vibration on a lathe

i have a 14" jet lathe with cast iron legs and i mounted the legs in 8" of concrete and on 6" and above peices i get vibation. this happens mostly when hollowing a bowl. does anyone have a solution? thank you, Tom
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
At what stage of the turning are you getting vibration? green or dry. Is the head lock positively on? About the headstock release? Is the blank well balanced? When you have nothing mounted on your spindle what is the wobbling reading.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Balance and speed. Lots of people think it's some sort of macho thing to brag about how much weight they put on their lathe to keep it from shaking loose, but the best thing to do for both you and the machine is to get best balance early. Means time at the bandsaw or the chainsaw getting close to round, and angling the end grain cuts under to get rid of the dead weight you'll be cutting off to match the curve anyway.
Takes care of the leverage. Difference in mass acts in proportion to the distance from the axis of rotation. Now get the speed down. Start sloow and well-held, especially with help from the tailstock. My lathe has eight speeds from 200 to 3600. I use two. Three sixty starts bigger out-of-balance stuff, and everything finishes at 690. It's a luxury I appreciate after my old 12" with 600 minimum.
If you made your own stand you could let good Physics and Geometry lessons help you design it to spread forward to counter the thrust of the heavy portion coming over the top, with weight down near the floor behind, where it'll want to lift at the same time. Not that you'd want to neglect the above, because Newton says a collision is a collision, and it all happens in your bearings.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I have the same lathe WITHOUT any extra weight, and I have 13 in bowls run smooth as cream.
How about some more information--
What's vibrating? The lathe itself or the work surface?
Does the lathe vibrate without any work on it?
Are you talking about vibration when you first mount the piece (before you've rounded it?)
Do you expect to mount any piece of wood on the lathe turn on the power and have it run smoothly because of the extra weight?
I do everything I can to reduce vibration by balancing the piece before turning it on, because I think of the problem of replacing overloaded bearings.
Try asking this question on rec.crafts.woodturning and see if you get some other answers.
Walt Cheever

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.