Hello again everyone,

My first CNC design was, in hindsight, perhaps a little bit ambitious for a first build. After building one of the sides I realized that welding was the only realistic option and that my current workshop just wasn't big enough to fit the machine (and it would weigh too much for the floor).

Rather than wait for the workshop to be built I thought I'd come up with a new design for a more modest sized CNC machine that will fit in the space I currently have. There's not much to see yet but I was hoping to get a bit of feedback on the pulley arrangement for the x-axis as this is an area that I'm not very familiar with. Firstly some pictures...

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The frame is going to be all extruded aluminium if possible. The blue sheet forming the bed is 600x600mm to (hopefully) give a cutting area of 400x400mm. Z axis travel will be fairly limited, perhaps as little as 50mm, as this machine is being designed to mainly cut aluminium.

The x-axis rails are SBR16 although I could probably fit SBR20 if necessary. The rails are sitting on 60x90 heavy extrusion as sold by KJN. There's 180mm between bearing block centres.

The ball screws are currently spec'ed as 1605 with 16 tooth HTD5 pulleys on the end (with extra long end machining). The stepper will be a nema23 but I've not picked one out yet. The stepper is fitted with a 32 tooth HTD5 pulley to give a 2:1 ratio.

The stepper and the two idler pulleys are mounted on a 10mm aluminium plate. For build simplicity the idlers are used to take up the slack on the belt rather than the stepper. The stepper is mounted using stand off legs. The belt length (at central idler adjustment) calculates as 1736mm

The plan is to have this machine standing vertically, or perhaps wall mounted, so that the x-axis belt is at the top.

My questions so far...

  1. Does the belt make enough contact with stepper motor pulley? I'd guess about 12 to 15 teeth are in contact with the belt.
  2. How is the 32 tooth pulley attached to the stepper shaft? There's only 15mm of shaft on the stepper so I'm guessing it will have to be a taper lock (also Belting Online don't bore 32 tooth pulleys at 6.35mm).
  3. Where can I get idler wheels from? Neither Belting Online nor Bearing Station seem to do them. I'm tempted to follow Jazz and use bearings and penny washers...


Cheers :-D