Very Grainy Screens Help

I have a HP 3500 CP Printer, Rip Wasatch 5.1, Image 4 color but does not matter cause even 1 color is grainy.
Ink HP UV
Have tried stoccastic and digital mezzotint screens, stoccastic is better.
I bought the printer very used so I had to download the drivers from HP.
In my printer list it says "HP Designjet 3000 (600dpi)
I have used numerous profiles and have tweak them also. It gets a little better but not sellable.
Could it be the fact that it is only 600dpi, but what did they do years ago when this was state of the art?
Could it be the Pigment Ink?
I have used Photo paper and vinyl, same results.
This is an old printer and I am doing ok with it except for this.
Any help would be greatly appreciated

 

Its time to upgrade to an new machine.

Picture what happens when you through pepper onto white paper it looks grainy this is you machine.

To create smooth colour you need light colours. You may have heard newer machines have cyan and light cyan. The light colours are used to smooth out the grainy effect but also to increase tonal detail. As for the res this is also a factor but it really is the light colour the more colour your machine has ie 8 colour machine or 12 colour etc the better the quality.

 

The grain or rough appearance can come from a number of different factors. While you do have an older printer it should be able to produce fairly nice output. Most new printers have 8 or 12 inks, but does it really give a better proof. Depends on how you look at it. Most commercial printers want their proof to mimic their press. What good is it handing your customer a proof created on a 12 color printer when your press only has 4 colors? The press doesn't have a light magenta or a light cyan or a light black so you have to ask yourself how will your proof match your press. Well, that depends on the inks, paper, printer and RIP. The software is responsible for cutting back the colors while making the proof mimic what your press is capable of. Most of the HP models output at 600dpi, even the newer models so I don't think your issue is the resolution. You could try running a demo version of another RIP or possibly try changing the inks. If a newer RIP fixes the problem then you would probably have to spend some money to get a new RIP for an older printer which may not make much sense. Try making adjustments in your RIP or the inks to see how that affects output.