Calibration

[twofieros]

How difficult will it be to calibrate the peachy printer? The FAQ states any container can be used for the resin bed but I see there could be difficulty in calibrating the Z axis if the vessel isn't a consistent volume as the resin rises from the water drip. For example. If the vessel was shaped like a V then the z axis change per drop will be less as the water rises to the top. It seems the ideal solution is something like a U with a flat bottom but then X and Y can change based on the height between the peachy and the resin surface. I get how this printer can print large items with a different sized container holding the resin but how is it calibrated for a change in the resin reservoir.

Having a print resolution of .1mm is fantastic only if the printer can be calibrated to the same tolerances.

[Spelljammer]

It is my understanding that the vessel size and shape can be put into blender so the Z height is always properly calculated.

[stringray]

I think the problem is a bit more complicated. Not only the size ( actually surface area ) of the container but also the volume of the printed object as this reduces the volume therefore the thickness of the resin. My understanding is
- peachy hangs above a container that has a layer of resin that will float above salt water
- the laser hardens the resin wherever it shines
- salt water is 'dripped' into the container at a constant rate and raises the resin so the next layer of the object can be drawn/printed
- by counting the drops, and knowing the volume of each drop and size of container, the current height of the resin can be calculated
Setup:
1. I want to print a solid sphere of volume 10 cubic cm, ie. 100ml
2. My container has surface area of 100 sq cm
3. I pour 110ml of resin in container, so the resin is 1.1cm thick
4. As the print progresses the thickness of the resin layer reduces, halfway it is only 0.6cm thick and towards the end it is only 0.1cm
Question:
a. How do you envisage calibrating the system for the increase in Z-axis by each drop
b. How much of the initial 1.1cm depth of the resin does the laser harden
c. Does the thickness of the hardened layer reduce as the resin is consumed?
d. How do you compensate for the usage of the resin during printing?

[gillza]

I think the problem is a bit more complicated. Not only the size ( actually surface area ) of the container but also the volume of the printed object as this reduces the volume therefore the thickness of the resin. My understanding is
- peachy hangs above a container that has a layer of resin that will float above salt water
- the laser hardens the resin wherever it shines
- salt water is 'dripped' into the container at a constant rate and raises the resin so the next layer of the object can be drawn/printed
- by counting the drops, and knowing the volume of each drop and size of container, the current height of the resin can be calculated
Setup:
1. I want to print a solid sphere of volume 10 cubic cm, ie. 100ml
2. My container has surface area of 100 sq cm
3. I pour 110ml of resin in container, so the resin is 1.1cm thick
4. As the print progresses the thickness of the resin layer reduces, halfway it is only 0.6cm thick and towards the end it is only 0.1cm
Question:
a. How do you envisage calibrating the system for the increase in Z-axis by each drop
b. How much of the initial 1.1cm depth of the resin does the laser harden
c. Does the thickness of the hardened layer reduce as the resin is consumed?
d. How do you compensate for the usage of the resin during printing?

a, c, d) I think assuming that the volume of the non-cured resin and cured resin stays the same it will not matter whether the layer of resin shrinks. The shrinking of the resin layer will be compensated by the increase in the salt water layer once the object is submerged layer by layer in the salt water. We only care about a total volume and assuming that all resin cures and does not expand/shrink the total volume pre and post curing will stay the same. Hope it makes sense, sorry for cumbersome explanation.

[Slatye]

a. How do you envisage calibrating the system for the increase in Z-axis by each drop

There's probably an easier method, but the simplest way I can see to do it is to just drop a ruler in the container, let it drip until the water has risen 10cm or so (the bigger the better), and count how many drops that took. If you can get it accurate to 1mm (should be fairly easy) over a 10cm total rise, that's 1% height accuracy - which is probably fine for most things.

b. How much of the initial 1.1cm depth of the resin does the laser harden

That'll probably be somewhat adjustable. If you scan super-fast, you get a very thin layer. If you leave the laser pointed at one spot for two hours, you end up with a very thick layer.

c. Does the thickness of the hardened layer reduce as the resin is consumed?

Unlikely, unless the resin layer floating on the water is so thin that the printer can't actually reach its standard layer thickness. Obviously the solution to this is to start with more resin.

d. How do you compensate for the usage of the resin during printing?

As gillza has said, that probably won't actually be a problem. The solidified resin still occupies volume in the bath, just like the non-solidified resin did.

If it is an issue (indicating that the resin shrinks or expands when solidified) it should still be fairly straightforward to fix. The software knows how much resin has been solidified, and therefore knows what volume change has occurred. If it knows the surface area of the liquid in the print container, the true height deviation is trivial to calculate.

[Compro01]

There's probably an easier method, but the simplest way I can see to do it is to just drop a ruler in the container, let it drip until the water has risen 10cm or so (the bigger the better), and count how many drops that took. If you can get it accurate to 1mm (should be fairly easy) over a 10cm total rise, that's 1% height accuracy - which is probably fine for most things.

Or assuming a constant drop volume, just divide that by the area of the container base (Assuming a near-perfectly rectangular container) to get the Z-level increase per drop.

[nka]

I saw some talking about using a ultrasonic device to confirm/check the height.

[stringray]

That'll probably be somewhat adjustable. If you scan super-fast, you get a very thin layer. If you leave the laser pointed at one spot for two hours, you end up with a very thick layer.

I still see a problem with the Z-axis resolution
Say I'm printing an object that has a 10cm square base and part way up I want a 1cm square post in the middle.
Also say the drip rate is one per second.


Initially, the laser covers the 10cm area in one second, say this hardens 1mm of the resin
When we get to printing the 1cm post in the middle the laser now covers the area in 0.1 seconds to harden 1mm of resin.
What does the laser do for the remaining 0.9 seconds?
Can it be switched off ?
If it continues to overprint the same area then the thickness of the harden resin will be > 1mm, potentially 10mm
Same problem if you slow the laser to 1/10 speed to cover the 1cm area, each spot now gets 10 times longer exposure.

[Slatye]

I'm not sure whether the laser can be turned off, but if it can't then it'd be easy to just put a little metal target outside the print bath to act as a beam absorber. When you don't want the laser to be hardening any resin, you just point it at the metal target. A 20mW laser isn't going to cause any damage to that no matter how long it stays there; in fact you could probably make the target out of cardboard and still have no damage.

[nka]

I think it will be easier to turn it off. It's just cutting the power of the laser (not the whole assembly) !