Out of round pen body

[Lawrence Witter]

I am turning kit-less pens from acrylic on a 7" X 14" metal lathe and have what is becoming a serious problem. The turned blank is out of round or, more correctly off center. It seems that when i start, the cutting tool puts pressure on the blank's end causing the blank to bend until the tool gets to the spot where the body is thick enough to resist bending.

So, what can I do to fix this PITA? Any and all help is appreciated!

Best regards,

Larry

 

[Dale Allen]

There has to be something else going on here. I assume that the end is not supported but I cannot image putting that much pressure on the end of the blank. It would be gouging in substantially.
Maybe take much lighter cuts.

 

[Russell Hodge]

Check for vibration, alignment, and you need the sharpest tools.

 

[low_48]

I think a picture of the setup on the lathe would be of great benefit for us to help you. We don't know how you are holding the acrylic, what cutting tool you are using, if you are using a dead or live center in the tailstock (if you are using anything there at all........You get the idea. Just telling us you have a problem leads to guessing by everyone.

 

[DaveTTC]

I am turning kit-less pens from acrylic on a 7" X 14" metal lathe and have what is becoming a serious problem. The turned blank is out of round or, more correctly off center. It seems that when i start, the cutting tool puts pressure on the blank's end causing the blank to bend until the tool gets to the spot where the body is thick enough to resist bending.

So, what can I do to fix this PITA? Any and all help is appreciated!

Best regards,

Larry

Does your blank have a tube insert.

This is an out there idea so maybe try on a bit of scrap if you have some. Perhaps freezing it and turning it frozen might help. Remember it could become brittle while frozen so careful with the pressure applied to the ends. Be sure to let us know when you work it out.

 

[Paul in OKC]

If you are hold the parts in a three jaw chuck, there may not be enough support for the blank, depending on how far out your blank is sticking out. The farthere away from the chuck unsupported the more issues with the blank 'moving' on you.

 

[Marc]

Are you turning on a pen mandrel? If so, you might be putting to much pressure on the brass nut that comes with the mandrel which can cause the mandrel to bow from the pressure. An accessory called a mandrel saver can correct that issue.

 

[thewishman]

Are you taking a lot of material off at one pass? do you have enough clearance to support the backside of the blank with a finger to resist the bending?

 

[dbledsoe]

Make sure the end of the blank is supported by the tailstock live center. That is the only way you can get true cuts on this stuff that bends.

 

[Lawrence Witter]

Thanks to all who offered their suggestions, they led me to see my problem from another angle and, i believe, my work will improve. I've begun using a live center in the tail stock, changing inserts more frequently.

Best regards to all,

Larry

 

[Penultimate]

Make sure your live center is aligned to the head stock.
Check your cutting tool height. it should be on center. Mount a piece of metal in the chuck and turn it to a sharp point. Place a long thin piece of plastic on the bed and scratch a line in the plastic at the chuck center line. Thats your tool height.
Check your chuck jaws to be sure they are closing together and on center. I checked runout on my chuck and determined I get the best results by always tightening the check in the same chuck key position.
Good luck.