CamBam
News:
 
*
Welcome, Guest. Please login or register.
Did you miss your activation email?
February 21, 2020, 03:39:20 am


Login with username, password and session length


Pages: [1]
  Print  
Author Topic: Double Check Yourself - From 0.0095 backlash down to 0.002  (Read 1043 times)
Bob La Londe
CNC Jedi
*****
Offline Offline

Posts: 3859


^ 8.5 pounds on my own hand poured bait.


View Profile WWW
« on: September 06, 2019, 01:04:27 am »

I put my Hurco KMB1 back in service a while back, but I was getting .0095" backlash on the Y axis.  It was driving me bonkers, but I needed the machine so I couldn't tear it down.  I just had to cut everything in conventional and program to compensate.  I finally started tearing down the Y and found the nut on the stacked ACBs on the drive end of the ballscrew was barely finger tight.  I'm not sure.  I made a special crown socket for it a while back.  After releasing the tab washer the nut moved when I just barely touched it with the socket.  While I was positioning the tabs in the notches.  Don't know how I left it that loose.  I was sure I tightened it with a torque wrench to about 50 lbs.  

I was going to order a new set of ACBs, but they aren't cheap and they would take a couple days to get here.  Just on a lark I decide to reinstall everything.  Just .002 backlash now.  The machine should be less than .001, but .002 could just be wear over time in the ball nut.  The machine is almost 40 years old afterall.  (Made in the early 1980s) The Y axis carries more load than either other axis as well.  

I might take it back apart and have somebody repack the ball nut with oversize bearings, but not today.  
« Last Edit: September 06, 2019, 03:43:40 am by Bob La Londe » Logged

Getting started on CNC?  In or passing through my area?
If I have the time I'll be glad to show you a little in my shop. 

Some Stuff I Make with CamBam
http://www.CNCMOLDS.com
lloydsp
CNC Jedi
*****
Offline Offline

Posts: 8138



View Profile
« Reply #1 on: September 06, 2019, 01:12:36 am »

Well, it's neat you found that issue, Bob.  Between 0.095 and 0.002 is a HUGE difference!

Lloyd
Logged

"Pyro for Fun and Profit for More Than Fifty Years"
Bob La Londe
CNC Jedi
*****
Offline Offline

Posts: 3859


^ 8.5 pounds on my own hand poured bait.


View Profile WWW
« Reply #2 on: September 06, 2019, 03:42:54 am »

Oops. Meant .0095.
Logged

Getting started on CNC?  In or passing through my area?
If I have the time I'll be glad to show you a little in my shop. 

Some Stuff I Make with CamBam
http://www.CNCMOLDS.com
lloydsp
CNC Jedi
*****
Offline Offline

Posts: 8138



View Profile
« Reply #3 on: September 06, 2019, 11:32:05 am »

 Wink  That's still a pretty-significant change.

L
Logged

"Pyro for Fun and Profit for More Than Fifty Years"
Bob La Londe
CNC Jedi
*****
Offline Offline

Posts: 3859


^ 8.5 pounds on my own hand poured bait.


View Profile WWW
« Reply #4 on: September 06, 2019, 17:18:13 pm »

It makes it practical to prepare blanks on the machine for hinged molds.  I make the hinge feature with several thousandths tolerance as molds are aligned with pins.   Before I had to program a HUGE tolerance. 

Logged

Getting started on CNC?  In or passing through my area?
If I have the time I'll be glad to show you a little in my shop. 

Some Stuff I Make with CamBam
http://www.CNCMOLDS.com
Bob La Londe
CNC Jedi
*****
Offline Offline

Posts: 3859


^ 8.5 pounds on my own hand poured bait.


View Profile WWW
« Reply #5 on: September 25, 2019, 20:21:54 pm »

It makes it practical to prepare blanks on the machine for hinged molds.  I make the hinge feature with several thousandths tolerance as molds are aligned with pins.   Before I had to program a HUGE tolerance.  

I ran a part yesterday way to aggressively in some 4140HT with a 1/2 inch mill.  It cooked the mill, overheated it, and tore up the edges, but inspite of all that there was no discernable chatter.  In the past I always got some chatter during circular interpolation or when making Y axis cuts.  

I think my cut would have been fine with an AlTiN coated mill.  I think it would have been good because I was not getting any sparks or red chips.  Chips more about 90% blue or lighter.  Its just that after a while the carbide started to give off a dim glow.  

I'm ordering some new coated mills (finish and roughing) right now.  

P.S.  The mill already had some damage.  Its just the only one I had that didn't have aluminum specific geometry in that size. 
« Last Edit: September 25, 2019, 20:28:24 pm by Bob La Londe » Logged

Getting started on CNC?  In or passing through my area?
If I have the time I'll be glad to show you a little in my shop. 

Some Stuff I Make with CamBam
http://www.CNCMOLDS.com
Pages: [1]
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines

Valid XHTML 1.0! Valid CSS! Dilber MC Theme by HarzeM
Page created in 0.121 seconds with 20 queries.

Copyright © 2018 HexRay Ltd. | Sitemap