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I will be boring a 2.5" hole trough a .75" thick plate of 8620. on the back side of the plate several .25" features have been cut. Will a .75" boring bar with a carbide insert handle this interrupted cut without destroying an expensive insert?
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Use a larger bar for a 2 1/2" bore, a negative rake insert with a large nose radius.
Such as this one on the left, the one on the right is for non ferrous metals and would fail quickly.
Last edited by Bented; 12-23-2020, 05:56 PM. -
Hold the bar as short as possible, there are different grade of inserts just for that application.
Keep everything as rigid as possible, tighten up your gibs and watch your feeds and speed.
A .75 bar held at 7/8 long is pretty rigid.
Last edited by redlee; 12-23-2020, 05:50 PM.Beaver County Alberta CanadaComment
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I agree with the advice to use a larger bar. Your small boring bar might lead to chatter, causing failure of the carbide insert. That was my experience with a similar situation.Comment
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It'll work fine. Just be careful approaching the interrupts. No need for a bigger bar with that short extension.Southwest UtahComment
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Don't be surprised if you use carbide and it chips.
and then..... finish it with HSS and can't break it....Comment
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The most important thing that has not been mentioned yet is grade of carbide. I had some Sumitomo inserts that were for heavy interrupted cuts in steel and stainless steel, and they were practically indestructible. Every good insert maker makes rugged inserts, but you have to get the right one.Comment
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Inserts for interrupted cuts work a charm,
This Monday I bored an outer ball bearing race out of the end of a roller, beforehand someone decided that cutting mostly through the race with a die grinder in multiple positions would work, it didn't.
This merely made it an interrupted cut and therefore the boring much more difficult.
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Another factor, even for a carbide boring bar, is flexibility in the machine. The bar may be rigid, but there is more structure to the machine, plus the work itself.
When the cutter gets around to the interrupted portion, it will spring into that, taking a deeper cut as the metal at the end of the interruption slams into the tip of the cutter. That can break things, inserts, boring bars, or other parts. And it leads to an irregular cut that is not truly circular.
Depending on the rigidity of the machine, it may be wise to take lighter cuts so that there is not too much force when the tip is whacked by the re-starting of the cut.CNC machines only go through the motions.
Ideas expressed may be mine, or from anyone else in the universe.
Not responsible for clerical errors. Or those made by lay people either.
Number formats and units may be chosen at random depending on what day it is.
I reserve the right to use a number system with any integer base without prior notice.
Generalizations are understood to be "often" true, but not true in every case.Comment
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Diameter of the hole is irrelevant, you can bore a 10' hole with a 3/4 bar.
Hes only going 3/4" deep.Beaver County Alberta CanadaComment
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It is relevant if one has to make time on the job, punching out .100" doc passes with a 3/4" boring bar is asking a bit much of the tool.Originally posted by redlee View Post
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Yup your right, but the OP said he has a 3/4 bar Im assuming thats what he has to work with.Originally posted by Bented View Post
I didnt see anything about .100 cuts in his post.
If he had access to a full shop Im assuming he wouldnt post the question.Beaver County Alberta CanadaComment
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A 3/4 bar sticking out 1 1/8..
I don't think bar flex is as big an issue at .1 DOC....as restofthelathe flex ..Comment
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3/4” boring bar hanging out only a inch is pretty damn stout. I would expect to get 0.1” doc even on my hobby lathe and hobby time.. 0.2” or 0.3” cut would be a different matter.Originally posted by Bented View PostLocation: Helsinki, Finland, EuropeComment
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Yep, that "restofthelathe" flex.Originally posted by 754 View Post
It can bite you on inserts, either breaking them when they hit the other side of the "interruption", or depending on the lathe, stalling it (belt slip, maybe) and then breaking the tip when trying to disengage it and re-start.
Not applicable to large machines so much, but definitely a factor on lighter ones when a piece of larger work is tried.Last edited by J Tiers; 12-24-2020, 12:55 AM.CNC machines only go through the motions.
Ideas expressed may be mine, or from anyone else in the universe.
Not responsible for clerical errors. Or those made by lay people either.
Number formats and units may be chosen at random depending on what day it is.
I reserve the right to use a number system with any integer base without prior notice.
Generalizations are understood to be "often" true, but not true in every case.Comment
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