0 or low backlash threads

[lentzie]

I am working on a precision adjustment mechanism using 1/4 -40 threads. I would like to reduce thread backlash to a minimum. Using a tap and die set on a metal lathe I have gotten good results however there is still too much slop for my needs. I would greatly appreciate any advise.

Thanks,

Dave.

[vladdy]

for standard [as opposed to ballscrew style] threads the only two I have seen that appeared reasonably easy for home shop contruction were both 'squeeze' style nuts..
the first was a plastic [delrin or similar] nut / flange combination that was slotted and used a rubber band around it to reduce diameter slightly and reduce freeplay, the nut had a groove around the end to hold the band..
the second [and I have some here on appx 1/2" two start screws] were also slotted, but the outside end was a slightly larger diameter than next to the flange..they use a spring that pushes out from the flange and and against a washer, which squeezes the slotted outside end down, again reducing freeplay..
the photo is probably easier to understand than my description...

..enjoy..

[Hogger]

You won't get good results with standard tap and die sets, they have too much built in clearance, you could tap the I.D. thread and get an adjustable die for the O.D. thread, or the best way would be to cut the O.D. thread yourself with a single point threading tool.

[lerman]

In order to answer the question, it would help if you told us more.

What is the total range of adjustment? What is the applied force?

If the range of motion is small and the force is small, backlash can me eliminated by a spring acting against the threads.

Ken

[lentzie]

Thanks guys for the suggestions.

The adjuster is being used on a woodworking spokeshave. There is one adjusters attached to each end of a 3 1/2" blade. Adjustment is made by hand turning a 9/16 knurled knob. The usefull range of adjustment is .125. To be safe I am assuming a 75lb axial load on the thread. The problem I have encountered is that the slightest amount of thread backlash translates into chatter on the workpiece. I have found a way to eliminate the backlash however it is very labor intensive. I part the internally threaded piece in two then solder it back together on the externally threaded piece after taking up the slack. Basically the old double nut trick. I have considered using a spring but I think a spring strong enough to eliminate the chatter would make the tool difficult to adjust with the knurled knob. I am going to try Hogger's suggestion first and cut the thread with a single point tool.

Thanks again,

Dave