[mike^3]

Hello all!

I bought a used cnc knee mill but the Z axis spindle column (the shiny part that goes in and out/up and down) jams about half way down. On my spindle tear down I literally had to rubber mallet the thing out. I checked the diameter at the top and bottom and seem to be the same.

I Figure someone must of had the quill all the way down and hit the column and tweaked it ever so slightly.

Or 30 years of milling caused thermal expansion at the top portion of the column.

QUESTION:

How can I fix this issue?

I thought if I mounted the casing in a lathe and I identified where the high spot was or where the bend is at, then just grind and make it straight. (Well not completely straight but not so bent.)

Or just hone the inner part of the spindle?

[m4martin]

I assume you are referring to an interact?
If so, the quill is driven down with a pair of ballscrews, I wonder if one ballscrew is worn, and pressing unevenly on the quill?
Some engineers blue might help identify the pinch point on the quill itself maybe?

[TarHeelTom]

Don't know what mill you've got, but....

I've got a series 1.

Seems like I remember reading in the Bridgeport manual that the only reason to ever take out the outside portion of the spindle is to replace it. And if you take it out, you then HAVE to replace it.

The inner portion is relatively easy to take out, but you should order a new SET of bearings for it first.

In my mind, the cause of the spindle jamming is most likely the lubrication has failed.

Tom

[JRoque]

Hi all,

I'm going through a similar situation with my Bridgeport Series I clone. In my case, the problem is that the splined section of the spindle is bent and it catches depending on spindle angle position. Here's a recent video I shot of the bend: Mill Bent Spindle - YouTube.

I'm going to try to straighten that out over the weekend.

Regards,
JR

[mactec54]

mike^3

What model machine do you have Boss ???

I don't think the quill will be bent in any way that is causing it to jam

So it depends on what model you have is to what is causing the quill to stick/jam, a photo of the machine would be good

The other thing with these Quills is when using them for milling, you want to have them up as high as you can, if drilling you can use the full travel of 5"

[TarHeelTom]

Don't know if this is the answer or not, but I see new Spindles for sale on eBay frequently.

Tom

[mactec54]

TarHeelTom

You can't just buy a spindle to fix the problem on these CNC machines, The quill is fitted to each housing & are not interchangeable, you would have to have the quill & it's matching housing or a complete head change, they are easy to fix, if they are not scored up

[tc429]

I agree with jroque, the spline might just be draggy...even if not bent, the thing may have been used for decades in a certain part of the quill range, causing wear/step in the spline. with spindle fully up, hold the brake, try rotating the spindle back and forth by hand- should be a few thou 'klunk' clearance...move it down to the tight area, see if its still there- if its still got clearance, yeah, your housing is damaged(or rack/pinion/front guide) but if its tight, your spline is just messed up.

a invaluable trick a old machinist taught me on how to fix threads with a hammer I found works just as well on splines. if you have a tight thread, just hit it radially while turning it by hand- the nut will forge any high spots back down, no filing, nothing...works like a dream. we had a atc spline gearbox a guy was working on in the shop, had been trying to hone/polish/whatever half a shift and it was still sticking- I just happened to walk by, asked what was going on, suggested trying old Joe Buehner's thread trick- tapped it half a dozen times and was smooth as silk- he was pissed that it was so easy

dunno whatever happened to old Joe, but he was a heck of a maintenance machinist, moved south like 20 years ago... but that one little tip has saved me countless hours.

[machintek]

I have seen this issue on a few machines. In all these cases the spindle had a twist in the splined section. The spindle and quill assembly moves freely where the spline is not bent but when the twisted section tries to go through, it cannot due to a lack of clearance. The best way to verify this is to unlock the back gear lever. As the spindle goes down it will drag the splined gear hub and bull gear down with it.

[JRoque]

Hi all. As a follow up and to answer the "can it be fixed?" question, here's the "after" video of my bent spline spindle



Most of that deflection on the indicator is being caused by my hand spinning the shaft and a nick on the ID of the spline. The jam on the feed is gone now. On someone's advise, I used a snug fitting pipe to bend the splines back into shape. If the OP's spline is twisted, that will be more difficult to work but not impossible.

Regards,
JR