Can I bring those metal cake decorating turntables, and metal pastry tubes, in my checked luggage on a plane? These things are metal and pretty sharp.
Yes, you can take your cake baking items in your checked in luggage.
As a general rule you can even take sharp knives in checked in luggage. The only precaution that airport security (like the TSA for the USA) asks is that the sharp edges are packaged in such a way that staff can not cut their hands on them if they decide to hand-check the case.
If you bring the items in their original packaging, you should be alright. If they come without proper packaging, wrap them in enough paper or fabric and put on a paper outer layer taped close with 'sharp edges' written on it. For flights leaving from non-English speaking areas, you can/should add the same message in the local language.
Here is a link to the site of the TSA, with the list of items allowed in carry-on and check-in luggage. As they do not mention cake making items, I would follow the rules for knives as it is one level more dangerous.
Any sharp objects in checked baggage should be sheathed or securely wrapped to prevent injury to baggage handlers and inspectors.
Other countries have slightly different rules but I have never heard from any that does not allow sharp objects in hold luggage, when well packaged. Some would even allow cake making items in hand luggage but I think that is pushing the boundaries.