Core-XY based on Rat Rig V-Core and Duet 2 Ethernet



  • @deckingman

    I have a steel table welded for my Prusa MK3, that's over 50kg. The high mass has reduced the set-up rocking about a lot. I can see what you mean re stiffness, and I would also not have 4kg of moving mass on my printer, at least not on the V-Core I am building now. But to come up with the idea is pretty fascinating. What steppers do you use for your XY axis ? Are they driven directly from the Duet or do you have external drivers ?

    Jan



  • Just in case ppl are interested, my preliminary idea of a hotend mount for my V-Core is here:

    https://www.thingiverse.com/thing:3490910

    It is UNTESTED so far, I only worked of the original V-Core Fusion 360 files. I don't even have the V-Core kit yet on hand.

    Jan



  • @snoozer said in Core-XY based on Rat Rig V-Core and Duet 2 Ethernet:

    @deckingman
    What steppers do you use for your XY axis ? Are they driven directly from the Duet or do you have external drivers ?

    Jan

    These ones https://www.omc-stepperonline.com/nema-17-bipolar-59ncm-84ozin-2a-42x48mm-4wires-w-1m-cable-and-connector-17hs19-2004s1.html

    Nema 17s driven from the Duet. Rated current is 2.0 Amps and I run them at 1800mA. Bear in mind that I use two separate XY gantries - one for the hot and and one for the extruders. So my 4kgs of mass is spread across two gantries and thus 4 motors.

    (The load balancing is yet another XY gantry with yet another 2 motors).



  • @snoozer said in Core-XY based on Rat Rig V-Core and Duet 2 Ethernet:

    @dougal1957

    Also added to my link list. deckingman also recommended the Keenovo heaters, I have looked at them and they do a great variety of them, the price is very good (Customs or at least VAT will be added on arrival). My main concern is the adhesive, but it must be good otherwise it was not recommended I guess.

    Jan

    Not only do Keenovo do a great variety but they will also do you a custom one if you so wish. I now get mine without Temperature sensors in them as I prefer to use my own.

    Doug



  • Ratrig offers an anodised alluminum 3mm bed in the kit. As far as i have used it, it seems great. Plus anodising makes it insulated.



  • @deckingman

    Just watched your video of the 5x BT extruder upgrade. Its all V-Slot mechanics your are using ? Must be a good system if you are still with that. I have read about ppl having issues with flats spots on the wheels when the printer is sitting for a while, you never had that ? Did you deliberately chose to load the wheel lateral on the X axis or did your design just work out better with the space you have available this way and the loading direction is accidental ?

    I did check the Aluminium supplier you suggested, no shipping to IRL, same with a couple of other suppliers from the UK. A friend of mine lives part time in Newcastle, I get him to bring one back for me. The price really is reasonable in compare to what I find local.

    How is your glass plate held in place ? It looks almost as if you have a slot in system ?

    Thanks
    Jan



  • @snoozer So many questions ....

    Yes it's all OpenBuilds Vslot.

    No, I've never had a problem with flat spotting the wheels. There is only one reason why that can happen and that is if the wheel doesn't rotate freely and scrapes along the rail. It's exactly the same as locking the brakes on a car (before the days of ABS) and then the tyre scrapes along the road.

    IMO there is only one reason why the wheels may not rotate freely and that is due to poor assembly. The eccentric spacers must be adjusted so that when a carriage is fitted to a rail, if that rail is then tilted, the carriage will slide under it's own weight. At the same time, there must be no "play" in the carriage.

    I have had occasions when using OpenBuilds gantry plates, even with the eccentric spacers backed off completely, the carriage is still too tight. That is an unacceptable situation. One solution that I have used is to enlarge the small hole that takes the wheels on the other side of the gantry plate. This allows the bolt with the non-eccentric spacers to move slightly further away from the rail which then gives the necessary clearance. One other thing that can make the wheels bind is over tightening the lock nuts. However it is achieved, the wheels must rotate freely on the rails and not bind.

    Regarding the lateral loading of the wheels on the X carriage, I guess you mean the fact that the wheels are either side of the rails, rather than being top and bottom. There are three reasons for this. One being that I use two parallel rails. The carriage has 6 wheels in total, 3 per rail with two inner fixed wheels, and one outer adjustable wheel. This arrangement helps to keep the rails parallel. The second reason is that I always like to have the wheel bolts supported both ends, like an axel. Rather than having the bolts fixed at one end only, which means that they could flex. So it's easier to have a top and bottom plate with the "axels" fitted vertically between them, rather than using a single plate which would need bosses hanging down to support "axels" running horizontally. The third reason is that with wheels top and bottom, the hot end would have sat too high unless I had spaced the rails further apart to allow it to sit lower. This would have meant losing even more Y travel. Although the engineer in me would have preferred to have the wheels top and bottom, this works well enough.

    The glass is clamped to the bed using two "L" shaped sections of aluminium extrusion. These have slots in the side through "T bolts" screw into the edge of the aluminium plate. So I press down in the extrusions then tighten the bolts.

    Hope that all makes sense.



  • @deckingman said in Core-XY based on Rat Rig V-Core and Duet 2 Ethernet:

    IMO there is only one reason why the wheels may not rotate freely and that is due to poor assembly.

    Don't forget junk bearings! Though far less likely on a good quality OpenBuilds wheel.



  • Thanks for the info. I can't wait to get the V-Core kit, its two weeks now I think since I ordered, I hope they will ship it next week. I will find out how well its designed then regarding tolerances and stiffness.

    After watching the YT video with the Bondtech extruders I had a nosy on their website, they do pretty nice stuff, Bondtech just was never on my radar.

    Jan



  • @snoozer I did find that when I ordered my first lot of VSlot from RatRig, that delivery wasn't as quick as I would have liked. Subsequently, I've bough all my OpenBuilds stuff from Ooznest here in the UK. That doesn't help you though......



  • @phaedrux said in Core-XY based on Rat Rig V-Core and Duet 2 Ethernet:

    @deckingman said in Core-XY based on Rat Rig V-Core and Duet 2 Ethernet:

    IMO there is only one reason why the wheels may not rotate freely and that is due to poor assembly.

    Don't forget junk bearings! Though far less likely on a good quality OpenBuilds wheel.

    Well I wouldn't want us to fall out over it, but I'd argue that fitting junk bearings falls under the heading of poor assembly. Junk bearings seldom start life as being smooth and perfect and then fail a short time after - they are usually junk to start with and it's pretty easy to tell. Likewise Delrin wheels can sometimes have seams or casting marks that need to be dealt with by the application of fine grit abrasive. Washers and other metal parts can have burrs which need to be removed. Bits of swarf or grit can sometimes be found and need to be removed. For sure these things could all come under the heading of "defective parts" but they should be checked and either discarded or rectified as part of the assembly process in my opinion.



  • @deckingman

    I got my steppers, Duet 2 and Titan Aero from Ooznest, they don't have a V-Core kit and as a 1st self build I thought I go with a mechanical kit to not get lost in my project....... Once I get all work OK I will check what path to take next. I have my eye on getting a CNC mill, but that's not yet a fully formed plan, just an idea to have better resources for future builds..........

    Jan



  • @snoozer I have found the service from Ooznest to be first class and have no hesitation in recommending them. Of course, they don't do a 3D printer kit so I understand why you chose RatRig.

    Re CNC mill. I guess it depends a lot on what you want to do with it. Most of the OpenBuilds designs that I have seen are more what I would call CNC routers, rather than milling machines. For operations such as drilling, you need a lot more Z travel. I'd be a bit concerned about the rigidity of the column on those OpenBuilds designs that I've seen which have a reasonable amount of Z travel.

    If a router type CNC mill will do what you want then fine - go for it. If you want to do more than mill slots and shapes, then I think you need cast iron slide ways, with "T" slots that you can clamp a vice to, a very rigid column, precision ground spindle, adjustable jibs, etc. Personally, I need to machine mostly small aluminium or brass components and for my usage case I'm looking at buying a "proper" milling machine then maybe converting it to CNC at a later date. The conversion shouldn't be difficult - at least for a 3 axis machine. It's more less just a matter of replacing the hand wheels with stepper motors I'd have thought.



  • So I checked with Rat Rig last WE, they came back to me and the V-Core kit is apparently shipping this week. I hope the wait has an end soon now......



  • @deckingman said in Core-XY based on Rat Rig V-Core and Duet 2 Ethernet:

    ... machine then maybe converting it to CNC at a later date. The conversion shouldn't be difficult - at least for a 3 axis machine. It's more less just a matter of replacing the hand wheels with stepper motors I'd have thought.

    Slightly OT now, but, have had the same thought - seems the low end machines come with lead screws instead of ball screws so may have to replace the screws or accept some backlash. At least that was my conclusion.



  • @bearer

    I know in Mach3 you can work with backlash compensation, seen a bunch of stuff on YT. I believe in the F360 CAM module there is also something regarding backlash that can be configured. With a dovetail guide on a machine it would be a tight enough fit that you dont have it "bouncing" around and its likely to only come into play on changing direction. On an actual milling machine (remembering back to 1st apprenticeship) you only operate in one direction for cutting, not back and forth because the tool rotation and the type of cut dictates which direction to cut. Its not like a router. The move back is usually not a cutting move but instead a move to get the tool of the surface and fast travel and then re engaging. If you move in the axis that is responsible for your surface measurement then yes, you must take backlash or play into consideration. If you cut a perimeter around a part then you would have to compensate for backlash as well but you should be able to measure that and it should not change unless your lead screw or the lock is wearing out.

    For me personally I am looking into a CCC (Cheap and cheerful China) type CNC router. 200-300mm bed size will do for me. Mostly light aluminium and sheet plastic stuff and engraving front panels etc.....



  • @bearer

    And one thing I have totally ignored in my post above, a proper milling machine would have linear encoders on the axis as such, not on the drive. That would by default compensate for positioning errors cause you have a closed loop system. Still you would take out the backlash play I guess by moving over the point and move back to accurate position you have the load on the correct surface on you drive. Closed loop steppers would not solve that in the same way cause that reading is not aware of the actual position of the work piece but only of the drive.

    Jan



  • @snoozer Ahh, those comments about "actual milling machines" and "apprenticeships" take me back almost 50 years - long before the days of computers let alone CNC machines. Long before linear encoders and DROs (Digital Read Outs) in fact. But yes, you are absolutely right about backlash. It was always assumed that any machine (mill or lathe) would have backlash so any cut was always made by moving the tool to a position beyond the start point, then commencing the cut from the same direction.



  • @deckingman

    My 1st apprenticeship was in 1986, not yet 50 years. In the workshop for apprentices we had DROs on the milling machines (Deckel, a well known German brand) and you could program the machine to cut out the feed after x mm but not real CNC there yet,we where supposed to learn 😉 I have also a vague memory there was mechanical sliders that could be set to cut out the feed...... just vague memory, can't remember exactly how that worked.

    Jan



  • @snoozer We are going off topic but as it's your thread, I guess it's OK. I pre-date you a bit - my apprenticeship was from 1969 to 1975. In the days when men were men, boys were boys and calipers had vernier scales. Calculators hadn't been thought of so we used slide rules and log tables.☺


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