Side cutting

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Dale Grice
Posts: 84
Joined: Thu May 26, 2011 2:53 pm
Location: Stone Mountain, GA

Side cutting

Post by Dale Grice »

Been working on a set of frames for a live steam locomotive. I'm into milling pedestal jaws with both frames pinned together. Total depth is 1.6"

I've got a 3/8 dia end mill. I think it is flexing too much. The end mill dia is right on 3/8. I go out to what the DRO says and when I measure, I am 0.008 undersize. And I only can measure the top. I can't get down in the bottom pedestal. My inside Mic is missing the needed shaft. I'm concerned the bottom frame is too tight.

Guess I need to find a bigger dia end mill that is long enough. Or buy one. And wait on shipping. :>(

But with a larger dia end mill, I won't be able to get into the top corners.

Any thought or ideas - especially on any tricks to reach in and measure the width?

Thanks much,

Dale Grice
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rudd
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Re: Side cutting

Post by rudd »

Your endmill is no doubt flexing some. That is an awfully long EM, can you use a shorter one? Smaller cuts will help. You'll still need to figure out how to get up into the corners.

I use telescoping gauges for internal measurements, I think they would work here. (Get decent ones, the cheap ones are near useless. )
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This method worked for me, there was still a bit of flex, but the large dia. of the endmill kept it to a minimum, still had to to a bit of educated filing after.
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Harold_V
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Re: Side cutting

Post by Harold_V »

You'd be well served by avoiding the use of die sink (long) end mills unless they are absolutely necessary. When they are, they should be gripped as short as they can possibly be, to minimize the amount of flex. Ensure it's sharp, too. A dull die sink end mill borders on being useless. Take advantage of the (positive) rake of the flute to pull the cutter in to the work by taking the final (SHALLOW) cuts by climb milling. That requires a tight machine, or locks set to limit the cut's ability to self feed. Dangerous in the hands of a fool (not implying you are), but a very effective way to improve the cut. Use extreme care in the corners.

One of the things that you can do to determine how much deflection you're getting is to go to a corner, on location, and plunge. Take it slow with the feed, allowing each flute to take a small amount (three thou, for example). Because you change to an end cutting proposition, side pressure is limited, if not eliminated. That should help with achieving a straight cut, and will provide a surface by which you can judge the amount of deflection you're getting.

Don't try to take the entire cut in one pass when you go for size. Step down, allowing the end mill to take the cut in successive passes, to help lower cutting pressure. You'll still be using the extreme end of the end mill, but it will still reduce pressure, lowering deflection.

You may also consider the use of a short end mill, going as deeply as you can, then switching to the longer end mill. Anything you can do to limit the amount of material in contact with the end mill should help.

If you choose to go to a larger diameter end mill, you can switch to the desired diameter and clean out the corners to the prescribed radius. That used to be common practice before wire EDM made it possible to create tight corner radii.

Harold
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Dale Grice
Posts: 84
Joined: Thu May 26, 2011 2:53 pm
Location: Stone Mountain, GA

Re: Side cutting

Post by Dale Grice »

Thanks for all the suggestions. All great ideas. Hadn't thought of those. And the telescope gauges - DOH - I do have a set. I think my mind is wrapped up in making sure I don't make any mistakes and am not thinking through alternatives.

Dale
Projects:

1.6 CB&Q O1a Mikado
1.6 CB&Q NE7 Waycar

RR Supply 90 ton Logging Mikado
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