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PM 3520 mounting it to a cement floor

Eldon DeHaan

Eldon DeHaan

Joined
Dec 11, 2009
Messages
20
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97
Location
Salt Lake City, Utah
... I don't want to dance any more. I trying to find our what to use to keep my PM from dancing when I turn off centered work. I typically use 1 1/2" x 12" x 12" soft maple, faceplate mounted and I move my 4" FP to different positions on the back of stock to create different center points of turning. See the attached finished work to get an idea of what I turn. 1-DSCN0971.JPGMy first attempt was to add a shelf and 6- 60lbs bags of sand. I have the 18" bed extension in the lower position and the head stock moved all the way to the end to utilize a larger diameter wood. I love this feature for this type of work. Anyway in this situation I could only get about 425rpm with our shaking the crap out of the lathe when I moved the face plate to and off center location.
The second attempt was to remove the sand bags and bolt the lathe to the floor by placing an 1/2" x 2" x 23+" steel bar drilled to slip over the top of the levelers and then bolted the bar to the the floor on each end, using 4- 1/2" x 6" weage bolts. Since my floor was not level I ended up screwing the levelers down about an inch and a half from the base of the leg, big mistake. I thought I was all set..put my off center work on the head stock and slowly brought up the speed. At about 530rpm I was back at doing the dance, and I am now left with 2 bent leveling legs and a lathe that has its mind set on dancing.
Any ideas or thoughts...Thanks
 
Eldon DeHaan said:
... I don't want to dance any more. I trying to find our what to use to keep my PM from dancing when I turn off centered work. I typically use 1 1/2" x 12" x 12" soft maple, faceplate mounted and I move my 4" FP to different positions on the back of stock to create different center points of turning. See the attached finished work to get an idea of what I turn. View attachment 7827My first attempt was to add a shelf and 6- 60lbs bags of sand. I have the 18" bed extension in the lower position and the head stock moved all the way to the end to utilize a larger diameter wood. I love this feature for this type of work. Anyway in this situation I could only get about 425rpm with our shaking the crap out of the lathe when I moved the face plate to and off center location.
The second attempt was to remove the sand bags and bolt the lathe to the floor by placing an 1/2" x 2" x 23+" steel bar drilled to slip over the top of the levelers and then bolted the bar to the the floor on each end, using 4- 1/2" x 6" weage bolts. Since my floor was not level I ended up screwing the levelers down about an inch and a half from the base of the leg, big mistake. I thought I was all set..put my off center work on the head stock and slowly brought up the speed. At about 530rpm I was back at doing the dance, and I am now left with 2 bent leveling legs and a lathe that has its mind set on dancing.
Any ideas or thoughts...Thanks
Click to expand...

Bolting to the floor using shims instead of the leveling bolts would be a more substantial mounting. It may be necessary to drill the holes in the legs out to use large enough wedge bolts. But, even with a positive attachment to the floor, flexing in the legs and headstock will be noticeable. Regardless of the method used to hold the lathe to the floor, whether by bolting or weighting, a piece that is out of balance will increase the loading on the bearings and structure of the lathe. If the lathe is bolted, the likelyhood of using increased rpm's and greater imbalaces is higher.

A method of counterbalancing the offset turnings would be much better for the machine. From your description, it sounds like you are screwing a faceplate to several locations on the backside of the turning to obtain the different offsets. If so, then you are already dealing with the screw holes left from the multiple faceplate locations. Attaching weight(s) to the backside to balance the piece when offset would result in additional screw holes, but if your method eventually removes or covers the faceplate screw holes, the counterweight attachment holes should not be an issue.
 
You are in the right track to get the lathe level.
You can pour 4 pads on your floor and get those level then bolt the lathe on those.


Ditto on balancing the turning. If you get a good balancing system you may not need to bolt the lathe to the floor.

You might screw a 25" 3/4" plywood disc to a 10" faceplate. True up the edge
Then screw the work to plywood disc and move it off center by screwing it in a new locations.
Remember to put the screws where you don't plan to turn. :-)

Counter weights can be screwed to the back of the plywood disc.
Small faceplates or extra chuck jaws work for counter weights as will any chunk of metal with holes for screws.
Distance from center changes the effect of the weights. Further out makes it weigh more....

The idea is to get the plywood disc and all the stuff screwed to it in balance so that if you spin it by hand it does not have an obvious heavy side.
If it has a heavy side screw more weights on the light side.

Have fun,

Al
 
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I agree with Dale that balancing the work piece is the proper solution. Trying to bolt it down amounts to masking the real problem and would result in much greater stresses in the structure as well as the bearings. It probably also would not completely stop the lathe from shaking. Our club did own a Powermatic lathe and just rolling it around and transporting it for several years was enough to develop serious cracks in the cast iron legs. I can imagine that bolting the lathe to the floor and turning lots of out of balance things could eventually cause the same thing to happen to your lathe. As Dale and Al suggested, counterweights can be used to balance the piece. The bearings will thank you and it won't be necessary to take extreme measures to keep the lathe from walking.
 
I have the Jet 1632 which is the smaller cousin of the 3520.

I drilled out the leveling pad holes then set red head wedge nuts into the floor to match the holes in the legs. I used the nuts instead of the bolts so I didn't have to lift the lathe over the studs sticking out of the floor.

http://www.homedepot.com/p/Red-Head-3-8-in-x-1-5-8-in-Steel-Drop-In-Anchors-50-Pack-01891/100154222

I used shims of plywood to level the lathe. I started with 1/2 BB ply cut square slightly larger than the feet and drilled a hole. I added 1/8" masonite shims to rough level it, and then shaved the plywood until level.

I cut threaded rod and inserted it through the hole into the wedge nut and added a regular nut and washer on top to complete the job.

The result is a significant reduction of vibration and a total reduction of lathe walking across the floor.
 
I'm the odd gal out, and I approached it a different way. I make tons of off center work. Since the movement is at the head & caused at the head, I bolted my lathe to a very heavy cabinet that holds wood and heavy metal, and then bolted the cabinet to the wall. Hard to shake a whole house! this approach has worked for me for 20+ yrs.
 
One of my friends used to turn very out of round hollow forms. To stabilize his 3520 he increased the foot print. He added long 1/2" thick 4" angle iron that was about 8' long. I was amazed at the lack of vibration.
I think a combination of counterbalancing the work and increasing the footprint size would work
 
Counterbalancing your "chuck" (mounting/fixing instrumentality) is the preferred method for turning off-center. Methods have grown out of oval-turning jigs, and you'll find a lot of work being done by Aussie turners. A different solution to controlling lathe vibration was "invented" by John Williams. You'll find his website and description here http://www3.sympatico.ca/3jdw8/antivibration.htm

I can attest to John's method because I used it to stabilize my first lathe, a JET 1236. I tried sandbags and even a pile of concrete blocks that probably tripled the weight on the lathe, but with so many flexing parts and joints in the leg-stand, it made little difference. 40 pounds of concrete in a 5 gal bucket set about 12" above the height of the spindle and the JET ran like a 1,000lb machine even when roughing a octagon log section bowl blank.

Caveat: If you try John's method, do not skimp on how you attach the weight. The support structure has to be beefy, rigid, and well made, and attachment to the lathe ways must be very robust. Just as importantly, making the mistake of "if some's good, more's better" could be deadly. I needed only 40 lbs on a 18" post to solve my problem. I was not, however, turning off-center work.

PS: I actually considered adding one of these to my 900lb Stubby 1000 when I was testing its limits and turning large, out-of-balance stuff. But attachment presented real issues and I kind of "graduated" from that "See! I made THIS Big Thing!" phase when Memsahibe mentioned that I could start dusting them and looking for a bigger house as display space was all taken.
 
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Dale Miner said:
A method of counterbalancing the offset turnings would be much better for the machine.
Click to expand...

Dale has suggested a key element, and if this were taken into consideration, a complete solution can be found. No matter what method of attaching a wood lathe to floor, walls, ceiling, etc., the one thing that remains a constant is the out-of-balance condition. The movement of the lathe can be controlled, but the stresses on the machine and bearings remains the same, or increased, due to lack of flexability.

My kind of turning doesn't include much out-of-balance turning, but I did a basic bolt to the concrete floor with the Red Head anchors Michael suggested earlier in this thread. Usually any vibration I have is minimized with an adjustment of rpm. Being one who constantly searches for solutions to my shop problems, I believe I'd find a way to counterbalance the turning itself so it is evenly balanced and runs smoothly.

The thought that occurred to me is to modify a faceplate with some method of attaching weights to the circumference, and a way to test the balance. I balance heavy high speed grinding wheels where I work, and there is a special jig used to find the balance point. It uses four bearings mounted to a cradle that supports a specially made spindle revolving on those four bearings. The balance point is found by gravity while making adjustments to the location of the movable weights. Something similar to this can be easily made, if the need were critical enough to go through the effort to make one.

This counter balance would be the best solution, but it should be understood that several balancing sessions may be required as the weight distribution changes during the turning stages of completion......all depends on what perfect balance is worth to the turner. I would think it would be a very critical part of achieving very nice cleanly made cuts from lathe tools.

ooc
 
One more thought about balancing the load as several of us have pointed out to be the preferred solution has to do with safety. Safety has been getting a lot of attention on this forum recently from the perspective of protection from something that flies off the lathe at high speed. However, we need to think about safety from the more proactive perspective of doing things in a way that minimizes the likelihood of pieces flying off the lathe in the first place.

It is very important to recognize that no matter how well a lathe is mounted to solid structure, doing that does absolutely nothing to improve the safety aspect. My lathe isn't bolted down because I have to stow it out of the way when it isn't being used. I have turned some really heavy irregular shaped chainsawed pieces weighing over 80 pounds without problems because I always go to great pains to get the piece well balanced before turning on the lathe.

I also make sure that the piece is well secured because other things can create opportunities for disaster such as poking a gouge into where it shouldn't be while making interrupted cuts or hidden fractures that can suddenly allow a large chunk of wood to break free.

The bottom line is that balancing the turning is not only the best method for addressing the vibration issue, but it as also an excellent practice to improve safety. Periodically, I receive a prospectus for one thing or another and while each is unique, one thing they have in common is a statement to the effect that, "past performance is not a guarantee of future returns". I think that it would be a good idea for woodturners to approach the way that we do things with the same awareness that things can go wrong and just because nothing bad happened while doing something unsafe in the past, that doesn't imply anything about continuing to do things unsafely.
 
Bolting a lathe down, to anything, scares me. Personally I feel it will give a false sense of security because you won't have vibrations (at least those associated with out of balance turnings).
I just have visions of everything going well, then the lathe coming out of the ground like it got picked by a tornado. I am not saying these are real fears, or anything founded by actual science, stress analysis or anything real.

I have turned some big items (36") and some big out of balance stuff that had to be put on the lathe with an engine hoist, but not big offset stuff. What I see mostly is counter balance in these situations.
 
Lots of industrial machines are bolted to the floor, but from what I've seen, it's the vibration isolators that are fixed and the machine just floats on them.

From everything I've been told, by people who I believe to know way more about it than I do, bolting a wood lathe down will focus vibration on the bearings and the bearing chases plus, in the case of a cast iron lathe like the Powermatic, doing so will induce stress cracks in the castings.

Bottom line: Learn how to counter-balance the work piece with weights; it's not hard to do.
 
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Steve Worcester said:
Bolting a lathe down, to anything, scares me. Personally I feel it will give a false sense of security because you won't have vibrations (at least those associated with out of balance turnings).
I just have visions of everything going well, then the lathe coming out of the ground like it got picked by a tornado. I am not saying these are real fears, or anything founded by actual science, stress analysis or anything real.

I have turned some big items (36") and some big out of balance stuff that had to be put on the lathe with an engine hoist, but not big offset stuff. What I see mostly is counter balance in these situations.
Click to expand...

Had not thought about this and have not wanted to except 1st lathe Delta Midi and was locked in workbench vise. I think Steve and Mark have hit the nerve. If the lathe cannot move then something's gotta give, somethings gotta give ....ok you get the message. And speaking of industrial machines they are built much heavier than the equipment we use and will stand more than our lathes will as far as stresses and vibration.
 
PM 3520 Mounting to the floor

I want to thank everyone that have replied to my question on mounting. You advice and words of wisdom have me thinking in a different way, safety first... Thanks again, I'll followup with my results.
 
I worked in industry where hundreds of lathes and milling machines were used and none ever had out of balance rotating loads.

Vibration isolators kept vibrations in the earth from affecting precision on the machine and not the other way around.
 
Mark Mandell said:
Ha! Very similar (but way more elegant) to John Williams' rig
Click to expand...

Both methods are essentially adding a parasitic mass. Neither method reduces the forces the machine has to absorb from the imbalance.

In John's method, it also has an effect of restraining movement from both below AND above the headstock when not operating at or near a harmonic. The restraining effect is like walking out on the end of a 2x4 cantilevered 3 feet and bouncing up and down, and then sliding the 2x4 out another 3 feet on to a support and trying to bounce. Much more rigid in the second position, but the force from bouncing is the same. We have all noted that sometimes a slight change in rpm up or down will reduce vibration. The reduction in vibration from the slight change is a result of 'tuning' the speed away from a harmonic of the structure of the machine. By adding a parasitic mass, the machine's harmonic is lowered and finding a speed above the first harmonic at a still fairly slow speed is possible. The load on the bearings from the imbalace is not reduced by avoiding a harmonic, just the amplitude of the vibration.
 
Dale Miner said:
Both methods are essentially adding a parasitic mass. Neither method reduces the forces the machine has to absorb from the imbalance.

In John's method, it also has an effect of restraining movement from both below AND above the headstock when not operating at or near a harmonic. The restraining effect is like walking out on the end of a 2x4 cantilevered 3 feet and bouncing up and down, and then sliding the 2x4 out another 3 feet on to a support and trying to bounce. Much more rigid in the second position, but the force from bouncing is the same. We have all noted that sometimes a slight change in rpm up or down will reduce vibration. The reduction in vibration from the slight change is a result of 'tuning' the speed away from a harmonic of the structure of the machine. By adding a parasitic mass, the machine's harmonic is lowered and finding a speed above the first harmonic at a still fairly slow speed is possible. The load on the bearings from the imbalace is not reduced by avoiding a harmonic, just the amplitude of the vibration.
Click to expand...

Understood, Dale. The point is the lathe and load are much more stable, and don't dance at the "new" working speed, so the machine doesn't need to be bolted down. The iron outriggers described by John Lucas may function in a similar way by spreading the force over a much larger floor area.

As you can tell, physics is not one of my areas of concentration:D
 
Mark Mandell said:
Understood, Dale. The point is the lathe and load are much more stable, and don't dance at the "new" working speed, so the machine doesn't need to be bolted down. The iron outriggers described by John Lucas may function in a similar way by spreading the force over a much larger floor area.

As you can tell, physics is not one of my areas of concentration:D
Click to expand...

Mark,

I hope my post did not come across with a negative tone. It was just meant to explain the 'why' of the dampening effect. My background includes a lot of vibration analysis and correction. Sometimes succesful. :-)
 
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