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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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Speeds when facing
If you are facing a 5" diameter work in a lathe do you increase the RPMs as
you near the center? -- Michael Koblic, Campbell River, BC |
#2
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Speeds when facing
"Michael Koblic" wrote in message ... If you are facing a 5" diameter work in a lathe do you increase the RPMs as you near the center? -- Michael Koblic, Campbell River, BC Yes.... Ed |
#3
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Speeds when facing
"Michael Koblic" wrote:
If you are facing a 5" diameter work in a lathe do you increase the RPMs as you near the center? Surface feet per minute decreases as you move toward center. I don't think too many people stop and change speeds as they face though. Start out at the right speed and accept that you will be slow at center. My Clausing has a varidrive so I actually could give the speed control a turn as I head in if I was in a hurry CNC lathes have a constant surface speed mode that ramps the spindle up as you approach center. Also have a G code to say do not go about a certain rpm. Wes |
#4
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Speeds when facing
Yes, increasing the speed would be the preferred method.
On a machine with a fixed spindle speed, if the speed was selected for the smaller portion of the diameter, I expect that there are few lathes that won't demonstrate some chatter at some point on a 5" diameter facing cut if the spindle speed remains constant. As the cutting tool approaches the center, the surface speed (SFM) decreases, reaching zero at dead center. This same effect is taking place at the center of a twist drill. The SFM is essentially zero at the center of the drill point. The cutting edge SFM increases toward the outer edges of the cutting edges. WB .......... metalworking projects www.kwagmire.com/metal_proj.html "Michael Koblic" wrote in message ... If you are facing a 5" diameter work in a lathe do you increase the RPMs as you near the center? -- Michael Koblic, Campbell River, BC |
#5
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Speeds when facing
On Thu, 11 Sep 2008 16:44:48 -0700, "Michael Koblic"
wrote: If you are facing a 5" diameter work in a lathe do you increase the RPMs as you near the center? Yes. Most CNC lathes have a feature that does this for you when you program the appropriate command You also have to do the same when using a cut off tool However...in most HSM applications, you really dont need to do so. Gunner |
#6
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Speeds when facing
On Sep 11, 7:44*pm, "Michael Koblic" wrote:
If you are facing a 5" diameter work in a lathe do you increase the RPMs as you near the center? -- Michael Koblic, Campbell River, BC I've never seen a problem when cutting at low speed with HSS. |
#7
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Speeds when facing
"Jim Wilkins" wrote in message ... On Sep 11, 7:44 pm, "Michael Koblic" wrote: If you are facing a 5" diameter work in a lathe do you increase the RPMs as you near the center? -- Michael Koblic, Campbell River, BC I've never seen a problem when cutting at low speed with HSS. Well, surface finish can go to pot when speeds are too low, and the variation in speeds across a large face is one of the classic problems in machining. When CNC came in, a very big deal was made of the fact that you could program for constant surface speed to overcome the problem. In some old textbooks you'll see different comments upon it, one of which was a suggestion to preferentially cut from the center out, adjusting speed for the minimum that would give you a clean cut near the center and counting on the heat tolerance of HSS to carry you through to the outside diameter. This is iffy, of course, but it's the way it frequently was done in production, back in the days of HSS tools and manual machines in high-volume manufacturing. I don't think there's any really good solution with a machine that can't change speeds during a cut. It's been a while since I read the old articles and books that talked about it but I don't remember any clear answers. I've run into the problem myself, which was one of the first things that motivated me to try using brazed, carbide-tipped inserts on my old South Bend. They handled it pretty well, especially in cast iron, which was giving me fits. -- Ed Huntress |
#8
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Speeds when facing
"Ed Huntress" wrote in message ... "Jim Wilkins" wrote in message ... On Sep 11, 7:44 pm, "Michael Koblic" wrote: If you are facing a 5" diameter work in a lathe do you increase the RPMs as you near the center? -- Michael Koblic, Campbell River, BC I've never seen a problem when cutting at low speed with HSS. Well, surface finish can go to pot when speeds are too low, and the variation in speeds across a large face is one of the classic problems in machining. When CNC came in, a very big deal was made of the fact that you could program for constant surface speed to overcome the problem. In some old textbooks you'll see different comments upon it, one of which was a suggestion to preferentially cut from the center out, adjusting speed for the minimum that would give you a clean cut near the center and counting on the heat tolerance of HSS to carry you through to the outside diameter. This is iffy, of course, but it's the way it frequently was done in production, back in the days of HSS tools and manual machines in high-volume manufacturing. I don't think there's any really good solution with a machine that can't change speeds during a cut. It's been a while since I read the old articles and books that talked about it but I don't remember any clear answers. I've run into the problem myself, which was one of the first things that motivated me to try using brazed, carbide-tipped inserts on my old South Bend. They handled it pretty well, especially in cast iron, which was giving me fits. -- Ed Huntress some times its the metal... I got some metal that welds real good, but turning/milling no good, as the engineer at the steel place, where I bought it, "that stuff don't machine very well, but welding is good" So, its kept separate from the other metal. xman |
#9
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Speeds when facing
"robert" wrote:
I got some metal that welds real good, but turning/milling no good, as the engineer at the steel place, where I bought it, "that stuff don't machine very well, but welding is good" The other side of the coin is 12L14 Wes |
#10
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Speeds when facing
Wes wrote:
"robert" wrote: I got some metal that welds real good, but turning/milling no good, as the engineer at the steel place, where I bought it, "that stuff don't machine very well, but welding is good" The other side of the coin is 12L14 Wes I have read here and other places that leaded steels don't weld well . How do they braze ? Though it's not likely I will be using any , since my main source doesn't carry it . Inquiring minds and all that ... -- Snag '90 Ultra "Strider" '39 WLDD "Popcycle" Buncha cars and a truck |
#11
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Speeds when facing
On Fri, 12 Sep 2008 15:04:32 -0700 (PDT), Jim Wilkins
wrote: On Sep 11, 7:44*pm, "Michael Koblic" wrote: If you are facing a 5" diameter work in a lathe do you increase the RPMs as you near the center? -- Michael Koblic, Campbell River, BC I've never seen a problem when cutting at low speed with HSS. The specific problem tends to be that, if you are using carbide or HSS at high speed, you can get a beautiful finish on the outside. Swarf coming off yellow or blue (for carbide). At some point towards the centre the speed will fall into the region where the Built Up Edge phenomenon occurs. The surface finish will go to hell during this range. As the tool gets closer to the centre the finish will still be bad, because there is a rough gob of steel welded to the tip of the tool. Running HSS below the BUE region all the way will avoid the problem, but can still benefit form changing the speed as the cut progresses if possible e.g. from maybe 50rpm at 5" to 250 at 1". This is easy if you have a variable speed drive. It's a waste of time if you need to do belt changes. Running carbide above the BUE region can get a bit scary towards the centre of the part :-) PS. The best way to get a nice finish is to slap the part on the surface grinder after facing BEG Mark Rand RTFM |
#12
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Speeds when facing
On Sep 13, 7:37*pm, Mark Rand wrote:
On Fri, 12 Sep 2008 15:04:32 -0700 (PDT), Jim Wilkins wrote: I've never seen a problem when cutting at low speed with HSS. The specific problem tends to be that, if you are using carbide or HSS at high speed, you can get a beautiful finish on the outside. Swarf coming off yellow or blue (for carbide). At some point towards the centre the speed will fall into the region where the Built Up Edge phenomenon occurs. The surface finish will go to hell during this range. As the tool gets closer to the centre the finish will still be bad, because there is a rough gob of steel welded to the tip of the tool. Running HSS below the BUE region all the way will avoid the problem, but can still benefit form changing the speed as the cut progresses if possible e..g. from maybe 50rpm at 5" to *250 at 1". This is easy if you have a variable speed drive. It's a waste of time if you need to do belt changes. That's what I've seen, too, but I'm not sure enough of the details to post them for posterity. I try to keep the speed below yellow chips with HSS and up in the blue chips with carbide. If you stop to change belt speed the bit will leave a ring on the work. Good HSS will take the heat. A lot of my bits are Medium Speed Steel from Enco, which at least are easy to grind. With practice I've learned how to recognize and mostly avoid built-up edges and their rough finish. In general I think it's from following the bit grinding and honing instructions in old lathe manuals and water-annealing bad steel. For some reason facing out seems to leave a better finish. Maybe it has to do with wear and play on my 1965 lathe, or because it's a shear cut. PS. The best way to get a nice finish is to slap the part on the surface grinder after facing BEG Mark Rand Before I bought one I filed and sanded out the tool marks with a single-cut pillar file and fine SiC paper on a steel block. The amount of work involved is -why- I bought the $100 worn-out surface grinder, which has been very useful for finishing and for sharpening tools. |
#13
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Speeds when facing
As everyone has said ... YES
On my old import lathe it was a bitch because of fixed speeds. It was a lot better when I outfited that machine with a DC motor. On my Clausing 5914 with its varidrie and power crossfeed it's no problem, kick in the crossfeed drive and twist up the RPM as it cuts in :-))) This is a MAJOR reason to get a VFD for your lathe... --.- Dave "Michael Koblic" wrote in message ... If you are facing a 5" diameter work in a lathe do you increase the RPMs as you near the center? -- Michael Koblic, Campbell River, BC |
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