't know for how long!!)
Anyway my purpose is clearly to achieve a good machine that works well!
Which can be at this point an alternative to these guides and still a good way to proceed with another approach ?

Well, as you said, in the Hiwin (or any serious manufacturer's) catalogue, there's the procedure to linear guides selection. Just apply the procedure to your machine specs, and you will know what type of rail you need. Once you have calculated the load per axis, try to find on the different manufacturer's catalogue the lightest possible rail and block, with the better precision. Some other serious manufacturers : Misumi, SFK, NSK, Bosch, Rexroth, INA, Igus...

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Collective intelligence emerges when a group of people work together effectively. Prusa i3 Folger (A lot of the parts are wrong, boring !)

I just wanted to say that I don't think calculating the loads makes much sense on a coreXY design. I am sure that you will end up finding that if your design has no moments or torques in operational load scenario, then you can use the smallest of the smallest.

I do not know the system you are asking about, but in general it is more about choosing something that is practical and works with the rest of your setup. Especially it must be practical in a way so that you don't get some bad load scenarios.

What I am trying to say, is that your original setup:

Quote

I've used 3 of this [www.robotdigg.com] , two on the sides and the third on gantry.
System works good, smooth and without jerk with 400 of feedrate and 7000 for accelerations (I think also with 500 and 9000)
The only issue is some noise that I think is due to resonance of components and also due to the temporary "wood case" on wich is placed!!

Maybe could work fine already. When I look at your photo I am thinking that maybe your have some slack in the system and the gantry stops being perfect perpendicular to the two rails? That will create a moment of rotation pushing your rail carriage into the sides.

Try the following, one at a time:

1) Lubricate the rails
2) Release two of the screws on your rails so that the gantry is free to rotate about the rail carriage (only secured by one screw)
3) Do some good testing. Run with only movement in 45 deg to use just one motor, run x and run y and see when the problem is the worst. Maybe you discover something!

4) Clean the rails and smear part by part with some good color indicator. Then you make some test moves and see where the carriages makes contact to the rail. Maybe you discover that it is scraping in particular spots and you can either design against that or simply scrape the material off to when you no long have contact. It is a method commonly used in the industry especially for tooth contacts. Below you see the yellow indicator with the gear contact clearly showing:



Be careful when applying the indicator. It takes very little.

You can also twist the most outside belts 180 degrees, so they are running with the smooth side on the bearings.

Well, a proper set of pulleys and idlers with few extra bearings will cost you about 1% of the overall cost of the machine. As alignment is very important on any machine, and especialy on a CoreXY, maybe you don't wana save on that fiew.

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LarsK
I just wanted to say that I don't think calculating the loads makes much sense on a coreXY design.

I'm surprised. Mecanics and structures are all about calculations, or what the 5/7 years studies are for ? There's no negligible factors, even on small systems like Repraps. When I was student, somethimes we thought a component "will be good enough" but when calculations time comes, it was clear that wasn't the good component to use. Most of the times, calculations reveals things we did not thought about. Take the prusa i3 for example. How can you pretend printing proper 100µ layers with 8mm rods ? They're wrong for both X and Y axis. By the way, on the Y axis, the combination of the threaded rod chassis and the two long 8mm rods makes physicaly impossible to get a straight motion. With calculations, the right diameter to use is 12mm.

Don't do calculations if you don't need precision or speed. Then you will accept what your machine can provide, whatever the result. But if you don't do calculations, you're walking blind in a unknown environment. Your components choice may be "good enough"... or not ! There's a lot of help threads and machine that can't work through the web. The good question to awnser is "Am I ready to invest my money and my time with my eyes wide shut ?"

Edited 1 time(s). Last edit at 04/07/2015 05:18AM by Zavashier.

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Collective intelligence emerges when a group of people work together effectively. Prusa i3 Folger (A lot of the parts are wrong, boring !)

Quote
Zavashier
Well, a proper set of pulleys and idlers with few extra bearings will cost you about 1% of the overall cost of the machine. As alignment is very important on any machine, and especialy on a CoreXY, maybe you don't wana save on that fiew.

Quote
LarsK
I just wanted to say that I don't think calculating the loads makes much sense on a coreXY design.

I'm surprised. Mecanics and structures are all about calculations, or what the 5/7 years studies are for ? There's no negligible factors, even on small systems like Repraps. When I was student, somethimes we thought a component "will be good enough" but when calculations time comes, it was clear that wasn't the good component to use. Most of the times, calculations reveals things we did not thought about. Take the prusa i3 for example. How can you pretend printing proper 100µ layers with 8mm rods ? They're wrong for both X and Y axis. By the way, on the Y axis, the combination of the threaded rod chassis and the two long 8mm rods makes physicaly impossible to get a straight motion. With calculations, the right diameter to use is 12mm.

Don't do calculations if you don't need precision or speed. Then you will accept what your machine can provide, whatever the result. But if you don't do calculations, you're walking blind in a unknown environment. Your components choice may be "good enough"... or not ! There's a lot of help threads and machine that can't work through the web. The good question to awnser is "Am I ready to invest my money and my time with my eyes wide shut ?"

1) You are comparing the load carrying smooth rods on a Prusa with the not load carrying rails on the coreXY. The rails in question will be supported by the underlying structure - The situation is completely different and can in no way be compared.

2) In all my time at the university and all my professional life I very rarely recall starting with a smaller part then needed. I always chose something too big and then when doing the math I find that the part can be much smaller. But that may just be me (this is not true for fatigue consideration which can be much more tricky to estimate)

3) Regarding your Prusa and 8mm rod - I calculate that for a 8 x 300 mm rod your extruder needs to be ~1.4 kg heavy to see a deflection of 0.1mm (load evenly divided between the two rods). That sounds like a very heavy extruder to me. Also - The 0.1 mm will be the difference for a part that is 300mm wide. From the extreme edge to the center and to the edge again. On a 100x100 part it will be less than 0.03 mm (not linear relation)...

Finally, are you really able to print parts on the Prusa where a static 0.1 mm matters?

Me - [uy.linkedin.com] - Not updated, I am working in Brazil these days.
I have a delta kossel ish type, no Prusa. About to finish my CoreXY

Well, The situation is different, but you suppose the structure is stiff enough for the linear rails. Everything matters. We're both professionnals, I'm sure we will agree whatever. For the Prusa I3, you calculate with a static load. Redo your calculations with a dynamic load, the values will change. A flex of 0.1mm is the layer height, it should just clogg up the nozzle ! Hopefully, the 8mm rods don't flex that much, but too much for me. I calculate the 8mm rods may flex about 0.05mm at the centre under 1N of dynamic load. So it could potentialy introduce a 50% error on layer height. That's big enough to me. It's a principle, but to get a 0.1mm resolution, the tolerance can't be 50%. I work for the Aircraft industry, and tolerence is 0.5% max. For a reprap 10% sounds pretty enough. And 8mm rods can't offer that tolerance. Anyway, all that don't help mdcompositi to find his guides.

Edited 2 time(s). Last edit at 04/08/2015 06:25PM by Zavashier.

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Collective intelligence emerges when a group of people work together effectively. Prusa i3 Folger (A lot of the parts are wrong, boring !)

Quote
Zavashier
Well, The situation is different, but you suppose the structure is stiff enough for the linear rails. Everything matters. We're both professionnals, I'm sure we will agree whatever. For the Prusa I3, you calculate with a static load. Redo your calculations with a dynamic load, the values will change. A flex of 0.1mm is the layer height, it should just clogg up the nozzle ! Hopefully, the 8mm rods don't flex that much, but too much for me. I calculate the 8mm rods may flex about 0.05mm at the centre under 1N of dynamic load. So it could potentialy introduce a 50% error on layer height. That's big enough to me. It's a principle, but to get a 0.1mm resolution, the tolerance can't be 50%. I work for the Aircraft industry, and tolerence is 0.5% max. For a reprap 10% sounds pretty enough. And 8mm rods can't offer that tolerance. Anyway, all that don't help mdcompositi to find his guides.

We agree.

I feel that what is really needed is some best practice guidelines and standardization. On both levels. Both for choosing the correct component and for calculating. I asked you in the my last post if 0.1 mm really matters - The truth is that I myself really do not know. I do not know what sort of tolerance the best of best people achieve and what is realistic etc - I see some forum posts but really anybody can say that they measured with their measuring tape and the part was within 0.001.... Some solid documentation and investigation required in this field.

Well, it realy depends of what you expect. 0.4mm is ways enough for printing a missing Ikea Knob for domestic use. If you're into small caraters printing the more precision you reach, the better. To me, 0.1 matters a lot. For example, if you try to print parts with tappered holes, a 0.1mm error, and your can't screw in. I print usualy with 0.2 and 0.3 nozzle. With that nozzles even a 0.05mm gap may matters.

I expected too much of my Prusa I3. So I upgraded it in many ways. I had a 0.2mm cup at the centre of my 3mm glass. That causes problems on parts meant to be dead flat. At last, with a 4mm dead flat mirror plate, my 6-7 first layers was way better. But, I wondered why at the centre, the filament was too squeezed when the edges were perfect on that dead flat plate. I thought one of the X rods was not straight. I unmounted and measure with a straight edge, and they were pretty straight. With a dial gauge mounted on the carriage, I measured a small flex at the centre (calculation should have tell). But when I ran a test print, I noticed the flex increased a lot. I already changed for precision bearings so they can't be to blame. It was the dynamic load. And the faster the printer, the worst the gap. The perfection quest is endless (or your money is the limit !). When I correct a problem, it light up a new one !

My thought is anything matters. Structure, components, precision alignment, vibrations attenuation... To get a nice print with 0.1 layers, you need a 0.01 precision tool. That's true for a lathe, a mill, a 3D printer or any other tool. Actualy, whatever reprapers says about a supposed 0.001mm precision, our repraps are far away to print with a 0.1mm overall precision. Just because of the layers, you can't be realy flat on the vertical surfaces. The slicer introduces a lot of errors too, that's why I prefer small nozzles that divide the slicing errors. Actualy, a good mill or lathe is ways more precise.

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Collective intelligence emerges when a group of people work together effectively. Prusa i3 Folger (A lot of the parts are wrong, boring !)

Quote
Zavashier
Well, The situation is different, but you suppose the structure is stiff enough for the linear rails. Everything matters. We're both professionnals, I'm sure we will agree whatever. For the Prusa I3, you calculate with a static load. Redo your calculations with a dynamic load, the values will change. A flex of 0.1mm is the layer height, it should just clogg up the nozzle ! Hopefully, the 8mm rods don't flex that much, but too much for me. I calculate the 8mm rods may flex about 0.05mm at the centre under 1N of dynamic load. So it could potentialy introduce a 50% error on layer height. That's big enough to me. It's a principle, but to get a 0.1mm resolution, the tolerance can't be 50%. I work for the Aircraft industry, and tolerence is 0.5% max. For a reprap 10% sounds pretty enough. And 8mm rods can't offer that tolerance. Anyway, all that don't help mdcompositi to find his guides.

Infact!!
the discussion has taken a completely different direction !!!
even if the topic you have treated is interesting !!
can someone suggest some test files that I can use (45 degrees for example) and other parameter that I can apply on my system?
soon I'll receive other sheet metal and component for Z axis so I can try first print test!
I think that guides have a perfect parallelism 'cos sheet metal was created by laser cut, belt and pulleys have a good tension!

can someone tell me how much are velocity and accelleration for a good working corexy?

Hi mdcompositi... where did you finally find the best price on this linear slide???? I will be using this same slide in my build...

best,

Patrick

these are provisional for me!
I want to install a better quality type!
can you post a pic for your system ?

Edited 1 time(s). Last edit at 04/20/2015 06:41AM by mdcompositi.

all I have at the moment are extruded rail 2020 frame. lots of stuff ordered though. are the ones you have really loose???? does it slide more like a kitchen drawer than a cnc????