Backlash Nut On Z Axis?

[Imacman]

Hi I'm sure this question has been asked 100's of times... but I can't seem to find an answer, so here goes...on my current build ( I am using parts bought from George In Toronto..ie Gantry, Rails, Bearings, End Supports ) I am using ACME Threaded rod 1/2" 10tpi on the Z axis. I amusing good quality Delin nuts to attach the Z Axis to the tool holder plate, so my question is... being that the weight of all the parts attached to the ZAxis Bearings ( Router Included ) will be about 10 lbs in the verticle direction.. Di I even need an antibacklash nut or set up on the Z Axis? it seems to me, unless I'm missing something that the weight on the ACME rod will always be on the bottom face of the Lead screw and always in contact with the top side of the Derlin nut? So is an AB nut needed here? Thanks In advance.

Imacman

Newfoundland

[Ark1]

No. Providing that the rails and guides always stay perfectly clean and the head never hangs up. You are correct in stating that the screw will always be loaded due to gravity, However the little bit of extra cost may provide a lot of assurance in case the Z gets hung up.

Ark1.

[Imacman]

Ok Thanks!... So I think My solution, is to not get to concerned about a top quality AB nut setup on the Z axis, but rather use perhaps 2 derlin nuts, one connected to the tool plate and bearings, and the other preloaded with a spring pressing on the secured nut... it's a simple cost effective AB nut solution that should work 'IF" it's ever needed as you say incase of a hang up. Does this sound logical?

Thanks

Imacman

Newfoundland

[Ark1]

Originally Posted by Imacman Ok Thanks!... So I think My solution, is to not get to concerned about a top quality AB nut setup on the Z axis, but rather use perhaps 2 derlin nuts, one connected to the tool plate and bearings, and the other preloaded with a spring pressing on the secured nut... it's a simple cost effective AB nut solution that should work 'IF" it's ever needed as you say incase of a hang up. Does this sound logical? Thanks Imacman Newfoundland

There is always a bit more to the job than is considered. As the mass of the unit gets larger the speed of the machine will be slower. This gives time for the unit to stay settled. In lighter machines, the travell speeds are normally higher, gravity plays a lesser role. You didn't mention the amound of lash in the stock nut and screw, but I would recomend usings an anti backlash nut or smiliar to maintain accuracy.

Ark1.

[Imacman]

Thanks For the replies.... So now I think my logic is very flawed.... as I was in Sketchup playing with designs...it occurred to me, that if I do not have a decent preloaded AB nut setup on the Z axis... I'm thinking there maybe play in the Z System as the cutting/carving bit makes contact and interacts with the piece, as it travels up and down... So if my 'New Found Logic" / imaginings are correct, the process of the bit grabbing the work material would certainly expose any backlash that is available ( for lack of a better way to say it )... OR.... am I overthinking this whole process???

Imacman

Newfoundland

[Ark1]

Originally Posted by Imacman Thanks For the replies.... So now I think my logic is very flawed.... as I was in Sketchup playing with designs...it occurred to me, that if I do not have a decent preloaded AB nut setup on the Z axis... I'm thinking there maybe play in the Z System as the cutting/carving bit makes contact and interacts with the piece, as it travels up and down... So if my 'New Found Logic" / imaginings are correct, the process of the bit grabbing the work material would certainly expose any backlash that is available ( for lack of a better way to say it )... OR.... am I overthinking this whole process??? Imacman Newfoundland

One of the things I have leaned over the years just doing general machining is that the machine must have MASS to reduce chatter with standard Acme screws. Trying to machine a small part years ago in standard drill press broke bits as the tool grabbed the work. In a carving operation, the machine will be moving rather quickley and although it is expected that the Z is weighted even gravity takes a little time for the head to move in the correct direction. Think of standing on a trap door and the floor drops out underneath you. For a fraction of a second you are barely moving before the fall. The carving program is going to have that head moving up and down and even possibly be weightless as it rapidly changes direction. The machine must be as stiff ( no backlash ) as you can get it without impeading performance.

Ark1.