Metal Lathe Tutorial 21 : Speeds & Feeds
Summary
TLDRIn this informative episode of 'Lathe Skills', Quinn delves into the complexities of 'speeds and feeds' in machining, debunking common misconceptions and guiding hobbyists through the process of determining optimal cutting parameters. He emphasizes the importance of surface speed, explains the limitations of generic charts, and provides a step-by-step method to calculate spindle RPM and feed rates tailored to individual machines. Quinn also demonstrates the impact of various speeds and feeds on surface finish, encouraging viewers to experiment within safe limits for better machining results.
Takeaways
- π Speeds and feeds is a complex topic with nuances that can be overwhelming for beginners, often leading to a search for simplified guides or charts.
- π The script emphasizes the importance of understanding where speeds and feeds numbers come from, rather than just using them without context.
- π Surface speed is a fundamental property in machining, and while units may vary, the goal is to determine the appropriate spindle RPM for the task.
- π Common charts for surface speed are often based on unspoken assumptions and may not be accurate for all machining setups, especially for hobbyist machines.
- π οΈ The Machinery's Handbook provides detailed tables for calculating speeds and feeds, but they are calibrated for professional settings with more aggressive cutting parameters.
- π¨ There are two main approaches to calculating speeds and feeds: the correct, detailed method involving depth of cut, feed rate, and surface speed calculations, and the more common shortcut method often used by hobbyists.
- βοΈ Depth of cut is a critical factor influenced by machine rigidity, setup, and urgency of the task, with different materials like aluminum, brass, and steel requiring different approaches.
- π Feed rate is determined by the machine's capabilities and is often limited by the number of change gear options available on hobbyist lathes.
- π The relationship between spindle RPM and feed rate is crucial as they both contribute to the final surface speed, affecting the quality of the cut.
- π The script advises against using aggressive cutting parameters from professional guides on hobbyist machines, as they can lead to machine damage.
- π¬ The process of determining optimal speeds and feeds involves a balance of factors including material removal rate, machine power, and desired surface finish quality.
- π Experimenting with different speeds, feeds, and tool nose radii can yield a range of surface finishes, from rough to mirror-like, depending on the setup and material.
Q & A
What is the main topic of the video 'Blondie Axe - Lathe Skills' episode 21?
-The main topic of the video is 'Speeds and Feeds,' which is a critical aspect of machining that the host, Quinn, explains in detail.
Why does the host mention that speeds and feeds is a complicated topic?
-The host mentions that speeds and feeds is complicated because it involves many variables and nuances, which is why there aren't many quick summaries or straightforward guides available.
What is the fundamental property that the host is focusing on in the context of machining?
-The fundamental property the host focuses on is surface speed, which is measured in surface feet per minute (SFM) in the Imperial system.
Why does the host say that the units for surface speed don't matter in the end?
-The host says the units don't matter because the ultimate goal is to determine the spindle RPM, which can be derived from various units of surface speed regardless of what they are.
What is the common mistake the host points out regarding the use of charts for surface speed?
-The common mistake is that these charts often have unspoken assumptions about cutting conditions, and they are usually calibrated for professional settings with more aggressive numbers that may not be suitable for hobbyist machines.
How does the host describe the correct way to calculate speeds and feeds?
-The host describes a three-step process: 1) Select the depth of cut, 2) Figure out the feed rate, and 3) Convert the derived surface speed into spindle RPM.
What is the significance of the nose radius of the cutting tool in relation to the feed rate?
-The nose radius of the cutting tool is significant because it affects the surface finish. The host suggests that the feed rate should be less than half the radius on the nose of the tool to ensure the best possible surface finish.
What does the host mean by 'the correct way' and 'the way that everybody, especially hobbyists, tend to actually do it' when referring to calculating speeds and feeds?
-The 'correct way' refers to the detailed three-step process involving depth of cut, feed rate, and spindle RPM calculation. The 'way that everybody tends to do it' likely refers to using simplified shortcuts or charts without considering the nuances of their own specific machining setup.
How does the host demonstrate the effect of different speeds and feeds on the machined surface?
-The host demonstrates this by machining parts at various speeds and feeds, showing the resulting surface finishes and explaining the relationship between the chosen parameters and the outcome.
What is the importance of the surface speed in tool wear according to the host?
-According to the host, surface speed is an extremely important factor in tool wear, especially in a production CNC shop, and it has a significant impact on tool life, which is why it is extensively covered in the Machinery's Handbook.
How does the host suggest hobbyists approach calculating feed speed on a mill, given the limitations of their equipment?
-The host suggests that hobbyists map the feed speed to the power feed control knob by zeroing out the hand wheel, accounting for backlash, and timing how far the power feed moves the workpiece over a fixed amount of time.
What is the host's advice for hobbyists who want to understand their machine's capabilities better?
-The host advises hobbyists to go through the calibration process he described to determine the upper bounds of speed and feed for their particular machine and then adjust based on their comfort level.
Outlines
π§ Introduction to Machining Speeds and Feeds
In this introductory segment, Quinn, the host of 'lathe skills', embarks on a comprehensive exploration of 'speeds and feeds' in machining, a topic of significant complexity. He acknowledges the common desire for a quick summary of this subject but emphasizes the importance of understanding the derivation of the numbers used in machining. Quinn clarifies that while surface speed is the fundamental property sought, the unit of measurement is irrelevant as the ultimate goal is to determine spindle RPM. He critiques existing charts for their inaccuracies due to unspoken assumptions and promises to guide viewers on creating personalized charts based on first principles, taking into account the nuances from the Machinery's Handbook.
π Calculating Speeds and Feeds from First Principles
Quinn delves into the detailed process of calculating speeds and feeds from first principles, starting with the selection of depth of cut, which is influenced by machine rigidity, setup, and urgency. He discusses the common materials used by hobbyists, such as aluminum, brass, and steel, and their respective depth of cut ranges. The second step involves determining the feed rate, which is often limited by the machine's capabilities and is crucial for calculating surface speed. Quinn explains the relationship between spindle RPM, feed rate, and surface speed, highlighting the importance of these factors in achieving the desired surface finish. He also touches on the impact of the cutting tool's nose radius on the feed rate selection for optimal surface finish.
π Translating Surface Speed into Spindle RPM
This paragraph focuses on the conversion of calculated surface speed into spindle RPM, a critical step in the machining process. Quinn provides a method to adjust the baseline surface speed using scaling factors based on feed rate and depth of cut, derived from Machinery's Handbook. He emphasizes the importance of calibrating one's lathe using this data and provides specific RPM ranges for different materials like steel, aluminum, and brass, considering both roughing and finishing passes. The segment concludes with a demonstration of the impact of aggressive cutting on the machine and the material, illustrating the need for careful selection of cutting parameters.
π Practical Demonstration of Speeds and Feeds
Quinn presents a practical demonstration of the effects of different speeds and feeds on the machining process. He shows the results of roughing and finishing passes using calculated parameters for steel, brass, and aluminum. The demonstration includes visual and auditory cues to convey the intensity of the machining process and the importance of proper setup and support. The segment highlights the consequences of pushing the limits, such as loss of grip and induced taper due to inadequate support. Quinn also showcases the potential for achieving a mirror-like finish with the right combination of speeds and feeds, emphasizing the importance of experimentation within the calculated bounds.
π Understanding the Nuances of Milling Speeds and Feeds
In the final paragraph, Quinn addresses the complexities of calculating speeds and feeds for milling operations. He explains the concept of 'inches per tooth' and how it is influenced by the power feed rate, spindle RPM, and the number of flutes on the cutter. Quinn acknowledges the challenges faced by hobbyists in controlling these variables, especially with manual mills, and suggests methods for approximating feed speed. He also touches on the importance of being aware of nuances such as milling orientation (climb vs. conventional) and slot cutting, which can affect the cutting forces and, consequently, the selection of speeds and feeds. The segment concludes with a reminder of the value of understanding these principles for hobbyist work, despite the availability of simplified formulas and rules of thumb.
Mindmap
Keywords
π‘Speeds and Feeds
π‘Surface Speed
π‘Machinery's Handbook
π‘Depth of Cut
π‘Feed Rate
π‘Surface Finish
π‘Nose Radius
π‘Spindle RPM
π‘Cutting Conditions
π‘Hobbyist Machining
Highlights
Introduction to the complexity of speeds and feeds in machining.
The importance of surface speed in machining, measured in surface feet per minute.
Critique of existing charts for surface speed due to unspoken assumptions about cutting conditions.
Explanation of the correct way to calculate speeds and feeds in a three-step process.
The significance of depth of cut in determining machining parameters.
How to select feed rate based on machine capabilities and material properties.
The relationship between feed rate and surface speed in achieving desired surface finish.
Technical explanation of how nose radius of the cutting tool affects surface finish.
Demonstration of calculating spindle RPM based on surface speed and material diameter.
Calibrating a lathe based on data from charts and the Machinery's Handbook.
Practical examples of speeds and feeds for different materials like steel, aluminum, and brass.
Visual demonstration of aggressive cutting passes and their effects on the machine and material.
The impact of cutting conditions on tool wear and machine longevity.
Macro lens comparison of surface finishes from different cutting passes.
Discussion on the biggest contributor to tool wear: surface speed.
Common shortcuts for calculating speeds and feeds and their limitations.
The nuances of calculating speeds and feeds for milling operations.
Advice on adjusting feed rates on manual mills with variable power feed settings.
Conclusion emphasizing the value of understanding speeds and feeds for optimal machining.
Transcripts
hello Internet my name is Quinn and this
is blondie axe
this is lathe skills a series of quick
videos on getting started in machining
this is episode 21 speeds and feeds yes
the one everybody's been waiting for
this is a meaty topic so let's go speeds
and feeds is a very complicated topic
and I think that's why you don't see a
lot of really great videos or kind of
quick summaries of this topic everybody
always wants like a quick summary of
speeds and feeds just tell me what to do
right okay fine
here's the numbers you should use got it
no don't go back and try to freeze frame
your YouTube player because I'm going to
show you where those numbers come from
and how to get those numbers for you
you know Machinery's handbook devotes a
hundred pages to this topic and there's
a reason why there's a ton of nuance to
it however there are some kind of rules
of thumb and there are some shortcuts
that I think hobbyists can take and I'm
going to show you you know what happens
when things go right yeah and we're
gonna push things to fail you're on my
little machine so that's gonna get
exciting stay tuned for that the
fundamental property that we're after
here is surface speed in the Imperial
machine shop we measure that in surface
feet per minute but that's a really
stupid unit the thing is though the
unit's don't matter we're ultimately
after a spindle RPM so it doesn't matter
what we use to get there it could be
centimeters per deck a second or King
George's thumbs per fortnight doesn't
matter if like most beginners you
frantically googled around looking for
some kind of guidance on speeds and
feeds mostly what you'll find are these
charts of surface speed that people have
produced and you know they'll
confidently state things like steel
should be cut at 120 surface feet per
minute it'll have a formula so you can
convert your the diameter of your part
or your cutter into surface feet per
minute and that's all you need to know
the problem is that these charts are all
varying degrees of wrong they all have a
set of unspoken assumptions about your
cutting conditions so what I'm going to
show you here is how to work forward
from first principles to basically make
your own chart for your particular
machine now most of those homemade
charts are getting their information
from this section of Machinery's
handbook and so there's a series of
tables in here for different materials
so here we're looking at 10:18 mild
steel and do you know the Brinell
hardness of your mild steel I bet you
don't but
most people are assuming you know
somewhere in this range here ninety 220
surface feet per minute for high speed
steel so you know this is where those
numbers come from that you find in all
those charts however what nobody ever
seems to mention is that the tables in
Machinery's handbook are calibrated for
a hundred and twenty five thousand of
cut and a twelve thousand feed rate now
for the hobbyist those are extremely
aggressive numbers those are very
unlikely to be numbers that your average
hobbyist machines can achieve remember
Machinery's handbook is a professional
tool for professionals who have big
machines and are trying to maximize
production so if you try and push your
bench top hobbyist machine to 1/8 inch
depth of cut that's a quarter of an inch
off the diameter on a direct read hand
wheel a quarter inch diameter reduction
at 12,000 you're gonna blow that machine
up so I hope you got the warranty I
think I can summarize this in that there
are two basic ways that you can
calculate speeds and fees there's the
correct way and then there's the way
that everybody especially hobbyists tend
to actually do it the correct way is a
three step process step one is to select
your depth of cut now this is generally
dictated by three things it's dictated
by the rigidity of your machine the
rigidity of your setup and how much of a
hurry that you're in if you've got two
hundredths out of a move off a dimension
obviously you want to do that as quickly
as possible so you're not standing
around all day for this exercise we'll
assume that your setup is as rigid as it
can be for your machine so you've got
good tail support you've got a good grip
with your Chuck you know all those sorts
of things so from there it's really down
to the material that you're cutting you
know the most common hobbyist materials
are going to be aluminum brass and steel
for aluminum and brass they're very easy
to cut so 60 70 80 thousand that cut all
you know all within the realm of
possibility now a steel we're much more
in the four teeth out of cut range kind
of at the upper limit I don't typically
get that aggressive with steel and my
little machines I tend to stick around
you know 30,000 of cut or you know sixty
sixty to eighty thousand wheel for a
direct read hand wheel so step one
establish your depth of cut step two is
figuring out your feed rate now with
larger machines with complicated
transmission
or electronic leadscrews or things like
that you may have a lot of choices on
feed rate however with hobbyist benchtop
machines like this you're probably only
going to have one two or three choices
here so this is typical of these
benchtop machines you're going to have
change gears in here that are set up for
specific feed rates so there's on this
particular machine there are two sets of
change gear options for power feeding so
there's a course set and a fine set the
course set is incredibly fast and I
don't know why you would ever use them
so you're going to start with the fine
set and the fine set is what's installed
on the machine in this case from the
factory and so this tells you what your
actual feed rates are for both turning
and facing because this machine also has
power cross feed now on these tables
here for a given gear set there are
three options C a and B and those
correspond to the quick change gearbox
so for a given set of change gears
you've got three feed speeds and this
chart tells you precisely what those
feed rates are now these units here are
in thousandths of an inch per rotation
of the spindle which is a very logical
way to measure feed rate and here's why
we measure feed rate in distance
traveled per rotation of the spindle
because as you recall from the surface
finish video the lathe is always cutting
a helix and like I said at the top of
the show ultimately what we care about
here is the surface speed of the cutting
tool over the material however you know
people think of rpm as being the only
thing that contributes to surface speed
that in diameter but in fact the feed
rate also contributes to that and as you
remember from your junior high math
classes you know we've got two vectors
to get the final velocity you add them
together so in this case we've got one
vector here coming from the spindle rpm
that's you know contributing to our
velocity and then you've got a second
vector here that's coming from your
power feed rate contributing to your
velocity and so this the sum of these
two vectors is ultimately going to be
your service feet per minute and this is
what we care about so part of the reason
that we start with power feed rate and
in this calculation is because we have
less control over that rpm we have lots
and lots of choices but power feed rate
is much more limited but we do have a
couple of choices you know on this
machine that I'm Dennis
straining we have three choices for
power feed rate so how do we choose
between them well there are three things
that go into our decision for feed rate
first is once again how big a hurry
we're in if we have a lot of material to
remove we want to be feeding as fast as
possible to is the power of the machine
the the feed rate is limited by the
horsepower of the machine and how
aggressively you know it can pull that
cutter through the material and the
third main factor is surface finish now
recall from the surface finish video
that one of the main contributors to
surface finish is the radius on the nose
of your cutting tool what I said in that
video is that the affect of the nose
radius is basically to smear the thread
cutting lines that would otherwise exist
if the tool was sharp nosed again since
the lathe is cutting helix a nose radius
kind of blurs the lines well now that
we're trying to choose feed rate it's
time to get technical about this or best
possible surface finish the rule of
thumb is that you want your feed rate to
be less than half the radius on the nose
of your tool and that ensures that each
lap around that helix
some portion of this curve is gonna be
there to smear out the the tool marks
from the previous pass so guesstimating
this guy with the calipers this
particular tool has a nose radius
between 10 and 15 thou so I'd be looking
for a feed rate somewhere like 500 bucks
mmm surface finish so if I'm setting up
to do a finishing pass with that tool I
just showed we know that we want a power
feed rate somewhere 5,000 feet gear
range on this machine because I'm not
insane and so on the turnin section here
and I've got three options I've got
10,000 or five or two and a half
thousand the a or C range five or two
and a half though but for finishing I'm
always going to go with the C range
because that's gonna ensure that each
lap around that material is going to be
within my nose radius once again
grounding tools by hand it can be tricky
you know exactly what your nose radius
is so just go as fine as you can for
finishing
but once again for this exercise we're
trying to determine the upper bounds how
aggressive we can be with all the
variables for speeds and speeds so we're
going to resume our calculations using
this 10,000 will use steel so I've
established my depth of cut the maximum
that I can do is 40,000
most I'm comfortable with and my feed
rate the maximum on that machine is
going to be 10,000 so I go to my
materials chart here and Machinery's
handbook and let's take this 120 surface
feet-per-minute number as my baseline
and then I multiply that base speed by
this scaling factor for my feed rate
which is 10,000 tells me that I can
increase that speed by 1.08 and this
reflects the difference between the
12,000 the tenth our eight that I'm
going to be using and then we look up my
depth of cut and we find it there's an
additional scale factor of 1.15 because
this 47th out depth of cut is going to
be quite a bit less than the 125 that
the original table was calibrated for so
with our depth of cut and our feed rate
established the final step is convert
that surface speed that we derived into
a spindle rpm and this is done based on
the diameter using this chart here so I
like to do this for a one-inch diameter
so that's going to be the diameter of
the stock for the lathe or the cutter
for the mill and one-inch is kind of a
nice average of things you're going to
be working with in a hobby shop and then
you can mentally fudge these numbers up
or down for smaller or larger stock or
cutters so for steel for example we're
typically going to end up in this
surface speed range so we're gonna end
up somewhere between like 450 and 800
rpm so a great exercise is to calibrate
your lathe based on this data so
starting with the surface
feet-per-minute baselines on those other
charts which again are for an eighth
inch depth of cut and a twelfth AO feed
rate and then modify those numbers using
this chart for you know the maximum
depth of cut that your lathe can handle
you need to those materials and then
modify it again for whatever your
fastest feed rate is that you're going
to use and that's going to give you the
upper bounds of RPM and feed rate for
each of your materials and then you can
kind of go down from there now that's a
lot of fooling around so I've done that
math for you for a typical bench top you
know hobbyist lathe and the nine or ten
inch swing range and if you have larger
machines these numbers will still work
they'll be you know more conservative
than you need or steel your base speed
is 120 for a roughing pass of four teeth
out of cut and
10500 RPM a finishing pass of 10th our
less that's a two and a half thousand
rate 800 RPM for aluminum your base
speed is 500 for a roughing pass of
60,000 cut that's a ten thousand two
thousand rpm finishing pass of tenth our
lists you want a two and a half thousand
as much RPM as you can muster for brass
your base speed is 350 for a roughing
pass of sixty thousand of cut and a ten
thousand hundred RPM for a finishing
pass of tenth our less you want a two
and a half thousand as much RPM as you
can muster okay so let's see what those
numbers actually look like on the
machine so this is the roughing pass
that I just calculated for you in steel
and this is definitely what I would
consider the most aggressive cut that I
would ever do on this machine and steel
it looks pretty calm on video but in
real life there's a lot of noise a lot
of smoke and overall quite a lot of
drama you can see when I wind the cutter
back how it drags a fair bit on the
surface and that spring pass tells you
how much load there was on that cutter
because it sprung back quite a bit once
that cutting force was removed and here
you can see that the chip action there
is okay it's not breaking as soon as it
should the grind on my tool might not be
perfect might need honing but it goes to
show why I don't typically run the
machine this hard now let's see if we
can clean up that finish using the
finishing pass numbers that I just
showed you and that's pretty good but I
think we can do better so just to show
you the affected speeds and feeds have
on your surface finish here's a little
higher rpm and a finer cut this is a
5000 cut and that's a very fine finish
indeed for mild steel anyway and here's
a roughing pass with those brass numbers
now you can tell when you're really
pushing brass because it's wheels like a
banshee
now let's see what happens if we push it
too hard so this is that same tenth
outfit but I've put some aluminum shims
in there so the Chuck doesn't have as
good a grip you can see that the force
of the feed rate is actually pushing the
part into the Chuck and has caused it to
lose its tail support and well
everything's gone pear-shaped quite
literally you can see in addition to the
dreadful finish that there's a taper in
there that's been introduced because the
part got pushed out of the tail stock
just to show you how much wiggle room
there can be in these numbers here's
that same 60,000 if cut very rigid set
up sharp nose tool mind you but a very
fine feed the fineness this machine will
do and look at how nice that finishes
that's actually quite a good final
finish for this part so as you can see
play with the numbers and you'll find
that there's maybe more possibilities
than you thought quick sidebar note that
that wasn't actually 1,400 rpm as I said
in the numbers that was actually a
thousand rpm because I'm my lathe that's
as high as I can go without moving the
drive belts so it just goes to show that
there's a fair amount of wiggle room in
these numbers especially at the higher
rpm ranges now let's look at the other
extreme here's a tool with a huge nose
radius and I'm doing a very light pass
extremely fine feed an extremely high
rpm and that finish is like a mirror
this is probably the best finish that
you're going to get right off the
machine without any kind of polishing so
play with the extremes of the numbers
just to see what's possible you might be
surprised just to drive this point home
let's take a look at these parts under
the macro lens so here's the roughing
pass that we did on the brass and you
can really see the tool marks there very
clearly from that sharp nose tool and
the aggressive feed is also going to
make this effect much worse but now
let's look at that finishing pass that
we did with the exaggerated round nose
tool and this finish is so good that the
camera the macro lens on the camera
actually has trouble focusing it can't
quite resolve the surface on it now over
here on the steel this is the finishing
pass and it's definitely good for mild
steel but it's not gonna win any mirror
Awards
pop quiz what do you think is the
biggest contributor to tool where is a
depth of cut no it is surface speed this
is an extremely important topic in a
production CNC shop so much so that the
big book devotes an entire section to
calculating it full of lots of more
tables
the hobby shop that doesn't matter a
whole lot but be aware that the tables
in the big book are calibrated for 15
minutes of tool life so if you want your
tools to last longer than that yeah
things down a bit
so that's the complete process of
determining speeds and feeds for your
particular cutting setup from first
principles now why doesn't anybody
actually do it that way at least not on
YouTube well first of all it's a lot of
fooling around it's a lot of math it's a
lot of looking up tables in this very
expensive book so people have shortcuts
the most common shortcut that you'll see
is this one you take your surface
feet-per-minute for the material from
the big book here or from a chart that
was most likely copied from the big book
and you just simply take that speed
multiply it by 4 divide it by the
diameter of your stock or your cutter
and this mostly works and it's mostly
fine why does that mostly work because
it's obfuscating all of these very
important cutting conditions that we
talked about like depth of cut and feed
rate and surface finish and so on well
because people are taking those numbers
from these charts and Machinery's
handbook again which are calibrated for
1/8 inch depth of cut and 1/12 our
revolution feed rate but ignoring that
calibration and using lower depths of
cut and lower feed rates in general at
least in the hobby shop and the end
result is that if you use that shortcut
formula you're running slower than
necessary and that's mostly fine you
know running slower to a point is always
okay and can be more pleasant for the
hobby shop you know it's sort of less
dramatic there's less heat less smoke
less you know noise from the machine
less wear and tear on the machine so you
know running slower is okay and these
formulas work for most people because of
that because they are under estimating
the ultimate speeds and feeds that you
know you can use on your particular
cutting setup so feel free to use those
shortcuts but I think it's helpful to
understand where they come from and I do
think it's a useful exercise to go
through this calibration that I
described for your particular machine
and kind of know what that upper bound
is and kind of work down from there to
wherever you feel comfortable on speed
and feed for your particular machines
we've been focusing mainly on the lathe
here because it's easier to understand
but speeds and speeds on the mill has a
lot more nuance in modern milling
operations the unit that we use to
measure speeds and feeds is a little
different here we talked about
inches per two inches per tooth refers
to the amount of material that's scooped
out by each tooth as it comes around and
goes through the work and this is a
combination of three variables first of
all the power feed rate how fast the
stock is being pushed through the cutter
by the power feed and then it's also a
function of the RPM which is controlling
how quickly these teeth are coming
around relative to that table feed and
this is also affected by the number of
flutes on the cutter because of course
the more teeth you have coming around
the less each tooth gets to take for a
given table feed and RPM interest per
tooth is a very valuable and important
metric on modern CNC machining where you
can tightly control all these variables
for optimum performance on the manual
mill and especially the hobbyist manual
mill don't really have the luxury of all
that data because while we can control a
lot of these variables like depth of cut
and number of flutes and rpm the table
feed rate is a lot more tricky because
either you're feeding manually in which
case your feed rate is you know however
good your arm is feeling that day or
you're using some sort of power feed now
on some larger mills if the power feed
is driven via transmission you might
have known gearing and there may be
markings on your power feed controls
that tell you you know say an inch per
minute rate for feed but on a lot of
mills you've got an electric power feed
like this almost certainly and it's got
these utterly decorative numbers on the
dial here that don't mean anything so
how you calculate feed speed so this
process is simply a matter of zeroing
out your hand wheel make sure you take
out the backlash in that guy as well
zero that guy out and then you need to
know how many thousands are on one full
revolution so this particular mill has a
hundredth out on one revolution and
you're just simply gonna run your power
feed for a fixed amount of time say 10
seconds and just see how far it went
so for the current setting on that power
feed knob it went 380,000 10 seconds
which is two and a quarter inches per
minute to give or take so now you can
kind of map that speed to this knob so I
don't know let's say the 4 is up so you
might call for 2 and a quarter inches
and you know that you know smaller
numbers are gonna be less than that and
larger numbers are gonna be more than
that but you don't know that the scale
is linear it may not be and there's no
kind of markings or anything on here so
yeah honestly this whole exercise is a
little fruitless on these crappy hobby
power feeds so what I would suggest is
just set it low however the good news is
you can pretty much gloss over that
nuance for the most part and use the
same rules of thumb same formulas same
numbers just using the diameter of your
cutter instead of the diameter of the
stock however it is worth being aware of
some of this nuance so that you can
fudge the numbers up and down a little
bit as needed for example if you're face
milling it's clearly going to make a
difference if your n mill is fully
engaged or you know is only engaged on a
little bit of the material you know all
this is going to affect to a pressure
and thus you know how hard you can push
your surface speed and it matters if
you're a climb milling or conventional
milling but I'll be covering some of
those details in the mill skills series
but then if you're doing things like
slot cutting it gets even more
complicated because you've got one side
conventional milling on one side climb
milling so the differential forces on
the cutter complicate all these
variables and if you really want to get
into it Machinery's handbook does have
tables for all of this including you
know adjustment factors to feeds and
speeds based on slot cutting or
different levels of engagement of the
face mill but you really don't need to
do that for Hobby work so I hope you
found this useful please do like
subscribe comment etc and consider
supporting me on patreon and we'll see
you next time
you
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