TBC Issues

[tangoman]

G'Day Folks,

I need to pick your collective brains again !

I switched to TBC rather than a mandrel a while back and am suffering from cracking of my blanks at the live centre end, not every one but enough to be very annoying.
I assume I am putting too much pressure on the tube and blank and hence forcing the ends to expand and crack.

One possible remedy may be too switch to a skew (less cutting pressure?) from my Pen Pro - what do you think ?
Another possible remedy would be to turn myself some bushing with 60 degree holes in to fit the centres.

Whats your experiences with this and how did you avoid/reduce this problem ?

This pen is a classic example, two cracks in the cap resin at the live centre end !


Regards,
Cam

 

[1080Wayne]

Well , the sharper the tool , the less pressure you have to apply to prevent spinning on the live center . That said , some materials are more brittle than others . What have you been using ?

 

[NittanyLion]

I've never used a pen pro or other carbide chisels, but I turn many blanks "bushingless" with a very sharp skew. The key is to be razor sharp, and apply just enough pressure as not to spin the blank. It also is better for me to turn at very high speeds. Hope this helps....

 

[Ironwood]

I turn 90% of my pens BC no bushes, using my carbide PenPro, I am yet to crack a blank yet, Touch wood.
My guess is you are using too much tail stock pressure. Try just snugging the tailstock up until you can't spin the blank easily by hand, and yes you will have to go very steady until you have the corners turned off, if it starts to spin, just give the tailstock hand wheel a tweak and keep going. I turn my plastics at 3000+ rpm.

 

[TonyL]

+1

My guess is the same as Ironwood's. I turn my plastics between 2300 and 2700. I could try higher RPMs, but I satisfied with the results at the 2300 to 2700 range. I use EWT carbide blades. I only tighten my tailstock to the point where the blank will not spin freely under light to moderate tool pressure. Many times my initial setting is slightly loose and then I will give it (ts) an 1/8 inch turn or less.

FWIW

 

[tangoman]

Thank You !!

Folks,

Many thanks for your replies. It does appear I am tightening my tailstock too much so I will try to be much gentler from now on and also turn at a slightly higher speed !1

Much appreciated,
Cam