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CoreXY

Posted by kapperi 
CoreXY
February 24, 2018 09:31AM
I have been looking for CoreXy machine designs for a while now. I allready chosen D-bot as my choice of printer, but then I noticed that chinese mgn9 linear rails are dirty cheap nowadays.

Frame and linear components for D-bot costs rougly 150€ and it is mainly 2040 - size framing

On the other hand it costs about 120€ to make similar with linear bearings from china.


Mechanical part is not a problem(I make it for a living) BUT! Is mgn9 rails enough for 300x300x300 3d printer and are there any reasons that I should choose wheels over rails???
Re: CoreXY
February 24, 2018 09:37AM
HiWin makes quality parts. There are a lot of very crappy knock-offs that use the same part numbering scheme (MGN-xx), making people think they are getting HiWin parts. I wouldn't waste money on the knock-offs. Either buy HiWin parts or get quality Japanese/German/'merican parts. You can often find deals for new old stock or used Japanese linear guides on ebay for little more than the cost of crappy HiWin knockoffs. Look for THK, NSK, or IKO brands.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: CoreXY
February 24, 2018 10:52AM
Yes I know that original Hiwin bearings are top of the line...

Just thinking that are those cheap linear rails better than V-slot wheels.

We use Hiwin bearings and rails at work but prices are huge to 3d printer. Bearing only costs 40e and the rail is 100e per meter.

I want to do printer with these bearings it would cost me over 500e just for the rails and bearings. Offcourse these are little bit larger than mgn9

Edited 1 time(s). Last edit at 02/24/2018 10:52AM by kapperi.
Re: CoreXY
February 24, 2018 04:50PM
I just bought two new old stock IKO guide rails for $68 shipped. There are a lot of deals like that if you take the time to sift through the listings.

In the past I have purchased used linear guides and never been disappointed. I'd rather take my chances on a used Japanese guide than a new HiWin knockoff.

From what I have read, the V-slot wheels are better than the knockoff linear guides, but the form factor can be a problem, especially if you want to enclose the printer.

Edited 1 time(s). Last edit at 02/24/2018 04:52PM by the_digital_dentist.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: CoreXY
February 25, 2018 12:41AM
I've built the D-bot based on Robotdigg mgn12 rails. I'm very happy with the quality of the rails, but shippings adds up to the bill quite a lot.
They also have mgn9 rails, but mgn12 became some sort of standard for 3D-printers. There are lots of parts designed for the 20x20mm carrier screw-pattern.
Re: CoreXY
February 25, 2018 02:10AM
In my opinion v slot wheels are just as good as slides. I have had no problem enclosing a printer with them as the actual wheel assembly does not protrude further then the extrusion itself. This means I can bolt panels to the same extrusions used for the wheels with no problems.

My main gripe is that the form factor is much larger then mgn rails. This is somewhat offset by the flexibility of the system though. I find it much easier to design for openbuilds parts, whereas linear rail needs to be mounted to something .
Re: CoreXY
February 25, 2018 04:15AM
Quote

I have had no problem enclosing a printer with them as the actual wheel assembly does not protrude further then the extrusion itself.

V-wheels without a supporting backplate? Hmmm.. it's like single side mounted idlers. sad smiley

Three answers, three opinions. I somehow expected that grinning smiley
Re: CoreXY
February 25, 2018 12:05PM
Digital Dentist, thats what they call overengineering... smiling smiley

I have looked datasheets and I think that mgn9 is more than enough for 3d-printer, at least if its hiwin made.

Whats the benefits of v-slot wheels. Are those silent, cause main thing for me is that linear movement is silent.

Offcourse I'm going to choose rails if theres nothing better with wheels. I think that both can be built with same costs. Off course I have to design my own thing with rails but, that is just designing and that I can do...
Re: CoreXY
February 25, 2018 01:17PM
9mm linear guides are probably fine in 3D printers, but don't seem to show up surplus nearly as often as 12 and 15 mm parts. I used some 24x8 mm rails for the X and Y axes in UMMD.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: CoreXY
February 27, 2018 12:21PM
Quote
o_lampe
Quote

I have had no problem enclosing a printer with them as the actual wheel assembly does not protrude further then the extrusion itself.

V-wheels without a supporting backplate? Hmmm.. it's like single side mounted idlers. sad smiley

Three answers, three opinions. I somehow expected that grinning smiley

Correct, but does it matter if the wheel posts bend away from the plate slightly? You can still remove slack from the system with the eccentric spacers and the only real downside in that situation is uneven wear on the wheels. Mine have been running for 2 years with only a slight dent forming in the wheels. Further to this, the dent appears to be quite even on each side so I don't believe the posts are noticeably bending away from the plates due to a lack of support on both sides.

If I was making a CNC I would definately use two plates. I would also avoid the openbuilds 3mm plates as they do have a slight wiggle to them that a 5mm+ plate wouldn't. All negligible for 3D printing though
Re: CoreXY
February 28, 2018 03:37AM
I got prices for real Hiwin bearings...

MGN9C1 is 80€ per bearing and 420mm of rail.

HGR15 is 62€ per bearing and 400mm of rail

EGR20 is 71€ per bearing and 400mm of rail

All of these are very high quality and all of those is good for even small router (PCB for examble). I can get all of the V-slot things to with one rail costs...

So it is V-slot or chinese rails or round bars, Which one?
Re: CoreXY
February 28, 2018 04:03AM
My delta printer uses Robotdigg 440C stainless MGN12 linear rails and carriages. They are Chinese made but not as cheap as some. They worked well just as they arrived, whereas I have heard of other users of Chinese linear rails having to replace all the ball bearings. So I recommend them.


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet [www.duet3d.com].
Re: CoreXY
February 28, 2018 06:58AM
Hey, those are excellent prices. Do you dc24 think that those are good enough for corexy printer?

Price with those I think that I put rails for Z-axis too.
Re: CoreXY
February 28, 2018 09:28AM
Quote
kapperi
Hey, those are excellent prices. Do you dc24 think that those are good enough for corexy printer?

Price with those I think that I put rails for Z-axis too.

I haven't built a CoreXY printer, so I don't consider myself qualified to answer that.


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet [www.duet3d.com].
Re: CoreXY
March 01, 2018 12:26AM
I added some german quality balls in my Robotdigg mgn12h rails, because there were missing some. Then found, they run smoother when I replaced them all.
Removing all the balls and cleaning the tracks is also a good idea. There was a bit of dirt in mine. But it requires calm hands to replace the balls.

The stainless rails from RD seem to have different ball size. The carrier showed a little wiggle.

IMHO a Delta is more of a challenge for rails than CoreXY, so go for it.

Edited 1 time(s). Last edit at 03/01/2018 12:30AM by o_lampe.
Re: CoreXY
March 01, 2018 04:54AM
Ok, I´m going to go with the robotdigg rails... Cheaper to do than v-slot thing and looks more professional..

And I´m allways be able to upgrade the rails with real hiwin ones...

Quickly looked I can get rails and aluminium profiles with the price of V-slot aluminium profiles of D-bot design...
Re: CoreXY
March 01, 2018 08:31AM
The bearings are an integral part of the linear guide. If the manufacturer couldn't be bothered to use the proper size or a sufficient quantity of balls, what else did they skimp on? Why would anyone pay money for something like that?


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: CoreXY
March 01, 2018 09:48PM
Damn you Digital Dentist, I was so sure about those rails and now you got me thinking...

There seems to be real hiwin sledges for 20$ per piece, does it fit to that cheap rail?

For z-axis I'm thinking that I put rails to the back and with three ballscrews(chinese) One between rails to the back and another ones to middle of bed or to the front corner of printer. How does this sounds. For the hotbed I'm going to iterate Dentists idea of kinematic mount.

Or should the xy sledge move up and down? Like in the voron2
Re: CoreXY
March 02, 2018 12:47AM
I wouldn't mix cloned and original parts.
It seems, like you are building a copy of my D-Bot with three ballscrews and linear rails. Mine is still a WiP, but already prints excellent.
Moving the XY gantry up/down, means you have to deal with the belt tension AND the weight.
OTOH, with three ball screws you won't see any racking of the cantilevered bed.

TDD seems to live in a land, where used Hiwin or other genuine stuff falls from the sky, right into the scrap yard next to him winking smiley
That's not the case for many other countries.

Edited 1 time(s). Last edit at 03/02/2018 12:51AM by o_lampe.
Re: CoreXY
March 02, 2018 01:54AM
You're right with the mixing thing, DD lives in somekind of dropzone I guess...

I'm now pretty sure about the structure of my printer.

I'm going to put 3 ballscrews to bed, one in back and to at the center of printer. Two of aluminium bars at the front going to be 10cm to center to make more room to handle pieces in hotbed. Hotbed structure will be like in DD's printer. Hopefully without adjusting screws.

Corexy mechanism will be bolted right in the aluminium profile and controller board is going to be mks sbase.

Is 2020 enough or should I go with 3030 profile. Any thoughts? Bed will be 300x300 and Z over 300mm
Re: CoreXY
March 02, 2018 04:11AM
I wouldn't let my dog (if I had one) use 2020 to build a 3D printer. Go with the larger stuff.

Ball screws will probably allow the bed to drop when power to the Z motor is cut, if everything is aligned well.

I definitely would not mix bearing blocks and rails from different manufacturers. Linear guides are systems, not parts.

I live in a once industrial part of the US, the area commonly referred to as the "rust-belt" because of all the closed factories and rusting machinery that people imagine they are full of. Or is it because it's where the US automakers used to make most of the cars, back in the good ol' days when they couldn't be bothered (or didn't know how) to protect the steel from rust, and the salt on the roads in Winter perforated every body panel? One of the guys at the makerspace used to be in the industrial scrap business so he knows all the people in that business around Milwaukee. People from the makerspace (there are probably about 30 of the 300 members who build machinery) make the rounds to the scrappers pretty regularly, so they know us and they set aside stuff they think we might use, like t-slot aluminum extrusions, fork lift motors and VFDs, etc. We always bring cash.

When I built UMMD, I wasn't working to a schedule, or to someone else's BOM. I knew I needed certain types of parts and started watching for deals on them. One day I found about 20m of 4040 t-slot at a scrap yard and paid $60 for it. Unless you're trying to set printing speed records, the sizes of linear guides don't matter much as long as they are long enough. I check ebay, and when I see a deal, I buy. Eventually you accumulate the parts you need. I make 3D models of the parts as I acquire them, and the printer design takes shape around them. I picked up the set of linear guides linked in the post above because they were good and cheap, but I don't have a project in mind for them yet, probably another printer, but who knows? If I don't use them, someone at the makerspace will buy them from me and use them.

As with other things, when it comes to finding good deals on parts, patience is a virtue, and luck favors the prepared mind. It doesn't hurt to be in a group like the Milwaukee Makerspace, either...


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: CoreXY
March 02, 2018 08:07AM
Thats the problem. Theres no makerspace here, scrapyards try to get more money than new ones from ebay...

Carparts are half the price from internet than from scrapyard.

Its called FinnishTax, everything costs more...
Re: CoreXY
March 02, 2018 09:00AM
Quote
the_digital_dentist
I wouldn't let my dog (if I had one) use 2020 to build a 3D printer. Go with the larger stuff.

Ball screws will probably allow the bed to drop when power to the Z motor is cut, if everything is aligned well.

I definitely would not mix bearing blocks and rails from different manufacturers. Linear guides are systems, not parts.

So do you think I go with the 3030 or is 2040, you build your megamaxsuperhyperturbo with 4040? So I think with much less Z, I could go with 3030.

Ball screws will allow the bed drop, but could I use geared Nema to stop that?

Edit: God tha PLA is so easy to print. If only it could come in better strength..

Edited 1 time(s). Last edit at 03/02/2018 09:01AM by kapperi.
Re: CoreXY
March 02, 2018 02:12PM
I'd probably go with the 3030 over the 2040. I think assembly might be a little easier.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: CoreXY
March 02, 2018 03:02PM
Ok, I'm going go with that then.

Let the designing(copying) start..

Ps. Fusion is full of crap compared to creo what I'm using at work...
Re: CoreXY
March 02, 2018 06:11PM
After the printer is built, you will never say, "gee, I wish I had used smaller t-slot". A printer's frame can't be too rigid.

A geared stepper may help with the bed-drop problem. If the combo of screw lead and gear ratio are sufficiently high the motor's detent torque will be multiplied enough to support the weight. UMMD uses a worm gear reducer to ensure that the load can't drive the motor in reverse.

Edited 1 time(s). Last edit at 03/02/2018 06:24PM by the_digital_dentist.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: CoreXY
March 03, 2018 03:46PM
Careful about going to larger extrusion, as the rail might be too small to straddle the slot.
MGN12s just barely cover slots in 20 series, and want to use M3 bolts.
So unless bolting another plate over the 3030, with a shallow tight fit slot and tapped M3 holes, you may want to consider 2040 or larger 20 series extrusions.
Absolutely would need solid plate if using MGN9s.

Yea, cheap Chinese rail/block combos are a hit miss. Typically missing balls and are either too loose or too tight on the rail.
Forget about swapping blocks and rails, or adding blocks.
I bough over a thousand balls and match fit for the rails/blocks I got from China.
All done and said, could have, should have bought better hardware to start.

G'luck
Re: CoreXY
March 03, 2018 06:28PM
All the t-slot I have encountered (industrial stuff) has a slight concavity in the faces at the slot. That's done so that when you bolt parts to the extrusion, the the slot will distort slightly and provide spring force to hopefully keep the bolt from loosening. That concavity also means that there's no flat place for a linear guide to sit on the extrusion. I milled a 0.25 mm deep slot in the extrusion surface to give the Z axis linear guides in UMMD a flat surface to sit on. You can see it in the t-slot just above the end of the linear guide rail in this photo:



It might be tricky to mount the linear guides on extrusion if you don't have a milling machine to make a slot, but you can always bolt a piece of tooling plate to the extrusion and mount the linear guide on the tooling plate.

Edited 1 time(s). Last edit at 03/03/2018 06:30PM by the_digital_dentist.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: CoreXY
March 04, 2018 08:46AM
It wont be hard with Haas VF-4 what I can use...

I was thinking about using waterjetted aluminium plate under the rails but I cant think of way to attach the plate without bringing it out of the extrusions...

I want to do another level above the extrusion to get proper enclosement.

Today I was printing my I3 XLSteel over 70mm/s and it was foing great quality. I was printing PLA. Please tell me that theres some advantages with corexy, can it do faster speeds? Any other advantage?
Re: CoreXY
March 04, 2018 09:12AM
The biggest advantages of CoreXY over the i3 type machine is that the bed moves in Z instead of Y, so it doesn't throw the print (or the massive bed) back and forth at high speed. For tall prints that can be a real problem on an i3 type machine, especially if the print has a small footprint on the bed. There are other architectures that move the bed in Z, too. For any given size bed, the coreXY machine can have a smaller footprint because its depth dimension doesn't have to be at least 2x the Y axis dimension of the bed. CoreXY machines are build using box-type frames (usually), which tend to be more rigid than the inverted T usually used for i3 type machines.

When you move the bed in Z there are all sorts of potential problems that are a function of the Z axis mechanism. Cantilevered beds tend to bounce and that will cause print quality problems. It doesn't matter if you're lifting a bed or an X axis, if you use bad screws and/or multiple motors, you're going to have problems.

CoreXY can print fast, but it depends on how you build it and the controller you're using. It doesn't matter what architecture you use, print quality is always a trade for speed. It's a lot easier and cheaper to build a bad printer in any architecture, so you see a lot of bad builds in every architecture. The thing that ultimately limits print speed/acceleration is the fact that you're extruding molten plastic from a nozzle. Once it leaves the nozzle, it goes where it wants until it cools off.

The mechanisms to move the nozzle/bed around are relatively easy. Controlling extrusion is the biggest problem in 3D printing.

Edited 1 time(s). Last edit at 03/04/2018 09:16AM by the_digital_dentist.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
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