Check for twist in lathe bed
Quote:
Originally Posted by
Roger Chandler
.. The leveling system is pretty much like the 3520b on the G0766.
(Sorry if this has been checked and I missed it. This is a long thread.)
Before experimenting with the leg loading, I suggest testing for twist in the lathe by checking the alignment of the headstock and tailstock. Correcting twist with the leg levelers can equalize stress in the bed casting caused by even slight unevenness in the floor or improper leveler adjustment. The entire cast iron/steel bed can easily flex and twist significantly. Checking for and adjusting for this is the FIRST thing I do when moving a lathe, even if a short distance. I want the alignment perfect on my lathes.
If you look up "wood lathe tailstock alignment" you will find all sorts of things recommended including adding shims and pressing on the tailstock while tightening. I actually shimmed the tailstock on my first Jet 1642 before I found out about the simple leg adjustment technique.
The procedure, very quick. Put a drive center with a point in the headstock. Put a live center (or even another drive center with a point) in the tailstock and slide the tailstock until it the points almost touch. If the two points are in perfect alignment, good.
If the points are in horizontal alignment when looking straight down but out of vertical alignment when looking from the side, this is bad. I have not yet seen this on any of the lathes I've checked.
If the points are OUT of alignment horizontally, a common issue, the fix is usually easy.
- If the tailstock point is too far towards you, twist the bed back into alignment by raising an appropriate leg - the easiest is the front leg on the tailstock end of the lathe. Untwist the bed by cranking UP a bit on the adjuster or with a shim under the leg. This should pull the two points into perfect alignment.
- If the tailstock point is too far towards the far side of the lathe, adjust either the far right or front left leg.
I have had to do this on both of my Jet 1642s and my Powermatic 3520b after moving them. Each time it brought the lathe back into alignment.
A recent case: When turner Mark StLeger was doing an all-day demo at the Knoxville club last April he noticed the tailstock and headstock were out of alignment on the club's Jet 1642. This was a problem for a precise operation he was planning. I opened my big mouth and said I could fix it. During a break a few seconds of leg adjustment put the tailstock into perfect alignment. Whew! Actually, I wasn't worried since I had aligned that same lathe the same way several times in the past since it gets moved around a lot.
When I'm demoing something that can benefit from the tailstock alignment I always check the lathe and align it before I start. Such alignment is as not critical for spindles between centers but it can cause all kinds of issues when using the tailstock close to the headstock, such as when working on turned boxes, vessels, platters and bowls, or with thin spindles held tightly on the drive end and with the tailstock on the other end. Problems from alignment can be worse with hard, dry woods.
I don't know if this alignment will have any affect on the vibration issue in this thread, but I would check it first.
BTW, leveling the lathe (or table saw, etc) to the earth's gravity is nice but usually not necessary. What IS necessary is that the bed of the lathe or the table of the saw be in a perfect plane. A twisted bed or frame can cause a variety of problems. IMHO. Now for a billiards table...
JKJ