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$#!&%# Boring Issues!
- Thread starter clevinski
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While I agree that a good inserted tip carbide boring bar is far better than these Chinese bars, I have used them many times on my Sherline lathe for diameters much larger and deeper than this so I know they work. They don't finish as well as a good carbide or cobalt bar, though.
These bars have ~ 5 degree positive lead so they actually will bore a decent flat bottomed bore. I've found that they require higher speeds than you are using - I use about 1500 RPM on mild steel. They like a decent depth of cut - try 0.015 - 0.020: for roughing and about 0.005" for a finish pass. I, too, avoid dragging the bar out of the cut and prefer to cut only going in. Be sure to maintain a constant feed rate on entrance to the bore; don't stop or hesitate as you enter or you can chip the tip. I use coolant but don't flood it.
I also found that the steel shanks have variable degrees of hardness, meaning some are sort of hardened and most aren't hardened at all. This creates all sorts of issues due to the impact of tangential forces, especially on finish cuts. The best solution I found is to set the cutting height to center height plus 0.010". This helps a great deal to avoid chatter and dig in. On finish cuts try not to take too light a cut; as mentioned, about 0.005" is about the lightest cut these bars will tolerate before they start to resonate. You will need to experiment to find out what a given depth of cut does to the ID. By that I mean if you dial in a 0.005" cut and the ID only opens up 0.009" then you need to adjust your depth of cut or rough to an ID less 0.009" before dialing in the finish pass.
Hope that's all clear. Try adjusting the cutting height (+0.010") first and see if that clears the problem up. Be sure you use zero radial rake on the tip (flat, not angled) and keep the bar parallel with the ways as well. These bar can handle very slight angling to reduce the effects of radial forces but this works best on through bores; on a closed bottom bore like this keeping the bar parallel to the ways seems to work best.
These bars have ~ 5 degree positive lead so they actually will bore a decent flat bottomed bore. I've found that they require higher speeds than you are using - I use about 1500 RPM on mild steel. They like a decent depth of cut - try 0.015 - 0.020: for roughing and about 0.005" for a finish pass. I, too, avoid dragging the bar out of the cut and prefer to cut only going in. Be sure to maintain a constant feed rate on entrance to the bore; don't stop or hesitate as you enter or you can chip the tip. I use coolant but don't flood it.
I also found that the steel shanks have variable degrees of hardness, meaning some are sort of hardened and most aren't hardened at all. This creates all sorts of issues due to the impact of tangential forces, especially on finish cuts. The best solution I found is to set the cutting height to center height plus 0.010". This helps a great deal to avoid chatter and dig in. On finish cuts try not to take too light a cut; as mentioned, about 0.005" is about the lightest cut these bars will tolerate before they start to resonate. You will need to experiment to find out what a given depth of cut does to the ID. By that I mean if you dial in a 0.005" cut and the ID only opens up 0.009" then you need to adjust your depth of cut or rough to an ID less 0.009" before dialing in the finish pass.
Hope that's all clear. Try adjusting the cutting height (+0.010") first and see if that clears the problem up. Be sure you use zero radial rake on the tip (flat, not angled) and keep the bar parallel with the ways as well. These bar can handle very slight angling to reduce the effects of radial forces but this works best on through bores; on a closed bottom bore like this keeping the bar parallel to the ways seems to work best.
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Looks like a typical mill boring bar / boring head use, and just about all the time, I have to tweek those with the grinder. I think this is all you need, made out of scrap. Works with any holder. Works for internal threading, boring, "0" rings, snap rings, its all in the grinding. Quick rough sketch, this is
all you need, nothing fancy, and no brainer.
all you need, nothing fancy, and no brainer.
Re: $#!&%# Boring Issues!
Hi, Rich,
I agree the that the type of boring bar you showed is more rigid and likely to give better results. What you describe (the tool dragging on the side) is exactly what I think is happening when the movement of the carriage gets difficult. I'm going to try to give the tool a little more relief and raise it to compensate for flexing. I love the idea of bluing the tool surface to verify I have clearance; I'm definitely going to try that. Unfortunately, I can't use a shorter tool because this length is needed to get all the way through the part. I mentioned the mini-lathe aspect because, when I've looked in the past, it seemed more difficult to find a smaller-shanked bar that I could hold in my OxA tool holder.
Thanks also for the info on the diamond lapping/grinding machines. I'll check that out.
- - - Updated - - -
Mikey,
Thanks for all the excellent information; I will certainly implement your suggestions. One point I need to clarify is that this is a through-bore, not a closed bottom.
Hi, Rich,
I agree the that the type of boring bar you showed is more rigid and likely to give better results. What you describe (the tool dragging on the side) is exactly what I think is happening when the movement of the carriage gets difficult. I'm going to try to give the tool a little more relief and raise it to compensate for flexing. I love the idea of bluing the tool surface to verify I have clearance; I'm definitely going to try that. Unfortunately, I can't use a shorter tool because this length is needed to get all the way through the part. I mentioned the mini-lathe aspect because, when I've looked in the past, it seemed more difficult to find a smaller-shanked bar that I could hold in my OxA tool holder.
Thanks also for the info on the diamond lapping/grinding machines. I'll check that out.
- - - Updated - - -
Mikey,
Thanks for all the excellent information; I will certainly implement your suggestions. One point I need to clarify is that this is a through-bore, not a closed bottom.
Thanks, GK... The issue I have in this case is that I'm starting with a 1/2 inch hole and boring up to 5/8 inch. So there's very little space.
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Make a split bushing to hold smaller diameters. Rich
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OK then I would flatten a little with the grinder the back side of the boring bar (for the depth) and shorten up the cutter. Just enough to clear the half inch. I think most will aggree that as time goes on, you will be making a lot of custom tooling more than likely for a one time use . And what I meant by
flatting, I was thinking of a 1/2 boring bar only because thats what I happened to have for stock.
flatting, I was thinking of a 1/2 boring bar only because thats what I happened to have for stock.
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Sorry, Charlie,
I misunderstood that this was a through bore. You can still use the bar parallel to the ways and cut cleanly but if you choose to angle it then you can do so up to about 15 degrees of cant provided the shank of the tool clears. I've tried both ways and frankly don't bother angling the bar, mainly because it didn't make much difference.
I would suspect a lot of us have tried these Chinese bars - why not at $10 per set - but if I had to do it all over again, knowing what I know now, I would start accumulating a set of good inserted tip bars for boring on the lathe. I would only buy carbide bars; you can go with steel but you will eventually buy carbide for the added depth capacity so I would skip steel bars to save money in the long run. I realize this is an entire discussion in itself and don't mean to derail anything - just some food for thought.
I misunderstood that this was a through bore. You can still use the bar parallel to the ways and cut cleanly but if you choose to angle it then you can do so up to about 15 degrees of cant provided the shank of the tool clears. I've tried both ways and frankly don't bother angling the bar, mainly because it didn't make much difference.
I would suspect a lot of us have tried these Chinese bars - why not at $10 per set - but if I had to do it all over again, knowing what I know now, I would start accumulating a set of good inserted tip bars for boring on the lathe. I would only buy carbide bars; you can go with steel but you will eventually buy carbide for the added depth capacity so I would skip steel bars to save money in the long run. I realize this is an entire discussion in itself and don't mean to derail anything - just some food for thought.