Pm 3520c headstock not locking solid

[Mike Novak]

Hi

I’m getting a lot of vibrations on my 3520c. After a lot of testing, I have found that the joint between the headstock and bed ways is not locking up solidly. When it’s vibrating, if I put my finger over the joint, I can feel the movement between headstock and ways. Even with very light cuts I sometimes get vibration severe enough I worry it will damage the electronics in the drive.

Here is what I have done so far to correct it, with no luck:
1) double checked level and all 4 feet on ground with even pressure.
2) double checked alignment between headstock and tail stock. This should rule out any twist in the bed.
3) used a fine stone to smooth out any small dings in the ways.
4) glued fine sandpaper to ways, and used that to lap the mating surface on the headstock flat.
5) made sure the underside of the ways where the clamps block hits is clean with no burrs or dings.
6) adjusted the clamp block so I can get maximum pressure when locking the handle. In other words, the eccentric is near top dead center when locked.
7) tested on a different drive pulley to rule out any weird harmonics in the drive.

So two questions for this group, especially if you have a 3520c

Should the joint between the headstock and ways be perfectly solid? Am I expecting too much?

If it should be perfectly solid, what else should I be looking for?

 

[Richard Coers]

Make a larger clamp block. More area, more pressure. Of course the joint should be solid. I have no idea what perfectly solid would be. The locking lever is large, put some more muscle in it. Don't lock it from the front, go around and use both arms. You need to apply more pressure than is used on the tailstock. You may want to use a piece of float glass and some bluing to check the flatness of the bed and headstock. But my guess is you aren't putting enough torque into it. Call Powermatic and ask if you can use an extension pipe to tighten it down.

 

[Dean Center]

Yes, it should lock solidly. How long have you had the lathe? Has it always done this or is the problem new? Where along the bed do you have the headstock positioned? (over the leg/at one end would be most solid) Have you tried sliding the headstock to a new location? (could there be a rough spot or burr on the underside of the way(s)?) My first thought was that you'd gotten some debris, like a piece of wood chip, underneath the headstock, but that would have shown up with your already thorough investigation. Hopefully somebody more knowledgeable than I can chime in.

With respect to Richard, it shouldn't take a platoon of longshoremen to lock it down.

 

[Mike Novak]

I have had the lathe a couple years. Bought it used. Vibration has been a problem right along.

I put as much pressure on the clamp lever as I can. So much I need to use my mallet to unlock it.

I think next step is to make up a larger clamping block.

Not sure where to get float glass?

 

[Lou Jacobs]

Long shot here: is it possible that the bolt that goes through the clamp block has worn/sloppy threads? Poor mating between the nut and the bolt could keep it from staying tight. I have this lathe, going on 4 years old, and the headstock mates to the bed perfectly with only moderate pressure on the lever. I’ve never felt an issue with vibration between the two components.
Follow-up question: have you checked that the leg attachments to the bed are all tight?

 

[Russell Nugent]

Just about an glass shop will have float glass. It's extremely flat because of its manufacturing process. I use a piece of 3/8 float glass for flattening hand planes.

 

[Isaac Fisher]

You need to adjust the locking mechanism. The eccentric cam should not go to top dead center when you lock it.

 

[Brent@TurnRobust]

With the headstock clamped down, check to see if there is a gap between the headstock and lathe bed using feeler gauges. The thinnest one in most sets is .0015, which is about half the thickness of a sheet of common typing paper. You shouldn't be able to get it inserted anywhere. It might start just a wee bit, but it shouldn't go freely into any contact area. If you can't get the feeler gauge insertered, your vibration may be elsewhere. For instance, on any lathe, it's also really important that all four feet are carrying about the same amount of weight. To find out if one of them is not carrying their load, get something running out of balance on the lathe, and then check each foot for vibration like you did on the headstock. Put your finger on the foot and and on the floor at the same time. If one of them is wiggling more than the other, lengthen out your leveling pad a bit, or slip a thin shim underneath that foot. Also, putting a thin hard hard rubber mat - think conveyor belt, under each foot does wonders for minor, but annoying vibrations. Where I live, "baler belting" which comes in 4" widths at any farm service store, works great for this application. Spongy rubber may actually exacerbate vibration.

 

[Doug Rasmussen]

, if I put my finger over the joint, I can feel the movement between headstock and ways. Even with very light cuts I sometimes get vibration severe enough I worry it will damage the electronics in the drive.

That seems to be very telling. In my experience the finger test can be surprisingly accurate at detecting very fine movement.

I don't know anything about this lathe or its clamping mechanism. But my first thought is to try and slip a shim between the bed and the headstock at one end when the clamp is fully loosened. Even a layer or two of paper might be enough.

Surely a call to PM tech support would be a good idea.

 

[robo hippy]

It should lock down solid. First I would clean off the bottom of the headstock because wood chips and dust can work their way under there. In my experiences, if chips get under there, the main thing this did was make it so that the tailstock and headstock did not line up perfectly. Sounds like you did that. Next, I would check the nut that holds the pressure plate in place. They are locking nuts, usually with nylon inserts to keep them in place, and they can work loose after lots of use. I think the old pressure plate on my 3520A was about 4 inches wide by 6 or so long. I think I would want my pressure plate to be slightly concave rather than convex. That would make for better clamping than one that is convex. I would not expect that to be an issue though. That should be sufficient to keep the headstock stable, but bigger would not hurt. For sure, you don't want the same pressure plate on the headstock that is used on the tailstock or banjo. Other than that, I don't know.

robo hippy

 

[Joe Kaufman]

Check for paint on the underside of the bed where the clamp block contacts the bed. I had areas of complete paint coverage around the bed casting cross braces. Looks like the machined surface wasn't masked before painting. The paint is difficult to remove.

 

[Bob Vaughan]

 

[Darryl Fective]

I worry about the suggestion of more leverage on the locking arm. I'm no metaulurgist or engineer, but if the ways get pulled upward at all, it could create a high spot that makes a rocking action even more likely, no matter how much you reef on it. If you slide the whole thing over a few inches and clamp it, is it the same, or improved?

I think checking that the bed ways are clean, straight, and coplanar is a good start. Same with the mating surfaces on the bottom of the headstock. May need some muscle and a set of gauge blocks for that.

 

[Lou Jacobs]

View attachment 65178

Bob, this looks like it could well be Mike’s issue, but I wonder if you could have just ground down those high spots that were rubbing on the headstock casting? Or did you feel that the steel plate would be a more rigid solution?

 

[Bob Vaughan]

I first considered grinding the high spots down but a full length plate seemed a better solution. Those four gripping points seemed like a chance to flex.
When the 3520 first came out, this was a problem area. I've seen a clamped 3520 headstock fall in the floor. This was on Christian Buchard at Arrowmont. I happened to be in the shop that day and saw it happen.

I suspect subsequent models and improvements may have eliminated that risk. I'd hope so anyway. After seeing that failure, I decided I didn't want anything to do with that original clamp.

 

[Lou Jacobs]

When the 3520 first came out, this was a problem area. I've seen a clamped 3520 headstock fall in the floor. This was on Christian Buchard at Arrowmont. I happened to be in the shop that day and saw it happen.

Wow! Thanks for the fascinating clarification. Was this an earlier model than the C?
Whoops, on closer re-reading I see you said an earlier model. Sorry!

 

[Gabriel Hoff]

Hi

I’m getting a lot of vibrations on my 3520c. After a lot of testing, I have found that the joint between the headstock and bed ways is not locking up solidly. When it’s vibrating, if I put my finger over the joint, I can feel the movement between headstock and ways. Even with very light cuts I sometimes get vibration severe enough I worry it will damage the electronics in the drive.

Here is what I have done so far to correct it, with no luck:
1) double checked level and all 4 feet on ground with even pressure.
2) double checked alignment between headstock and tail stock. This should rule out any twist in the bed.
3) used a fine stone to smooth out any small dings in the ways.
4) glued fine sandpaper to ways, and used that to lap the mating surface on the headstock flat.
5) made sure the underside of the ways where the clamps block hits is clean with no burrs or dings.
6) adjusted the clamp block so I can get maximum pressure when locking the handle. In other words, the eccentric is near top dead center when locked.
7) tested on a different drive pulley to rule out any weird harmonics in the drive.

So two questions for this group, especially if you have a 3520c

Should the joint between the headstock and ways be perfectly solid? Am I expecting too much?

If it should be perfectly solid, what else should I be looking for?

If you absolutely had to, could you bolt the headstock to the ways? Then it would become a fixed headstock lathe and you never have to worry about it vibrating or moving. Just a wild suggestion if all else fails...

 

[Bob Vaughan]

Let me clarify "early".
Around 1997.
My 3520 is now so old I have to use orthopaedic turning tools.

 

[Mike Novak]

View attachment 65178

I’m amazed how much they cost reduced the clamping plate. This is what it looks like on a “c”. 3.75” steel disc 9/16 thick. I’m going to make a better block

 

[Bob Vaughan]

Yuk!
Making a better clamping plate is a good call. The bed gap should be 2.5" or was when they first started out. It may be some metric variation these days.
I've no idea what that groove is for.
That took some effort to get that head off and upside down for that photo.

 

[Vincent Vogel]

This is really dissapointing to hear, I was thinking about buying a 3520C while they are 15% off. Now I have to think about whether it's worth the money or look at someting else.

 

[Lou Jacobs]

I've no idea what that groove is for.

I believe what you’re seeing as a groove is really the “tenon” (for lack of a better word) that extends below the headstock to fit in the bed gap. I may be wrong.

This is really dissapointing to hear, I was thinking about buying a 3520C while they are 15% off. Now I have to think about whether it's worth the money or look at someting else.

Vince, as I said in my earlier response, I’ve got a four year old 3520C and have not had a similar experience with the headstock locking down tightly. It’s always been rock solid. If you’re thinking of buying this lathe, can you find one to test drive and see what you think?

 

[Vincent Vogel]

I believe what you’re seeing as a groove is really the “tenon” (for lack of a better word) that extends below the headstock to fit in the bed gap. I may be wrong.

Vince, as I said in my earlier response, I’ve got a four year old 3520C and have not had a similar experience with the headstock locking down tightly. It’s always been rock solid. If you’re thinking of buying this lathe, can you find one to test drive and see what you think?

Thanks Lou, I'm going to look at a 3520B that a guy in our woodturning club has on Monday (it's not for sale but going to look and see what one looks like). I called Rockler and Woodcraft and they don't have any in stock to look at.

 

[Lou Jacobs]

I called Rockler and Woodcraft and they don't have any in stock to look at.

Vince, if you’re ever on the road from Butler going through Baltimore, you’re welcome to stop by and check mine out. (Though this is a 3520 C, not B) .

 

[R Henrickson]

Thanks Lou, I'm going to look at a 3520B that a guy in our woodturning club has on Monday (it's not for sale but going to look and see what one looks like). I called Rockler and Woodcraft and they don't have any in stock to look at.

Based on extensive experience with both Bs and Cs, I would definitely recommend a used B over a new C -- and not just because of the money saved.

 

[Bob Vaughan]

I believe what you’re seeing as a groove is really the “tenon” (for lack of a better word) that extends below the headstock to fit in the bed gap. I may be wrong.

Vince, as I said in my earlier response, I’ve got a four year old 3520C and have not had a similar experience with the headstock locking down tightly. It’s always been rock solid. If you’re thinking of buying this lathe, can you find one to test drive and see what you think?

A tenon it is. Had I looked at the photo more carefully, I wouldn't have asked that question.

The cam mechanism for the headstock is necessarily flimsy compared to what it could have been. This design feature limits the the clamping force of the headstock clamp. A more robust clamp handle and shaft may risk damage to the bed rails. In the years I've been using my 3520, a moving headstock has never been an issue with the shop-made clamping plate.

A new user may try to use the tailstock ram to compress the drive/live centers in the wood and run the lathe that way. Not a good strategy because too much pressure can indeed make the headstock slide, but that much pressure will also have a bad effect on the turning.

 

[Dave Landers]

I have a 3520B - this is the headstock clamping plate:

Looks about the same as the one on the tailstock (the manual does have different part numbers).

I've had my B for around 8 years - never had a headstock vibration problem. Although a couple months ago, I had spindle alignment issues that turned out to be gunk buildup under the headstock. Didn't take much debris to throw it off - I could sure see how debris in a strategic spot could also end up with vibration (although it sounds like you've cleaned yours up way better than should have been necessary).

 

[robo hippy]

View attachment 65178

Bob, I am trying to figure out how that was able to rub on the headstock. That should not be an issue. I had a 3520A and it had a cast iron pressure plate. I broke it when coring some black locust. Fortunately the headstock just tipped forward on the lathe bed and the bowl stopped it from falling all the way off. They balked at sending me a new one. I told them that the newer models, still A's, switched to a metal plate for a reason and to send me one. The one that came was too thick for the screw that was on the bottom, but a neighbor welded up a 1/2 inch thick plate, about 4 by 6 inches, with 2 spacer bars to sit in the ways of the lathe.


As for bolting the headstock down, that may eliminate some of the vibration, but not all of it. A "new" thing in lathes over the last 20 or so years, is a cone or bell housing for 'added clearance' away from the headstock tower. This is supposed to give 'better' access to the bottom of the bowl, which can come in handy for twice turned bowls. What this does mechanically, is put your mounting spot farther off of the headstock, which adds to vibration issues. This is similar to what happens with hollow forms. If you engage the tailstock, vibration issues go away. I prefer to turn without the tailstock. This is the main thing, as far as I am concerned, that gives a vibration advantage to the Vicmark lathes. Look at their headstock and the mounting point for your chuck is closer to the headstock than any of the cone/extended headstock lathes. My 3520A had a slight notch in the headstock tower to allow for better access to the bottom of a twice turned bowl. I never used the tailstock on it when turning bowls. If I was to do twice turned bowls, I would probably finish turn at least half of the outside of the bowl before reversing. I have found that a BOB (bottom of bowl) gouge does seem to do a better job of getting that lower part of a twice turned bowl. I have a couple of spindle detail type gouges with a ) shaped nose and 65 degree bevel which are ideal for this purpose.

robo hippy

 

[Bob Vaughan]

Bob, I am trying to figure out how that was able to rub on the headstock. That should not be an issue.

robo hippy

The tops of the early clamp plates and the bottoms of the headstocks were 'as cast'. The yellow line of paint can be seen on either side of the plate in my new plate photo. The top the original clamping plate was also 'as cast'. Mike Novak's nice photo shows the bottom of the later headstocks to have been machined. On the USA-made models this casting roughness on the opposing surfaces sometimes touched under pressure and thus prevented full potential clamping pressure. I doubt if all of the early lathes had this tolerance issue, but some surly did.

I'll agree to a point about the extended nose headstocks can be whippy. Some makers have been very successful in addressing this problem. Below is a spindle to the Powermatic 3420 (bottom) and a spindle from a Oneway 2436 (top). This contrast should speak for itself with no excuses.

 

[Vincent Vogel]

Based on extensive experience with both Bs and Cs, I would definitely recommend a used B over a new C -- and not just because of the money saved.

I would be interested in what is better about a B model over the new C model. A new one will have a warranty and a used one most likely won't.

 

[Dave Landers]

I would be interested in what is better about a B model over the new C model. A new one will have a warranty and a used one most likely won't.

I have a B and have demoed on a C a number of times (and our club has a C).
The C has a movable magnetic control panel, and the side of the bed ways are flat rather than curved (so the controls or any other magnetic thing will stick).
The C's indexer is easier to use and has 48 positions (7.5º) vs the B's super-awkward 36 (10º) positions.
The C finally updated the spindle lock to one that will stay locked.
The tool rest lock in the banjo is bushing clamps rather than set-screw and holds the tool rest much more securely, but it takes some getting used to. It requires more care/attention to remove/replace a tool rest.
The headstock spindle has a larger "bell" or whatever it's called so the bulk of the headstock is less likely to get in the way.
Most of the rest is functionally unchanged.
IMO, about the only thing they didn't "fix" is the banjo and tailstock still bump into each other, and the tailstock "leans backward", requiring you to extend the quill farther than should be necessary.

 

[R Henrickson]

I have a B and have demoed on a C a number of times (and our club has a C).
The C has a movable magnetic control panel, and the side of the bed ways are flat rather than curved (so the controls or any other magnetic thing will stick).
The C's indexer is easier to use and has 48 positions (7.5º) vs the B's super-awkward 36 (10º) positions.
The C finally updated the spindle lock to one that will stay locked.
The tool rest lock in the banjo is bushing clamps rather than set-screw and holds the tool rest much more securely, but it takes some getting used to. It requires more care/attention to remove/replace a tool rest.
The headstock spindle has a larger "bell" or whatever it's called so the bulk of the headstock is less likely to get in the way.
Most of the rest is functionally unchanged.
IMO, about the only thing they didn't "fix" is the banjo and tailstock still bump into each other, and the tailstock "leans backward", requiring you to extend the quill farther than should be necessary.

I owned a B for several years. I bought it used. As far as I know it is still doing fine for the new buyer after eight more years. They are nearly indestructible. I sold it for 90% of what I had paid. I also had a Jet 1642 which I kept. I preferred the Jet to the B.

Indexing on the B was poor (such as not being able to do 45* intervals!). Even wth the C, however, I think it is more convenient to use an indexing wheel.

I have encountered a variety of minor quality problems on the C. The final point about the basic design made above is crucial -- not only do "the banjo and tailstock still bump into each other" -- I think a bump-out has been added to the base of the C tailstock. In combination with the tool rest hole being left of center on the banjo, with certain lengths between centers you have only about half the extension of the quill available after you extend it across the gap. Perhaps not a problem if you turn medium or larger bowls, hollow forms, and pieces longer than a few inches.

I've also wondered what the covered space in the PM tailstock is intended for -- perhaps live center storage? I do a lot of relatively small small turnings. I've found that if I open that cover so that my hand can move into the open space created I have better access and greater freedom of movement for working close to the axis. Useful in working on small pieces.

 

[john lucas]

The C also has acme threads in the tailstock quill. Makes extending tge quill much faster and tge threads are square and beefy.

 

[Dave Landers]

I've also wondered what the covered space in the PM tailstock is intended for -- perhaps live center storage? I do a lot of relatively small small turnings. I've found that if I open that cover so that my hand can move into the open space created I have better access and greater freedom of movement for working close to the axis. Useful in working on small pieces.

Friend of mine says it's to keep shavings out of your soda.
I removed the door on mine and it's now convenient to have a place to set small things etc.

 

[Richard Coers]

Yes, it should lock solidly. How long have you had the lathe? Has it always done this or is the problem new? Where along the bed do you have the headstock positioned? (over the leg/at one end would be most solid) Have you tried sliding the headstock to a new location? (could there be a rough spot or burr on the underside of the way(s)?) My first thought was that you'd gotten some debris, like a piece of wood chip, underneath the headstock, but that would have shown up with your already thorough investigation. Hopefully somebody more knowledgeable than I can chime in.

With respect to Richard, it shouldn't take a platoon of longshoremen to lock it down.

We have no idea if the OP's strength. Based on our demographic, he may be arthritic, weakened from nerve damage, or no restrictions at all. Maybe he can't apply the same strength as you. I just suggested an extension that requires less muscle. I assume you have never worked on farm machinery or big trucks. A piece of pipe is in everyone's tool box if they work in those trades. I don't understand why the great exaggeration of "a platoon of longshoremen". I don't see that as showing respect at all.

 

[Lou Jacobs]

I've also wondered what the covered space in the PM tailstock is intended for -- perhaps live center storage?

I keep my live center, wireless earbuds, wireless remote for the dust collector, and occasionally a baggie of nuts or other snack in there. It’s very handy.

 

[Dean Center]

We have no idea if the OP's strength. Based on our demographic, he may be arthritic, weakened from nerve damage, or no restrictions at all. Maybe he can't apply the same strength as you. I just suggested an extension that requires less muscle. I assume you have never worked on farm machinery or big trucks. A piece of pipe is in everyone's tool box if they work in those trades. I don't understand why the great exaggeration of "a platoon of longshoremen". I don't see that as showing respect at all.

I meant no disrespect, Richard. I just didn't want the OP to think it was simply a matter of using a great deal of force. That was how I read your prior suggestion. The Internet's wonderful ability to generate misunderstandings strikes.

 

[Mike Novak]

Looks like the problem is the bottom of the headstock was not quite flat. It was slightly convex. Less than a .0015 shim. I filed down the center portion a bit and the vibration is greatly reduced. I need to file it a bit more to get it perfect. Thanks for all the ideas!

here are some of my observations about the “c”.

The tail stock design does impose some limitations. The tail stock leans back, and the clamp block sticks out front so you can’t get it right up against the tail stock. There have been times when this was an issue.

For the tool rest clamp, I added a spring between the two clamp blocks to push them apart. This eliminated needing to fuss with it when changing tool results.

It’s called a 3420, but it’s not long enough to put a 34” workpiece between centers unless the headstock and tail stock are both hanging off the end of the ways. I suspect the tail stock design was to save iron by making the ways shorter.

I would have preferred a 3 speed pulley. They got it down to two by over speeding the motor. It works, but can be really noisy.

All the improvements people have mentioned over the b are really nice.

 

[Bob Vaughan]

I'm delighted to see that the problem source has been defined and a solution executed. A convex bottom shouldn't have been there but sometimes things can slip through quality control. I had to solve a little glitch on my 3420 when I first got it.

 

[robo hippy]

I turned some table legs on my A, and there was just barely enough room for a 29 1/4 inch table leg. I think it does measure 34 inches between the tailstock quill and the headstock spindle mount. My Robust was one of the early ones, and it has 3 speeds, and I agree that is my preference. I have a Vicmark 240 which also has 3 speeds. One other thing they should do is have minimum shut off speed at 10 or so rpm. I have ranted about this part before. With the B and C models, I think low speed range is 1200. For me, that was too slow for some of the smaller bowls I was turning. I could get used to it though. For coring, you need the low speed range. If some one ever comes up with an automatic transmission for changing lathe speeds, it would be a good idea. If I wasn't retired, I think I would have my own lathe built, but too many other things to do....

robo hippy