Mini lathe tail stock too high
|Pat Bravery||11/05/2019 15:28:29|
87 forum posts
I have got an Amadeal CJ18A mini lathe and I put an 8 inch test bar in between a 3MT in the chuck spindle and a 2MT in the tail stock whereby I was able to adjust the tail stock quite easily. Then I decided to check the test bar for horizontal and found that the DTI show that the tail stock is higher, over the 8 inches, it rises by 0.18mm. I have stripped the tail stock and checked for swarf and burrs and anything that could cause it and reassembled it dry and I still get the same result. The lathe has not had much use so it should not be caused by wear, any ideas? I could put a shim under the headstock I suppose but am I missing something. Thanks Pat
|Fowlers Fury||11/05/2019 16:00:56|
323 forum posts
Pat, how did you measure with the dtiI that the tailstock was higher?
|Martin of Wick||11/05/2019 16:28:28|
|92 forum posts|
I commiserate with you having suffered similar tailstock issues on this lathe and another smaller sino lathe.
I am no expert but from my understanding, this is not an uncommon problem. I had the same lathe and encountered similar issues with erratic tailstock readings. In my case, the problem was due to an incompletely reamed MT2 taper in the barrel, but even when this was sorted, I spent the best part of half a day setting it to be collinear with the bed and centred on the head.
Before even considering shimming the headstock, I would advise the first action is to check and confirm the headstock spindle is collinear with the bed in xy and zx plane. You will need preferably a 3 MT test bar or 3/2 MT sleeve. If it appears the spindle is aligned accurately, move on to tailstock (if the spindle is not aligned, depending on severity,you will have to decide whether you wish to attempt to rectify yourself of contact Amadeal and request a replacement).
Next ,check the fitting of the MT2 test bar in the tailstock and absolutely confirm that you can see no play in the taper as it enters the barrel (push backwards and forwards with some vigour to confirm this). In my case It took me a while to recognise that the MT2 was only being griped at the narrow end and there was 10 thou of play at the front of the barrel (partly because I didn't want to believe it!)
With headstock spindle alignment checked and the MT2 in the tailstock fully retracted, can you get the two centres to line up point to point perfectly? (the ruler on the points trick will be an adequate test of this). Do the points stay fully aligned when the tailstock barrel is extended? If not, perform whatever adjustments you can on the tailstock and repeat tests. It is more of a concern If the tailstock is significantly too high when the barrel is retracted, and at this point you may wish to contact the vendor.
You don't say whether you are testing with barrel in or out and whether you have clamped stock and barrel for test and tightened carriage gibs, so will assume you have. After the tests suggested, if there is still a significant rise on the test bar, then the issue could be with the barrel bore or tailstock mating surfaces.
In that case you may be able to shim one end of the tailstock body to sole plate so the barrel is not pointing at the sky while still getting the centres to align. This worked for me on a similar class of lathe, but took hours of to-ing and fro-ing to get to the point where drills could be used from the tailstock without obvious flexing and binding.
It may be that the solution would turn out to be skimming the tailstock - an awkward job so I would see what the vendor has to say if this is the case. You should not have to shim up the headstock for a misaligned tailstock, but it would be a solution in the last resort.
|4687 forum posts|
Possibly! I don't know if your Amadeal has the same adjuster system as my Warco did, but it certainly wasn't easy to adjust the tail-stock on that machine.
The effect I had was a kind of figure of eight movement high-low/right-left around perfection coupled with an unwanted jump at the last moment, usually when tightening up. Tweaking went repeatedly: poor, better, nearly right (hurrah), poor again(temper tantrum).
I never sussed out exactly why the adjustment was so awkward, but put it down to the relatively crude method and/or indifferent finish of the block inside the tail-stock. Chief suspect in my case was the uneven surface of the block causing the tail-stock to tilt. I never found out because after a wasted afternoon I suddenly got it right. There may be a knack to it, because thereafter I was always able to re-align the tail-stock fairly quickly - no more than 5 or 6 attempts taking about 10 minutes. Practice makes perfect, or possibly continued adjustment flattened a bump! .
Perhaps your easy adjustment of the tail-stock left the thing wonky and it's worth having another go?
|Pete Rimmer||11/05/2019 19:46:53|
|416 forum posts|
I agree with Martin check first that the headstock has no nod and do the same for the tailstock ram. If both the headstock spindle and tailstock ram prove to be parallel to the bed (and each other) then either shim the headstock or scrape the tailstock. 8 thou is a lot to scrape but not so bad on a small area like that. You could mill most of it and scrape the rest.
|Pat Bravery||11/05/2019 20:24:34|
87 forum posts
Thank you all very much for your replies and suggestions, I fitted the test bar between the two centre's and locked the tailstock and the barrel so there was no movement, checked the headstock bearings for any lift and adjusted the tailstock laterally with the DTI on the top slide and the barrel about halfway which went very well and I am satisfied with that measurement, then I decided to check the horizontal along the top of the test bar using the same DTI and found the discrepancy. Tomorrow I will have a closer look at the MT's, I did clean them with a rag but will be worth a closer look. I think that the answer will be in something that I have overlooked so I will have another go tomorrow and report back. I have had the lathe about 3 years and only use it occasionally so there should not be much wear on the slides and all the other adjustments are about right. Once again thanks everyone for you suggestions, regards Pat
|Martin of Wick||11/05/2019 20:56:47|
|92 forum posts|
The mini lathe comes out of the box pretty much OK for simple work. It is only after while that you start to notice that all is not as it should be, on longer spindles, deep drilling, and precision work etc, by that time it is probably out of guarantee.
As stated above, the tailstocks are quite crudely finished and offer poor adjustment, such that you can spend an entire day chasing your own tail trying to get some degree of repeatability in the setting.
Both my C1 and C3 clones were a right PITA to bring to an acceptable condition (even after sorting the C1 with shimming and the C3 by reaming and lapping due to the badly cut MT socket)
To try to reduce the general level of frustration when you recommence investigation, I suggest you allow plenty of time, take a good note pad for readings and sketches, take readings twice to check consistency by rotating testbar and repositioning the DTI and in general try to trap or minimise all other sources of measurement error to fully identify the issue . You will get there in the end, it just takes monumental patience. And when you do achieve reasonable performance, you will never ever want to disturb the tailstock again! Should you feel the urge to turn tapers, use a tailstock taper turning attachment if only to protect your sanity!
|Neil Wyatt||11/05/2019 21:58:28|
16556 forum posts
I would fully extend the tailstock and (1) test along the top of the extended barrel to see if it is level and (2) see if it consistently locks in the same position.
I fitted a brass gib to my tailstock to make it easier to adjust alignment.
Make sure the screw under the tailstock is keeping it pulled down.
On my ancient Clarke CL300 (~20 years old now!) the tailstock needed a shim. JS gave me a SEIG one a few years ago, but it was high for the CL300 (perhaps not surprising it wasn't matched exactly!) so I machined the top part of it to fit my Clarke base without a shim.
Going back to (2) above the recent Seig tailstock barrel is a MUCH more accurate fit in the matching tailstock than the old Clark pair were/are. I had been planning to fit a guide collar around the old one.
|Pat Bravery||12/05/2019 11:05:19|
87 forum posts
I have had another look at the tail stock and inspected the MT2 socket and can see nothing obvious however I fully extended the barrel to 60mm and ran the DTI along the top and it is perfectly collinear so the fault must be with the MT2 socket. Could I fit a MT2 reamer into the chuck and gently feed it into the socket, my thinking is that it must then be in line with the head stock or should I remove the barrel and reamer it on the bench, ant thoughts would be appreciated. Regards Pat
3695 forum posts
No you can't safely do that. Reaming it in situ will not work when the misalignment is as much as you say (.18mm/.008" ) . The reamer will tend to follow the old hole. But the high headstock will tend to lift it upwards. So you will probably end up with an oval hole, or something worse.
Reaming on the bench is not going to move the hole down lower because again, the reamer will follow the existing hole.
What you need to do is machine just under .18mm/.008" off the base of the tailstock to lower the whole unit. Tailstocks are often set at the factory (on good quality lathes) to be a thou or two higher than the headstock spindle to allow for wear over time. (But 8 thou is way too much.) If your tailstock is in two pieces to allow for horizontal alignment adjustment, that interface is where to remove the metal from. (assuming all burrs etc have been removed already?).
But first there are a couple of things to check. 1 is to check tailstock height at different points along the bed to make sure the bed is straight. I have seen one small Chinese lathe with well over 10 thou bend at teh far end of the bed. In that case it sagged downwards, but upwards could be just as possible.
2 is to make sure your headstock spindle is aligned vertically with the bed. If it's not, the headstock mounting surface will need machining or scraping etc to bring it down parallel to the bed. No point in machining the tailstock to match a headstock that yet needs adjustment.
Edited By Hopper on 12/05/2019 11:28:39
|Pat Bravery||12/05/2019 13:39:38|
87 forum posts
Thanks for that, I will have another look at it later in the week as I am away for a few days. I do appreciate your advice and you have probably saved me from blundering into the job. I intend to recheck all measurements and if the readings are still the same I will still very lightly ream the tail stock MT2 socket on the bench to eliminate ovality and if the error is still there I will take the bottom tailstock plate off and skim the .18mm off the topside of it. I will report back probably next weekend. Once again thanks to everyone for the advice, regards Pat
|4687 forum posts|
In similar circumstances I've found it pays to trust nothing! Try putting a 25 x 300 mm bar in the chuck and positioning the DTI at the end of the overhang. You might be surprised how easily a hefty bar bends under finger pressure. As the tail-stock adjustment is done by screws pushing against a block, a poorly formed block could jack the tailstock up and bend the test bar enough to make your DTI reading suspect. Something's wrong but I'm not certain you've nailed the cause yet. So far the thread has suggested:
As fixing the wrong problem would introduce unpleasant new complications, I suggest it's worth narrowing the possibilities, for example a cutting test might eliminate measurement error or provide more clues.
Tracking down the cause of a 0.18mm error can be challenging. As Martin said ' I suggest you allow plenty of time, take a good note pad for readings and sketches, take readings twice to check consistency by rotating testbar and repositioning the DTI and in general try to trap or minimise all other sources of measurement error to fully identify the issue . ' Martin's advice fits with my experience - whenever the cause isn't bleeding obvious, it's amazingly easy to be led astray by misleading measurements.
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