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Chester 920 cross slide & Backlash

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Jon Harrison 314/10/2021 18:41:19
5 forum posts

Spotted a few old posts on this subject. The under slide nut on mine is quite worn and I can't get rid of the backlash.

Just wondering if someone found a UK supplier of a replacement nut that will fit?

If I read it correctly, can the front section ahead of the slot somehow be used to eliminate backlash. Saw one with 2 horizontal front end grub screws which suggested that that particular one could be adjusted.

Have pictures to add but can't figure how to do that on this forum as they're files on the computer and don't have urls etc

Andrew Tinsley14/10/2021 19:06:30
1488 forum posts

The "leadscrew" for want of a better word and the captive nut are really a bit undersized. Most people would replace with a larger diameter cross slide screw and a new machined nut, in say bronze. Doing this mod also allows you to increase the range of the cross slide.

Look on line for "Tricking out the 920 lathe". This will give the details as will some other sites (920 lathe forum for one). The trick of partially sawing through the nut and then using grub screws to enlarge the gap, is at best a bodge and it won't be long before you are back to square one, with lots of backlash.

Andrew.

Howard Lewis14/10/2021 19:15:09
5348 forum posts
13 photos

The grubscrews on the front of the cross slide are to adjust the gib strips, so that the cross slide moves without sideways play.

If your lathe is a Warco, have you approached them for a new nut?

If not, find the imported and ask them.

Bear in mind that 920 ,lathes may have been made by different factories, (Such as Sieg, Real Bull or Weiss ) so whilst spares from another Lathe may fit yours, others may not.

You have to have some backlash between Leadscrew and Nut, or the parts would be immovable. So to find 0.25 mm backlash might be quite acceptable. A skilled operator can produce superb work on a badly worn machine.

HTH

Howard.

Jon Harrison 314/10/2021 19:57:37
5 forum posts

It's a 920 Chester in white so maybe from the 80's or 90's.

That part sawn nut was on it when got it - thought the cut looked on the rough side / unofficial.

I'm not up to making that part and the left hand thread which is why I'd like to find one off the shelf.

It doesn't do a lot of work, mainly screws and ramrod tips for antique flintlocks and percussion beasties.

Chris Evans 614/10/2021 21:01:24
avatar
1960 forum posts

Google leadscrew and look at the suppliers. I used "Automotion Components" (am I allowed to say that ?) for my 14"x40" lathe. You will need to know pitch required and left or right hand. I bought 1 metre of trapisoidal leadscrew and a bronze nut that could be adapted to suit for around £60 Had enough to make three screws.

Andrew Tinsley14/10/2021 21:30:10
1488 forum posts

As far as I know, Chester are the only people in the UK to still offer the 920. Usually they have no spares stock and need to order from China. Prices are reasonable but the postal costs are very steep. The quality of the spares isn't brilliant in my limited experience.

Grizzly in the US are usually much better on stock and prices, but the cost of postage and customs  to the UK is even worse than the Chester quoted prices from China. The quality is not brilliant either.

Much better to take the bull by the horns and re engineer the cross slide drive. If you are not up to it, then find someone that can do the awkward bits for you, otherwise you will just have to put up with the backlash as it is, bodging the nut isn't a good solution. It would appear that someone has already done the bodge and the nut is now even more worn.

Andrew

Edited By Andrew Tinsley on 14/10/2021 21:34:30

Edited By Andrew Tinsley on 14/10/2021 21:46:02

Jon Harrison 315/10/2021 08:20:39
5 forum posts

Looked at the Arceurotrade one

specification...

C6-511 Cross Slide Screw Nut

  • Dimensions: 30x23x21mm excl. Boss
  • Boss: ø12x9mm with fixing hole tapped M5
  • Thread Pitch: 2mm

can't tell if that would be any good though.

Does someone have the precise spec for the Chester one. I might just know someone who could make it.

With the existing nut and backlash, precision engineering just isn't there.

Am I right in thinking the Chester was rebadged Warco (?) in the US at one time?

Jon

John Rudd15/10/2021 08:39:38
1439 forum posts
9 photos

The cross slide lead screw is M8 with a lh thread.

I had to make a new one for my 9 x 20 when the original snapped...Silver steel is good enough for a replacement..

not done it yet15/10/2021 08:45:45
6350 forum posts
20 photos

Let’s go back a bit.

Is the backlash the same at the extremities of travel the same as the mid-point/most used section? If the same all the way along, it is the nut which needs changing. If tighter at the ends, the screw is worn in the centre.

How much backlash is there? Compare that to the pitch, to assess how badly it is worn.

To post pictures you need to put your files into an album on the forum - and post from there. I expect searching for ‘posting pictures’ or ‘making albums’, or similar will provide practical details.

Backlash only affects dial-setting until it is taken up when setting. Easy enough if the backlash is constant along the screw. Many fit DROs to overcome any real issues between dial and real physical position.

there is also the possibility that backlask could be apparent due to end-float of the screw - it may just need shimming?

vic newey15/10/2021 10:13:26
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102 forum posts
59 photos

Lathes feed screw and nut replacement

tony Griffiths Lathes site has an advert for replacing any leadscrew, nut etc of any lathe type

I have seen the same service by the same man offered on Ebay,

Ebay. same man

Andrew Tinsley15/10/2021 10:46:01
1488 forum posts

I renovated a Chester 920 and it really does need a fair bit of work to get a decent lathe . It wasn't so much worn parts, but a poor design, Quite a few bits needed upgrading over standard, before it became a pleasant machine to use. Upgrading the cross slide leadscrew and nut to 12 mm was one of the things plus using a bearing to control the end float. The standard nut and 8mm leadscrew isn't really up to the job.

Andrew.

Martin Connelly15/10/2021 11:34:51
avatar
1901 forum posts
205 photos

I made a replacement leadscrew for a friend which had an m12x1 thread (RH) over a distance of 165mm. The first 100mm of the thread is truly worn out on one side of the thread and the last 65mm is like new. This was from an industrial as opposed to hobby machine (not a lathe or mill but can't remember what, some sort of tool grinder I think). I still have the original leadscrew as potential raw material. If this worn out leadscrew is used with a worn out nut then variable movement and backlash would be the result. The requirement for a lathe of a LH thread would make the production of a nut a bit trickier than the leadscrew but should be doable. Just practice on some bits of scrap first then cut the leadscrew thread to match the nut. If possible use a travelling steady to cut a long thread to avoid flexing issues along the workpiece.

steady threading.jpg

Martin C

Jon Harrison 315/10/2021 13:30:25
5 forum posts

Gentlemen, thank you all for the really valuable and informative input.

Have emailed several recommended companies / individuals and awaiting replies.

Given my current usage which is quite low I will initially be quite happy to have a working lathe, producing accurate nicely finished work. As aims and ambitions grow I'll hopefully develop more advanced skills

Vic15/10/2021 16:09:55
2920 forum posts
8 photos
Posted by Andrew Tinsley on 14/10/2021 19:06:30:

The trick of partially sawing through the nut and then using grub screws to enlarge the gap, is at best a bodge and it won't be long before you are back to square one, with lots of backlash.

Andrew.

It’s a standard part, not a trick as you call it on some machines. Pretty sure my 626 milling machine has one. wink

I’ve not needed to adjust it yet but nice to know I can before needing to buy a new part.

Jon Harrison 322/10/2021 11:08:50
5 forum posts

Back again

Couldn't get one made at anything like affordable so went back to tightening the grub screw into the nut. Appears to work ok.

Worked through everything and bar 1 issue it's much better than it was. Mf'd12/ 98 so not as old as I thought.

Current issue is the Woodruff key on the cross slide winder. The slot in the screw is worn, the winder is fine. Fix? Insert shim to tighten it?

While here, I was looking at the drive pulleys which don't appear to match the diagram on the plate.

A is the top one driving the chuck and faces in?

B is the intermediate pulley with a belt driven from the motor and faces out

C is at the bottom direct from the motor and faces outwards

Anyone have a picture of the 920 setup to hand so I can compare?

Russell Eberhardt22/10/2021 15:21:14
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2710 forum posts
86 photos
Posted by Jon Harrison 3 on 22/10/2021 11:08:50:

Anyone have a picture of the 920 setup to hand so I can compare?

That lathe has a big following in the US. It is usually referred to as the 9x20 lathe. Try a Google image search for 9x20lathe and you will find hundreds of pictures. There was a 9x20lathe group on Yahoo (I was a member when I had one) but it has now been moved, I think to groups.io you could try there.

Russell

Russell Eberhardt22/10/2021 15:59:29
avatar
2710 forum posts
86 photos

I've just been looking through my old files and have found a PDF file of the Grizzly manual which gives all the information on belt set ups and much more. If you send me a PM with your email address I can send you a copy.

Russell

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