Cross feed screw

[dennisa49]

Hello,
A question of tightening a cross feed.
I have a 9 x 20 (AL51G) Hare and Forbes lathe. Overall not a bad little machine.
However the cross feed has the standard 5+ graduations of slack between
moving the wheel and the slide beginning to react.
Has anyone tried machining a new screw and or internal thread, found a way to
tighten the action please?
The gib keys are properly adjusted, no slack in the slide itself.
Many thanks for any forthcoming advice,
Kind regards, Dennis

 

[bazmak]

The slack is called backlash and is difficult /expensive to get to zero
Not familiar with your lathe but most lathes have adjustment to improve/reduce backlash,usually with the feed nut.The small cheap lathes
have screws to rock the bronze nut but the larger better models have a split nut that can be opened to tighten the feedscrew on the nut.Take it apart and have a look by which time you will have further input from others with
some experience with this model Regards barry

 

[goldstar31]

I also had a 'generic' 918/920 which had a Myford nose!
As Barry rightly remarks, there should be a split nut to take up some of the slack. Having said that, there is no guarantee that the feed screw is also worn and also that the tolerances and fit are poor or good. These are a matter for measurement and inspection and no amount of postulation here will suffice.

The only reasonable solution is to have locks and stops and decent DRO's. At least, it also solves the conversion between Imperial and Metric working.

If, and I really mean IF, taking up slack by mechanical means does not solve some of the problem ie makes for acceptable working, there is no reason not to 'tin' the nuts. Long before DRO's and such were commonplace, I tinned the feed screws on a worn out ex WW2 Pools Major lathe. A lot of arm twisting after sooting the feed screws was the order of the day.

Again, if the feed screws are zinc alloy( like Myford's) they CAN be carefully squeezed. Again, not for internet 'discussion'- a bit of an art form.

Having said all this, it is a question of going back to first principles in machine tool measurement. Well, that's my take.

 

[dennisa49]

Thanks for info, about 30 minutes back I was berating myself for not considering a DRO system of some sort. Then kind Goldstar suggested the idea.
The backlash in the machines are inherent to the system.
A mod is in order.
Once again your input is highly valued.
Regards Dennis

 

[goldstar31]

Thanks for info, about 30 minutes back I was berating myself for not considering a DRO system of some sort. Then kind Goldstar suggested the idea.
The backlash in the machines are inherent to the system.
A mod is in order.
Once again your input is highly valued.
Regards Dennis

Speaking of 'mods' might I venture a couple or so?

As mine came, the lowest speed was not 100rpm but 130Rpm. You know the English 240/250 volt affair! So two variations spring to mind to avoid getting terrified at the speed of saddles arriving at alarming speeds.

My first one was changing the pulleys to something somewhat slower and the second was to convert the beast to 3 phase and relax a bit. Both work and are documented. Pulleys are needed plus lots of belts but heigh ho? and dead cheap.

The second is the funny tee slots in the saddle. I'm a Myford guy really and the slots run sideways on a 920. I simply made a subplate out of a bit thick sheet- I think that it was 28mm. Whatever it was, I simply drilled and tapped it to take such things as a vertical slide, rotary table and rear parting off tool post( George Thomas design).

If you get quite enthusiastic, you can add a Cleeve swing boring tool affair and life becomes more accurate and quite leisurely.

I've sort of lost count at the mods but it happens in old age:hDe:

The odd thing in it, is that I returned all my Myford dedicated bits back from the 918/920 to not just one Myford but- TWO. I've spent the children's inheritance

Does this help you?

Norman

 

[tornitore45]

My cross slide has 10 division =0.010" and has never kept me from hitting the target diameter. It will be 0.020 before I bother to adjust the backlash screw.

Backlash is no more than a nuisance, never kept anyone from doing precision work.

A funny thing is happening to my lathe, is getting more and more accurate as it ages.

 

[Herbiev]

http://www.ebay.com.au/itm/like/181...%3D705-213732-5960-0%26rvr_id%3D1029605020817
I have found these ballscrews eliminate backlash considerably

 

[deverett]

http://www.ebay.com.au/181845682502
I have found these ballscrews eliminate backlash considerably

That set me thinking about a Myford modification to the cross slide. Basically it is the addition of two roller thrust bearings, one each side of the leadscrew bracket. While not eliminating backlash, it does make the operation of the leadscrew much smoother.

Dave
The Emerald Isle

 

[BillWood]

Hello,

I made an acetal nut as per this post, interesting and fairly easy to do.

http://bbs.homeshopmachinist.net/threads/43645-Making-Acetal-leadscrew-nuts-the-easy-way

reduced my backlash from 0.030" to zero and initially it was far too tight and a right pain to use.

So if you try that method you really need to somehow create a tiny bit of backlash to loosen it up and either wrap the screw with plumbers tape (or alfoil ?) prior to making the cast or have a way of reaming it out a bit.


Bill

 

[rodw]

Backlash is no more than a nuisance, never kept anyone from doing precision work.

My thoughts exactly. Dennis, I have a H&F lathe and backlash is easy to manage and live with. I think you are worrying about nothing.

 

[Wizard69]

My cross slide has 10 division =0.010" and has never kept me from hitting the target diameter. It will be 0.020 before I bother to adjust the backlash screw.

Backlash is no more than a nuisance, never kept anyone from doing precision work.

A funny thing is happening to my lathe, is getting more and more accurate as it ages.

Excellent words of wisdom. If the ways are in good condition and the gibs properly adjusted backlash is easy to live with on a manual lathe. One just needs to tune their mind to the idea of taking out the backlash. Sloppy saddles, that is machines with loosely adjusted gibs or lots of wear in the ways are a bigger factor in holding tolerance and getting good finish.

 

[BillWood]

I've noted the above comments about backlash being an inconvenience rather than a problem.

I found it terribly confusing when I had 0.030" on the 2nd hand lathe when I first bought it. That's why I made the acetal nut which was initially equally painful being far too tight.

Any tips or ways of thinking that help one to live with backlash?

Bill

 

[dennisa49]

Thanks for the advice and hints, much appreciated.
You are right it is an inconvenience rather than a hindrance to accuracy.
It is the return to position, I have set up a digital DTI which indicates
the zero point.
I will be very happy if this is the biggest problem I have in retirement.
Kind regards,
Dennis

 

[10K Pete]

I've noted the above comments about backlash being an inconvenience rather than a problem.

I found it terribly confusing when I had 0.030" on the 2nd hand lathe when I first bought it. That's why I made the acetal nut which was initially equally painful being far too tight.

Any tips or ways of thinking that help one to live with backlash?

Bill

Machine tool basics: Always turn the feed screw to move the tool into the work. Don't laugh; think about it.

If turning an OD, turn the screw on the cross slide clockwise, right? If you
were aiming to set the dial for "35" and went past to "40", oops! DON'T BACK THE SCREW TO "35" ON THE DIAL!! Turn the screw counter clockwise way past the target "35" and come up on it again.

Am I making sense here? By always turning the screw, to move the tool,
in the SAME direction (pushing the tool, NOT pulling it) then there is no lash in the movement to position.

For boring the same applies but maybe in the opposite direction, right?

Repeat: Always turn the screw to move the tool into the work!! I doesn't matter if there is a few thou or a quarter inch of lash, you push the tool with the screw so there's no clearance between the screw and the nut.

This applies to all feed screws on all machines.

Pete

 

[tornitore45]

What Pete said +

Soon enough you develop the feeling how far to back up when overshooting the dial setting. Suppose you are aiming for 30 division and reach 35 divisions, reversing rotation is initially very easy, without feeling any friction because the tool is not moving, when you start feeling a drag, you know the screw is now pushing the opposite side of the nut. At this point back off the overshoot and more because you must reverse again (going now in the right direction) until you feel the drag again, hopefully you back up enough to be far from the target when you feel the drag; let say at the 22nd division. Now move from 22 to 30 without overshooting.

It takes 3 minute to describe in writing but 1.7 seconds to do.

 

[BillWood]

Pete and Mauro,

Thanks.

Will have another go with the original loose nut.

Bill