On another note if you have purchased blocks and want to join them together to make a structured fixture you will find the 3/8 bolts don’t fit through the unthreaded holes like they’re supposed to. I just drilled out my 2,4,6 blocks with indexable r390 and it cut through that hard steel no issues. Now I can slip 5/8 bolts through and screw two blocks together as a right angle and don’t need a right angle plate.
[Edit for accuracy] While the exact temperatures will vary a bit by alloy, halting the quench above 400f(200c) may result in a significant lower-bainite structure rather than the [generally] harder martensite structure traditionally sought in quenching. Not necessarily a bad thing, lower bainite generally requires little to no tempering and can have similar properties to heavily tempered martensite.[good for springs, eg] I believe the process name for the procedure is austempering, though you are in a hybrid temperature range. (in austempering the "tempering" step is more of a holding point in the quench to give the bainite time to form) 230c/450f** is a typical start temperature for martensite[Ms or 1%] 175c[M50] and 70c[M90]. (**mid range, for W1 tool steel or 1070 plain steel. 1018 is up at 470c(but why quench 1018?)) Many low alloy steels have a martensite finish temperature [Mf/M100/M99(depends on which books you have)] well below room temperature, but 20c is about 7% retained austenite[M93] in W1 tool steel. The retained austenite may be converted to a ferrite and cementite structure during tempering.(specifics are temp and time dependent) In practice martensite is temperature but not time dependent, while pearlite, spherodite, and bainite are both temperature and time dependent. (which is why rapid quenching of austenite can skip past them and form martensite) Strictly speaking martensite is also time dependent but its formation propagates at the speed of sound, so instant in practice.
Addendum to my last post. Low carbon steels have the highest Ms temperature. As alloy and carbon content increases the martensite transition temperatures drop. The following are all in Celsius. Clearly carbon has the biggest effect. "The equation is valid only if all the alloying elements are completely dissolved in the austenite. Ms = 561 - 474C - 33Mn - 17Ni - 17Cr - 21Mo For high-alloy and medium-alloy steels Stuhlmann has suggested the following equation: Ms(°C) = 550 - 350C - 40Mn - 20Cr - 10Mo - 17Ni - 8W - 35V - 10Cu + 15Co + 30Al" (so 1050 steel would have an Ms of about 320c and W1 about 200c) This can be altered in hyper and hypoeutectoid steels with very accurate control of the austentizing furnace temperature, such that the effective level of *dissolved carbon is altered. But this gets beyond the realm of video comments.
Marc, I know that was tough material, so you slowed the couterbore rpm way down. But... what surface speed should be used in general for counterboring in mild steel? Cheers, Glenn
Hi Glenn, the cutting speed is the same for all operations. For mild steel I would suggest around 120 F.P.M. The problem isn't the RPM, it is the feed. Form tools offer a large cutting surface to the part, this requires a lot of force to feed the tool into the part and the end result for many machines is that we just can't feed fast enough. As an example lets take a four flute counterbore around 3/4" ø. For mild steel we would calculate at 120 FPM around 640 RPM. To feed the tool without chatter I will want a tooth load of at least 0.004". The feed would have to be 640 X 0.004 X 4 = 10.24 inches per minute. That is an impressive feed and almost impossible to attain with most drill presses. The answer is simple, lower the RPM until you get to a point were you can feed the tool comfortably without chatter. It has been my experience that four times slower works well for most home type drill presses. I hope this helps, Marc L'Ecuyer
Marc, much appreciated for the explanation. I was hoping for some quick rule of thumb that I could apply to the diameter of the tool to get a approximate RPM. You know, something like on reamers - half the speed double the feed -kinda thing. Just something practical I could use when I go to use one of these counterbores. Glenn
Glenn Davis Hello again Glenn! The biggest problem with counter bores is chatter. Chatter is caused by an insufficient chip load (as is the case for reamers and counter sinks). Turning at slower RPM's permit you to maintain a good chip load from start to stop. Because we naturally slow down the feed towards the end of the hole, the chatter often appears at the end of a cut. So a good rule of thumb would be to stay around 100 RPM's for holes 3/4" or smaller. Reduce even more if hole is larger. It is important to feed positively right to the bottom of the hole and retract as quickly as possible.
Hi Andy, you have a good eye! I made a booboo! To force the students to use both the taper and the bottoming taps I usually order hand taps that do not have reduced shanks. As is clearly visible at minute 13:35 of the video, I am using reduced shank taps. Even though it is only partially reduce (they cannot be run through the part completely) the taper tap I am using can produce a completely thread for this depth of hole. Thanks for the comment since it permits even more explanations and that will benefit others. Marc L'Ecuyer
I'm looking forward to part 3, I don't think there is enough information about precision grinding on the Internet.
Another excellent video. Looking forward to the other parts
Marc,
Very nice. Looking forward to the grinding video.
Enjoyed and studied. Thanks, Marc.
very good video, thank you for your time.! Greetings from Argentina
another good video Marc ty
On another note if you have purchased blocks and want to join them together to make a structured fixture you will find the 3/8 bolts don’t fit through the unthreaded holes like they’re supposed to. I just drilled out my 2,4,6 blocks with indexable r390 and it cut through that hard steel no issues. Now I can slip 5/8 bolts through and screw two blocks together as a right angle and don’t need a right angle plate.
[Edit for accuracy] While the exact temperatures will vary a bit by alloy, halting the quench above 400f(200c) may result in a significant lower-bainite structure rather than the [generally] harder martensite structure traditionally sought in quenching. Not necessarily a bad thing, lower bainite generally requires little to no tempering and can have similar properties to heavily tempered martensite.[good for springs, eg]
I believe the process name for the procedure is austempering, though you are in a hybrid temperature range. (in austempering the "tempering" step is more of a holding point in the quench to give the bainite time to form)
230c/450f** is a typical start temperature for martensite[Ms or 1%] 175c[M50] and 70c[M90]. (**mid range, for W1 tool steel or 1070 plain steel. 1018 is up at 470c(but why quench 1018?))
Many low alloy steels have a martensite finish temperature [Mf/M100/M99(depends on which books you have)] well below room temperature, but 20c is about 7% retained austenite[M93] in W1 tool steel. The retained austenite may be converted to a ferrite and cementite structure during tempering.(specifics are temp and time dependent)
In practice martensite is temperature but not time dependent, while pearlite, spherodite, and bainite are both temperature and time dependent. (which is why rapid quenching of austenite can skip past them and form martensite) Strictly speaking martensite is also time dependent but its formation propagates at the speed of sound, so instant in practice.
Addendum to my last post.
Low carbon steels have the highest Ms temperature. As alloy and carbon content increases the martensite transition temperatures drop. The following are all in Celsius. Clearly carbon has the biggest effect.
"The equation is valid only if all the alloying elements are completely dissolved in the austenite.
Ms = 561 - 474C - 33Mn - 17Ni - 17Cr - 21Mo
For high-alloy and medium-alloy steels Stuhlmann has suggested the following equation:
Ms(°C) = 550 - 350C - 40Mn - 20Cr - 10Mo - 17Ni - 8W - 35V - 10Cu + 15Co + 30Al"
(so 1050 steel would have an Ms of about 320c and W1 about 200c)
This can be altered in hyper and hypoeutectoid steels with very accurate control of the austentizing furnace temperature, such that the effective level of *dissolved carbon is altered. But this gets beyond the realm of video comments.
Marc,
I know that was tough material, so you slowed the couterbore rpm way down.
But... what surface speed should be used in general for counterboring in mild steel?
Cheers,
Glenn
Hi Glenn, the cutting speed is the same for all operations. For mild steel I would suggest around 120 F.P.M. The problem isn't the RPM, it is the feed. Form tools offer a large cutting surface to the part, this requires a lot of force to feed the tool into the part and the end result for many machines is that we just can't feed fast enough. As an example lets take a four flute counterbore around 3/4" ø. For mild steel we would calculate at 120 FPM around 640 RPM. To feed the tool without chatter I will want a tooth load of at least 0.004". The feed would have to be 640 X 0.004 X 4 = 10.24 inches per minute. That is an impressive feed and almost impossible to attain with most drill presses. The answer is simple, lower the RPM until you get to a point were you can feed the tool comfortably without chatter. It has been my experience that four times slower works well for most home type drill presses. I hope this helps, Marc L'Ecuyer
Marc, much appreciated for the explanation.
I was hoping for some quick rule of thumb that I could apply to the diameter of the tool to get a approximate RPM. You know, something like on reamers - half the speed double the feed -kinda thing.
Just something practical I could use when I go to use one of these counterbores.
Glenn
Glenn Davis Hello again Glenn! The biggest problem with counter bores is chatter. Chatter is caused by an insufficient chip load (as is the case for reamers and counter sinks). Turning at slower RPM's permit you to maintain a good chip load from start to stop. Because we naturally slow down the feed towards the end of the hole, the chatter often appears at the end of a cut. So a good rule of thumb would be to stay around 100 RPM's for holes 3/4" or smaller. Reduce even more if hole is larger. It is important to feed positively right to the bottom of the hole and retract as quickly as possible.
How would you; slightly, (1/2 turn Clockwise), rotate a threaded rod, ground Flush?
why not just run the taper tap further through to get full threads all through the hole?
Hi Andy, you have a good eye! I made a booboo! To force the students to use both the taper and the bottoming taps I usually order hand taps that do not have reduced shanks. As is clearly visible at minute 13:35 of the video, I am using reduced shank taps. Even though it is only partially reduce (they cannot be run through the part completely) the taper tap I am using can produce a completely thread for this depth of hole. Thanks for the comment since it permits even more explanations and that will benefit others. Marc L'Ecuyer