External Vibration Causing Poor Grinding Results

toolmonger · Jun 21, 2017

About a year ago I started noticing poor results from our CNC tool grinder, primarily showing up in the od relief grind finish of end mills. The grinding between the primary and secondary relief was somewhat wavy. Video inspection showed peaks and valleys of .0002-.0008. The odd part was it was not consistent in when it was happening or how close together the waves were on the part being ground. I found that the slower I ran the program, the closer the waves were to each other. In addition, at first it was an intermittent problem and more recently has gotten much more regular.

After a visit from the factory rep, we somewhat ruled out the machine as being the problem. In the end, I have discovered that the quickly expanding industrial laundry next door installed a new machine about 20' away from this machine and that machine is vibrating the concrete floor, causing the problems. I am fairly certain this is the culprit, because having a water bottle sitting on my grinder when that machine is running shows distinct vibrations in the water. When that machine is off, the water is very still.

The machine's cast iron base is approximately 3' x 3', with 2 6x6 plates in the front and one 6x6 plate in the back which sit directly on the concrete floor. A bolt in the machine base centers the plate and provides adjustment. I recently purchased three 1" x 7" hard felt/rubber vibration pads and we installed them this week. We simply raised the machine and slid the pads under the steel plates. After leveling the machine I have tried it out, and it appears to have solved the initial problem. No more wavy grinds, even when that dryer is running. However, it has causing a different problem, and that is the machine now seems unstable. When rapid traversing of any kind happens, that whole machine shakes, or somewhat wobbles on the pads. It does stop before any grinding would happen, but it has me worried about what problems that side to side movement may be doing. I also see this movement when the machine is probing.

Sorry to be so long winded before asking a question.....

I am wondering if I used the wrong vibration pads? It is now occurring to me that maybe one large pad (3' x 3') would have been more stable. The other option is to move this machine as far away from that vibration source as possible and go back to just the steel plates. This is not an easy option in my situation due to the layout of our shop.

Is there a way to measure vibration in a floor? If so, does anyone know an acceptable limit of vibration for this type of operation?

Thanks

Mike

DDoug · Jun 21, 2017

"Fully isolated Foundation" is what you need.

I have detailed these for balancing machines, so as not to get
vibrations from the surrounding machines.

Saw cut the existing floor, about 12" all around large than the complete machine.

Dig down about 3', apply padding on sides and on bottom.

Pour concrete with re-bar and anchors to match machine tool.

SIP6A · Jun 21, 2017

You need to contact a supplier of vibration mounting pads that can come in and measure the vibration and will then recommend a pad that will damp out the frequency range you are getting from next door.

they can also recommend pads that will deal with the issue of the machine shaking when in rapid.

charlie gary · Jun 21, 2017

Why not offer to buy some vibration pads for the laundry equipment?

dgfoster · Jun 21, 2017

There are various smartphone vibration measuring apps. Might just download one and put the phone on the floor. I have used them to sort out vibration problems in spindles and motors.

Denis

ifixcnc · Jun 21, 2017

We have had good luck with
UNISORB(R) Vibration Isolation Pad Materials

DMF_TomB · Jun 21, 2017

i have seen where Steel Channel 6" or 8" welded up with reinforcement rod filled with concrete. then that was put on the isolator pads
.
basically machine was bolted to a few tons (or more) of concrete and steel that was sitting on rubber or springs. the heavy base resisted movement as the machine was relatively light weight

toolmonger · Jun 21, 2017

Thanks to all who have responded. I really like the smartphone app comment and will try that.

These products happen to be from Unisorb, and I have been in contact with them this morning. By the way, Unisorb sent me these 3 pads and three 1/2" pads as samples, I have not paid for them. I thought I would throw out a plug for them since we are talking about them. Their engineer suggested I try the 1/2" thick pads as those should not move quite as much. I am going to install those in a few days, as my rigger is not available until next week. If that doesn't work, I will take further measures.

Mike

Forrest Addy · Jun 21, 2017

You wouldn't think a laundry would vibrate a slab floor but consider a rotary drum washer containing a ton or two of semi-solid mass thumpety-thumping at 10 RPM: unless the supporting floor is thick and solid and supported by the underlying grade there may be floor deflections conducted to nearby precision machinery regardless of an intervening wall. The problems is the floor and the proximity.

The machine seems to be small. Can it be moved?

Well, maybe you're stuck with the location.

I'm not too sure if I understand how the machine was mounted on the resilient pads, There was mention of hold down bolts but maybe I missed something.

The whole idea of resilient mounting is to de-couple the machine from vibrations conducted through the floor. If a resilient pad was interposed between machine and floor solidly bolting the machine through the pad would defeat the resiliency because of the rigid bolts. There would have to be compliance between the bolt head and the machine and also some form or resilient bushing between the bolt and its passage through the machine's foot.

This makes traditional leveling problematic but in a stiff machine like a CNC grinder mounted on three pads no particular leveling is required except that needed to return coolant to the sump. Shifts and tilts from moving masses on the grinder (reciprocating tables, etc) may cause slow visible movement of the whole however I doubt this would affect the geometry between wheel and work.

My suggestion is to leave the hold-down bolts loose - gapped, even - and see if the machine wants to "walk" in normal operation. I doubt it because grinders are usually very smooth running - but it pays to be on the cautious side. If the resilient pads are ineffective, I suggest pneumatic isolators. PITA and expensive but they work very well even if their wobbly compliance seems distressing to the seasoned observer. The alternative would be a spring supported seismic mount. Very expensive from a manufacture but easy to cobble up from junk.

toolmonger · Jun 21, 2017

Forrest Addy said:
You wouldn't think a laundry would vibrate a slab floor but consider a rotary drum washer containing a ton or two of semi-solid mass thumpety-thumping at 10 RPM: unless the supporting floor is thick and solid and supported by the underlying grade there may be floor deflections conducted to nearby precision machinery regardless of an intervening wall. The problems is the floor and the proximity.

The machine seems to be small. Can it be moved?

Click to expand...

The cast iron / polymer base is approximately 3'x3'. This supports an approximately 6'x5' enclosure. I could move it, but we are already pressed for space and moving it would mean moving other machines/work stations.

I'm not too sure if I understand how the machine was mounted on the resilient pads, There was mention of hold down bolts but maybe I missed something.

Click to expand...

The bolts I mentioned are simply adjusting bolts. The 3 of them each slip through a hole in the casting, and provide a means of leveling/adjustment.

The whole idea of resilient mounting is to de-couple the machine from vibrations conducted through the floor. If a resilient pad was interposed between machine and floor solidly bolting the machine through the pad would defeat the resiliency because of the rigid bolts. There would have to be compliance between the bolt head and the machine and also some form or resilient bushing between the bolt and its passage through the machine's foot.

Click to expand...

Thank you for addressing that...I was wondering how that worked. I didn't think bolting it down would be a good thing, based on a similar thought process to what you said. I just wasn't able to articulate it like you did...

My suggestion is to leave the hold-down bolts loose - gapped, even - and see if the machine wants to "walk" in normal operation. I doubt it because grinders are usually very smooth running - but it pays to be on the cautious side. If the resilient pads are ineffective, I suggest pneumatic isolators. PITA and expensive but they work very well even if their wobbly compliance seems distressing to the seasoned observer. The alternative would be a spring supported seismic mount. Very expensive from a manufacture but easy to cobble up from junk.

Click to expand...

As I mentioned in an earlier post, I think I am going to try the 1/2" pads that Unisorb sent me. It would seem to me that the thinner the pad, the less apt they are to shift in a side to side manner.

Since I am still thinking about it, how about the idea of a 3x3' pad, between the concrete and the machine. I would still have the 3/8" x 6" x 6" steel pads on top of the Unisorb pad, and it would seem to be that by "connecting" the three points of the feet I should eliminate the side to side movement. I think tomorrow I will take a few pictures of the machine base so you can see what I am talking about.

Thanks,

Mike

DMF_TomB · Jun 22, 2017

many machines need to be mounted to a thick slab of concrete which can be isolated from the rest of the building by rubber or springs
.
not many machines can just sit on the floor with no bolts holding it from rocking. i have seen lathes start wobbling from out of balance loads and resonating vibrating can get really bad at times.
.
i have seen small machines mounted to a foot thick slab of granite and the granite block could be on 3 pads of rubber. 4 supports things can start rocking easy. 3 supports more stable

winger · Jun 22, 2017

Vibro/Dynamics vibration isolators, machine mounts, helical isolators, wire rope isolators

All the shop equipment is sitting on these Micro/Level Elastomer Isolators. Prior to that the tenth indicator on the table had a full swing from the presses running.
Couldn't even indicate in a vise when the press was running.

Likely save a lot of bearing in the shop machines also.

Dave

ShakiraRoy · Jun 23, 2017

There are different cell phone vibration measuring applications. May very well download one and put the telephone on the floor. I have utilized them to deal with vibration issues in axles and engines.

dgfoster · Jun 23, 2017

ShakiraRoy said:
There are different cell phone vibration measuring applications. May very well download one and put the telephone on the floor. I have utilized them to deal with vibration issues in axles and engines.

Sort of like in post 5 above? Always good to at least scan the prior posts....

Denis

JST · Jun 23, 2017

Vibration issues are not solved best by trial and error, although it CAN work.

The isolator system used must be one that does not transmit the frequency range that is a problem, obviously. But, it may be that other frequency ranges are not a problem, and the isolators may even need to be stiff in those ranges in order to stabilize tha machine, as you have found.

The best idea is to determine what frequency range the dryer machine next door produces. Then you know what has to be isolated. It appears from your statements that the supports may need to be stiff for lower frequencies so that the machine does not lurch around as it moves its parts.

You may be able to find ou from the manufacturer of the grinder what sort of range the machine movements have, frequency-wise (or maybe use the cell phone app). And, some study of the vibrations coming from the dryer, either a good engineering study, or maybe something as simple as a cell phone app, can give you the problem range.

An engineering study would give the two ranges, and the engineer should be able to recommend a solution

If the engineering study is not practical for you, since you can find the mass of the machine in the specs, talk to a maker of machine vibration dampers, giving them the info on what needs to be blocked, what needs to be a stiff support, and machine mass. They should be able to recommend a good solution.

dgfoster · Jun 23, 2017

Given the availability of sensitive vibration measuring phone apps, I would assume the OP has actually measured the vibration in question and should know it's amplitude, direction and frequency. He could have tested his grinder at various rotational speeds (if not using a VFD, at least while powering up and down) to look for harmonics.

I would also think the laundry machine in question does not run 24/7. So, seeing if the grinder malfunctions on Sunday afternoon just like Monday at 10AM may be informative.

If the vibration can be demonstrated to come one from said neighboring laundry machine, then the OP could be time and money ahead to work with the laundry to isolate its machine and stop the problem at its single source. That all depends on that owner being amenable. Otherwise, the OP may have to eventually isolate a number his own machines.

Time for for an update from the OP as to what he has learned to date....

Denis

JST · Jun 23, 2017

A good engineering examination of this could include a "general" isolation plan, plus a plan for mounting the grinder in such a way as to avoid the "lurching" problem. My gut feeling on that is it would involve an isolated base of concrete, and that being isolated from the floor. The mass of concrete to control the lurching, as well as lower the resonance of the isolating means.

Of course, the key issue is how much mass of concrete, and what sort of isolation..... which depends on the sort of vibration coming in.

As DGF implies, there could be a different problem in future, a different problem machine. That suggests the plan for directly isolating the grinder, as opposed to a solution at the source.... which would be done again when the laundry puts in another dryer, or replaces that one with a different type.

The first step may be to check with the manufacturer, who you would suppose HAS TO have run into this issue before.

toolmonger · Jun 23, 2017

dgfoster said:
Given the availability of sensitive vibration measuring phone apps, I would assume the OP has actually measured the vibration in question and should know it's amplitude, direction and frequency. He could have tested his grinder at various rotational speeds (if not using a VFD, at least while powering up and down) to look for harmonics.

I would also think the laundry machine in question does not run 24/7. So, seeing if the grinder malfunctions on Sunday afternoon just like Monday at 10AM may be informative.

If the vibration can be demonstrated to come one from said neighboring laundry machine, then the OP could be time and money ahead to work with the laundry to isolate its machine and stop the problem at its single source. That all depends on that owner being amenable. Otherwise, the OP may have to eventually isolate a number his own machines.

Time for for an update from the OP as to what he has learned to date....

Denis

So, a bit more information, and a few tests...

The laundry next door has many machines, and they keep adding more. These are very large machines, not your typical laundromat units. Maybe 5 times that size. The machines closest to the wall between our businesses are grouted to the floor. I don't think isolating those machines is the answer at this time.

I downloaded an IPhone APP called Vibroscope Lite. (thank you to those that suggested that, I would not have thought of it) It works great. That APP has several sensitivity settings. I was not able to get any measureable results until I turned it to the 2nd most sensitive setting. The "measurements" show up as a continually scrolling screen, similar to a heart monitor, with continual blips/peaks as it scrolls. I have placed it on many different surfaces at various times of the day to measure differences. To no surprise the floor has the most. I have sat it on several machines/tables and obviously have sat it on the Saacke grinder at various places. I can still get readings when I place it on the X axis table on the Saacke, but roughly 1/2 of what I get on the work table next to the grinder.

Note on the testing...Of all the machines I tested with this APP, our Walter saw grinders seemed to have the best results. We have two of these, about the same distance as the Saacke and I was unable to get a visible reading at the same setting I was testing everything else at. They are also the heaviest machines I have at around 6000 lbs. The Saacke is around 4000 lbs.

So, I have continued to run the machine for the past couple of days. If you remember, my original question/comment was that I have somewhat solved my finish problem and was worried about the movements during axis movement. I am quite pleased with the finish improvement, but am most likely going to install the 1/2" Unisorb pads next week, in hopes of lessening these movements.

Mike

dgfoster · Jun 23, 2017

Mike,

interesting follow up. Having the ability to actually measure what is going on is mighty helpful in troubleshooting. And you will be able to measure how much difference the mats actually make---cool.

Denis

Joe Gwinn · Jun 25, 2017

Typically, one starts with the source, those industrial washing machines. Is there any reason they cannot be up on wire-rope isolators?

Then you also isolate your grinder.

Doing the isolation in both places makes the measures needed at each place more reasonable.

It may also help to cut the floor slab between your and your vibrating neighbor, so the slabs can move independently. This assumes that we are on the ground floor. If the slab cannot be cut, then big isolators are needed. Many industrial buildings have thin pre-stressed concrete floors that are very lively - one can feel towmotors passing by with ones feet.

It sounds like you both are renting industrial space, so you may need to involve the landlord.

Joe Gwinn

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