Spindle bouncing up an down

[mattinaustin]

I think I may have a problem with my non-CNC IH spindle. If I set up a block under the tool and then lower the spindle, there is about .03" of vertical slack that gets taken up between when the tool hits the block and when it starts to dig in. This happens whether the micro adjust is engaged (spindle plunging lever is locked) or just using the spindle lever. The slack is resisted against by the weight of the spindle.

With the spindle lever (not the spindle lock) tightened and the spindle lowered some using the micro adjust, I can lift the spindle up with my hands the same .03". I am basically lifting the weight of the spindle so its kind of heavy, but not resisting anything in particular. I can not do this with the spindle lock engaged.

When milling aluminum this manifests itself when plunging into stock using the micro adjust...the mill hits the aluminum and starts digging in, but not as much as the micro adjust says (this is not just backlash). If I just leave it as is and let it run, it will eventually sink in (the weight of the spindle fights against the slack). For example, if I use the micro adjust to plunge .10" into the aluminum. The scale will read that I have turned a full revolution on the micro adjust. However, the .03" of slop will have been subtracted from that since the tool is having more resistance than the weight of the spindle. If I don't wait long enough after plunging to let the spindle settle, I will not be at .10" depth. However, if I give it some time, the weight of the spindle will eventually drive the cutter to its full depth.

The other place this is a big problem is when I am coping a thin wall tube with a hole saw. The saw will jump up and down .03" as I am making the cut and cause to much vibration and chatter. This hurts the hole saws as well.

Does that make sense? If so, is this normal? I know I could raise and lower the head to do this, but I wouldn't have the mirco adjust gauge to read. When I look in the wonderfully well written and simple manual (note sarcasm), it says this in the trouble shooting section (this is the way it is written):

13.5 Shake of spindle and roughness of working surface has taken place during performance:
(1) The gap of spindle taper is too wide --- adjust the gap in proper or replace bearing with new one.
(2) Spindle loosening up and down --- Make two of inner bearing covers on the top tight each other. Do not over-tight two inner bearing covers with the taper bearing, it is OK as long as no gap between them.
(3) The gap of taper sliding plate too wide --- Adjust the tension of proper

sections 4,5, and 6 don't apply.

Sounds to me like I have problem #2, but I don't understand what it means.

I had a problem with leaking seals when I first got the machine (see Nov post). I think maybe I did something wrong when I put it back together, but I have no clue what?!?!

Any tips or help appreciated.

Thanks,
--Matt

[holbieone]

sounds like you have some loose spindle bearings

[holbieone]

I had a problem with leaking seals when I first got the machine (see Nov post). I think maybe I did something wrong when I put it back together, but I have no clue what?!?!

i don't know what king of bearings you have but if they are thrust bearings they only go in one way correctly

did you forget to grease them

[Cruiser]

have you read about the cantelevering ? Now you know what it is we were talking about !

[mattinaustin]

Thanks for the replies. As far as the bearings go, I didn't actually remove any during the seal replacement (http://www.cnczone.com/forums/showthread.php?t=26850). So I don't know how I could have messed them up. Is there a way I could check for this?

I did read some about cantilevering, but this is the actual spindle moving up and down, not the head. Is that the same symptom? Plus, I have the newer IH mill with the larger pate which is supposed to take care of the flexing a little better.

Thanks again for the replies and help!

--Matt

[carlquib]

Hi Matt,

Sounds like a simple issue of backlash in the spindle feed mechanism. I don't know if the IH mills have a way to adjust for this or not. I haven't had the head on mine apart yet. Some of the other chinese mills I have worked on have a split gear system that allows you to take up most of the backlash by adjusting the offset between the gears. Did you have the feed mechanism out when you replaced the seal? The other simple solution, though not great, is to gently apply the spindle lock to create some drag on the spindle. The third solution would be to lock the spindle and crank the head down, ala the way it works when the machine is cnced. I know you said that you wanted to use the fine feed scale, but why not set up a dial indicator to measure the plunge? Let us know what you finally work out.

(Edit)
After I did some more review of your posts I saw that you have had the feed mechanism out. I couldn't see any method for adjusting the lash. I went and measured my mill and it is identical to yours. I have .027 of lash. I have never worried about the lash too much because I added a quill DRO. I suspect that if you want to use the quill you will have to do what I suggested earlier and apply some drag to the quill with the lock. Or use the head and measure the movement. I guess this is one of the reasons that some machinists like to use the knee when they have to have acurate plunge depths. I imagine that even a new bridgeport would have some spindle lash.

-brian