I Got That Wood Grain Pattern Again..............

[Jaakko Fagerlund]

Kind of OT, but Elninios pictures of the workpieces remind of one turd at work, he is a CNC miller and leaves that kind of finish on mold inserts and pockets and everything. Guess who gets to clean up those with hard handwork by files, stones and generous use of an angle grinder, with high hopes that the customer doesn't check/care for flatness...

[JoeLee]

Highpower in post #27 has a photo with a pair of parallels being attached to long blue bars. Not sure what they are; but do those bars just "hang out"? Not saying they cause the patterning in JoeLee's case but bars hanging out will add to the vibration.

Sometimes when I use large g-clamps to hold stuff I find draping a wet towel over the ends of the clamp screws reduces vibration.

Cheers,

Norman

Any thing that hangs out too far from it's holding source, be it a chuck or a vise will vibrate but that results in a chattered finish.

JL...................

[JoeLee]

I read somewhere that one should actually set the tram just a little off "perfect". And then let the low side do a trail cut.

Another item: I didn't notice in the posts if you have been locking the quill. After getting advice from a seasoned pro, I now always lock it and use the knee feed.

Geoff

That may be OK for milling but boring and drilling will result in error, very noticable error the deeper the hole is. I would prefer to be as perfectly trammed as I can get it.

JL................

[Zero_Divide]

Okay when you are using power feed how do you make sure feedrate is constant?

My guess is you dont
The force required to move x axis along the slides will vary depending on weight distribution and wear patterns that would affect feedrate.

Slight variation in chipload will shift grooves ever so slightly to create the woodgrain patterns

From the patterns i observed through a microscope i can tell for sure the distance between those grooves was slightly varying and that must have led to those marks.

Again on cnc it only happens when spindle speed or feedrate is jumping up and down. Which happens rarely enough unless you are trying.

[Elninio]

Kind of OT, but Elninios pictures of the workpieces remind of one turd at work, he is a CNC miller and leaves that kind of finish on mold inserts and pockets and everything. Guess who gets to clean up those with hard handwork by files, stones and generous use of an angle grinder, with high hopes that the customer doesn't check/care for flatness...

The dothead immigrants who can't speak english working for barely (or below) minimum wage? The pictures of the millwork are separate from the study which was a simulation.

[Elninio]

The spinning head has momentum which normalizes the varying chip load, it's the resonance that's the problem (or the blessing, if you consider woodgrained on metal an act of god).

[Zero_Divide]

Head-maybe.
But powerfeed is just a simple motor that moves slower if higher resistance is encuntered.
Also because its gear driven it will have not smooth motion , but there will be jerks in the movement.

[A.K. Boomer]

Highpower in post #27 has a photo with a pair of parallels being attached to long blue bars. Not sure what they are; but do those bars just "hang out"? Not saying they cause the patterning in JoeLee's case but bars hanging out will add to the vibration.

Sometimes when I use large g-clamps to hold stuff I find draping a wet towel over the ends of the clamp screws reduces vibration.

Cheers,
Norman

All that stuff needs to be considered - including the length of the leads that work the X axis getting shorter or longer with the loaded side as its being ran through the centrally located lead nuts and mounts...

Zero D. I don't think you get to say that word on here... but now you have to leave it up so people know what im referring too...

[Highpower]

Highpower in post #27 has a photo with a pair of parallels being attached to long blue bars. Not sure what they are;

Cheers,
Norman

Just spring loaded keepers that hold the actual parallels against the vise jaws. Keeps the parallels from falling over when changing parts/material in the vise.

http://www.kurtworkholding.com/acces...lel_keeper.php

[Elninio]

Head-maybe.
But powerfeed is just a simple motor that moves slower if higher resistance is encuntered.
Also because its gear driven it will have not smooth motion , but there will be jerks in the movement.

That's true, I know because I made a powerfeed once with a weak motor and my coupling wasn't perfectly centered, so every turn had a high and low spot.

[JoeLee]

Okay when you are using power feed how do you make sure feedrate is constant?

My guess is you dont
The force required to move x axis along the slides will vary depending on weight distribution and wear patterns that would affect feedrate.

Slight variation in chipload will shift grooves ever so slightly to create the woodgrain patterns

From the patterns i observed through a microscope i can tell for sure the distance between those grooves was slightly varying and that must have led to those marks.

Again on cnc it only happens when spindle speed or feedrate is jumping up and down. Which happens rarely enough unless you are trying.

Well you don't but the power feed is more consistant than if you were cranking the table by hand, also how much chip load can there be when your taking .0005 per pass???? my guess is not much.

JL.......................

[Zero_Divide]

Well you don't but the power feed is more consistant than if you were cranking the table by hand, also how much chip load can there be when your taking .0005 per pass???? my guess is not much.

JL.......................

Chipload is an advancement of a cutter per flute per revolution its not how thick the material you are removing is.

Powerfeed will give you slightest variations of tool advancemet that will give you a pattern, but will not be severe.enough to screw it up completely.

I dont have a better theory.

[1200rpm]

i had a similar thing going on with my mill/drill - i wrote it off to it being a less than rigid machine.
then my drawbar threads started to strip so a made a new drawbar - the problem went away.

after looking closely at the old drawbar it was obvious the threads were cut really crappy and were not straight or concentric.

i think tightening it put some uneven stresses on the spindle/collet and produced a "pattern"

[JoeLee]

1200, thats interesting about the draw bar threads but I can't see how that would cause vibration as long as the taper is seated in the spindle.

I milled the same piece of alum. this morning using my 3" shell mill this time. I ripped it right down the center and got no pattern.
So............ why is it that the 2" shell mill produces the pattern and the 3" does not???? I tried different speeds and feed rates and still no pattern. I was also using the same type inserts in the 3".


JL....................

[Rosco-P]

Just a wild shot, could the 2" shell mill be unbalanced? Try mounting it between centers horizontally and spinning it by hand with no inserts. Does it come to rest at a random spot or is one portion always facing down?