Turning between Centers - Tube Flare

[bcoyne]

Attempted my first TBC last night. What Fun!! Really puts the feel of being an artist into woodturning. Problem was I got really bad tube flare. What did I do wrong?

Turned with busshing down to size. Then took the bushings off and sized, sanded and finished. I did have problems keeping tension on the blank, so it would stop turning during the CA finishing steps. Did I over tghten the tailstock?

The bushings and tube left marks on the center's. Will this cause unwanted wear on the center's?

Thanks all
Bob

 

[jkeithrussell]

Attempted my first TBC last night. What Fun!! Really puts the feel of being an artist into woodturning. Problem was I got really bad tube flare. What did I do wrong?

Turned with busshing down to size. Then took the bushings off and sized, sanded and finished. I did have problems keeping tension on the blank, so it would stop turning during the CA finishing steps. Did I over tghten the tailstock?

The bushings and tube left marks on the center's. Will this cause unwanted wear on the center's?

Thanks all
Bob

If your bushings are putting permanent marks on your centers, then your centers are not hardened steel and you should probably replace them.

If your tubes are flared, you are over-tightening the stock.

 

[MobilMan]

I haven't started turning between centers yet but have thought about the smooth centers against the smooth tubes. Just a thought but wonder if it would hurt to glue 3-4 narrow short strips of sandpaper to the dead center to help get a grip on the tube. That way you wouldn't need much tailstock pressure. The paper will get a little bite in the tube.

 

[JimB]

I've only done about a dozen pens this way but to me it sound like you have 2 problems. First, I think you are over tightening. I say that becuase you should not have the bushings or tubes leaving marks on your centers even if they are 'soft" metal (mine are I I don't leave marks). Second problem seems to be that something is coming loose and causing your blank to no longer turn with the centers. This may be becuase of flaring from over tightening or that your tailstock is not tightened well to the bed of the lathe.

Either case, over tightening or under tightening can contribute to flaring. When you mount the blank without the bushings you want it snug, not tight or loose.

 

[leehljp]

Probably Two problems:
1. NOT tight enough
2. Tail Stock loosens and walks.

1. I did some personal experimenting and and found that for me, the tube flares because of SLIPPAGE. Metal build up or transfer is because of metal rubbing metal, not because of pressure of being too tight on my tests.

In a car wreck, a piece of metal that comes loose and skids down the road has no more pressure than the weight and speed of the metal itself but it scratches and leaves metal filings. It is the speed differential that causes metal to transfer.

Too much pressure _will_ flair the tube and probably split the tube in one or two spots. The way to tell, other than having a split tube, is to look at the end. If it looks "Reamed" then it is probably from slippage and too little pressure. If it is flared without being reamed, That would be too much pressure. Reemed where metal scoring takes place is slippage.

Saying this another way - Could be semantics, my tiredness and half Japanese mentality but trying to say it another way - if there is slippage and scoring, that is more likely too loose; If it is not slipping and there is _no_ scoring / scratching then that is too tight. Too tight will probably show up in a crack in the blank too.

2. It is well known that tail stocks "walk" or move back a fraction of an inch. I think "JCollazo" makes special lock nuts for the tailstock lock because of this very problem with the standard lock nuts. IF not noticed, the tail stock backs up 1/100 of an inch, pressure is backed off, slippage occurs and metal to metal scoring takes place in a circular pattern around the blank and centers.

3. If slippage is taking place because of sanding or rubbing, the tail stock is not tight enough or the pressure of sanding and rubbing pressure are probably much more than needed.

 

[Constant Laubscher]

I have turned a center and file small grooves in it that grip the tube/blank with minimal pressure and no slipping. This works great for me. If I have to put a percentage on it I would say that I about 1% of the blanks would split or crack and I turn 200 or more at a time for the inlay kits.
One more thing I have to mention is that I am using NOVA chuck.

 

[bitshird]

Try using bushings made for turning between centers, or make some out of delrin for sanding and applying CA. you can also use a 5 or 6 center drill, and counter drill a 60 degree hole in the larger end of the bushing, it will require either a metal lathe or a beal collet set up or making a pen for a machinist. for 7mm pens, it's a problem, Paul in OKC was going to start making between center bushings, but not sure if he found enough time to do them.

 

[smitty]

I make my own bushing for finishing. The finished OD is just a little bigger the the OD of the tube. I tried it with no bushing and I would flare the tube every time. So I made a under size set of bushing for every brass tube size I have. I have no more problems with flaring and CA chipping off the ends.

 

[bcoyne]

Findings

I took everyone comments into consideration and have tried a few more blanks, but with the bushings. I discovered that I was getting this very fine black dust inside the tubes. Which lead me to look at the bushings, thinking metal to metal shavings. What I have noticed is that I am getting reaming on the bushings. I am going to try Leehljp suggesting and keep the tailstock tight. It might be slipping on me.

Thanks for all the imputs.

Will post my findings.