# Thread: UK G0704 CLONE CONVERSION & WORKSHOP BUILD

1. Originally Posted by Mad Welder

and Hoss thanks for the link...
Happy to help.
Hoss

2. One of the things I do for a living (and have for many years) is machinery vibration analysis. Let's see if I can do this without writing a book.......to keep it simpler, let's confine it to vibrations from the machine itself and exclude external sources.

Some important basics:
1. All rotating machines vibrate.
2. The frequencies of vibration (yes there are more than one) are related to the rotational speed of the machine's components.

For example, with the G0704 these would always include the motor run speed (1XM), gear mesh frequency (GM), spindle speed (1XN) and bearing related frequencies (BSF,BPIR,BPOR), along with naturally occurring harmonics of those frequencies. While cutting there would also be a blade pass frequency (spindle speed x # of teeth on the tool).

Structural resonances can produce local increases or decreases in these vibration levels with no change in level of force in the machine. It's important to distinguish between the presence of large forces (imbalance, misalignment, etc.) and dynamic amplification of the internally generated forces by a structural resonance, because how you address them will be different.

Resonance is simply the natural frequency of a component or combination of components. All structures have a resonant frequency - it becomes a problem when some forcing frequency comes close (+/- 10%) to the resonant (natural) frequency of a structure.

With a variable speed machine you can easily identify a structural resonance by slowly increasing the speed and observing at what speed the vibration is greatest.

Once you have identified that a resonance related vibration is present, there are four ways you can approach it:
*Change the exciting frequency - this is the easiest, change the speed of the machine.
*Stiffen the structure - This method raises the resonant frequency of the structure.
*Add mass to the structure - This method lowers the resonant frequency.
*Add a dynamic absorber to the structure.

I'm sure there will be questions - be advised I'm travelling with limited access to email & will get back to you as quickly as I can.

Tim

3. Originally Posted by RTTIM
......Structural resonances can produce local increases or decreases in these vibration levels with no change in level of force in the machine. It's important to distinguish between the presence of large forces (imbalance, misalignment, etc.) and dynamic amplification of the internally generated forces by a structural resonance, because how you address them will be different........

Thanks for the analysis and you have just explained in detail one thing that was on my mind regarding resonance

4. Originally Posted by RTTIM

Structural resonances can produce local increases or decreases in these vibration levels

Once you have identified that a resonance related vibration is present, there are four ways you can approach it:
*Change the exciting frequency - this is the easiest, change the speed of the machine.
*Stiffen the structure - This method raises the resonant frequency of the structure.
*Add mass to the structure - This method lowers the resonant frequency.
*Add a dynamic absorber to the structure.

Tim
Excellent detail on this Tim
Ive quoted for me some areas of your post.

So from what you say resonances affect vibration which was my thinking
and the reason I thought about adding mass (sand) to my stand even though
Ive not identified it as producing resonance, however due to the structural properties of it Im pretty sure it will be.

thus
reducing resonance will affect vibration, and to note Im not an experience guy in this field
but am a mechanical engineer which got my head working...

And adding Mass (Sand in my stand) will lower resonance thus reducing vibration? (av i got this correct?)

If I am correct - do you think its worth a shot to see results?

Cheers

John

5. Some pics on progress today just for the sake of it.

Pumbing of One Shop Oiler comming on nicely
Aiming for a tidy system from combined ideas from other members.

Decided to drill and tap a hole to drip feed onto the Y axis screw as shown in pic.

On the workshop side; Some pics of extra foil ceiling insulation over polystyrene sheets.
And to add a pic of my Tool Box thats come in handy that I bought
many years ago......

6. Originally Posted by jdurkin
Excellent detail on this Tim

And adding Mass (Sand in my stand) will lower resonance thus reducing vibration? (av i got this correct?)

If I am correct - do you think its worth a shot to see results?

Cheers

John
It kinda depends. Increasing mass doesn't lower the resonance, it lowers the resonant frequency - shifts it down.

First you need to determine if the vibration is a structural resonance.The rotational speed related frequencies I mentioned in my first post are what we call forcing frequencies, as they are the source of excitation of a structural resonance, typically when they are within +/-5-10% of the resonant frequency.

Vibration due to an excited resonance is unique in that it peaks at the resonant frequency and falls off fairly rapidly both above and below that frequency. By contrast things like misalignment, imbalance or gear/bearing faults will continue to increase in amplitude as the speed increases.

In industrial applications we use accelerometers and FFT analyzers, but you don't need anything that sophisticated. clamp something like a 2-3" dia. pipe cap to your table and fill it half full of water. Slowly increase the speed and watch the water. If the vibration amplitude peaks at a specific speed and falls off above and below that speed, you have identified a structural resonance. How you address it depends on where it is in the operating speed range. If it's towards the higher end of the speed range, increasing stiffness will move the resonant frequency higher & possibly out of the normal operating range. By contrast, if the resonance is towards the lower end of the speed range, then adding mass to lower it is probably the better choice.

Don't think I'd use sand. In practice, I use 25lb bags of lead shot - laid across a bearing housing, for example, to increase mass & change it's resonance.....or hydraulic/screw jacks to increase stiffness. You can use something like cast iron or steel plate, but be sure it's clamped solidly to the structure. Make sure the mill is bolted really solidly to the stand. You can also add something like a piece of steel plate between the mill & stand to increase the mass.

What we've discussed so far is addressing no load vibration issues, and it is the first step. When we start adding operational vibration sources like cutter blade pass frequency it gets stickier. For example, all the resonance correction in the world won't help a column whose stiffness is insufficient to stand up to the forces of a heavy cut in a hard metal. The only options here are to either reduce the load or increase the stiffness of the column (like shown in the link Hoss posted).

Again, I have greatly simplified this. Tell you what....my converted G0704 won't be here for another week or so, but when it arrives and I get it set up, I will run some vibration spectra and post the results here.

Tim

7. Originally Posted by RTTIM
It kinda depends. Increasing mass doesn't lower the resonance, it lowers the resonant frequency - shifts it down.

First you need......................................................

Tim
Cheers Tim

Clear as bell for me that reply mate.
Be nice to see what you come up with mate - a post of result would be great

John

8. Love the pics John keep them flowing, the Oiler manifold and supply pipes are very tidy thanks for sharing and the workshop sure looks a nice place to work during the cold evenings ....

And Tim outstanding explanation posts, thanks a million for sharing and yup keep those clarifications flowing too your methodology for description is extremely easy to comprehend and gain knowledge from, ever think of going into private commerce as a lecturer or trainer to support and advise company engineers ...

9. Originally Posted by Mad Welder
Love the pics John keep them flowing, the Oiler manifold and supply pipes are very tidy thanks for sharing and the workshop sure looks a nice place to work during the cold evenings ....

Cheers mate, yeh will keep the pics comming, (I alway look out for pics myself
on other posts)

I'd have had the X and Y oiler
plumbing done last night however my M5 tap is crap.
Just ordered some more quality taps off ebay from I guy Ive bought taps from before and some 0-20w oil

When taps land in a day or so Ill post pics

10. Excellent work here. This will provide to be an invaluable guide for me. I never thought about a one shot oiler (or lubrication) until now! How could I miss that?

11. Originally Posted by feederic
Excellent work here. This will provide to be an invaluable guide for me. I never thought about a one shot oiler (or lubrication) until now! How could I miss that?
Thought this would help ye mate, did you buy stepper mounts from Billy or just for the ball nuts?

12. I bought the stepper mounts and linearmotion ballnut mounts. They shipped just yesterday actually.

I will be ordering the linearmotion ballscrews shortly. There is so much information to assimilate I am a bit overwhelmed right now.

1. ###### Benchtop Machines &gt; New G0704 - CNC Conversion - Page 7
10-02-2013, 04:07 AM