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Uneven cut

Posted: Sat Mar 28, 2020 7:24 pm
by Fastadam
I have a new to me Taiwanese Husky knee mill. I noticed that I am getting an uneven cut but in a bit of a pattern. The picture is a bronze casting and I noticed it while cutting along the Y axis. I am not sure if I should be looking to make a gib adjustment on the table, or if I have a problem with the spindle. Has anyone had a similar problem? Does anyone have a fix?
Thanks
Adam

Re: Uneven cut

Posted: Sat Mar 28, 2020 8:38 pm
by choprboy
Are you climb milling or conventional milling? Also, are you maintaining a constant traverse speed or stopping/starting? Looks like climb milling with a stop/start and a bit of backlash in the X.

Re: Uneven cut

Posted: Sat Mar 28, 2020 8:52 pm
by Fastadam
I was conventional milling while feeding it as smoothly as possible with no stops along the way.

Re: Uneven cut

Posted: Sat Mar 28, 2020 10:33 pm
by Richard_W
I would check to see if the pattern had the same spacing as the pitch of the screw in the Y axis. If it does? You may have a bent screw on the Y axis? Wouldn't hurt to check the gib either.

Re: Uneven cut

Posted: Sat Mar 28, 2020 10:45 pm
by John Hasler
Check all the gibs. A loose one can do that because of the cyclic force you apply to the table as you crank.

Did you have the x axis locked?

Re: Uneven cut

Posted: Sat Mar 28, 2020 11:08 pm
by Fastadam
Did you have the x axis locked?
I think I had the knobs locked but I honestly dont recall. At the time of cutting I did not notice the finish problem. Now I will be conscious of all setup parameters. I will also check the Gibs to see if they can be a bit tighter and do some test cuts.

Re: Uneven cut

Posted: Mon Mar 30, 2020 5:14 pm
by LIALLEGHENY
How heavy a cut were you making? What kind of cutter were you using? If you try the same setup and same end mill with a piece of aluminum do you get the same result?

Try taking a light finish pass, couple of thousands , climb milling, and try a higher helix mill .

Nyle

Re: Uneven cut

Posted: Tue Mar 31, 2020 6:47 pm
by Fastadam
After adjusting the gibs on the y axis, I feel like I have removed a lot of slop. I did a light test cut (.005) on a piece of aluminum and it shows much better results. I used the same 1/2" diameter 2 flute cutter that i had used previously. I locked the x axis as i moved along. The conventional cut direction still shows a bit of waviness, however I cant feel it with my finger. The climb cut does looks smoother than the conventional direction.

Re: Uneven cut

Posted: Wed Apr 01, 2020 1:55 am
by Harold_V
From the first picture, it wasn't obvious to me that the pattern generated was along the length of the piece shown. With the second image, it's now clear that the problem you see isn't related to the gib of the machine, but the cutter itself. If you examine the end mill cutting edges I'm quite sure you'll see the same pattern. Easy to fix. Use a different end mill, or sharpen the same one (requires a cutter grinder).

I should note that it's quite common for a pattern to display when using the side of an end mill. Modern grinding technology has improved them considerably, however.

H