Creating a Bond Ladder

I am creating a bond ladder.

The aim is to create a perpetual (as long as possible) revenue stream every month. 

Here's how it is going to work. 

I plan to buy 6 months time deposits or 6 months T-Bills, one at a time, once every month. 

At the end of 6 months, the first time-deposit/bond will mature, and I collect the interest. At the same time, I put the capital back into another 6 months time deposit/TBill. 

Conceptually it looks like this:

And it continues as long as the interest rates are above 3.5%.

I have already set up the first 3 tranches.

The first 2 tranches were set up using StashAway Simple Guaranteed, at the interest rate of 3.5% p.a.

The third tranche was set up using 6-month TBill, at the interest rate of 3.73% p.a.

So why did I use Stashaway Simple Guaranteed when TBills offer higher interest rates? No particular reason, but when I saw 3.5% in Stashway Simple Guaranteed, I thought it was good and I put money in - the process was easy and straightforward. Later I thought since TBills offer slightly higher interest rates, I should switch to TBills instead. 

So from now on, I will be able to earn $175-$184 every month, as long as interest rates stay above 3.5% p.a.

If you have spare cash, set up your own Bond Ladder today!

Any flaws with this method? Comment below.