Sunday, June 3, 2007

Chatter



I have been thinking about a recent question that I got about lathe chatter. It seemed so simple at first, Do I use a steady rest to reduce vibration? I don't, I use my hand to steady the spinning workpiece. But that is just the tip of the iceberg of the steps and trials that I have had on my path to reducing vibration. One of my goals with this blog is to make woodworking more approachable, you don't need any mystical skills. There are just lots of mistakes and lessons, generally easy ones, that need to be had before things seem "simple". Often, once you know something, it is difficult to remember what it was like before you knew it or the path you took to knowing it.

Vibration is one of the largest obstacles to turning wood. And vibration begets vibration. Once a piece starts vibrating, the turning becomes rough and patterned, control and surface quality are difficult to regain. There are many factors that need to be addressed. The machine, the wood, the tool in hand and of course, the operator skill.

Today I'll talk about the machine. Lathes vibrate. I have an old (late fifties) benchtop Rockwell lathe with a belt that must be manually moved to change speeds. This is a perfect testing ground for vibration! The first thing to address though is the floor. I used to work out of my basement, not good. But I had my lathe on a concrete floor and bolted to a concrete wall, good. This, along with some sandbags on the lower shelf helped to steady my old lathe pretty well. Now, in the new shop, with its lovely wood floor (better on the legs and tools) my lathe absolutely rumbles. Not having the time to deal with the floor (a concrete pad seems in order), I have turned my attention to the other variables.

The motor should be checked for undue vibration. Undo the belts and let it spin on its own. A glass of water on the lathe bed is a good indicator. I have tried just about everything to reduce the transfer of motor hum. Rubber washers, motor on a hinge, tighter belts, looser belts, new bearings, you name it. One thing that I know helps, is the link type belts, with the proper length. I've used them ever since they stopped a bandsaw from walking across the shop. Checking the bearings and alignments of pulleys etc... can go a long way toward the goal of silencing vibration. There is good literature available about tuning up your lathe, after all, it's a great opportunity to blame the tool!

Honestly, I've sort of given up on further machine tinkering. Being an instructor and travelling to different schools to teach puts me in an awkward position. If I can only get results from a perfect machine, I risk being less than impressive on the rest of them! So I have turned my attention to the other factors, which I will cover soon.

4 comments:

Philip said...

One simple solution to reduce vibration is to get/buy 300lbs of sand, in bags, and park them under the bed on a couple planks, or whatever can be suspended under the bed between the legs. The local Big Box Store has play sand and it worked miracles for me, and I have a big PM lathe.

Anonymous said...

Peter, Well I thought my lathe chisel were sharp, not so. After sharpening them, I got much better results. Not perfect, but at least controlable. Bob Glenn

Orion said...

Do you have any recommendations on size and brands of lathes for spindle turning? Certainly the bigger (and usually more expensive) the better but would an old craftsman be just a frustration for a new turner or an acceptable route to go? What about your reccomendation for a minimum horse power?
Reamers are also another mystery to me. Did you purchase yours or make your own. I did read somewhere in your blog that you use a six degree taper but what type of construction is it?

Peter Galbert said...

Orion,
I am no expert on lathes, but I can say that I use an old delta rockwell that has a 36" bed and a 3/4 horsepower. I bought my lathes at an auction and at a resale shop, one was about $70 (a major bargain with a 24" tool rest) and the other was about $325. I found the old rockwells easy to work with and solid. I put new motors on and bought new drive centers and live tailcenters. Delta still has a lot of the parts for these lathes. But really, if your just starting out, an inexpensive new lathe may be simpler, it all depends on your temperament. Pretty much anything that spins wood can be worked with. As for the reamer, I make my own. John Alexanders Greenwoodworking site has instructions for making one like I use. The only difference is that I sharpen both sides of the cutter. They are also available from Elia Bizzari. He can be found at the WindsorChairresources.com under suppliers. Good luck