Overkill?

[lgalla]

From reading tons of posts on linear guide sizing and ballscrew whip,I think many home built machines are overkill.
I just ran a large commercial machine to-day,5X10,10Hp.This 100grand machine has 20mm linear guides and 25mm/5mm ballscrews.
The Y screw is about 7' and no whip at 600ipm cutting.
The X screws are 12' to allow for the tool changer.No whip here,but they have a novel support system which swings out of the way as the ball nut passes.
If this machine runs on what seems to be small guides and screws for the size and weight of the machine,est 8,000lbs,I feel confident to use the same on my smaller,lighter machine design.
Larry

[ger21]

With regards to THK type rails, yes, most homebuilt machines are way overbuilt. 20mm rails can handle some serious loads. Even the 15mm's can. But I think when people see how small the 15mm rails are, they think that they're just not big enough.

As for the ballscrew, are you sure it was a 5mm pitch screw? That's 3000 rpm at 600ipm. Our machine at work uses screws with about a 25mm lead, so the screws are actually turning quite slowly most of the time.

[lgalla]

Sorry Gerry,I am only guessing at the pitch.Looks similar to ballscrews I have.How would I measure the pitch?Threads per inch?Also the angular contact bearings and free support ends are massive,much larger than I expected.15mm looks too small and we see guys wanting 35mmrails for a 24"by36"machine.If one asks on the Zone about loading and rail sizing,one could save a bundle using smaller rails fit for the task.
Larry

[ger21]

The pitch is the distance of one revolution of a single thread. For single start ballscrews it's the distance between the grooves.

[Glacern]

High helix angle is a good indication of a high lead, low pitch screw. Many of the machines I build use 1" x 1.000 four start screws.

15mm blocks and rails are sufficient for most home built machines, but even a small amount of force can be amplified many times if there's a long moment force. For example, if you've got a long Z-axis, it's important to have a tall gantry bridge with the y-axis rails spread apart as much as possible.