Sieg SC3 7x16 Mini Lathe Question...

GrifterGuru said:
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.
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Any noise related to the in balance?
 
Now, as some on here will remember, during a bearing change to angular contact bearings, I managed to make a series of daft mistakes with a hydraulic press and (amongst other things) broke the front-most as-supplied ball bearing, leaving the cage firmly stuck on the spindle near the spindle flange.

I tried everything I could think if and the damn thing wouldn't come off, so I ended up using a bench grinder to grind away at the stuck cage until the cage split on it's own and was able to be removed. It must have been under a lot of expansive pressure to split even that relatively thin remaining material after the grinding (I suspect I had pushed the bearing onto an inaccurately machined part, an enlarged fillet if you will, at the shoulder of the head of the spindle).

Anyhow, during my somewhat clumsy grinding, I had nicked part of the spindle head (the thicker shoulder that should butt up against the front most bearing) a bit [ahem] and had removed, probably about 10% of the mass of that bit of the head.

Before I had attempted the bearing change, I noticed at around 1230 RPM, the lathe would vibrate a bit, and then quieten down somewhere around 1280 RPM.

So I had this almost certainly unbalanced spindle and nothing else (the spindle I had on my 7x14 was just different enough from the C3 and SC3 to have to go through the original importer and they said 6-8 weeks for a replacement) so I thought "What's the worst that can happen?" and (a lot more carefully this time) put the new bearings on this rather abused spindle.

Now unexpectedly, I seem to have no worse problems with vibration than I had before. It's now just moved to a range of 1520ish - 1565ish RPM; a slightly smaller range...eh...:dunno:

So to sum up. It may be a bearing change will fix it for you but with my experience, I suspect it's something you'll have trouble fixing. It hasn't got in my way so far and at some point I'll get a Boxford or an ML7 and it will cease to be a problem. ;)
 
Two issues:

- The dual hole patterns on the spindle - add a bit of metal (I used lead - easy) to the odd hole. (I have a 4-inch spindle and have not found it necessary to added metal to the access hole for the headstock seal ring.) The plug is then removed if mounting a four-jaw chuck.

- The 4-inch 3-jaw scroll is out of balance. I discovered this by watching the chuck suspended on horizontal 1/2" drill rod. Note in the image the heavy area with three rings. It's hardened, but I drilled/ground small holes in that area.
 

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@SouthernChap Interesting experience.

As I said prior, once I pull the spindle and have the bearings off (no, I am not using a hydra-press even though I have one), I will be seeing about whether the spindle is out of balance.

@Smithdoor the imbalance is present whether a chuck is mounted or not, just to a lesser degree.

@CraigH interesting thought....
 
GrifterGuru said:
@SouthernChap Interesting experience.

As I said prior, once I pull the spindle and have the bearings off (no, I am not using a hydra-press even though I have one), I will be seeing about whether the spindle is out of balance.

@Smithdoor the imbalance is present whether a chuck is mounted or not, just to a lesser degree.

@CraigH interesting thought....
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How are you going to balance the spindle.
 
CraigH said:
Two issues:

- The dual hole patterns on the spindle - add a bit of metal (I used lead - easy) to the odd hole. (I have a 4-inch spindle and have not found it necessary to added metal to the access hole for the headstock seal ring.) The plug is then removed if mounting a four-jaw chuck.

- The 4-inch 3-jaw scroll is out of balance. I discovered this by watching the chuck suspended on horizontal 1/2" drill rod. Note in the image the heavy area with three rings. It's hardened, but I drilled/ground small holes in that area.
Click to expand...
How do you balance a scroll?
 
mac1911 said:
How are you going to balance the spindle.
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The spindle, except for the "odd hole" is pretty well balanced. See my post above as to adding weight. The bare spindle will not exhibit much vibration even without the weight.

To add the weight to the spindle, look at the spindle face. There is a three-hole pattern for three-jaw scroll chucks; the pattern for mounting a four-jaw independent chuck uses ONE of the holes of the three-hole pattern, and three other holes. One of those holes is the "odd hole". With the added weight, there are then two symmetrical patterns of holes - a three-hole pattern and a two-hole pattern, each evenly spaced.

When you look at the spindle holes for a bit, you will see the "odd hole".
 
mac1911 said:
How do you balance a scroll?
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Drilling/grinding in the non-critical parts of the heavy side. A crude operation, but was absolutely necessary on my 4-inch 3-jaw chuck (LMS 5100). In the image I posted above, the heavy part is the upper location. Note the area of three rings there, and only two rings elsewhere. (small grinding points and small masonry drills will be needed)

Since the scroll is relatively light, I could not figure out how to check the "work". I assembled and disassembled the chuck several times to check its balance.

BTW, to test for this run the bare chuck body throughout the speed ranges and there will be no vibration.
 
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