Sieg SC3 7x16 Mini Lathe Question...

[GrifterGuru]

Ok, a quick question and a bit of an odd one, for those who may have more knowledge on the subject.

Last August (2023) I acquired a brand new SIEG SC3 7x16 lathe. Yes, the Brushless model.

No, I do not have the spindle speed DRO, so I am uncertain of the exact spindle speeds involved.

Up until two weeks ago, I had not run it up past the 5th segment mark around the speed control dial. Never had a problem previously or noted one given what I have been turning up until now not needing that much spindle speed. I have always run a 4" chuck on an adapter plate given the spindle has an 80mm flange and I only have 4" chucks to hand courtesy of my other lathe which I am currently in the middle of completely rebuilding (another 7x16 with a 100mm spindle flange).

Last week I needed to turn some aluminium, so chucked it up in the lathe and ran the spindle speed up to the sixth segment. As soon as it hit that segment, it started vibrating, so spun it up further and whilst it lessened it was still there. I immediately shut it down, removed the stock from the chuck, closed the chuck up and spun it up again. Hit the sixth segment and, yep, vibrations.

Remove the chuck, repeat run up, yup, vibrations.

Remove change-gear train, run up again and same thing, vibrations.

Removed belt and spun motor up on it's own, no vibration, so that proved it is limited to the headstock.

I have gone through and checked the belt gear on the spindle for being concentric and true and that is fine.

It is not belt tension causing the issue.

It is not excessive torque on the spindle nuts pushing against the bearings causing pre-load.

I chose to unbolt it from 50mm worktop it is bolted to in order to try a theory. I slowly spun it up after re-fitting the chuck. Just as it got into the 6th segment on the dial, the machine, rather than vibrating, started rocking back and forth so I shut it down.

Removed the chuck, spun up again and once again it rocked, but not so violently.

Having spoken to the company I purchased from, we are both drawing the conclusion of bearings (they are supplying upgraded replacements), but I am also wondering if it could be something else such as a slightly imbalanced spindle or am I completely off the mark?

I just want to cover all bases to ensure that as and when I replace the bearings that it will be the end of the problem.

Anyone else had this issue and resolved it with just new bearings or was something else the issue?


Yes, I bolted it back down for the time being. no, I will not be using it unti lthe issue is resolved.

 

[Smithdoor]

I photo would.
It could the grease could be problem. It will move all to one side.

Dave

 

[GrifterGuru]

In many years, I have never known grease to cause an inbalance in a bearing. It is also unlikely given the constant use when combined with how grease is worked through the bearings during use.

 

[mac1911]

Ok, a quick question and a bit of an odd one, for those who may have more knowledge on the subject.

Last August (2023) I acquired a brand new SIEG SC3 7x16 lathe. Yes, the Brushless model.

No, I do not have the spindle speed DRO, so I am uncertain of the exact spindle speeds involved.

Up until two weeks ago, I had not run it up past the 5th segment mark around the speed control dial. Never had a problem previously or noted one given what I have been turning up until now not needing that much spindle speed. I have always run a 4" chuck on an adapter plate given the spindle has an 80mm flange and I only have 4" chucks to hand courtesy of my other lathe which I am currently in the middle of completely rebuilding (another 7x16 with a 100mm spindle flange).

Last week I needed to turn some aluminium, so chucked it up in the lathe and ran the spindle speed up to the sixth segment. As soon as it hit that segment, it started vibrating, so spun it up further and whilst it lessened it was still there. I immediately shut it down, removed the stock from the chuck, closed the chuck up and spun it up again. Hit the sixth segment and, yep, vibrations.

Remove the chuck, repeat run up, yup, vibrations.

Remove change-gear train, run up again and same thing, vibrations.

Removed belt and spun motor up on it's own, no vibration, so that proved it is limited to the headstock.

I have gone through and checked the belt gear on the spindle for being concentric and true and that is fine.

It is not belt tension causing the issue.

It is not excessive torque on the spindle nuts pushing against the bearings causing pre-load.

I chose to unbolt it from 50mm worktop it is bolted to in order to try a theory. I slowly spun it up after re-fitting the chuck. Just as it got into the 6th segment on the dial, the machine, rather than vibrating, started rocking back and forth so I shut it down.

Removed the chuck, spun up again and once again it rocked, but not so violently.

Having spoken to the company I purchased from, we are both drawing the conclusion of bearings (they are supplying upgraded replacements), but I am also wondering if it could be something else such as a slightly imbalanced spindle or am I completely off the mark?

I just want to cover all bases to ensure that as and when I replace the bearings that it will be the end of the problem.

Anyone else had this issue and resolved it with just new bearings or was something else the issue?


Yes, I bolted it back down for the time being. no, I will not be using it unti lthe issue is resolved.

At this point you have one option. Try the bearings.
Unless you have a way of balancing the spindle assembly.
Is there any crud built up in the spindle bore?

 

[GrifterGuru]

At this point you have one option. Try the bearings.
Unless you have a way of balancing the spindle assembly.
Is there any crud built up in the spindle bore?

Spindle bore is spotlessly clean. After every job, I completely clean the lathe down even to the extent of cleaning the leadscrew and half nuts to remove any trace of swarf.

 

[markba633csi]

Probably an imbalance in the spindle drive pulley or spindle itself

 

[GrifterGuru]

Probably an imbalance in the spindle pulley or spindle itself

Looked at the spindle pulley as one of the "elminate any possible issue" checks. It was one of my first thoughts but went through a series of logical elimination steps to get to that point. Checked out without issue.

Spindle is directly driven, hence why I checked it.

Regarding spindle balance, I will know the answer to that as soon as the new bearings arrive.....

 

[mac1911]

Looked at the spindle pulley as one of the "elminate any possible issue" checks. It was one of my first thoughts but went through a series of logical elimination steps to get to that point. Checked out without issue.

Spindle is directly driven, hence why I checked it.

Regarding spindle balance, I will know the answer to that as soon as the new bearings arrive.....

I was curious my self and stumbled across this.
Interesting if its viable.
Used to have a shop near me that could balance anything. They mainly did drive shafts and flywheels. Sadly long closed.

 

[homebrewed]

I have read of mini lathe vibration problems that were due to the asymmetrical hole pattern in the spindle flange. You might try installing some screws+nuts in the holes and see what happens.

 

[GrifterGuru]

I have read of mini lathe vibration problems that were due to the asymmetrical hole pattern in the spindle flange. You might try installing some screws+nuts in the holes and see what happens.

With zero load and no chuck the vibration is still there. it is not due to the 120 degree separation of the chuck fixings.

Have also tried using a weight at each point of the flange using each fixing hole and that only worsens it.