[revwarguy]

In our maker space, we have a CNC router table rebuild going on that uses the Avid motor drive and a R&P setup. One of the members wants to mount the rack with the teeth pointing up so that he can use gravity to hold the pinion against the rack. He claims that mounting the rack with the teeth pointing down and using a spring to hold the pinion against the rack will cause premature wearing of the spring. Anyone ever seen the spring wear out and need to be replaced?

[Jim Dawson]

I suppose over a long time a spring might lose some of its spring, especially if being over stressed. But normally this would not be a problem that you would see if the spring is correct for the application. Besides, springs are pretty cheap.

Rack teeth pointing down helps keep the crap from building up in the teeth.

Maybe your co-member had a bad experience with a spring at some time?

[islaww]

The benefits of having the teeth pointed down to help prevent debris build up far outweighs any rare, and possibly unheard of benefits of preventing spring failure.

[Wildkard]

There is no benefit to mounting that way, springs wear out from compression/decompression cycles not being held compressed. It's likely you will wear out several sets of pinion gears before you lose any appreciable spring rate on the tensioning spring.

[mactec54]

In our maker space, we have a CNC router table rebuild going on that uses the Avid motor drive and a R&P setup. One of the members wants to mount the rack with the teeth pointing up so that he can use gravity to hold the pinion against the rack. He claims that mounting the rack with the teeth pointing down and using a spring to hold the pinion against the rack will cause premature wearing of the spring. Anyone ever seen the spring wear out and need to be replaced?

He may mean the wear of the Rack and Pinion; with this design both the Rack and Pinion will wear out many times before you will have any spring problems, up or down it's a bad design to start with, a fixed mounted Pinion is the best method for a Rack and Pinion.

Mounted up or down with this design, does not change anything the loading will still be the same.

Rack with the teeth down is the only way for a router like this, the other way would be sideways but still will get dust and junk in the teeth, so Rack teeth down is always going to be the best way.