3520b wobble

[Ben Pierce]

Hello Everyone,

Been off the forum for a while. Moved twice and am finally trying to get back to turning after about two years. Apparently I lost more skill than I'd expected to. I had a couple of horrendous catches in a hunk of green ash before walking away to revisit my basics! When returning to some finish turning on an old bowl I discovered a fair amount of runout in the spindle. I checked to be sure the chuck wasn't the issue, and tried two different faceplates. No luck getting the bowl to run true out at the rim end.

I've torn the machine down several times, checking everything-- pulley is aligned and tight, headstock is tight, so then I had the bearings changed. New bearings, same problem.

Before I assume that I've damaged the spindle and drop $250 for a replacement, can anyone think of anything else that might cause the wobble?

Ben

[Barry McFadden]

Do you only get the runout on the old bowl or any blank you put on?...... I'm just wondering if the old bowl has developed runout since it was first turned.

[Ben Pierce]

Anything I put on there.

[Kevin Jenness]

What are you measuring? I would register a dial indicator on the inside of the Morse taper and judge by that. For lack of an indicator adjust the end of a tool rest near the taper and use a feeler gauge.

[Ben Pierce]

Kevin, I haven't measured it, it's just that everything I put on turns up to a certain point and then vrub vrub vrub, is obviously not running true.

I don't have a dial indicator but I do have a feeler gauge. Can you explain that a bit further? Thank you.

[John K Jordan]

Kevin, I haven't measured it, it's just that everything I put on turns up to a certain point and then vrub vrub vrub, is obviously not running true.

I don't have a dial indicator but I do have a feeler gauge. Can you explain that a bit further? Thank you.

I'm not Kevin, but I use dial indicators to check many things. One is well worth having around the lathe, drill press, and other equipment. You can spend $100s of dollars on a name brand or get a useful one for much less. This one is not only affordable but has the easiest type of magnetic base to use: https://smile.amazon.com/Clockwise-T.../dp/B07C756TCM

I just checked my 3520b by several methods including the one Kevin mentioned and could detect no runout: mount the magnet base on the lathe bed and put the rounded tip of the indicator just inside the 2MT socket on the spindle, compressing the spring on the indicator a bit. Rotate the spindle by hand. If something is bent the needle will move back and forth. I saw zero movement in the needle indicating the inside of the taper at the opening was running true. There are also three places on the 3520b spindle with flats you can measure (if they are clean of finish or spots of rust) or you can mount a good chuck and check the runout on a smooth circumference on the outside.

runout.jpg

You can also mount some sort of drive or rotating center in the lathe spindle and test it. You can mount a good Jacobs chuck and grip a piece of metal rod or even a drill bit and check the runout on a smooth part of the shaft.

But even with a little runout or wobble in the spindle anything you turn from scratch in a chuck or faceplate will be come out perfectly round until you remove it and try to remount it. But even with no runout, remounting round things in a chuck can be expected to wobble until trued up since the chuck jaws can crush the wood fibers and it's almost impossible to get perfect registration. The out of round or wobble can be much worse, of course, if the wood has moved due to moisture or humidity change. The only thing to do is turn it again to get it round, assuming there is enough wood thickness.

JKJ

[Dave Mount]

I suspect you've already checked this, but a while back I picked up some wobble on my 3520B and it turned out to be little smudge of fine sanding dust on the face of the spindle where a chuck or faceplate bottoms out. Little rust could do the same. Probably not your issue but thought I'd throw it out there. On my machine I was surprised I'd never noticed it.

Best,

Dave

[Ben Pierce]

John, thank you for this. I'll get my hands on a dial indicator. Meanwhile I'm trying to wrap my mind around your last paragraph. Even if I have a bent spindle, it would turn smoothly a piece of wood freshly cut down on said spindle?

[John K Jordan]

John, thank you for this. I'll get my hands on a dial indicator. Meanwhile I'm trying to wrap my mind around your last paragraph. Even if I have a bent spindle, it would turn smoothly a piece of wood freshly cut down on said spindle?

Yes, you can even deliberately introduce a wobble in a turning, typically done in off-axis turning. This is usually done in stages - turn a bit on the axis, offset the axis and turn a bit more, repeat. You can get nicely spiraled and other odd and interesting shapes! You can buy special off axis chucks and jigs or do everything with standard holding methods.

For example, here's a little bud vase from maple, between centers, 3 axes on one end, two on the other:

bud_vase_comp_IMG_8238.jpg

And this picture has one "crazy" aluminum golf tee I turned on the wood lathe (crazy wooden golf tee idea courtesy of Frank Penta):

aluminum_brass_plastic.jpg

Of course, turning anything off-axis can give you some vibration to deal with, the same as a bent spindle. If the spindle is damaged it can create other problems so I'd want it fixed or replaced. If it is bent, a good machine shop might be able to straighten it. I've straightened some shafts over the years although I don't qualify as a "good" machine shop!

JKJ