Spindle runout

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SteveHGraham
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Re: Spindle runout

Post by SteveHGraham »

I wonder if you've worn out your 3/8" collet, or if there is crap inside it interfering with the fit.
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RSG
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Re: Spindle runout

Post by RSG »

Steve, your questions have made me think and I have had a few milling boo boos, both times with a tapered endmill on aluminum pulling the part out of the fixture in the mill, a collision if you will. It was with the 3/8" collet both times. I am wondering if this could be the cause?
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John Hasler
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Re: Spindle runout

Post by John Hasler »

RSG writes:

> @ John Hasler - you mention re-positioning the collet in the spindle but I'm not sure how you would do that when the collet will only go in one way based
> on the guide pin.

Can't, then. My mill uses MT3 collets and most Bridgeports I've seen no longer have guide pins so I forgot about that. But it looks like you established that the collet is bad anyway.
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GlennW
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Re: Spindle runout

Post by GlennW »

I'd recommend a Hardinge 3/8" collet and a 3/8" drill blank (not drill rod) for further investigation.

Especially if 3/8" is the size you use the most.

I'd also scour out the spindle bore to make sure there are no particles stuck to it.

I've never looked at Lyndex R8 collets, but in 5C their tolerances are not as good as Hardinge. If I recall correctly, Hardinge are good for about a tenth or two and Lyndex are around three to five tenths.
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RSG
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Re: Spindle runout

Post by RSG »

More investigation.

I took some pictures of the inside of the spindle and was surprised to see galling on three points where the collet touches. Upon turning the spindle with the DTI in place I think it's not as bad as I first thought. When touching each section of the wall that isn't scored it's reading around 3 tenths. I'm thinking it's the collet but I'd appreciate others input from the board. Pics below

So the question is: Should I attempt to re grind the spindle AND buy better collets (Glenns suggestion of the most used sizes from Hardinge) or, just start with buying the better collets?

Image

Image
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SteveHGraham
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Re: Spindle runout

Post by SteveHGraham »

You can't test the spindle without the collets, so I suppose they (or at least one, as Glenn suggested) should come first.
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John Hasler
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Re: Spindle runout

Post by John Hasler »

I doubt that you can improve the spindle by grinding it yourself. The most I would do is stone out any high spots in the galled area. But first get better collets.

What is the condition of the back bearing?
RSG
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Re: Spindle runout

Post by RSG »

John Hasler wrote:What is the condition of the back bearing?
I think the bears are fine? I can't hear anything out of the norm and as mentioned they haven't had that much run time on them.

Is there a method of testing the bearings without having to pull them? Can you put a DTI on the spindle and maybe push on the spindle to see movement?
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John Hasler
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Re: Spindle runout

Post by John Hasler »

RSG wrote:
John Hasler wrote:What is the condition of the back bearing?
I think the bears are fine? I can't hear anything out of the norm and as mentioned they haven't had that much run time on them.

Is there a method of testing the bearings without having to pull them? Can you put a DTI on the spindle and maybe push on the spindle to see movement?
I mean the back bearing in the taper: the straight part. Your good results with the 3/4" taper seem to me to indicate that it's ok, though.

> Can you put a DTI on the spindle and maybe push on the spindle to see movement?

Sure. I get less than .00025" spindle sideplay (measured against the quill, not the table) on my mill, but of course it started life as an Avey drill press about fifty years ago.
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ctwo
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Re: Spindle runout

Post by ctwo »

looks like a ridge on that collet. Maybe they are soft, and you said it's been crashed a couple times? Even though I mentioned grinding the spindle in place, it would be the last resort, maybe even after replacing bearings.

I am working on the same sort of thing on my BP CNC, and I am convinced all my troubles are with the tool holding.
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spro
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Re: Spindle runout

Post by spro »

I see that ridge too. That means during a crash, the spindle was spinning around a collet. That also means that the key/pin is either missing or mushed. If it is mushed, it presents an inordinate inner diameter to the minute clearance of any collet. That in itself could throw a collet off center. When the collet "spins" or really the spindle is spinning over it, we have three sharp edges driven into the spindle bore. That upsets the taper, as is evident. You can't have a ridge like that without effecting the inner taper.
Here is where it gets scary. If it were a long taper, there are reamers and lapping tools to regain the long taper. With R-8, short acute taper, how does it locate?
John Hasler
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Re: Spindle runout

Post by John Hasler »

> With R-8, short acute taper, how does it locate?

It's my understanding that it locates by the back bearing, which is why I asked about it. But if it was damaged I wouldn't expect the good results he got with the 3/4" collet.
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