I want to raise/lower (via hand-crank) a 200lb load on the Z-Axis with approx 8" of travel. Application is heavy grinding. Backlash is not a concern.

What I want to build is a beefy version of what you see in the included photo.

I'm new to this, but my initial research suggests that I may want Frelon-lined bearings as opposed to ball/roller bearings, in order to better tolerate the grinding dirt.

The 200 lb load would be centered approx 7" from the rails.

I'm guessing that I would want two vertical rails or shafts that are about 8" apart. I gather that I would want 4 carriages (2 per rail), with the lower pair about 12" below the upper pair. The carriages would be ganged together on a vertical plate, and I would have a horizontal work rest mounted to the vertical plate.

What kind of shafting/rails would be best? It seems to me that un-supported shafts would provide the most support to forces that are perpendicular to the shaft. However, rigidity seems to be an issue with un-supported shafting.

What about positioning a screw-jack (as the drive mechanism) underneath the work rest (like a Bridgeport), instead of a lead-screw in the rail assembly?

What is the best way to safely lock the carriage assembly in position?

Any comments or advice are appreciated; thank-you.

For the lifting mechanism, I would look into Nook Ball screw Jack, not the Acme which will require more power.
You could either obtain a motor brake combination, or obtain a through shaft jack, fit the motor drive to one side and a brake on the other.
For the rest, teflon slides etc, I suggest you send for a free Misumi Catalogue, They have a huge wealth of products and engineering information.
I see you do not need a motor so just omit that, the rest stands.
Al.

thanks; I'll look into that.

I would not want the ball-screw screw-jack if I'm going to crank by hand, correct?

If the budget runs to it, I would go with the ball screw type, you would just need to put a hand wheel on the shaft.
If you have a double ended through-shaft, you could put a electric brake or other on the opposite end.
Al.

thank you (sorry about the delayed response).

what exactly will the electric brake do? (I assume it will stop the ball screw from turning?) How does it work?

You mentioned locking the carriage in position, so I assume you need a holding device when you are not lifting or lowering the load.
The DC electric style brake, consist of moving part fixed to the opposite end of the rotating shaft, and the other section fastened to the Jack body, With the power off the brake is applied by pressure of the moving part to the fixed body, Applying A DC voltage releases the pressure plate and allows free movement.
You can get them very small and compact.
Al.

slick, thank you