Newbie question: at what angle do you position the cutting bit to the work being cut? I have purchased a few books including the Amateur's Lathe and there is no listing of this. Do you put it a 5, 10 15 degree angle to the work? Does the cutting edge face in the direction of the bit travel or away?
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Cutting Bit Relation to Work
- Thread starter navycwo
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Really good question. The short answer is you position the tool to produce the desired result.
There is no correct angle, but normally you would position the tool so the cutting edge is from perpendicular to angled away from the chuck. The most important consideration is that there is clearance for the non-cutting edges of the tool.
Try playing around with the angles and see what works the best for the particular job you are doing.
There is no correct angle, but normally you would position the tool so the cutting edge is from perpendicular to angled away from the chuck. The most important consideration is that there is clearance for the non-cutting edges of the tool.
Try playing around with the angles and see what works the best for the particular job you are doing.
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This is a great question, that I have struggled with a lot. As a newbie myself, I've never read any reasons why the tool should be at a specific angle, so I have always adjusted the angle so that when the tool and toolpost/tool holder get close to the chuck, nothing will CRASH into the moving chuck or jaws before I get to the end of the cut. Don't actually know if this is correct or not, but I think this is what Jim was talking about, if not, some one please correct me. Navycwo, keep the newbie questions comming, thanks, JR49
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The angle you are asking about is called the Lead Angle. Lathe tools, at least the HSS ones, are ground with a geometry intended for use with the shank perpendicular to the work piece. This is why roughing, finishing and facing tools all have varying shapes and angles - the lead angle of the tool changes with its intended purpose.
The ground-in angle of the side cutting edge becomes more acute as we go from a roughing tool to a finishing tool. As this side cutting or lead angle increases, more of the side cutting edge is engaged with the work so cutting forces increase; this is why we typically will take a smaller depth of cut when finishing.
When using most general purpose lathe tools we can vary the lead angle of the tool (make the side cutting edge more or less acute) to suit our purposes by turning the lathe tool to different angles. In general, we want to use as much lead angle as the cut will allow (to produce the best finish possible) as long as there is no chatter. If we do encounter chatter, and this is most evident on thinner work pieces that deflect away from the tool, then we need to reduce the lead angle. Reducing lead angle is equivalent to reducing depth of cut and increasing feed and chatter is reduced. The reason this works is simple. As the lead angle decreases the amount of side cutting edge in contact with the work decreases so cutting forces decrease and less deflection occurs.
This is a long-winded way of saying that the angle of your lathe tool can, and should, be varied to suit your purposes. When taking heavy cuts you want to reduce the lead angle. When taking sizing or finishing cuts you want to increase the lead angle. A lot depends on how your lathe tool is shaped but, in general, these tactics will apply. Lead angle is a very useful way to modify the impact of cutting forces. Give it a try.
The ground-in angle of the side cutting edge becomes more acute as we go from a roughing tool to a finishing tool. As this side cutting or lead angle increases, more of the side cutting edge is engaged with the work so cutting forces increase; this is why we typically will take a smaller depth of cut when finishing.
When using most general purpose lathe tools we can vary the lead angle of the tool (make the side cutting edge more or less acute) to suit our purposes by turning the lathe tool to different angles. In general, we want to use as much lead angle as the cut will allow (to produce the best finish possible) as long as there is no chatter. If we do encounter chatter, and this is most evident on thinner work pieces that deflect away from the tool, then we need to reduce the lead angle. Reducing lead angle is equivalent to reducing depth of cut and increasing feed and chatter is reduced. The reason this works is simple. As the lead angle decreases the amount of side cutting edge in contact with the work decreases so cutting forces decrease and less deflection occurs.
This is a long-winded way of saying that the angle of your lathe tool can, and should, be varied to suit your purposes. When taking heavy cuts you want to reduce the lead angle. When taking sizing or finishing cuts you want to increase the lead angle. A lot depends on how your lathe tool is shaped but, in general, these tactics will apply. Lead angle is a very useful way to modify the impact of cutting forces. Give it a try.
Mikey I understand what you are saying with decreasing or increasing the lead angle. I'm still having a problem of knowing the relationship of different shape bits to the work, not knowing where the cutting surface of the bit is. Is there a chart of pics of bits showing the cutting surface that should be against the work?
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I tried inserting some pics but am not having a lot of luck with that. Have a look at this for a general idea of how each tool type is supposed to work.
http://www.americanmachinetools.com/images/Fig7-5.gif
The cutting always takes place near the very tip of the tool. It will be either the very tip of the tool or the side cutting edge or both doing the work.
http://www.americanmachinetools.com/images/Fig7-5.gif
The cutting always takes place near the very tip of the tool. It will be either the very tip of the tool or the side cutting edge or both doing the work.