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.

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