I am machining some Polycarbonate and have a 25mm plane that is routed down flat. I am using a 3.175(1/8") endmill. I have an overlap of 0.5mm When I finish there is no surprise-I end up with some of the characteristic swirl patterns in the bottom but also more pronounced, annoying lines where the bit runs overlap. I am using cheap equipment (Sainsmart 3018) so there is a lot of vibration of course. Adding methylene chloride cleans up a lot of the "fog but the lines remain. Needless to say I would like to improve on this and reduce the lines. Has anyone done this or has suggestions. I would think if I finish with a 1/4 bit (more stable) it would help clean up the areas that the bit can reach. Maybe there are some facing/endmills out there that would do a better job too. Thanks Fritz
Thanks Peter. I am not sure what you mean by a "front to back" trimming. My Stepover is set to 0.5mm but I have tried a few other values. Is that what you are looking for? I am attaching a picture of what the machine does -I use Fusion 360. Fusion is too dumb to display the dimensions but we are dealing with a pocket of 3/32" depth and about 0.9" breadth. I have to look more into the software but Fusion generates its own G-code and I want to see if it has an option to finish up the runs perpendicular to the ones shown. That would help some. With a ballnose scalloping is a way of life but I am "cheating" and trying to use the flat bottom endmill to as a surfacing bit. The surfacing bit that you mention is a 1" bit--too large form most of my cases. Ideal would be a 1/8" surface bit which I don't know of. Perhaps there is a 1/4 out there. How does 3-flutes help in this case? The cut is very shallow and with an air hose there is not any chip build up. The rate/tooth is faster of course but I a running my motor at less than 1/4 full and I have already tried speeding it up. I note that your SB-7014-DC has 3 flutes and 1/4" dia. Maybe it would run cleaner than what I am doing now. Unfortunately some of my channels for this design will be around 0.1" requiring very tiny bit. Thanks again Fritz
Try using a fine diamond hone to take the tiniest bit off the very tip of the bit - you need the smallest radius on the edge of the bit that you can achieve. Alex.
Tramming, not trimming - i.e how perpendicular the endmill (rather Z axis) is, in relation to the imaginary XY plane. If its tilted, the "angle" engagement of the bottom of the endmill creates the tell-tale ridges you mentioned "Tramming" the machine involves making sure everything is perfectly perpendicular Y rails perfectly parallel to each other so the flat plane at the bottom is perfectly flat (not warped) Z uprights perfectly perpendicular to the Y rails to ensure Z moves perfectly squarely up and down X axis both squared to the Y rails (perfect 90 degree corner cuts) and also perfect parallel to the bed in the X direction Spoilboard is a perfectly flat XY plane in all directions, no warp Router is adjusted clockwise/anticlockwise when viewed from the front to be perfectly parallel to the Z axis (not at any angle) I see a fusion file, but no Picture
Fritz, maybe you should use two different bits. One to do the fine cutting and one to do the bottom surfacing since the 1/8" bit is not really the ideal surfacing bit unless the pocket you surface is really small.
Just call this a trim-tram job. Sorry about the fusion file--I meant to send the attached jpgs. The Pocket is usually 1mm to 2mm deep. And the breadth in this sample is 30mm but they can go all the way down to 1mm (I am tuning them to a sonic source). Regarding trimming the machine setup, esp. the z axis---I am dealing with a cheap machine here and that is not easily an option. That said I think the performance should probably do better than I am seeing- Tampering with the bit end as Alex says makes sense. And using 2 bits as Justin mentioned is where I am headed at the moment-I thought perhaps doing a finish job along the main channel center with a 1/4" bit would help. It won't get into the narrow sides but I am not as concerned with this. -I will try when I get a chance Once I have reasonable lab results here we will probably send the drafts to a qualified machine shop with better equipment (and hopeful kept in good alignment!) Thanks all Fritz
I thought you meant pictures of the cut quality on the final piece to look for problems based on the visible symptoms
Dang-- I was trying to squeak by without showing that---but I'll come clean on it. Here it is in the attachment--welcome to 8th grade shop again! cheers Fritz
Thanks ok the ridges go all directions, so not (only) tramming then. Does look like it may be melting the bottom a bit. Are you using coolant?
No coolant. Probably a squirt of water couldn't hurt. I ran down to 100rpm on the bit (not sure of the calibration but that is slow) and increased the travel speed. Also tried some other combinations--Never can be certain if melting is occurring but none of the tell-tale signs. The "ridges" certainly are shallow-you can't feel or measure them but of course they are there--probably more visible because it is clear plastic. The bits are cheap ones - when I get a chance I will get some better ones and also look at 1/4" for the main part of the routing. thanks fs
