well the first thing is to STOP modelling in inches and switch the the far more sensible millimetres :-)

It really does make a lot more sense than going in the other direction.
Most slicers only do millimetres, just sooo much easier for calculations than the bizarre and archaic inches in base 8.
When you're dealing in movements measured in 100th's of a millimetre - having the software convert back and forth between base 8 and base 10 - just makes no sense.

As far as your material thickness goes - 0.25 inches = 6.25 millimetres

I mean it's even difficult to represent measurements in inches in a decimal format.
what on earth is the decimilisation for 3/36ths of an inch ?

If you really can't change your working habits - simply convert your design to mm in turbocad, then save it as a new file with the prefix/suffix: in millimetres.
And use That file to generate your stl's

No clue what slicer dremel use - but given the machines are mostly made by flashforge under licence, it might well be a variant of flashprint.