use 'TryParse to validate your sources are Type 'float:
float f1 = 0.0;
if (! Single.TryParse(frontWtTextBox.Text, out f1))
{
tSTextBox.Text = $"invalid input in frontWtTextBox.Text: {frontWtTextBox.Text}";
}
Note: written from memory, not tested.
Put breakpoints in your code and single-step through it (F11): observe what happens.
If the end-user is entering floats with another delimiter, like a comma, you may need to provide a culture specific IFormatProvider: [
^]