Another good video! Engineers tend to think about stuff like thermal coefficients of expansion, but machinists definitely need to think about these things too when working to high tolerance. This is also another good reason to put the heat into the chip rather than the part when machining.
Another variable is the scales of the readouts on mills we often trust for hole spacing etc. They are usually made of glass which has it's own lower rate of thermal expansion so even if you compensated for the metal expansion with the display, you could still be out. This is one of the selling points of the magnetic scales that use steel balls in a tube rather than optical glass. On a large machine over several feet for example, because the steel balls expand at the same rate of your steel workpiece, the readout should be pretty accurate regardless of shop temperature.
sahkram I agree totally, in fact it is critical to allow for the expansion coefficient if you are to end up with the correct size product. This is the same as with machining which was indicated on this video although perhaps does not illustrate the problems that can manifest themselves if temperature verses application of product are properly taken into account. Things like incorrect press fit size comes to mind. Cheers from John.
You rock Don !
Thanks for continuing to teach us guys who never got a chance to apprentice with someone like you.
Another good video! Engineers tend to think about stuff like thermal coefficients of expansion, but machinists definitely need to think about these things too when working to high tolerance. This is also another good reason to put the heat into the chip rather than the part when machining.
Another variable is the scales of the readouts on mills we often trust for hole spacing etc. They are usually made of glass which has it's own lower rate of thermal expansion so even if you compensated for the metal expansion with the display, you could still be out. This is one of the selling points of the magnetic scales that use steel balls in a tube rather than optical glass. On a large machine over several feet for example, because the steel balls expand at the same rate of your steel workpiece, the readout should be pretty accurate regardless of shop temperature.
One of the reasons measuring and machining in the tenths range from one shop to another can be very difficult.
bcbloc02 Running for tenths is an endless race in the shops... So happy when it's constant... ;-)
Thanks for sharing that, I never realized how much aluminium grew, no wonder I've missed the mark a few times when the aluminium got hot from turning.
Steve S That's why you should do the roughing cuts, let cool and finish... When result is critical, counts for steel too... ;-)
Lots of flood coolant tends to really help in holding tight tolerances by keeping temps consistent. :-)
the growth of metal is called the coefficient of expansion and is used extensively in mold making.
sahkram I agree totally, in fact it is critical to allow for the expansion coefficient if you are to end up with the correct size product. This is the same as with machining which was indicated on this video although perhaps does not illustrate the problems that can manifest themselves if temperature verses application of product are properly taken into account. Things like incorrect press fit size comes to mind. Cheers from John.
Da shit you yankees!! 60 degrees... 90 degrees... Can't you use units like all the rest of the world?