The search for the elusive X-axis idler rod

Preamble

I bought a P3Steel v4 printer, see P3Steel from Poland – A tale of despair, dismay and woe. The X-axis carriage with also laser cut steel parts. The X-axis idler rod which acts as an axel to the 608zz bearing was missing. This is my search to find it.

The part in question

These images show the part:

The width of the idler is shown here:

Width of the X-axis idler
Width of the X-axis idler

The thinner line, at the top of the photo, is the actual width as the end plate protrudes one of the side plates, by about 1 mm or 2 mm.

The image below shows a clearer image of the distance, b, between the outer opposing faces of the two plates:

The distance between the two opposing outer faces
The distance between the two opposing outer faces

Question posted on StackExchange

See Is the 8mm x 20mm bearing axle for the X-axis idler (of a P3Steel) a custom part?

Options available

There are the following options:

  • Use a bolt
  • Contact the Spanish designers to see if they can supply one – my supplier can not, they used a bolt
  • Make a rod

The dimensions

Of the X-axis idler, note that the top face is inset by 2 mm from the top of the edge plate. The bearing axel is shown in grey:

Dimensions of X-axis idler end
Dimensions of X-axis idler end

Of the bearing axle

8mm_smoothrod_x-idler

Dimensions:

  • Space between circlip and outer plate of plate, a
  • Distance between outer faces of plates, b
  • Diameter, D
  • Width of circlip groove, w
  • Distance between circlips, x
  • Overall length of rod, y
  • Distance from circlip to rod end, z

where,

  • a = 0 – 0.3, or 0.5 mm
  • b = 18 mm
  • D = 8 mm
  • w = 0.3 – 0.5 mm
  • x = 18.6 – 19 mm
  • y = 20 – 24 mm
  • z = 1.5 mm

Note that,

  • x = b + 2a
  • y = x + 2w + 2z

The part

I got this 7.8 mm x 40 mm pin for 10 baht in Ban Mo, Bangkok:


I have marked in it where a groove needs to be cut for a circlip, which is 18.5 – 19 mm from the pin head. It may also need to be cut to length, although this isn’t essential.

Then placed it in a drill


and while it span, I held an old hacksaw


next to the chuck, and wore a groove into the pin.


Once that was done, I went to fit the pin and bearing, into the X-axis idler end. However, the 608zz bearing is 7 mm wide, and a 628zz is 8 mm wide, but the cavity, in the X-axis idler end, is 12 mm wide. Therefore some washers are required. The 608zz bearing outer diameter is 22 mm, 628zz bearing is 24 mm, therefore a penny washer of 25 mm or 30 mm would be required to maintain the GT2 belt in place. As the washers are 2 mm thick, or 1.5 mm for these:

Penny washer data
Penny washer data

then that leaves 2 mm gap, when using a 608zz bearing, or a 1 mm gap, when using a 628zz bearing. So, for a 608zz bearing, one could use a thin 0.8 mm thick 16 mm washer between the penny washers and the 608zz bearing, on each side – so two 0.8 mm washers. If one is using a 628zz bearing then, in theory, the additional 0.8 mm would not be necessary.

Penny M8 washer:

Larger than 30 mm

Standard 16 mm thin M8 washer:

Standard 16 mm M8 washer:

However, a 30 mm washer does not fit very well as the edges of the washer will touch the end of the two nyloc nuts, which secure the side plates:

30 mm washer is too big
30 mm washer is too big

A couple of ultra thin washers/shims may be able to keep the 30 mm washer away from the nyloc nuts.

As the 608zz is 22 mm in diameter, then the 30mm washer gives a “lip” of 4 mm, which is a nice depth. Using a 25 mm washer would result in a lip of only 1.5 mm, which is rather small. A 28 mm washer would give a 3 mm lip, which is a fair compromise – however, these do not exist! It could be possible to file the washer, by spinning it (in a drill) and filing the edge down by 1 or 2 mm.  Of course, the depth of the lip may not matter, for a taught GT2 belt, but for perfection’s sake…

Looking at the flanged bearings:

  • F608zz the flange diameter is 25 mm (against the 22 mm bearing diameter);
  • F628zz the flange diameter is 27 mm (against the 24 mm bearing diameter)

On most flanged bearings the flange diameter ranges from 1.5 mm greater (F623zz) to 3mm (for the F608zz/F628z)z , giving “lips” of 0.75 to 1.5 mm.

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