|Sebastian York||16/12/2018 23:05:31|
|14 forum posts|
Good evening all.
Can anyone offer some advice re my M300 and spindle run out/bearings...
Owned it for several years now and had the bedways ground about 11 years ago...all seemed well...but its been in store for the last 7 as not been in a position to use it. its not a hard used machine.
Recently got it back up and running, and initially had some trouble getting a good surface finish...lines in the workpiece and general roughness...
levelled the taper out by adjusting the feet so turns true...but just cannot get the finish right...and will not hold its trueness.
run out seems to get more as the lathe speed increases...and periodically (with 3 jaw chuck) will just suddenly start to wobble...meaning work that was true as had all been done in the same chuck, suddenly starts to visibly wobble...
even a struggle to dial anything in using a 4 jaw...and will suddenly spin out of true
cant feel any movement, or produce a noticable reading on the dti... but is it possible that the bearings are either loose, or damaged?
thank you for any input
|David George 1||17/12/2018 07:54:23|
1836 forum posts
Hi Sebastian you need to do a bit of investigation. Put a piece of about 25mm bar in the chuck sticking out at least 6 inch. Put a dial indicator on the side of the bar and give it a tug looking for movement. Secondly take the top off the headstock and and have a look at the spindle housing and nuts are ok. Pull the bar forward back and up and down looking for movement. That's where I would start. Is there oil on the spindle? as maybe it has leaked or gone thick with being stood. Turn it slowly with lid off looking for lube and keeping fingers out. Where are you as maybe I or someone who may live nearby could help.
|Andrew Johnston||17/12/2018 10:43:53|
6601 forum posts
The bearings would be the last thing I looked at. First I'd look ensure that the gap piece, if you have one, is correctly seated. I spent a year faffing about trying to get my M300 turning paralle near the chuckl, only to discover the gap wasn't seated properly. Then I'd forget the chucks and try a collet chuck, or between centres turning. It's only too easy to get a poor finish, and the main causes are the material and incorrect speeds and feeds, especially if you're using insert tooling. Make sure everything else is tight and functional. I had an issue with faint banding; turned out that one of the bolts holding the top slide had stripped.
Only once all other issues have been dealt with would I look at adjusting, and possibly replacing, the bearings. You'll need a second mortagage to replace the bearings like for like.
22746 forum posts
Could the drive belts from the motor have taken a "set" over 7 years of standing idle? that could set up vibrations.
Not sure how the gap piece being off would affect the work "suddenly starting to wobble" but would affect accuracy and being able to turn parallel.
What conditions was it stored in? warm and heated or cold and damp.
1614 forum posts
If not a "hard used machine", then why the bed regrind?
Are the camloc pins for the chucks adjusted properly?
Is the headstock refitted/tightened down correctly?
Any noise from the bearings?
Some pictures and/or video may help too.
|Tony Pratt 1||17/12/2018 12:16:54|
|1962 forum posts|
All good advice above, I would also take the chuck off to eliminate any problems with that.
|Sebastian York||17/12/2018 16:51:59|
|14 forum posts|
Thank you for all the input so far gentleman.
Its not a gap bed so that eliminates that possibility.
I had the bedways ground as I had the money, and wanted to be certain they were good...After purchase I noticed some damage to parts of the machine (main traversing handwheel on the saddle has been damaged and welded back on by its previous owner, not sure if the machine previously took a fall or was seriously knocked into, but was enough to smash the webs holding the handwheel together...)
Running the machine with a chuck (any chuck) fitted there is a pronounced vibration through the whole machine, but is not noticeable when running without anything fitted. CamLocks are adjusted evenly. Have adjusted the drive belts. Head is tight on the bed and doesn't move.
Lathe was stored in a garage.
With a 0.01mm dti mounted on the cross side, and the nose bearing on the spindle, there is no readable end float...however when holding the spindle at either end and pushing/pulling, it is possible to read between 0.01 and 0.02mm lateral movement...so far have not been able to find my 0.001mm dti to fully test the endfloat.
When cutting the following happens...
On fine cuts, lines are visible and surface finish is poor, but it is possible to turn a true straight diameter (2" bar held in 3 jaw chuck approx 9in long)...but by traversing the saddle back along the workpiece(away from the headstock) the tool continues to cut, as if the workpiece isn't on the same axis as the cut towards the headstock...surface finish improves and lines less visible with a heavier cut, but then it cuts a taper...and again, if you traverse away from the headstock, the tool re engages with the workpiece...
I sincerely hope its not the very very expensive bearings...but the lateral movement is concerning me...
the vibrations increase with rpm...the faster the gear, the more noticable...
Edited By Sebastian York on 17/12/2018 16:54:37
|Andrew Johnston||17/12/2018 17:17:38|
6601 forum posts
To start with, what's the material, and insert or HSS tooling? Is the material supported by the tailstock? It's normal for the tool to take a fine cut on the way back, to do with deflections during cutting. Same thing for heavy cuts giving a taper, especially with no tailstock support. With insert tooling heavier cuts usually, but not always, result in a better finish.
I don't know why the machine should vibrate with a chuck, unless the chucks are unbalanced. If I get a chance this evening I'll look at end float on my M300. The preload should be adjusted with the spindle and bearings warm. Did you do the measurements cold?
The most likely cause of the broken handwheel is that the lathe fell over, probably when it was being moved. Lathes are top heavy and once they start to go you're not going to stop them. Is there any other evidence that the lathe has toppled, like damage to the cross slide handle or scuffing on the stand?
|not done it yet||17/12/2018 17:18:26|
|6809 forum posts|
Cutting on the ‘back stroke’ indicates poorly adjusted gibs or a worn slide somewhere - allowing the carriage or cutter to ‘skew’. Try locking the cross slide and compound to try to locate the offending
The vibrations could be generated either inside or outside the gearbox. Is it the same in all gears? Is it a single drive belt or more? Are pulleys tight on their shafts?
You will have to check everything out in a logical fashion to exclude each part of the drive sequentially, I think.
8676 forum posts
Cutting when moving away from the headstock isn't unusual. It's partly because the tool bends in the opposite direction when cutting away from the headstock and partly because a different cutting edge is presented to the work.
If the lathe was OK before it went into storage and has only started vibrating 7 years later, the implication is that something has stiffened up or fallen off and effected the balance. I'm liking Jason's suggestion that the belts have taken a set, that is they have stiffened into shape around the pulleys. When the lathe is powered up they give the machine a good shaking. If it's easy to do take the belts off to see if they're rigidly stuck in one shape. With luck you only need new belts.
Otherwise, with the lathe turned off, try turning the chuck by hand through many revolutions, It should turn with equal difficulty at all times. If you find it tightens and loosens, hunt for whatever is causing the tightness. I'd do that by disengaging everything that can be disconnected between the motor and spindle one at a time until the chuck spins freely. Leadscrew, power traverse, change-gears, geabox etc. If you find a suspect ask again, there are several possibilities and someone will probably be able to help.
After 7 years in storage it's possible more than one thing has gummed up - persist!
If testing doesn't find a simple cause, it could get expensive - damaged motor, bent spindle, shot bearings etc. That repaired hand wheel might be a clue. Let's hope not! They don't seem likely to me, not on a lathe that hasn't been used.
Edited By SillyOldDuffer on 17/12/2018 17:33:26
|David George 1||17/12/2018 17:31:42|
1836 forum posts
Hi have you checked the saddle if the handwheel has been damaged is the saddle crabbing when it is traversed. Try putting a dial indicator on the saddle resting against the side if the bed and wind it back and forwards to see if there us any movement. Also have a look at the gears in the end of the headstock possibly removing or disconnecting one to see if they are ok. Look at the lubrication in spindle and gearbox.
|Alan Waddington 2||17/12/2018 18:41:10|
|523 forum posts|
Reckon if it was the bearings, your ears would be the first to know, have encountered a few M300’s with problem headstocks and every one sounded like a bag of spanners.
|Andrew Johnston||17/12/2018 20:47:33|
6601 forum posts
Having done the important things, like write and post most of my Christmas cards, I've just made a couple of measurements on my M300 spindle. Measurements were made on the front face of the spindle, with no chuck.
I first measured with the spindle cold; firmly pushing back and forth on the spindle produced a movement of about 0.01mm. Then I ran the spindle at 800rpm for 15 minutes under no load. Repeating the measurement I couldn't see any movement of the needle. After running the headstock front cover wasn't warm. When I've used the lathe a lot it is just warm to the touch. I suspect that would load the bearings even more and further reduce the axial movement under cutting loads.
So at first glance it would seem that the axial movement seen by the OP isn't a problem.
|Chris Trice||17/12/2018 22:34:50|
1375 forum posts
The intermittent nature of the "wobble" doesn't suggest belts to me unless something bearing wise is very loose. If you can get the chuck to wobble, put a piece of bar in it, spin it up and when it does it, offer up the tip of a pencil to the bar so it just marks to see if the wobble happens once a spindle rotation. This would indicate a bearing problem or possibly a bent spindle. If the lathe has been dropped, the chuck could have impacted with something.
|Chris Trice||17/12/2018 22:41:38|
1375 forum posts
You could also try centre drilling a piece of bar and then keeping it in the chuck and supporting it with a centre in the tailstock to load it towards the headstock and then run the lathe to see if the wobble disappears.
|Nicholas Farr||17/12/2018 23:42:23|
3360 forum posts
Hi Sebastian, long term storage without any rotation of the bearings, can produce indentations, albeit only a few microns deep, on the resting elements of the bearings due to any vibrations that the machine may be subject too. This may be possible if it is stored in a place close to a busy road, for instance, especially if there are many heavy lorries using that road frequently. However this would be an exception rather than a rule and you should eliminate all other possible causes of the vibrations you have (some likely ones have been mentioned already) before considering changing or altering the bearings. You should, however, have hardly any detectable end float of your spindle.
22746 forum posts
I suppose we should ask was it OK in the 4 years between regrind and when you stopped using it? This would eliminate the possibility of previous damage and point towards something that has happened in storage.
My thoughts on the belts was that at certain revs there may be a frequency that causes more vibration than at other times.
|Sebastian York||18/12/2018 09:58:24|
|14 forum posts|
Good morning gentlemen.
When I stopped using it years ago due to work and life taking over it was, from memory absolutely fine...but then I was also far less knowledgable / experienced than I am now...and even now I am still a very much a novice...
Tried with a variety of materials, and different cutting tools, tipped and HSS...
I will continue to investigate all avenues as described here...will also order some new belts and fit them. Tension wise currently they are free to turn through 90 degrees...is this either too tight or loose? lathe spins up freely and there is no belt slip...and I can feel no tightness any where in its rotation.
I cannot see any further damage to the machine...but it has been repainted during its regrind...so this would likely hide any scuff marks...no other damage visible on the machines other hand wheels. As the saddle run on the "V's" would it be able to crab at all since the regrind?
my use of the machine was, and is very minimal, but I don't know its history...or how it was used/treated prior to y ownership
When the bedways were re-done the lathe was reassembled by the guys who did the grind...cant remember the name but it was in Nuneaton somewhere...bronze bearing strip added to the Gib strip so thats all been done too...and they indicated no hint of any problems when I collected it...very little play in the compound or cross slide...
As for a bent spindle...how likely/hard is it to do such a thing? sounds very expensive and alarming! How often does this happen? and most importantly how would one measure for such eventuality? I don't think this is the case with me admittedly, as it spin true, then suddenly induces a visible run out...as if when the bearings get warm they move...
By way of example over the weekend I was turning a piece of stainless to 35mm OD, and bore dia of 28mm...3 jaw chuck...machine had been running for 30mins plus on and off so was warm, but not excessively hot...all was well, then within a few fine cuts went from spinning true, to a very visible run out wobble...checked all the obvious again such as chuck tightness, mounting etc...this happens regularly, and not just a one off...this is what initially led me to think bearing issue...that and I get a chattery finish...
As I want this to be right, I am edging towards making the lathe a little project first, strip and rebuild to get it perfect, and in doing so I will learn all about it...and once all is clean, burrs removed etc then I should be able to fully set up a very accurate machine as I know the beds good the rest should just be a case of clean and adjust...as long as the spindle isn't bent....
Thank you again for all input.
|Nick Taylor 2||18/12/2018 10:23:51|
|102 forum posts|
Hang on, so you turn the OD then for some reason it suddenly starts to run out? For this to happen the chuck must be either loose or the spindle is about to fall out. Sounds a bit funny to me... you must have a fairly obvious problem.
How much runout does it have? does the body of the chuck/spindle nose runout as well?
22746 forum posts
Could it be worn chuck jaws, light cuts in stainless with a tipped tool may well want to push the work rather than cut and that could make the work move and start to wobble.
As Nick says if the whole chuck wobbles then that would eliminate the jaws.
Please login to post a reply.
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.