I recently purchased a Profitec T64 grinder and Pro 300 espresso machine.

In my previous setup, I would dose based on weight: 18g of beans and 30g out for a double shot.

However, the T64 is a time-based dose. After doing some reading on the T64, I've read a recommendation to use 6.5 seconds for a double shot.

Holding 6.5 seconds as a constant grind time, I'm aiming for a 30g double shot between 25 - 30 seconds.

With 6.5 seconds of grind time, I'm seeing between 19g and 21g of ground coffee (verified using a scale).

Using 6.5 seconds, 19 - 21g of ground coffee, I've found a grinder setting that lets me hit 30g of coffee in 25 - 30 seconds.

It's a good, but not great, double shot.

So, my question is whether I'm approaching the new hardware in the right way? Is holding the grind time constant the right approach? Or, should I try to set a grind time BASED ON the amount of time to get 18g of ground coffee?

I know that the grind time to hit 18g (or other fixed amount) of ground coffee will vary as I make grinder adjustments to try and dial-in the shot, based on tests or timing. My concern is that if I'm changing the grind time shot-to-shot to try and hit a fixed amount of ground coffee seems complicated.

So, what's the best process for a time-based grind approach? Or, is there a different approach entirely I should use?

I typically will change bags once a week, so I'll have to dial-in the machine on a regular basis.

Timer definitely comes last.
You should first dial in the grinder and determine the dose size and coarseness you will need.
Once you decide on the dose AND have the grinder adjusted to the right size, then you set the time in order to reproduce the dose you decided on.
There is a lot on here about how to dial in the grinder, but here is a video on the topic:
https://baristahustle.com/blogs/barista ... l-together

Time based grinders are usually for coffee shops that want to maintain consistency through the day after dialing in the morning (and a couple/few times) during the day. They are a little tougher for home use since we use a bag of beans over the coarse of days/week as opposed to hours. i.e. If 10 seconds produces 18 grams today it wont 2 days from now and won't produce a grind that has the same flow.

Home use definitely needs more dialing in, which is why a number of us go for single-dosing. Otherwise, you will go through alot of wasted coffee for dialing in regularly.
At one time, I would regularly waste 2 shots of ground coffee for every one that I drank when I used a Robur-E (with timer) at home.

PS Just did a quick search and a number of people do single-dose with your grinder, so it is doable.

Thanks, that's helpful. And, the BH video was a good overview.

Maybe single-dosing is the way to go, in general. Perhaps the timer's just not useful for me at home.

Time to start over on dialing-in the grinder.