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New mill, what's considered normal vibration?

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denkenz

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#1
I have a new to me Rong Fu RF45 (not a clone). Still sitting on some 4x4s while I make a stand for it. This is my first mill and I've been messing around trying to check it out. I put a .0005 indicator inside the spindle taper (R8) and turning the spindle by hand get runout within 1 gradation of the indicator, so < .0005. However, I noticed that my hand can influence the reading a bit. I tried checking under power on the lowest speed with the indicator mag base clamped to the table, but get the indicator oscillates too rapidly due to the vibration.

So my question is, is this to be expected for a mill drill like this or does this indicate an issue with the motor?
 

Bob Korves

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#2
Checking it under power does not tell you much that you did not know from the static test, hand turning the spindle. .0005" is OK for that machine.
 

denkenz

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Right, the spindle is well within the gradation, so more like .0002-.0003 which should be just fine for my purposes. The force of my hand does push it in an out a bit though, so I was hoping doing it under power would provide a more precise reading.

I've seen youtube videos showing TIR readings taken under power with no vibration artifacts. So is this an artifact of a geared head or is there some vibration coming from the motor that I should address?
 

ddickey

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#4
What is your slowest speed?
 

mikey

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I have an RF-31 so different machine but power transmission should be similar. By that, I mean that the spindle should run in two tapered roller bearings inside the quill. The top of the spindle is splined and is driven by a gear that interfaces with the spindle. The top of the spindle has to be constrained in some way to limit radial play and on Rong Fu mills, this is usually done by a drive sleeve that is supported by radial bearings just above the level of the quill.

Excessive run out can come from either the quill bearings or the drive sleeve bearings.

It is always best to check concentricity while the spindle is NOT under power. To do this on a gear head mill, you may have to disengage the drive train up top to enable you to turn the spindle by hand. Excessive run out may mean that the bearings are either no good or it may mean you need to adjust preload. Ideally, you want static spindle run out somewhere around 0.0002" or less.

You can also manually push and pull on the spindle on top and that will give you an idea of the condition of the drive sleeve bearings; if the indicator needle jumps all over the place then those bearings need to be replaced.
 

denkenz

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#6
60 rpm according to the chart on the machine
 

NortonDommi

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#7
I have a RF-45 clone and pretty much what mikey said. Where is your indicator mounted? If on the table are all locks done up? Basically a good machine for home/small workshop use use. There is a really good post on rebuilding the head of one somewhere here. All bearings are standard sizes and not expensive if you ever do need to get into it.
 

denkenz

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#8
The machine was essentially new. Still had shipping grease on it and the plastic table covering. Never cut anything, sat in a warehouse for 2 years. I have no reason to suspect spindle bearings being bad, and the TIR reading I'm getting seems to support that.

I'm not sure how I would disconnect the drive gear or put it in neutral otherwise on this model? I understand the RF31 is belt driven. On the RF45 the motor is directly connected to the drive train, no belts or pulleys.

The seller did say they had to replace a capacitor on the motor, so I would suspect the motor more than anything else.
 

mikey

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#9
I may get some push back on this but here goes. The OEM bearings used on these machines are not high quality bearings. I doubt they even have an accuracy class rating. They will do the job in a hobby shop, especially if you set the preload properly on the quill bearings and then maintain those bearings over time, but spindle concentricity will be limited to what those bearings can do.

If I had your mill and I found excessive run out, I would pull the quill, clean and relube the spindle bearings and then adjust preload to minimize run out. I would also pull the drive sleeve bearings out and throw them away; replace them with Nachi deep groove radial bearings that can handle high radial and axial loads. That will give you the best shot without spending too much money (maybe $20.00 for the Nachi bearings, shipped). The reason for replacing the drive sleeve bearings is that they support the upper end of your spindle and affect the life span of the spindle bearings. In addition, all power transmission goes through those drive sleeve bearings.

My RF-31 has Nachi drive sleeve bearings and FAG class P5 spindle bearings. Spindle run out is under 0.0001" TIR . You can't even tell an end mill is moving when it runs so yeah, the bearings make a difference if the amount of run out you have doesn't meet your needs.
 

NortonDommi

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#10
No push back here Mikey. The standard bearings are as you say 'of a class' Z or ZZ for the gearbox so decent -2RS ones are worth the money just for peace of mind. If all is fit for purpose and does what you want it to do I'd check it over and use it while deciding what mods you want to make. Table leadscrew nuts are pretty crap too but again for the price it is a lot of machine and a bit of fettling can make it a very good machine, I certainly have no regrets.
To put in neutral move the Hi-Lo lever to the midway point, with a bit of practice it will become automatic when changing a bit. Any notchiness when changing gears will be a burr on the shaft keyway, this was the only fault I found on mine. Very easy to do when you do the oil change.
 

Bob Korves

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The standard bearings are as you say 'of a class' Z or ZZ for the gearbox so decent -2RS ones are worth the money just for peace of mind.
Z is single shielded, ZZ is double shielded (metal shields), -2RS is double sealed (rubber seals). That nomenclature says nothing about accuracy class.
 

coffmajt

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#12
Until you get your new machine fastened down to some mass, you will have difficulties knowing where vibration is coming from and it can cause a number of problems. A heavy base with cross braces will help if you can do it. Also unless your quill is locked down, even hand pressure can cause movements a test indicator will easily register but may be meaningless to achieving a satisfactory finish on your parts == Jack
 

NortonDommi

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#13
That nomenclature says nothing about accuracy class.
Yep! As Mikey mentioned the bearings are of a class but what class is doubtful and debateable. They work but when the time comes there are much higher quality with closer tolerances that can be fitted and which will make a noticeable improvement to the machine. I also don't think shielded bearings at the top of the gearbox are a good idea as they do not get much in the way of splash lubrication and the stock grease is meager and again of unknown quality.
If something works and does the job I believe in running it until it needs work and by then hopefully the notebook has a list of modifications to do at the same time and most of the parts are sitting ready to go. I can't find the safe place where I put the piece of paper with the bearing numbers on it so I can't say what class they are meant to be.
This is on another site but has one of the best write-ups on these that I have found: http://www.metalworkingfun.com/showthread.php?tid=405
denkenz, I hope you got it at a good price and I'm sure you will be happy. They are noisier than belt drive and some people convert them.
CNC Cookbook has some good info too: https://www.cnccookbook.com/cnc-projects/ Scroll down to the CNC retrofit page there is articles on Epoxy Granite fill etc.
 

mikey

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#14
I can't find the safe place where I put the piece of paper with the bearing numbers on it so I can't say what class they are meant to be.
Cracked me up! I put so many lists in "safe" places that I cannot find. I even took to putting my lists on the computer but I can't find the file they're in when I need them. I usually find them when I'm looking for something else and it is long past the time when they were needed. Getting old ain't for sissies!

By the way, I suggest at least a class P5/ABEC 5 for a spindle. There are more accurate classes but the spindle on an Asian machine is just barely capable of the accuracy a P5 bearing provides so I would stop there.
 

Mark Needham

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#15
Yep, bet your spindle bearings just need a nip up. RF30, mine was the same.
 

BaronJ

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#16
Hi Guys,

I mentioned in another thread that from new my mill had a rhythmic noise that varied with speed. It also had a plastic gear in the train. It was some time later that I found out that the gear was slightly off center and presumably causing the noise.

I made and replaced it with a steel gear and the noise went away.
 

magicniner

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#17
I have a Rong Fu 400 DVM Mill Drill, it's like a giant drill press on steroids, and it runs as smooth as silk from 150rpm right through to 3000rpm.
None of my mills have noticeable vibration when running, bolted down or not.
 
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