New mill, what's considered normal vibration?

D

denkenz

Registered
Registered
Joined
Oct 16, 2018
Messages
10
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?
 
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?
 
What is your slowest speed?
 
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.
 
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.
 
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.
 
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.
 
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.
 
You must log in or register to reply here.
Back
Top