Rotating Ballnut - design ideas

[Jonathan]

You can ignore the stuff about critical frequecy/deflection of the screw with the spinning nut. I had a dim moment and forgot you were supporting the nut with bearings. Its late or at least that is my excuse!:cry:

Interestingly I've since found that when you rotate the ballnut the critical frequency still has an applies - the end fixity is just better which, in my case, gives 1250rpm. So 12500mm/min. I think I'll be lucky to get that much out of my motors anyway so I'm not going to worry.

I just got prices for the screws:

2 of RM1610-2000mm with nut and end machined(both ends machined same as A type )
238 usd
1 of RM1610-900mm with nut and end machined(standard end machining)
72 usd
Sub-total
310 usd
Air express shipping
127 usd
Total
437 usd
-----------------------
Offer tow:

2 of RM2510-2000mm with nut and end machined(both ends machined same as A type )
269 usd
1 of RM1610-900mm with nut and end machined(standard end machinings)
72 usd
Sub-total
341 usd
Air express shipping
168 usd
Total
509usd

I'll go for the second option - the price difference is not as much as I expected. The smaller screw is for the Y-axis. I've decided to get both ends of the big screws machined to fit the BK type support ... that should enable me to tension the screw using the nut on either end.

I have also acquired a pair of 7206 FAG bearings cheaply, so I'm hoping I can use them instead of 7207. The obvious problem is that the bearing bore is only 30mm, and with the screw passing through it being 25mm the shaft will be very thin - about 1.5mm.