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Eliminating toolmarks

Fractal

Cast Iron
Joined
Dec 9, 2003
Location
VA USA
How do you guys eliminate toolmarks? What tricks do you use to minimize them during milling operations? Do speeds and feeds have a major role to play or is it pretty much down to the removal of chips before they get caught under the tool?

Joe
 
Every tool leaves marks. You can only eliminate them by polishing. When machining, you can only make them less noticable.

Good finishes come from preperation. Rigid set-ups, sharp tools, correct speeds & feeds, coolant where possible.

If you're "re-cutting" chips, you're dulling your cutter faster and gauling material during the cut. It's best if you have some means of evacuating the chips. This can be by flood coolant, air, vacuum, or how the part is machined. A good example how they machine aluminum wheels now. Most are done on inverted spindle vertical lathes like the Mori Seiki AZL series. The chips fall away from the part eliminating many finish problems. They also use PCD (polycrystaline diamond) tooling.
JR
 
OK, now you know that every cutter leaves tool marks.

With a bit of skillful draw filing, you can eliminate the cutter marks and not got the parts out of tolerance or out of shape.

If you are pocket milling especially in aluminum, you can only hope to reduce tool marks or make pretty tool marks by taking fine, uniform finishing passes.
 
I've read of some guys writing programs to run a wire brush over a surface to create a more uniform appearance. This would only apply to toolmarks that you can see, but cannot feel with your fingernail.

The proper endmill, and/or using a wiper insert, makes a big difference in the finish, as does the depth of the last cut, of course.

Maybe Gar will chime in here, with some tips on runout and cutter vibration ;) :D
 
Some thoughts on tool marks....
Run out will cause tool marks. In the case of a face mill, lets say 5 inch.... Runout will cause the mill to cut like a fly cutter. Deep on one side and little or no cutting on the other. This causes ripple marks on the finished part.
Machine squareness or lack of it will cause marks to appear on the finished part. Usually out of square conditions will show up as swirl with the open end of the C or U pointing to the high side of the cutter. This condition is also caused by an out of tram condition.
Some of the bigger older machines were set up with what they called heel in the cutter to prevent the cross hatch that you get when the machine is square. This "heel" also reduced chatter in the bigger face mills.
I was at a customer that wanted the sindle out of tram so as to put milling marks in the finish. And you thought square was necessary.
Regards... Walt
 
Most end mills have sharp corners and when cutting on the face, will leave a poor finish. This is especially true with a dovetail cutter. To reduce this to an acceptable level, use a fine diamond if carbide or regular stone if steel and put a small radius on the corners by hand. Use a microscope if necessary. This will make a real nice cut. I figured that out quite some time ago. This is why lathe tools typically have a small radii. As far as the side cut, spindle accuracy and end mill accuracy will control the finish. Assuming the feed rate is where you want it.
 
put a small radius on the corners by hand.
Atta boy Laminar....I was taught that many moons ago when machining mold base pockets. We would use only Weldon endmills(in the 1.5-2" dia range) with their exclusive "cup end". Take brand new $100 cutters and hand dress with fine india stones a wee little rad on the corners and all those digs would go away.
 
And then when they dull a bit, do it again and again. A nice new dovetail cutter cuts horrible until the points are rounded. Also, it's good to have corners with a slight radii so the load path can turn the corner easier.
 
Radius the cutting edges on whatever tool you are using, and adjust the feeds accordingly. I was having a horrible time with my first shaper until I mounted a cutter that came with it that had a generous radius. I learned a lot that day, in a very short time, one of those, CLICK moments when you put lots of stuff together in your head.
 
I know this is an old thread but one of my readers referenced it in an e-mail on the topic. Here is my answer to him:
1. Usually, facing any metal in a vertical mill will create circular marks on the work. This can be caused by:
a. Chips being pulled through the workpiece by the cutter. This is pretty much normal and you cannot stop it. I have a small CNC mill that is perfectly trammed and a work surface after facing is so smooth I cannot feel anything with my fingernail when pulled across the surface. I use a vacuum to pull the chips off as they are formed. However, circular patterns are still cut into the workpiece but they are so shallow they cannot be felt.
b. The milling cutters are not perfectly ground and one or more tips are longer than the others and cutting deeper into the work surface.
c. Using milling cutters with too many flutes. My machine shop instructor told us that 3-flute cutters were the best compromise for allowing the chips to escape, that 4-flute (and more) cutters tend to drag the chips round and round, marking the workpiece.
d. Using square or flat milling cutters. I find that the Bull-Nose cutters (rounded corners) leave a much smoother surface than those with sharp corners. Boeing regrinds all the flat cutters into Bull Cutters before sending them into the machine shop. Probably one of the reasons tool suppliers are now starting to list off-the-shelf Bull Cutters.
e. The milling machine head is out of tram. If you can feel lines in the workpiece in the direction of table feed while you were facing, then the mill head needs to be aligned with the mill table. One cannot perfectly align the head but there are ways to minimize the misalignment.
i. One of the easiest mistakes to make after tramming (aligning) the head of your Bridgeport or similar mill is to tighten the 4 bolts that prevent the mill’s head from rotating without torquing them. Bridgeport recommends torquing the bolts on my mill to 25 ft-lbs and then to 50 ft-lbs. Otherwise, as they warn, “Improper tightening of these could cause a choppy quill movement.” What I found is without a torque wrench, I didn’t tightened the bolts enough and the head would then move on me under heavy cuts.
f. What I have found is a stream of air directed right on the junction of the workpiece and the cutter, where the chips are formed, would get rid of them as well as any other method and keep the workpiece and cutter cool at the same time. I had purchased a mist coolant system only to find that I usually could leave the fluid valve closed and just use the air.
g. I have yet to see any facing operation that did not leave marks in the workpiece. Everyone either uses secondary operations like lapping to remove the marks or if they will not be visible in the finished, work, ignores them.

Mike Rehmus
Editor, Model Engine Builder magazine
Model Engine Builder Magazine. Model IC engines. Clubs, Events, News, New models, Chat. Model Engine Building Enthusiast
 








 
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