Out of round jr gents

[Tiger]

I am constantly finding that my jr gent lids where the pen clip sits is slightly out of round. The 3 other places where th hardware meets the timber seem fine, I don't notice the transition on them but with the pen clip I've checked the few JRs in my collection and there is some me OOR on all of them, although in some cases it's very slight. I turn between centres, I do not force the tools and they are sharp so can't work this out, I don't have this problem with other kits. Note that this is the JR gent 1 kit was that I'm referring to.

 

[ed4copies]

Do you use bushings? If so, turn your own and see it the problem is gone.

 

[rd_ab_penman]

TBC without bushings and use your calipers.

Les

 

[jttheclockman]

So you now have to first ask the question is this happening with any other kits if you turn between centers on them also. If not, then you ask yourself am I using bushings when turning without a mandrel on the Jr. kits. If so then the possibility of OOR bushings is high. Change bushings or turn without. But like you and many others that post questions there is not nearly enough info to make a more accurate diagnoses. Now there are many threads on file here that deal with OOR problems. You can do a search here and read up on them or get back with some details of your procedure. Many other possible answers can be had such as lathe points being off, CA built up on live and / or dead center causing tube or bushing to not seat properly, live center has a bad bearing, dirt in the ways of the live or dead center mandrels. So you see too many things to go wrong. It could also be the kits themselves.

 

[leehljp]

OOR has many several possible causes. One not mentioned so far is the wood and sanding. Wood with a fair amount of soft grain between hard grain - the soft grain can sand down faster than the hard grain and leave one side over or one side under in size.

 

[Tiger]

I did say in the opening post that I'm turning between centres but I do use bushings to get to ball park, about 0.5 mm or 20 thousandths over I then remove the bushings and do the rest between centres. Centres are clean ie no CA buildup and blanks are Dymondwood so material is consistent. I use digital calipers throughout and the fit is perfect except for the lids which are perfect on 1 axis but slightly narrow 90 degrees to the perfect fitting part.

 

[ed4copies]

Since it only occurs on that pen kit, use your caliper to determine if the kit top is out of round.

 

[Tiger]

Since it only occurs on that pen kit, use your caliper to determine if the kit top is out of round.

Excellent suggestion but it has really opened up a Pandora's box!
I checked some other JR kits and found that the lids were possibly a thousandth out but that could just be user error with the digital caliper however when I measured my finished blank there was as much as 0.07 mm difference or almost 3 thousandths difference depending what part of the blank l measured, this shows a fair OOR issue. I then measured some other completed pens and also found some slight OOR differences but one cannot tell unless you know it's there. The Jr gent kit is possibly less forgiving in that the lid has a tapered top with a thin centreband so any OOR is easier to spot. Question is do we aim for zero OOR, is that even possible on the cheaper lathes? I moved into TBC to minimise OOR and although it has been reduced I obviously have not conquered it entirely. The blank rotates on the lathe smoothly, no vibration and yet there's still OOR.

 

[jttheclockman]

OK some questions are getting answered. I suggest to use the bushings all the way to completion or try doing the entire cap without bushings. (suggest the first one highly) I say this because you can be having 2 different center lines and there is not enough meat left to correct it. What type bushings are you using?? If they are the stock bushings and you are trying to use a standard dead and live mandrel they may not be lining up in the same place every time thus the various degree of OOR. Now if you are using bushings that are designed to be used between centers than I highly suggest using them all the way through. Just because you put a tube between centers and tighten the end stock does not mean that blank is sitting dead center on the tips. Fractions of mm can be blown up very easily.

Next thing is when you go to finish the turning and and take off the bushings what are you using to turn it down??? Sandpaper or turning tool. If using sandpaper it is always a good idea to back the paper up with a piece of wood. Too much variance with your finger tips.

 

[Rifleman1776]

This is a tricky situation to answer without being there, watching you work and/or turning with your equipment to compare results. I suggest eliminating possible causes. Like, toss the bushings and buy some new ones. I consider bushings disposable items anyway. One trick I long ago learned (probably from this forum) was to make a very tiny bevel on the end of the turned blank. This creates a shadow effect and disguises tiny flaws. However, on reading your first post my immediate thought went to the lathe not being true. Put a center on the live side and a center on the tail, bring them right up to each other but not touching. With the lathe off look to see if they line up perfectly. Then turn on the lathe and look to see if there is any deviation from a perfectly true spin. The two points should stay in perfect proximity to each other with the lathe running. If they don't you have found your problem.

 

[Dale Allen]

My initial 'guess' would be that the bushings are causing the OOR and unless you really try to correct it with turning tools it will persist. Especially with wood but less so with plastics. The OOR just stays there if you are using sandpaper on the final sizing.
Here is something to try.
Prep a blank as usual with the bushing down to where you would just put it between centers. Remove the bushings and put it between just the centers. Now draw a pencil line all the way around the blank about 1/8" from the end(without the lathe running). Now turn on the lathe and with a very, very light touch, begin to cut at the pencil mark with a sharp scraper.
If the blank is perfectly round, you will take the pencil mark off all the way around without advancing the scraper.

 

[Tiger]

Some excellent suggestions there! When I do use the standard bushings I do get to a point where I am 0.5 to 1 mm over. The next step is to use a skew laying on its thick edge and very lightly knock off any high spots, after a few passes theoretically the blank should not have any OOR issues assuming the lathe is running true which I believe it is. Using the skew also leaves a very good finish and allows me to sand at 600 grit and above, sometimes I need to go down to 400 grit. I did some experimentation and using digital calipers and taking multiple readings by measuring a blank at multiple points after rotating the lathe that the blanks were reasonably concentric at least within 1 to 2 thousandths of an inch. I then found that after some sanding that the 1 to 2 thousandths would become 2 to 3 thousandths even though I was using 600 grit or higher so the sanding was introducing some more OOR I think. By the way I also use the skew as a scraper to bring down my CA finishes, the idea there being to knock off the high spots before sanding so as you can see sanding is minimised yet some OOR is still creeping in. I will keep experimenting and trying out some of the ideas mentioned and appreciate your feedback.

 

[More4dan]

With mini metal turning lathe the typical runout (OOR) is about 3/1000". I'm guessing the wood lathe isn't quite that good, throw in our inability to hand hold cutting tools precisely while turning and sanding. You can check the runout with a good test gauge on your dead center when chucked in your head stock. 3/1000" on a wood lathe by hand is pretty darn good.


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[Tiger]

With mini metal turning lathe the typical runout (OOR) is about 3/1000". I'm guessing the wood lathe isn't quite that good, throw in our inability to hand hold cutting tools precisely while turning and sanding. You can check the runout with a good test gauge on your dead center when chucked in your head stock. 3/1000" on a wood lathe by hand is pretty darn good.


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Good point which raises the question, maybe we should learn to live with a little OOR? I just hate it though when you have a pen in your hand and the transition between wood and pen part is mostly ok except for one small part of it.

 

[More4dan]

The best I've been able to do is when I make a kitless pen and turn and finish the wood/acrylic and metal parts assembled. Regardless of OOR they will be identical dimensions.


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[philipff]

Center the tube in a set of jaws. Verify the center by using the tailstock 60d live point and then lock the blank in the jaws. Turn the ends square by using a round nose scraper or spindle gouge until you strike metal. Done. Reverse and repeat. Done. Mount between centers, use a caliper to get exact fits and finish sanding & finish. Done. Takes time but it is foolproof, and saves $$ on bushings and confusion. P.

 

[Tiger]

Center the tube in a set of jaws. Verify the center by using the tailstock 60d live point and then lock the blank in the jaws. Turn the ends square by using a round nose scraper or spindle gouge until you strike metal. Done. Reverse and repeat. Done. Mount between centers, use a caliper to get exact fits and finish sanding & finish. Done. Takes time but it is foolproof, and saves $$ on bushings and confusion. P.

How does this differ from the conventional TBC, only difference I can see is that you square up the blank first?

 

[Ironwood]

How does this differ from the conventional TBC, only difference I can see is that you square up the blank first?

For best results you need to have the ends perfectly straight and true, otherwise when you tighten the blank between centres the blank will distort and you will end up turning out of round pens. Attention to detail pays off with everything you do.

 

[Tiger]

How does this differ from the conventional TBC, only difference I can see is that you square up the blank first?

For best results you need to have the ends perfectly straight and true, otherwise when you tighten the blank between centres the blank will distort and you will end up turning out of round pens. Attention to detail pays off with everything you do.

I meant to say square the blank first using Chuck jaws.
I square with a barrel trimmer unless the material is very soft in which case I'll use disc sander with transfer punch in a drill chuck.