Help With Large Out of Balance/Off Center Turnings

[Steve Doerr]

I have several slabs of very nice burl (12” to 23” diameter) that I would like to use for wall hangings/shields. I would like to turn some of them so that the center of the turning is not the center of the burl slab. I have tried Googling techniques and jigs that would help balance the turning so that your lathe doesn’t walk across the shop. So far, all that I can find related to the topic is off-centerede spindle turning and turning small off-center blanks that don’t really require any counter balance. Looking for ideas, pictures, articles, etc that talk about the technical side of turning something like this.

Any help that anyone can provide would be GREATLY appreciated.
Steve

 

[Charlie Knighton]

See Nick Agar ...... Internation Turner.....

basically mount blank with glue gun and straps to 30 x 30 or larger mdf ......use face plate to attach mdf to lathe.....move face plate to different positions to have multi-axis for blank.....add weight to mdf to help balance

for burl glue would be hard to get off....make a nest for burl and strap to mfd.....u can move nest around using weight for balance for double bowls or such

SEE Nick Agar

 

[hockenbery]

What Charlie said.
Be carful- slow speeds light cuts, big lathe...

A large backing board of plywood. Counter weights can be screwed to the plywood.
Be sure the screws holding the plywood are secure using a second piece of plywood 4” -10 larger diameter than the you largest faceplate between the faceplate and the backing board glue and screw together. I would use at least a 10” faceplate.

Small faceplates and other metal objects with holes in them work fine as counterweights when secure out of the cutting path
Bad luck to cut a faceplate with a turning tool.

Practice with a small piece. Take a half log and cut an irregular shape from it on the bandsaw to match your Burl at 1/2 or 1/3 scale to start.
Finding a lathe to fit it on is a challenge. A ONEWAY 2436 with the large outboard would let you get close to one end of the 24” piece safely.

Did some really small pieces in Christian Burchard class a long time ago.
Maybe 8x4 size. Need a big lathe and slow speed. I used an ancient Thompson boring bar that weighs 10 pounds to do the initial cuts withnanscraping tip.

 

[Richard Coers]

Pretty long discussion here. http://www.aawforum.org/community/index.php?threads/counterbalance-jig.8782/

 

[John Jordan]

This is a typical large piece from Mark Gardner. They are often cut and reassembled after turning. Faceplates for counterweights as Al suggested.

Be patient-this can kill you.

John

 

[Steve Doerr]

Thanks everyone for your input. I will be making a large face plate out of tow pieces of 3/4" plywood (so it is 1 1/2" thick). I'll be starting with with some small items and working up to some large items. The other thing is that I keep the rpms below 500, and make sure that I use counter balance weights to make sure the face plate is balanced. I'll keep everyone posted on my progress.

 

[Bill Boehme]

I have a very large and heavy 10 inch cast iron faceplate made by Oneway. I find that I use it a lot more than I had originally anticipated because it's mass effectively swamps out any unbalance that is present in blanks that I mount between centers.

 

[Don Wattenhofer]

Thanks everyone for your input. I will be making a large face plate out of tow pieces of 3/4" plywood (so it is 1 1/2" thick). I'll be starting with with some small items and working up to some large items. The other thing is that I keep the rpms below 500, and make sure that I use counter balance weights to make sure the face plate is balanced. I'll keep everyone posted on my progress.

Instead of keeping it below 500 RPM start out at the lowest speed your lathe will go then increase the speed until the lathe threatens to walk away then back off to a smoother speed. Another point to consider is that the farther out from the center you are cutting the higher the surface speed.

 

[Steve Doerr]

I have a very large and heavy 10 inch cast iron faceplate made by Oneway. I find that I use it a lot more than I had originally anticipated because it's mass effectively swamps out any unbalance that is present in blanks that I mount between centers.

Billy, I looked at those and may end up getting one. I'll see how my 22" plywood face plate does mounted to my 6" steel face plate.

 

[Steve Doerr]

Instead of keeping it below 500 RPM start out at the lowest speed your lathe will go then increase the speed until the lathe threatens to walk away then back off to a smoother speed. Another point to consider is that the farther out from the center you are cutting the higher the surface speed.

That is what I'm planning on doing. And yes, I understand that the further out you go the faster it is turnings. For example if the shaft is turning at 500 rpm, then at just over 23 inches its turning at 1200 rpm. Way too fast for something that is off center in my opinion.

 

[hockenbery]

That is what I'm planning on doing. And yes, I understand that the further out you go the faster it is turnings. For example if the shaft is turning at 500 rpm, then at just over 23 inches its turning at 1200 rpm. Way too fast for something that is off center in my opinion.

You have the right idea but wrong units
The rpm (revolutions per minute) is the same regardless of diameter

The difference is the velocity of the wood at a given radius which equates to the length of wood coming by the cutting edge in a unit of time.

 

[Steve Doerr]

You're right Al. Thanks for catching that. I think it must have been a case of ol' timer's disease

 

[Bill Boehme]

Billy, I looked at those and may end up getting one. I'll see how my 22" plywood face plate does mounted to my 6" steel face plate.

I am planning to cut a 20" diameter circle out of ¾" Baltic birch plywood and attaching it to the 10" faceplate mainly for holding a large end grain piece of mesquite.

 

[Steve Doerr]

I am planning to cut a 20" diameter circle out of ¾" Baltic birch plywood and attaching it to the 10" faceplate mainly for holding a large end grain piece of mesquite.

Billy, my 24" Baltic birch plywood face plate is 1 1/2" thick. That gives me the ability to anchor weights and to secure my turnings without worrying about the wood face plate breaking on me.

 

[Robin Thompson]

One option out there is a Vicmarc balancing system. I don't own one so i can't comment on the unit. You might consider this if you had multiple off center pieces you want to turn.

 

[Charlie Knighton]

was not aware of this from vicmarc.....cool

 

[Steve Doerr]

Thanks Robin, that is an interesting piece of equipment.

 

[John Tisdale]

Steve,
With a large out-of-balance burl you might consider filament tape on the outside, assuming natural edge. You can buy a lot of tape for the cost of one emergency visit to the dentist.
Doing larger off-balance requires minimal speeds - developing a turning style for sub-300 and even sub-200 rpm takes some time.
Good luck and send pics
John
John