5/16 instead of 8mm

Hi guys.

I have a printed set for 8mm rods/bolts, but im having some issues getting that size for a good price. Imperial threaded rods are cheaper, so, i was thinking about using 5/16 threaded rods/bolts insted of 8mm ones.

It would have any effect on the printer?, its really a low diameter difference... Maybe i can compensate that difference with teflon tape?

Edited 1 time(s). Last edit at 08/18/2012 11:55AM by nic0laz.

For the threaded rod 8mm vs 5/16" makes literally no difference. For the smooth rods 5/16" will work, but will not work with LM8UU linear bearings. You would have to have bearings or bushings made specifically for 5/16" rod.

8mm smooth rods are no trouble to come by!

Thanks!

Hi nic0laz:

I use 5/16 threaded rods and nuts. However the 5/16 SAE washers were too big. I had to order M8 washers from McMaster. I got the rods threaded rods and M8 drill rod (also very cheap) from Enco. It was by far the cheapest source. For the z axis drive I used stainless M8 rod, since only a little was needed, and the thread quality is so much better. Check out my BOM and build instructions for the stock numbers. Just search for "Simplified Ball Bearing Mendel" to find it. Also, Enco has free shipping every month with a special code. Look on the machinists BBS to find it. I usually look on the one that Home Shop Machinist magazine runs.

john

For the Z-axis you may have to alter the steps in your configuration.h

I used Josef Prusa's calculator website

Then I went into my configuration.h file in the arduino .pde file and found this part:

//// Calibration variables
// X, Y, Z, E steps per unit - Metric Prusa Mendel with Wade extruder:
#define _AXIS_STEP_PER_UNIT {80, 80, 3200/1.25,700}

Then I commented out the second line and made the adjustment and now it looks like this:

// SAE Prusa Mendel with Wade extruder
#define _AXIS_STEP_PER_UNIT {80, 80, 2267.718,700}

This worked for me.

Edited 1 time(s). Last edit at 08/20/2012 02:58PM by a_shorething.

a_shorething's reply was correct for 5/16th rods. However, if you want to go even more specific and potentially make a miniscule difference in print quality, use 2267.718321038048.

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Charles S.
Software Engineer
Prusa Mendel I2, RAMPS 1.4, Marlin 1.0 R2, Pronterface, Slic3r

heh heh. Nice. I think I need to update my files. I didn't think more than 3 decimal places would make a noticeable difference, but I will defer to the software engineer every time.

I built the basic frame with 5/16 because Metric is expensive in the US -
5/16 is readily available at ACE Hardware.

All three moving axis are 8mm rod & threads at 1.25mm pitch. Because
I have built to also use as a 3D Mill; both the x & y axis rods are 12mm with
other structural changes for strengthening.

I found McMaster-Carr on www.mcmaster.com in the US a good place
to source Metric smooth and threaded rod.

The Metric lateral bearings I bought cheaply on eBay with free shipping:
The 608 bearings from a local skateboard shop.

Edited 1 time(s). Last edit at 09/09/2012 12:10AM by Scrachbuilder.

Big thanks to you guys. Saved me from having to post to find the answer, as I am running 5/16 rod and my 10mm test is only ~7mm.... That adds up after a few!