RepRap Builder

Fred's RepRap and FabScan Website

JUNE 2013

Cutting Rods and Waiting for Parts


June 2013

The basic idea of a RepRap, i.e. the principle of self-replication, is that you obtain the printed parts (everything of white plastic in image 5 on the home page) from a friend who has made him/herself a RepRap. After completion of a RepRap first prints to make are a new set of gears for the extruder (they wear and will need replacement) and a new set of printed RepRap parts for someome else to build his/her RepRap. In my case, having no friends with a RepRap, the construction of the RepRap started with buying the required printed parts on eBay from a seller in Spain. I was not very impressed by the printed quality of the parts: layer separations were present and needed to be dealt with using the hot knife blade and the hor air blower of the Dremel Versatip (see webpage about tools). Apparently a fast print job had been done with a large size extruder nozzle opening (0.5 mm or larger?).
Next step was acquiring 8 mm diameter threaded and smooth rods, nuts, washers and bolts from the local hardware shop.
Then cutting all rods to the required lengths:

Cutting the rods
Image 1: Cutting the rods ( LP 2013)

The following lengths had to be cutted:

Threaded rods:
1 x 450 mm threaded rod fot the low center rod;
2 x 450 mm for the top rods;
6 x 380 mm for the frame vertex;
4 x 300 mm for the lower rods on the front and back side;
2 x 280 mm for the Z-axis drive rods.

Because M8 stainless steel threaded rods usually come in standard lengths of one meter a total of six rods are required in the following combinations:
Rod one: 450 + 450 mm
Rod two: 450 + 380 mm
Rod three: 380 + 380 mm
Rod four: 380 + 300 + 280 mm
Rod five: 380 + 300 + 280 mm
Rod six: 380 + 300 +300 mm
All rods can be cut with a disc metal cutter. The remaining ends from cutting should be kept for making idlers.

Smooth rods:
2 x 400 mm for the X-axis;
2 x 410 mm for the Y-axis;
2 x 360 mm for the Z-axis.
All lengths can be cut from three rods of each 1 m length of smooth steel rod:
Rod one: 410 + 400 mm
Rod two: 410 + 400 mm
Rod three: 360 + 360 mm
Again t
he remaining ends from cutting should be kept for making idlers.

For cutting the rods I had constructed a number of (wooden) cutting jigs or guides which enabled fast and accurate cutting of all the required lengths of rods.

After cutting all rods ends had to be bevelled with the bench grinding machine and (for some threaded rods) the threads had to be reworked with an M8  thread cutting die.
Next steps were assembly of the RepRap frame. This was a relatively quick job, but prior to assembling the frame it was necessary to clean all 8 mm diameter openings in the ABS construction parts by reaming with a precision reamer. The reamer was obtained second hand on the internet and it took a delivery time of one week.  Also, prior to assembly of the smooth rods I needed to mount the linear bearings onto these rods and these bearings had been ordered from a supplier in China. It appeared that the linear bearings were travelling on a slow boat from China as it took over a month before they arrived.

The roller bearings arrived three days after ordering from Spain. A total of four type 608ZZ roller bearings (used in roller skates!) are required for the RepRap: two for the extruder and two for the idlers in the X- and Y-axes. Image 2 shows a 608ZZ roller bearing:

608ZZ roller bearing
Image 2: 608ZZ Roller bearing ( FRS 2013)

The use of idlers is as idle rotating belt guides and these are made of four washers, two nuts and one roller bearing. I found that the standard 8mm outer diameter (OD) washers were not suitable for constructing idlers but that instead a smaller OD 8mm washer had to be used.
Normally, an idler consists of a roller bearing on an axis with two washers at each side and it is compressed together with two M8 nuts. The function of the washers at one side are as follows: a smaller washer fixes the inner bearing to the axis and the larger 30 mm OD fender washer acts as a guide for the belt.
Image 3 shows the three different sizes of 8 mm washers:

8 mm washers
Image 3: 8mm ID washers with different OD ( FRS 2013)

For constructing an idler the left and the right washer will need to be used but for construction of the RepRap frame the washer in the center will need to be used for protecting the ABS parts from the nuts carving into the plastic.

Image 4 shows the smaller OD washer on a roller bearing and it can be seen that the washer covers only the inner ring of the bearing.

roller bearing
Image 4: Roller bearing with smaller OD 8 mm washer ( FRS 2013)

Image 5 shows the larger OD washer on the roller bearing and it can be seen how the larger washer prevents the outer ring from idling when compressed against the bearing.

Bearing with larger washer
Image 5 Roller bearing with larger OD 8 mm washer ( FRS 2013)

Finally, image 6 shows the assembly of an idler with the correct sizes of washers:

Idler assembly
Image 6: Idler assembly ( FRS 2013)

By the way, it is not a very good idea to start assembling the RepRap on the dinner table when you prefer to maintain a good relationship with your partner.


Last Updated on: Mon Nov 10 21:26:29 2014