Sieg SC3 7x16 Mini Lathe Question...

[mac1911]

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.

If it made it worse do you think maybe the holes or lack of weight in those empty holes could be a problem.
Or at least part of it.

 

[GrifterGuru]

I doubt it. It was the off-centered weight that caused the imbalance. Once the weight was removed, it went back to the usual "imbalance" noted in the original post.

I have tried what I can to deduce the issue and so far, without stripping the headxtock (whilst I await the new bearings), I have been looking at all potential causes.

Still looking at bearings and spindle balance. Once the spindle is out, I can check that for balance between a pair of centres to see if there is an underlying imbalance in the spindle. If there is, I can deal with that.

 

[Huub Buis]

Measure the radial and axial runout of the spindle. A bend spindle or bad bearings will cause runout.

Replacing bearings is not always an easy job and can cause damage to the spindle or head stock. If the lathe is new, I would return the lathe for replacement.

If you spin up the lathe to its max RPM and turn of the power, the spindle will still keep turning. If vibrations are gone, it is the BLDC controller.

 

[GrifterGuru]

Oddly enough, I have done that and the Vibration is still present, so definitely bearings or spindle. Will check the spindle later once I have removed it and have it between centres.

As to bearings themselves, I have pullers, so no undue stresses will be exerted on the removal of them. Other than that, I will be freezing the spindle prior to fitting the new ones.

 

[Huub Buis]

As to bearings themselves, I have pullers, so no undue stresses will be exerted on the removal of them.

When I pulled the spindle from the mini lathe, it took so much force I was afraid that I would crack the head stock. At that point, the pulling forces already damaged the bearings (that where OK before disassembling) so I continued. I did manage to remove the spindle and replaced (upgraded) the bearings.
My mini lathe was fitted with common ball bearings. These where press fitted on the spindle. The upgrade bearings where contact angle bearings that needed a snug fit. The spindle shaft however was on press fit tolerance and needed some work.

 

[GrifterGuru]

When I pulled the spindle from the mini lathe, it took so much force I was afraid that I would crack the head stock. At that point, the pulling forces already damaged the bearings (that where OK before disassembling) so I continued. I did manage to remove the spindle and replaced (upgraded) the bearings.
My mini lathe was fitted with common ball bearings. These where press fitted on the spindle. The upgrade bearings where contact angle bearings that needed a snug fit. The spindle shaft however was on press fit tolerance and needed some work.

Been there, done that already on the 7x I am rebuilding. Had to get the emery out on the spindle for that so the bearings were a light interference fit since I went with Taper roller bearings.

The replacement bearings the company are sending for this one are Angular contact, so I will need to deal with the spindle on this mini before fitting them. Should'nt have to do this on a machine less than 6 months old, but hey ho.

Just "add it to the list"...

So far I have done the "two half nut" conversion (remove lead-screw cover/guard), now angular contact bearings.

This was only supposed to be an interim machine to get some turning done that I need to carry out for the other lathe and it is fast becoming a PITA. Caught myself looking at new apron castings earlier that had the dovetail for the half-nuts and a bearing recess for the apron handwheel gear. I soon shut the page out. Not doing that. Not now, not ever. Bad enough rebuilding one lathe, not going down that road with this one since I plan to sell it later down the road.

 

[homebrewed]

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.

The hole asymmetry is due to the fact that the spindle flange is designed to accept chucks with both 3 and 4 attachment screws. As a result there is a variety of angular separations. Three holes at 120 degrees are not compatible with a regular 4-hole pattern. At best one of the 3 120-degree holes is used for the 4-screw chuck but that's as good as it's going to get.

Putting one single weight in a hole will unbalance things, but maybe I'm not understanding your comment -- you say "a weight", not "weights" so that's my interpretation of your comment.

 

[GrifterGuru]

I tried single and paired (opposite as well as offset) weights. Nothing doing.

I also rotated the spindle by hand again and actually noted a notch/snag in the rotation. Not repeatable at the same location of the spindle flange so it tends to lend weight (pun not intended) to the bearing theory that was drawn by the supplier as well as myself.

Wierdly enough, I dont have this issue on the other lathe with a 4" spindle flange. That is smooth as salted-butter and spins without any form of inbalance whatsoever whether run with a chuck or without.

 

[homebrewed]

I tried single and paired (opposite as well as offset) weights. Nothing doing.

I also rotated the spindle by hand again and actually noted a notch/snag in the rotation. Not repeatable at the same location of the spindle flange so it tends to lend weight (pun not intended) to the bearing theory that was drawn by the supplier as well as myself.

Wierdly enough, I dont have this issue on the other lathe with a 4" spindle flange. That is smooth as salted-butter and spins without any form of inbalance whatsoever whether run with a chuck or without.

Interesting! Do you have the change gears engaged? Also wondering if the forward/reverse gear setting makes a difference, in terms of the snag in the rotation. The gearing associated with those isn't going to be a 1:1 relationship with the spindle, hence my questions.

I don't see how some funny business in the forward/reverse and change gear chain could cause the vibration you're experiencing. But that hesitation or snag may nor may not be related to the vibration so it would be good to determine if it's a real problem or just a "feature".

Please let us know how the bearing replacement works!

 

[GrifterGuru]

Will do on the bearings.

No to the change gears / tumbler being engaged/fitted. Removed the gear change gears and removed the entire plate carrying the tumbler and idler gear.

Still a hitch/snag when rotating the spindle.