Turning between centers question

[soligen]

When turning a pen between centers with a custom CB, and you want have The upper & lower flush, what procedure is best? I'm thinking betweeh centers in inherently more accurate way to turn than a mandrel. Several options come to mind:

a) Dont do it - turn on a mandrel so the upper & lower are adjacent.
b) turn the parts individually using calipers to match diameters
c) somehow (but I dont know how safely) turn both pieces together between centers.
d) Create one segmented blank with the CB in it (multiple ways to do this) and turn the pen as one piece, then part the blank apart once it's done.
e) Any others option or advice?

I've had some accuracy issues with section flushness (some good, some just OK) and the perfectionist in me is looking to improve.

Thanks

 

[ed4copies]

Dennis,

If your lathe is turning correctly, I believe "a" is the correct answer. Use a "professional" mandrel (can be shortened or lengthened by the two nuts at the MT end), just long enough for both blanks and no spacers between them.

Don't know how you could be any more accurate, but I am willing to learn if someone has a better method.

 

[ldb2000]

Ed is right Dennis . The mandrel is your best bet in this case as long as you have bushings for both ends and something to support the middle , like a spacer or like in the challenge the lower tube . If not then I would pick option "B" , use your calipers to get the two halfs as close as you can . Thats what I do when I doing a kitless and there are no bushings to work with . You will be supprised just how close you can get this way .

 

[KDM]

I made my own mandrel and I'm very happy with it. BUT, I always turn my blank down between centres in order to get it round. Once it's round, I can centre drill it. I never drill the blank out on a drill press. Sometimes, I turn the whole pen on centres and then part off, BUT this has diadvantages. You can press teh live centre in too far and shatter the blank, you can squeeze the blank too hard in the chuck (if you're using a chuck) and crush it. Also, while it's turning, wood is very bendy and polyester resin is very brittle. A big advantage of putting it on a mandrel is that you will already have CA'd a brass tube in, giving it a beit of extra strength.

What's the objection to using a mandrel?

 

[soligen]

OK, I'll stick with that and work on technique. I'm getting a slight ovalness, and the that also affected my finish application as I had a low spot nect to a high spot on the other blank. then, when I seperated for final finishing is where I think I introduced tegh most difference.

Is it actuially possible to get a joint you cant feel with your fingers - or am I dreaming here lol

 

[ed4copies]

OK, I'll stick with that and work on technique. I'm getting a slight ovalness, and the that also affected my finish application as I had a low spot nect to a high spot on the other blank. then, when I seperated for final finishing is where I think I introduced tegh most difference.

Is it actuially possible to get a joint you cant feel with your fingers - or am I dreaming here lol

It is possible. However, if you are using wood, tomorrow you MAY be able to feel it, even if you could NOT today. Wood moves---darnit!!!

Now, let me tell you about RESIN!!!!!
(It moves a lot less!!)

 

[soligen]

What's the objection to using a mandrel?

No objection per-se. Just wondering if there is a more accurate way becasue tubes and bushings are not totally snug to the mandrel. My "lathe" is already not the most accurate, so I need every edge I can get. Between centers I can turn on a custom made drive center that (in theory) helps mitigate run-out

 

[ldb2000]

You are using a metal lathe so a mandrel works ok . Using a wood lathe is a totally different animal . There are stresses using hand held tools for turning that cause mandrels to flex and cause out of round conditions . Using a metal lathe is more accurate but you will never know the pleasure of using your hands to create a gentle curve to a blank so even though a metal lathe is more accurate a wood lathe gives you a personal satisfaction when your pen is done that you can't understand using a metal lathe .

 

[soligen]

It is possible. However, if you are using wood, tomorrow you MAY be able to feel it, even if you could NOT today. Wood moves---darnit!!!

Now, let me tell you about RESIN!!!!!
(It moves a lot less!!)

Hmmm - the best joint I did had an antler CB - maybe thats why.

Decided to hold off on resin. I'm sharpening challenged and my tools are cheap. I need to sell some pens so I can get a woodchuck :biggrin:

 

[ldb2000]

OK, I'll stick with that and work on technique. I'm getting a slight ovalness, and the that also affected my finish application as I had a low spot nect to a high spot on the other blank. then, when I seperated for final finishing is where I think I introduced tegh most difference.

Is it actuially possible to get a joint you cant feel with your fingers - or am I dreaming here lol

Yes it is but it takes lots of practice .

 

[Paladin]

Newb question...

When turning a pen between centers with a custom CB

What is a CB?

 

[ldb2000]

Center Band .

 

[KDM]

You are using a metal lathe.

Me or soligen? I know I am. Yeah, you're right about the oter stuff. I'm making a tool rest and looking ant buying a set of small chisels. My lathe is great for precision and straight edges, but pens need to be roundy!!

I'm getting a slight ovalness

If you ARE using a metal lathe, I imagine the only thing that could be causing this is the mandrel bending. Try removing less material at a time. If it's a wood lathe, once the ovalling has started, I think it might be difficult to remove. Once the material starts pushing the tool, then the tool starts bouncing back on to the material, accentuating the effect. Try changing speed. Try a speed appx 2/3 of whatever you're currently using (the theory being that the tool will "bounce" back into a different location).

 

[soligen]

If it's a wood lathe, once the ovalling has started, I think it might be difficult to remove. Once the material starts pushingthe tool, then the toool starts bouncing back on to the material, accentualing the effect. Tray changing speed. Try a speed appx 2/3 of whatever you're currently using (the theory being that the tool will "bounce" back into a different location).

This may be part of it. I turned to round between centers, then drilled - which is close, but not perfect. Once on the mandrel it need to be re-trued.
I was trying to take very little off with a very firm hold on the tool. Didn't think of varying the speed - I'll try it next time.

 

[jskeen]

another approach that you might try is to turn the two blanks close to size using calipers, and sand to medium grit, but not ready to finish. then partially assemble the pen, ie if a slimline type, press in the tranny, if a double twist press in the coupler and screw on the tranny, but leave both ends open. Then put the pen together and mount between centers as a unit and do your final sanding and get ready to finish, then separate and finish. The goal is to get the pen to feel seamless when it's assembled, so if you get both parts perfect on the mandrel, and then assemble a little off, it's going to feel off. Give it a try, worst case, you're out a pair of tubes, or may need take a little off with a different method and try again.