Subtleties of climb milling

I'm converting my PM25 mill to CNC. I understand that climb cutting is the norm with CNC. Is this true?
 
Conventional for roughing , climb for finish cut . Climb achieves a much better finish .
 
devils4ever said:
I'm converting my PM25 mill to CNC. I understand that climb cutting is the norm with CNC. Is this true?
Click to expand...

Very much so. Your machine should have very little backlash to no backlash (preloaded screws) so the normal concern with climb milling doesn't apply. The only time this isn't true is when someone tries to do a CNC with stock ACME screws.
 
Tozguy said:
Just checking, you were conventional milling in one direction, then move the end mill over and climb mill back in the other direction?
Click to expand...
Nope. Conventional milling all the time: (free of work) step X, move Y into the work, then Y back through & past the work, once past the work step X etc. That's why I thought I was being safe; but that first encounter on Y after stepping X was a doozie.

Due to this incident I've been looking into ways to minimize the backlash.
 
Last edited:
homebrewed said:
This is a story about something I encountered during a milling job on my Sieg SX2 mill.

The issue of climb milling can be tricky. I once encountered something I call "deferred climb milling" while milling a slot in a steel plate. I had the plate installed so the depth of the slot was in the Z axis, so Z was fixed and I was moving X and Y. So the side of the end mill was doing the cutting. The procedure was: after finishing one pass on Y, move Y back so the next pass would be a conventional milling operation. Step X over by the DOC my mill/EM could handle, then do another pass. Here's the deal. If I had moved X while the end mill was in contact with the work, that would have been a climb milling step, so there was some backlash in X waiting to be yanked forward by the cutting forces. So when I brought the end mill into the work to start the next cut, the backlash IN X came into action, increasing the DOC enough that the end mill grabbed the work and stalled the motor in an instant. Fast enough that it unscrewed the collet nut holding the end mill!! What did I do wrong? I failed to lock the X axis. I'm fortunate the end mill didn't break, or throw the work across the room.

Since that time I have tweaked/modified my mill to reduce the backlash in X and Y, enough to permit light climb milling in steel -- but I still make sure to lock all the undriven axes when I'm milling, Mill. Unlock. Step. Lock. Repeat....
Click to expand...

When milling a slot be it open ended or enclosed, if the cutter is the width of the slot then you cut in one pass and the cut will be half conventional and half climb. So any forced to drag the cutter into the work should be canceled out by an equal force trying to push it out.

If you are widening a slot you can you can conventional mill in one direction, move the cutter across the required amount and continue conventional mill coming back in the opposite direction. You can do this in both open ended and enclosed slots.

This holds true for any shape slot or cavity, be it square, rectangle even a many sided shape. And of course it is also true for milling the outside of a job, again of any shape.

When you finished roughing out he cavity, then by all, means if you wish make a final very light cit in the opposite direction and climb mill for a better finish. Making sure to have all locks and gibs tight. The light cut will of course vary with the size, weight and condition of your machine.
 
homebrewed said:
It might seem like a no-brainer then to put ball screws on your manual machine, but their friction is so low that they can move under the machining forces -- they won't hold their position. And if you're climb milling that isn't a good thing -- the table could self-feed, despite your hand on the crank. Sounds bad to me.....
Click to expand...

a friend-milling foreman at a relatively large manufacturing company-has at times got me machines/parts being scrapped. although they are hi-tech they do use manual machines. i took the ball screws off a bridgeport that was being scrapped and put on mine. i asked the same question and he just laughed. said they climb mill daily on the bridgeport with ball screws. years later i've had no issues.
 
i often climb mill on my benchtop PM-727v. the machine just likes that better. typically i am taking less than .015" per cut in HRS or stainless, so i am not really hogging it out.
 
I've noticed that cutting slots full width (matching the cutter) using an end mill will tend to cut oversize, probably due to the climb activity bouncing the cutter around. I suspect you are better off with an undersized or smaller end mill and making multiple passes after hogging out the middle of the slot. Maybe using odd numbers of flutes gets around this? I am curious as to other's experience with this application.
 
I just read this thread with interest since I had something similar happen to me this weekend. I apologize if I'm hijacking but it's related.

On my new 833TV I was running a 12" long climb cut along X under power with a 1/2" three flute roughing mill (in an end mill holder) on 1/2" thick aluminum. When the table reached midway it started jump;ing. That's the only way I can describe it. You could see the table jump and hear the cutting difference. I was making about 10 passes removing about 1" of material in total (since it wouldn't fit in my chop saw) in .1" increments and this happened on nearly every climb cut pass but not on the return conventional cut. I crept up to the .1" DOC in small increments on subsequent passes. Speed and RPM were working great with no chatter, etc. Until it hit the middle of table it appeared to be in perfect harmony. Slowing things during the "slip" didn't make much difference.

.1" DOC in 1/2" aluminum with a roughing end mill climb cutting doesn't seem like to big of a cut for this machine. Again, it was cutting great with no issue until it hit near the middle of total X travel.

Today I was checking gibs. I put a test indicator on the edge of the table. Pulling the end of the table to me I was getting more than .015" movement. When I moved the table the measurement stayed. It didn't return closer to 'zero'. I tightened the gibs to where I could feel the table a bit tighter when moving Y and was able to reduce it to about .004". I could probably tighten the gibs more but I'm not sure what amount of movement is acceptable or normal.

I measured the backlash in the dials. Y is .007" and X is .013". I found this thread a bit earlier and I don't think it applies given how little backlash I have but I'm not sure what is normal for a machine like this.

Something tells me this could be leadscrew related. If it were the split nut I'd expect to see that throughout travel. I ran the table to either side of X and looked at the leadscrew. I ran it under slow power and looked for any chips, cuts, nicks, etc., and it appears to be 100%.

Could the Y axis gibs being out that much cause this? That's the only thing I've found that seemed out of whack.
 
parshal said:
I just read this thread with interest since I had something similar happen to me this weekend. I apologize if I'm hijacking but it's related.

On my new 833TV I was running a 12" long climb cut along X under power with a 1/2" three flute roughing mill (in an end mill holder) on 1/2" thick aluminum. When the table reached midway it started jump;ing. That's the only way I can describe it. You could see the table jump and hear the cutting difference. I was making about 10 passes removing about 1" of material in total (since it wouldn't fit in my chop saw) in .1" increments and this happened on nearly every climb cut pass but not on the return conventional cut. I crept up to the .1" DOC in small increments on subsequent passes. Speed and RPM were working great with no chatter, etc. Until it hit the middle of table it appeared to be in perfect harmony. Slowing things during the "slip" didn't make much difference.

.1" DOC in 1/2" aluminum with a roughing end mill climb cutting doesn't seem like to big of a cut for this machine. Again, it was cutting great with no issue until it hit near the middle of total X travel.

Today I was checking gibs. I put a test indicator on the edge of the table. Pulling the end of the table to me I was getting more than .015" movement. When I moved the table the measurement stayed. It didn't return closer to 'zero'. I tightened the gibs to where I could feel the table a bit tighter when moving Y and was able to reduce it to about .004". I could probably tighten the gibs more but I'm not sure what amount of movement is acceptable or normal.

I measured the backlash in the dials. Y is .007" and X is .013". I found this thread a bit earlier and I don't think it applies given how little backlash I have but I'm not sure what is normal for a machine like this.

Something tells me this could be leadscrew related. If it were the split nut I'd expect to see that throughout travel. I ran the table to either side of X and looked at the leadscrew. I ran it under slow power and looked for any chips, cuts, nicks, etc., and it appears to be 100%.

Could the Y axis gibs being out that much cause this? That's the only thing I've found that seemed out of whack.
Click to expand...
Was your Y-axis locked?
 
You must log in or register to reply here.
Back
Top