Acurracy for turning

Signed-In Members Don't See This Ad
Joined
Aug 13, 2016
Messages
1,460
Location
Surprise, Arizona
What accuracy do you look for when turning your barrels? Is 0.005" acceptable? 0.001"? Less than 0.001"? Just looking to improve my work from the best. I know there's a little leeway when the barrel butts up to beaded hardware, but what about smooth hardware like a slim or Euro style? Thanks for all replies.
 
Signed-In Members Don't See This Ad

magpens

Member
Joined
Feb 2, 2011
Messages
15,913
Location
Canada
I try for accuracy of better than + 0.001", - 0.000" on barrel diameter compared to the actual measured hardware.

Not sure I actually achieve that.
 
Last edited:

leehljp

Member Liaison
Joined
Feb 6, 2005
Messages
9,314
Location
Tunica, Mississippi,
I do settle for .001 on cast resin and on wood but I shoot for .000 and generally get it it. If I had a machining lathe (metal), I most certainly would dial in finer settings in many situations. Just to be clear, I over turn my blanks - down to .003 or .004 below the size and build them back up with CA. At this point it isn't about how many times I add CA on with paper towel on to the pen, It is about how much thickness of CA that I have. It is difficult to build up perfect matching CA levels by doing x number of CA wipe ons. It isn't about the x number of CA layers, it is about the CA thickness - to bring it to the finished level that matches pen components after sanding and buffing. (BTW, I don't used PT that much as the PT drinks 10 times more CA than is added onto the blank.

Feel:
There were several posts on the subject some time ago on what the hand can feel. Seems like it was .0002 or .0004 or something like that. It has been ages since I last saw or commented on such a post.

A hint that someone passed on a long time ago: When you get a troublesome blank and work and work on it, taking finish off, adding it back on: If the finished blank is .002 or .003 larger than the finial, CB or nib, slightly round over the ends with MM 6000 and re-polish. This works well with pens that have curves as well as straight, and especially ones with non smooth (engraved/designed) components.

Getting back to your original: I don't settle .003 differences. I will settle for .002 on occasion, such as for kids (young grand kids that are going to lose them) but that is not for a pen that I would sell.

I think since you are looking at perfect fits, this is the kind of attitude that will greatly enhance your pen turning skills and output. Some people will not know the difference, but some people will fill your pen and KNOW that you make a superb pen. I used one of my pens in a wedding I performed; later two separate guests that I did not know came and asked to see the pen. Both commented on the design, and both commented on the "fit and finish" and how smoothly it transitioned from the blanks to the components. They did not make pens but they were pen aficionados.
 
Last edited:

leehljp

Member Liaison
Joined
Feb 6, 2005
Messages
9,314
Location
Tunica, Mississippi,
I will add in something else here that I didn't above that affect the tolerances: Bushings, Mandrels and sharp tools.

Sharp tools:
With inexperience, there is a tendency think of the skew or scraper as sharp when in fact it might not be sharp enough. Even with carbide, the edges will dull and with inexperience it will still seem sharp.
WHAT does this have to do with tolerances/accuracy? When your kitchen knife (if you are a cook) is not as sharp as it was a week ago, what do you do? You either sharpen it or apply more pressure. People who overlook the need for fresh sharpness gently apply more pressure in the turning. Applying pressure will cause mandrel to flex .001 or .002 and give a non concentric blank by as much as .004 or more. Another reason I don't use mandrels.

Bushings:
Is your bushings loose? Do they drop into the tube or slide in fairly precise? Loose bushings will cause .004 - .006 Non concentricity - (or in the vernacular out of round.) PLUS, how loose or tight are the bushing holes on the mandrel? Lightly tight but Smooth is what is needed. Loose - can cause the OOR or Non Concentric.

Mandrels:
Already mentioned: Flexing shaft, bent shaft without knowing it, loose bushings on it. The bushings' inner hole will wear and so will the mandrel. Not enough to be noticed to the eye but if you use a caliper, you can probably measure wear on the mandrel after two or three years. And the ever so slightly dull tool causes the inexperienced to apply a miniscule amount more pressure which will cause the mandrel to flex by .001 or .002 and I am probably being generous. How tight do you bring your tail stock into the mandrel? Too tight will cause it to flex. Are you using a 60° center on the tail stock? I was surprised when a fellow here had never heard of 60° centers absolutely needed for the tail stock to use in a mandrel. Back 10 years ago, that was a "mantra" in advice given to new turners. The "wood" points on non "60°" centers will cause enough wobble to cause non concentric turnings that will be almost visible.

Loose Bushings in tubes will do the similar on TBC as it will on mandrels. Quality bushings or making your own might be a solution if you can't afford higher priced quality bushings.

Lastly, I know people who have been turning on lathes for years. They know how to overcome and work around the inefficiencies of mass mfg'ed bushings and flexing mandrels. That comes with experience and keeping tools sharp.
 
Last edited:

BeeAMaker

Member
Joined
Jan 30, 2017
Messages
695
Location
Elkhart IN, USA
I would say more than 0.001 is the difference between a $30 pen and a $60 pen (just throwing numbers, but you get the idea) My OCD won't allow me to feel any "ridge" between parts. :D

Another word on the Bushings, my first wooden pen I turned and polished right down to the Bushing, nice and smooth. After assembly the wood was over the nib by almost 0.3mm (0.0118") I like the pen, but it bothers me so I will probably put it back on the lathe at some point.
So don't trust your bushings. Now I measure the nib and compare it to the bushing. Get it close with the bushing and then finish to the actual parts size. lesson learned.

I have also (after buying 2 different mandrels) have already switch to TBC, I like it much more better :glasses-nerdy:
 

brownsfn2

Member
Joined
Jun 23, 2011
Messages
1,574
Location
Plain City, OH
I shoot for +/- .003.

I think that up to .005 is not really noticeable with one exception. Make sure that the blank is never over turned where the material is less than the pen part. Customers will feel a transition from smaller to larger as opposed to larger to smaller. So if there is a ridge from material to pen part then it will be more noticeable. Hope that helps.
 
Joined
Aug 13, 2016
Messages
1,460
Location
Surprise, Arizona
Thanks for the replies so far.

I do settle for .001 on cast resin and on wood but I shoot for .000 and generally get it it. If I had a machining lathe (metal), I most certainly would dial in finer settings in many situations. Just to be clear, I over turn my blanks - down to .003 or .004 below the size and build them back up with CA. At this point it isn't about how many times I add CA on with paper towel on to the pen, It is about how much thickness of CA that I have. It is difficult to build up perfect matching CA levels by doing x number of CA wipe ons. It isn't about the x number of CA layers, it is about the CA thickness - to bring it to the finished level that matches pen components after sanding and buffing. (BTW, I don't used PT that much as the PT drinks 10 times more CA than is added onto the blank.

Feel:
There were several posts on the subject some time ago on what the hand can feel. Seems like it was .0002 or .0004 or something like that. It has been ages since I last saw or commented on such a post.

A hint that someone passed on a long time ago: When you get a troublesome blank and work and work on it, taking finish off, adding it back on: If the finished blank is .002 or .003 larger than the finial, CB or nib, slightly round over the ends with MM 6000 and re-polish. This works well with pens that have curves as well as straight, and especially ones with non smooth (engraved/designed) components.

Getting back to your original: I don't settle .003 differences. I will settle for .002 on occasion, such as for kids (young grand kids that are going to lose them) but that is not for a pen that I would sell.

I think since you are looking at perfect fits, this is the kind of attitude that will greatly enhance your pen turning skills and output. Some people will not know the difference, but some people will fill your pen and KNOW that you make a superb pen. I used one of my pens in a wedding I performed; later two separate guests that I did not know came and asked to see the pen. Both commented on the design, and both commented on the "fit and finish" and how smoothly it transitioned from the blanks to the components. They did not make pens but they were pen aficionados.

Thank you for a very informative post. This is exactly the kind of advice I was looking for. I've been turning to within .003 but I think it's time to up my game a little bit. I'm going to get within .001 on my next few pens while trying to get .000 I'll be using acrylic first, then moving to wood and trying to underturn slightly then build up with CA as you suggested. I never thought about the paper towel drinking up most of the CA. I'll try using a plastic baggie over my finger when I get to those.
 

TonyL

Member
Joined
Mar 9, 2014
Messages
8,902
Location
Georgia
I intentionally finish mine at .001 over the hardware with a slight downward radius to create the illusion on the material meeting the h/w exactly. I just like them that way.
 

JPW062

Member
Joined
Nov 3, 2016
Messages
156
Location
Ohio
There were several posts on the subject some time ago on what the hand can feel. Seems like it was .0002 or .0004 or something like that.
A square 90* step on a flat piece of metal, maybe. In my experience it needs to be about double that. In any finish or material commonly used for pens(acrylic wood, poly, whatever) that ridge is going to round over quickly and be less noticeable.

The bushings are not made to .001 precision. They are very cheap. Probably turned on screw machines if not raw just castings. Then we sand on them.
My guess is a pen must be off .005 before the gap/step is noticeable to a normal person. Probably .010 before it is bothersome. If used regularly that will round/grime over quickly.
 

Curly

Member
Joined
Nov 20, 2010
Messages
4,828
Location
Saskatoon SK., Canada.
My guess is a pen must be off .005 before the gap/step is noticeable to a normal person. Probably .010 before it is bothersome. If used regularly that will round/grime over quickly.

A sheet of copy paper measures just under .004" thick. Unless you have very calloused fingers that is easily felt. So is .001" or .002". On a pen if the finished end has a slight radius then the edge won't be noticeable if it is slightly proud of the pen part. If below you will feel the edge of the hardware.

On to the subject of measuring with calipers. They are not used in any precision industry if needed measurement accuracy / precision / tolerance is approaching .001" simply because they are not capable of repeated measurements giving consistent results as they rely on operator "feel" when using. If you try it yourself you will see. Take a good drill bit (shank end) or ground rod and take 10 measurements with your eyes closed. When you think you have the reading when you close the jaws open your eyes and see what you get. In all likeyhood there will be an error among them. Do it with a softer material like wood and the readings becomes worse. Give the caliper to someone else and you will see a different range of readings. Either worse or better than yours. In most instances you don't need to close your eyes and you will still have a range of readings. One mans .001" is another mans .002" at times. If you really want to measure to .001" or less then you should be using a good micrometer. To qualify the above I worked in aerospace manufacturing as an inspector for 27 years. It is pretty much impossible to recommend making pens to tight tolerances when the parts in the kits are not consistent.
 

jttheclockman

Member
Joined
Feb 22, 2005
Messages
19,082
Location
NJ, USA.
I am with you Pete. I am not as concerned with that kind of accuracy. I do use the calipers but if I am within .002 or .003 it stays and I will not fuss with it. the more I fuss the worse things get. My pens are not museum quality and never will be. Life is too short to sweat the small stuff. people buying all these fancy gaudy PSI kits should not even worry about accuracy when there is so much sticking out on those kits you can get lockjaw from a cut. :) My concern when making a pen is the quality of the finish to the point no scratches can be seen with the naked eye and the shape. I hate bulbous and outrages shaped pens so I tend to stay away from those shapes. I am a bushing to bushing guy.

But everyone is different as seen from the pens posted here over the years.:)
 

JPW062

Member
Joined
Nov 3, 2016
Messages
156
Location
Ohio
A sheet of copy paper measures just under .004" thick. Unless you have very calloused fingers that is easily felt. So is .001" or .002". On a pen if the finished end has a slight radius then the edge won't be noticeable if it is slightly proud of the pen part. If below you will feel the edge of the hardware.
I didn't say it couldn't be physically felt, I said most won't notice it. In the pens I make there is clearly a joint there. Most peoples fingers will glide right over a .005 step at a joint.
I also have experience in aerospace. No one is turning to .000 tolerance. The best machinists I have ever worked with using $400,000 lathes don't make that claim. People making that claim simply don't understand what they are saying. As you hinted, this is further evidenced by the fact that they are discussing accuracy of one or two thousandths when measuring with Calipers. In my experience most woodworkers think calipers are called micrometers. One of the basic rules of measurement is to get accurate reading the tool must be able to read ten time as small of a number as is being recorded. My $250 Mitutoya Calipers will read .0005. Meaning they are only good to read .005. The $20 Chinese import calipers used by most wood workers read to .001. Meaning they can only be used to .010. At best. Calipers are junk, and as stated you have to be very careful with pressure. On steels an experienced machinist using calipers for hours a day can take more accurate measurements once feel is developed, but I won't believe it on soft woods. If they make a mistake they better not tell the inspector that catches it they were being lazy and using the calipers when they needed to use mics though.
My experience measuring kit parts and bushings is they aren't held to the tolerances described(.001 or less).
Most of the pens I see have tear out from squaring the blank with a mill that far exceeds .005.

Ive manufactured and inspected parts held at the discussed tolerances and much tighter tolerances. I'm not seeing it on the pens I have had my hands on.
 
Last edited:

Brian G

Member
Joined
Jul 2, 2013
Messages
1,567
Location
Bloomington, MN
Just for sake of clarity, when somebody says (for example) they are accepting ±0.004", they are really talking approximately ±0.002 because it's averaged over opposite sides, true?

If my tightly trimmed fingernail catches either the blank or the component, then it's not good enough for me. I'd rather it catch the blank a little, but I'm not averse to disassembly and lightly rounding over the edge.
 

Curly

Member
Joined
Nov 20, 2010
Messages
4,828
Location
Saskatoon SK., Canada.
Just for sake of clarity, when somebody says (for example) they are accepting ±0.004", they are really talking approximately ±0.002 because it's averaged over opposite sides, true?

No it actually means that the tolerance is +0.004" above and -0.004" below the desired dimension, for a total range of 0.008".
 

Brian G

Member
Joined
Jul 2, 2013
Messages
1,567
Location
Bloomington, MN
Thanks. I didn't word that well in the context of pen turning. I was thinking along the lines of measuring the diameter of mating component with a caliper, pushing the ABS feature to set to 0.000, then measuring the barrel. The value is the over/under, but divided by two it's how much the mating edge is over/under.
 

magpens

Member
Joined
Feb 2, 2011
Messages
15,913
Location
Canada
Don't forget that there is another problem when measuring the fit of the turned blank to the hardware ... the turned blank is often tapered towards the hardware junction, especially if you have been sanding it. . So getting an accurate measurement with calipers is a bit dicey. . You want to make the measurement as close to the end of the blank as possible. . It is even more of a problem with a micrometer unless the anvils have knife edges.

With calipers extremely close to the end of the blank, there is a tendency for them to slip off .... and perhaps even compress the material. . So I am often left wondering what I am in fact measuring in actuality.
 
Joined
Aug 13, 2016
Messages
1,460
Location
Surprise, Arizona
Thanks for everbody's opinions, there is some great information here. I've improved my fit a great deal since joining, but realize it's my weak point. After reading these posts I don't think I'll stress too much over it but I'm going to shoot for .001 to .002 over. Getting within .003 has produced some very nice pens for gifting, but I still want to kick it up a notch.
 

JPW062

Member
Joined
Nov 3, 2016
Messages
156
Location
Ohio
Has anyone measured the run out on their wood lathes? I haven't seen many wood lathes that have that little run-out.
 

jttheclockman

Member
Joined
Feb 22, 2005
Messages
19,082
Location
NJ, USA.
Has anyone measured the run out on their wood lathes? I haven't seen many wood lathes that have that little run-out.

It is not the runout on the lathe because you overcome this. It is all about how far you turn down or do not turn down a blank and then if wood how much finish you add to build back up. That is where the deficiencies come in.
 

Sylvanite

Member
Joined
Jul 18, 2006
Messages
3,090
Location
Hillsborough, North Carolina, USA.
Wood especially (but other materials too) moves (swells and shrinks) with changes in temperature and humidity. What is flush with pen hardware today will not be flush as the seasons (and weather) change. Therefore, I think that seeking perfect fit is an exercise in futility.

I generally aim for a blank that is 0.002-0.003" proud of the mating hardware when assembled; and I round over the edge slightly when sanding. That leaves a joint that most people do not feel even when the blank expands or contracts.

In practice, that means I turn and sand a few thousandths shy so that my finish builds back up to slightly proud of the pen components.

I hope that helps,
Eric
 
Last edited:

Curly

Member
Joined
Nov 20, 2010
Messages
4,828
Location
Saskatoon SK., Canada.
Has anyone measured the run out on their wood lathes? I haven't seen many wood lathes that have that little run-out.

Runout shows up as a problem when drilling with the tailstock. Holes don't stay centred and the end where the drill enters can be bigger than the headstock end.
 

JPW062

Member
Joined
Nov 3, 2016
Messages
156
Location
Ohio
It is not the runout on the lathe because you overcome this.
https://en.wikipedia.org/wiki/Run-out
How exactly do you overcome the run-out? Sanding down to the bushings may eliminate it to some degree right up against the bushings, at least as pertains to one being able to feel it, but then I don't think one is going to get close to .001 accuracy as the bushings and parts aren't held to that tolerance in my experience. The kits would be considerably more expensive if the were. Once you are eccentric you aren't going to make it concentric within .001 using you feel, eyesight, etc. If you have found a way I would love to know more.


It's like drywall repairs. It really doesn't need to be super flat. It needs to be super smooth.
 
Top Bottom