Lathe spindle alignment

[Iain DownsParticipant @iaindowns78295]

Hi, Huu,

My 0 starts about 50mm from the spindle as that's about as far as the cross slide will go. The lathe has a single prismatic feature so should not be too subject to wear. I have, however, just tuned up the clamps to the bottom of the bed (I suppose they're gibs) and dropped the lift from 0.04mm to about 0.02. Any tighter and the cross slide won't move.

Chris. I think I need the lathe back together to use the famous Rollies Dad method, which I think boils down to using averages.

Michael. there will be some droop, but this should not have much affect as long as I'm close to the centre of the bar (which is effectively vertical over a short distance).

And I've measured in both directions and get the same results.

More tomorrow!

Iain

[Michael GilliganParticipant @michaelgilligan61133]

Keep up the good work, Iain

MichaelG.

[HopperParticipant @hopper]

What you have done is essentially the same as the infamous Rollies Dads Method, ie taking a bar that may or may not be dead straight and dead true and taking readings with the bar rotated through 360 degrees and taking an average. Job's good.

The acid test will be doing a turning test, where cutting forces acting on the machine can give a different result from static measurements. Recommended turning test bar is steel 1" diameter sticking out of the chuck by 4".

[HuubParticipant @huub]

Posted by Hopper on 12/06/2023 23:28:07:

The acid test will be doing a turning test, where cutting forces acting on the machine can give a different result from static measurements. Recommended turning test bar is steel 1" diameter sticking out of the chuck by 4".

You are right, static measuring and actually turning can/will give different results.

I prefer making a " Rollies Dads" test bar because it is easy and cheap to make and because it is running true it makes adjusting a lot easier.

[HuubParticipant @huub]

Another cause for the bump in the measurements could be some "damage" on the trapezial part ( single prismatic feature) of the lathe bed. If something drops on this part, it will cause a dent and also high spots near the dent. You can grind away these high spots using a small stone.

[Howard LewisParticipant @howardlewis46836]

Without having waded through the whole thread, will climb onto one of my hobby horses.

If the lathe is not secured to the bench, the bed maywell be twisted. The cassting will have stress relieved itself and twisted once it had been machined.

As already mentioned "Rollie's Dad's Method" is the way to remove twist from the bed.

(Read Ian Bradley's "The Amateur's Workshop", or his " Myford 7 Series Manual" which describe the techniques already mentioned. )

Removing the headstock, will have made this task more difficult, since you will be unsure whetehr you are aligning the headstock or removing twist.

Moral:

Always gor for the simplest things first. The Headstock might have beem aligned, and the bed just needed the twist removing.

But, you are where you are.

I would suggest, having bolted dfown the lathe, trying to take twist out of the bed by using a sensitive level on the cross slide,, at each end of the bed, by travesring the Saddle from one end to the other.

Ian Bradley will tell you which side of the tailstock mounting foot should be shimmed / adjusted. (I prefer using screw adjustment to be more precise. )..

Once that is done, as accurately as possible, then you can use the Alignment bar and start aligning the Headstock.

Good Luck!

Howard

[Iain DownsParticipant @iaindowns78295]

Hi, Huub.

Ways are stoned, but that part of the bed looks OK anyway.

Howard. All this makes sense, but the bench is way out of true and sorting that out to the point where I'm near where an engineers level would indicate would be a goodly amount of work.

However, the thread has persuaded me that this would be a good thing to do and I will add it to my todo list. Probably associated with adding in a heavy baseplate as suggested earlier.

Iain

[Niels AbildgaardParticipant @nielsabildgaard33719]

Posted by Iain Downs on 13/06/2023 14:24:41:

Probably associated with adding in a heavy baseplate as suggested earlier.

Iain

You are better of with the same amount of material as a short fat square tube of steel or a short fat block of some mineral or concrete.

 

Edited By Niels Abildgaard on 13/06/2023 15:26:53

[old martParticipant @oldmart]

Ian, could you use these results to move the headstock and retest? Also, a set of tests at the top of the bar rather than the side would check the other variable. I don't know just how sensitive a level would be needed to find any twist in the length of the bed. I have two Moore and Wright levels, I will try testing them for sensitivity and if one looks promising, I could lend it to you.

Edited By old mart on 13/06/2023 16:26:02

Edited By old mart on 13/06/2023 16:29:14

Edited By old mart on 13/06/2023 16:33:46

[BazyleParticipant @bazyle]

To experiment with bed twist on a small lathe just put the top bar of a large F clamp in the bed slot to the right of the tailstock or similar contrivance to arrange a large horizontal lever that twists the bed. Hang a brick on the lever while observing your indicator.

[old martParticipant @oldmart]

Bazyles method would not need the level and is a good idea. I added a block of aluminium to raise up the headstock of the Atlas12 x 24 lathe to allow room for adjustable "levelling" at the tailstock end. So far the lathe bed has not needed any adjustment and is very accurate with the tailstock end loose.

[Iain DownsParticipant @iaindowns78295]

An Engineers Level (0.02mm / 1000mm if I recall) is one of the many things I've bought because, 'some day I'll need it'. Perhaps this is now!

I'm out tomorrow and need to finish a project, so it may be a few days before I get back to measuring.

I've now got the lathe back together (not without a couple of scares!) and cut a test bar. However, I'm not sure I particularly trust what I've written down, so I will have another look later in the week and report back.

Thanks all.

Iain

[old martParticipant @oldmart]

You will have to sit your level on a suitable parallel to clear the prismatic bed, and shim the headstock end temporarily to get the bed close enough to see the bubble. You might find a twist, or the bed might be perfect.

[Howard LewisParticipant @howardlewis46836]

Iain, You have a PM.

The important thing is that the level gives the same reading at both ends of the bed, to indicate a lack of twist.

It is of much less importance if the lathe leans slighty towards or away from you.

Chances are that a lathe sitting on an uneven bench will show twist. (Probably, once the casting was machined, it will have started to stress relieve itself, and twisted anyway )

A used machine might well have been fixed down so as to , inadvertently, twist the bed, and it has stayed, at least partly that way afterwards.

Hobby machines are designed and built down to a price, so the casting is unlikely to have been stress relieved before machining. If a new lathe, out of the box, can be out of line when checked, stress relieving will not have been high on the list of priorities.in that factory.

Things would be different with a high quality high precision industrial machine; and reflected in the price!l

[Iain DownsParticipant @iaindowns78295]

Having put the lathe back together, I've turned down a piece of (what I thought was ) EN1A and then drill and started to bore. The outside is kind of OK, but the inside is a mess. Screeching and an almost knurled effect.

I've tried another piece of steel with similar results. In some ways this is worse, The cutter is being seriously deflected. I suspect the second piece of steel (origin unknown) may be tougher than my little lathe is happy with (boring anyway). The first deflects less but resonates badly.

I would like to suspect the steel rather than what I've done with the headstock and re-assembly, but wanted to seek some more expert opinions before I strip the lathe back down again…

Help!

Iain

[Howard LewisParticipant @howardlewis46836]

If the OD turns smoothly, and parallell, the lathe would seem to be OK, so no need to strip it.

Why risk upsetting things now that you have got it aligned.

Since the problem seems to be confined to the boring operation, it could be the tool that is the problem.

I would check: mounting (Boring bars are rarely as rigid as ordinary turning tools, being longer, and often thinner)

Rake angle?

If the boring bar is on centre height, are the clearance angles correct?

Is the speed that you have previously used for this tool appropriate? Chatter usually means a lower speed is needed, especially wherev the tool is not rigid.

Using a boring bar, the depth of cut is likely to be smaller to cope the reduced rigidity.

The "knurled" finish suhhests that the tool is vibrating badly, digging in and out of nthe cut.

Howard.

[Michael GilliganParticipant @michaelgilligan61133]

Hang the expense … try turning bit of nice Brass

MichaelG.

[Iain DownsParticipant @iaindowns78295]

Thanks Howard,

I meant to say in the previous post that this was attempted with both HSS and carbide insert (the sharp aluminium type). Also with various speeds from 500 rpm up to 2000. I've also swapped out the insert and I've tried cuts from wafer thin to 0.5mm.

The insert bar has worked well in the past and is my goto bar for boring. What I'm doing is duplicating a piece (45mm long, OD 20mm, ID 16mm) which I'd made before the changes which work OK. That really was EN1A, but now run out .

I've ordered some more EN1A Pb and will re-try with that before I consider stripping the lathe again.

Iain

[Iain DownsParticipant @iaindowns78295]

I think we swapped Michael. I will be patient and try the EN1A.

Iain

[HuubParticipant @huub]

Posted by Iain Downs on 15/06/2023 12:56:14:

The insert bar has worked well in the past and is my goto bar for boring. What I'm doing is duplicating a piece (45mm long, OD 20mm, ID 16mm) which I'd made before the changes which work OK.

The 45 mm long part has a 2 mm wall thickness. That results in a lot of flex especially when turning the inner diameter. Not an easy part to make!

If possible, I would turn the inner diameter first and mount the part in a 4 jaw chuck (no part stick out) to reduce the flex of the part. Bore the hole 15 mm thick and finish using a 12 mm inner turning bar. Let the inner turning bar stick out 47 mm max. Select a feed/rev as slow as possible. On my mini lathe in manual mode, that is 0.1 mm/rev. Bring the stock to final diameter using a cutting depth of 0.05 mm or even less. A sharp insert (for alluminum) should work fine.
If there is chatter, reduce the RPM and cutting depth if possible.

On my mini lathe, I only have a 3 jaw chuck that has a 16 mm bore. So the part would stick out quit a lot. I would follow the same procedure but turn CNC at a feed of 0.02..0.05 mm/rev.

[Iain DownsParticipant @iaindowns78295]

Hi, Huub.

The one I've made was OK apart from narrowing towards the chuck by about 0.03 mm. I 'fixed' this with some emery and it was at least good enough for a prototype (a high speed milling spindle).

What I'm actually doing is drilling out to 14mm and then boring the remaining 2mm with the last passes being very fine (helped by some telescoping bore gauge).

Then bring down the outer dia (from 25 / 27 mm depending on the stock) to 20mm.

I'm holding a piece of 65mm bar in my 3 jaw and parting it off after the turning and boring, then turning it round in a 20mm ER32 collet to face off – or perhaps I thought the parting off was good and I just finished on some emery. Can't remember now.

Sadly, autofeed on this lathe is not particularly fine and is a pain to set up. I don't use it. Instead practicing a steady hand – well eventually it will get steady!

Iain

[HuubParticipant @huub]

Posted by Iain Downs on 15/06/2023 15:42:17:

Hi, Huub.

I'm holding a piece of 65mm bar in my 3 jaw

Sadly, autofeed on this lathe is not particularly fine and is a pain to set up. I don't use it. Instead practicing a steady hand – well eventually it will get steady!

 

If you can hold a 65 mm bar in the 3 jaw, your lathe and tool post are probably rigid enough to hold a long boring bar.

Putting a stepper on the lead screw solved the gear switching on the mini lathe. My bigger lathe has besides the change gears, a 2 and 3 position lever to select 6 different feeds.

If it need to be accurate, I use the CNC to turn an opposite taper. That requires 3 finish passes and 2 thickness measurements. That is a lot easier and faster than setting up the alignment.
For accurate drilling you still need an aligned setup.

High speed contact angle bearings are pretty expensive and requires very accurate machining. That is beyond the capabilities of me and my lathe.

Edited By Huub on 15/06/2023 18:48:51

[HuubParticipant @huub]

Posted by Iain Downs on 15/06/2023 15:42:17:

The one I've made was OK apart from narrowing towards the chuck by about 0.03 mm.

Sadly, autofeed on this lathe is not particularly fine and is a pain to set up. I don't use it. Instead practicing a steady hand – well eventually it will get steady!

If you get 0.03 mm narrowing when using the top slide, then you have to check the alignment of the top slide.

• Put a thick bar in the chuck.
• Mount an indicator on the bar using a magnetic holder.
• Set the indicator on a point of the moving part of the top slide and zero the dial (or note the value). Mark the position of the indicator on the moving part of the top slide.
• Feed the top slide 50 mm and use the carriage to reposition the indicator at the marked position. The indicator will now show the alignment of the top slide.

[HopperParticipant @hopper]

Is your boring bar small enough for the 14mm hole? If you use too big a boring bar the heel of the bar can rub on the inside of the hole and cause the kind of serrated finish you mention. For 14mm hole you might need a small insert boring bar with 6mm or 8mm shank or so, not a big fat 12mm shank.

Also, slowing down the rpm for boring can help reduce chatter.

[HuubParticipant @huub]

Hopper,

You are right to check if the boring bar is small enough. I mark the "critical sides of the boring bar" with a sharpy and check if the boring bar doesn't contact the hole.

I have a 12 mm boring bar (S12M SCLCR06, CCMT060204 insert) that fits a 14 mm hole.

The CCMT0602xx boring bars are the "smallest". For larger diameter holes, I prefer the DCMT0702xx inserts in a Q style holder because chips don't build up so easy on Q type insert holders.

[Author]

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