HOMEBREW Z AXIS WIERD BACKLASH

[dgalaxy]

I have built a home brew z axis for my bridgeport when i test the for backlash on the actual quill bracket which bolts to the ball nut there is zero back lash but when test on the end mill or collet spindle i have any where between .005 and .008 i really dont understand how this can happen isnt it all bolted togethere in the spindle is there a bolt o need to tighten on the quill man i am totally lost ' can there be slop im just totally lost now

it just seems to me if there is no back lash in the quill itself how can there be backlash on the end mill put a picture on there it is hard to see the black arrows any advice would be highly appreciated

John

[One of Many]

Originally Posted by dgalaxy I have built a home brew z axis for my bridgeport when i test the for backlash on the actual quill bracket which bolts to the ball nut there is zero back lash but when test on the end mill or collet spindle i have any where between .005 and .008 i really dont understand how this can happen isnt it all bolted togethere in the spindle is there a bolt o need to tighten on the quill man i am totally lost ' can there be slop im just totally lost now it just seems to me if there is no back lash in the quill itself how can there be backlash on the end mill put a picture on there it is hard to see the black arrows any advice would be highly appreciated John

Chances are you have found spring in your coupling against the drag of the quill, not backlash.

Check for a motion lag between your bracket and the quill stop ring or whatever is used to drive the works. Sometimes those stop rings can become loose. The quill stop ring and its mounting surface can also become tweaked from repeated abuse against the quill stop. Poor adjustments in the power feed kickouts can induce damage on them too. Possibly all evidence of its previous life?

From the picture and no offense, but that is a lot of mechanical advantage for the distance and strength of the assembly. If you are seeing spring in the Z against an indicator, I am a-scared.... imaging what it will be under cutting loads.

DC

[neilw20]

Is all of this just attached by a couple of bolts on hex extensions?
What takes the vertical load when moving the z-axis. I see you are pushing the spindle up and down through a slot in the front of the machine.

That piece of hex looks like a good spring. Is it steel?
You have a structural problem.

[dgalaxy]

I built this from cris brunos plans i have come to the conclusion i can either remake it out of 1/2 plate instead of 1/4 but then i will have to make the coupling longer because am running 2 to 1 pulley not 1 to 1 --or buy an Elrod I do have centroid brackets on the x-y That came with the machine these work awsome no problems It also has a knee bracket but i was told that these arent very good i only have one more 29" nema42 and at 2to1 i was told it might not run the knee wat do you guys think . i posted some more phots please check it out and tell me what you think

John

[neilw20]

John

The front plate which has no holes (except the mounting ones) will take vertical loads nicely. The load appears to be coupled across through the bottom plate only. This forms a parallelogram that can flex. Temporarily clamp a spacer between the 2 plates at each side and see if the freeplay becomes significantly less. Yes, you have no backlash, but what about stiffness. If the plates are aluminum then they are 3 times as springy as steel. Young modulus is about 30,000,000 for steel and 10,000,000 for AL. That is is, for a given load, the AL will spring 3 times as far as steel. Move the quill down until it sitting on something solid - a piece of HARDWOOD, then put a clock under the edge of the large flat vertical plate, and try to move the quill down (VERY CAREFULLY) 0.001" at a time. You will see the dial move!