Intermittent Boring Head Chatter

TCasals · Sep 18, 2018

Alrighty folks, help me out; boring 2.500 to a depth of 7ish inches in 316L on a worn out 40 taper VMC. Tolerance is not tight (+- .003), but for a lot of reasons, boring with a head with a TPGT insert from one end is the name of the game. All suggestions aside for milling the hole, I have a "why in the hell is this happening" query, which is that about 1/3 of the time we get a beautiful normal cut, and the rest of the time is chatterfest.

Doesn't seem to be related to insert freshness, and I've tried a bunch of strategies to try to make it cut consistently but I can't nail down why it just goes wild most of the time and cuts like butter the rest. For what it's worth, the fixture is as rigid as they get. Smaller nose radius would probably make this go away but, well, I don't have any in the toolbox right now.

thermite · Sep 18, 2018

TCasals said:
Alrighty folks, help me out; boring 2.500 to a depth of 7ish inches in 316L on a worn out 40 taper VMC. Tolerance is not tight (+- .003), but for a lot of reasons, boring with a head with a TPGT insert from one end is the name of the game. All suggestions aside for milling the hole, I have a "why in the hell is this happening" query, which is that about 1/3 of the time we get a beautiful normal cut, and the rest of the time is chatterfest.

Doesn't seem to be related to insert freshness, and I've tried a bunch of strategies to try to make it cut consistently but I can't nail down why it just goes wild most of the time and cuts like butter the rest. For what it's worth, the fixture is as rigid as they get. Smaller nose radius would probably make this go away but, well, I don't have any in the toolbox right now.

2/3rds "chatterfest", 1/3 NOT? I'd not class as intermittent chatter atall.

I'd say your environment was pre-disposed FU to WANT to chatter and you are getting AWAY with it not so doing only on an intermittent 1/3 of the time basis.

Besides rigidity, you need some reserve of "over-damping" so the "worn out" factor isn't given a chance to even START that game, 'coz once it HAS begun, you are in resonance for the duration.

2CW This ain't new ground.

DMF_TomB · Sep 19, 2018

TCasals said:
Alrighty folks, help me out; boring 2.500 to a depth of 7ish inches in 316L on a worn out 40 taper VMC. Tolerance is not tight (+- .003), but for a lot of reasons, boring with a head with a TPGT insert from one end is the name of the game. All suggestions aside for milling the hole, I have a "why in the hell is this happening" query, which is that about 1/3 of the time we get a beautiful normal cut, and the rest of the time is chatterfest.

Doesn't seem to be related to insert freshness, and I've tried a bunch of strategies to try to make it cut consistently but I can't nail down why it just goes wild most of the time and cuts like butter the rest. For what it's worth, the fixture is as rigid as they get. Smaller nose radius would probably make this go away but, well, I don't have any in the toolbox right now.

.
ratio of length boring bar sticking out to boring bars diameter is the most important factor. many a boring problem has stopped by using a shorter boring bar
.
316 SS can be full of hard spots. often boring bar will resist cutting harder areas

Terry Keeley · Sep 19, 2018

Try these inserts and I bet it goes away forever:

ISCAR Cutting Tools - Metal Working Tools - TPGT-SP : 555424 - TPGT 2--SP

I like the 908 TiAlN PVD coating.

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Intermittent Boring Head Chatter

TCasals

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thermite

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Diamond

Terry Keeley

Titanium

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