I've attached a picture of the test cut I did with a 0.001" diameter ( 25 micron) end mill. I think the boss wanted to give me something fun to do and perhaps he wanted to see what I'd do with it....
There was no doubt in my mind this machine wasn't going to deliver all we wanted from this, but he asked if I would try...so I did...very hard actually.
The machine is a Tormach PCNC -440 vertical mill. About 1.5 HP....smaller than a bridgeport, and of Chinese Origin.
https://www.tormach.com/pcnc-440/?utm_source=adwords&utm_term=tormach&utm_medium=1530712282&gclid=EAIaIQobChMIv66coam84AIVj6GzCh3fmAa3EAAYASACEgJdAPD_BwETo see if the geometry we were after was even close to being attainable, I configured a test that would challenge all three axes. A simple profile pocket. It would show all three axis errors and not take long to cut.. I have things to do, so I didn't want to spend a lot of time programming this. As it was it was programmed with the machine conversational language. Easy peasy.
The pocket shows a center square that is supposed to be 1mm square. The slotted "Mote" all around are supposed to be 0.050 mm wide, and 0.025 mm deep. The program called for 0.006 mm DOC so several passes were required to get to full depth.
The machine spindle is a grease pack angular contact affair. As such it's limited to 10,000 rpm maximum. That is extremely slow for a cutter of this size....
but it is what it is.
I began by seeing what kind of run out would the shank of the tool have in an ER 25 collet holder. These holders are Bespoke Tormach quick change items. First test showed 25 micron run out! I think rotated the holder in the spindle until I found a minimum runout of 0.007 mm. I marked the spindle and holder with a sharpy. If I installed the holder in that position, the runout stayed right there. Now 0.007mm runout ( 0.00025") isn't very good with a 25 micron end mill.....
.but ....it is what it is.Next I did some checks on the repeatability of the axes, specifically the Z axis as I felt that errors there were going to break end mills....and it was a good thing I did.
the best I could manage was 0.050 mm repeatability. That's terrible..even with "full size" end mills....so I decided to try giving the machine a few pumps of oil from it's one shot oiler while I did the measuring. That resulted in 0.005 mm repeatability!!! Much better!!!! Uses a LOT of oil to do this......
but .....it is what it isNext I wrote a "do nothing" program that had the tool plane 4" above the table, and just let it run for 10 minutes at speed..to get everything up to temperature. that would have affects on everything , so I figured I would set home and zero's after this. and then cut.
Then I brought the tool holder and actual tool over to our OGP optical comparator, to get a tool height....cause you can't see the ))@(()# thing!!! It maxed the machine out, but we got a number 68.332mm.
Back to the machine, I had nearly everything I needed. Tool length, diameter. Now I needed Z zero. The position of the work with respect to the tool....not an easy thing to figure if you can't see it and cant' touch it! I set up my USB video microscope and put a gage block on the part to give me room to get the camera in. I offset the tool by the 3 " gage block, and compared the images....Now. I can see everything, but paralax was killing me. At some point, you take your best guess and go with it! ( see attached picture at 225 X maginfication...)
But it is what it isOK set up an air jet on the cut zone.
Now....hit cycle start while pumping the 1 shot pump until Z stopped. I then watched the G code scroll and when it got to a z axis change, I would pump some more!.
Interestingly, the machine moved 0.005 mm per step and not 0.006 as instructed....
In any case, on the last cut the pump was pulling air!...so the last cut was different than the previous...somewhere in the the end mill broke..I think later than earlier..but it's hard to say.
It was finishing the outside ring when it broke...the remnant of the broken endmill is still there in the part...that was when the oil supply dropped, so I'm calling it the cause.
You will notice the slots are a good deal wider than 0.05. Between runout, and stick slip in the X and Y axis, the width got wider. ..
My CEO was impressed!....and that was worth it....but I'm glad it's done...on to more productive endeavors!!!
The last couple of pictures show the glue chuck I made to hold the lexan, and the "chicklet" cut out of the picture frame with the little feature in it, and the 1 shop pump with the feed lines full of air...
Dave