How to transfer catalog previews without photo files

[daniels93364562]

I have two separate laptops with different lightroom catalogs and photos. I keep my photos backed up on external drives because of the file size and move them onto the computers when I want to edit/export. I want to have both catalogs merged and see previews without having to upload the photos. I figured out how to transfer and merge catalogues. However, after merging, the preview of the files are not there. I tried merging the catalog preview folders together from the merged catalogs. Despite integrating several gigabytes worth of preview files, the new transfers show no preview. Is there a way to get the preview transfered and merged without having to first upload all the photos.

There are thousands of photos and I could only upload and delete in stages because of internal storage limist. Also I'll have to rebuild some file paths for the ones from each side. For now I just want previews so that I can easily look and see what I want to upload. 

{Moved from Lightroom Cloud to Lightroom Classic Forum by Moderator}

[Rob_Cullen]

I assume you are using Lightroom-CLASSIC!

I do not know what or why you are "Uploading"!

See this blog article for help-

MULTIPLE COMPUTERS- How to use (Lightroom Queen)

[daniels93364562]

Thank you for taking the time to respond.

Yes I am using Lighroom 6.0

I had a hard drive fail on me this year so I don't want to work off of a hard drive so I do want to move files when I'm going to edit them. 

[Rob_Cullen]

I don't want to work off of a hard drive

Lightroom v6 will require the original files connected on a Hard-drive at these times-

Importing, Building standard Previews, Developing, Printing, sending a Book to Blurb.

There is no way around it- that is the nature of the Catalog database system that Lightroom uses.

What is a Lightroom catalog? | The Lightroom Queen

Where should you store your photos? | The Lightroom Queen

Smart Previews is possible a work-around, but with limitations.

https://www.creative-photographer.com/smart-previews-lightroom/

Moving files when you want to edit them is a bad idea IMO and prone to errors and frustration.

Failed Hard-drives can only be answered by having the files on another physical backup hard-drive! (as you have)

The only successful way to use ONE catalog on two computer installations of Lr6 is to have the Catalog AND the original files (or the Smart Previews with the limitations) on a portable hard-drive that can be swapped from one machine to the other.

I tried merging the catalog preview folders

Not possible!- Lightroom can only create the Preview cache from the Originals ( or  Smart Previews). The Preview cache is dynamic- changing all the time to cater for different zoom views, 1:1, thumbnail sizes, etc, and needs the originals connected. Only an "Import from another Catalog" will merge the Preview cache with the Catalog.

I can only see you using the external drive with catalog and photo files to swap between computers. Anything else is an exercise in complication and frustration!