A Project Quest

[Bill Gruby]

Need three gears to use in the raising and lowering of the wheel. There will be two lead screws to handle this task so a third gear is needed to make both turn in the same direction. I want them to be 4 inch diameter. OK so far?

Need the pitch diameter. I have the OD and I have the # of teeth (48) ------ PD = ND / N+2

N # of teeth
D OD of the blank gear

PD = 48X4 / 48+2
PD = 192 / 50
PD = 3.84"

All gears the same, 48 teeth it is. 48 was used because none of the others I tried had an even PD. I tried 60, 45, and 40 and none were less the 5 decimal places.

"Billy G

 

[Bill Gruby]

Bill now has the prints I finished. He will post them as he gets them done. I am going back go work on the gear box.

"Billy G"

 

[Tony Wells]

Question, Bill. What is your approach to synchronizing these leadscrews to compensate for the backlash that will exist in that geartrain? And will it be adjustable?

 

[rwm]

Interesting question Tony. What amount of back lash would be significant? What tolerances are we shooting for on the height adjustment? .001" or better? I assume the height screws will be very fine in pitch?
Robert

 

[Tony Wells]

Robert, I'm not really sure. It just made me think of the way a wood working planer is built, with two elevation screws. It may be that if the intermediate gear is used to actually drive the individual screws, once they were synchronized they should wear at almost identical rates and not create a side loading problem for the ways or guides for the head. And since like all plain screw methods, we operators would always approach the target location from the same direction, and if over-shot, move back and try again......it may not be an issue. But in original construction, I would think that there will need to be a good way to "fix" the relationship between the two screws as closely as possible. Just thinking out loud.

 

[Bill Gruby]

Raising and lowering should have near zero backlash. The weight of the motor should in theory keep it in the same side of the thread both up and down. If not our thought is to use a counterbalance to keep it there. Now back lash in the lead screw will be dealt with using double nuts, one above and one below the top plate. Each nut will be adjusted to one side of the thread and locked with a set screw. This will hold the backlash down and keep the screws in sync. Adjustable at any time.

"Billy G"

 

[Billh50]

Couple quick Prints for Billy G to look over.

 

[Bill Gruby]

You are correct the center (intermediate) gear will drive the two screws simultaneously Tony. I don't believe this type set up will allow the screws to go out of sync.

Good Bill. Everyone please keep in mind that anything can change at any time during the build.


"Billy G"

 

[Billh50]

Billy G,

Here's a sketch of the timing belt Idea I had for moving the table left to right.
Let's see what others think also.

 

[Bill Gruby]

Thank you Bill, that's pretty much what I thought it would be when you suggested it today. Will definitely keep that in mind.

"Billy G"