Diagnosing a Milling Machine problem

Discussion on all milling machines vertical & horizontal, including but not limited to Bridgeports, Hardinge, South Bend, Clausing, Van Norman, including imports.

Moderators: Harold_V, GlennW

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Re: Diagnosing a Milling Machine problem

Post by Harold_V » Fri Dec 14, 2018 5:22 pm

I meant the relief of the cutting edge. Thanks for the closeups of the end mill. I do not see what I thought I was seeing, but it's clear to me that the end mill is the problem. Once slightly dull, end mills, as well as most cutting tools, experience what might be called a "melt down". Cutting pressure increases dramatically and performance virtually disappears. It is for that reason that the admonition to quickly change dull tools is given. A dull tool can be restored to proper performance with a minimal removal of material, while a dull tool, rounded from use beyond reason, will require a large amount of stock to be removed. With an end mill, that destroys the tool's rake angle, often rendering it useless. Even though they may be sharp, they don't cut worth a damn, and there would be no room for chips, were it able to make them. That's particularly true in small diameter end mills.

In this case, it's clear that the tool is not performing properly, and is most likely the reason for moving in the collet. If you have another end mill, you would benefit greatly by trying it. I suspect you'll see a drastic change in the outcome. Also, assure that you are NOT running the end mill too fast. The wear I see on the one shown could be from that condition, although it should be more uniform (all teeth identical).

Cutting tools should not raise large burs on the edges of cuts. There will be a slight edge, but if it's extreme, as it is in the original picture, you should suspect that the tool is no longer sharp.

Look for any shiny surfaces on cutting tools that might occur immediately behind the cutting edge, which should be a distinct sharp edge, with no blurring, and absolutely NO radius. If there's any of either, the tool has surpassed it's useful condition and should be sharpened.

In order for those with limited experience to fully understand what a cutting edge should look like, it is my advice that a NEW cutter be obtained, for close scrutiny. Pay particular attention to what cutting edges look like. They should be pristine, with no evidence of rounding. Identify the primary and secondary grinds, so you have a better understanding of how a tool cuts, and why it loses the ability.

Wise people talk because they have something to say. Fools talk because they have to say something.

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Re: Diagnosing a Milling Machine problem

Post by spro » Fri Dec 14, 2018 6:13 pm

I rarely reply after Harold because he has already laid out the particular reasons. In the expanded view, it is a horrible end mill. The only thing it has going for it, is the helix and that unwinds it.

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Re: Diagnosing a Milling Machine problem

Post by KellyJones » Sat Dec 15, 2018 11:49 am

Thanks all for the thoughtful replies. I found it helpful.
Kelly Jones, PE
A life spent making mistakes is not only more honorable, but more useful than a life spent doing nothing.
George Bernard Shaw

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