How to adjust the alignment of the head-stock on a BG1224 lathe

[DaveyRParticipant @daveyr]

I’ve spent hours and days attempting to correct the alignment on my BG1224 and the result … still got runout.

[DaveyRParticipant @daveyr]

Hi folks. I'm looking for some help getting my BG1224 lathe head-stock aligned so that it doesn't turn a taper. Until recently I've managed because my work hasn't been that critical, but now I'm endeavouring to turn some parts that need greater accuracy, and I seem unable to shift the head-stock so that I can get it to run true.

I've loosened all the (4) head-stock allen-headed bolts and tightened the left-hand one after loosening the right hand one, expecting the head-stock to have turned. Oh BTW, I'm using a true bar, borrowed from a friend, held in the chuck, checked its concentricity which appears to be within a thou.

I'm close to my wit's end. Perhaps I'm missing some additional head-stock securing bolts? Would a sledge-hammer help?

Anyone able to offer me any help, please?

[Thor 🇳🇴Participant @thor]

Hi Davey,

Don't think a sledge-hammer is the right tool. Has something happened (accident) that may have knocked the headstock out of alignment,?

How much of a taper does the lathe turn over 100 to 150mm?

I assume you have already followed Harold Hall's advise on setting the lathe to turn parallel?

Thor

[DaveyRParticipant @daveyr]

Hi Thor, no, not read Harold Hall's piece, but willing to try almost anything. Not that I'm aware – in terms of accident or anything similar. I was aware when I bought it that it wasn't 'perfect', but until this last week, hadn't needed to turn any great length. The dial gauge says it's 0.6 of a mm at 400 mm.

I'll now take a look at Harold's advice.

Thanks in hope.

[Thor 🇳🇴Participant @thor]

Hi Davey,

If your lathe turns a 400mm long bar with a difference in diameter of 0.6mm, that is too much, so you need to do something.

Did you support the 400mm long bar with the tailstock? Or was it just held in the chuck? When I test my lathes I use a testbar that is protruding about 150mm from the chuck (no tailstock support) and is 25 to 30mm diameter. I have one larger diameter collar close to the chuck, another at the end of the testbar. The testbar is also centre drilled so I can use it when testing tailstock alignment.

Thor

PS. Forgot to mention this has been discussed before.)

 

Edited By Thor on 19/05/2018 15:13:13

[DaveyRParticipant @daveyr]

Mmm, not terribly helpful.

The lathe was moved into a newly built workshop extension and at that stage I spent a while levelling the bed. At this point I used a pro' engineer's level and got the bed within a thou or two of being spot on, but since this brought me to today's condition, I was left believing that the problem lay at the head-stock end.

I'd learned from another BG1224 user that there were several securing/locating bolts on this model, and so, today (as I mentioned earlier) I loosened them and began to try to shift the head-stock by loosening on and tightening the other adjusters. Since it needed (as it were) to be rotated anti-clockwise I tightened the left-hand one, having already loosened the right-hand one. The left became tight almost immediately, though the right was still loose.

I cannot see any other bolts that secure the head-stock …

At a loss!

[DaveyRParticipant @daveyr]

Hi Thor and thanks.

Yes, test bar is 30 mm diameter and unsupported by a tail-stock, initially only 250 mm out of the chuck and this produced a broadly similar result..

[Thor 🇳🇴Participant @thor]

Hi Davey,

Hopefully someone more knowledgable than me lives near you and can visit and be able to help you, a bit too far for me. Good luck.

Thor

[DaveyRParticipant @daveyr]

Thanks Thor. Am reading through all the previous posts in the (vain) hope that I might find something there to help. Seems I've done most of the stuff recommended. I did wonder if the head-stock bearings might have been loose, but no, no movement discernible.

Hey ho, who said life had to be without its little troubles?

[Dave HalfordParticipant @davehalford22513]

You don't say how much use the machine has had.

Is the saddle too loose? If the back lifts try tightening the clamp till it drags a bit.

Will a dial gauge on the tail stock run parallel? If so it's likely bed wear (assuming you move the saddle a lot less than the tailstock.)

Does it run parallel if you just use the top slide?

[BazyleParticipant @bazyle]

I'm guessing the 4 bolts you undid are vertical and hold the headstock down. If so it might be glued in place by paint wicked into the gap. I'm not clear why loosening hold down bolts would be expected to move it sideways. Perhaps you are referring to some horizontal bolts designed to shift it sideways?
It might need a few gentle taps to actually break the bond.

[DaveyRParticipant @daveyr]

Thor … good news (for me at least). Having spent a while reading and thinking I went back to the lathe and decided to loosen both of the adjustment bolts and inserted my trusty level between the end of the way and the head-stock and exerted gentle pressure while I tightened the head-stock securing bolts. Then used my dial indicator and rechecked the run-out on the test bar.

Wow. Down to 6 thou.

Same procedure, loosen head-stock retainers, more pressure, re-tighten, recheck: 3 thou.

Tighten all bolts fully, re-check, still 3 thou.

By the time I'd put everything back together, cleaned up and locked up I was knackered, but satisfied. So, thanks to you and your ideas and encouragement, and my 'Persuader Lever Bar' it's back to something like ok. Tomorrow (if I'm allowed) I'll cut a test bar using the tail-stock support.

Thanks again mate!

[Neil WyattModerator @neilwyatt]

Having seen similar discussions many times my advice would always be to start by checking there is no play in the headstock bearings – put an indicator on the bar near the chuck and pull the far end around with modest force. A small amount of movement may be acceptable, especially with plain bearing lathes.

Now with the lathe unstressed and unadjusted with the headstock end of the bed firmly fixed down and the tailstock end with fixings no more than hand tight.

Then use 'rollies dads method' which is ideal for a decent bar held in a chuck. (google will bring up a very clear pdf on how to do this, it's not unique to Rollies dad, but that has become the de facto name for the process.)

Packing the near or far headstock foot shoudl be enough to get everything perfick, if required.

If you want to tighten up the tailstock bolts, repeat the test and you will probably need to add or remove packing.

If the lathe was aligned in its old home, this should be able to sort it.

Because it measures the actual alignment of the spindle rather than a proxy (bed being level) it is more accurate.

As you have moved the headstock, all bets are now off and you may need to move it again if it is now too far out of whack.

Neil

[Thor 🇳🇴Participant @thor]

Hi Davey,

Glad to hear you have reduced the problem to 3 thou. Good luck.

Thor

[DaveyRParticipant @daveyr]

Hi Neil, and thank you for your helpful input. As I said in my previous post, using the test bar in the chuck and with 300 mm unsupported (run out on the bar less than 1 thou) the difference between the chuck end of the bar and within 5 mm of the end of the bar near the tail-stock is around 3 thou.

This struck me as being well within my needs for accuracy. Tomorrow I'll do Rollie's Dad's test process with fingers securely crossed.

[OldironParticipant @oldiron]

Posted by DaveyR on 19/05/2018 15:16:13:

Hi Thor and thanks.

Yes, test bar is 30 mm diameter and unsupported by a tail-stock, initially only 250 mm out of the chuck and this produced a broadly similar result..

I am not familiar with your lathe but this seems to be an awful lot of stick out unsupported to turn work or even use a test bar. What taper do you have in the spindle and are you using adaptors to mount the test bar? I would say that most times the head stock is not the problem as they usually have some form of locating wedge/pins etc. As the head stock was so difficult to move I cannot imagine it being that far out of true. Could be dirt in the spindle bore or dodgey reducing adaptor for the test bar. As Neil said, if you have moved the headstock it could now be out of position.

regards

[DaveyRParticipant @daveyr]

Hello again. Thought I'd provide a bit of an update after yesterday's discussion.

This morning I rechecked the levels (using an accurate machine level) and found it hadn't changed since I originally levelled it. I then re-ran the checks using the test bar and found it to be exactly 3 thou at 300mm.

I went on to check the tail-stock for true, and unsurprisingly it was out. After a few to'ings and fro'ings with the adjusters it was spot on.

I then did the Rollies' Dad's test and it was within between 1 and 2 thou – very surprising to me.

So, thanks to you (all of those who corresponded). I'm so chuffed to have a lathe that I can now use with some degree of certainty that it'll produce acceptable results.

Dave R.

[Phil WhitleyParticipant @philwhitley94135]

Good, you got a result, well done BUT…………………you should really work from the machine spindle, not a chuck, as three jaw chucks are generallt at least 3 to 4 thou out when new, that is why you should never start with a bar the "rignt" outer diameter. if you turn all the surfaces of your component, then it is all concentric, if you use the outer diameter of the bar as a finished size, then the rest of your work will be out by the amount of error in the chuck. You should always put the test bar into the spindle taper, not into a chuck.

[Neil WyattModerator @neilwyatt]

Posted by Phil Whitley on 20/05/2018 18:18:23:

Good, you got a result, well done BUT…………………you should really work from the machine spindle, not a chuck, as three jaw chucks are generallt at least 3 to 4 thou out when new, that is why you should never start with a bar the "rignt" outer diameter. if you turn all the surfaces of your component, then it is all concentric, if you use the outer diameter of the bar as a finished size, then the rest of your work will be out by the amount of error in the chuck. You should always put the test bar into the spindle taper, not into a chuck.

That's why I advised Rollies Dad's Method – it compensates for any chuck inaccuracy, which is why Dave got a better (very respectable) result using it.

Plus, don't ever rely on an unproven cheap test bar, there are rogue ones out there.

Neil

[HopperParticipant @hopper]

Good you got it dialed closer than it was.

What you need to do now is hold a piece of 1" diameter bar in the chuck so it sticks out about 4 to 6 inches. Take a cut along it to true it up, then take a very light cut, say one or two thou, along the full length. Measure the taper actually turned on the job. This tells you the true story of your lathe's performance under real-world working conditions. If there is more than half a thou taper along that distance, you should be able to get it spot on by placing thin shims under either the front or rear lathe bed mounting foot at the tailstock end. The Myford ML7 manual available freely on the net gives the specific procedure for this.

To save a bit of time, you can relieve the middle section of the abovementioned test piece so its smaller diameter than the two ends, so you only have to turn a narrow band at each end rather than the full length.

[Author]

Posts