Turn between centers question

[pshrynk]

Can TBC be used for pens that have two blanks? I've tried to glean the answer from the threads here, but can't quite get the answer. Logically, it seems that you should be able to, but there seems to be some of you that are talking like it shouldn't be done.

 

[mecompco]

The only difference is that of course, you turn one barrel at a time. Other than that, no problems.

 

[pshrynk]

Cool. Gonna have to try that, then

 

[Dehn0045]

I recommend TBC without bushings, use digital caliper to turn to match the diameter of pen parts. If you are using bushings you might be able to get away with using a 2-sided bushing in the middle, but the time savings would be minimal. You can save a little time by finishing on a mandrel. For me, it is TBC, no bushings, turned one at a time, finished one at a time -- if I try to cut corners my results suffer...

 

[MRDucks2]

Hey, Sam, the problem I have run into trying TBC without bushings is the need to bump up my tension and splay the ends of my brass tubes a bit. Is that an issue with tool sharpness, aggressive cut or the fate of my HF lathe?


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[Dale Allen]

I make my own TBC bushing from 304 brass and I do it on a HF wood lathe, the big one.
If the bushing is properly made the pressure is against the end of the tube and as such it almost cannot damage the tube. My bushings are tight enough that sometimes I have to use a vise grip pliers to get them out. That way I know there is no slop in the fit.

 

[magpens]

Hey, Sam, the problem I have run into trying TBC without bushings is the need to bump up my tension and splay the ends of my brass tubes a bit. Is that an issue with tool sharpness, aggressive cut or the fate of my HF lathe?


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Instead of a dead center in the headstock, I use a diamond coated cone (for more friction driving force) ... the cone is actually meant for sharpening mortise chisels and I bought it at Lee Valley but they are available at HF and Grizzly.

 

[Dehn0045]

Hey, Sam, the problem I have run into trying TBC without bushings is the need to bump up my tension and splay the ends of my brass tubes a bit. Is that an issue with tool sharpness, aggressive cut or the fate of my HF lathe?


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It hasn't been an issue for me. I do turn round prior to drilling and drill on the lathe, so the brass is reasonably centered. I use HSS tools and sharpen quite often. Sometimes I will use bushings until I am within 0.020 or so and then finish up without, this works pretty good with light finishing cuts. I also think higher speeds are better, I usually am at 2400 rpm. I've turned hard woods, soft woods, stabilized woods, and antler this way without issues. I don't think the lathe is an issue. You could try roughing up your dead center with some sandpaper. I do like Mal's suggestion about using a diamond cone. Hope this helps.

 

[MRDucks2]

Now that you mention it, I was still trying to turn square blanks round between centers. May have just been the beating they were taking. Will try the same thing with a round blank and see what happens. Been drilling on lathe. Have yet to find a use for a drill press.


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[Dehn0045]

I made a batch of 12 slimlines once (I'm not a production guy), I was definitely happy I had a drill press that day... Usually just collects dust though

 

[TonyL]

Even Barry Gross, who uses a mandrel, advises to turn one barrel at a time to avoid exposure to run-out.

 

[tonylumps]

I have not ever had a problem turning with a mandrel.l bought TBC bushings for some of my best selling Pens .Went back to the mandrel.I grant you I replace my mandrels frequently and use a mandrel saver

 

[pshrynk]

Riffing off another thread that was hijacked to the TBC topic and using calipers, I am leery of the calipers approach, mostly because of the "oh, fark!" factor that I can imagine that is involved. With bushings, there is at least a visual "Quit grinding, dummy!" point. I think I need to be a lot better and more skilled before I jump in that deep end of things. Maybe I'm too timid. Thoughts?

 

[MRDucks2]

Right now I turn two barrel pens on a mandrel with mandrel saver, single barrel pens with bushings no mandrel or between centers. On the the mandrel or with bushings but no mandrel I still verify bushing diameters against the pen parts before I start to get a feel for how close I can go. Once I get there I measure then turn. You get a feel for how much you take off with different materials/tool combinations. I have found once I start measuring I become more conservative and seldom end up removing more than .5mm at a time unless I consciously make an effort to do so.

When using no bushings, I tend to stop earlier and measure more. On weeks I turn 1 Pen, it takes more time. When I turn 2-4 pens a day or a few days back to back, my eye becomes better calibrated.

Have been bitten once by a non-stabilized blank that had a soft band of wood just before I would normally stop. Turning fine, getting closer then the Skew cut much deeper/quicker than it had been when it hit the soft wood. Ended up small on both ends, tear out at center on lower barrel and just right at center on the upper barrel.

That pen became one of my everyday pens.


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[ajollydds]

Riffing off another thread that was hijacked to the TBC topic and using calipers, I am leery of the calipers approach, mostly because of the "oh, fark!" factor that I can imagine that is involved. With bushings, there is at least a visual "Quit grinding, dummy!" point. I think I need to be a lot better and more skilled before I jump in that deep end of things. Maybe I'm too timid. Thoughts?

I use bushings to get close to final size and then switch to no bushings and calipers. Don't be timid, you'll catch on quick. Practice on scrap blanks.

 

[Troy Cole]

I wanted to use the system of measuring with calipers to final dimensions. My problem is that most of my pens taper down to the ends of the barrel. So to get an accurate measurement I have to measure exactly at the tip of the barrel. For some reason this has proven to be difficult to get accurate measurements.
Just wondering if this is an issue for other turners.

 

[pshrynk]

My understanding of the system they talk about is that there is a conical doohickey on each end of the blank and therefore must be some space to measure. With the PSI TBC, however, it is designed to be used only with bushings, so not so much.

 

[Dehn0045]

I wanted to use the system of measuring with calipers to final dimensions. My problem is that most of my pens taper down to the ends of the barrel. So to get an accurate measurement I have to measure exactly at the tip of the barrel. For some reason this has proven to be difficult to get accurate measurements.
Just wondering if this is an issue for other turners.

Tapered fit can be more challenging, but it also tends to be less noticeable when it's not perfect. I normally do very little taper, but recently made some perfume holders for a friend that had more shape. I don't really have a secret, just use more care when measuring to be sure that you're measuring the very end of the blank. I find it's easier to measure if I take the blank off the lathe.

 

[Dieseldoc]

TBC has a learning curve just like all of our tools. Me for one after using the TBC have not gone back to bushings. Another thing using TBC will force you to have better tool control , meaning less tare out because of making lite clean cuts.

Charlie

 

[MRDucks2]

When I measure the parts I target a less than or equal to size. Say a part measures 11.06mm. I shoot for 11 or slightly less. If I hit 11.06, great. Otherwise 11 or 10.98 is fine. What I have found is if the wood is larger by a tiny amount you can feel it when holding the pen. If the metal. Is larger by a tiny amount, you don't really notice. Probably because our corners on the wood at sharper than those on the metal parts and likely why some folks round over or bevel the wood edges. Haven't tried that yet.

For measuring on tapered surfaces, I just slide the knife edge of the caliper up to the lip of the wood the gently step it up onto the the edge of the blank stating as close to the end as I possibly can.


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