How to cope with slack in a leadscrew, feedscrew, etc

[Tim StevensParticipant @timstevens64731]

Many of us struggle with the slack in our measuring systems, a particular problem when you move a tool two or three times in one direction, and then need to go back.

There is a potential solution (which does not involve expensive recirculating ball systems etc) and I ask if it is a well known dodge I have not come across myself:

Add an adjustable ring to the fixed scale (the one with the zero pointer, that is) and give it an extra pointer. Something as simple as two or three turns of spring wire holding around the fixed scale with the end bent to make an extra pointer. Then fix a dial gauge to detect movement of the tool, bed, etc, and turn the handle clockwise until the scale shows zero against the fixed pointer. Then reverse the rotation, and stop as soon as the dial-gauge pointer starts to move back. The handle will have moved back by the amount of slack in the system at that position. Now move your new extra pointer so it lines up with the zero on the handle scale. Take off the dial gauge and put it back in its cosy dry drawer.

Now, to move the tool, bed, etc in either direction a known amount, you can rely on the appropriate indexing line – the makers' line or your new added wire one – depending on which way you are moving. So add a sticker with arrows to remind you which one to use for what.

Of course, it will not give totally accurate results if the wear or slack in the system varies from the middle to the ends, but it should save errors much more cheaply than a full- bloodied DRO?

Go on, chaps, tell me that this appeared in an article published by Tubal Cain (the biblical one) and known to every properly qualified whizz since then …

Cheers, Tim

[Tim StevensParticipant @timstevens64731]

A possible solution, but is it a new idea?

[John HaineParticipant @johnhaine32865]

I've not come across it, a neat idea!

[HopperParticipant @hopper]

I think it was Tubal Cain's father who first did it, with a chalk mark made with chalk he dug from the side of the mountain himself using a shovel made from iron he melted down in his home furnace.

The digital age approach is to use a felt pen.

I think you can claim ownership of the wire pointer idea though. Nice one.

[Neil LickfoldParticipant @neillickfold44316]

The spring wire is a good idea, then one thing less to be remembering.

Just noting the amount you have to turn the dial back is usually good enough. I have seen where people have a spring on the cross slide to keep it in tension towards the feed screw handle. I have also seen where people have put small pneumatic cylinder to act like a spring as well on the X axis with a near constant pressure reservoir attached. ( a bike tyre tube ).

Neil

[John ReeseParticipant @johnreese12848]

I was taught to always feed to the final setting by turning the crank in the same direction. as an example always approach final position by turning to the right. If you go too far, back way off and approach aain by turning right.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Reese on 27/01/2017 21:41:10:

I was taught to always feed to the final setting by turning the crank in the same direction …

.

Quite so, John

Although Tim's idea is 'clever' I cannot really see the benefit … it is usually necessary to do as you say; because otherwise the tool will likely be dragged across the backlash with unpredictable, but generally undesirable, consequences.

MichaelG.

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