iTopSpin

Please login or register.

Login with username, password and session length
Advanced search  

News:

ITSA General Assembly: December 5th - 12th

Author Topic: elliptical turnings  (Read 2054 times)

Jack

  • Demigod member
  • **********
  • Posts: 3317
elliptical turnings
« on: August 07, 2013, 06:00:40 PM »

hey guys i was just wondering if somebody might have any insight into why my attempts at turning a top have always ended up eliptical??? that is to say one side is higher than the other or it turns out oval when i get done, no grain or density variance at all in the wood, just always turns out that way @_@. could it possibly be the fact im using rasps instead of gouges??? hope somebody knows thanks for reading  ;)
Logged

the Earl of Whirl

  • ITSA
  • Olympus member
  • *
  • Posts: 6241
    • St. Jacob Lutheran with a tops page
Re: elliptical turnings
« Reply #1 on: August 07, 2013, 06:50:07 PM »

Weird!  Really interesting.  What a great story to share later on after you are making championship tops!
Logged
Happiness runs in a circular motion!

Jack

  • Demigod member
  • **********
  • Posts: 3317
Re: elliptical turnings
« Reply #2 on: August 07, 2013, 09:02:23 PM »

Weird!  Really interesting.  What a great story to share later on after you are making championship tops!
omg now thats a compliment!!! thanks  :D
Logged

Neff

  • Global Moderator
  • Demigod member
  • *****
  • Posts: 2665
    • My Website!
Re: elliptical turnings
« Reply #3 on: August 07, 2013, 11:11:31 PM »

is the wood wet?
are your tools dull?
is your work piece secure?
what color are your pants?
Logged

Kirk

  • ITSA Jr.
  • Hyperhero member
  • *
  • Posts: 1277
Re: elliptical turnings
« Reply #4 on: August 08, 2013, 12:14:24 AM »

Rasps? Do you mean on top of the lathe?  If so then any variation in the wood (like grain) would cause out of round. This is especially true if you are cutting cross grain (a pain but good for strength and balance)
Logged

Jack

  • Demigod member
  • **********
  • Posts: 3317
Re: elliptical turnings
« Reply #5 on: August 08, 2013, 02:14:07 AM »

is the wood wet?
are your tools dull?
is your work piece secure?
what color are your pants?

wood is dry
tool is sharp
piece is secure
pants are.....wait....where?.... someone stole my pants!!!!!! well they were khaki  :'(
Logged

Jack

  • Demigod member
  • **********
  • Posts: 3317
Re: elliptical turnings
« Reply #6 on: August 08, 2013, 02:18:20 AM »

Rasps? Do you mean on top of the lathe?  If so then any variation in the wood (like grain) would cause out of round. This is especially true if you are cutting cross grain (a pain but good for strength and balance)

yes a wood rasp, and yes "on top" of lathe i think  :-[ . and yes i am cutting against the grain so you think that might be whats causing the problem???? also do you think if i switch to a gouge it would eliminate the problem????
Logged

johnm

  • Ultrahero member
  • *******
  • Posts: 850
Re: elliptical turnings
« Reply #7 on: August 08, 2013, 07:00:17 AM »

I assume that your technique with the rasp is to hold the rasp with one or two hands against the surface of the workpiece as it spins.  With this approach, the rasp is always cutting and variations in the wood and/or variations in applied hand pressure can cause different cutting rates at different places around the circumference of the workpiece.  If you notice the rasp and your hands "bouncing" as the material turns this is likely what happens and your natural (delayed) response to a bounce up (high spot on the material) is to apply more pressure while your natural (delayed) response to a bounce down (low spot on the material) is to apply less pressure.  This combination of your reactions which are out of sinc with the proper action of heavy pressure at the high spots and reduced pressure at the low spots can lead to a kind of resonance which just increases the out-of-roundness rather than correcting it.

A gouge or scraper in combination with a proper tool rest is the way to go.  While cutting, the tool rest provides a fixed reference distance from the center of rotation, and anchoring the cutting tool against the tool rest ensures you are cutting at the same distance from the center of rotation for the entire circumference thus making the piece round (in this geometry the tool automatically takes a heavier cut at the high spots and a lighter cut at the low spots which is exactly what you want).  Changes in wood characteristics around the material will still present regions which cut easier/harder that others so without practice and recognizing when to take lighter cuts, you can still experience the "bounce" effect but it is easier to see by watching the distance from the fixed position of the tool rest to the moving end of the cutting tool.  Be aware that "catches" of the cutting tool by the workpiece are more likely than with the rasp approach so always be careful.
Logged

lincolnrick

  • ITSA
  • Hyperhero member
  • *
  • Posts: 1234
Re: elliptical turnings
« Reply #8 on: August 08, 2013, 12:12:30 PM »

With regards to using a gouge I was taught ABC. Anchor, Bevel,Cut.  Anchor your tool to the tool rest before you start the cut, lower the tool until the bevel is rubbing the piece, then raise the handle until you start cutting into the wood.

If you're using a tailstock to help secure the piece you're headstock/tailstock may also be out of alignment. If so this may cause 'ovaling' of the wood.
Logged