On Tue, Jan 10, 2023 at 11:26 AM, Carl wrote:

... slit the nut before tapping the M10x1 LH? ...

Maybe I am missing something, I am not versed in screw geometry or standards.

If I understand correctly, what would be happening is that the 7.0mm hole made to tap the M8x1.0 LH thread would get a lengthwise slit, say maybe a max of 0.3/0.4mm wide, would then be clamped so as to close that slit/gap and then threaded to M8x1.0 LH.

I think that the result would be a smaller albeit not precisely round (ie: slightly oval) hole to thread but as we are talking brass and not steel, this would not be a problem when making threading, provided due care was taken.

If for the sake of this exercise we take the slit+clamped hole to be just as round as the un-slit one, I think that what we would end up with would be an M8x1.0 LH thread made in a hole a wee bit smaller than usual practise advises, say M6.80 instead of M7.0.

When the clamp is released, the slit will then spring open and as a result the now threaded hole will go from the (estimated) 6.80mm to the nominal 7.00mm, taking the both the crest and root of the M8x1.0 LH thread further away from the lead screw's axis.

If I am correct, I think that the screw would have quite a bit of play.

Make sense?

Thanks a lot for your input.

Best,

JHM

Hello Jay:

On Tue, Jan 10, 2023 at 04:30 AM, Jay Perez wrote:

Based on Julius' and other comments I modeled some of the other options discussed.

Thank you very much for your detailed CADs.? 8^D
Much obliged. ? 8^D

... not sure I'm correctly visualizing the clearances ...

My bad.
I should have detailed it properly.

Here's a quick & dirty sketch, approximately to scale.
No match for your CADs but I think it gets the idea across:

As you can see, there's really not much room for anything but oil and swarf.
Even so, brass has a way of constantly setting up residence in there.

Yesterday I attempted an idea similar to the one shown on your second drawing but using a small piece of silicone sheathing from some high temperature cable, just to see how it behaved.

The silicone cable was (as expected) too soft and quickly deteriorated, but I think we may be on to something.
I have to see where I can get small teflon/delrin balls.

With this flawed OEM design and with no room around the nut, I think that the only possible way for something to press against the feed screw threads is from above.

But it has to be separate from the screw that holds the nut in place, unless the solution is something with very tight tolerances.
ie: it would have to work with the screw in place and as tight as it should be, maybe a tiny piece of hard teflon in the right shape.

The screw is M4, rather small, but if an M6 flat head screw like this one ...



... with a concentric M2 grub screw running inside were used, there's may be a possibility.

The grub screw could have a 60° point, like this one but would have to be made from brass or hard teflon and just plain slot type, no allen head required.



You would first tighten the nut in place with the M6 screw and after the sloide is in place, thegib is properly adjusted and the feed screw/ways oiled, you would tighten the brass/teflon grub screw till it runs on top of the feed screw thread and the backlash is acceptable.?

Eventually the grub screw would wear down and have to be replaced.

The problem with this is that all those allen screws are impossible to drill/thread.
Don't ask me how I know.? 8^°

It is a rather complicated solution but there may be a way to do it.
Have to play a bit with fire, water and oil.

Thnak a lot for your input.

Best,

JHM

On Tue, Jan 10, 2023 at 04:30 AM, Jay Perez wrote:

Based on Julius' and other comments I modeled some of the other options discussed.

Thank you very much for your detailed CADs.? 8^D
Much obliged. ? 8^D

... not sure I'm correctly visualizing the clearances ...

My bad.
I should have detailed it properly.

Here's a quick & dirty sketch, approximately to scale.
No match for your CADs but I think it gets the idea across:

As you can see, there's really not much room for anything but oil and swarf.
Even so, brass has a way of constantly setting up residence in there.

Yesterday I attempted an idea similar to the one shown on your second drawing but using a small piece of silicone sheathing from some high temperature cable, just to see how it behaved.

The silicone cable was (as expected) too soft and quickly deteriorated, but I think we may be on to something.
I have to see where I can get small teflon/delrin balls.

With this flawed OEM design and with no room around the nut, I think that the only possible way for something to press against the feed screw threads is from above.

But it has to be separate from the screw that holds the nut in place, unless the solution is something with very tight tolerances.
ie: it would have to work with the screw in place and as tight as it should be, maybe a tiny piece of hard teflon in the right shape.

The screw is M4, rather small, but if an M6 flat head screw like this one ...



... with a concentric M2 grub screw running inside were used, there's may be a possibility.

The grub screw could have a 60° point, like this one but would have to be made from brass or hard teflon and just plain slot type, no allen head required.



You would first tighten the nut in place with the M6 screw and after the sloide is in place, thegib is properly adjusted and the feed screw/ways oiled, you would tighten the brass/teflon grub screw till it runs on top of the feed screw thread and the backlash is acceptable.?

Eventually the grub screw would wear down and have to be replaced.

The problem with this is that all those allen screws are impossible to drill/thread.
Don't ask me how I know.? 8^°

It is a rather complicated solution but there may be a way to do it.
Have to play a bit with fire, water and oil.

Thnak a lot for your input.

Best,

JHM

On Sun, Jan 8, 2023 at 08:44 PM, Jay Perez wrote:

... have used something similar on the Z axis of my 3D printer.

There are quite a few variants and all have the same principle: a spring.

Bridgeport mills use a 'split nut' ...

Ahh, Brigdeport milling machines.
Serious stuff.

Crude but effective.

Many intelligent solutions are.
But it doesn't look crude to me.? 8^)

... cut a gap into the nut to allow it to be compressed ...

There would be no problem with that.
Just maybe, given the size of the nut, finding a thin enough saw blade.

... a mechanism that allows you to squeeze it slightly ...

That's the exact moment at which the elephant enters the room.

Like I mentioned previously, the OEM nut is a 10mm cube and the way it moves in is 10.5mm high.
So there's only ~ 0.50mm vertical space available.

As the saddle is made from die cast aluminium, the way is shaped like a flat bottomed inverted cone
to facilitate the separation from the die during manufacture.

It measures 13.5mm at the top and 12.5mm at the bottom.

So the nut moves along the centre of the way with barely any wiggle room.
ie: ~ 0.50mm at the bottom, ~1.50mm to each side at the top and ~1.00mm at the bottom.

I'm afraid I don't see room for a clamp + set screws there. 8^/

Idea:
I have been wondering if the M4x0.7 screw than holds the nut in place could push a very small brass/teflon/? bearing against the 8.0x1 thread and help reduce the backlash.

Or maybe the screw could be made from very hard brass and have an acute/pointed end.

ie: by design (in theory), the feed screw axis and the M4 screw axis intersect at 90° and as a consequence of that, the screw's point would run inside the thread and (hopefully) reduce or eliminate the existing backlash.

Make sense?

Obviously (if it works) such a screw would have to be replaced when the point gets worn and start to slip.
But anything is better than this incredible design flaw from Emco's engineers.

Once again, thanks for your input.

Best,

JHM

On Sun, Jan 8, 2023 at 03:17 PM, Richard wrote:

... available from Arc Euro in the UK as a spare ...

Indeed ...
Thanks for the heads up, I had seen it last week while looking for a solution for the backlash in my U3, thinking that maybe a part from some other lathe could be modified/adapted.

Good to know this one fits.? 8^)

... make my own from 1/2" bronze bar ...

Last year I made a nut (sans the spigot) to use along with the original nut and a coiled spring to separate them, making a device such as those used in hobby CNC machines to reduce backlash:



But it was a failure as there is very little space between the top of the feed screw and the bottom of the slide:



It is ~ 0.90mm without counting the crest of the feed screw thread, so it is probably down to ~ 0.70mm.
A coiled spring expands under tension and altough I managed to file/sand one and make it work to reduce the backlash, at some point the slide would jam.

The nut is a ~10mm cube and the way it moves in is 10.5mm high by 12.5mm at the bottom and 13.5mm at the top.
Not much room below the nut and not much to either side.

Thank you very much for your input.

Best,

JHM