First TBC

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Todd in PA

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Picked up some 60 centers, and gave it my first attempt at turning without a mandrel. It didn't turn out and I think I know why. The end chipped out and was glued back on. Ultimately the blank came apart, though there is glue pretty consistent on the brass (i used clear gorilla).

The issue seems to be that the brass fluted out while turning. I did snug it up some mid way. I did not use any bushings. I also didn't get to finish it. Am i doing this right or am I missing a piece of equipment for TBC?
851D5127-0A62-4CB6-967A-B950BE515E6B.jpeg
 
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mark james

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I'd recommend using TBS bushings. On occasion I have done what you did - simply using the tube/blank between 60 degree live/dead centers, and yes, I also would flare out the tube with too much pressure. But, with not enough pressure, the tube would spin, hence more tightening.

So good news, try the TBC bushings. (I think that will eliminate the problem above, well, maybe not the blank splattering). 😊
So bad news, the cost for the TBC bushings is onerous (I'm being polite).
So good news, you can try to turn your own TBC bushings with aluminum rod.

Oh, and I will agree with Ken above - (1'st) Mandrel bushings; (2'nd) TBC bushings is also very fine.

Happy Trails!
 

magpens

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@Todd in PA

I adopted the TBC method of turning pen blanks some 8 years ago, using 60* centers, and have never had any problems.
I do not use any bushings whatsoever, not even the so-called TBC bushings which are now available fairly readily.
The pen blank, tubed and trimmed accurately to the required length is just held between the 60* centers by pressure from the tail stock.

There has never been any significant flaring of the brass tube in my experience with TBC during these 8 years.

This may be because I do my turning on a metal-working lathe and I always try to keep the pressure from the tail stock down to a minimum
Of course, there is no way to measure that pressure. . I guess that I have developed a feel for the pressure needed to keep the blank from slipping.

Also, for the dead center in the head stock I use a diamond sharpening cone which may provide more friction than a simple steel center.

I bought that dead center cone here :-

 
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Todd in PA

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Thank you for the replies. I think I have a better understanding. More practice tomorrow.

The blank was a pine cone. I probably would have had a better chance of success with a solid hard wood blank. But the softer material exposed what I was doing wrong, so that's not entirely a bad thing.
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leehljp

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Thank you for the replies. I think I have a better understanding. More practice tomorrow.

The blank was a pine cone. I probably would have had a better chance of success with a solid hard wood blank. But the softer material exposed what I was doing wrong, so that's not entirely a bad thing.
That is precisely why I do not use CA or epoxy or Clear Gorilla glue for tube glue-ins. I use expanding poly gorilla glue. It adheres over the whole length. Many have been successful with CA, Epoxy and non expanding Clear and many "think" they have 100% contact, but they don't.

You can fill the drilled hole in the blank completely with epoxy or clear Gorilla glue, and then wipe the epoxy (or thick clear Gorilla glue) thickly around the tube, but once you start pushing the tube in, air bubbles and whole voids are created with the thick viscosity of those glues. And blowouts occur. Clear Gorilla glue will not expand as does normal polyurethane Gorilla glue, therefore it does not fill voids as poly does, and thereby making for weak connections on delicate blanks as you discovered.
 

jttheclockman

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@Todd in PA

I adopted the TBC method of turning pen blanks some 8 years ago, using 60* centers, and have never had any problems.
I do not use any bushings whatsoever, not even the so-called TBC bushings which are now available fairly readily.
The pen blank, tubed and trimmed accurately to the required length is just held between the 60* centers by pressure from the tail stock.

There has never been any significant flaring of the brass tube in my experience with TBC during these 8 years.

This may be because I do my turning on a metal-working lathe and I always try to keep the pressure from the tail stock down to a minimum
Of course, there is no way to measure that pressure. . I guess that I have developed a feel for the pressure needed to keep the blank from slipping.

Also, for the dead center in the head stock I use a diamond sharpening cone which may provide more friction than a simple steel center.

I bought that dead center cone here :-



And this is why Mal I said this. #26 post in this thread.
https://www.penturners.org/threads/bushings.169684/


Todd--- in the thread link above that I supplied I mentioned my method when it comes to turning blanks. To me and this is just me there is no need to start turning a blank without bushings or even spending money on TBC bushings. When you get close to finish size of blank you can switch to TBC method because at that point you are putting way less pressure on the blank when turning or at least you should be because you are taking off finite material to get to finished size and smoothing the blank out. I always finish every blank with a well sharpened skew. TBC bushings will wear down just as the normal ones if hit with tools and sandpaper so why pay twice the price for them. Just my opinion.
 
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magpens

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@jttheclockman

"And this is why Mal I said this. #26 post in this thread.
https://www.penturners.org/threads/bushings.169684/

1) John, what are you referring to by using the word highlighted in purple : this ?? <---- Can you please address this first

2) If you are talking about the so-called "flaring" ..... <---- And then deal with my following statements about flaring


I don't see how you can visualize any flaring to occur in the method I use, which is detailed in the thread you reference.

The brass tube is fully enclosed, end-to-end, in the blank material, which is SOLID material starting at a diamter of about 0.75"
 

jttheclockman

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@jttheclockman

"And this is why Mal I said this. #26 post in this thread.
https://www.penturners.org/threads/bushings.169684/

1) John, what are you referring to by using the word highlighted in purple : this ?? <---- Can you please address this first

2) If you are talking about the so-called "flaring" ..... <---- And then deal with my following statements about flaring


I don't see how you can visualize any flaring to occur in the method I use, which is detailed in the thread you reference.

The brass tube is fully enclosed, end-to-end, in the blank material, which is SOLID material starting at a diamter of about 0.75"
Mal my point is when you describe TBC you do not always tell people what you do and I have seen it many times here. That is why I said you have to be careful when talking about TBC. There are down sides to using the method because of pressure needed to keep that blank from spinning. With bushings you are putting pressure on the ends of the tube and also the ends of the blank. When TBC the pressure is on the inside of the tube and such a small surface. That is all I am saying. Weather you use a metal lathe or wood lathe means nothing. You still are holding the blank the same way. Now maybe you can control the cutter better with a metal lathe I do not use one so have no way of knowing this. But most people use a wood lathe.

TBC bushings are a different animal because you are still using a bushing but instead of a mandrel you use a live and dead center.
 

PatrickR

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@Todd in PA
I was never able to keep the flaring from happening. The problem is that when you lower the pressure eventually the blank will stall and when that happens flaring will happen. No way around it. kind of a no win for me, too much pressure, too little pressure also your dealing with metals of vastly different hardness.
You can get universal TBC bushings that use the standard bushings, minimizing cost and they work well for me, but get good ones. There is a company that makes SS ones that are very nice. I'll look for the website and add it.
(no affiliation)
 
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PatrickR

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Is there evidence that (limited) flaring of the brass tube weakens/impedes the assembly of the final pen?
I have found that the thin end makes it harder to sand the tubes to the correct length and removing the hard shoulder makes assembly touchier. - ie. Putting pressure on the wood and finish
 

howsitwork

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Ive never seen a diamond cone so thanks for that Mal. 👍

I think it's been too much pressure so the advice above should,solve it but also, if you can, resin impregnating or stabilizing the blank might help firm it up a bit.

I'm not going down the PU vs resin vs ca for tube glue up rabbit hole!🤷‍♂️

Do whatever works for you folks !🧘🏻‍♂️
 

Mortalis

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I believe part of the OPs problem is due to the blank material. PIne Cone is not solid and requires support. That support needs to come in the form of hard stabilizing like Cactus Juice and no gap gluing. For the no gap gluing, I do not recommend using any type of CA glue for mounting the blank to the tube. It just dries way to hard and brittle, IMHO. Also, did the OP rough up the tube? two part epoxy is your friend. Plug up the insertion end with plumber's putty or Dental goop or Playdoh....you get the idea.
Another issue that will cause the blank to spin TBC is dull cutting tool. When I am TBC I sharpen my tools very frequently on each blank turn.
I also will only tighten the tailstock until the blank will not spin when I grasp the live center point between my fingers.
I will get some chamfering of the ID of the tube but I've never seen the tube flare as in the above picture.
I try to use the appropriate bushings but I find the 0.001" - 0.005" clearance built into them and ID of the tube I can feel after assembly. I've learned how to resolve that by slightly rounding the end edge of the finished blank before applying CA finish.
 

magpens

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Oh man, don't let that sucker spin in your tube. You'll end up with a short tube really quick. :p

@Mortalis . . . What I am about to say might be perfectly obvious to some. . I think it is still worthwhile saying.

Mr. Mortalis, I think we are finally getting to the crux of the issues with TBC now, sir !! . . . The light has finally come on !!!

Please forgive my wordiness. . Also, "Someone" whose name appears above in this thread is going to say "I told you so .... many times before."

A DETAILED DISCUSSION OF POTENTIAL PROBLEMS ASSOCIATED WITH TBC ( TURNING BETWEEN CENTERS )

The friction between the diamond cone and the brass tube, which the diamond cone directly contacts, is the key.
This friction due to the diamond particles goes a long way to prevent the blank from spinning ( slipping ) on the cone shape.
This friction is the reason that I have had as much success as I have had with TBC because I have always used the diamond cone.
With REASONABLE pressure from the tail stock I have not experienced troublesome spinning of the blank on my diamond cone dead center.

The problem described and STUNNINGLY ILLUSTRATED in this thread has brought some fundamental matters to light.

The fundamental RISK associated with TBC is now elucidated with good clarity ..... finally. . The RISK is BLANK BREAKAGE.

The fundamental RISK is the destruction of the blank being turned on the lathe, as seen above, whether it is a wood lathe or a metal lathe.
The problem in understanding the RISK involved with going to TBC is that there are two (or more) things happening at the same time.

I believe that the essential points are as follows : . ( FORGIVE MY WORDINESS .... I NEED TO GO THROUGH THIS STEP-BY-STEP FOR MYSELF )

Using conventional bushings :
1. The use of bushings inserted into the brass tube ends has a problem ... namely the bushings do not EVER fit 100% properly ... there's always slack.
2. A technically more precise way of saying this is that bushings can not be made to fit into the brass tube perfectly.
3. The bushings have to be made a LITTLE SMALLER in diameter than the I.D. of the brass tube ... some might call this a tolerance consideration.
4. Also, if a mandrel is used, there is a tolerance consideration for the fit of bushings on the mandrel ... I.D. of bushing hole to mandrel diameter.
5. Hence, the inherent inaccuracies with using bushings ...

..... When a blank is mounted with bushings, the blank axis may not exactly be on the rotational axis of the lathe => off center, or eccentricity.

Using the TBC ( Turning Between Centers) method :

6. Someone then recommends the elimination of mandrel + bushings .... use conical centers at both ends of the blank => dead + live center.
7. But now, the conical centers introduce new issues ... there is now a radially outward force on the inner surface of brass tube due to conical shape.
8. Previously, the bushings applied a purely longitudinal force to the blank ... flat end of bushing "ridge" against flat end of pen blank
.... No force problem, but the problem might be that the blank is not centered on the rotational axis of the lathe => off-center shaping of blank.

9. With TBC, using conical 60-degree centers, we can get the blank "perfectly" centered on the lathe rotational axis ....
.... but .... the contact area between the cone-shaped dead center in the head stock and the brass tube in the blank is now greatly reduced.

10. The reduced contact area results in a reduction in the FRICTIONAL driving force at the head stock end of the blank => blank may slip on cone

11. So, with TBC, to prevent the slippage at the head stock end, the LONGITUDINAL FORCE applied by the tail stock MUST BE INCREASED.
...... This increased force increases the friction to prevent the slippage.
12. But .... there is a downside : because of the shape of the cone, some of that increase in longitudinal force becomes a radially outward force.

13. This radially outward force is applied to the inner surface of the brass tube .... THAT IS POTENTIALLY VERY BAD FOR THE PEN BLANK.

14. THE PEN BLANK CAN BREAK due to this outward force .... as seen above.

15. The outward force is actually applied by the dead center cone to the inside surface of the brass tube at the end of the brass tube.

16. Brass is a SOFT METAL and it can and does expand outward due to the force .... the radial expansion of the brass tube end is called "flaring".

17. The OUTWARD FORCE, which causes the "flaring" of the brass tube end, gets passed on to the BLANK MATERIAL.

18. The BLANK MATERIAL CAN BREAK, as we can see has happened in the above example of the use of TURNING BETWEEN CENTERS.

19. The glue between the blank material and the brass tube will not prevent this breakage of the blank ...

20. The breakage is internal to the blank material. . STABILIZATION of the blank material MIGHT HELP ... but don't count on it.

So there we have it .... POINT-BY-POINT .... or step-by-step. .

USING the TURNING BETWEEN CENTERS ( TBC ) method of blank turning HAS A SERIOUS RISK ASSOCIATED WITH IT ... BLANK BREAKAGE.

The use of SPECIALIZED TBC BUSHINGS may have a VERY GOOD PURPOSE WHEN your pen BLANK is FRAGILE AND SUBJECT TO BREAKAGE.

However, WITH special TBC BUSHINGS, you STILL HAVE a possible PROBLEM with your BLANK TURNING SLIGHTLY OFF CENTER.

I think I am going to create a new thread in the "Penturning sub-forum" with the above text repeated, almost word-for-word.

I acknowledge the frequent warnings about TBC that have come from @jttheclockman .
I have now come to the realization that his warnings PROBABLY relate to the risk of blank breakage resulting from brass tube "flaring".
However, I needed to go through this step-by-step detailed explanation for my own sake .... I hope this may be a help to others also.
The reason I have never experienced the problem associated with TBC is that I almost always use a very sturdy blank material.
I generally do not use materials that have a low tolerance to breakage, such as the "pinecone" blank material used in this thread.
In the above example, described in this thread, that was not the case. . The blank material is weak and breakage resulted.

Thank you for your patience .... all of you who have read this "thesis" .... and especially you, too, John @jttheclockman .

John, PLEASE ..... if you insist on saying "I told you so !" ..... go ahead .... but .... I ALREADY HEAR YOU LOUD AND CLEAR !!

All of the above may be perfectly obvious .... it was obvious to both you and me, John. . But I think that some may benefit from reading the words.
The fact that this thread shows the problem(s) so clearly makes this a very valuable thread ..... I hope that my words have value to some also.

One final word of warning :

The potential problem associated with TBC will be exaggerated if your brass tube is not glued into your blank with the ends accurately aligned.
If the blank material extends out beyond the end of the brass tube a "little bit", the conical drive centers used in TBC may contact the blank.
If they do contact the blank material at the ends, your BLANK is HIGHLY LIKELY TO BREAK due to the outward pressure from the conical centers.
 

leehljp

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@Todd in PA
I was never able to keep the flaring from happening. The problem is that when you lower the pressure eventually the blank will stall and when that happens flaring will happen. No way around it. kind of a no win for me, too much pressure, too little pressure also your dealing with metals of vastly different hardness.
You can get universal TBC bushings that use the standard bushings, minimizing cost and they work well for me, but get good ones. There is a company that makes SS ones that are very nice. I'll look for the website and add it.
(no affiliation)

Patrick, This is not a response just to you, but to all and including you.

• I am the one that started TBC on this forum. At the beginning I called it "mandreless" but a couple of others began to call it TBC "Turning Between Centers" and I quickly capitulated. :)

• Because I was living overseas at the time, I did not have quick access to a 60° drive center (dead drive) and at that time 60° TBC bushings had not been invented. So, I made my own drive center here and posted it (and used mandrel bushings with it):


Then JohnnyCNC, noting that most commercial bushings were very sloppy fittings and also knowing the good "drive centers" were 60°, he started making the first ones that I am aware of.

SOME MISCONCEPTIONS:
A 60° drive center is NOT absolutely necessary if mandrel bushings are used.
Look at the photo of the first drive center (aluminum) used for TBC: You can see the scoring on the end where I used the mandrel bushings.

Some other explanations:
In general:
1. It is best to use bushings to get started to bring the blank to "near finished size".
• Without bushings, flaring will probably take place.

2. To Finish, take the Bushings off and use Between Centers without bushings to add and complete the Finish, CA or other.
• This was the reason TBC (Mandreless) originated. But other advantages and benefits were realized after using this method.

3. I use Mandrel Bushings most of the time as they work OK but not with as great of a fitting as custom made 60° bushings.
• Mandrel bushings can be used on TBC easily.
• 60° bushings are tighter fitting.

STARTING OFF with TBC works best with bushings - OR Flaring will probably take place for most people. Skilled and well experienced people may and can start off without bushings and they do not have flaring.

Summary (for most people):
• Mandrel bushings can be used on TBC as well as the 60° bushings.
• Start with bushings to get to near size - Then remove the bushings and return the blank to "between the centers" and finish.
• No flaring at this point for most people.
• TBC finishing (with CA and without the bushings) does not cause the problems of sticking bushings and chipping of CA off of the blank.

OTHER BENEFITS:
Much Less Out Of Round
Bent/Warped Mandrels eliminated
Too Tight Tail Stock on the mandrel eliminated.
Quick on/off for checking sizing and close viewing of finishing process.

Hope this helps
 

magpens

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@leehljp

Lee, THANK YOU SO MUCH for this information.

I probably was aware of your role in introducing TBC, but I had forgotten ..... SORRY !

As you may already be aware, I use TBC all the time in my pen making and I am a big fan of its benefits !! . :D :D :D

I have also made conical drive centers with an angle shallower than 60*. . I do not use them very much since I acquired the diamond-coated drive center which has an important part in my turning.
 
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PatrickR

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all of this makes me think of the old saying "there's more than one way to skin a cat".
i think that is the take away here for the OP. There is more than one way, find the one that works for you and perfect it.
 

Mortalis

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@Mortalis . . . What I am about to say might be perfectly obvious to some. . I think it is still worthwhile saying.

Mr. Mortalis, I think we are finally getting to the crux of the issues with TBC now, sir !! . . . The light has finally come on !!!
Since you replied/quoted my statement about a spinning diamond grinding tool and to keep anyone that is reading this posting from needing to wade through your exceedingly and unnecessarily long explanation I have abridged to the point I wanted to make.

You sir, obviously have little to no sense of humor, maybe just today or about this particular subject........but, Notice the tongued smiley face at the end of my post. Those tend to indicate humor or satire.
 

magpens

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Since you replied/quoted my statement about a spinning diamond grinding tool and to keep anyone that is reading this posting from needing to wade through your exceedingly and unnecessarily long explanation I have abridged to the point I wanted to make.

You sir, obviously have little to no sense of humor, maybe just today or about this particular subject........but, Notice the tongued smiley face at the end of my post. Those tend to indicate humor or satire.
@Mortalis

I sincerely apologize for offending you by calling you, "sir". . . . !! :D :D :D :D :D ( thanks for your unnecessary elucidation of those emoticons )

You must understand that I do indeed have a sense of humour ..... or "humor", as you "abridge" the word.

I was using the "sir" as a token of appreciation for casting some light on the weighty subject of a lovely pen blank's destruction and for stimulating my cortical neurons to explain the reason for that destruction ... a multi-faceted reason which has not previously appeared in full on this forum.
And, a reason which has been the subject of much discussion and deliberation for a considerable length of time, including by the OP of this thread.

Please accept my apology, sir ..... I mean it now, as I did previously, with the utmost respect. :D

And with regard to your statement that you "have abridged to the point I wanted to make" ... where can I read that abridgement ? .... Ha, Ha, Ha.

Or did you deliberately omit that abridgement simply to whet my appetite for it ?

And, what, exactly, was the "point" that you "wanted to make" ? . . .

Is it simply that I have no sense of humour "today or about this particular subject" ? . ( Yes, your spell-checker will flag the word "humour" ) :D
 

egnald

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Another option? PTownSubbie (and most likely others) sell TBC Bushing Adapters which are essentially a 60 degree on one end and a post on the other end that accepts standard mandrel bushings, more widely available than the special TBC bushings. It might be a good compromise for first turning with bushings and then without bushings. - Dave
 

leehljp

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Mal:" Is it simply that I have no sense of humour "today or about this particular subject" ? . ( Yes, your spell-checker will flag the word "humour" ) :D"

So what is wrong with "humour"?;)

I was so confused when I was transferred from the small rural grade school close to home - to the county seat school in the 5th grade. For years I stayed confused on why I misspelled certain words and got "million" mixed up.

Then when I moved to Tokyo in my late 30's and began to read international English with several British English writers, I suddenly remembered that my American grade school teacher had received much of her education in England! No wonder I spelled grey with an "e" instead of an "a" spelled catalogue instead of catalog, and mixed up numerous other words like that . 😁
 
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