Cut Quality issues

[letmefixit]

Anyone having problems with cut quality. My new mill, well under a year old and less than an hours cutting time on it has a terrible cut. Its almost like the spindle bearings are just wobbling around in the quill. Or is it that the quill has to much play in it. Take a look at the picture and tell me what you think. This is a 3/4" endmill cutting on the side. The block is 2x2 I was just trying to square it up, ant this is the finish that i got. Didnt matter how fast or how slow i went. This is also a brand new 3 flute endmill.

[Cruiser]

Too many variables in play to give an accurate "Root Cause".
It appears to be a harmonic, displacement of slack & inherent weaknesses.
Spindle nut preload could well be one place to look.
the natural tendency of the column to shake.
looseness in the any of the Gib adjustments.
Re Cutting of the chips can cause a harmonic skip pattern on surface, if any or more of the above is in play.
You can do some facsimile of my test cut, facing of all four sides, and increasing pressure to maximize faults and watch machine closely, even video all the week areas.
Note, that 2" of cut is quite a lot of pressure, and a good test in itself to find a weakness. Now, crank it up till you answer your own question !

[ninefinger]

I get the same surface finish when side milling - I was just attributing it to me not knowing what I'm doing, though I did try climb milling, conventional milling and a variety of speeds and feeds, flood coolant, air blast, etc but I couldn't seem to improve the finish very much. I'd be very interested to see if you come up with a solution - and if I get a chance to play and find one I'll let you know.

Mike

[pete from TN]

Do not underestimate the runout issues for a finish like this. Of course make sure your gibs are all adjusted properly,make sure you are using a good feed and speed and proper coolant. However having said that I found the most remarkable improvements in cut quality I made came from simply checking the cutter's runout. I am using the TTS system on my machine and initially I had decent cuts but I bought some cheapo chinese toolholders on ebay and found they had some pretty significant runout. SO I tried to true them up instead of sending them back to china which incidentally costs more than I paid for the damn things. That's another story however... Anyways, I put them in my lathe and did my best to true up the taper on each one of them. It was actually pretty easy to do. I also found that when you take the runout inherent in the spindle, and the runout that is in the toolholder of choice you are using and then the tool itself you can compound the runout significantly. I spent like two days one time just checking all of my toolholders and tooling to see what I had. What I found was pretty cool. First, these ER collet holders are pretty nice because I found that when you put a tool in them you can do two things to true it up, one is to clock the collet in the holder, another is to take a small ball hammer and tap on the side of the cutter that is offensive and you can then tighten it up and you might be surprised at how much you can influence the runout. The other thing I found helped a lot was that I put a center punch indicator mark on the side of the spindle body that I use for a reference. Then I take each individual holder and insert them and play with the clocking of the holder until I get the runout the best I can get it. Once it is as good as I can get it I put a center punch reference mark on the side of the toolholders body just under the one on the spindle body so when I put the tool back in I can get it really close without having to spend a bunch of time with the dial indicator. This has made a marked difference in my cut quality and these chinese spindles are less than perfect that is for sure. I can get many of my holders to spin really true with just a little extra effort. I did some surface finish tests awhile back and saved the pieces I used on my shelf in the shop and that was before I did the serious testing and adjusting. My wife was out there with me that day and she watched as I ran the tests. Then I did the same tests again with the new cutter setups, full flood coolant, and more careful clocking of the toolholders in the spindle using the center punch marks and my wife can verify that there was a vast difference in the cut quality and smoothness. Some of the cuts even looked like they were polished!! The better aluminum specific cutters fared better of course but the moral of the story is check your cutters for runout!!! This is not difficult to do but it is time consuming but it sure is nice to know when I put a tool in the collet I can either just snap it in there if it is not an important cut or if it is a critical surface finish cut I take the extra second or two to find the center punch marks and line them up before I torque it down.... Peace

Pete

[BobWarfield]

That's a damned good post, Pete. Sent you a note.

Cheers,

BW

[dertsap]

that finish looks like the result of climb milling on a manual or sloppy machine , are you climb milling or conventional , if your climb milling then try the other

[pete from TN]

thanks Bob, I was kinda surprised at how much difference it made. When you think of the more high quality commercial machines and tooling the runout is pretty impressive and they spend a lot of time and money to get them that way. Combine that near perfect runout with sometimes shrink fit tooling and a massive rigid machine and you get perfect cut quality even in difficult to machine materials. Even tho we use these semi-crappy chinese machines the same rule applies, if there is runout and looseness in the movements your cuts will just plain suck... that pretty much sums it up. Sending you email... peace

[letmefixit]

Well that's the end of testing for today. My spindle bearings went belly up on me this morning. (What the Heck) Spindle seized up solid. Anyone know how to get the quill and spindle to drop out of the head???

Also i tried both climb and conventional cuts. very minor difference. Did sweeping clean up cuts still couldn't get it clean. I'm using the spring style quick change out collet. The information that is coming in is terrific. Thanks for all your input.

DJ

[dbrija]

Well that's the end of testing for today. My spindle bearings went belly up on me this morning. (What the Heck) Spindle seized up solid. Anyone know how to get the quill and spindle to drop out of the head???

Also i tried both climb and conventional cuts. very minor difference. Did sweeping clean up cuts still couldn't get it clean. I'm using the spring style quick change out collet. The information that is coming in is terrific. Thanks for all your input.

DJ

Did you clean the gearbox when you first got the mill? If you search, you'll find threads about iron fine in the oil left over from the machining (of your machine). That all may explain your cut problem....

[saabman]

My machine also was about a year old and the spindle locked up (within hours of using it). Tommy took good care of me and replaced the spindle. The problem as he describes it is scant little grease on the spindle bearings. There were no signs of filings, just dry bearings. Tommy has since taken to repacking the spindle bearings before the machine leaves the shop.

[letmefixit]

Well my lower bearing race came apart.. Must not like the higher speeds of the Vector Drive and there was very little grease in that bottom bearing. Luckly the local autozone came through for me and had the bearing. Im sure its a super high persision bearing. NOT!!!!! So anyone try to retrofit angular contact bearings in one of these. Might just have to see if i can make it work. So even after the bearing change and i tride my side cuts they still look like heck.

So from what im reading from one of the other posts, this is kind of inhearent of the square coloum mills. Is this the case that others of you are finding. Has anyone found a way to stiffin the coloum and base so that this dosent happen???

DJ
ps sorry about the spelling... spell check is not working today.

[Runner4404spd]

Maybe i missed it, but i didn't see any mention of doc of cut and woc and rpm for the spindle. also a 3/4" diameter endmill trying to take a 2" doc is quite alot. there are alot of variables that would affect that cut. also if your taking a really light woc in aluminum i would get as many flutes as you can on the material at this point even a 5 or 6 flute end mill will be better than the 3 flute endmill you tried using.

if you are going to do this type of cut, then get a carbide endmill as well.
here is a list of things of why you got a bad surface finish

1. endmill not stiff enough (try carbide)
1.5 end mill not sharp enough (try carbide)
2. spindle bearings shot (apparently your addressing this)
3. head tram out of whack,
4. gibbs not tight enough
5. rpm to low
6. rpm too fast


this also brings up a good point, the endmill has to dig into the material to cut it. in your case, i think your endmill is bouncing off the surface and leaving you a chattered edge. this point to a sfm being too high, so slow down your rpm and accordingly slow down your feed.