Suspected damage to nose thread
|Peter Turvey||21/01/2021 09:23:42|
28 forum posts
I suspect the nose thread on the spindle of my 1966 Myford Super 7B has been damaged, causing runout on chucks etc. Have carefully cleaned and checked spindle register and parallel section, can see or measure no evidence of damage or embedded swarf. Checked threads for embedded swarf, looks like none.Found one bruised thread, stoned bruise out, to little improvement. See my YouTube channel **LINK** for videos of measurements.
First, are there any U.K. based specialists who could check spindle and reprofile nose threads? Reluctant to try this myself, lathe does not otherwise need reconditioning. U.K. lockdown has isolated us from usual sources of advice!
I could of course fit a new spindle, but could this be done without having to scrape the the front bearing, assuming it’s in good condition with no scoring.
Edited By Peter Turvey on 21/01/2021 09:27:21
|David Standing 1||21/01/2021 09:36:30|
|1292 forum posts|
That didn't appear to be a test bar in the chuck, but a piece of mild steel round bar, which could be like a banana.
Have you checked runout on the inside of the spindle? All of your videos check runout with something attached to the spindle. Is the morse taper on the inside of the spindle scrupulously clean, and undamaged?
Have you checked runout with a decent ground MT test bar in the spindle?
|bernard towers||21/01/2021 09:39:03|
|106 forum posts|
Sorry but can’t see your problem, spindle thread is not for concentricity the the longitudal and cross registers look after that. Measuring a collet chuck runout that far from the spindle I am not surprised at those readings. As for the readings from the chuck how old did you say your lathe was?
5174 forum posts
Don't panic Cap'n Mainwearing. I agree that the less than half a thou runout on the collar of the collet chuck sticking that far out of the spindle indicates there is nothing wrong with the spindle. That is a good reading for that set up.
But your first two videos showing the dial indictator reading off the piece of bar held in the three jaw chuck is telling you nothing at all about the spindle. Three jaw chucks, even when new, are lucky to run true within a few thou right up next to the jaws. That increases as you move away from the jaws. On these ancient Myford chucks, it is very common for the jaws to become bellmouthed and hold the job at all kinds of often-varying angles. And jaws can be otherwise strained from overtightening and wear. Also, as David said above, your bit of common bar could be bent like a banana and adding to the runout.
Be wary of using a test bar that fits into the taper in the spindle. The hobby grade ones have been found to not always be ground concentric so can give a false reading. Also, the internal taper often gets damaged and so holds crooked and gives a false reading not relevant to the spindle at large.
First thing you probably need to do is check how much slack you have in your headstock bearing. As measured by a dial indicator bearing on the spindle itself (not the chuck) and try to yank the spindle up and down using a bar held in the chuck. Should be half a thou maybe of movement max. There are multiple threasds on here about adjusting the Super 7 bearings if you do a search. It's a bit tricky.
Then there are also threads and an MEW article on regrinding your chuck jaws in situ with a dremel mounted in the toolpost with a special holding plate for the jaws.
But even then, if you want to hold a piece of bar dead true in the lathe, you need to use the 4 jaw chuck and a dial indicator to set it true. Otherwise, the three jaw is used for "roughing" and you plan your jobs so most or all operations are done in one setting so the different diameters end up concentric. Usually you start off with slightly oversized material and turn it down to size so that diameter is running concentric and likewise all others that follow.
PS, if there were a serious problem with the spindle nose thread, it would be difficult to screw the chuck on..
Edited By Hopper on 21/01/2021 10:16:07
|Tony Pratt 1||21/01/2021 10:18:01|
|1413 forum posts|
You are not checking the spindle in you videos, you need to check the actual spindle, i.e. the register diameter & the register face. From memory the Super 7 spindle is hardened so very unlikely to be damaged, the thread outside diameter can be checked with a dial gauge using an 'elephants foot' [large diameter] stylus to bridge the threads, you can also check the threads themselves by setting the lathe to cut the same pitch as the spindle thread & use a very small stylus to bear on the thread flanks but maybe tricky for a beginner?
|Peter Turvey||21/01/2021 10:23:15|
28 forum posts
Thanks for comments, I suspect that some defect on the spindle nose thread is tipping the chucks etc over.
Background is that I bought a new, good quality collet chuck from a reputable manufacturer last week, fitted it on the lathe and got 80 microns, about 3.2 thou runout (sorry to mix units) whatever I did.
Tried it fitted to a brand new Myford 2MT adapter fitted to the spindle and got about 20 microns, about 0.8 thou, runout.
So began investigations......I am asuming that I should have at least the same accuracy in both cases. I can't try the collet chuck on another Myford due to lockdown!
The Test Bar is a piece of ground silver steel,
Similar results were obtained with my Arrand Test bar in the 3 jaw chuck.
There is minimal runout on the taper inside the spindle.
The lathe is September 1966 by the way, but has seen little use for most of its life.
5174 forum posts
Mysterious with the collet chuck. But definitely your first two videos tell nothing. Three jaw chucks cant be trusted, even when new, even when holding ground bar.
But, chucks are held in place not by the thread but by the register collar behind the thread, both the outside diameter of it and the shoulder the chuck body snugs up against. So you need to put dial indicator on those two surfaces and look for runout. And you need to check bearing slack before anything. Loose bearings will let a good straight spindle move all over the place.
|David Standing 1||21/01/2021 10:37:31|
|1292 forum posts|
This then suggests to me, as stated in my previous post, a careful check for damage, or foreign objects such as swarf, inside the spindle taper.
There may be no runout on the taper at the spindle nose, but an issue inside the spindle nose taper.
Given that it is hardened, it would be difficult to damage the spindle internal taper, but very easy to get swarf, for example, inside it.
Also, has anything been done to the lathe leading up to the issues you report - has it been moved, dismantled in any way disturbing the spindle, etc?
If the spindle taper is clean and undamaged, and you carry out a bearing check as suggested by Hopper, then I suggest there is no issue as such, other than age of the lathe, and tolerance in chucks etc.
Minimum projection of collet chucks and work beyond the nose/chuck is important, as these will only amplify any runout.
899 forum posts
The videos of the tests on the register, register collar and internal taper (scroll the video thumbnails) are all nigh on perfect. If that was my lathe I would be quite happy. The thread would have to be seriously and visibly damaged to affect a screwed on chuck. As others have said testing anything held in the 3-jaw is a waste of time.
I am afraid my suspicions would fall on your shiny new collet chuck. First check that the thread depth is sufficient to allow the chuck to screw right up to the register collar. There is no simple way, that I know, to check if the chuck register is round, straight etc (bet someone here knows how to check it though).
Good luck and hope you get the problem sorted.
5174 forum posts
Journeyman: Aha. I did not see the plethora of other videos. Nothing appearing wrong there. Peter, I too would suspect your shiny new collet chuck.
What happens if you put that MT2 Myford nose adaptor into the taper in the spindle and get it running true as shown in the 3rd video, then you screw the collet chuck on the known true-running adaptor? If its a duff collet chuck it will run out of true there.
Edited By Hopper on 21/01/2021 11:43:33
|Dave Halford||21/01/2021 12:03:04|
|1287 forum posts|
All you have done is prove the spindle is fine and the collet chuck is not, I don't see why that leads you to think the spindle is now faulty.
I thought you were going to get an ER / MT2 collet set from RDG, where does this one come from? Any extra adapters add errors
Edited By Dave Halford on 21/01/2021 12:04:29
|Peter Turvey||21/01/2021 12:54:02|
28 forum posts
Hello everyone, many thanks for your responses,
Dave Halford - I did get a RDG ER32 Collet set, but had mixed results from it, not consistent on removal and refitting, getting variation on runout each time, suspected the backplate hole was slightly overisize hence new chuck. I do not want to post maker here as I have not demonstrated to my satisfaction that it is at fault, am awaiting a response from them, and others have had good results from these chucks..
Here is my reasoning
I first fitted the new chuck to the lathe spindle and got 80 microns runout. This was a consistent error on removal and refitting. Chuck spun on smoothly, became a little tighter when within a mm or so of the register.
Mounting the new collet chuck on the 2MT Adaptor, Chuck spun on smoothly all the way to the register, and improved the runout, reducing it to 20 Microns.
Observed an improvement on runout doing a similar test with the length of silver steel held in the 3 jaw chuck, and not removing the silver steel when moving the chuck from spindle to adapter.
So the errors all seem to be going the wrong way, hence my thoughts about the spindle nose.
Intriguing results, what is going on. Had a chuck come unscrewed a couple of years ago and faceplate spun on slightly tighter afterwards, (incorrect adjustment of thrust bearings after belt replacement, discovered on centre drilling), so that's largely why I focussed on damage to the spindle thread.
Hope this helps to set scene folks.
|noel shelley||21/01/2021 12:59:29|
|369 forum posts|
The super 7 spindle is hardened and unlikely to be the cause. A proper check on the spindle would indicate if the bearings need resetting. It is possible that there may be debris crushed onto the surface of the bore, careful use of a 2MT reamer should clear this. The concentricity of a collet and it's chuck is vital ! I had an interesting conversation with a seller of ER collets and associated tooling. There are numerous grades of accuracy ! AND you get what you pay for ? A poor quality chuck and a poor quality collet = poor accuracy. Please note I have NOT used the word cheap, price and quality are not always synonimous ! Noel
Edited By noel shelley on 21/01/2021 13:28:29
|old mart||21/01/2021 17:21:34|
|2675 forum posts|
I would be very surprised if there was any damage to the spindle. A chuck using a backplate is preferable to a direct fitting chuck. This is because you can fit the backplate on its own and skim the front perfectly true before fitting the chuck. A Myford spindle is a very strong design and you would have to hit it with a sledgehammer to cause any bad damage.
1357 forum posts
I'm with Old Mart here.
A possible thought, and a method I used when I bought a second hand 2 part chuck (of the RDG ER25 style)
Edited By peak4 on 21/01/2021 18:11:15
|Howard Lewis||21/01/2021 18:13:24|
|4428 forum posts|
I have only ever seen ONE 3 jaw chuck that did not show run out. Still don't really believe it.
If you can get one that shows less that 0.005" close to the jaws, on your test bar, it is not bad.
I once came across an old worn one showing 0.036" eccentricity!
The 2 MT spindle bore can be cleaned, hopefully completely, of swarf / debris by passing a bottle brush through it.
Pulling through a wad of clean cloth, like cleaning a Rifle barrel will also help,
As already said, the best chuck mounting is by a backplate. This should be a snug fit in the register of the chuck, when it has been skimmed on the lathe on which it going to be used. The same comment applies to the front face of the backplate. You should then have a backplate with a face which is perpendicular to the axis of that lathe, and a concentric tight fit in the chuck.
If the taper of the collet chuck runs out, then the problem is with the collet chuck, not the lathe spindle.
If you make a backplate with a recessed register for the collet chuck, that would mean that any run out in the collet chuck comes from within it (Lack of concentricity between the OD of its backplate and the taper of the chuck. )
Hopefully, you will get this sorted, to an acceptable limit of concentricity.
|Howard Lewis||21/01/2021 18:25:54|
|4428 forum posts|
Peak 4's method is the way to get the collet chuck /backplate OD as concentric as possible. (He typed whilst I was still thinking )
FWIW, do this before machining the register recess in the backplate on the lathe.
Hopefully, you will then be rid of that problem.
Howard (Fat fingers and no proof reader )
Edited By Howard Lewis on 21/01/2021 18:26:30
899 forum posts
I don't think you have seen all the videos, in the thumbnails that come up with the **LINK** there are several more that you need to scroll the display so that you can see them There are about 6 more off to the right. These clearly show the spindle register, register collar and taper being clocked. They show no appreciable runout. I would conclude that the spindle is perfectly acceptable.
The fault I believe is with the collet chuck, it shows runout when fitted to the spindle and runout on the Myford plug-in nose which is also running true..
1357 forum posts
Well spotted John, no idea how I missed them; Videos on youtube normally show for me as a series of tiles on the one page.
|197 forum posts|
Just been watching the last two videos ('collet chuck' & 'MT adaptor' - is the bruising that you mentioned in your first post that which is visible on the flank of the first full-turn back from the open end? ..there are some very experienced & pragmatic machinists responding to this thread, maybe if anyone else would care to take a look and comment - I recognise that it's hard to tell without having the thing in one's own hands, but if you can still see or feel even a slight irregularity, you could perhaps try another careful clean-up with a (shaped, if necessary) slip and see whether you can get the collet chuck a little closer - as noted above, with the stick-out that you have, it can only be some very few microns at the nose..
Maybe a little permanent marker applied to the threads in that area and trying the chuck on & off a couple of times might tell you more?
Edited By DiogenesII on 21/01/2021 18:55:19
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