Runnout when turning pens

[76winger]

Just looking for others observations: I see this show up in peoples postings repeatedly and just wonder how many people to and don't have problems with it?

It seems mostly it's related to using mandrels but I'm pretty sure I've seen some turning between centers having it as well. I would think TBC would minimize or elimiate it on a good solid lathe that doesn't have any bearings out of round or loose or whatever.

From my own experience, even with a Shopsmith for my lathe (which is not nearly as tight as a dedicated lathe) and mandrel, I have very little problems with it. The way I typically turn is with a skew and when I'm making those final fine slices as the body is getting down to size, my technique is lay the flat face of the skew directly on the bushing where it's just "riding" on it, then very lightly take those last few fractions of a millimeter off before sanding and finishing. So unless my bushings happen to be out of round (and maybe I've been lucky here), there's no visibly discernible runnout in the final turned body.

As I've thought about it, I'm wondering if it's because many that have the problem might be holding carbide scraper-type cutters, very tightly to the tool rest and any runnout from the mandrel is then translated into one side of the turned body being slightly thicker than the other side.

Maybe this has been discussed before, but my searching abilities usually don't find me what I'm looking for in forum searches, either finding too much to sift through or nothing.

Anyway, what's everyone's thoughts and observations on this?

 

[watch_art]

What do you mean by this:

holding carbide scraper-type cutters, very tightly to the tool rest

 

[underdog]

I have almost concluded that there are two types of folks who say they have no runout...

The first type are the people who simply don't care, or don't know, that they actually do have runout of .004"-.008" - it's good enough for them.

The second type are those who do care, and then actually eliminate most runout by turning between centers.

Just to let anyone know who cares... the human finger is sensitive enough to detect .001-.002" differences in surfaces.

 

[BRobbins629]

If you're talking about wood, I've seen blanks off the lathe with very little run out, perhaps in the range of .002" and after sitting for a few days be almost .010. That's a little on the extreme side, but I'm doing some experiments now with snakewood and those are the actual readings. The latest piece has no tube, a 3/8 hole in the center, and ranges from .565 to .575" diamater depending on where I measure. In this case, it has nothing to do with the lathe or tools. After it settles and stops moving, I plan to make it round before completing the pen.

 

[Paul in OKC]

This has come up several times, and there is an article in the libray about it. As an anull type person, the term is concentric. Out of round is oval. Hard to turn something oval with out an eccentric chuck. I turn both on a mandrel and between centers. No problem with mandrel turning. Some times the grain of the wood can cause issues when sanding. Being 'soft' on one side and hard on the other.

 

[lorbay]

I have run in my collet chuck and never really noticed it until I bough a new one for my mini lathe. So I need to get another new one for my big lathe. How do I know this?? I put a dial indicator on the inside of the collet chuck.

Lin.

 

[RSQWhite]

Everything that is turned has "runout".(IMHO) out of round (OOR) is the proper term and really what this discussion is about. The trained machinist eye can only discern about .010". Any out of round less than this is probably ok. Turning between centers with Johnny's bushings is no guarantee against this. Dull tools or excessive sanding(especially on punky wood) is probably the main cause of OOR. Lathe centers off by a few thousands is not the problem. When turning spatted or bark included wood it is very easy to get OOR no matter which which system I use (mandrel TBC. I have yet to to find that my equipment was at fault for OOR. My first lathe was a 1950 3 speed change the belt POS Shopsmith that had been dropped from the bed of a moving Pickup. I turned some very nice "round" pens with this machine. My next lathe was a PSI Turncrafter, same results. My current lathe is a DVR (Very Nice) and I still occasionally get OOR pens. The problem always comes back to me.
Sorry to be so long winded

Tim

 

[Curly]

Along with the other factors mentioned.

If the end of the tube is not trimmed/sanded square, the bushing, when turning between centres will wobble ever so slightly and that will affect the concentricity. Doesn't help the fit of the components either. :wink: Easy way to tell is after rounding the blank, with the lathe turning slowly touch the bushing with the tip of your fingernail and if you feel it tapping or pulsing, the end of the blank isn't square.

 

[Curly]

What do you mean by this:

holding carbide scraper-type cutters, very tightly to the tool rest

What Dave is doing with his skew is letting it follow from the bushing to the material, thereby minimizing the out of roundness. It floats with any wobble.

Held tight to the tool rest the tool cuts the outside round but if the axis of the bushing isn't the same as the turning axis there will be a difference of the wall thicknesses of the finished barrel. The inner circle not matching the outer circle.

Clear as mud eh?

 

[jd99]

I fought the runout problem when I first started this venture, tried several things. Found out the taper in my head stock is out, so I know where to put the shim stock to solve that. Then fought trying to get a good set of bushings that are concentric, gave up on that; now I TBC.

I still use bushings; But I make my own bushings, that are for TBC only and I turn them to tighter tollerances then I could buy from any manufacture some place, and they have a longer bearing surface to locate the tube.

I check for runout all the time, I can never get it perfect; after all it's a wood lathe, but my average is about a thou and a half to two of runout.

 

[tim self]

If the end of the tube is not trimmed/sanded square, the bushing, when turning between centres will wobble ever so slightly and that will affect the concentricity. Doesn't help the fit of the components either. :wink: Easy way to tell is after rounding the blank, with the lathe turning slowly touch the bushing with the tip of your fingernail and if you feel it tapping or pulsing, the end of the blank isn't square.

I believe this is the biggest problem we have. Having a cutter that is just slightly worn will cut it a bit off. I've started putting all mine in the collet to trim after turning round. Has almost completely eliminated my problem.

 

[76winger]

What do you mean by this:

holding carbide scraper-type cutters, very tightly to the tool rest

What Dave is doing with his skew is letting it follow from the bushing to the material, thereby minimizing the out of roundness. It floats with any wobble.

Held tight to the tool rest the tool cuts the outside round but if the axis of the bushing isn't the same as the turning axis there will be a difference of the wall thicknesses of the finished barrel. The inner circle not matching the outer circle.

Clear as mud eh?

Yep, that what I was referring to with a little better wording :wink:

And it's been a good discussion so far.

 

[Paul in OKC]

Everything that is turned has "runout".(IMHO) out of round (OOR) is the proper term and really what this discussion is about. The trained machinist eye can only discern about .010". Any out of round less than this is probably ok. Turning between centers with Johnny's bushings is no guarantee against this. Dull tools or excessive sanding(especially on punky wood) is probably the main cause of OOR. Lathe centers off by a few thousands is not the problem. When turning spatted or bark included wood it is very easy to get OOR no matter which which system I use (mandrel TBC. I have yet to to find that my equipment was at fault for OOR. My first lathe was a 1950 3 speed change the belt POS Shopsmith that had been dropped from the bed of a moving Pickup. I turned some very nice "round" pens with this machine. My next lathe was a PSI Turncrafter, same results. My current lathe is a DVR (Very Nice) and I still occasionally get OOR pens. The problem always comes back to me.
Sorry to be so long winded

Tim

No offense, Tim, but my pride as a machinist gets a little pricked on this one. I have always been able to determine as little as .003 run out when running a machine, on a good eye day less. All things being equal, if you turn plastic or even metal on the same equipment (just a reference) you will not turn out of round parts, technically. You will have a diameter that is true to the axis, but no a different center than the inside, thus 2 diameters that are not concentric. You can measure around the diameter and it should be round, but measure the wall thickness in a couple of places, it will be thinner on one side.
Wood density, and what curly said, I believe are the main issues with this.
As far as letting your tool 'ride' the bushing to start, unless you are real fastbiggrin , once you get off the bushings you will have the same problem.

 

[watch_art]

What do you mean by this:

holding carbide scraper-type cutters, very tightly to the tool rest

What Dave is doing with his skew is letting it follow from the bushing to the material, thereby minimizing the out of roundness. It floats with any wobble.

Held tight to the tool rest the tool cuts the outside round but if the axis of the bushing isn't the same as the turning axis there will be a difference of the wall thicknesses of the finished barrel. The inner circle not matching the outer circle.

Clear as mud eh?

Yep, that what I was referring to with a little better wording :wink:

And it's been a good discussion so far.

OOOOOOOOOOOOOH!!! I totally understand now! Thanks! Gives me something to think about when turning, now. :biggrin:

 

[rsulli16]

hi
another two cents worth
one thing that lessened it for me is this. after cuting, and before you start to sand, loosen the brass nut and rotate the blanks relative to the bushings a half tun, then sand.
seems to work for me
Sulli

 

[paintspill]

If the end of the tube is not trimmed/sanded square, the bushing, when turning between centres will wobble ever so slightly and that will affect the concentricity. Doesn't help the fit of the components either. :wink: Easy way to tell is after rounding the blank, with the lathe turning slowly touch the bushing with the tip of your fingernail and if you feel it tapping or pulsing, the end of the blank isn't square.

ding ding ding we have a winner.

this is what i find happens. to remedy this i have been turning down the blank and if i find an end is out of square i take it of and take it to the sander ever so carefully then remount it and check. it might take 1 or 2 tries but has worked wonders for me

 

[dbledsoe]

It may be obvious to everyone but me, but I discovered that if you have a little bit of crud (glue, sawdust, etc) stuck to the side of your tapered shank, it will be off center and create problems. With this kind of work, having some dirt/sawdust/CA, etc hanging around is pretty normal. Just need to keep it out of the tapers.

 

[76winger]

If the end of the tube is not trimmed/sanded square, the bushing, when turning between centres will wobble ever so slightly and that will affect the concentricity. Doesn't help the fit of the components either. :wink: Easy way to tell is after rounding the blank, with the lathe turning slowly touch the bushing with the tip of your fingernail and if you feel it tapping or pulsing, the end of the blank isn't square.

ding ding ding we have a winner.

this is what i find happens. to remedy this i have been turning down the blank and if i find an end is out of square i take it of and take it to the sander ever so carefully then remount it and check. it might take 1 or 2 tries but has worked wonders for me

I've always alleviated this in the beginning by using the backside of a barrel trimmer head with sandpaper mounted on it so as to ensure the end of the blanks are square going into the turning process. So I guess the premise of my question entered in with the fact the ends were already square, but it's clear in the discussion that some haven't been and realized concentricity problems because of it. Interesting

 

[76winger]

It may be obvious to everyone but me, but I discovered that if you have a little bit of crud (glue, sawdust, etc) stuck to the side of your tapered shank, it will be off center and create problems. With this kind of work, having some dirt/sawdust/CA, etc hanging around is pretty normal. Just need to keep it out of the tapers.

By this are you referring to the tapered heads used by those that turn between centers?

 

[dbledsoe]

Yes, I'm talking about the MT2 shafts and sockets. I found that I had a buildup of "stuff" on my drive center shaft that was keeping it from seating properly. I think it would apply also to mandrel shafts, if they get dirty or rusty.

 

[underdog]

I bought one of those green taper cleaners that some turners affectionally call the "green weenie". Since I use it frequently, there is very little crud build up in my tapers. And as far as my dial indicator can tell, there's no runout on the inside of them either.

I'm convinced that most of my runout, or offset is caused by one of two things...

First, the way I mill my blanks in the drill press doesn't allow the shaft of the milling cutter to true itself up inside the brass tube. I'm going to change that by putting the blanks in a vice, then milling with a hand drill. That should square things up a bit better. Then I'll see if my blanks do run a little more true on the mandrel.

Second, the aforementioned slop between mandrel shaft and the brass tubes (.004") lends itself to running offcenter. One way to correct this problem is just to turn everything between centers...