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Super 7 Lathe Clutch, Countershaft or Pulley Wobble

Quite a big wobble visible on countershaft pulley when clutch is engaged

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John Stucks01/01/2021 14:12:46
13 forum posts

Hi,

I’m trying to locate the source and solution to a wobble that you can see on the countershaft pulley when the clutch is engaged. When the clutch is disengaged the pulley looks to run true, and then when engaging the clutch it runs with a large wobble. This seems to feed down into the the workpiece and causes a bouncing cut without any successful clean cuts.

The problem happens with our without workpiece in, and also with our without the drive belt connecting countershaft pulley to the motor pulley. Also with or without the headstock engaged.

I have a new to me Myford Super 7. I’ve read the setup manual cover to cover, and I know I have some other setting up to do (proper stand and bed levelling, tool height etc) but because of the way I can recreate this wobble with as much disengaged as possible it seems it might be some sort of alignment located in or around the countershaft or clutch. But as I am new to lathes other than reading manuals and trying to find similar problems online it would be great to get some experienced opinions.

I can see the wobble in the workpiece, even when supported by the tail stock and is apparent enough to cause a non successful cut. I understand there may be more at play than just this pulley wobble causing my wobbly workpiece but I’m trying to locate and fix one problem at a time.

I have uploaded a video to show the pulley whilst engaging and disengaging the clutch so you can see the difference. Any help would be greatly appreciated. I have spent the last few weeks reading this forum so thought it time to join!

**LINK**

if I’ve missed any information off I’ll be happy to add what I can.

Thanks,

John

Martin Kyte01/01/2021 15:22:37
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2207 forum posts
38 photos

I would suspect badly set up headstock bearings. You can end up with the spindle running out if the rear bearings are not clamped together correctly.

The first thing I would do (as it's easiest) is disengage the headstock drive by flicking over the backgear drive key on the bull wheel but without engaging the back gear lever. This eliminates spindle rotation.Do you still get the wobble on the cluch pulley?

regards Martin

John Stucks01/01/2021 17:05:37
13 forum posts

Hi, thanks for the reply. I just tried what you suggested, using the drive key on bull wheel (if I understood it correctly) to disengage headstock (but it only didn’t spin if I held the chuck gently). The pulley on countershaft still wobbled when clutch was engaged. Thanks, John

noel shelley01/01/2021 17:29:14
369 forum posts
9 photos

Which clutch type do you have ? the early shoe type or later cone clutch in the primary belt drive cover .

John Stucks01/01/2021 17:34:40
13 forum posts

Hi, not entirely sure. Can you see from the YouTube video in original post?

noel shelley01/01/2021 17:36:16
369 forum posts
9 photos

Seen link ! Late clutch. Fit a new belt on headstock A29.5" or A780 and carefully re set the headstock bearings. Don't worry about the primary wobble yet.

Steviegtr01/01/2021 18:15:15
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1910 forum posts
252 photos

I would agree that the head bearings need to be adjusted. Also i always make sure the oil pot is full every day.

If you are not sure how to set up the bearings then search you tube. I think this guy does one setup.

Myford lathes

Steve.

Edited By Steviegtr on 01/01/2021 18:35:05

John Stucks01/01/2021 19:35:31
13 forum posts

Brilliant I will have a research and see if I can reset the headstock bearings. I’ll report back once I’ve tried that! Thanks, John

roy entwistle01/01/2021 20:30:50
1321 forum posts

I can't see the headstock bearings causing this. It looks like the clutch plate is wobbling so a worn clutchplate bush or a bent layshaft. Be very careful dismantling the clutch. Ball bearings, springs etc. fly all over the place.

Roy

John Stucks01/01/2021 20:36:05
13 forum posts

Hi, if it’s something to do with clutch, is there any way of testing that, or testing which bit it might be? Thanks, John

Hopper02/01/2021 00:12:02
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5174 forum posts
114 photos

I'm not seeing enough clutch wobble in the video that I would expect to influence turning finish at all. I don't think that is the source of your problem.

It looks like the material you are trying to turn is quite hard/tough. Is it a piece of unknown scrap? If so, replace it with a known piece of mild steel bought as such from a reputable supplier. Bits of unknown scrap often prove impossible to turn nicely.

Also, your indexable tool could be a source of trouble. It is sticking out of the toolpost too far for starters. And, hard to tell from the video, but it looks suspiciously like a 12mm tool shank, which would be setting the cutting tip more than 2mm too high above centre. Even a 10mm shank tool sits 20 thou or so above centre in a standard Myford 4-way tool post, which is made for old 3/8" tools, unless you mill down the toolpost base or the tool shank. Or you can use 8mm shank tools sat on packing strips of sheet metal built up to height. And do check the tip of that tool bit with a magnifying glass and make sure it is not chipped.

You could also try dropping the rpm by putting the belt on a medium speed headstock pulley and see if that helps.

And be aware that carbide tooling like that needs to take a decent depth of cut, say 5 thou or more. It often rubs and plays up if you try to take light finishing cuts with it.

Before you start fiddling with your headstock bearings, actually measure how much play you have in the headstock bearings. THis is best done by holding a long piece of stout bar in the chuck and pulling the end up and down. Measure movement of the spindle right behind the chuck with a dial indicator to get a reading. Dont adjust it if not excessive. There are threads on measuring and adjusting S7 headstock clearance on this site you will find with a search. Read them before proceeding.

John Stucks02/01/2021 01:31:21
13 forum posts

Thanks for the suggestions. In the chuck on that video is a piece of solid, clean mild steel. I’m using 10mm tools that are new, and tried with much less overhang than that, also tried locking any slide not in use and supporting workpiece with tail stock. But you’re right the tool is still slightly higher than centre so I have some 8mm tools on order. I tried on all 4 main speeds with similar results and was cutting around 10 thou each pass.

I did notice that when coming in with the cross slide for a pass at about 10 thou depth the tool pushed the workpiece slightly causing it not to engage the cut properly and adding to the nasty chatter. It looked like a combination of the workpiece moving under the pressure of the tool and the tool moving under some play in the cross slide. So I have a few issues to fix, just seems like the clutch wobble isn’t helping the workpiece movement.

I’ll have a look at headstock play and do some measurements before pulling apart. Thanks again for the reply,

John

Hopper02/01/2021 02:30:05
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5174 forum posts
114 photos
Posted by John Stuckey on 02/01/2021 01:31:21:

... I’m using 10mm tools that are new,... the tool is still slightly higher than centre...

...I did notice that when coming in with the cross slide for a pass at about 10 thou depth the tool pushed the workpiece slightly causing it not to engage the cut properly and adding to the nasty chatter.....

The higher-than-centre tool may be a large part of your problem then. The shiny (albeit chattery) surface on the job indicates the tool bit is rubbing rather than cutting. Which would be a result of being too high.

Visible movement of the job like that is indicative of either play in the headstock bearings or a bellmouthed chuck not holding the job solidly. Usually a centre will compensate for the lattter but not the former.

You will always get some slack in the cross slide feed screw and it does not affect cutting as long as you wind the cross slide out further than where you want to use it and then wind it back in to the exact point where you want to cut. This takes up the backlash just fine. You can minimise the backlash by tightening up the handle and lock nut on the feedscrew. Plus of course, it pays to make sure all your gib strips on the carriage and cross slide are set correctly.

Howard Lewis02/01/2021 04:32:07
4426 forum posts
8 photos

As Hopper says, the cutting edge of the tool must be on the centreline of the spindle for it to cut properly. Too high is useless.Only rubs rather than cutting. Too low means that all the tool angles are wrong, so that it does not cut properly, and encourages the work to try to climb over the tool. It can also try to pull the Cross Slide forward as the cut nears the centre of the job, which will not be good for accuracy..

Once you have set the tool on the centreline, and sorted the problem, then make yourself a Centre Height Gauge, and in future set all tools to that.

Making one will be a good learning exercise.

Buy a book such as L H Sparey's "The Amateur's Lathe" or Ian Bradley's "The Amateur's Workshop". These or similar books (Harold Hall on lathework? ) will tell how to grind and set tools, as well as basic principles.

Once the basic principles have been grasped, then becoming familiar with the machine and what it can do for you will make life easier and more enjoyable.

Find a local (Wher are you located? ) model engineering club, and join. Hopefully, before too long you will be able to meet other enthusiasts and learn from them.

Howard

not done it yet02/01/2021 07:47:24
5609 forum posts
20 photos

I think Hopper is on the money. The cutting geometry is wrong for some reason - could be tool height, slack in gibs or even carp cutting tips (origin of these?). The clutch output shaft, to me, does not appear to be the cause.

Reducing the overhang of the tailstock spindle should also help avoid deflection of the workpiece, if that is part of the problem.

You might achieve some enlightenment by video-ing the machine, while cutting, and playing the video back at the slowest speed possible...

Even try a HSS cutter? Have you measured the deflection of the headstock and tailstock under a reasonable side force? Have you measured the end-float of the spindle? There is little pint in trying to improve something if there is nothing wrong with it in the first place!

Try a lump of aluminium bar (it should cut more easily than steel)?

I honestly think you are looking for a fault that is nothing to do with the cutting results.

John Haine02/01/2021 09:09:40
3647 forum posts
197 photos

Whatever the tool geometry issue is, that clutch also needs fixing. My S7 has the same design and has no sign of wobble. You could easily have a dicky clutch, spindle play, and the wrong tool height. Test and fix one problem at a time.

bernard towers02/01/2021 09:27:16
106 forum posts
66 photos

Looking at your video and the mismatched colours of your lathe I would suspect mismatched / worn parts that have been used to build it, possibly a bent clutch shaft as mentioned earlier. If you made your location known maybe somebody local to you could help?

Edited By bernard towers on 02/01/2021 09:27:55

John Stucks02/01/2021 12:04:42
13 forum posts

Hi, thanks for all the responses, much appreciated. Yes it is clear I have a few things I need to work on to get up to par. Am trying to address them through lots of research and reading. Working my way through one of those books at the moment.

I live in Farnham in Surrey although lockdown at the moment is preventing much. I will definitely address tool height next, then measure the movement of workpiece under pressure, then measure headstock play. I’ll test cut then and see results and if clutch then needs looking at also. It sounds like there are a few things at once going on.

Thanks again, I’ll report back once I’ve done a bit more and upload another video.
John

not done it yet02/01/2021 12:23:01
5609 forum posts
20 photos
Posted by bernard towers on 02/01/2021 09:27:16:

Looking at your video and the mismatched colours of your lathe I would suspect mismatched / worn parts that have been used to build it, possibly a bent clutch shaft as mentioned earlier. If you made your location known maybe somebody local to you could help?

Edited By bernard towers on 02/01/2021 09:27:55

I hadn't noticed the different lathe parts (I’m not good with colours at the best of times). I am now wondering, prerhaps like you, if the grey bits are actually super 7 at all?

mgnbuk02/01/2021 12:43:59
929 forum posts
65 photos

I am now wondering, prerhaps like you, if the grey bits are actually super 7 at all?

The grey bits look to be the same as the grey bits on my mid-60s Super 7. The green bits around the headstock, though, are the bits that get broken when a Super 7 falls over backwards when not moved carefully enough.

A Super 7 on the maker's stand is very top heavy and unstable - if it starts to topple while being moved, it does so very quickly and the cast aluminium parts (mainly the green ones shown) get smashed when it hits the floor. I bought a second Super 7 in just such a condition cheap - it had a gearbox & mine didn't, with the whole sorry lot on a stand going for much less than gearboxes sold for at the time.

So my best guess on that clutch wobble is that the intermediate shaft is bent, probably as a result of a backwards fall that appears to have been responsible for the damage that necessitated fitting the green replacement parts.

Nigel B.

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