Wobble when turning

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jasonmac73

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Joined
Dec 19, 2016
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48
Location
Jacksonville, FL
My last few pens have had a wobble in the middle while turning. I though I had a bent mandrel so I took the bushing and blanks off and ran it on the lathe. It runs completely true. I loosened the tail stock really loose and still a wobble in the middle.

Anyone experience this issue?


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Look for "crapiola" in your headstock. A bottle brush, pushed into the morse taper should clean out easy stuff. Also clean the morse taper insert side.

IF you have a dead center, put it in the headstock, if it wobbles, the major possibility is as described above (which is how I learned this)
 
Jason,
There could be several reasons for this but the most common on people just getting started is using a mandrel and the standard tail stock center that came with the wood lathe.

The CAUSE in this situations is this: The Mandrel has a cup in the end; this cup is a 60° cup and needs a 60° live center point to fit into it. Most wood lathes come with a SHARPER point in the tail stock that is meant to grab into wood. Placing this sharper point, (the original equipment) into the cup of a mandrel causes that sharper point to "ball up" and then it wobbles.

Look for a 60° live center for the tail stock if you are using a mandrel.

AS mentioned there may be different reasons and I will let others mention those.
 
I bought a 60 degree live center about a year ago and been using it.

There is not an issue of build up on the mandrel morse taper or the inside of the taper.

The wobble seem to happen when there is barrels on the mandrel being turned. I notice when I am sanding because its very slight.

I took the barrels off and ran the lathe with the mandrel mounted between the head and tail stock as if I was turning and it runs perfect true.

Maybe I will lightly run a piece of sandpaper through the inside of my bushings. I suppose there may be a slight buildup inside since that is the only common factor.
 
Not an expert but I did stay at a Holiday Inn Express. I have a long pen mandrel and have to be careful about putting too much pressure on the blanks. Too much pressure will cause the mandrel to flex in the middle.
 
. . . When the barrels are on the mandrel . .

This helps.

1. as mentioned by Woodchipper - are you pulling up and tightening the tail stock too much when turning ? That is for you to determine. I am sensing after your reply that this is not your problem though.

2. Are your blanks squared perfectly to the tube BEFORE putting them on the mandrel? Unsquared blanks/tube will cause what you are saying as you tighten the nut on the mandrel. "Eyeballing" does not always equal "Square".

3. in some cases (and I don't "think" this is your case) - woods with wide softer grain between the hard grains get sanded off more as it turns - than the hard. The causes what is often referred to as "out of round" (OOR), and is caused by gripping the sand paper too tight around the round blank. The soft stuff sands off at a higher rate than the hard grain. This does not sound like your problem, but I did want to mention it.
 
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Check your mandrel again, seems like that is the issue. I would replace it and purchase a mandrel saver also to help eliminate the vibration. Hope you get it sorted out.

Rod
 
I was using a standard mandrel and went through the same thing. I presume I was warping the mandrel when tightening because it slowly got worse. At first I could feel it but not notice it in my pens. Eventually I could notice in my pens and replaced the mandrel system.

The problem went away. BUT, I bought the expensive live center precision mandrel system (not PSI) and two different sized shafts on the suggestion some bushing are loose, some are tight on a single shaft and that can cause similar issues. Lee's number 2 makes sense to be also because I was trying various squaring methods at the time and had a few flat but not square blanks.

In the end, I turn single barrels between centers. Still turn double barrels on the mandrel saver set up and the issue has went away. Oh, and keep sharpening/touching up your tools. Lessened my tendency to keep tightening the tailstock.


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I've had a problem with this before I bought my mandrel saver. Then all was good. Until a few weeks ago when I turned a pen and realized it was still happening. Turns out some of my bushings had holes that were just a tiiiiny bit bigger than my mandrel. I've got a PSI collet chuck that I use instead of the MT1 chucks that come with the mandrel. On the bushings whose holes were slightly oversized, I reamed them out to an even 1/4" and use a piece of TGP rod measuring exactly .250". This has worked much better for me, and I am contemplating drilling out ALL of my bushings this way, and drilling my mandrel saver to match (as it's ID is proper for an "A" mandrel and will not fit with the 1/4" rod).
 
MiteyF said:
. . .Turns out some of my bushings had holes that were just a tiiiiny bit bigger than my mandrel.
Click to expand...

Back when the Sierras first came out, there were several batches of bushings with off center holes. I lived overseas and usually ordered 2 SETS of bushings so that I could get 2 good bushings. Also, as you noted, some of the holes are maybe .01 or .005 larger than the mandrel.

JohnnyCNC recognized this early on (about 11 or 12 years ago) and started making precision fit bushings. The slop in normal bushings allow it to fall straight into the tubes and even feel loose inside, where as with Johnny's there was a precision fit feel.

Too much space and imprecise bushings can cause this also, whether it be the hole too large or bushing (that fits inside) is too small.
 
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