Trouble trying to save backups from failing Time Capsule. Any thoughts on my details below?

+1 with Bob.

You have likely wasted enough time.. as stated in the first post I did.

Since you have tried both methods, archive and direct copying, I think you are going to do a lot better cutting your losses and pull the hard disk from the TC. Most USB3 hard disk docks or enclosures will work fine with the disk plugged directly to your Mac.. it then depends on if the issue is the TC router side or the hard disk itself is failing.

Copying sparsebundles is not very successful. Archive is the right way to do it. There has been a lot more security added in more recent Mac OS which makes copying far more difficult.

In normal setup a full 2TB disk should copy in about a day.. 600GB in 11-15 days is ridiculous.

Since you have tried both methods, archive and direct copying, I think you are going to do a lot better cutting your losses and pull the hard disk from the TC. Most USB3 hard disk docks or enclosures will work fine with the disk plugged directly to your Mac.. it then depends on if the issue is the TC router side or the hard disk itself is failing.

How old is the TC and what model?

There are other "esoteric" approaches. You can directly copy by command line which is often more successful. You can actually turn on ssh and get into the TC firmware and use command line from inside so to speak. Not easy and you need some skills.

A backup tool like Carbon Copy Cloner could also do the job backwards so to speak. It is free to download and use for a month and I would be tempted to try it. They use rsync commands to do the copy which is much more efficient than finder. Still use the USB drive on the computer and just copy the sparsebundles to the computer and thence the USB drive.

I would change permissions beforehand. Again this is tricky but possible.

You might not be aware that the USB port on the Time Capsule is as slow as molasses on a very cold day. There are reasons for this......

1) The Port is an ancient USB 2.0 design

2) The internal processor in the Time Capsule is very slow as well, at least for the USB port. At best, speeds are going to be less than half the speed of a normal (slow) USB 2.0 connection. In practice, I've found that the speeds are closer to 1/4 to 1/3 of normal (slow) USB 2.0

3) Chances are, your new USB drive is USB 3.0. Unfortunately, that won't help when it is connected to the Time Capsule since the port will limit speeds as mentioned above. There also may be some additional slowing in the conversion process between USB 3.0 and 2.0.

So a few weeks sounds about right.

If you have the time and don't mind starting over, I would try connecting the new USB drive to your iMac.....not the Time Capsule...... and try the file copies that way to see if the estimated time is significantly better.

If things are still just as slow this way, then the "failing" Time Capsule hard drive may likely be contributing to things as well.

The archive function via Airport Utility and the usb 2.0 port on the Time Capsule estimated 15 days, but failed twice after less than one day.

Failure of the archive is highly suggestive of major failure of the TC due shortly. Maybe hard disk.. that particular seagate has the worst reputation.

Is getting the old backups off the drive important.. if not you could just save the disk for a rainy day and put a new disk in the TC and see if it works.. although at 6 years old you have really had a good run and it might really be better to move to something else.

Is it normal for the TC disk and the Data folder to disconnect on its own after a long period of time?

Yes.. sadly.

Particularly if the TC is not the main router in the network.

We have not gone over the actual setup of the TC on the network.

It is essential to have the TC plugged into the iMac by ethernet.

I would then mount the hard disk manually using IP address.

In finder use Go, Connect to Server.

Type in address SMB://10.0.1.1 (replace with the TC actual IP address).

Or use AFP://10.0.1.1 (same replace IP with actual) I find AFP is often more reliable. Later Mac OS tends to use SMB unless you deliberately mount the partition as above.

If the TC is not the main router set its IP to static value.. and turn IPv6 on Internet options to Link-local only.

Then give it another go.. but I feel like there are other things going on here.. not just network failure but perhaps disk failure as well.

With a 5+ year old Time Capsule, there is a possibility that the power supply is starting to head downhill as well. Although a quick tiny "blip" may not be noticed on an Internet connection, it can possibly cause a disconnection in the disk copy process.

So, one way to remove the power supply as a possible variable in the process would be to consider pulling the hard drive from the Time Capsule and placing it in a SATA to USB caddy for the transfer. The USB 3.0 speeds on the caddy will likely speed things up as well.

If you are interested, check out OWC.com for something like a NewerTech Voyager S3. Should be about $35 or so.

I've found Apple estimates to be all over the place, so they are really guesses more than estimates.