On Tue, 03 Nov 2009 21:07:50 -0800, David Nebenzahl
wrote:
In case I wasn't clear, the problem I was referring to was printing a
document on both front and back, where you first print the odd pages,
then run the stack back through on the other side and print the even pages.
Every non-duplexing HP LaserJet I've ever seen will **** up and jam if
you try to do this. The problem, as you said, is the curl imparted to
the paper by the fuser. I have had some success taking the first-printed
stack and "working" it vigorously to remove the curl, but it's a pain in
the ass, and not guaranteed to work.
Yep. You also have to let the stack cool down a bit. I also listed
some other problems that can cause paper jams when trying to print
double sided without a duplexer.... (cut-n-paste):
The printers expect the pages to be flat. Pages that have gone
through the printer tend to be slightly warped. That causes paper
jams. Remelting the toner on the back side of the page sometimes
causes the toner to stick to the rubber roller in the fuser, causing
exit jams. Paper doesn't like to slide smoothly off the stack in the
tray when there's printing on the back side. That's an especially bad
problem if you print a stack of paper, and then feed the stack back
through the printer again to print on the back side. The pages will
stick together. The rubber "feet" above the feed tray don't like to
push against printed paper, where the black areas are much slicker
than the unprinted white paper. It's usually not a problem with a
fairly new printer, but after the rubber feet get worn and slick,
things tend to slide.
Since there are other laser printers that don't have this problem, I can
only conclude that HP LaserJets have inferior feed mechanisms.
Yep, but there's a bit of a complexication. HP likes to built
printers that have a small footprint. That means that the paper
trays, which are always at the bottom of the pile, have to feed the
paper to the printer after making a 180 degree tight turn out from the
tray. The Panasonic 450(???) printer you mentioned had an externally
projecting paper tray, that allowed for a more straight line paper
input feed. That 180 degree turn is always a problem.
However, I do agree that HP could do a better job with their feed
mechanisms. The fix is rather simple. The typical Laserjet has the
absolute minimum amount of rubber in contact with the paper. Large
copiers have similar mechanism, but with much larger rollers on both
sides of the paper to maximize grip. They also have much thicker and
softer rubber feed rollers to maximize friction. If you want a really
reliable paper feed, it will look like a straight line offset press.
If you look carefully at the typical HP Laserjet, there are at least 5
feeds. I'll use the HP LJ 4000 as an example. The first is a simple
roller in the paper tray to get the paper started. After a 180 degree
curling turn, it goes to 4 D-shaped pickup rollers, which really do
the work. Under the paper is the separation roller, which supplies
pressure to the imaging drum. The paper then gets fed into the fuser
roller, and then to a series of exit rollers. Any one of these can
screwup and cause feed problem. Most common is the separation roller,
which is made of foam, getting clogged with toner. Next is the
polishing of the D-shaped pickup rollers from sliding across the paper
when the feed rollers slip slightly. The paper tray input roller
usually feeds correctly, but the paper can jam up against dirt and
filth on the tray in the area around the feed roller. Shredded paper
in the fuser assembly will usually stop the paper and cause a jam.
Exit rollers are usually fairly reliable, except when the fuser craps
out and the rollers get covered with toner.
And I do know what the hell I'm talking about: in a previous life I was
a printer (as in a real printing press, not desktop computer printers),
so I've dealt with lots of machines that eat paper.
Full disclosu I sometimes fix HP Laserjet printers. However, I'm
not factory trained or authorized. In the 1970's, I briefly owned a
commercial print shop. Mostly AB Dick and some Gestetner. I didn't
do the printing, but I sure got the complaints when they didn't work.
I also ran the college print shop and got some experience on hot lead
Linotype presses and Compugraphic (Harris) typesetters.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558