Feed Screw mis aligned

Hi guys,
I've noticed on my new lathe, that when I get to the last section of the feed screw, towards the headstock, that winding the lever wheel on the apron is not as smooth. its affecting my finish, and also when I use the auto feed, the lever is quite hard to dis-engage. I've also noticed some brass shavings in a small section near the headstock on the feed screw, which indicates that its rubbing off and wearing down the half nuts.

I assumed that maybe the feed screw was out, so I ran my dial indicator across it (in the keyway) to see how much.
It looks like it is lower at the headstock end by 20 thou or so.

I'm not too sure how to adjust this, other than drilling larger holes in the tailstock end, where the bearing block is that the feed screw sits inside of and shimming it out. I cannot see how to adjust it from the headstock end.

Anyone able to offer some suggestions n how to best solve this issue.


Middle :

Attachment 317530



Headstock end :

Attachment 317531

Oh, of course, I have not discounted that the feed screw is actually bent, which I cannot test unless I take off the apron and feed screw and test it.

First thing I would do is take the leadscrew off and see if the problem goes away.

Cant be much more help as I'm not had the leadscrew off one of these one shaft machines.
You might just need to adjust the bushing for the powerfeed.... if there is one, if its adjustable.(see no help there)

Stuart

> I've noticed on my new lathe, that when I get to the last section of the feed screw, towards the headstock, that winding the lever wheel on the apron is not as smooth.

Not sure what you mean. The big apron handwheel is acting on the rack, not the leadscrew. The rack itself can be adjusted up/down, sometime you may have to drill out the mounting hole a little to get more adjustment. If you have this problem with automatic feed disengaged, and it is not the rack alignment, then the only reason for the apron/saddle to bind towards the left or right end of the bed is if the uderside of the bedways is ground tapered (or thickened by paint or burrs or the like).

> its affecting my finish, and also when I use the auto feed, the lever is quite hard to dis-engage. I've also noticed some brass shavings in a small section near the headstock on the feed screw, which indicates that its rubbing off and wearing down the half nuts.

The lathe you have uses the half nuts only for threading, not for automatic feed. The automatic feed is done via the slot in the leadscrew and a worm. This lathe is known for a misaligned leadscrew - it should be parallel to +/-0.1mm to the bedways, but this test is not listed in this lathes test protocol. Alignment is possible on the right side by moving the leadscrew bearing braket up/down. But on the left side it would need some work on the Norton gearbox housing mounts. The leadscrew should be exactly at the center of the worm, and at the center of the half nuts, and parallel in both axes to the bedways. If the leadscrew is not in the center of the worm, or if the leadscrew is bent, automatic feed will be jerky and you will notice this very well on surface finish.

The Chinese 9x20 is also famous for the burrs left in the leadscrew after cutting the slot to "eat up" the half nuts when engaged. Depending on luck of the draw, it may be necessary to carefully deburr this slot (yes it is a time consuming hand job with a needle file). Sharp burrs have been known to completely ruin the half nuts within the first minutes of use, so be careful to check before threading the first time.

PS: I have not visited the Yahoo 9x20Lathe group for years, but some 10 years ago it used to have plenty of useful information on this particular lathe. I used to have an interest in it, because the design is a close copy of my Austrian Emco lathe, some parts are identical designs.

Quote:

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Originally Posted by cba_melbourne

> I've noticed on my new lathe, that when I get to the last section of the feed screw, towards the headstock, that winding the lever wheel on the apron is not as smooth.

Not sure what you mean. The big apron handwheel is acting on the rack, not the leadscrew. The rack itself can be adjusted up/down, sometime you may have to drill out the mounting hole a little to get more adjustment. If you have this problem with automatic feed disengaged, and it is not the rack alignment, then the only reason for the apron/saddle to bind towards the left or right end of the bed is if the uderside of the bedways is ground tapered (or thickened by paint or burrs or the like).

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Thanks for the response CBA
I se what you mean, that the apron handwheel is on the rack, and not the leadscrew.
I'm trying to work out where the rack can be adjusted up or down, there are two screws holding it into the cross slide. I cant see any other adjustment.

I'll check for paint burrs etc.

Quote:

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Originally Posted by oohsam

I'm trying to work out where the rack can be adjusted up or down, there are two screws holding it into the cross slide. I cant see any other adjustment.

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The rack has nothing to do with the cross slide. The rack is located right underneath the front Vee way. It is fixed there with several screws (about one screw every100mm). Because the rack is so long, it does not take much force to bend it. So if the threaded holes for the fixing screws are not drilled correctly, it is easy during assembly to end up with a bent rack. If the rack is too far away from the sprocket its no problem, the apron handwheel will just have a bit more backlash than necessary. But if the rack is too close, then the sprocket will become hard to turn. It feels just like if the saddle was binding. The automatic feed also uses the rack and there will be increased wear to its components.

In the past (8-10 years ago) the rack alignment was rarely the problem on this Chinese 9x20 lathe - it is usually adjusted on the loose side. But any quality issues may well have changed over time, and I have no experience with more recently made lathes of this model. The worm wheel misalignment used to be a much more frequent issue. A bent leadscrew is always a possibility, if the lathe had an accident in transit (anywhere from the factory to your home).



Whilst still in warranty, you may want to check for other problems that this machine used to have (again, they may well have fixed some or all these problems in the meantime):
- a wobbly/weak compound (they use too soft cast iron, too soft screws for the base, and the fit/finish between base and main body is not ground as per the original design). Can be partly cured with the 4-bolt clamp that you just made.
- the cross slide gib design has been simplified and is difficult to adjust. The thick gib strip is often bent or twisted, what causes localized binding of the cross slide.
- there is a safety clutch inside the large cogged wheel for the slow belt settings. It is only active at the very slowest speed setting. It is very badly made and usually does not work, people have disabled it by putting a pin through it. Also, on some machines they used brass bearings instead of oilite for this cogged wheel, and a turned shaft instead of a ground shaft, so it will bind up soon if not oiled daily.
- Spindle bearing preload is sometimes too loose, causing surface finish problems and difficulties holding dimensions. The spindle bearings are an extremely tight fit onto the spindle. Always (nobody ever reported them to be loose). This makes a fine preload adjustment totally impossible. The only way is with a mallet, trying again and again until by chance it gets right. To do it properly, one would have to remove the spindle and either grind the bearing journals, or use some emery cloth on the left bearing journal only, until the inner bearing ring can slide on with hand force alone (without tapping with a mallet).
- the small 5M Polybelt normally lasts several years of home use. But not if all the pulleys are not perfectly aligned on the same plane. Especially the idler wheel for the belt tensioner is often badly made - the Z shaped shafts are not at exactly right angles. If this idler wheel is not in any position of the tensioning arc always rectangular to the belt plane, then the belt will flip over, eg inside out. Once this flip over has happend, even if only for an instant, the belt is shot: it will forever keep flipping over. It must be replaced and the Z-shaped arm carefully bent in a vise until each of its shafts are perfectly parallel to to each other
- they use low cost motors with a centrifugal switch. If the switch stays closed it fries the start capacitor.
- the supplied 4-jaw chuck is a boat anchor
- the supplied 3-jaw chuck can have up to 0.5mm runout. I would try to exchange it if it has more than say 0.2mm runout whilst still in warranty.
- burrs left in the leadscrew slot after machining may act like a milling cutter and eat away the brass half nuts in only few minutes. Needs careful de-burring before using the half nuts for the first time.
- the included changewheels may not have the central hole in the center and/or not at a right angle, they may wobble excessively affecting surface finish with automatic feed. The bushings for the changewheels may be a press fit instead of a slide fit.
- and one final warning: do never try to take the headstock off the bed. It does NOT sit on the Vee ways. It is very difficult to adjust with the 4 adjusting grub screws provided and some paper shims (needs a test bar and a precision level and about one day of your time), and you never get it again aligned in all planes AND at the same height as the tailstock. Then you need to adjust the tailstock for height, which if too low is a very time consuming affair. Never touch the four nuts that bolt down the headstock, it has been torque shimmed at the factory (often using paper shims in between headstock and lathe bed) to be parallel with the bed. It is not easy to get it back in alignment.

Sorry but i found Chris's first reply to be rather confusing.
Clearly from Ooshams first post it is alignment of the leadscrew that is the problem, not sure why the rack was bought up. I would take the leadscrew out to be sure it is the problem, and then look to how it can be adjusted. You should fine the QCGB is a separate casting to the bed (it is on most lathes) and can be loosened and moved. Did the machine come with an exploded parts diagram in the manual? That should at least reveal some clues.

Cheers,
Ew

Quote:

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Originally Posted by oohsam

Hi guys,
I've noticed on my new lathe,..., that winding the lever wheel on the apron is not as smooth.

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Quote:

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Originally Posted by Ueee

Clearly from Ooshams first post it is alignment of the leadscrew that is the problem,

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I'm not so sure of that, on my lathe the apron hand wheel engages the rack, not the leadscrew. There may be a problem with the leadscrew but at least on my lathe you would not be able to tell using the hand wheel on the apron...


Jayson.

*** On edit***

If the half nuts are catching on the leadscrew this may cause it to feel "not smooth" so I guess the leadscrew could be the cause.

Hey guys,
Really appreciate all the replies. I went out with my tools and pulled half the thing apart (again) with more understanding of what does what.
I have an exploded parts diagram, but its terrible. I've been relying on youtube and other sites with images to work out how it all works. And of course info from you guys.

Firstly, there was more than one issue.
The feed screw was mis-aligned and meshing the half nut right at the headstock end of the lathe.
I pulled off the the rack that the apron meshes to, and that was mis aligned too, which wasn't helping. As soon as I undid 3 of the cap screws, it snapped upwards a few mm's. So the screws were holding it down.

i fixed the feed screw by drilling out holes in the bearing block at the end of the lathe. Screwed the apron back onto the cross slide, and left the screws fairly loose, so it had some wriggle room. Engaged the half nuts and turned the lathe on till i got to the head stock. Snugged up the cross slide/apron screws, and traversed the table. I was able to watch the lead screw moving up/down on the end (as those cap screws were loosened off too) and I worked out exactly where it needed to be.

tested it all out after much stuffing around, and I now have silky smooth table traverse along the whole table (there's a slight stick towards the tailstock end) but I couldn't get it perfect, I think it must be the rack because when I loosen off the screw in that spot it gets better, which I did, hopefully its not too lose.

Thanks heaps guys, Im over the moon that its all fixed and running smooth. It should help out heaps.
The halfnuts and auto feed disengage so easily now, it was almost impossible before when the apron got near the headstock. I had to coast a few times because i was worried of crashing the machine!

Cheers fellas. Hopefully this will be useful to someone in the future.
Its also helped me understand my machine a lot more.

Hi Oohsam,

Glad to hear you got your lathe sorted. You do learn a lot by taking them apart and fixing things. It's a pity that it seems a common thing with these Chinese lathes that people become very familiar with their machines purely by having to solve problems on a poorly assembled machine. Looking at all the troubles that I read, I think I'm pretty lucky with my Chinese 12x36! I only had a couple of issues.

Simon

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Originally Posted by simonl

Hi Oohsam,

Glad to hear you got your lathe sorted. You do learn a lot by taking them apart and fixing things. It's a pity that it seems a common thing with these Chinese lathes that people become very familiar with their machines purely by having to solve problems on a poorly assembled machine. Looking at all the troubles that I read, I think I'm pretty lucky with my Chinese 12x36! I only had a couple of issues.

Simon

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Simon, with Chinese lathes fit and finish gets better the larger (and more expensive) the lathe. The great divide seems to be 10". Below 10" swing they are all pretty badly put together and rarely work well out of the box. Above 11" fit/finish improves markedly, and above 13" there is another big overall jump in quality.

Oohsam, people have said the Chinese 9x20 comes in a kit. It is roughly preassembled, but only to make sure all parts are there. It is up to the owner to make it into a real lathe. The good news is, by investing some extra time you can make it into a quite good machine. And at the same time you can learn a lot about this specific design, as well as about lathes in general. Another way to look at it: this lathe retails in Australia for $11 per kilogram, and less on sale. By weight, that is less than you pay for a midrange quality treadmill made in China. You cannot expect the factory that makes these lathes to spend more than a couple hours on adjustments and alignments. Wages in China are not that low anymore.

Totally agree !

I somewhat knew what I was getting myself into. I Considered the next size up, for an extra $700 which would have given me some nice features (I kind of wish I had), like power feed on the cross slide, and the full gearbox, but for the $1100 that I paid, I am very very happy.

I could tell that the finish was not great, but I also like that there is alot of information on the internet about improving the lathe. Which I am doing slolwy!

Cheers

Hi cba,

That makes sense what you say about 9x20 v's 12x36 v's 13x40 (think that's the next size up) in terms of quality.

Hi Oohsam, you gotta love the net! No shortage of information on our Chinese lathes and mods for improving them!

Simon