Author Topic: Lead screw chatter..?  (Read 6267 times)

Carpenter84

Lead screw chatter..?
« on: August 18, 2018, 09:10:13 PM »
https://youtu.be/d41l03q5L6c

For your consideration.
This is my Y feed (obviously...). That chatter is coming from the lead screw in the nuts. When I got the mill I tore it down to clean it up and replaxe some items. I replaced the brass nuts with ones I made myself. X side is great, no issues, Y side chatters like this. Started about a year after. Mine are the two separate nuts, not the ones split half way in two. When I reinstalled them, I did a half way decent job to adjust the collar nut to adjust the backlash. X is .021", y is .009".
I'm wondering if when I threaded the nuts I went too deep or wide and there's not enough engagement? And it's chattering between the two nuts? Or, they need to be adjusted a bit tighter? I have a one shot oiler that I use regularly, but the Y side only gets whatever cascades down from the X nut. There's lots of oil, but what drips down out of the bottom of the Y nut is pretty thick with brass.
I fear if I jam a bunch of grease in there it'll just quiet a potential issue....
Thoughts?
Shawn

4GSR

Re: Lead screw chatter..?
« Reply #1 on: August 18, 2018, 09:27:34 PM »
What is that picture of?
Ken

bl00

Re: Lead screw chatter..?
« Reply #2 on: August 18, 2018, 09:33:24 PM »
Looks like a rorschach test.  I see a pigeon.

Watching the video it sounds like the screw is slipping through the threads.

gtermini

Re: Lead screw chatter..?
« Reply #3 on: August 18, 2018, 11:23:02 PM »
50% of the bridgeports I've ever worked on had that obnoxious Y chattter (intermittent, and always happens when you're trying to take a finish cut) , even the one fresh from the rebuild shop. Switch to Vactra No. 4 in the lubricator and it promptly goes away.

Greyson

Carpenter84

Re: Lead screw chatter..?
« Reply #4 on: August 18, 2018, 11:23:23 PM »
Oh weird, I see an eagle.
Itís the oil from the bottom of the brass nut sparkly with brass. I can see how the image is not all that great. Haha
Shawn

Carpenter84

Re: Lead screw chatter..?
« Reply #5 on: August 18, 2018, 11:28:21 PM »
50% of the bridgeports I've ever worked on had that obnoxious Y chattter (intermittent, and always happens when you're trying to take a finish cut) , even the one fresh from the rebuild shop. Switch to Vactra No. 4 in the lubricator and it promptly goes away.

Greyson

Ok, I feel mildly better.. still a lot of brass in the oil drippings tho.... That's concerning.

I am using chevron way lubricant 68. It was the closest my supplier could get to vactra #3 I think it was. What's the difference with #4? Thicker?
Shawn

gtermini

Re: Lead screw chatter..?
« Reply #6 on: August 18, 2018, 11:41:21 PM »
Yah 4 is thicker. Not gear lube thick, but noticeably more than #2.

Greyson

Carpenter84

Re: Lead screw chatter..?
« Reply #7 on: August 18, 2018, 11:56:44 PM »
I'll email my oil lady and see what she has. It'll be another 5 gallon life time supply. Lol.
But thank you for the suggestion.
Shawn

Carpenter84

Re: Lead screw chatter..?
« Reply #8 on: August 19, 2018, 11:43:52 AM »
Until I obtain something similar to vactra 4, would it be ill-advised to put some grease in the screw?
What is causing the chatter? Is it damaging? Is there a fix?
I have a lot of milling to do...
Shawn

4GSR

Re: Lead screw chatter..?
« Reply #9 on: August 19, 2018, 11:48:40 AM »
Add a can of STP to the oil to thicken it up a little.  Maybe two cans. 

Ken
Ken

Carpenter84

Re: Lead screw chatter..?
« Reply #10 on: August 19, 2018, 11:50:16 AM »
Hmm. That's a good idea... It's basically the same as engine parts minus the combustion.. and I can buy it locally. Thanks Ken.
Shawn

4GSR

Re: Lead screw chatter..?
« Reply #11 on: August 19, 2018, 11:55:40 AM »
I've done this in the past when I didn't way oil.  It does as it says, provides a tackyness that sticks to the walls of the cylinder. Do likewise to a lead screw. ;)
Ken

gerritv

  • Guest
Re: Lead screw chatter..?
« Reply #12 on: August 19, 2018, 12:52:34 PM »
I was looking at Liquid Moly to do the same when my way oil quart runs out. I found it difficult to find out what the thickener is in Vactra etc, but vaguely recall that it sounded similar to STP and LiquidMoly descriptions.

The brass filings would be concerning though as it indicates physical wear. Is there something stuck on the lead screw that is abrasive enough?


4GSR

Re: Lead screw chatter..?
« Reply #13 on: August 19, 2018, 01:11:36 PM »
.....................................................
The brass filings would be concerning though as it indicates physical wear. Is there something stuck on the lead screw that is abrasive enough?

Probably sand in the casting causing the abnormal wear is my guess.
Ken

Carpenter84

Re: Lead screw chatter..?
« Reply #14 on: August 19, 2018, 02:03:14 PM »
I doubt that. I had every single piece of the table off and cleaned. And I mean every piece...
Again, I made the brass nuts... So, it is highly possible something about my threading is off.
I'm think the brass in the oil could be from the chattering? Slamming the hardened lead screw around inside the threads.

To get me moving I emptied my one shot to soak the threads and squeezed some grease in the drain hole in the bottom of the brass nuts block thingy. The chattering calmed down.

There is oil that drips down but it is possible it is not enough. Kind of a dumb design actually. There is one oil tube dripping oil on the X screw then what drips down off the x drips onto the y. I usually do one shot when I start using the machine. I don't do more because I starts running down the machine from everywhere else. Dirty and wasteful. I may have to add another oil tube to do just the Y nut.
Shawn