A highly likely convert to between-center turning...we'll see

[gomeral]

I'm getting so irritated at out-of-round tubes...

I just bought a new mandrel because I'd originally turned several with the stock live center (before I realized the 60º thing). I barely tighten the brass nut on the mandrel so the blanks actually turn when I turn on the lathe. I barely tighten the tailstock against the mandrel, just enough so it doesn't squeak and the live center turns at headstock speed. I try gentle turning, not much pressure on the tools, not a lot of pressure when sanding...I think I've tried everything. Today I discovered an out-of-round tube on a slimline pen I turned on the brand-new mandrel, don't know how it (my pen) made it past "QC".

I've already placed an order with Johnny for bushings, but DANG I'm getting ready to throw this mandrel through a wall!



daniel

 

[rherrell]

It might not be your mandrel. Do you realize how many pens have been made using a mandrel before all this "mandrelless" stuff? Using a mandrel is perfectly acceptable and I still use one for some pens. Check your HS/TS alignment. And just because the tips of the centers line up doesn't mean everythings in line. Imagine if you have two pencils touching tip to tip. If you move the eraser end of one of them the tips will still line up but you will be "out of alignment". Also, if the ends of the blank are not square with the TUBE it can cause some trouble. Check the mandrel itself for straightness, I use this method.....

Don't be afraid to use a mandrel, it's a great tool that needs to be kept in your arsenal.:wink:

 

[davinci27]

There are some things you can do on the mandrel as well to avoid out of round. Here are some things I do to try to limit Out of Round blanks

1. Make sure the ends of the tubes are properly squared. This has fixed 90% of my out of round issues.
2. As you are turning, occasionally stop the lathe and twist the barrels on the bushings.
3. If as you get close to finished size you notice you are getting out or round at on end. Reposition the blank so that end is closest to the headstock.

The biggest thing for me is to start looking before I get to a finished size. Most of the time if there is and OOR issue, I can trace it back to the cause and find a way to fix it.

Ben

 

[leehljp]

It might not be your mandrel. Do you realize how many pens have been made using a mandrel before all this "mandrelless" stuff?

LOL. Sure has been a bunch. And I still have a bunch that I am proud of, but they still are OOR. Most of my OOR pens are from bushings drilled off center (I miked them), which is why I started buying at least 2 sets for a new pen design at the very beginning. Now I get bushings from Johnnycnc.

I would be willing to bet that if everyone put calipers to bushings, they would find many drilled off center by .005 or more.

It is a good idea to mike the bushings when you get them and if they are off center, by too much in your opinion, call the vendor and see what they say.

From what I have read in the past, the reason for "B" mandrels was because of too much flex of the "A" mandrel. Mandrel-less is from the same reaction for many, although for me (and I know a few others), I went mandrel-less for "finishing" benefits.

 

[turneretc]

Mandrel-Less??

Greetings to all. Am new here and have never heard of mandrel-less pen turning. Can someone suggest a source of info on this?

 

[leehljp]

Greetings to all. Am new here and have never heard of mandrel-less pen turning. Can someone suggest a source of info on this?

You asked for it:

http://www.penturners.org/forum/showthread.php?p=774463#post774463

The top half deals with CA application; The bottom half has a series of posts that deal with mandrel-less, a.k.a. No-Mandrel & Turning Between Centers.

For a quick picture, Scroll down to the second picture on this link to see the bushing/centers:
http://www.penturners.org/forum/showthread.php?t=38361&highlight=skogger (This link shows turning between centers/mandrel-less but is not about mandrel-less.)

Welcome Edward!

 

[turneretc]

Thanks for the info Hank it was very enlightening. Is anyone making the custom bushings in order to turn this way?

Edward

 

[rjwolfe3]

Johnnycnc is the man

 

[leehljp]

Thanks for the info Hank it was very enlightening. Is anyone making the custom bushings in order to turn this way?

Edward

Edward,

You will find that the bushings are more expensive, so I just wanted to warn you.

The reason is - they are custom made, made from higher quality steel, and machined to much higher tolerances too. I find them worth it. In the Mandrel-less set up, you can take the bushing off and use calipers to determine the final size. Then apply finish and you don't have the problems of bushings sticking.

The reason I mentioned this is because generally, bushings are considered a "consumable". Sandpaper wears them down, or the skew or scraper hits the bushing and wears them down too. Bushings usually have to be replaced after 30 - 50 pens on average. But if they are taken off for finishing, they don't wear down. That helps justify the price in buying the custom machined higher tolerance bushings.

 

[rick_lindsey]

Out of curiosity, how does an out-of-round bushing cause an out-of-round pen? Does that apply only to pens with larger than 7mm tubes? There are some slimline bushings in the shop that are *very* clearly out of round, but if my tube is on the mandrel on not on the bushing i'm not sure how that's going to cause my pen to be oor...

-Rick (who needs to buy himself a dead center)

 

[keithkarl2007]

applying too much pressure while turning can force the blank away from you as you turn. if i can i turn my blanks to round before drilling for the brass tubes. then its just a few light passes with a skew to finish