Colchester Student Spindle – Sanity Check!

[Taf_PembsParticipant @taf_pembs]

Hi All..

I’m fishing for any advice or just a sanity check really as I am loosing the will to live with my lathe..

My Colchester student has developed a ‘vibration’ for want of a better word.

Bit of background –

I began to notice it a while ago at higher RPM (up around the 1000rpm area) but put just thought maybe an imbalanced chuck / work piece / belt gone a bit weird etc

The headstock has always been the usual noisy Colchester but when I refurbished it one of the centre shaft dual gears was really ropey, nothing like the others and as the machine had been crashed in a previous life (to the point of shifting the lower gearbox gears on their shafts!) I presumed that it had been damaged and a second hand replacement was fitted.

Recently both of the centre shaft dual gears came up on ebay and looked to be in excellent condition and were ridiculously cheap (about 15 quid each! + post) so they very quickly got bought. After inspecting them and disbelieving the condition I set to fitting them. Prior to this I ran the lathe with no chuck through all the gears as well as varying the motor speed on the VFD to get a a decent base line of the Before.

I then noticed that there was now a pretty significant vibration at about 950 RPM (in top gear with VFD turned down a bit and in second to top gear with VFD cranked up a bit – so was not motor speed or VFD frequency related.

I replaced the gears and .. Wow.. what a difference .. in the noise level and the rhythmic ‘notch’ feel that was coming from the really bad one gone (I tried to avoid that gear when using the lathe).

However.. the vibration was still exactly the same.

This week I decided to find the source of it and so far this is what I have tried / eliminated.

It is not VFD Frequency or motor speed dependant.

Tried running 1 belt – each belt in each pulley groove – no difference.

Checked spindle bearing adjustment (no lift other than flex, no end float and spun free enough etc) – good.

Checked Spindle nose runout – pretty good, couple of 10ths (excellent for an old student!). I did dress grind it a while ago but only to skim off the burr high spots, I didn’t actually grind the spindle so to speak, only touched it enough to make the slightest of sparks but remove the high spot damage caused but its caring and gentle previous owner..s.

There was nothing obvious I could find.

So off with the lid and measured where I could between the sliding gear and the gearbox output gear at the rear. I was getting almost a thou of swing on the gauge.

When I first got the lathe and refurbished it, knowing the type of bearings they use – i.e. ludicrously expensive and no need for Gamet Super Precision unobtainiums, I did mark the position of the bearing cones on the spindle with a sharpie and that’s where they went back on. Never been a problem.

Thinking the spindle must be bent (lord knows how you could bend a spindle like that and I haven’t crashed it.. yet)I removed the spindle, stripped it and spun it using it’s bearing surfaces in some blocks – The only thing I could measure with a tenths indicator were scratches in the surface. No run out anywhere, on any surface or the front bearing mating face.

What I did notice was that the alignment marks of the bearing cones were not in line with what appeared to be a reference mark on the spindle nose front bearing mounting face (a small CLC 46 in a circle with a small X next to it). No bother I thought, it runs true.

So I reassembled the front bearing on the spindle in the same orientation as it was and adjusted it for preload. This however wasn’t easy, it was either on or off, no gradual build up as expected (see further down..). Reinserted the bare spindle into the head stock with only the front bearing cap plate bolted up to hold the bearing correctly.

Put the indicator on it towards the rear – see pic below – .. 4 1/2 thou of throw! So I added the rear bearing and adjusted that up and the throw came back to the original just less than 1 thou.

 

 

The high point was right where the keyway is for the sliding gear –

 

 

So I removed the spindle, removed the bearing and re orientated the bearing cones in line with the mark mentioned above. Re inserted and measured – 2 1/2 thou.. better.. and the high point is still exactly the same place.

Over the next day or so I have removed and reassembled the thing many vmany times, each time altering the orientation of the bearing alignment marks (but keeping them aligned to each other), marking the spindle accordingly and noting the throw for each point. the best I could get it to is 1.8 thou which for the bearing type is crap really.

What I did notice was that when I first got the thing and referb’d it the nose bearing looked perfect. This time the outer cup was grey and there were visible rotational lines and I can just about feel some roughness with a little finger nail. There was also some very fine ware material on the magnet in the sump. I have now fitted 2 extra magnets in the bottom of the headstock and also fitted magnets at the bearing oil points so now the oil has to pass over a magnet prior to getting to the bearings..

With the bearing looking like it now does, (any other bearing would be binned) I now thought I’ve nothing to loose so.. and don’t shout at me, I know I know.. 🙂 I reassembled the bearings on the spindle but with the cones reversed, applied some extra preload, plenty of oil and spun the spindle with a drill for a good while. The hope was that the miss alignment of the ‘ridges’ might roll them off a bit and aid with setting preload.

Worked out really well, some unpleasantly dark oil coming from it and the result was a much shinier and smoother cup – Could not believe that worked for such a bodge!

Cleaned up, rebuilt and recheck – 1.5 thou. High spot still in the same place.

So.. that looks about as good as I can get. Put the lathe back to functional and test – preload on front bearing much more gradual.

Still vibration but now at 1150 rpm instead of 950.

I suppose I’ll just have to live with it. The down side is that now the spindle nose has well over a thou of runout!

Before I now regrind the spindle nose and bore taper (has the same runout now) and be done with it what am I missing as I am at the end for me really..

The High point is always the same rotational position on the spindle. The only thing that can not alter is the position of the outer bearing cup due to the locating pin in the headstock face so in my head that means that the cup has worn oddly – does that compute?

 

Sorry for the essay!!

Cheers

Taf

[Taf_PembsParticipant @taf_pembs]

Sorry, should have added..

By vibration I mean the splash back (firmly attached with chuck key hanging rail) is shaking about and noisy, the whole lathe is physically vibrating !

Above and below the ‘resonant’ speed the vibration can be felt, especially resting hand on the head stock.

 

[MichaelRParticipant @michaelr]

You seem to have checked and sorted the headstock bearings, but is the lathe fixed securely to it’s cabinet or bench.

 

[MacolmParticipant @macolm]

One test you could do is to put the spindle in “neutral”, and drive it with an electric drill. Put a socket head screw in the chuck, and engage it with a ball end hex bit in the drill.

[Taf_PembsParticipant @taf_pembs]

Thanks folks..

No, the lathe isn’t bolted down to the concrete. Never bothered as I don’t do a great deal of big stuff.. it’s 650kg bulk tends to keep it still.

Good idea, I’ll try driving the assembled spindle in place, that will completely eliminate all the drive train. Cheers

 

Another thing I forgot to mention (Like the first bit wasn’t long enough!) was that altering the preload nut with the indicator still touching doesn’t alter the reading suggesting the nut face is true to the thread axis ( I should hope so as they went to the trouble of fitting Gamet SP bearings!).

 

Having just written tat last sentence, if I cant find the source of the throw then I suppose I could introduce an error under a bearing face to force the nut to pull the spindle back true?? Any thoughts??

Fag packet maths on a triangle calculator (which I have probably got wrong!) is suggesting about 0.4 thou lift to 1 side of a bearing to pull it back.. If it comes to that I’ll strip it and measure it properly.

Having said that, I haven’t tried mis aligning the bearing ‘alignment’ marks to see what, if any, effect that has.

Anything to stop the bouncing.

Cheers!

[Taf_Pembs]

On 7 December 2023 at 17:35 Taf_Pembs Said:

This time the outer cup was grey and there were visible rotational lines and I can just about feel some roughness with a little finger nail.

The bearing is knackered. Suggest you replace it before resorting grinding anything.

[Taf_PembsParticipant @taf_pembs]

Hi Andy, yes the bearing is knackered, as I said if it was any other bearing it would be in the bin but as they are effectively unavailable and if and when they do come available they are around £1500 or more so I have to make the best of what it is.

 

Success I believe, I spent another day basically leaving the front cone where it was on the spindle as that was as good a position as I could get so I just removed the rear cone and tried rotating it to misalign the ‘alignment’ marks and recheck. Eventually I narrowed it down to just over a thou.. good enough ..  and then with the rear bearing fitted and tensioned against the spring plate the run out where I was measuring on the spindle was down to less than half a thou. I even allowed a little cheer to myself!

So back out, re assemble the spindle properly with everything on it, back in .. again .. and spun it up.

Vibration virtually gone! Once it had run for a but I gave it a warming cycle to check I haven’t over tensioned the bearings – 15 – 20 mins at about 1600 rpm.. a little warm to the touch but far from hot so just about right and the spindle spins freely enough.. very happy indeed!

 

Checked the spindle nose for run out as that was now out due to the rest being changed.. not bad, about 1 1/5 thou total.. out with my bodged tool post grinder, it actually works really well..

 

Terrible looking weld on the die grinder, had a mandrill inside it to try and keep it straight and was trying to blob it on so as not to heat the thing too much and prevent it distorting.. it worked.

Dressed the spindle nose and then the internal nose taper.. ended up with a really good finish after a bit of faffing.. spindle speed etc so even happier.

Moment of truth – fit the face plate as that, although old looks virtually brand new with not single ding in the mounting surfaces. I thought I best blue it up first just in case to show where was good or not so..

Just by pushing it on before I’d even nipped up the collar it was solid on the taper.. gave it a light nip with the collar and had to use the spanner on the collar undoing it to get it to pop off! perfect blue transfer as well..

I suppose you have to get lucky once in a while. The spindle bore taper wasn’t so lucky, I had to re dress that after a coupe of taps on the compound before the bore adapter was a proper fit but no drama’s.

 

Thanks all for the suggestions, appreciate it and I’m calling it fixed.. plenty fixed enough for a neigh on 60 year old lathe.

 

Why all this came about I can only guess at but the problem came on very gradually, something ( a gear I presume) has worn a bit to create the metal debris in the headstock in the first place (nothing obvious that I can find) but now having some decent magnets in there and also the oil having to run over other magnets prior to getting to the bearings should help prevent it again…. I hope!

Now must get back to fiddling with that mil 🙂

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