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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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Basic question about roughing om a lathe
If I'm doing rough cuts on a lathe, where the finish is totally
immaterial, is there a difference if I take a .010 cut with .050 feed versus a .050 cut and .010 feed? I figure in both cases the cross section of the chip is the same (.010 x .050), so the rate of removal is the same (for the same speed). Putting it another way, is there an approach which maximizes rate of removal? I.e., maximize cut and set feed as high as you can, or vice versa? Maybe I should generalize even more and ask if there is a speed which maximizes removal. I.e., slow with big chips or fast with small ones? I have the feeling that all that matters is the power of the lathe. That for a given power, you can only remove so many cubic inches per minute and the combination of cut, feed, and speed is not very important. Or not? Thanks, Bob |
#2
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Basic question about roughing om a lathe
Bob Engelhardt wrote:
If I'm doing rough cuts on a lathe, where the finish is totally immaterial, is there a difference if I take a .010 cut with .050 feed versus a .050 cut and .010 feed? I figure in both cases the cross section of the chip is the same (.010 x .050), so the rate of removal is the same (for the same speed). Putting it another way, is there an approach which maximizes rate of removal? I.e., maximize cut and set feed as high as you can, or vice versa? Maybe I should generalize even more and ask if there is a speed which maximizes removal. I.e., slow with big chips or fast with small ones? I have the feeling that all that matters is the power of the lathe. That for a given power, you can only remove so many cubic inches per minute and the combination of cut, feed, and speed is not very important. It isn't just the power of the lathe, Bob. It's also the rigidity. - GWE |
#3
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Basic question about roughing om a lathe
You need to order my: " SPEED/FEED SMOKE COLOR CHART" available for $9.95 -
Visa/MC accepted. Use it to maximize your feed rates based on the color of the smoke being produced. |
#4
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Basic question about roughing om a lathe
Tom Gardner nospam wrote: You need to order my: " SPEED/FEED SMOKE COLOR CHART" available for $9.95 - Visa/MC accepted. Use it to maximize your feed rates based on the color of the smoke being produced. Ideally, the smoke should come from the chips and burning cutting oil. If it comes from the motor or drive belts, you need to back off just a tad... --Glenn Lyford |
#5
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Basic question about roughing om a lathe
"Bob Engelhardt" wrote in message ... If I'm doing rough cuts on a lathe, where the finish is totally immaterial, is there a difference if I take a .010 cut with .050 feed versus a .050 cut and .010 feed? I figure in both cases the cross section of the chip is the same (.010 x .050), so the rate of removal is the same (for the same speed). Some thoughts that come to mind. You may have trouble controlling a machined with the heavier feedrate/smaller DOC. The carriage will be moving faster. Secondly, the feed is typically heavily dependant on the nose radius of the toolbit. Now, you mentioned that the finish is immaterial but if your IPR is higher than your nose rad, theoretically you'd end up with significant scalloping. This may make a single finishing pass nearly impossible. The obvious correction is a larger nose rad. It occurred to me that having the shortest length of cut along the toolbit's edge reduces horsepower and rigidity requirements (smaller rad), but that may be a figure of my imagination. Indeed, if this was the case, the low DOC/high feed combination would be ideal. Shows how much I know... Regards, Robin |
#6
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Basic question about roughing om a lathe
"Tom Gardner" wrote in message . net... You need to order my: " SPEED/FEED SMOKE COLOR CHART" available for $9.95 - Visa/MC accepted. Use it to maximize your feed rates based on the color of the smoke being produced. Make your chips glow (may require face shield) and then back it off just a tad. Regards, Robin |
#7
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Basic question about roughing om a lathe
Tom Gardner wrote:
You need to order my: " SPEED/FEED SMOKE COLOR CHART" available for $9.95 - Visa/MC accepted. Use it to maximize your feed rates based on the color of the smoke being produced. Will that also work for British cars? |
#8
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Basic question about roughing om a lathe
"Rex B" wrote in message ... Tom Gardner wrote: You need to order my: " SPEED/FEED SMOKE COLOR CHART" available for $9.95 - Visa/MC accepted. Use it to maximize your feed rates based on the color of the smoke being produced. Will that also work for British cars? All except Jaguar. There usually isn't enough oil left in them to burn. Tom |
#9
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Basic question about roughing om a lathe
On Wed, 15 Feb 2006 15:37:40 -0500, Bob Engelhardt
wrote: If I'm doing rough cuts on a lathe, where the finish is totally immaterial, is there a difference if I take a .010 cut with .050 feed versus a .050 cut and .010 feed? I figure in both cases the cross section of the chip is the same (.010 x .050), so the rate of removal is the same (for the same speed). Putting it another way, is there an approach which maximizes rate of removal? I.e., maximize cut and set feed as high as you can, or vice versa? There is a magic feed and speed for carbide tooling. If you reach it you'll know because the work will barely heat up, the tool will last a long time, and you'll require one of those nice reflective fire suits in order to reach the lathe to turn it off. :-) In general carbide tooling will only take so much feed rate. This varies with the size of the bit but for 1/2" size tools it's generally in the 0.012"-0.018" per revolution phase. Much more than this and you won't be able to put enough front clearance on the tool without it breaking off. Depth of cut is governed by horse power, rigidity, and how well you can hold the work piece. Speed is governed by what material you're cutting. I don't know the SFM that the magic starts happening but it's up there pretty high. The real kink in finding it is the fact that there's a range between the magic speed and the normal top speed where the tool won't hold up. You have to make a pretty large leap of faith to get up to the speed where things really start happening. Of course once you reach this speed then you have to problem of getting back to the lathe and shutting it off. I've thrown huge heavy extremely hot chips for a 10' radius around a lathe before. Maybe I should generalize even more and ask if there is a speed which maximizes removal. I.e., slow with big chips or fast with small ones? Max removal is at big chip and fast speeds but takes lots of HP and rigidity to reach. I have the feeling that all that matters is the power of the lathe. That for a given power, you can only remove so many cubic inches per minute and the combination of cut, feed, and speed is not very important. There's also cutting tool capability and rigidity to throw into that equation. Machinery Handbook has formulas for HP needed for different cuts. Wayne Cook Shamrock, TX http://members.dslextreme.com/users/waynecook/index.htm |
#10
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Basic question about roughing om a lathe
Rex B wrote: Tom Gardner wrote: You need to order my: " SPEED/FEED SMOKE COLOR CHART" available for $9.95 - Visa/MC accepted. Use it to maximize your feed rates based on the color of the smoke being produced. Will that also work for British cars? Only if you pay proper homage to Lucas, the prince of darkness. Rich ;^)) |
#11
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Basic question about roughing om a lathe
Bob Engelhardt wrote:
If I'm doing rough cuts on a lathe, where the finish is totally immaterial, is there a difference if I take a .010 cut with .050 feed versus a .050 cut and .010 feed? I figure in both cases the cross section of the chip is the same (.010 x .050), so the rate of removal is the same (for the same speed). Putting it another way, is there an approach which maximizes rate of removal? I.e., maximize cut and set feed as high as you can, or vice versa? Maybe I should generalize even more and ask if there is a speed which maximizes removal. I.e., slow with big chips or fast with small ones? I have the feeling that all that matters is the power of the lathe. That for a given power, you can only remove so many cubic inches per minute and the combination of cut, feed, and speed is not very important. Or not? Thanks, Bob As it happens, I spent some time today explaining to a couple guys in my shop how to find and read the tooling usage charts in a couple different carbide suppliers catalogs (Sandvik and Kennametal). They were both consistant in that they had the wide variable on the depth of cut, where the inch per revolution feed rate was usually a relatively narrow range. Off the top of my head, there were lots of reccomendations of, for instance .006" to 012" per rev, .012"-.240" depth of cut. These ranges varied a lot, depending on the application(roughing finishing, etc) but had definate ranges beyond which they did not recomend going, so it was basically all about balancing the speeds feeds and depth of cut for the work at hand. Check a tooling catalog for the recomended speed/feed range for your tooling if you are using carbides. Whether or not your lathe can push the tool as hard as it was designed to be pushed may well be a different thing to have to consider. IIRC the South Bend book shows some examples of cuts quite a bit heavier than I would have considered wise on a machine of that size, and they also were of the low inch per rev/ deep cut variety, probably in back gear. Cheers Trevor Jones |
#12
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Basic question about roughing om a lathe
Make your chips glow (may require face shield) and then back it off just a tad. Regards, Robin For carbide maybe. For HSS I was taught to make the chips blue then back off. Randy -- Randy Replogle |
#13
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Basic question about roughing om a lathe
"Trevor Jones" wrote in message ... IIRC the South Bend book shows some examples of cuts quite a bit heavier than I would have considered wise on a machine of that size, and they also were of the low inch per rev/ deep cut variety, probably in back gear. A couple of years ago my tool and die instructor showed us how to rough down a Ø1" O1 (soft) punch, from square stock to round in the 4-jaw chuck. I think he was taking something like .250 DOC each side. Because of the square stock, this was a heavily interrupted cut. It looked like the toolbit was flexing about .010 or more every time it encountered the work (4 times/rev). The feed was not aggressive, but not conservative either. The lathe was in a back gear. Carbide would have been a significant PITA because of the interrupted cut. Two passes and it was done. Simple. Regards, Robin |
#14
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Basic question about roughing om a lathe
Back 'in the old days', I turned a lot of oil hardening & air hardening tool
steels, and would almost always rough anywhere from .100 inch to .300 DOC, feed rate between .003 to .010 IPR. Flood oil coolant. With a SFM of around 60 or 70 ?? Guess it was pretty much bury the tool if the setup would allow it. (Did pull a few parts out of the chuck, but....) Sharpend the tools so actual cutting edge was almost 90 degrees to axis of work, (seemed everything was working up to a shoulder) and thus any tool wear would tend to force tool out of cut without digging in, and kept nose radius approx. .02 inch. "Robin S." wrote in message . .. "Trevor Jones" wrote in message ... IIRC the South Bend book shows some examples of cuts quite a bit heavier than I would have considered wise on a machine of that size, and they also were of the low inch per rev/ deep cut variety, probably in back gear. A couple of years ago my tool and die instructor showed us how to rough down a Ø1" O1 (soft) punch, from square stock to round in the 4-jaw chuck. I think he was taking something like .250 DOC each side. Because of the square stock, this was a heavily interrupted cut. It looked like the toolbit was flexing about .010 or more every time it encountered the work (4 times/rev). The feed was not aggressive, but not conservative either. The lathe was in a back gear. Carbide would have been a significant PITA because of the interrupted cut. Two passes and it was done. Simple. Regards, Robin |
#15
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Basic question about roughing om a lathe
"Ace" wrote in message ... any tool wear would tend to force tool out of cut without digging in, and kept nose radius approx. .02 inch. On that note, I've found it's actually a very good idea to keep the body of the toolbit at very close to perpendicular to the work such that it's far less likely to flex away from the work and cause scoring marks around the part. It sounds like a non-issue, but I've had good success following this rule. Regards, Robin |
#16
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Basic question about roughing om a lathe
On Wed, 15 Feb 2006 21:57:35 GMT, "Tom Gardner"
wrote: You need to order my: " SPEED/FEED SMOKE COLOR CHART" available for $9.95 - Visa/MC accepted. Use it to maximize your feed rates based on the color of the smoke being produced. You finally brought it out? Coo!! It will go well with the original Speed/Feed Chip Color Chart I purchased from you last year. Now I get beautiful deep blue chips and fast production. The color chart is Great!! Though..you really need to update the section on turning Magneseum. Least thats what the fire department said. Gunner "A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences." - Proverbs 22:3 |
#17
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Basic question about roughing om a lathe
Bob, I'd really like to see some professional's answers to you question.
I can only offer the opinion of a hobbyist using a smaller lathe. (9" Sheldon) If everything else is the same; power, rigidity, cutting speed & direction, size and kind of metal, tool bit, finish, etc. etc. then as you well know, for any particular operation there is a 'best and max' combinaton of feed and depth of cut to remove the most metal per minute. IMO, charts & tables [& ng's ] give us useless info re what's 'best' for small machines and workpieces. For me, it's intuition from many failed cuts and tries til the lathe complained. I think your premise is correct, but trouble is that things are never equal. Ex: greater depth of cut to get under the skin of cast iron will remove more metal per minute or long thin spindle= less depth & greater feed vs short thick blank= deeper depth & less feed. YMMV, but remember I'm a rank amateur. Regards, Arch |
#18
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Basic question about roughing om a lathe
Bob Engelhardt wrote in
: If I'm doing rough cuts on a lathe, where the finish is totally immaterial, is there a difference if I take a .010 cut with .050 feed versus a .050 cut and .010 feed? I figure in both cases the cross section of the chip is the same (.010 x .050), so the rate of removal is the same (for the same speed). It makes no real difference. The load on the tool is nearly the same. In terms of time taking .01" passes at the higher feed rate will take longer. Particularly on a manual machine. Also the finish on the rough cut does matter. Feeding at a high feed rate will give you a rougher more "wavy" finish. Some of that waviness is very likely to show up in the finish turn. Putting it another way, is there an approach which maximizes rate of removal? I.e., maximize cut and set feed as high as you can, or vice versa? In the case of a .05" DOC and a .010 IPR feed rate, the resultant force on the cutting tool, and therefore your work, will be about 186 lbs. for a medium carbon alloy steel like 4140. For Aluminum it would be about 80 lbs. You are on the right track in your thinking here. The chip thickness for a given material determines the force acting on the tool and the work. The example of a .05" IPR feed rate is probably not practical unless you have a very large nose radius on your tool. A large nose radius will increase the cutting forces, as will a negative rake tool. You can calculate how much a bar of a given diameter will deflect for a given amount of load applied to the end of it over a given amount of unsupported length. When you exceed a certain amount of deflection you will get poor tool life no matter what else you do. Since you can also calculate the amount of force for a cut, you can find an optimum cross section size for your chip. In terms of time taken to rough down the material, the fewer passes the better. The idle time of retracting the tool, the carraige, resetting the depth, and re-engaging the feed all add up to extra non-productive time. Maybe I should generalize even more and ask if there is a speed which maximizes removal. I.e., slow with big chips or fast with small ones? Speed and depth of cut affect horsepower directly. Speed doesn't affect the load (feed, tangential, and radial force) acting on the tool and the work. So for a given maximum chip thickness, you should run as fast as you can while staying within the horsepower of the machine, and not melting the tool. I have the feeling that all that matters is the power of the lathe. That for a given power, you can only remove so many cubic inches per minute and the combination of cut, feed, and speed is not very important. Not so. For a given horsepower available at the spindle you will only be able to remove "X" number of cubic inches per minute of a given material at maximum. That much is true. But the amount of time taken and the economy of the operation will be affected by the variables of speed, feed, DOC, tool geometry, and the machinability of the material. Tool geometry only makes a small difference, and usually there is little to be done about the material. So speed feed and DOC are the biggest variables. You need to run at a speed that is not so high that it doesn't melt the tool. Nor do you want to run too slow. The pressure on the tool tip increases the lower the speed is. Run too slow with carbide or even HSS, and the tool will chip as the pressure is high. You also don't want to take too many passes as that adds idle time. A slower feed rate means that a lot more material will travel by the tool tip than would at a higher feed rate. So the tool life will be shorter. -- Dan |
#19
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Basic question about roughing om a lathe
greybeard ""greybeard\"@mcleodusa,net wrote in
: Higher speeds mean more heat on the tool, higher feeds mean more pressure, it's up to the operator to find the balance. Higher feeds mean higher cutting force, measured in pounds, not PSI. Higher speeds lower the pressure (PSI not Lbs.) on the tool tip. I would not recommend going to more than somewhere near .025 feed on anything, as far as single point tooling is concerned, you're asking an awful lot of that tool in terms of pressure that it has to stand. If you're looking to save time, moving the carriage back, feeding in and starting it again take time. Higher feeds will generally give less tool wear, but not without it's own cost. Light cuts are something I try to stay away from, they seem to wear the tool faster than a heavier cut. Lighter feeds do wear the tool sooner. Consider turning a one inch diameter for a one inch length. Each turn of the spindle at a one inch diameter means 3.1416 inches of material will pass by the tool tip. At a .001 IPR feed rate 3141.5927 inches of material will pass by the tool tip in a one inch length of cut. Kick the feed up to .010 IPR and only 314.1593 inches will pass by the tool tip in the same one inch length of turn. So not only does turning too slow waste time, it wastes tool life. -- Dan |
#20
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Basic question about roughing om a lathe
"D Murphy" wrote in message ... greybeard ""greybeard\"@mcleodusa,net wrote in : Higher speeds mean more heat on the tool, higher feeds mean more pressure, it's up to the operator to find the balance. Higher feeds mean higher cutting force, measured in pounds, not PSI. Higher speeds lower the pressure (PSI not Lbs.) on the tool tip. I would not recommend going to more than somewhere near .025 feed on anything, as far as single point tooling is concerned, you're asking an awful lot of that tool in terms of pressure that it has to stand. If you're looking to save time, moving the carriage back, feeding in and starting it again take time. Higher feeds will generally give less tool wear, but not without it's own cost. Light cuts are something I try to stay away from, they seem to wear the tool faster than a heavier cut. Lighter feeds do wear the tool sooner. Consider turning a one inch diameter for a one inch length. Each turn of the spindle at a one inch diameter means 3.1416 inches of material will pass by the tool tip. At a .001 IPR feed rate 3141.5927 inches of material will pass by the tool tip in a one inch length of cut. Kick the feed up to .010 IPR and only 314.1593 inches will pass by the tool tip in the same one inch length of turn. So not only does turning too slow waste time, it wastes tool life. -- Dan Dan, Your last two posts make a lot of sense to me. Thanks for the illumination. If I am following this correctly the tool radius would limit the feed rate as, if you exceed the radius in feed rate you begin to make threads and a rough finish. I tend to leave my feed rate set at .0042" and adjust the depth of cut and speed to get "happy sounds" from the lathe I can see from what you have said that I should be trying to up that feed rate to reduce tool travel time and wear. The QC box on my lathe has feeds listed from .0078" to .0042" so I have always stayed below .01" for feed but it looks like I could go up to 100 TPI on the threading chart and have a reasonable feed rate for a tool with 1/64" radius. Am I close to correct here? Thanks Glenn |
#21
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Basic question about roughing om a lathe
"Glenn" wrote in :
Dan, Your last two posts make a lot of sense to me. Thanks for the illumination. If I am following this correctly the tool radius would limit the feed rate as, if you exceed the radius in feed rate you begin to make threads and a rough finish. Right. Also the trailing edge of the tool will be cutting. Proper tool geometry isn't really designed for that. I tend to leave my feed rate set at .0042" and adjust the depth of cut and speed to get "happy sounds" from the lathe I can see from what you have said that I should be trying to up that feed rate to reduce tool travel time and wear. The QC box on my lathe has feeds listed from .0078" to .0042" so I have always stayed below .01" for feed but it looks like I could go up to 100 TPI on the threading chart and have a reasonable feed rate for a tool with 1/64" radius. Am I close to correct here? Yes. Just remember the higher the feed rate the greater the turning forces are. As a rule of thumb I would also limit the feed rate to about half of the radius. A 1/32" radius at a feed rate of .01 IPR should give you right around a 125 Ra finish in a proper set up on a good machine. A .01 IPR feed rate with a 1/64" tool nose radius will give you around a 225 Ra finish. I think that's too rough, and too much of the nose is buried into the cut. You also need to consider the shape of the tool tip. An 80 degree tool can take a higher feed than can a 35 degree tool tip. When roughing it's also better to have a positive lead on the tool if possible. But often a square shoulder is required on the part being turned so you have to use a 0 degree lead tool or a slight negative lead of 3-5 degrees. Try not to use negative lead tool for roughing. They aren't very good at it. -- Dan |
#22
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Basic question about roughing om a lathe
Thanks Dan,
I am going out to the shop now and spearmint a bit I have a 12" Atlas and use mostly carbide inserts or brazed carbide. I intend to make some toolholders for the QC to accept HSS cutting tools. Glenn "D Murphy" wrote in message ... "Glenn" wrote in : Dan, Your last two posts make a lot of sense to me. Thanks for the illumination. If I am following this correctly the tool radius would limit the feed rate as, if you exceed the radius in feed rate you begin to make threads and a rough finish. Right. Also the trailing edge of the tool will be cutting. Proper tool geometry isn't really designed for that. I tend to leave my feed rate set at .0042" and adjust the depth of cut and speed to get "happy sounds" from the lathe I can see from what you have said that I should be trying to up that feed rate to reduce tool travel time and wear. The QC box on my lathe has feeds listed from .0078" to .0042" so I have always stayed below .01" for feed but it looks like I could go up to 100 TPI on the threading chart and have a reasonable feed rate for a tool with 1/64" radius. Am I close to correct here? Yes. Just remember the higher the feed rate the greater the turning forces are. As a rule of thumb I would also limit the feed rate to about half of the radius. A 1/32" radius at a feed rate of .01 IPR should give you right around a 125 Ra finish in a proper set up on a good machine. A .01 IPR feed rate with a 1/64" tool nose radius will give you around a 225 Ra finish. I think that's too rough, and too much of the nose is buried into the cut. You also need to consider the shape of the tool tip. An 80 degree tool can take a higher feed than can a 35 degree tool tip. When roughing it's also better to have a positive lead on the tool if possible. But often a square shoulder is required on the part being turned so you have to use a 0 degree lead tool or a slight negative lead of 3-5 degrees. Try not to use negative lead tool for roughing. They aren't very good at it. -- Dan |
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