Hi all. I was just trying to cut a small pocket with on my Sherline CNC mill with a 1/8" endmill running wide open @6 ipm with a .025" depth of cut, 33% stepover.
I notice what looks like lost steps and may have been but what really has me concerned is the way I could see the entire headstock deflect when cutting in the -x direction. It would get to the corner of the pocket and I could see the entire headstock pivot a substantial amount.
Is there something loose I am overlooking? I had the chips cleared so it wasn't build up. With the amount of motion I was surprised the cutter did not break being 1/8". Anyone else have this problem? It only seems to want to twist when cutter -X and I have not seen it happen with larger cutters taking deeper cuts.
Any input appreciated
Mojo
Use a DTI against the head to make sure you know where things are deflecting. Then you can see about the cause. Sounds like the tool is whipping though if it only happens with smaller tools and not larger ones. A DTI will confirm what is moving, start there.
Thanks for the input but I don't need a indicator to tell me the headstock is moving. I can see it moving visually and on the workpiece in the cut area. The whole spindle/motor lifts or rather pivots up on the right hand side as the cutter moves left into the corner of the pocket. It is not just a tiny bit of movement that why I am wondering if something is not as tight as it should be or what.
Bo
Hi Bo. Take your T handle Allen wrench and check tightness of the screws at column base left and head left side. (If these screws are loose--then your mill is probably out of tram.)
Also check the four screws that hold the column to the base.
CR.
<Sigh> So why would this happen only on smaller tools and not larger ones which have more load? I'm not saying it doesn't happen, but you can't quantify where and how much without taking measurements.Originally Posted by Bowman
I don't know if anyone here can tell you any better that something is loose any better than you investigating to see whats loose and making sure the mill is in proper adjustment and tram.
I am going to tighten up everything I can and try to measure what deflection I can. It may very well be the L shaped motor mount bracket is a bit loose as well.
Will report back my findings hopefully something simple I am overlooking.
Bo
actually, a smaller tool "stalled" at the spindles maximum torque would exert more force on the workpiece than a larger tool. usually small tools arent pushed as hard, so you are generally correct, but in a stall situation, the small tool will "kick" more.
if the thing is visually "pivoting" though, they machine is either very very weak (unlikely cause home made mdf machines arent even that bad), or theres something very loose in the head/spindle/tool.
my kx1 which by most acounts is tiny and flexy will snap the cutting bit and rip an aluminium workpiece out of the vise long before exibiting visually noticable flex. in a situation like that (which has happened to me once) its going to flex .01" at most before something breaks (in my case, it pushed the workpiece out of its way). the sherline is alot "weaker" than a kx1, but so is the spindle. i really dont see this being a mechanical flex thing.
Ok I measured the deflection off the spindle and while a bit jumpy on the dial it is deflectiong off .01". It appears when looking closely that the motor and spindle itself are the only things moving. Do the spindle bearings require tightening now and then? I got this mill 2nd hand and retro fit cnc to it myself so I am not intimately aware of all its issues.
Also I tried to cut again this time removing climb milling and cutting CW. Now when the cutter gets to the lower right corner and makes its move to the left the head flexes and stays that way until reaching the top left corner of the pocket. I also finally broke the cutter lol and slowed the feed down to 4 ipm.
So I tried again with a .25" endmill and still encounter the same problem. Although it does not appear that the column or saddle are moving at all. It is almost as if the spindle is loose in the headstock but if that were the case it would happen in all directions I would assume.
I am just getting the idea that this little mill has to take super light cuts to avoid these deflections and loosing steps. Man I can't wait till my daughter gets off my dime and out of college so I can get some real heavy equipment. This maybe the hobbiest idea of milling but I find it frustrating as all hell. You finally get one little issue resolved to only find another and another and in the end you still only have this little mill. I want to make parts not watch them being made countless hours or trying to figure out how to mod the mill to make it work right. I guess hobbiest like tinkering with the machine itself as much as cutting parts but man I would really like to just cut some parts and not worry with the rest
Have to hand it to those that can sit there for hours turning those little handwheels making those tiny cuts they have more patience than I do.
Bo
.01" of play in the system (as opposed to flex) should be "feelable" if you grab the spindle nose and try to shake it. you should go around poking at the spindle and head area to see what is loose. it could be bad bearings, or a loose mount.Ok I measured the deflection off the spindle and while a bit jumpy on the dial it is deflectiong off .01". It appears when looking closely that the motor and spindle itself are the only things moving. Do the spindle bearings require tightening now and then? I got this mill 2nd hand and retro fit cnc to it myself so I am not intimately aware of all its issues.
Also I tried to cut again this time removing climb milling and cutting CW. Now when the cutter gets to the lower right corner and makes its move to the left the head flexes and stays that way until reaching the top left corner of the pocket. I also finally broke the cutter lol and slowed the feed down to 4 ipm.
So I tried again with a .25" endmill and still encounter the same problem. Although it does not appear that the column or saddle are moving at all. It is almost as if the spindle is loose in the headstock but if that were the case it would happen in all directions I would assume.
I am just getting the idea that this little mill has to take super light cuts to avoid these deflections and loosing steps. Man I can't wait till my daughter gets off my dime and out of college so I can get some real heavy equipment. This maybe the hobbiest idea of milling but I find it frustrating as all hell. You finally get one little issue resolved to only find another and another and in the end you still only have this little mill. I want to make parts not watch them being made countless hours or trying to figure out how to mod the mill to make it work right. I guess hobbiest like tinkering with the machine itself as much as cutting parts but man I would really like to just cut some parts and not worry with the rest
Have to hand it to those that can sit there for hours turning those little handwheels making those tiny cuts they have more patience than I do.
Bo
.01" isnt alot of deflection, not something youd typically see with your eyes when its happening especially since it would be gradual. the sherline might easily flex that much in use especially in agressive climb milling, but the way you are making this sound, it seems to be alot more than simple flex.
make sure you are using correct feeds for the material and cutter though. if the spindle speed is only 2000rpm and your cutting metal with a 1/8" bit, 4ipm might actually be much too fast.
Hmmm... I just tried a cut, full width of .250" endmill, .025" deep, 20IPM, and 3200 spindle speed, and didn't get much deflection at all.
I set up an indicator on the spindle body, with the magbase stuck on my Sherline's thin sheetmetal tool shelf, and still only saw about .005" deflection.
Here's a poor video of it.
I DO need to tune my new spindle card though, it doesn't seem to have the power that my old one had.
vlmarshall - I measured the same way with mag base on the steel enclosure off the headstock but from the other side. When cutting in the same direction as you I was getting the .01" reading. Thanks for the video. Btw my enclosure vibrates more than yours for sure lol must not be as solid.
Wish I had a higher speed spindle. Just recently upgraded to the new Sherline motor from the old DC motor they used to use.
The fiddling continues I guess until I figure out how to get more deflection out of the cut.
Bo
on a full width cut, the primary deflection forces would be perpendicular to the cut as thats the direction the bite of each tooth is largest. if you measured the deflection in the y direction... or just ran the cut test in the Y youd see something very different i think.Hmmm... I just tried a cut, full width of .250" endmill, .025" deep, 20IPM, and 3200 spindle speed, and didn't get much deflection at all.
I set up an indicator on the spindle body, with the magbase stuck on my Sherline's thin sheetmetal tool shelf, and still only saw about .005" deflection.
Here's a poor video of it.
I DO need to tune my new spindle card though, it doesn't seem to have the power that my old one had.
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