Why not use unsupported rails?

[JAZZCNC]

There are so meny variables when building a machine to it's accurecy. All this talk of unsupported or supported, profiled etc is a bit lost and pointless on 95% of DIY builds because of other areas of the machine that are completely overlooked or under estimated.!! . . .The BED and Z Axis being two of the main one's.

Most on here will Know by now I'm not into Calc's or simulated predictions so my view is based purely on personal experience and for machines over a certain length or width I just would not recommend or use unsupported rails. This Max length and width would be 300mm for X & Y Axis and I would NEVER use them on a Z Axis.
I've only ever made one Z axis this way and it was by far the weakest area of the machine and big regret, but alas and as is often the case it was down to cost saving as usual.!! This is why I URGE any one building to just spend the few extra quid and save them self's this problem and go for supported rails.

Profiled rails are very misunderstood.?? You don't build a machine with profiled rails for there strength, infact they would probably show a tad weaker than supported round if simulated like jonathan did.?
You use profiled rails for there accurecy, smoothness as well as there abilty to handle far far higher loads and in DIY usage for millions of years.!!
To be honest you don't have to be an engineer or an expert to see and feel the difference between round rail and profiled, the quality just ouse's out and by comparison round rail, supported or unsupported, are like baggy fanny's in comparison.!!

Another often unknown thing about profiled rails is there intolerence of poor design, shoddy materials or poor workmanship. They will bind and lock with the slightest of miss aliagnment or uneven surface so this again is the test of a well built machine.

John S test is a great test and if you want to test the accurecy and more so the repeatabilty then cut the Aztec calendar because this will soon show you how well your machine is performing. The Aztec calendar as very fine detail and with 855,000 lines of code It boucnce's about like a pogo stick so if your machine is out in the slightest degree it will lose position and show any error when recutting so removing any detail.