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Pm3520b...

T

turner23

Joined
Aug 15, 2007
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Hey all Powermatic turners,

I was turning a green, 19"x9" maple bowl blank (between centers) - weighed in at just over 40 pounds, and I noticed while roughing out the outside that my headstock was moving slightly. This piece of wood was not completely balanced, and I couldn't have been spinning it faster than 200-250. My question is, is it normal for the headstock to 'flex' under these conditions? I'm under the impression that PM builds their lathes like tanks, and nothing is broken or damaged as a result of the turning, but it did catch me off guard, and I didn't like to see the 'flexing'. So to all you turners who turn big...have you ever experienced this? I haven't checked in a while, but at one point the lathe was perfectly level in every direction; I haven't looked to see if the leveling feet are still equally supporting the machine...Just wanted to see what you all thought.

Cheers!
 
I haven't turned anything any larger than that but I have only noticed vibration, no flexing. At least I don't think it was flexing. Did you check the headstock lock. I move my headstock once and did't lock it hard enough. I noticed an excessive amount of vibration and stopped the lathe. That's when I suspected the headstock lock so I checked it and it wasn't locked all the way.
 
^^

Yeah, forgot to mention I did check and the headstock was nice and tight. My suspicion is that my lathe may have settled on my uneven basement floor, and the uneven pressure on each of the 4 feet allowed a little flex...but who knows
 
Turner,
Can you describe exactly what was moving relative to something that was not moving? Might help identify the problem. Sounds like that whole end of the lathe was moving.
 
I did have a lot more vibration before I leveled my lathe. All 4 feet need to have the same weight to keep the vibration down. By leveling the lathe in all 4 directions (or 2 if you want to look at it that way) it reduced my vibration considerably. You can also get more vibration if the adjustable legs are extended very far. fortunately ( I think) I'm short enough that I lowered the adjustable feet all the way. Then leveled it by adjusting the feet as little as possible.
 
turner23 said:
Hey all Powermatic turners,

is it normal for the headstock to 'flex' under these conditions?

I have a similar problem with mine. I see the flexing on the tail stock end when a blank is on even if it is a low speed. I posted a year or so about it but didn't get a lot in repsonse. To look at my PM the extended quill looks as if it is turning in something of an oval fashion. The piece can be secured with jaws or woodworm screw. It will be interesting to see if any more information surfaces.
Thanks
Click to expand...
 
Mike,
Think I know the answer to yours. When I use the cup center on tailstock to apply a little pressure when clamping a piece in a chuck, the chuck will sometimes try to pull the piece a few thou. off center. This will actually deflect the tailstock quill slightly. When the lathe is turned on there may be vibration and the tailstock quill can be seen to move slightly. When the tail center is backed off just a bit the vibration stops and of course the ts quill stops moving.

Even if you bring the ts up to a pre-existing center on a piece that's already clamped in a chuck, the ts may deflect slightly. Remember we're only talking about a few thousandths of an inch.
 
A forty pound block of wood is a challenge for any lathe and often one side of it is heavier than the other. This particularly is the case when it's from a tree that grew at an angle rather than straight up. It's sometimes the case that not simply slow speed is the answer. If one has continuously variable speed, often a slight adjustment up or down will at least reduce the vibration.

The main thing is to remove wood so the block weighs less, turning at a slow speed. If this is impossible, re mount the block so it is better balanced or take it back to the band saw and remove a little wood from the side that is heavy.

I don't know your lathe but it's best not to place a lot of strain on the bearings.

Malcolm Smith.
 
Richard, you are exactly right. I do tighten down quite a bit and it can be large or small, it makes no difference.

As far as out of round, it can be a nearly finished piece. Keep in mind not all do this, at least to the extent of others.

I hoped this would help or conincide with the original question. I certainly don't want to take away from that thought.

Mike
 
Yes, there was noticeably a heavy side to the blank. As that heavy side came 'round, the entire head stock seemed to move...I noticed it most when I looked at front base of the headstock, where is sits on the bed. It looked like the headstock was actually rotating a couple of degrees, which is not possible due to the channel in the bed. I do have the lathe up about an inch on the levelers, and like I said, I'm not 100% that each foot shares the weight equally. I'm going to try to lower the lathe as low as I can (considering very uneven floors), and tighten the feet down.
 
The responses seem to suggest leveling, and keeping the levelers short is the answer. I don't have a PM, but hope to soon 🙂 I'm also tall (6'3"), how do people recommend raising the PM without causing this problem?
 
Maybe a rocking headstock?

A while back I had what sounds like a similar problem. First I tried cleaning under the headstock as described HERE. When that failed to fix the problem I removed the headstock and found it wasn't flat and I had to hone the high spots, as described HERE. Maybe this will help.
 
Ron, I'm also 6'3" and use 3" high oak blocks to raise my PM high enough that I have eliminated a back ache I always had when it was lower, granted I do at times hace a little sway to the whole thing if turning an out of round piece. It'll let you know where the sweet spot in speed is.
Bill
 
A good friend who owns an 3520 A called yesterday and asked if I had turned a B model. He said he had vibration problems from the banjo. It isn't as beefy as our A models. I told him that I had not experienced it when I demo'd on one but then I probably wasn't pushing the lathe either. I don't think that's your problem but may be worth looking at.
 
jerhall said:
A while back I had what sounds like a similar problem. First I tried cleaning under the headstock as described HERE. When that failed to fix the problem I removed the headstock and found it wasn't flat and I had to hone the high spots, as described HERE. Maybe this will help.
Click to expand...

Jerry - My headstock on my 3520b is rock solid. I've only moved the headstock once since I've had it. How often did you move your headstock before you noticed your gap?

I wonder if moving the headstock a lot without making sure the ways are really clean might lead to a buildup of crud under the leading edge. Cranking down on the locking mechanism with one edge slightly elevated might warp the bottom of the headstock and put a high spot in the middle. Then when the crud comes out with a future move, you are left with a rocking headstock.

I regularly turn very large out of balance pieces on my 3520b. Yesterday I had a 120lb piece that I couldn't spin much over 200 rpm to start without rocking the lathe. I've never had any flex in the headstock or tailstock. No vibration in the banjo either.

Ed
 
john lucas said:
A good friend who owns an 3520 A called yesterday and asked if I had turned a B model. He said he had vibration problems from the banjo. It isn't as beefy as our A models. I told him that I had not experienced it when I demo'd on one but then I probably wasn't pushing the lathe either. I don't think that's your problem but may be worth looking at.
Click to expand...

John - Do you have a picture of your "A" banjo you could post? My "B" banjo seem pretty beefy to me??? Maybe I don't know what I'm missing. I'm really curious now.

Maybe the locking mechanism on your friends "B" banjo needs adjusting or the bottom of the banjo needs cleaning?

Ed
 
Ed I'll post a photo later tonight. My friend said that the castings inside were slightly different as well as the post being offcenter and thinner. Some people like the offcenter post and some don't. I couldn't tell that it made any difference in the way that I turn.
 
Rocking Headstock

Ed, I was just at the stage as a turner of scaling up the size of my blanks to max when I noticed the rocking by putting my finger next to the ways and the surface of the headstock. It is possible that I induced the high spot along the lock down shaft as you suggest, but I really don't think so. As the posts indicates at least one other turner had that problem, and ultimately sold the lathe. I could easily find the two high spots shown in the picture with a good straight edge and measure it with feeler gauges. Since I have honed it to measure flat no more problem. I also turned a long handle to give me better access to the lock down, and to make sure I can cinch it snug. No more problems in the last couple years. I really believe it was a manufacturing problem. I move my head stock all the time, and turn big blanks. Every so often I give it the finger test with a heavy out of round blank. No recurrence. That all said I keep my ways clean, and my headstock snug. Jerry
 
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