Conveyor belt as Y-axis

Hi,

I posted this earler on Mendel forum.

My mendel is still in pieces around the world ;-)
But an idea occurred to me while reading this blog:

charlespax.com

How about replacing the Y-axis with kapton conveyor belt on a static heated bed so that the conveyor belt movement replaces the Y-axis movement and when the piece is ready moves the ready piece away so that mendel could be used for continuous production. And even be used to print larger than bed pieces if over hangs can be printed.

My idea is a loop of kapton that has holes on both sides like tractor feed paper and sprockets that move it back and forth instead of bed. This would give less moving mass especially if the bed is heated.

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atorox

[finreprap.blogspot.com]

As already mentioned before this would of course require that the bed be twice as long in the Y direction as the height of the pieces that you want to print. Mendel is designed for 200 mm by 200 mm. With the kapton conveyor belt you would have to change this to 200 mm by 400 mm in order be able to print objects of the same size.

In addition you will need a strong vacuum to hold the kapton conveyor belt to the heated bed otherwise you will still get warping!

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

rhmorrison Wrote:
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> As already mentioned before this would of course
> require that the bed be twice as long in the Y
> direction as the height of the pieces that you
> want to print. Mendel is designed for 200 mm by
> 200 mm. With the kapton conveyor belt you would
> have to change this to 200 mm by 400 mm in order
> be able to print objects of the same size.
>

This I understand and I have a aluminum slab that is big enough 500x450 that I was planning to have milled for a heated bed or two.

> In addition you will need a strong vacuum to hold
> the kapton conveyor belt to the heated bed
> otherwise you will still get warping!

Would the vacuum be necessary if the belt is hold in tension with two axles that have sprockets?

And if vacuum is needed would a low vacuum made with aquarium pump or such be enough in this case?

I could have the bed milled with 5mm X 5mm gird of holes for vacuum like in some circuit board mills that I have seen. At least one of these had a regular vacuum cleaner that was used for both vacuum and removing milled material...

Problems I can see coming:

-How to make continuous belt form kapton?
-How kapton behaves if it is heated when tension? Will it stretch too much?

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atorox

[finreprap.blogspot.com]

atorox Wrote:
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> Would the vacuum be necessary if the belt is hold
> in tension with two axles that have sprockets?
>
> And if vacuum is needed would a low vacuum made
> with aquarium pump or such be enough in this
> case?
>
> I could have the bed milled with 5mm X 5mm gird of
> holes for vacuum like in some circuit board mills
> that I have seen. At least one of these had a
> regular vacuum cleaner that was used for both
> vacuum and removing milled material...
>
> Problems I can see coming:
>
> -How to make continuous belt form kapton?
> -How kapton behaves if it is heated when tension?
> Will it stretch too much?

I don't think the sprockets will be enough and an aquarium vacuum pump will certainly not be enough!

Take a look at nophead's HydraRaptor blog entry Suck it and see.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

rhmorrison Wrote:

>
> I don't think the sprockets will be enough and an
> aquarium vacuum pump will certainly not be
> enough!
>
> Take a look at nophead's HydraRaptor blog entry
> Suck it and see.

I have seen this but if the belt is kept in tension with sprockets and axles I was hoping that a lower vacuum would be enough to keep the belt flat. And on the other hand the vacuum can not be so strong that it hinders belt movement.

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atorox

[finreprap.blogspot.com]

Quote
atorox
I have seen this but if the belt is kept in tension with sprockets and axles I was hoping that a lower vacuum would be enough to keep the belt flat. And on the other hand the vacuum can not be so strong that it hinders belt movement.

Then you must have seen how huge his vacuum pump was and it was insufficient to hold down the kapton tape, so no - I don't think it will work since the force exerted by a large object on the outer edges is very strong.

BUT... build it and they will come.

In any case I don't think the addition of the vacuum will work much better than your sprocket drive alone.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

This seems to be a common misunderstanding. You cannot hold something flat by stretching the ends. It needs an infinite force.

Quote

When the film is flat any horizontal pull produces no vertical component at the centre, unless the centre is displaced upwards. Say we wanted no more than 0.25mm lift from a force of say 10N with a bed 100mm wide. A vertical displacement of 0.25mm at a distance 50mm from an edge would stretch the length by 2 * (sqrt(50^2 + 0.25^2) - 50), which is only 0.00125mm. So the mechanical advantage is about 200:1, so you would need a tension of 2000N just to get it nearly flat.

Keeping it flat to 0.1mm, a more realistic target, would require 100kN, even more for a 200mm bed!

A vacuum can only be as strong as one atmosphere and that is not enough. It certainly would make the film difficult to slide, and I would think sliding it would tend to break the vacuum.

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[www.hydraraptor.blogspot.com]

I have played around with wood CNC mill that has a vacuum table and it is enough to keep milled material on its place while milled at least in case of wood, plywood, particleboard and MDF-board and vacuum tables are used all the time in wood industry and I know that they have used vacuum table while milling film faced plywood but my experience has been that vacuum is not enough for plastic if you want to mill it in reasonable speed. In this table there are grooves for a foam gasket or blocs that have rubbery edges that keep the vacuum between the table and milled piece.

I would like to try making conveyor belt mendel either with or without vacuum but getting big enough piece kapton and the holes for sprockets in it probably will bee too difficult.

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atorox

[finreprap.blogspot.com]

WOOD does not contract.

The plastic exerts force on the kapton tape/film because it is contracting as it cools. The use of the heated bed reduces (but does NOT eliminate) this effect.

WOOD being milled does not exhibit this characteristic!

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

rhmorrison Wrote:
-------------------------------------------------------
> WOOD does not contract.
>
> The plastic exerts force on the kapton tape/film
> because it is contracting as it cools. The use of
> the heated bed reduces (but does NOT eliminate)
> this effect.
>
> WOOD being milled does not exhibit this
> characteristic!

How true ;-)

And still I can't get over the idea that if the belt is kept tight over the bed and a low vacuum is added inth equation the belt and extruded plastic should keep straight enough.

But I am/was hoping that conveyor belt would be feasible......
or at least doable.

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atorox

[finreprap.blogspot.com]

Quote

And still I can't get over the idea that if the belt is kept tight over the bed and a low vacuum is added inth equation the belt and extruded plastic should keep straight enough.

It's a fact, get over it What don't you understand about the simple applied maths I presented above?

Think of a guitar string. That is under very high tension but you can easily fret it and displace it by plucking it.

Can you think of any taught film or string that you can't displace the middle of with ease? It is why all washing lines, power lines, etc, hang in a catenary. Only an infinite tension will pull them straight.

Now think of a piece of ABS 20mm thick. It wants to curl up maybe 0.25mm. To hold it down you need to apply as much force as it would take to bend 20mm thick ABS. When it is cold that force is enormous but when the bed is heated is is a lot less, but still more that 15 lbs/square inch at sharp corners.

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[www.hydraraptor.blogspot.com]

I think I understand the math and I understand that neither tension nor vacuum is able to keep belt straight when stressed but could this conveyor belt with heated bed be used to get usable pieces that have warping like pieces printed on unheated bed?

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atorox

[finreprap.blogspot.com]

With a strong vacuum I was able to make objects that were usable, but had curled corners. When you build on an unheated bed you get a warped underside. With a heated Kapton be the underside is flat apart from the corners curling up.

If you are only interested in self replication, rather than a generally useful machine, then you could just design all your parts to not have sharp corners.

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[www.hydraraptor.blogspot.com]

The need for a rigid bed keeps coming up, which doesn't work well with the ideal of a conveyor belt that we can print on forever.

So a segmented belt (clamped on the edges when printing) comes up. Similar to your (nopheads) thin steel sheet held down by magnets, but cut into sections so it'll roll around the ends. But that will leave lines on the underside of the part when printing is done. And a segmented belt has other challenges.

How about a "belt" with exactly two segments, each the size of the normal print bed. The would be swapped back and forth, with the action of pulling them back in (but not the act of pushing them out) bending them slightly, enough that the now cool parts detach and are swept off into the bag under the printer. The thin material would cool quickly, and the central aluminum bed would stay hot.

The next logical step after having several exchangeable thin steel print beds. i.e. have only two, with a automatic part removal mechanism. Still a technically challenging design, but might be actually workable.

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I'm building it with Baling Wire

atorox,
great idea, but a flexible belt will likely never make it for the reasons that nophead and others are saying. When the ABS piece begins to harden and shrink, it exerts a strong upward and inward force. When the Kapton tape is glued onto the bed, especially a heated bed, the shrinkage is reduced and the forces are transferred from the Kapton tape to the bed. To make a conveyor belt bed, I suggest you make one like a tank, with 3 or more heated beads linked together. Then, when you have finished one piece, the group of plates advances one, the formerly active plate now faces downward, and the new plate is in the working zone. If you don not heat the one that just finished, but heat the current one and preheat the next one up, then the pieces will tend to pop off as the aluminum rapidly shrinks. Also, someone else has found that blowing cold air over a just finished piece makes it pop off.

Three or four plates would be permanently mounted to a motor and pivot. 5 or more and you could put hinges between each plate and rotate them like a rigid conveyor belt. With 6, you can have the exit plate level also, although I think angling it down to have parts cool, pop off and fall into a receiving bin.

Mike

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Team Open Air
Blog Team Open Air
rocket scientists think LIGHTYEARS outside the box!

I always blow cold air to cool my bed, but the parts never pop off of their own accord. Sometimes I can snap them off by hand, other times I have to flex the bed or use a hammer.

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[www.hydraraptor.blogspot.com]