measuring spindle vibration

[bahed]

I was talking to Ron Reed at PreciseBits about router bits and we were also talking about ways to get better cuts. One thing he mentioned was to run my Spindle (I have a 5 HP Colombo) as fast an rpm as possible that also runs smoothly as well.

He advised me to chuck in a typical bit into the collet, start at 24,000 rpm, then put my hands around the spindle body while someone lowered the rpm a little at a time on my VFD and see where I noted where it smoothed out.

I tried it and not sure how accurately I was able to sense it so I was wondering if there was some cheap way of somewhat accurately measuring the vibration of a rotating motor. I'm a wood worker, not a machinist - so I was hoping someone had some suggestions. My father-in-law has an oscilloscope and I read an article that mentions using a piezoelectric accelerometer. They range on eBay from about $60 to $600. Even if I bought the cheapest one I still would likely need some sort of interface between it and the oscilloscope.

Suggestions ?

[Brady Watson]

Bret,
You need pretty sophisticated instruments to be able to glean any kind of meaningful data when checking for spindle run-out in a particular RPM range.

I also run two 5hp Colombo spindles & one gets some harmonics around 16,500 RPM while the other is around 15k. After doing a bearing change to ceramic on one of them, I found that the top bearing, which is an ABEC7 version of a GM alternator bearing - is usually the one that goes out & causes the spindle to take on some noise. It didn't degrade the cut, it just got noisier.

You might want to look at other places on your machine for 'slop', as the spindle is one of the last places where you are going to find anything noticeable. Check all pinions, that the racks are greased, and all v-roller bearings & most importantly - every place that v-rollers ride. Take 220 sandpaper to the rails to polish them up and remove metal build-up. Don't worry - you'd be hard pressed to mess them up doing it by hand. Look for steel forged/smeared downward that is causing the v-rollers to have a rough ride.

Rough rails & non-greased/worn out pinion gears will affect your cut quality more than anything else on these machines.

-B

[bahed]

Good to know. I don't suspect any problems, I guess I was just following up on that conversation that I had.

[MogulTx]

I was looking at buying an AXYZ router and the fella had an iphone... on which he had installed an app that was for earthquakes or acceleration or some such, and he said he would test bits and collets by chucking them up and running them, then place the iphone against the running spindle. He was able to get meaningful data from the vibration....... maybe we should think simply here and see if an iphone app might give us as much as we need in this respect.....?

[bahed]

Fantastic ! Unfortunately I still have a flip phone... awaiting Verizon's 4G roll out this summer... if my battery's ability to hold a charge lasts that long.

I did a quick search and there are apps for Droid phones as well. If anyone wants to test it out, I would be over the moon. I don't think I need to get that accurate, just a relative thing where I can tell where my spindle is smoothing out - might also be good for increasing the lifespan of my bearings.