Anyone have a good source for 8mm smooth rod for the Prusa Mendel? In my town I get this look of incredulity: “Metric?!?”
McMaster.com is where I get it from.
@Theo_Walker no, 5/16" will not work.
5/16 works for me. I live in metric world but got hold on some really cheap 5/16. Printed down to 0.05mm without any trouble. The reason it works is that the linear bearings/bushings will never be mounted exactly straight, so the lock on to the rods just fine.
I’ve seen various people report that their LM8UU would fail and lock up on the undersized rod or show too much play. Then they switched too true 8mm rod and their machines started running properly again.
Either way, the lifespan of any bushing/bearing will be severly degraded on undersized rod since a bushing will only have a line of contact instead of an contact area and wear down heavily on that line. Bearings won’t have enough ball rows transferring the (albeit small) forces, and with the bearing mounted “diagonally” to compensate for play, there will be very uneven loading on the whole bearing assembly.
5/16" might work for you but 8mm just works for everyone.
Even though i live in Germany and Mcmaster would be a PITA to order from, i’ve looked at their pricing a couple of times and their 8mm rod is very reasonably priced. There’s no reason to go for 7.9375mm rods instead.
5/16 will NOT work. It is absolutely incorrect, and they don’t make linear motion bearings for such rod.
I, personally, ordered 8mm precision ground 17-4PH from Amazon.com - it comes amazingly straight, tolerances are right on the money, it’s stainless so it won’t corrode, and 17-4PH is slightly harder than 304 stainless so you won’t wear grooves in the rod with the LM8UUs.
$32.65 for 6ft of the stuff, cut it to-length with a hacksaw (get a groove started with a cutoff wheel for a dremel is usually my suggestion, in order to keep the hacksaw from jumping around)
Quite often I find that it is just dumb luck that my printer works at all
This is the rods I use: http://uk.farnell.com/duratool/7090500/ss304-round-bar-5-16-pk3/dp/7090500
“Either way, the lifespan of any bushing/bearing will be severly degraded on undersized rod since a bushing will only have a line of contact instead of an contact area and wear down heavily on that line.”
^This is exactly what my experience has been with 5/16 rod. I sanded down the grooves that had built up in my rods a week ago, and they are already coming back. I purchased the rod Anthony linked above and I’m looking forward to replacing my existing rods.