Platen Gap vs Paper thickness setting - what is difference?

[narikin]

Can someone explain what the difference is?

I'm printing on large Platine rolls and have set the custom paper thickness pretty wide (0.5mm) which surely means the head will be adjusted higher, but I still get head strikes sometimes. I've shifted the Platen Gap up a bit as well, and that seems to help, also increased the vacuum, but is there any answer that will fix it. A big print ruined can easily be $75 of ink & paper in the trash.

afaik, a higher-than-necessary platen gap means a slightly less sharp image, is that right?

(Epson P20000)

[mearussi]

Just max out the head height, it doesn't really hurt except maybe softening your fine detail a little. Also, if I have any questions about paper thickness I put my calipers on it and do my own measurements instead of just trusting the data sheet. Paper thickness can vary a little from batch to batch.

[narikin]

Thanks.  My problem is that I go to a huge effort to make these XL images as sharp as possible (Phase IQ4, MF $$ lenses, advanced sharpening routines, native resolution, no interpolation, etc) so... really don't want to trash the wonderful detail by using a higher head height / platen gap than strictly necessary! 

I guess I got to keep nudging it till it reliably clears and stop at that.

[mearussi]

Thanks.  My problem is that I go to a huge effort to make these XL images as sharp as possible (Phase IQ4, MF $$ lenses, advanced sharpening routines, native resolution, no interpolation, etc) so... really don't want to trash the wonderful detail by using a higher head height / platen gap than strictly necessary! 

I guess I got to keep nudging it till it reliably clears and stop at that.

I understand, but what are you looking at these prints with, a magnifying glass? My suggestion is you just try a small section and see if you can really tell any difference, and if you're printing on canvas or matte paper you won't.

BTW, if you want the sharpness print possible switch to white film instead of paper. The 100% polyester "paper" is perfectly smooth  and so will show the finest detail possible whereas the texture in even the highest gloss paper will lower the resolution. It also has little if any paper curl making it much easier to mount. Its only drawback is that it does scratch easily, but the end results are worth the effort as it's almost like printing on metallic paper without the metal look. It does have OBAs though but if it's framed behind UV glass that won't matter.

[JRSmit]

The paper thickness setting also has an effect om the paper transport. What to consider is also the thickness the printer "experiences", which usually a bit more than measured with a caliper.

Head strikes are best controlled with platen gap. And yes too large a platen gap will reduce the sharpness. Also head alignment must be done with given platen gap.

With the canson platine paper it is wise to reduce the platen suction significantly.

[stockjock]

With the canson platine paper it is wise to reduce the platen suction significantly.

I'm curious why you suggest reducing the vacuum suction for Canson Platine?

[JRSmit]

The paper by itself is quite soft, therefore easily marked by the structure (rigdes between the plenum chambers) of the platen. Also when INK is applied it becomes even softer.

[narikin]

Head strikes are best controlled with platen gap. And yes too large a platen gap will reduce the sharpness. Also head alignment must be done with given platen gap.

With the canson platine paper it is wise to reduce the platen suction significantly.

Intersting and useful contribution Jan - thanks for sharing!

I too was confused by the suction point - it seems contradictory, but will happily try.

and an excellent point about Platen gap needing an alignment for very best printing.

The paper thickness setting also has an effect om the paper transport. What to consider is also the thickness the printer "experiences", which usually a bit more than measured with a caliper.
With the canson platine paper it is wise to reduce the platen suction significantly.

so you're suggesting going higher than the caliper measures - if I get 0.4-0.5mm Platine-type paper - set it at 0.6mm? or even more...

[JRSmit]

I measure with a caliper, and round up to , so of i measure 0.34 i would go to 0.4mm.
Most printers have paper thickness in multiple of 0.1mm
The new Epson surecolors actually have step size of 0.01mm, but also a re-engineered paper transport. So all new.;-)

[NeilPrintArt]

Here is a quote from Larry Kaufman (Epson Product Manager) posted on this forum in 2018 in response to the question of 'difference between platen gap and paper thickness'.......

"Platen Gap does not depend on paper thickness (in the vast majority of cases) it is based on paper type.
Paper thickness controls the dot timing of the printhead in high-speed, bi-direction mode so that both directional passes line up accurately.

A paper type that exhibits more curl or tends to buckle under high ink load should use a higher platen gap than one that lies flat.

Example: Single Weight Matte will use 2.4 (it can buckle), Premium Luster (260) will use 1.2 and Luster is a "thicker paper".

The objective of the Platen Gap setting is a safety margin for the print head, meaning no strikes on the media.

If you are using an Epson media then auto is a good way to go, if you are using a different media the setting will depend on the base Epson media you were told to use by that vendor.
In general 1.6 should be fine for Fine Art and Canvas materials, 1.2 for most photo, glossy and semi-gloss media and back to up to 1.6 for Baryta and Platine type media.

If you see a head strike (ink scuff on the media after the leading edge) increase the platen gap.
If strikes are occurring on the leading edge look at the margin settings, which are also based on media type"

Also...about suction setting with Canson Platine, I am today printing with that paper and getting 'ridge marks' from structure of paper path due to softness of paper and reducing suction helps (but does not eliminate completely) marks

[JRSmit]

In my opinion Larry Kaufman got it wrong. The platen gap is litteraly the distance of the head from the platen, regardless of the thickness of the paper. But Epson media types may have different platen gaps coded in. Paper thickness setting does have an influence on the paper transport, changing it will f.i. change the feed accuracy. It also has a key role in the head-aligent - as does platengap- . Think of it as focising your camera, it is about the distance the inkdrop has to pass to hit the paper.
Given the extremely small size of the drops and the needed accuracy of the placement on the paper, you have to set the paper thickness and platen gap properly and do the head-alignmnt with those settings. The 'auto' setting for platen gap is then an unwanted variabele, as you Will never know what gap it will choose.

[erik.brammer@me.com]

It would be very surprising to me, too, if the platen gap was not a function of media thickness. I am trying to find out what that function looks like.

Example from a recent printing exercise done on my relatively new Epson P900, so I am still learning:

I printed an A4 test sheet of Hahnemuehle Fine Art Baryta Satin and found head strikes on the trailing portion of the sheet. I had setup the paper as recommended by Hahnemuehle  in their handling instructions "HFA_EpsSC-P700_PK_HandlingInstruction_EN.pdf" packaged in the profile folder for that paper. I take it that the handling instructions are all the same for Hahnemuehle's gloss papers that use Photo Black (PK) rather than Matt Black (MK) - maybe my understanding is completely off here. Those handling instructions for PK tell us to choose media type "Epson Premium Luster".

I then used Epson Media Installer to look at some of the settings: Epson Premium Luster is defined with a thickness of 270 microns and a platen gap of 0.9 mm. Hahnemuehle Fine Art Baryta Satin has a thickness of 370 microns, so after my head strike situation, I am inclined to setup a platen gap of 1.6 mm which would be around the mid point between the settings for Epson Premium Luster and those for Epson Velvet Fine Art Paper which is the base media type recommended for thicker Hahnemuehle's fine art papers such as Photo Rag 308 or Ultra Smooth. These have a thickness of 480 microns, while Epson Velvet Fine Art Paper is defined with a thickness of 480 microns and a platen gap of 2.1 mm. So that midpoint setting for Hahnemuehle Fine Art Baryta Setting seems to make sense to me.

There is also some reading in German under the following 2 URLs:

https://www.photolux-shop.de/info/epson-drucker-papiereinstellung.html
https://www.photolux-shop.de/info/epson-media-installer-p700-p900.html

You can use deepl.com for translation - it usually does an excellent job in translating, much better than Google Translate based on my experience.

It would be great to create a database for proven settings for different printer models and media types from different vendors.

Best regards,
Erik

[erik.brammer@me.com]

I should correct myself - the Epson Media Installer offers the following platen gap settings:

0.9 mm
1.2 mm
1.5 mm
2.1 mm
3.5 mm
4.5 mm

So I have defined Hahnemuehle Fine Art Baryta Satin with a platen gap of 1.5mm

[JRSmit]

Your choice should work, the paper will show little swelling, but it is not perfectly flat. Zo IT culd becyou need to choose platen gap one step wider to prevent some slight head touching the paper occasionally.

[MfAlab]

Platen Gap is "gap between the printhead and the platen". This is written down in Epson Service Manual. That means the distance between the print head and the black support plate surface. It is not the distance between head and paper, but the default setting will change by paper types. If you leave it on standard/auto, it means printer will choose for you according to the paper type you use. See the "Platen Gap Determining Sequence" in attachment. In old days, Epson did not show actual values of platen gap setting. The numbers hided behind narrow, standard, wide, wider, widest. See the attached image 2, which is the PG Settings List in Epson 9900/7900 Service Manual.

Now we can set a specific platen gap value on newer printer models for custom papers. If you do so, that's not about paper thickness. The (platen gap) - (paper thickness) is real distance between head and paper. The platen gap is wider, the distance between head and paper is wider. Because of that, many manuals/user's guide/mechanics said it's head-paper distance just for simplification.

[erik.brammer@me.com]

Thank you, Kang-Wei Hsu, but I am afraid that this information tops up my personal confusion. In the second chart you attached, let's look at those columns:

1. Paper thickness, first entry: Either nothing specified, or up to 0.8 mm: So far, so good.
2. Menu setting: What menu setting does this relate to and where? On the printer? I think the P900 doesn't have such a menu item. In the driver? In Epson Media Installer?
3. Media table or printer driver platen gap setting: How does interact with column 2?
4. Platen gap value: That would be clear if I knew how to maneuver through columns 2 and 3.

For the time being, I think I will continue to use my "interpolation" approach based on the correlation between paper thickness and platen gap setting in the Epson media type definitions.

Cheers,
Erik

[MfAlab]

Thank you, Kang-Wei Hsu, but I am afraid that this information tops up my personal confusion.

Forget the old data and setting, you are using Epson Media Installer on newer printer. Just set the PG value you want to use.

I posted the table just for explaining Epson controls platen gap secretly in the past. The value changes by paper type and setting, that confuses users.

[erik.brammer@me.com]

Thanks for the clarification.