Sunday, 28 February 2010

Trapezoidally $crewed

Revisiting the threaded rod, I had a look at Roton and eBay to get an idea of options and prices.
  • A trapezoidal screw with nut and flange from Roton gives 3mm effective pitch and comes to around US$90 plus shipping for 1000mm.
  • A ballscrew with ball nut and flange from Roton gives 12.7mm effective pitch and comes to around US$252+shipping.
  • eBay has varying offers, but it looks like AUD $80 up for trapezoidal or ballscrews with nuts is about what you need to expect to pay. They're are shipped from overseas, so damage & claims risk are higher.
Way too much money for me at this stage.

That leaves the cheap solution of Bunnings threaded rods (iso metric screw threads), which come in at around $9 for an M12, 1000mm, pitch 1.75mm; or Whitworth 1/2" (12.7mm), length 36" (914mm), 1/12" (2.12mm) pitch.

Given the pitch, Whitworth moves 21% faster but metric may offer better choices for ball bearing. And it's metric and so am I!

The cheap solution might mean that the nuts will start smoking oil due to low efficiency and high friction, and that the stepper motor will have to run at quite high speed because of the small pitch. That, in turn, might give the screw some whiplash.

Let's check on ball bearings and go for 1/2" or 12mm threaded rods...


Anonymous said...

Hi Thomas,
If you decide to go with 12mm threaded rod, I have 5201 angular contact bearing and 6201 radial bearing you can use to hold the rod. They are 12mm ID and 32mm OD.
I can give you some to try if you want.
Msg me on ebay if your interested.

Thomas, the Infinitely Wise said...

Dan: Sent an email. Thanks.

justint said...

When is the next update of your blog?

Thomas, the Infinitely Wise said...

justint: Just did. Back to posting with substance soon...