I need advice. I manage to get my hand on 3pcs. of this beauty Rexroth Bosh PSK 60 precision linear stages. It go maximum travel of 455mm with overall length of 675mm without motors attached. The accuracy is 5 microns. I would like to gain the full benefit from the accuracy maintaining maximum build volume and speed.
So what do you think I would benefit most with Delta design or with CoreXY. I am dismissing Cartesian design as I don’t want to move significant amount of mass with high speed.
A timing belt (or fishing line/spectra) is an integral part of a CoreXY design (which is a Cartesian design, BTW); you can’t possibly build a CoreXY with this.
If you’re asking about what motors to drive it with, I’d recommend ones with a low degree of turn per step and planetary gears. Should be able to take advantage of it’s precision that way. Oh, and lucky you!
Tom I don’t want to implement exact coreXY design but I could mimic it with this lines with attaching both sliders to the lines. I just want to avoid classic implementation of Cartesian design like Prusa or Printrbot as I don’t want to move entire table with high speed. I want to attach the table to Z axis instead of the Y like most classical implementation of Cartesian design.
So let me clarify Gantry/Cartesian designs required complex construction. From other hand Delta is simple for construction but there are few week points variable resolution and effector attachment that could lead to lost of precision.
As per the motors I will use Sanyo-Denky Step-Syn motors made in Japan directly attached. 200 steps per rev. With High Voltage drivers 24/36V.
You’ll be forced to move a significant amount of mass with high speed any way you go about it. That’s the nature of ball screws; you have to rotate them to create linear movement and they are solid pieces of steel.
Both Delta and CoreXY are designs that rely on low moving mass to achieve high print speeds. The only way you’ll overcome that is by using more powerful motors.
Imho, the best use for these beauties is as the Z-axis on a CoreXY or even better as a base for a home built CNC mill. (Neo7CNC on youtube, he uses these on his mills)
I really don’t want to mess anymore with belts and their elasticity. I have Printrbot Plus which I manage to tune it for perfect results but if I want to get accurate dimensions (bellow 0.1mm deviation) I should dramatically reduce the acceleration to 700 in the firmware. This actually increase the time significantly for the prints. I replaced the stock belts with PU/Steel Core which improve the quality dramatically and I also replaced entire table to reduce the weight to 700gr. But with this lines I really want to ensure that I will get 0.01mm accuracy every time. I will also build close chamber with heating/cooling with peltier elements to be able to control the ambient temperature in the chamber up to 1 degree.
I will use Nema 23 motors with 2.6A current same as my CNC so motors should not be an issue. Planetary gearbox with small backlash will cost me fortune and it is really hard to find 3 equal pieces in ebay as bargain.
I just really want get good working machine overcoming what comes from the regular vendors Everyone state layer resolution without mentioning repeating accuracy of the machine which represent the actual resolution of the machine.
George, Cartesian does not mean a moving table, it’s simply a coordinate system which means activation of a single motor only affects a single axis.
The prusa setup with moving Y axis, and dual Z rods is typically referred to as a mendel-style. It is also cartesian. The only things not cartesian are scara, delta, etc. Even corexy/xz are cartesian with the simple rule that you’re turning the activation axis by 45 degrees.
You could do a delta design with these, but man, that’d be a tradeoff. Great linear railing only to throw it on a design that is inherently difficult to get accurate. I’m not sure what I’d do with 3 of these.
I would almost build a router table with these. They look extremely heavy for 3D printing. Maybe I’d use them to make a Z axis for a non-delta.
I don’t think you’ll get the speed you want using these for XY motion. You say belts are bad but it’s more a matter of designing the mechanism well and choosing the proper belt.
Jeff,
I don’t want to say belts are bad, I have printer with belts that produce fairly accurate parts. I just want more that what I could reach with belts. Even a factory assembled stage with belt will not be rated better than 0.1mm repeatable position accuracy as there are too many if with belts. I saw that there are new development in this area with carbon reinforced belts but this is not accessible for me as a hobbyist.
I have CNC and this was my initial idea for this lines. Than I calculated how often I print against mill. Milling is not something that hobbist like me will do. First it is much more expensive per part than printing. I have hard times supplying the material for my CNC. Most of the good materials require quantity as they are sold on sheets 3x2 m. Mistakes are extremely unforgiving there and etc. So at the end I think if I get better printer than CNC I would benefit more.
This lines by specification could reach speed of around 5m/s with acceleration up to 3000m/s2. Additionally Rexroth advice production usage around 20% of the maximum speed. 1000mm/s is much more than what I ant to achieve. I would like accurate print with 90mm/s with good acceleration.
I like Delta as it will be simple but I have never manage to find a good way to attach the Effector. Maybe magnetic one is good but don’t look to me reliable.
The other option is to attach the print head on a sliders like Ultimaker for example and to attach this slider to the lines and support the on the other side with just linear bearings. But the construction looks really complex to me to be build in my garage.
That is why I need advice which design will suits best to this lines.
@George_Novtekov It’s not just the slides limiting speed, but that’s part of it. Ball screws reduces the motion per revolution, so you need more RPM to achieve the same speed. Which is fine with many servo motors. Step motors aren’t necessarily very good with speed. 90mm/s exceeds the speed you can get with many step motors given your screw lead, I even found a few that would choke at a third of that. 90mm/s printing speed needs 1080RPM and I suspect you want your non-printing moves to be faster, so say 2000RPM, and that narrows down your options considerably.
Yea that’s just too fine of a lead to direct drive with steppers. With NEMA23 steppers on 5mm lead screws you would be limited to something like 33 mm/s.
25mm lead or faster would work. That would put you at 360 RPM at 150 mm/s. But then you’re adding rotational inertia of the screw into the mix. Lots to it but IMO ball screws in high performance linear ways are in the domain of high performance servo systems.
You could overdrive them with a timing belt to get an effective pitch that works for your motors.
