Keep in mind IR thermometers are sensitive to the reflectivity/emissivity of the materials they are used on, and the shiny PEI surface can be a bit tricky. Try measuring the temperature of a mirror that your warmed up with your hand and you’ll see a similar problem.

If you want to test more accurately, put some matte tape on the bed and then measure the temperature then.

That said there is also a chance for the heat bed to be a bit lower than target temperature, since the temperature control and feedback occurs at the bottom of the bed where the thermistor is, not at the top, and is separated by a layer of magnetic adhesive and coated metal.

An enclosure might help a bit, but not a lot. What are you using for a plate, just spring steel? You will lose a small amount of heat to that. If it’s glass and steel, then you will lose more. The temperature sensor is pretty close to the actual heating element, and the heating coil doesn’t cover the entire bed, so there will be hotter areas and cooler areas—like an electric griddle if you’ve used one of those in a kitchen before.

Glass helps because it’s a good thermal conductor, but because it’s another layer to heat (and lose heat into) you need to bump the temperatures a bit, and it also comes with the caveat of weight, which isn’t ideal on a bed slinger.

Overall though, if you’re printing PLA and having bed adhesion issues at 68 degrees the temperature probably isn’t the issue.

Adhesion I’d totally recommend cleaning your surface with soap and water (surface depending) and then messing with temps. With abs and petg I’ve found that even a bit of finger print residue is enough to cause a part to come away from the bed, next I’d check first level height. I’ve very rarely found the bed temp to be the reason I lost adhesion.

That is wicked smaht

The edges are going to be cooler if everything is working the way it’s designed (especially on a bed slinger), since the heater doesn’t go all the way to the edges and because of increased airflow. One of the reasons I was thinking about getting a Prusa XL is because it has multiple independent bed heaters.

An enclosure will help some. When I’m printing near the edges I also up the bed temp 5 to 10 degrees depending on room temp.

Metal flex sheet is going to conduct heat differently than the Creality standard surface plus it’s shiny metal meaning it’s difficult to measure with IR If you are having issues, then up the bed heat

I think you might be using the IR gun incorrectly.

The area which is being measured may be partially off the edge of the bed.

What the heck are you printing that requires 75C of bed temp with no walls?