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Face milling finish

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Active Member
Active Member
Oct 2, 2013
Take a look at the finish I am getting when face milling aluminum with a 4-flute 3/4" end mill. See those wrinkles? The finish feels glassy smooth, but those wrinkles bother me.

I'm using a Sieg SX 2.7 mill. I've been very happy with it except for this. There IS about 0.0005" runout at the end of the spindle, so I think this is the problem. But the runout on my old mini mill was no better, and I got wrinkle-free finishes when face milling.

The finish when end milling is great, and the y-axis alignment is spot on (no head sag, from what I can tell).

So is this a consequence of the runout? Thanks for your ideas.



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H-M Supporter - Premium Member
H-M Supporter-Premium Member
Feb 1, 2015
From the marking, it looks like you are using the side of the end mill rather than the end. Face milling will leave arc shaped markings.

Assuming that you were side milling, it looks like chatter, which can be caused by a number of factors. Machine rigidity or fixturing rigidity, non uniform feed rate, dull end mills, and tool vibration can all cause effects like you show. It also looks from the marks that you tried a full depth finishing cut. This presents a lot of surface area to the end mill which can cause chatter. I had a similar problem running a 2" depth finishing pass on some parts that I made a few years back. I was using my Tormach CNC and a 1/2" diameter x 2" length four flute end mill. No matter what I tried, I couldn't eliminate the vertical lines.

Where possible, I have had better finishes by face milling. Tormach has a product called the super fly (
) that provides excellent finishes. I believe that the geometry of the cutter. I took the lead from them and reground the cutters on my old face mill by using a radius on the tip of the cutter. My face mill uses cut off 1/2" lathe bits rather than inserts. This gives me mirror-like surface finishes.


General Manger - Proofreading Dept.
Active Member
Aug 15, 2013

I have an SX2.7 (LMS 5500) and get the same “chattery” finish when I climb mill too aggressively. Was the work piece in the pic climb milled?

In any case, try this and see if it helps, after your last roughing pass, or even after a light finishing pass, make a spring pass in the climb milling direction.

Do you lock down the Z and Y axes when you make X-axis passes? That can also reduce chatter.

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