You have 2 options for converting your Thrift Savings Plan into a retirement fund that will permit the inclusion of precious metals in their physical form.
#1. TSP Transfer
Here, your current IRA custodian (this may be for the TSP or for a different IRA) sends a distribution check to the new custodian. There is no limit on the amount of times this can be done. Many, many people have already done this successfully and are now enjoying the benefits that a self directed IRA offers.
#2. TSP Rollover
With this method your existing custodian sends your retirement funds to you and it is then your responsibility to place the funds into one or more IRAs within 60 days. If you exceed that deadline the IRS will consider the transaction to be a withdrawal and you will be liable to pay taxes on it.
The same funds can only be rolled over once per twelve month period for the tax deferred status to be maintained. You can however rollover different parts of your fund in different stages with no limit on the amount of times that can be done.
It is essential that you mark each deposit as a rollover as opposed to a contribution. This is because a contribution is restricted to $5,500 per year if you are under 50, or $6,500 per year if you are over 50.