Mini Kossel, Cherry Pi III or The Griffin?

Hi Guys,

I am interested in building a delta printer but I am stuck as to which one to go for and could do with some advice please. The ones I have narrowed it down to is the Mini Kossel, the Cherry Pi III and the Griffin. I am currently leaning towards the Cherry Pi III but with me having no experience with delta printers I am unsure what the differences are.

I think they're all essentially very similar. The major difference between the original Mini Kossel and the others is the use of 1515 extrusions, rather 2020. The Cherry Pi (and I think the Griffin too) use magnetic rod ends, rather than ball joints. I've never used magnetic joints, but I like how simple Traxxas rod ends are.

That said, you can find vertexes for a 2020 Kossel on Thingiverse, and I've actually just completed modifying and printing the vertexes for my own Kossel 2020 build (soon to be on Thingiverse once I complete the carriages to match). I'm using T-Slot extrusions, and it differs from others by mounting the extrusions at a 45 degree rotation, so that V-Wheels can ride on the corners of the extrusion, just like the Kossel Clear...

Depending on the scale you're going for, I'd say go for 2020 extrusion. It's often a similar price to 1515, and it probably makes for a much more rigid frame (bigger vertexes, more surface area contact with the vertex). Whichever design you go for, they're all good, and you'll find that a lot of parts are interchangeable.

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iira
I think they're all essentially very similar. The major difference between the original Mini Kossel and the others is the use of 1515 extrusions, rather 2020. The Cherry Pi (and I think the Griffin too) use magnetic rod ends, rather than ball joints. I've never used magnetic joints, but I like how simple Traxxas rod ends are.

That said, you can find vertexes for a 2020 Kossel on Thingiverse, and I've actually just completed modifying and printing the vertexes for my own Kossel 2020 build (soon to be on Thingiverse once I complete the carriages to match). I'm using T-Slot extrusions, and it differs from others by mounting the extrusions at a 45 degree rotation, so that V-Wheels can ride on the corners of the extrusion, just like the Kossel Clear...

Depending on the scale you're going for, I'd say go for 2020 extrusion. It's often a similar price to 1515, and it probably makes for a much more rigid frame (bigger vertexes, more surface area contact with the vertex). Whichever design you go for, they're all good, and you'll find that a lot of parts are interchangeable.

The Cherry Pi3 doesn't use magnetic joints any more but does still use steel balls (Look in the cherry pi thread for more detail) basically the rods are held in place by a spring loaded cord between the effector and the tower carriages on each leg. It works very well

Doug

Thanks for the info,

I have decided that I want to use 20x20 extrusion and vslot wheels and have a 300mm diameter bed with approx. 350mm build height, im guessing all of these machines could scale up to that. I also would really love to have good auto levelling. Im not sure about the Griffin, it looks like a great machine but there is very little in the way of pictures / videos of it working and what can of quality it prints.

There are many videos etc for the mini Kossel and the cherry pi iii and I am very impressed, I just can't decide which one to go with, I couldn't find build instructions for the cherry pi ii (im probably looking in the wrong places) and I'm abit unsure about have to drill holes etc in the steel balls for the effector.

I'd also like to (although im not sure how) use optical endstops, I have read that there are benefits for using these i.e. they cant stretch and rarely break and offer better precision (that's not my opinion its just what ive read)

Drilling holes in ball bearings is fairly easy. There are two main types of bearings, chrome steel and carbon steel. The chrome steel bearings are hardened all of the way through. Carbon steel bearings are case hardened and have a soft interior. Carbide drills work for both, but if you want to thread the holes, then you'll need to get the carbon steel bearings. This ebay seller has a good reputation and the drills are made by Kyocera: [stores.ebay.com] (I've ordered from him several times).

You can make a jig to hold the ball bearing by drilling a hole in a scrape piece of 1/4" steel (or aluminum) that is smaller than the diameter of the ball bearing. Put the bearing in the hole and add a heavy washer and clamp the setup down. There are lots of other ways to make a jig to hold the bearing securely, it depends on what your skill level is and what machines you have available.

You can purchase the 8mm ball bearing I use on Cherry Pi from various EBay suppliers already drilled. They are used in stop motion photography I think

Ah I didn't realise you could buy them pre-drilled, that certainly makes the cherry pi iii very tempting, Is there any kind of build instructions available for it? I know there is a thread all about it with lots and lots of pages on it (which I think is great) but im not sure if there is any build instructions in it.

Would it be an issue if I added a 300mm dia heatbed to the build?

There are no build instructions as such but all you need to know is in the thread and I can answer any specific questions for you on there as well. Better in the thread than PM as it benefits all. To go to a 300mm diameter you would need to go about 350 on your cross braces. If you go much taller than the standard 600mm towers you will probably need larger (2040) extrusions to combat twist, or brace the towers somehow. You will also need longer delta rods. I use 80% of the distance between tower centres. Look at my Larger Slice of Pi thread. There are alternative bottoms, tops and covers on there for 2040. All other parts are the same.

The CPIII is pretty easy to put together, you can use something like the T3P3 Mini Kossel build instructions as a general guide, and something like this for the extruder.

Regards,

Les

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Thanks for the replies,

I really like the Cherry Pi III and the support around it too, I think I need to sit down and read every page of the cherry pi thread, I am a bit confused by the different variants of the parts (magnetic/non-magnetic, some pictures show the arms with and without wire and springs attached), I don't know why but im not keen on magnetic parts on a printer, I can just imagine it coming apart. I would like to make the non magnetic version using something like an E3D head and incorporate auto levelling (not sure where the STL files are for that).

I will ask any further questions in the cherry pi thread.

Thanks

Just by way of clarification. The current Cherry Pi model is the IIIS. In all respects except the delta rod attachment it's the same as the Cherry Pi III. That III used ball magnets and home made metal 'sockets' to attach the rods. This design was ok upto 60 or 70mm/s faster than that and the rods sometimes came loose mid print. The IIIS was an attempt, so far successful, to remedy that. The IIIS uses 8mm drilled ball bearings from EBay as the rod ends. The 'sockets' are now printed into the relevant parts and a length of Spectra 100lb fishing line and a 79.4mm x 4mm spring, again from EBay, holds each set of rods in place. I now regularly print at 100mm/s and have not had any issues. There are, currently, two effector designs available. The first uses a JHead Bowden hot end and uses the tip of the nozzle as the Z probe via an integrated microswitch. The second, later design, dispenses with the Z probe and takes an E3D style all metal hot end. If you build the machine with a cold bed than the PSU will fit neatly under the bed. If you choose to go with a heatd bed then you will need an external ( I use an Xbox One) PSU. The thread has got really long but if you slog through it you will see how the design iterations have come about. All the parts are available either on Thingiverse [www.thingiverse.com] or as attachments in the various posts.

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Horse Renoir
Thanks for the replies,

I really like the Cherry Pi III and the support around it too, I think I need to sit down and read every page of the cherry pi thread, I am a bit confused by the different variants of the parts (magnetic/non-magnetic, some pictures show the arms with and without wire and springs attached), I don't know why but im not keen on magnetic parts on a printer, I can just imagine it coming apart. I would like to make the non magnetic version using something like an E3D head and incorporate auto levelling (not sure where the STL files are for that).

I will ask any further questions in the cherry pi thread.

Thanks

I never liked the idea of a magnetic connection either, which is one of the things that drew me to the CPIIIs. I am using stainless steel trace wire crimped, instead of the spectra braid. I even made a printed jig, so making them is a breeze. You just need to decide which hotend and which electronics to use. I have an effector design for the genuine E3D V6 and mounting brackets for the Smoothieboard. Don't discount a Duet for the electronics though, DC42 latest firmware now works with Deltas, and I could easily knock up some brackets for it.

Regards,

Les

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I think my question matches the thread so i just use it for my specific question in choosing a delta design:

I am also thinking about building a delta and the bigger slice of cherry pi sounded interesting to me. But i want to have a really heigh build volume of about 80cm.
So i was thinking to go with 30mm bosch-rexroth extrusions. I couldn't find any v-rollers for them? Has anybody experience with that? Is it worthwhile to go with even
bigger extrusions?

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tstone
I think my question matches the thread so i just use it for my specific question in choosing a delta design:

I am also thinking about building a delta and the bigger slice of cherry pi sounded interesting to me. But i want to have a really heigh build volume of about 80cm.
So i was thinking to go with 30mm bosch-rexroth extrusions. I couldn't find any v-rollers for them? Has anybody experience with that? Is it worthwhile to go with even
bigger extrusions?

Yes the parts if scaled correctly will work with 30x30 but how about goint with the 20x40 stuff (Add additional bracing if required) then the std parts will work

I myself am going to add some 20x40 extrusion vertical connected to the cross pieces and then enclose the whole thing in Ally sheet which should stiffen everything up

HTH

Doug

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dougal1957
Yes the parts if scaled correctly will work with 30x30 but how about goint with the 20x40 stuff (Add additional bracing if required) then the std parts will work

Well actually i have been thinking about 30x60 . Designing some new parts is part of the tinkering fun so i don't care if i have to redo them. I guess normal scaling
wouldn't work anyhow. If i don't find a v-roller for the bigger profiles thats probably the route i am going to choose.

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dougal1957
I myself am going to add some 20x40 extrusion vertical connected to the cross pieces and then enclose the whole thing in Ally sheet which should stiffen everything up

The ally sheet might help but i guess the cross pieces might not help to much with bending?

The Cross-bracing is not necessarily for bending, its for resisting a delta's biggest problem, torsion.

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tstone
couldn't find any v-rollers for them? Has anybody experience with that? Is it worthwhile to go with even bigger extrusions?

There are some wide rollers here that fit 8mm slot.

Regards,

Les

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The open build V Wheels fit 8mm slot too.

Hi Andy

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AndyCart
The open build V Wheels fit 8mm slot too.

Do you think that the v-wheels work on bosch rexroth extrusions too?

Best regards
Tim

Edit: I was confused due to the V-Slot extrusions at the openbuildspartstore. As far as i see the bigger slice uses rexroth extrusions so it should work.

Edited 1 time(s). Last edit at 02/12/2015 04:51PM by tstone.

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tstone
Hi Andy

Quote
AndyCart
The open build V Wheels fit 8mm slot too.

Do you think that the v-wheels work on bosch rexroth extrusions too?

Best regards
Tim

Edit: I was confused due to the V-Slot extrusions at the openbuildspartstore. As far as i see the bigger slice uses rexroth extrusions so it should work.

Not sure how well the mini v wheels would work on slot 8. I have some Motedis 30mm B-Type Slot 8, and the top of the slot is about 9.20mm wide, while the wheel does run in the bottom part it doesn't touch the top part. In comparison, with the 6mm slot, the wheel touches the top and bottom corners of the slot as shown in the following image...




Regards,

Les

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