Author Topic: worn out half nuts  (Read 144 times)

savarin

worn out half nuts
« on: November 04, 2018, 07:46:10 PM »
I believe I may have a major problem with my lathe (generic 9x20)
This is the second time I have had the half nut threads wear away.
The first time it happened I hadnt had the lathe long and the problem was swarf collecting inside and preventing the nuts from fully closing.
I sorted that out by making a new lever, placing the detents further apart and adjusting the mechanism ensuring the nuts fully clamped onto the lead screw and regularly cleaning out any swarf.
I stripped and reassembled and re adjusted it this time, most of the thread had gone but I needed to finish a job so had a go.
A couple of things I checked.
The saddle travels from end to end and the lead screw doesnt move up, down, in, or out so its in alignment with the worm and tail stock end bearing and the half nuts clamp firmly to the leadscrew.I will also check out the leadscrew for straightness some time but it doesnt wobble in the tain stock end is not bolted down so I'm assuming its pretty straight.
BUT
When I engage the threading lever to clamp the half nuts to the lead screw the lead screw flexes inwards towards the bed.
This has caused wear in the worm housing bearing at that position as well so its been going on a long time.
I have thought of placing some shims behind the worm housing to move it inwards towards the lead screw and possibly facing the tail stock end bearing down to move the lead screw inwards the amount it seems to flex.
The threads on the lead screw also appear to be very sharp on their edges and in particular where the keyway is cut and from the colour of the dust seems to be actually cutting the half nuts.
Major questions -
Where can I purchase the half nuts without the 12 to 16 weeks delivery time I'm being quoted in Australia?
Is it feasible to dress the complete thread on the lead screw to remove all the sharp edges? (or worth it)
Can anyone suggest any other things I could do? (other than purchasing a better lathe)
Thanks

4GSR

Re: worn out half nuts
« Reply #1 on: November 04, 2018, 08:18:17 PM »
That is a common Asian lathe found all over the world.  My immediate guess is buying the half nuts and a new lead screw from Grizzly Industrial.  Yeah, shipping may eat your lunch, but buy two sets so you have a backup on hand.  There maybe someone direct from Twain you could buy from and have them shipped direct to you.  Shipping maybe cheaper, too.  As for "will they fit?", I'm sure you will have to do some fiddling to get them to work. Won't be perfect right out of the box. Ken

4GSR

Re: worn out half nuts
« Reply #2 on: November 04, 2018, 08:25:11 PM »
Never understood why the Asians put a fine thread on that lead screw! >:(
They could heave easily made it a 10 pitch Acme or Trapezoidal thread and worked a lot better.

If your very adventurous, which you are, you could change the pitch to 10 threads per inch.  But doing that would require a whole new set of gearing for the gear train.  Woudn't be hard to do.  It would require another lathe to do the work on since your half nuts are gone currently.
Ken

Carpenter84

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Re: worn out half nuts
« Reply #3 on: November 04, 2018, 08:48:23 PM »
None of those options seems terribly appetising. I don't much envy your position currently, Charles. Good luck. Keep us posted.

And I thought it was difficult to get things to Canada quickly for a reasonable cost...
Shawn

First 9x42 column mill,
Enterprise 10x28 lathe,
Ko Lee 6x12 surface grinder,
Airco dip/stick 160 welder,
Fully stocked wood shop.

f350ca

Re: worn out half nuts
« Reply #4 on: November 04, 2018, 09:04:22 PM »
Im not familiar with your lathe Charles  but would like to give a couple of opinions.
If the lead screw stays in alignment to the apron as you move it then I wouldn't alter the bearing at the tailstock. That would change the alignment.
If the half nuts are pushing the lead screw inwards wouldn't removing material from the surface where they meat the apron stop that.

Hope Im understanding whats happening.

Greg

savarin

Re: worn out half nuts
« Reply #5 on: November 05, 2018, 12:59:40 AM »

If the half nuts are pushing the lead screw inwards wouldn't removing material from the surface where they meat the apron stop that.

Greg
Hmmm, hadnt thought of doing it that way, a bit difficult getting around the alignment pins but doable I think.

savarin

Re: worn out half nuts
« Reply #6 on: November 05, 2018, 03:07:51 AM »
Update on the half nuts pushing the leadscrew towards the bed.
The apron is held on with two bolts only, with some experimenting I found that by engaging the half nuts whilst the apron is loosely held then tightening them aligns everything up as it should be. One problem solved.

chips and more

Re: worn out half nuts
« Reply #7 on: November 05, 2018, 09:49:43 AM »
Donít know about your lathe? I was having threading problems on my lathe. Took the apron off and discovered a support bushing that aligns the lead screw was worn. This bushing is about 2Ē away from the half nuts on my lathe. The lead screw must have been flopping around because of the worn bushing. Anyway, made a new bushing and all is good now.

savarin

Re: worn out half nuts
« Reply #8 on: November 07, 2018, 07:22:56 AM »

You can see how worn the nuts are below, they look better in the photo than real life.
Whilst awaiting the new ones I thought I should clean and adjust as much as I could.
 Todays job was to check out the cross slide, it had a tiny rock between two corners.
 A bit of scraping got it sitting flat with full contact for the full length.
 Next I will be drilling and tapping for two more gib screws.
 Now another question, Would this be a good idea and worth doing to improve cross slide oiling?
 Grinding out hollows on the black lines and feeding them with a ball oiler, if so how many oilers per side?
 and Is there a better pattern?

4GSR

Re: worn out half nuts
« Reply #9 on: November 07, 2018, 08:27:04 AM »
Way too many zig zags there. They don't have to extend end to end as you show them.  About 2/3's cover is all you need.  Grind the grooves in a snake pattern, not zigzag.  Those 90 degree cuts will not let oil flow to the next 90 degree cut. I prefer oil cups over ball oilers on the cross slide.  Ball oilers limit the amount of oil you can get in them at one shot.  At least with a oil cup, the oil will gravity feed as it is needed until emptied. I'll try to find a picture of one I did on one of my lathes.  Ken

Jake Parker

Re: worn out half nuts
« Reply #10 on: November 07, 2018, 08:46:41 AM »
+ 1 on a long curvy line with one oiler in the center.
My CAD (crappy animated drawing) has the oiler in green.

4GSR

Re: worn out half nuts
« Reply #11 on: November 07, 2018, 10:29:55 AM »
+ 1 on a long curvy line with one oiler in the center.
My CAD (crappy animated drawing) has the oiler in green.

That's perfect!

The point of inducing oil does not necessarily need to be in the middle.  It can be near either end or both ends.

Ken
Ken

savarin

Re: worn out half nuts
« Reply #12 on: November 07, 2018, 08:09:08 PM »
That looks easier and makes more sense,  thanks.