Vibration on PM 3520B.

[Hilel Salomon]

In another thread, I related how a large walnut bowl exploded. My first reaction, after first aid that is, was that the bowl was spinning too fast. That may still be the reason, but I've also noticed that lately, large rough blanks get the lathe skipping and hopping as I'm roughing them out, and it may be that the machine is vibrating more than it should. Recently, I had to get my hydraulic table/cart out and move the machine back to its original position.
Is there some way I can measure or determine if something is wrong w/the headstock? Should I add sand bags to increase the weight of the machine? Up until recently, I didn't have a noticeable problem, but perhaps there is a question regarding the headstock that I need to address.
Thanks, Hilel.

[Gary Max]

Slow your speed down---the wood will flex less. This may be just me but I never move the belt---it stays in low range.
I have a 4224 and if it jumps around I am doing something wrong.

[Steve Schlumpf]

Hilel - if you moved your lathe, then chances are that you need to level it again. You would be amazed at how much a lathe will flex when it is just slightly off level!

[Jeff Nicol]

Hilel, I was having some trouble after I had a large blank on the lathe and sped it up to much and it jumped around and moved it out ov level. It was still between centers so that was good. But any way I added 200lbs of sand in a 7" deep box on the shelf I have the width and length on the legs. Now I have not had any trouble but still make sure to watch the speed when the blanks are out of round. Bumpy bouncy learning is no fun!

Jeff

[Tom Hintz]

I've never had a problem with my 3520B but I always start new blanks very slow and gradualy bring the speed up as I get it more round/in balance. I have had some 50-pound-plus chunks on it and never had it move or anything without extra weigtht added.

[Dan Forman]

Moving it at all can cause it to go out of level, even if all legs are touching the floor, the cast iron can flex. I added a ballast box with sand like Jeff, but also put three concrete blocks construction blocks on top of the head stock, which helped reduce vibration for me. There is something about having the center of gravity near the spindle which aids in reducing vibration. I found that by doing a search a while ago when I was having the same problem as you.

Another mod I did was inspired by Jeff - he made an oak trestle for his lathe to sit on, replacing the leveling feet that came with the lathe, which also raised the lathe higher. I didn't need any more elevation, but once I got the lathe leveled, I measured the distance between each foot and floor, and made individual oak risers for each foot. I still needed to make a couple of shims to fine tune (veneer thin slices on the bandsaw), but that dial out most of the residual vibration. The levelers that come with the lathe are not all that substantial, and allow for some movement when set high, as was required on my sloping basement floor.

I'll post a pic of this later.

Dan

[Dan Forman]

Here is the thread that talked about ideal weight distribution for taming vibration, look toward the bottom of page one and top of page two.

http://www.sawmillcreek.org/showthread.php?t=101271&highlight=vibration

Dan

[Dan Forman]

Here are some pics of my stabilization efforts. In addition to the sand ballast box in the usual spot...

http://i98.photobucket.com/albums/l279/T-Caster/P1020301.jpg

This is my attempt to raise the center of gravity as suggested in the thread I linked to earlier. I think I'll make a wooden platform to raise them higher, effectively raising the C of G without adding more weight, and giving me a few more cubby holes too, which, incidentally, remain free of chips, unlike the top of the headstock before the bricks, where I used to keep my odds and ends.

http://i98.photobucket.com/albums/l279/T-Caster/P1020305.jpg

I also replace the adjustable feet with these oak blocks, which are stuck to the legs with double stick tape, just in case the lathe begins to hop about some. I did have to slice a couple of very thin shims on the band saw to make fine adjustments. I leveled the lathe first, then measured the distance from the bottom of each leg to the floor with a dial caliper, and set the fence by trial end error with a scrap until I had it right, then cut the blocks. Came out pretty close.

Both of these steps resulted in a noticeable reduction in vibration with an unbalanced load, so it's worth the trouble. I tried removing the sand ballast to see if it helped once the bricks were in place on the head, and it did, so I put it back. So much for pure theory.:D

Dan

[Angie Orfanedes]

Dan...aren't you worried that the concrete blocks may flop over on the spindle, and ...aaaaargh!

[Jerry Sambrook]

Lyle Jamison's Bowl Making video gives a real good tip about balancing out a lathe for vibration.

In reality, the lathe does not have to be level, it does need to have equal pressure on all four feet during the turning stage.

He did a nice job of winding up the lathe to a slow/moderate speed, and then showing how to remove the vibration at that point. Then you can ramp up the lathe even more (if so inclined).
Actually, Lyle has quite a number of good little tidbits of information in his video set.

The other thing is to pin the lathe in place with two bolts into the floor so that the lathe does not walk. Then, once set for a better vibration free mode, it will tend to stay that way for a long time.
The reason for only two, is you do want some flex in the system, so that there are no internal stresses built up through the machine.
You don't even have to firmly bolt it down, just have pins long enough to keep the lathe from walking

Jerry

[Dan Forman]

Dan...aren't you worried that the concrete blocks may flop over on the spindle, and ...aaaaargh!

Nope, they aren't going anywhere, gravity and friction are your friends. I wouldn't use a speed that would induce enough vibration to move them.

Dan

[Dan Forman]

Lyle Jamison's Bowl Making video gives a real good tip about balancing out a lathe for vibration.

He did a nice job of winding up the lathe to a slow/moderate speed, and then showing how to remove the vibration at that point. Then you can ramp up the lathe even more (if so inclined).
Actually, Lyle has quite a number of good little tidbits of information in his video set.
Jerry

I'd like to see that!

Dan

[jason lambert]

I bought the 3520B and I have a nasty vibration between 800 -1200 RPM. Lathe alwas did new out tof the box, doesn't matter if I move it or level it etc. Anyhow power matic sent out some repair place that had never worked on a lathe they came twice replaced the pully and belt and scratched it all up finally they told me it is a harmonic vibration and there is nothing that can be done. I called powermatic and wanted a new head piece and I would send them the one back I had but never got any were.

Anyhow be careful around certain speeds. Mind will blow things apart in the above range I can't turn big things at all in that range with out chatter or vibration or it flying off at me, weight might help but I am not going to try balancing cinder blocks on a vibrating lathe.

[JerHall]

Hilel,

You mentioned a concern about the headstock. Years back my headstock base ended up slightly out of flat which resulted in the problem you described. I honed it flat and that did the trick. See discussions:
http://sawmillcreek.org/showthread.php?t=116980
and http://mustardmonster.weebly.com/ (go to the Mechanical/Maintenance page, then "head stock rocking")

This problem is not obvious, but deadly if it exists. I also turned a long handle for the headstock cam lock to make it easier to lock the headstock down.