Lathe slide wobble

[syrtismajor]

Has anybody else had this trouble with their lathe?
Mine is a Sieg II Metal Lathe that has an annoying feature that I cannot remove. Ever since I got it I have followed every tutorial online to make it as good and reliable as possible. This includes taking the whole thing apart, cleaning every last screw, polishing every moving part and carefully reassembling it. The increase in performance is very noticeable, I'm happy to call it my new lathe since it replaced my older Sieg I.
Now, both the cross slide and compound slide have proved to be the snag. At first the quality of the slide was a little questionable due to their machining marks etc. but I manage to solve that with excessive polishing. All of the slide areas now have a shiny surface rather than the previous 'gritty' appearance. I was hoping this would take care of the little 'wobble' they had that led to some annoying vibration.
If this sounds a little confusing, hopefully my 'crap-o-cad' will help...

A is how I set up the slides. The screw holds the jib in place which isn't quite the correct shape. Since only one side connects, I cannot foresee this being much of an issue. I tighten all of the holding screws until the slide moves freely.
B is what happens when I'm running the lathe. Generally It's not noticeable until I cut steel where a vibration starts. The little gap (by the red arrow) opens up to about 1/4 of a millimetre leading to the cutting head suddenly vibrating. This can lead to a broken tool or a distorted part. What really confuses me is that the opening will not go beyond that 1/4 of a millimetre.
I have tried tightening the holding screws to remove any chance of vibration, but that locks up the slide completely which sort of ruins the point of the lathe...
I've checked the mating parts on the other side of the slide and they match up perfectly, this was using a permanent marker pen so there is no chance that is where the wobble originates. The only area that I can see causing this where the jib is located as it must give some room to let this happen. Maybe it's rotating a little? If so, what can I do to fix it?

 

[jack620]

Do your gibs have small flat spots cut into them where the gib screws seat? Maybe they do but your picture doesn't show them. The way you have drawn it the force from the gib screws would tend to want to tilt the gib. The gibs on my lathe have small pockets so that the screws press against a flat face.

Like this:

 

[goldstar31]

Between my two lathes, there is chalk and cheese in construction of the gibs.
Neither is perfect and even the Myford Super7 with gear box and power cross feed. Ideally, the gibs should FILL the Void and be pinned through the gib itself to prevent the gib moving.
You will see that in writing this that that I have criticised possibly two of the better class of machine. The cheaper machines- frankly are horrible.
So what can be done? Well, I've written this before but the cheapest and easiest is to change the gibscrews from vee pointed ones to ones with rounded ends( Like my Myford ones)
Again, I recommend that a pin is drilled to stop 'forward and back movement' I did this-- years ago to my pre-war Perfecto vertical slide. It's George Thomas - the Guru of all things model engineering.
The next thing is tp o FILL THE GAP which is arguably cheap machining anf- heigh , ho, once the gib has been put in place in the factory-- that's it. When you have to clean, oil and adjust later, you are sadly o your own. The forum is full of the problems of newcomers who have reached the problem. Yes, firms like ArcEuro Trade in the UK with sell better gibs-- made out of brass. By no means perfect but life is a bit easier.
Myford- in the arguably most expensive cross slide gib has/had a split gib( its quite a long slide) and each are held by gib screws- in TWO directions. Digressing- Myford suplles laminated shims- to make things easier. UI seems to recall that each leaf is 2 thous thick.
So ideally, one literally makes a tailor made new gib- which isn't easy.
So buyong a packet of assorted steel shims and actually sticking them to the ones which came seems the best idea.

Of course, there is a more modern way and that is to fill the airgap with epoxy resin compouned/

I jope that the foregoing will make future adjustments a little simpler

Norman

 

[syrtismajor]

Do your gibs have small flat spots cut into them where the gib screws seat? Maybe they do but your picture doesn't show them. The way you have drawn it the force from the gib screws would tend to want to tilt the gib. The gibs on my lathe have small pockets so that the screws press against a flat face.

That was one of my first "fixes" where I milled flat pockets into the jib as it was one my first thoughts. That way they are pushing against a flat surface rather than tilting the jib. The original jib did not have these, just indentations where the screws were forced into it at the factory.

 

[syrtismajor]

Between my two lathes, there is chalk and cheese in construction of the gibs.
Neither is perfect and even the Myford Super7 with gear box and power cross feed. Ideally, the gibs should FILL the Void and be pinned through the gib itself to prevent the gib moving.
You will see that in writing this that that I have criticised possibly two of the better class of machine. The cheaper machines- frankly are horrible.
So what can be done? Well, I've written this before but the cheapest and easiest is to change the gibscrews from vee pointed ones to ones with rounded ends( Like my Myford ones)
Again, I recommend that a pin is drilled to stop 'forward and back movement' I did this-- years ago to my pre-war Perfecto vertical slide. It's George Thomas - the Guru of all things model engineering.
The next thing is tp o FILL THE GAP which is arguably cheap machining anf- heigh , ho, once the gib has been put in place in the factory-- that's it. When you have to clean, oil and adjust later, you are sadly o your own. The forum is full of the problems of newcomers who have reached the problem. Yes, firms like ArcEuro Trade in the UK with sell better gibs-- made out of brass. By no means perfect but life is a bit easier.
Myford- in the arguably most expensive cross slide gib has/had a split gib( its quite a long slide) and each are held by gib screws- in TWO directions. Digressing- Myford suplles laminated shims- to make things easier. UI seems to recall that each leaf is 2 thous thick.
So ideally, one literally makes a tailor made new gib- which isn't easy.
So buyong a packet of assorted steel shims and actually sticking them to the ones which came seems the best idea.

Of course, there is a more modern way and that is to fill the airgap with epoxy resin compouned/

I jope that the foregoing will make future adjustments a little simpler

Norman

I was expecting shims as a possible solution... bit of a pain as the gibs (jibs my error) aren't exactly square (diamond?) for this to work. I'll try a Heath Robinson version of this however to see if it does make a difference.

 

[goldstar31]

I was expecting shims as a possible solution... bit of a pain as the gibs (jibs my error) aren't exactly square (diamond?) for this to work. I'll try a Heath Robinson version of this however to see if it does make a difference.

I hope that you get an Improvement

Cheers

norman

 

[jack620]

I have tried tightening the holding screws to remove any chance of vibration, but that locks up the slide completely which sort of ruins the point of the lathe...

I fitted a gib locking screw to my cross slide. I tapped a 3/16" thread through the cross slide casting between two gib screws. A ball bearing was inserted in the hole then a 3/16" cap screw was fitted. The ball bearing prevents the screw head from chewing into the gib.

You can do the same to the topslide, but I chose to replace the topslide with a solid toolpost mount. This made a HUGE improvement to the rigidity of the lathe when parting-off. I can post pics if you want them.

 

[ShopShoe]

Some other things spring to mind:

In your polishing, could you have made your dovetail surfaces less parallel with each other? It is easy to do this with handheld tools like files and stones.

Making new gibs (jibs) might be worthwhile. You can dress the screw locations as Norman suggests, or add the pins, or both.

There are some threads here and elsewhere where extra adjusting screws are added. (I.E.: where your lathe may have come with three, you end up with five or six.)

Just so all bases are covered, you should replace the screws it came with higher quality ones if you did not do that already.

What jack620 says above is true: removing the topside (compound), or tightening its screws completely, will increase rigidity. Making sure that tool "stick-out" is small and you are working in the middle of slide travel will also reduce the leverage pulling on the slide and increase rigidity as well.

As a last thought, I think we are all talking about cross slide rigidity here. If you are actually concerned about the saddle lifting off the bedways there are different issues there: Look for the tapered-gib modification or about shimming the gibs. My apologies for mentioning this if this is not your concern.

--ShopShoe

 

[SmithDoor]

I seen epoxy by Devcon WR.
The machine tool rebuild used on opposite from the jib adjustment. Work great just like new.

Dave

Between my two lathes, there is chalk and cheese in construction of the gibs.
Neither is perfect and even the Myford Super7 with gear box and power cross feed. Ideally, the gibs should FILL the Void and be pinned through the gib itself to prevent the gib moving.
You will see that in writing this that that I have criticised possibly two of the better class of machine. The cheaper machines- frankly are horrible.
So what can be done? Well, I've written this before but the cheapest and easiest is to change the gibscrews from vee pointed ones to ones with rounded ends( Like my Myford ones)
Again, I recommend that a pin is drilled to stop 'forward and back movement' I did this-- years ago to my pre-war Perfecto vertical slide. It's George Thomas - the Guru of all things model engineering.
The next thing is tp o FILL THE GAP which is arguably cheap machining anf- heigh , ho, once the gib has been put in place in the factory-- that's it. When you have to clean, oil and adjust later, you are sadly o your own. The forum is full of the problems of newcomers who have reached the problem. Yes, firms like ArcEuro Trade in the UK with sell better gibs-- made out of brass. By no means perfect but life is a bit easier.
Myford- in the arguably most expensive cross slide gib has/had a split gib( its quite a long slide) and each are held by gib screws- in TWO directions. Digressing- Myford suplles laminated shims- to make things easier. UI seems to recall that each leaf is 2 thous thick.
So ideally, one literally makes a tailor made new gib- which isn't easy.
So buyong a packet of assorted steel shims and actually sticking them to the ones which came seems the best idea.

Of course, there is a more modern way and that is to fill the airgap with epoxy resin compouned/

I jope that the foregoing will make future adjustments a little simpler

Norman

 

[tornitore45]

Pocket in the jib require a fairly thick jib. Otherwise, the jib screws should have a conical head with the angle matching the dovetail angle. That way the contact is a line instead of a point and there is a force pushing the slide down. Better jet, a flat headed set screw should push a round insert with the face contacting the jib slanted. That is the way my Sieg 9x20 is set up and have no problem parting steel.

 

[terryd]

Has anybody else had this trouble with their lathe?
Mine is a Sieg II Metal Lathe that has an annoying feature that I cannot remove. Ever since I got it I have followed every tutorial online to make it as good and reliable as possible. This includes taking the whole thing apart, cleaning every last screw, polishing every moving part and carefully reassembling it. The increase in performance is very noticeable, I'm happy to call it my new lathe since it replaced my older Sieg I.
Now, both the cross slide and compound slide have proved to be the snag. At first the quality of the slide was a little questionable due to their machining marks etc. but I manage to solve that with excessive polishing. All of the slide areas now have a shiny surface rather than the previous 'gritty' appearance. I was hoping this would take care of the little 'wobble' they had that led to some annoying vibration.
If this sounds a little confusing, hopefully my 'crap-o-cad' will help...View attachment 124802
A is how I set up the slides. The screw holds the jib in place which isn't quite the correct shape. Since only one side connects, I cannot foresee this being much of an issue. I tighten all of the holding screws until the slide moves freely.
B is what happens when I'm running the lathe. Generally It's not noticeable until I cut steel where a vibration starts. The little gap (by the red arrow) opens up to about 1/4 of a millimetre leading to the cutting head suddenly vibrating. This can lead to a broken tool or a distorted part. What really confuses me is that the opening will not go beyond that 1/4 of a millimetre.
I have tried tightening the holding screws to remove any chance of vibration, but that locks up the slide completely which sort of ruins the point of the lathe...
I've checked the mating parts on the other side of the slide and they match up perfectly, this was using a permanent marker pen so there is no chance that is where the wobble originates. The only area that I can see causing this where the jib is located as it must give some room to let this happen. Maybe it's rotating a little? If so, what can I do to fix it?

Hi Syrtism,

Just a thought - it struck me this morning after reading about your problem yesterday that the gib key could be sitting on the slideway when you tighten the grub (set) screws to adjust it.

Let me explain my thinking. When tightening the gib adjusting screws normally the forces involved should force the cross slide carriage down onto its slideways as the angle of slope is negative, however if the key is already down on the slideway and the screws engaged in detents (not absolutely the correct word but I hope it describes the shallow hole machined into the key) it cannot slip down any further the only force left as you tighten the screws is a lifting one causing the carriage to lift on the gib key resting on the slideway which I think is what you describe as 'wobble'.

If the gib key was already bottomed out when you originally tightened the screws and you used the witness marks to drill the detents the key would be permanently bottomed out and the screws sitting in the detents would force the carriage to lift, getting worse the more you tighten them.

Perhaps try a narrower piece of stock as a temporary key ensuring that it is not resting on the slideway at any time. Chock it up when fitting with a small strip of something, brushcutter line perhaps or even a strip of wood, which can be removed easily. Inexpensive and quick to do so worth a try?

If successful you could perhaps modify your existing key by removing material from the bottom. If not it's 'back to the drawing board'. Best of luck,

stay safe and healthy,

TerryD

 

[tornitore45]

FWIW I rather have two flat surfaces with tool marks mating than two surfaces super-polished by hand that may be no longer flat. Tool marks are good for oil retention as long as they are fine and on flat surfaces.

The single largest shortcoming of the Sieg is the 2 bolts ring holding down the compound, is not strong enough and diametral bolts allow rocking on the other (perpendicular) diameter. There are design for a better, 4 bolts method of securing the compound.

 

[goldstar31]

I would recommend that you leave well, alone!

 

[ignator]

syrtismajor Why do you believe this is a compound slide issue? Just what material are you cutting? Using what speeds and feeds? Your description about .25mm of gap between the slide surfaces, did you actually measure this?
Are you sure it's not the whole lathe going into harmonic oscillations causing your problem?
I've had my 10x24 bench lathe do this with any attempt to do parting in steel. The fix was to bolt it to a slab of steel to make it rigid. The lathe was on a sheet metal stand, leveled. It would "dance" on the floor with any light cuts during parting. And all I could figure was the whole lathe bed was oscillating.
Your Sieg II Metal Lathe is a bench lathe as well. Are you sure your not pushing it beyond it's cutting limits? Is it bolted down to a solid bench?

 

[johwen]

Looking an the photo at the top of the article if the dimple holes are too big for the end of the gib screws it would allow the gib to move on the screws. I believe this is the reason for the vertical chatter movement. If this is the case reverse the Gib and dimple with conical seats and points on screws

 

[terryd]

Has anybody else had this trouble with their lathe?
Mine is a Sieg II Metal Lathe that has an annoying feature that I cannot remove. Ever since I got it I have followed every tutorial online to make it as good and reliable as possible. This includes taking the whole thing apart, cleaning every last screw, polishing every moving part and carefully reassembling it. The increase in performance is very noticeable, I'm happy to call it my new lathe since it replaced my older Sieg I.
Now, both the cross slide and compound slide have proved to be the snag. At first the quality of the slide was a little questionable due to their machining marks etc. but I manage to solve that with excessive polishing. All of the slide areas now have a shiny surface rather than the previous 'gritty' appearance. I was hoping this would take care of the little 'wobble' they had that led to some annoying vibration.
If this sounds a little confusing, hopefully my 'crap-o-cad' will help...View attachment 124802
A is how I set up the slides. The screw holds the jib in place which isn't quite the correct shape. Since only one side connects, I cannot foresee this being much of an issue. I tighten all of the holding screws until the slide moves freely.
B is what happens when I'm running the lathe. Generally It's not noticeable until I cut steel where a vibration starts. The little gap (by the red arrow) opens up to about 1/4 of a millimetre leading to the cutting head suddenly vibrating. This can lead to a broken tool or a distorted part. What really confuses me is that the opening will not go beyond that 1/4 of a millimetre.
I have tried tightening the holding screws to remove any chance of vibration, but that locks up the slide completely which sort of ruins the point of the lathe...
I've checked the mating parts on the other side of the slide and they match up perfectly, this was using a permanent marker pen so there is no chance that is where the wobble originates. The only area that I can see causing this where the jib is located as it must give some room to let this happen. Maybe it's rotating a little? If so, what can I do to fix it?

Hi,

Reverse the gib key so that there are no pockets for the screws and use round end screws so that points don't dig into the strip and the screws will be able to slip downwards slightly under the pressure on the angled gib key and pull the carriage down onto it's slideways - and make sure that the key is not too wide now that you have polished the surfaces of the slide.

To be honest the slideways should not be too polished as grinding marks will retain lubricant and as long as those marks are not aligned they will slide as well as polished surfaces, that was the effect of those lovely scraped surfaces that we saw in days gone by. Those surfaces were not perfectly flat or poished but they moved oh so smoothly.

TerryD

 

[jack620]

Reverse the gib key so that there are no pockets for the screws and use round end screws so that points don't dig into the strip and the screws will be able to slip downwards slightly under the pressure on the angled gib key and pull the carriage down onto it's slideways -.

I don’t think that will help. Those screw pockets are there for a reason. There are tens of thousands of lathes in the world with gibs just like that. I think reversing the gib will just cause the gib to be pushed upwards potentially making the problem worse.

 

[SmithDoor]

It sounds like it is a manufacturer error not wear.

Dave

Hi,

Reverse the gib key so that there are no pockets for the screws and use round end screws so that points don't dig into the strip and the screws will be able to slip downwards slightly under the pressure on the angled gib key and pull the carriage down onto it's slideways - and make sure that the key is not too wide now that you have polished the surfaces of the slide.

To be honest the slideways should not be too polished as grinding marks will retain lubricant and as long as those marks are not aligned they will slide as well as polished surfaces, that was the effect of those lovely scraped surfaces that we saw in days gone by. Those surfaces were not perfectly flat or poished but they moved oh so smoothly.

TerryD

 

[terryd]

[/QUOTE]

I don’t think that will help. Those screw pockets are there for a reason. There are tens of thousands of lathes in the world with gibs just like that. I think reversing the gib will just cause the gib to be pushed upwards potentially making the problem worse.

Hi,

There are also many lathes and machines that do not have those screw indentations and they work perfectly. The gib key should not be pushed upwards as it is a parallelogran in section not tapered section. The indentations in gib keys are mostly there to prevent the gib key slipping in relation to the moving part of the machine, or so I was told by a shop engineer who worked for Boxfords for most of his working life. Unfortunately he passed away some years ago so I'm no longer in contact with him, but one day perhaps - who knows, and besides, there's nothing lost in trying my suggestion except perhaps 5 minutes of shop time!

Stay safe and healthy,

TerryD

 

[goldstar31]

I'm sorry but I keep on repeating that 'a litt;e learning is a dangerous thing' and in my workskshop- which isn't more than a little wooden shed- I have a plethora( a lot) of machines with all sorts of gib assortments.
My mill drill- Cheap and Chinese has tapered gibs whilst my home made Quorn tool and cutter grinder has a cylindrical illar- but no gib as such but clamps and a 1" thread( which sorts the talkers from the can doers However the sliding the other way i.e. horizontally, had to slide on precise bores- except for one which takes a split clamp. The there are the ball handles and clamps- and so the merrygoround rotates. The Stent is even more hilarious because it should be cast iron on ast iron-- and isn't. It is all welder=d mild steel--- and works. The Deckel clone t&c is -- what it is. Oh, dear me YES. The Chinese are quite different as they are experts not in econmis and politics but have political economy and will smile at your suggestions---- and please themselves. As we will eventually discover.
The Myford Super7B PXF is almost a totally different machine to its cheaper ML7 and whilst it shares simlar gibs on the lathe shears it adopts the - or has changed from the narrow guide system but the top slides are 'pretty simlar' but they both have locking gib screws( with locknuts)
The ML7 has a set of trapezoidal gibs in the cross slide but the Super7 has a irregular shaped PA~IR of gibs which are located from the top of the saddle but are pressed against triangulated shears.
My two vertic slides are sort of ' ordinary but should be pinned. However, the Potts Universal milling - winds attachment winds up and own and round from the INSIDE.
THe SIEG C4 is almost normal except that there are TWO grub screws impinging on one another.
That lot is MINE, there are other variations. Nylon gib strips?

Merely a few notes from the real world


Norman