Development corexy

Quote
MKSA

Quote
the_digital_dentist
.....
Your CAD model looks like you have put bearings on the ends of the screws, but if I understand what you're doing correctly, the screws aren't going to rotate, so bearings won't be needed.

Congratulation doc, you are the only one who spotted the obvious fault ! In fact, the screw WILL rotate at an unpredictable speed depending on nut friction and counter motor torque. Imagine the result !

As for the rest, indeed plenty of question marks.The three ball supports, wrong, and more complicated to make/align than the correct solution !

Of course, the screws will rotate. They have to !
Where have you two been at physics classes?

Quote
MKSA

Quote
the_digital_dentist
.....
Your CAD model looks like you have put bearings on the ends of the screws, but if I understand what you're doing correctly, the screws aren't going to rotate, so bearings won't be needed.

Congratulation doc, you are the only one who spotted the obvious fault ! In fact, the screw WILL rotate at an unpredictable speed depending on nut friction and counter motor torque. Imagine the result !

As for the rest, indeed plenty of question marks.The three ball supports, wrong, and more complicated to make/align than the correct solution !

Edited 1 time(s). Last edit at 09/30/2017 04:59AM by andornot.

Thank you for all the input, having really looked into the design and the complications of it and having to use two more steppers motors i am going to look into other methods to move the z axis.

Really auto levelling is not required for a Cartesian printer as it only needs to be set once, z probe for z height maybe useful. In the next week i will be posting the redesign of the corexy, with a new chassis design.

If you use a single motor to drive the 3 leadscrews, then you can use the Z probe to tell you how much you need to adjust the leadscrews (or bed levelling screws if you have them) manually. See [duet3d.com].

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Well, the non-captive approach is unique for the Z, though I can see where it adds wiring complications, and additional weight to the bed.
Just for reference, here's an image of a system where the screw doesn't rotate for those who are still confused...

The concept is pretty simple- instead of turning a massive screw, you fix the screw and drive the nut. This is usually used in high speed machines where turning a long screw fast results in "whipping". It's a lot easier to control a small, low mass nut than a long, flexible, heavy screw.

---

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
the_digital_dentist
The concept is pretty simple- instead of turning a massive screw, you fix the screw and drive the nut. This is usually used in high speed machines where turning a long screw fast results in "whipping". It's a lot easier to control a small, low mass nut than a long, flexible, heavy screw.

Yea, I've seen fixed screws for laser cutting machines capable of 1600mm/sec feeds and even higher rapids (close to 5000mm/sec). In machine shops, we call it KFC, short for "Kung Fu Crazy" fast!
For a 3d printer, especially the Z that only needs to index layer by layer, no appreciable benefit to using this configuration can be gained. Other than the cool factor

I would like to see a Z moving by spinning the nuts via pulleys & belt been thinking about it for some time, just not got around to doing it.

Quote
o_lampe

Quote
MKSA

Quote
the_digital_dentist
.....
Your CAD model looks like you have put bearings on the ends of the screws, but if I understand what you're doing correctly, the screws aren't going to rotate, so bearings won't be needed.

Congratulation doc, you are the only one who spotted the obvious fault ! In fact, the screw WILL rotate at an unpredictable speed depending on nut friction and counter motor torque. Imagine the result !

As for the rest, indeed plenty of question marks.The three ball supports, wrong, and more complicated to make/align than the correct solution !

Of course, the screws will rotate. They have to !
Where have you two been at physics classes?

So please explain the Z movement with both the screw and the nut rotating (the nut is part of the stepper rotor) !

---

"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Quote
MKSA

Quote
o_lampe

Quote
MKSA

Quote
the_digital_dentist
.....
Your CAD model looks like you have put bearings on the ends of the screws, but if I understand what you're doing correctly, the screws aren't going to rotate, so bearings won't be needed.

Congratulation doc, you are the only one who spotted the obvious fault ! In fact, the screw WILL rotate at an unpredictable speed depending on nut friction and counter motor torque. Imagine the result !

As for the rest, indeed plenty of question marks.The three ball supports, wrong, and more complicated to make/align than the correct solution !

Of course, the screws will rotate. They have to !
Where have you two been at physics classes?

So please explain the Z movement with both the screw and the nut rotating (the nut is part of the stepper rotor) !

The lead screw is fixed

---

www.andornot.co.uk, selling new products, including smoothie boards and other useful parts for 3D Printers:

AndOrNot buildplate launched, available in 6 inch, 8 inch, 12 inch and 17 inch square introductory discount code "20reprap"
And Or Not Build Plates

Quote
MechaBits
I would like to see a Z moving by spinning the nuts via pulleys & belt been thinking about it for some time, just not got around to doing it.

It's usually done the other way because it's pretty easy to couple a screw to a motor, pulley, or bearing, and a lot harder to add bearings and pulley teeth to typical lead nuts. What would would be the advantage of driving the nuts in a printer's very slow Z axis that would make it worth the trouble (!) and expense (?) to do it?

---

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

What do people think of using a scissor table principle to raise and lower the z axis? Has this ever been done on other printers?

---

www.andornot.co.uk, selling new products, including smoothie boards and other useful parts for 3D Printers:

AndOrNot buildplate launched, available in 6 inch, 8 inch, 12 inch and 17 inch square introductory discount code "20reprap"
And Or Not Build Plates

People bring it up every few months. The problem is making it stable and accurate enough to keep the platform level as it moves up and down.

I saw a prototype machine a year or so ago by some Master's or PHd student in new Zealand (?) that used a Sarrus linkage for the bed lift. Not sure how well it actually worked, and I don't recall how it was driven. That's the problem with getting old. You file this stuff away and can't retrieve it any more. Too many years of the slowly accumulated brain damage caused by one beer at a time...

[www.youtube.com]

Oops! here's the machine I was talking about:

[www.youtube.com]

Edited 2 time(s). Last edit at 10/03/2017 05:21PM by the_digital_dentist.

---

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
MKSA

Quote
o_lampe
Of course, the screws will rotate. They have to !
Where have you two been at physics classes?

So please explain the Z movement with both the screw and the nut rotating (the nut is part of the stepper rotor) !

Sorry, I have to apologize. I fooled myself, because I knew the leadscrew does rotate. But you have to keep it from spinning to get axial movement.

Next time, I keep my big mouth shut...
O_Lampe

Re: scissor table
The steps/mm would change over height, so would the accuracy and torque.

Quote
o_lampe

Quote
MKSA

Quote
o_lampe
Of course, the screws will rotate. They have to !
Where have you two been at physics classes?

So please explain the Z movement with both the screw and the nut rotating (the nut is part of the stepper rotor) !

Sorry, I have to apologize. I fooled myself, because I knew the leadscrew does rotate. But you have to keep it from spinning to get axial movement.

Next time, I keep my big mouth shut...
O_Lampe

OK, at least you apologize !
Everybody assumed the leadscrews were in ball bearings top and bottom as can be seen in the picture, just DD (and me) noticed it was wrong.
Anyway, although it can work provided the leadscrews are fixed, it is too complicated without any advantage (to level the bed with three leadscrew+motors can be done simpler but frankly, not worth it).

Edited 1 time(s). Last edit at 10/04/2017 12:43PM by MKSA.

---

"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Quote
the_digital_dentist

Quote
MechaBits
I would like to see a Z moving by spinning the nuts via pulleys & belt been thinking about it for some time, just not got around to doing it.

It's usually done the other way because it's pretty easy to couple a screw to a motor, pulley, or bearing, and a lot harder to add bearings and pulley teeth to typical lead nuts. What would would be the advantage of driving the nuts in a printer's very slow Z axis that would make it worth the trouble (!) and expense (?) to do it?

Which is why i've never got around to it, but I like heath robinson so why not, and because you can.
The thought of sticking the TR8 nut into a bearing & or pulley, motor mount & belt doesnt seem too hard to do, so at some point worth a try.

As for what would be the advantage your probably more qualified to answer, but If a lead or ballscrew works better with pulley & belt, perhaps the same is true for the nut.

Nice simple moving leadscrew nut
moving Z axis --- fixed leadscrew

motor fixed to bed
leadscrew nut rotating in bearing in bed
flange pulls / pushes bed up/down

Yeah thats what mine looks like in head, though not fixed to bed but to X arm,
nut into a 10mm pulley, but some fleshing out still needed for the exact joint config.

Edited 2 time(s). Last edit at 10/04/2017 09:25PM by MechaBits.

Quote
andornot


The lead screw is fixed

Not what you wrote earlier : "The 3 z screws are located in bearings top and bottom (not clear on the picture), allowing the linear screw to rotate, ".
As Schopenhauer wrote: "The worst moment in an argument is when you realize you are wrong !"
Anyway, it was fun.

---

"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

i have decided to build a d-bot, its for son's christmas present and i will get a better understanding of corexy machines. Does anybody have experience of building such a machine and any improvements to it?

---

www.andornot.co.uk, selling new products, including smoothie boards and other useful parts for 3D Printers:

AndOrNot buildplate launched, available in 6 inch, 8 inch, 12 inch and 17 inch square introductory discount code "20reprap"
And Or Not Build Plates

Quote
andornot
i have decided to build a d-bot, its for son's christmas present and i will get a better understanding of corexy machines. Does anybody have experience of building such a machine and any improvements to it?

That's a shame... your machine looked better then a Dbot.

V slot wheels and printed plates are not a great combination in my opinion. The heavy pre load you must place on the wheels with the eccentric nuts tends to bow the plastic mounts. The other downside is that you must tighten the wheels to the plates, and if you use cheap bearings they bind... Loosen the nuts, and the wheels are sloppy though. Buy good bearings, and make sure to use metal plates as much as possible. The 3mm plates offered by openbuilds are good but not brilliant. In the end you will want custom plates to fit your own needs.

You can get delrin wheels from china that are considerably cheaper, and quality is not hugely important on these. I have used both openbuilds delrin wheels and chinese ones... The chinese ones have a tight fit on the bearings and they are tough to get out, but once you make the wheel it doesn't need to come apart. The delrin is 'tougher' from china, but wear over time seems equal. My printer has been in constant use for at least a year now.

I've built a D-Bot, but with improved stepper brackets, three ballscrews for the bed and linear rails. The improved brackets were from spiffcow
I also bought metal corner brackets.
The gantry connectors are not yet perfect. I'm currently building a CNC-mill to make them from aluminum.
All-in-all it works perfect, I'm really afraid to take it apart.

Quote
Origamib

Quote
andornot
i have decided to build a d-bot, its for son's christmas present and i will get a better understanding of corexy machines. Does anybody have experience of building such a machine and any improvements to it?

That's a shame... your machine looked better then a Dbot.

V slot wheels and printed plates are not a great combination in my opinion. The heavy pre load you must place on the wheels with the eccentric nuts tends to bow the plastic mounts. The other downside is that you must tighten the wheels to the plates, and if you use cheap bearings they bind... Loosen the nuts, and the wheels are sloppy though. Buy good bearings, and make sure to use metal plates as much as possible. The 3mm plates offered by openbuilds are good but not brilliant. In the end you will want custom plates to fit your own needs.

You can get delrin wheels from china that are considerably cheaper, and quality is not hugely important on these. I have used both openbuilds delrin wheels and chinese ones... The chinese ones have a tight fit on the bearings and they are tough to get out, but once you make the wheel it doesn't need to come apart. The delrin is 'tougher' from china, but wear over time seems equal. My printer has been in constant use for at least a year now.

So i would really be better carrying on the design of my corexy and buy my son a cheap printer to learn 3d printing. Any recommendations on a cheap printer to learn how to print?

---

www.andornot.co.uk, selling new products, including smoothie boards and other useful parts for 3D Printers:

AndOrNot buildplate launched, available in 6 inch, 8 inch, 12 inch and 17 inch square introductory discount code "20reprap"
And Or Not Build Plates

Quote
andornot

Quote
Origamib

Quote
andornot
i have decided to build a d-bot, its for son's christmas present and i will get a better understanding of corexy machines. Does anybody have experience of building such a machine and any improvements to it?

That's a shame... your machine looked better then a Dbot.

V slot wheels and printed plates are not a great combination in my opinion. The heavy pre load you must place on the wheels with the eccentric nuts tends to bow the plastic mounts. The other downside is that you must tighten the wheels to the plates, and if you use cheap bearings they bind... Loosen the nuts, and the wheels are sloppy though. Buy good bearings, and make sure to use metal plates as much as possible. The 3mm plates offered by openbuilds are good but not brilliant. In the end you will want custom plates to fit your own needs.

You can get delrin wheels from china that are considerably cheaper, and quality is not hugely important on these. I have used both openbuilds delrin wheels and chinese ones... The chinese ones have a tight fit on the bearings and they are tough to get out, but once you make the wheel it doesn't need to come apart. The delrin is 'tougher' from china, but wear over time seems equal. My printer has been in constant use for at least a year now.

So i would really be better carrying on the design of my corexy and buy my son a cheap printer to learn 3d printing. Any recommendations on a cheap printer to learn how to print?

Sure, why not just make this printer with your son? Enjoy the learning curve together, with input from both of you.

Quote

Sure, why not just make this printer with your son? Enjoy the learning curve together, with input from both of you.

+1 for building it together.
When I was a kid, my parents gave us a ready built H0-railway track for X-mas. What a wasted opportunity to spend quality time with your son(s).

Just order some steppers, belts and extrusions and print the neccesary stuff beforehand, then do the rest together.

Edited 1 time(s). Last edit at 10/25/2017 03:00AM by o_lampe.