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300mm PVC/acrylic tube as a shell

Posted by lhartmann 
300mm PVC/acrylic tube as a shell
August 28, 2017 05:35AM
I was thinking about building a delta printer inside a 300mm tube, using it both as structural support and heated build chamber.

PVC is really cheap and acrylic would look really nice. The second is 6x as expensive, but when diluted over the total cost of the printer it is probably worth it.

Anyways, I don' want to redesign the entire mechanical system. Which open-source delta would be a good starting point?
Re: 300mm PVC/acrylic tube as a shell
August 29, 2017 10:43PM
You want to build a printer inside a closed tube? That's like building a ship_in_a_bottle challenge.
Do have the machinery to cut and drill the tube accurately?
You could build a delta with alu-extrusions and linear rails first. Then check if such tube would leave enough clearance for the carriers and rods to add the tube in a slide over fashion.
Re: 300mm PVC/acrylic tube as a shell
August 30, 2017 08:28AM
neat idea, maybe you find a way of securing it to the frame during printing and take it of afterwards as a stabilizer of sorts
Re: 300mm PVC/acrylic tube as a shell
August 30, 2017 09:00AM
Actually the tube was supposed to replace all the aluminium extrusions, a PVC tube that thick is quite rigid.

The tube would also be open on both ends:
- The bottom you place over the printbed when in use. You get a removable printbed as a bonus, but requires auto bed levelling.
- The top should be a cover to hide the filament spool(s) inside the printer. Bonus: Heated filament storage for PVA/Nylon. Maybe not good for PLA....

Not sure it would be nearly as hard as a ship-in-a-bottle, but it is a good analogy. Assemble everything you can outside, then put it in. Most parts that need handling then would be close to one of the ends of the tube, so easily accessible.

Not sure how accurate the cuts and drills would have to be...
Re: 300mm PVC/acrylic tube as a shell
August 30, 2017 11:11PM
When you want to go without aluminum extrusions, you'd screw the linear rails right into the tube, but then the carriers and rod spacing would have to be very narrow. Or you'd have to print some posts to mount the rails onto.
Re: 300mm PVC/acrylic tube as a shell
August 31, 2017 03:41AM
I was thinking something like this for the bottom supports. 3x M3 bolts+nuts, 2x 8mm rods, 2x 623 bearings on the center for a pulley.



I was just wondering how far apart should I make the 8mm rails so I could use other printer's parts with minimal modification.
Also where exactly to place the belt bearings.
Re: 300mm PVC/acrylic tube as a shell
August 31, 2017 10:51PM
I see a minor problem with your bottom bracket:
If you try to clamp the 8mm rod, the radius of the bracket won't be true anymore. The more you clamp it, the more it will be pushed away from the shell. That would lead to inaccurate rod positions.
Re: 300mm PVC/acrylic tube as a shell
September 07, 2017 01:47AM
I like this idea, assuming you can precisely cut the holes you need to mount the linear components and presuming your tube is actually round, or if not you can measure and compensate for any imperfection in the tube. Seriously consider using rails though, as they are inherently stiffer and straighter than rods. Mounting them to the inside of the tube would be quite easy to do.

Edited 1 time(s). Last edit at 09/07/2017 02:00AM by DjDemonD.

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Re: 300mm PVC/acrylic tube as a shell
September 07, 2017 10:08AM
300mm tube would have a small (tiny) print area. You may be able to get offcuts of larger pipe from a company that does underground piping.

+1 on using rails.
Re: 300mm PVC/acrylic tube as a shell
September 07, 2017 10:15AM
Maybe making it small might make it more likely to be accurate and perhaps the tubing more likely to be accurate. I have a microdelta with a 100mm print bed but it's surprising how many things it prints whilst the 330mm x 460mm kossel Xl sits quietly nearby.


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Re: 300mm PVC/acrylic tube as a shell
September 07, 2017 10:29AM
When you say rails you mean like hywin or v-slot extrusions?

Anyways, that is a great idea. They are both probably much easier to mount. We could just screw directly to the tube, no printed mounts required.

As for the tube diameter I mentioned 300mm for it is easy to get here. If we use a parametric design tool such as Fusion 360, FreeCAD or OpenSCAD, then nothing stops us from changing the diameter to match any tubes we get.
Re: 300mm PVC/acrylic tube as a shell
September 07, 2017 10:57AM
Yeah Hiwin, MGN12H or similar, I have it on good authority the ones from robotdigg are very good and cheap. Basically, the best linear motion so far for 3D printers are rails, then v-slot and rollers (if good quality) then rods.


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Re: 300mm PVC/acrylic tube as a shell
September 07, 2017 12:19PM
Yup we have a PCB CNC mill based on something that looks like MGN12, it is crazy accurate! Pricewise, though, a single 500mm guide with skate is as expensive as all three columns and rollers using 20mm V-slots.

Can we really use all the extra accuracy of the rails on a 3D printer? Feels kinda weird attaching high end linear rails on a sewer-rated PVC pipe.
Re: 300mm PVC/acrylic tube as a shell
September 08, 2017 12:34AM
Forget PVC pipe! This design deserves to be seen through Acrylic pipe. It's also more likely they try to manufacture them accurately.
Maybe they use an injection mold for them instead of an extruder?

Edited 1 time(s). Last edit at 09/08/2017 12:35AM by o_lampe.
Re: 300mm PVC/acrylic tube as a shell
September 08, 2017 12:46AM
I am quite excited about this idea, lhartmann - would you be offended if I built something like this also? We could share ideas....

Just looking at prices for 300mm diameter acrylic tubing and were talking £150+
I think the tubing is going to have to be salvaged rather than new, sure its a simple frame idea but not at £150 plus maybe £45 for 3 rails, my microdelta with two printed parts and 3 rails is a simpler/cheaper frame.

Edited 2 time(s). Last edit at 09/08/2017 12:51AM by DjDemonD.

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Re: 300mm PVC/acrylic tube as a shell
September 08, 2017 02:26PM
Pricing is exactly why I considered PVC tubes, they are 1/12 the price of similar acrylic ones: R$ 600 buys 6m x 300mm x 4mm PVC, or 1m x 300mm x 2.5mm acrylic.

Maybe building most of it in pvc, and a 20cm section on acrylic as a window on the base? Anyways, PVC + sandpaper + spray paint yields some nice looking things too.

If I wanted to keep this idea to myself then I would not have posted it on the forums. Collaboration was the intention all along. :-)

Can we get this done by just redesigning the rail+stepper mounts? What carts an extruder mounts could we import into this project?
Re: 300mm PVC/acrylic tube as a shell
September 08, 2017 07:46PM
Doing some modelling on OpenSCAD... I have a feeling we could hide the belts inside the V-slot profiles, just using a GT2-16 pulley on top and a couple of 623 bearings on the bottom (or one of those toothed idlers). This should put the belts deep enough to clear the rollers, and would make it look like the carriages are moving by themselves.



Also found this guy on thingiverse that used PCBs as carts/effector mounting plates. Neat idea, PCBs are rigid and have a low profile, which is useful given the diameter limitation. He did not take full advantage of his concept, though. LED lighting would have been a really nice feature.
Re: 300mm PVC/acrylic tube as a shell
September 08, 2017 08:45PM
Quote
lhartmann
...
Also found this guy on thingiverse that used PCBs as carts/effector mounting plates. Neat idea, PCBs are rigid and have a low profile, which is useful given the diameter limitation. He did not take full advantage of his concept, though. LED lighting would have been a really nice feature.

I got inspired by dc42's smart PCB effector. My version is dumb.
Re: 300mm PVC/acrylic tube as a shell
September 08, 2017 09:00PM
Could always cut out a section between the X and Y towers for a flat or even curved piece of acrylic sheet. Going to need a door to pull the parts out of and to get to the effector for filament changes anyways.
Re: 300mm PVC/acrylic tube as a shell
September 08, 2017 09:05PM
Quote
kasom
Quote
lhartmann
...
Also found this guy on thingiverse that used PCBs as carts/effector mounting plates. Neat idea, PCBs are rigid and have a low profile, which is useful given the diameter limitation. He did not take full advantage of his concept, though. LED lighting would have been a really nice feature.

I got inspired by dc42's smart PCB effector. My version is dumb.

If yours is dumb, then mine has to be....refrain from using the wrong word here....so how about dumber?


Re: 300mm PVC/acrylic tube as a shell
September 08, 2017 11:37PM
Placing the belts inside the extrusion is definitely possible. ( see D-BOT CoreXY )

Screwing the extrusion directly to the tube wall, might stress the pipe. Tighten it differently at one of the towers could end up in an egg shaped printer.
Re: 300mm PVC/acrylic tube as a shell
September 09, 2017 12:59AM
Personally I would go for linear rails rather than wheeled carriages on extrusion, they are simpler, more accurate in my experience, and they would give a slightly bigger build space. You might need a thin strip of something between the linear rail and the tube, to keep the edges of the linear rail sliders clear of the walls of the tube. Maybe a series of printed spacers, with one side curved to match the tube.

This construction reminds me of the Unibody of the Tiko delta that was on Kickstarter AFAIR.

Edited 1 time(s). Last edit at 09/09/2017 01:00AM by dc42.

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Re: 300mm PVC/acrylic tube as a shell
September 09, 2017 02:35AM
Yes it certainly does, I'd envision it with a "door" cutout at the base, all the motors and electronics in the top.

Drilling the holes in the tube using a cnc would be great, but maybe as a cheaper alternative we can model where we want the holes then 2d print a paper template to wrap around the cylinders to mark the holes.


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Re: 300mm PVC/acrylic tube as a shell
September 09, 2017 02:50AM
Quote
o_lampe
Placing the belts inside the extrusion is definitely possible. ( see D-BOT CoreXY )

Screwing the extrusion directly to the tube wall, might stress the pipe. Tighten it differently at one of the towers could end up in an egg shaped printer.

Why use extrusion at all otherwise it's a 2020 frame printer with a tube over it rather than being a tube frame printer?


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Re: 300mm PVC/acrylic tube as a shell
September 09, 2017 04:27AM
Yes the idea is pretty similar to the tiko 3d, but without the fancy design and kickstart scam. I got to it while struggling with a heated chamber for my el-cheapo i3 clone, i saw a huge PVC pipe on a hardware store and thought it would make a cool heated delta.

Originally I thought about no doors on the base, maybe not even rails all the way down. I was thinking of having the print bed detached from the main body, and connected only through gravity. Much like the tiko again, except I wanted a heated bed for ABS.

extrusions are not for support, just for linear motion. I guess one could try just rollers and springs to keep them against the PVC... Maybe a second delta "ineffector" upside down connected to the same carts, and a rubber strap pulling the effectors together? 3 aluminium flatbars could then be used as guides, and 4 bearings on each cart should keep them stable by rolling against the PVC-flatbar joints.

Another crazy idea is Delrim. I've seen people use it as anti backlash nuts on cnc machines, so I think it can take quite some stress. Maybe this plastic could make a good sliding cart directly over aluminium/PVC.

Anyways I like the idea of getting a few more mm in build volume, that the hiwin rails allow over vslots... If we ditch the pcb cart then the magnet ball joints may even be mounted a little closer to the tube walls. This would require the belts to run outside the carts, not on their face, but should be an easy enough change. Is 150-170mm build diameter realistic?

@kasom: Hello "this guy." smiling smiley
Re: 300mm PVC/acrylic tube as a shell
September 09, 2017 06:09AM
There are some "inner roller bearing guides" at robotdigg.
The'd probably allow you to save even more build space.

Question to Delta kinematic experts: Is it possible to mount two rods per tower with a vertical distance instead of the typical horizontal pattern?
That's three rods in a bottom plane and three rods 40-80mm above. The heatsink and fans etc. on the effector use this vertical room anyways.



PS: added a quick sketch to make it clear
@lhartman: let me know if you want to keep this OT out of this thread, but I feel a slim carrier and effector would suit here well?

Edited 2 time(s). Last edit at 09/09/2017 06:24AM by o_lampe.
Re: 300mm PVC/acrylic tube as a shell
September 09, 2017 06:20AM
I was considering that vertical offset of arms too. It would work on the carriages, but if we use regular ball joints then the hotend would spin freely around its own axis, changing height in the process. In other words, it would be underconstrained.

You could fix it if one of the arm sets was coupled with regular bearings, free to rotate vertically but locked horizontally. Math would deviate from original deltas, though, since the effector would now be rotating around the modified rail.
Re: 300mm PVC/acrylic tube as a shell
September 09, 2017 06:34AM
You are right, there is a twist in that idea ( pun intended )
You can't lock it with regular bearings, the DOF is required for printing.
Re: 300mm PVC/acrylic tube as a shell
September 09, 2017 06:44AM
ONE arm with regular bearings on the effector.
TWO arms with ball joints on the effector.
ALL arms with ball joints on the rails.

Edited 1 time(s). Last edit at 09/09/2017 06:49AM by lhartmann.
Re: 300mm PVC/acrylic tube as a shell
September 09, 2017 08:04AM
Just wondering what vertical stacked arms does for you? It won't make the effector smaller.

I was thinking might be quite cool leaving the bottom of the tube open and essentially just placing the printer over a bed/table/piece of glass/tshirt whatever you want to print on. With decent z probe and auto calibration this works. It should be heavy enough not to move about.

About rails/extrusions absolutely no need to extend them to the base of the tube printer they only need to start at approximately 1/3 to 1/2 of the arm length above the bed level,depending on how close to the towers/rails you want to be able to print.

Another thing I considered on the microdelta was having the motors mounted to the rails, you can fix the lower pulley to the rail as well. This cuts down on fixings and hardware required, you can even incorporate an endstop bracket also.



Sorry for diagram best I could manage on a phone with my finger.

Edited 4 time(s). Last edit at 09/09/2017 08:34AM by DjDemonD.
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