Rescuing a 920 lathe!

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Rescuing a 920 lathe!

This topic has 47 replies, 11 voices, and was last updated 20 February 2018 at 20:01 by Andrew Tinsley.

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9 February 2018 at 16:24 #340621
Andrew Tinsley
Participant
@andrewtinsley63637
At last I have the Chester 920 lathe in my workshop. seems in good condition and requires the usual upgrades.

it came from a fellow modeller who has been stricken with Alzheimer disease. He has unfortunately done some very strange things to the machine including throwing away the splash back and gear cover door. This isn't much of a problem, but he has done some even stranger things with the motor and associated pulleys!

The pulley wheels are mounted on what is called a Bracket plate (part nos P4000201) which is screwed to the side of the headstock. Now this bracket plate has been thrown away! I have most of the bushes and all of the pulleys.

Can anyone who has a 920 do dimensioned sketch of the bracket plate? The hole positions for the pulley bushes and idler gear is really all I want. I would buy a bracket plate from Chester, but they need a picture of the spare part, which I have not got!

I just hate trying to lay out something like this. I always seem to get it wrong! However I might just have to give it a try.

Andrew.
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9 February 2018 at 16:24 #18844
Andrew Tinsley
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@andrewtinsley63637
9 February 2018 at 19:39 #340644
Oldiron
Participant
@oldiron
Hi Andrew Sorry cannot help you with this but I am sure some one will have some kind of answer soon.

regards
9 February 2018 at 19:45 #340645
John Rudd
Participant
@johnrudd16576
Andrew,

The bracket plate is secured to the head stock casting with a number of socket head cap screws…

I can measure mine next time I am back at the other house ( up for sale..) but in the mean time,

The motor drives an idler pulley,which also houses the clutch for screwcutting, the idler runs in a slot to provide primary belt tension.

The motor can also drive the main spindle directly, the upper 3 speeds…using the large 710 belt

Do you have the belt tensioning assembly too?

Edited By John Rudd on 09/02/2018 19:47:03
9 February 2018 at 19:47 #340646
michael howarth 1
Participant
@michaelhowarth1
Have a look at Steve Bedair's 920 website.

Mick
9 February 2018 at 19:52 #340650
Andrew Tinsley
Participant
@andrewtinsley63637
Hello Old Iron,

It is all a bit of a puzzle, certain things have been dismantled ,like the change wheel set up and the pulley system! He has made a direct drive to the headstock from the motor, which is screwed to the bench rather than bolted to the machine!

It is no use asking the poor chap, as one is very unlikely to get any sort of answer, unfortunately.

I can make the change wheel bushes and set that up, because the holes are extant. But the pulley system is a bit more difficult. I am going to have to make a new bracket plate and play with the existing pulleys and pulley wheels to get some idea where the pulley bushes go.

I think it is one of those jobs that will be easy as soon as you get stuck in. Too much thinking probably makes the job seem much worse than it actually is!

Thanks,

Andrew.
9 February 2018 at 19:52 #340651
Andrew Tinsley
Participant
@andrewtinsley63637
Deleated!

Edited By Andrew Tinsley on 09/02/2018 19:53:56
9 February 2018 at 20:00 #340654
Andrew Tinsley
Participant
@andrewtinsley63637
Hello Mick,

None of the 920 websites including Steve Bedairs actually shows anything much of practical use. I have – the manuals from Grizzly and Chester and again one can get a rough idea of where the pulley bushes go, but it is a bit of a fiddle!

Thanks,

Andrew.

P.S.It would be a shame to break the lathe and sell it as spares, it has had very little use.
9 February 2018 at 20:16 #340656
Redsetter
Participant
@redsetter
I think Amadeal still supply the 920 lathe, so may have a more sensible spare parts service than Chester.
9 February 2018 at 20:22 #340658
Andrew Tinsley
Participant
@andrewtinsley63637
Hello John,

I missed your post! That really is kind of you! Some measurements would make the job so much easier! I am missing the belt tensioner wheel , but have the lever and spring and I believe the correct bush for the job. The Chester manual shows an excellent exploded view of the tensioning arrangement and that should be easy to copy!

Send me a PM when you have time to take a look at your 920. I really think I should return it to original condition. I am going to give the lathe to an impecunious friend, if I can get it sorted. I can help him do the mods and alignment etc.

Once done it is actually a rather decent lathe. But you need to spend quite a bit of time rebuilding it. Another friend had a 920 which was fully sorted and a joy to use, unlike the machine from the box! Pity he sold it, otherwise I would have been over there with pencil paper and ruler!

Thanks again,

Andrew.
9 February 2018 at 20:51 #340663
Redsetter
Participant
@redsetter
I have just been out in the cold to have a look at my 920, but I think it would be difficult to measure accurately enough without dismantling.

To be fair I have always found Chester quite helpful by phone or email if you contact them directly and explain what you need.

The belt tensioner is a bit hit and miss, and does not work equally well in all positions, so don't feel obliged to copy it exactly!.
9 February 2018 at 21:40 #340672
Vic
Participant
@vic
Could a three phase motor and invertor be an option instead of swapping pulleys?
10 February 2018 at 12:23 #340813
Andrew Tinsley
Participant
@andrewtinsley63637
Thanks Redsetter and Vic,

I appreciate that it is difficult to measure up with pulleys in place and I don't expect anyone to dismantle their set up just to take measurements! However, even some very rough and ready measurements are better than none.

If I do get the lathe up and running, I may well do a conversion to VFD drive as I have a spare 3 phase motor and an old inverter hanging around the workshop and I could do with the space! The reason for this is that the slowest speed on the lathe with the conventional pulley set up would be just over 100rpm, which is on the high side. Just putting a VFD on the existing direct drive would be a bit limiting in range of speeds.

Thanks again,

Andrew.
10 February 2018 at 12:29 #340816
Vic
Participant
@vic
It’s never straightforward is it Andrew. Good luck with the Lathe whatever you end up doing. They are a nice lathe once set up.
10 February 2018 at 19:43 #340868
michael howarth 1
Participant
@michaelhowarth1
If I get a chance tomorrow I will photograph my lathe set up for you and try and put in some dimensions. You will at least then have some photographs for Chester. I have always found Tony a very nice man to deal with. I would second the 3 phase inverter drive being fitted……it totally transforms this lathe.

Mick
10 February 2018 at 21:25 #340888
Redsetter
Participant
@redsetter
OK, but no guarantee – please check!.

Bracket plate 8 mm thick, 230 mm front to rear, 220 mm top to bottom, ignoring the curved section which projects down over the motor. Front edge is on C.L. of headstock spindle, Top edge is 3 mm below top face of headstock.

Motor spindle to idler spindle 115 mm centres. Headstock spindle to idler spindle 205 mm centres. Where these arcs cross is the position of the idler spindle on the bracket plate. The hole is oversize to allow adjustment.

Belt tensioner arm pivot to idler spindle 55 mm centres, and they are in line horizontally.

Belt tensioner lever pivot to arm pivot 35 mm centres. The hole is 40 mm diameter and centered 28 mm from the bottom edge of the bracket plate. The vee belt is Gates no. 5M710.

I think that's about right – hope it helps, and maybe Mick H can confirm.
10 February 2018 at 22:06 #340893
Andrew Tinsley
Participant
@andrewtinsley63637
Thanks Mick and Redsetter,

Those dimensions are great and I won't be upset if you are a little out! I will speak to Tony at Chester, just in case they would have a bracket plate . I should think that is about one of the unlikeliest spares to carry for the 920. Hence I didn't really have much hope that Chester would have one, but worth asking, one never knows!

Thanks again,

Andrew.
10 February 2018 at 22:39 #340899
Les Jones 1
Participant
@lesjones1
Here is a picture of the drivebelts on my Chester DB-10G before I modified it with a 3 phase motor and VFD

I think it is similar to the 920 lathe so it may be some help.

Les.
11 February 2018 at 14:01 #340967
michael howarth 1
Participant
@michaelhowarth1
I wouldn't argue with anything that Redsetter has given you in the way of dimensions. The set up that Les Jones has photographed is pretty much the same as my 920 except that the belt tensioner bears down on the top of the drive belt. I took some photos this morning but because of the positioning of my lathe it was very much a case of pointing the camera and hoping that something useful was snapped. I think I mentioned that my lathe is inverter/variable drive and I would never go back to the original set up. With variable drive you do not need the upper pulley / clutch setup which would normally be driven from the motor via a toothed belt. The drive is taken from the pulley set on the motor direct to the mandrel pulley. I loop the belt over the centre drive pulleys and don't even use the belt tensioner so I have a built in clutch. I used to get through quite a lot of those drive belts before I fitted the variable drive and they are now mighty expensive. Touching wood, I have not replaced a belt in 2 years since fitting variable. I think that you said you have an inverter/motor…….if you use that you do not need a backplate and in my opinion you will have a much better, more tractable machine. A piece of 8mm mild plate would suffice to fill the gap. If you wished to incorporate the belt tensioner, the design is a bit crude with loads of latitude for a positioning bolt. Have a look at my set up and I will be happy to answer any further questions. Ihope this will have been of some use. Mick
11 February 2018 at 14:24 #340970
John Rudd
Participant
@johnrudd16576
Andrew,

I have genuine Gates 710 belts if you need one or two, but not at machine supplier prices. Contact me via private message if you need to.
11 February 2018 at 16:01 #340986
Andrew Tinsley
Participant
@andrewtinsley63637
Hello Les and Mick,

Thanks for the help and encouragement. Mick your suggestion of just using the 3 step pulleys and a VFD has really put the cat amongst the pigeons! I would like to get speeds between 50 and 2000 rpm. Is this feasible without running the motor too slowly (cooling concerns)? I suppose I could work it out, but it is easier to ask!

Thanks again,

Andrew.
11 February 2018 at 16:43 #340990
John Rudd
Participant
@johnrudd16576
Posted by John Rudd on 11/02/2018 14:24:15:

Andrew,

I have genuine Gates 710 belts if you need one or two, but not at machine supplier prices. Contact me via private message if you need to.

Just been and checked….the belts are 730 not 710. Although some of the 9 x 20 lathes were fitted with the longer blt like mine…..Sorry for the mis-information.
11 February 2018 at 16:48 #340992
Redsetter
Participant
@redsetter
As a matter of interest, does anyone know the difference between the 920 lathe that uses the 710 belt and the one that uses the 730, as the belt length is fairly critical?
11 February 2018 at 17:16 #340997
michael howarth 1
Participant
@michaelhowarth1
Just guessing really, but I suspect that it has something to do with the motor mounting.

Mick
11 February 2018 at 17:24 #340998
michael howarth 1
Participant
@michaelhowarth1
Andrew, I have had no problems running mine at low speeds. I do not have any expertise in inverter / motor technology but I suspect that it will depend on your outfit. I am pretty sure that some knowledgeable person on this site could answer the question for you in more detail. Having said that, with the original setup you are going to get a speed of between 100 – 120 rpm anyway and that can be more than just annoying when you only want 50. I am probably talking rubbish but what about an additional 12v cooling fan eg from a computer? It seems to me that you have not got a lot to lose by trying it out.

Mick

Edited By mick H on 11/02/2018 17:26:04
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