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Posted by Bruce in Bangkok on April 24, 2008, 8:56 am
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On Wed, 23 Apr 2008 23:43:05 -0700, "Michael Koblic"
>
>> All these numbers are approximate, too slow increases tool life, fine
>> for a home shop, that likes to watch the machine. Coolants and lubes
>> will make a big difference.
>> Faster wears the tool tip quicker.
>
>Is there not some negative impact on the cutting tool if it is running too
>slowly? I have recently gone through the same deliberations and have to say
>that good tables were hard to find on the net.
Nope, you can run it as slow as you want. It is the high speeds that
do you in.
>
>I read a book which included correct speeds in a chapter. Their caveat was
>not to let the tool "rub" - whatever that means. My take on it was that this
>happens at slower speeds than recommended but could not understand it
>completely.
>
"rubbing" would be insufficient clearance on the tool bit.
>They also suggested that the speeds you quoted should be adjusted according
>to the operation: For instance for countersinking they suggested using
>speeds 1/3rd of those normally recommended.
That is usually correct but it has less to do with cutting speed then
being a multi edge cutting tool. Reamers are also prone to this
problem which has to do with being a multi edge cutting tool. Reamers
are also prone to this problem which has to do with multiple cutting
edges not cutting evenly or "chattering" leaving a poor finish or out
of round hole.
>There were also notes about the feed speeds and the material of the cutting
>tool affecting the correct cutting speeds, so in the end I was rather
>confused. Nowadays I rather tend to err on the slow side...
Look at it this way. The cutting speed is the highest continuous speed
that the tool will sustain. Now, stock removal is a somewhat different
story and you may find that because of old age, a lack of machine
rigidity, more frequent tool dulling, or other factors a slower
cutting speed coupled with a higher feed rate MAY remove more material
per hour/day the a higher cutting speed with a lower feed rate.
Bruce-in-Bangkok
(correct email address for reply)
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Posted by Spehro Pefhany on April 24, 2008, 12:52 pm
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On Thu, 24 Apr 2008 19:56:33 +0700, Bruce in Bangkok
>On Wed, 23 Apr 2008 23:43:05 -0700, "Michael Koblic"
>
>>
>>> All these numbers are approximate, too slow increases tool life, fine
>>> for a home shop, that likes to watch the machine. Coolants and lubes
>>> will make a big difference.
>>> Faster wears the tool tip quicker.
>>
>>Is there not some negative impact on the cutting tool if it is running too
>>slowly? I have recently gone through the same deliberations and have to say
>>that good tables were hard to find on the net.
>
>Nope, you can run it as slow as you want. It is the high speeds that
>do you in.
>>
>>I read a book which included correct speeds in a chapter. Their caveat was
>>not to let the tool "rub" - whatever that means. My take on it was that this
>>happens at slower speeds than recommended but could not understand it
>>completely.
>>
>"rubbing" would be insufficient clearance on the tool bit.
Or insufficient feed rate!
Cutting speed is only half the equation-- you also need to consider
the feed rate (thou per tooth or whatever).
The cutting edges have to be moved into the work fast enough that they
bite in and don't just rub against the work (feeding too fast causes
different problems).
The feed rate in thou per tooth is independent of the cutting rate, so
if you are turning very slowly the feed rate will be slower in terms
of inches per minute, but the same in terms of thou per tooth, if that
makes any sense.
The optimum feeds and speeds are dependent on the type of tooling,
coolant used, the material being cut, whether it's a roughing or
finish cut, and other factors. Google for some numbers. I've generally
used 80 sfm for HSS tooling into mild steel.
More in Wikipedia: http://en.wikipedia.org/wiki/Speeds_and_feeds
>>They also suggested that the speeds you quoted should be adjusted according
>>to the operation: For instance for countersinking they suggested using
>>speeds 1/3rd of those normally recommended.
>
>That is usually correct but it has less to do with cutting speed then
>being a multi edge cutting tool. Reamers are also prone to this
>problem which has to do with being a multi edge cutting tool. Reamers
>are also prone to this problem which has to do with multiple cutting
>edges not cutting evenly or "chattering" leaving a poor finish or out
>of round hole.
>
>>There were also notes about the feed speeds and the material of the cutting
>>tool affecting the correct cutting speeds, so in the end I was rather
>>confused. Nowadays I rather tend to err on the slow side...
>
>
>Look at it this way. The cutting speed is the highest continuous speed
>that the tool will sustain. Now, stock removal is a somewhat different
>story and you may find that because of old age, a lack of machine
>rigidity, more frequent tool dulling, or other factors a slower
>cutting speed coupled with a higher feed rate MAY remove more material
>per hour/day the a higher cutting speed with a lower feed rate.
>
>Bruce-in-Bangkok
>(correct email address for reply)
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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Posted by Jim Wilkins on April 24, 2008, 5:34 am
Please log in for more thread options wrote:
> FPM for common metals using High Speed Steel tools:
> Hard Steel/Stainless 50
> Soft Steel/Iron 100
> Brass 200
> Aluminum 500
=2E..
> So, if you have a 6" diameter steel blank in the lathe. =A0The
> circumference is 6" x 3 (Pi) =3D 18 =A0divided by 12 to get feet =3D 1.5'
> circfunference.
> Since steel is 100 fpm, =A0100 / =A01.5 =3D 66 RPM for the best
> productivity.
> Dave
Make a spreadsheet with the speeds for your lathe or mill as rows,
common work diameters as columns, and the FPM formula in the cells. If
you don't have MS Excel you can download Calc from Openoffice.org.
Jim Wilkins
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Posted by on April 24, 2008, 8:27 am
Please log in for more thread options > If you know a site, or if you have a list of the speed requirement for
> turning metals on a lathe, I would appreciate it. On my quick change gearbox
> on my lathe it shows the speeds, but I like to know how fast I should have
> the spindle turn if I'm turning let's say aluminum and soft steel
> maybe...The same maybe, if I could impose for a milling machine as well....I
> used to have all this stuff, but whenever my grandson visits me, and he
> needs small things, he borrows it, and then forgets to give it back to me.
> Then if I need it, I can't put my hands on it....Peter
I will probably be shot down in flames for this, being a mere tyro,
but...
At school, we were told where to look in the textbook for the optimum
cutting speeds - they do vary with the material.
BUT - these were the max speeds in a production environment and were
designed to get maximum ECONOMIC life out of the tooling - faster
meant unacceptable tool wear and so increased downtime and cost,
slower meant...you didn't get as much work done. (The temptation is,
of course, to run it fast and take big hogging cuts - fine if you know
what your doing...)
Run it at a speed you feel comfortable with, slow is not a BAD THING
if you aint doing it for a living and being paid per job. Dont let it
rub on one spot, heats up the tool, stuffs it.
Feed rates are probably more important, IMHO. But agin, slow is better
than too fast.
So saying that, one of the instructors faced off a topslide mounting
plate I was making - insanely and dangerously fast to me, but he got
a BEAUTIFUL finish, in one pass - but then, as a toolmaker now a
teacher, he knew what he was doing....
From memory, (again, probably wrong - its in my locker at school..)
the Southbend 'How to run a Lathe" book, widely available as a free
download has the formulas - a great quick reference guide. Pity its
in imperial, I am being taught exclusively in Metric. Can think in
metric now for machining, still in feet/inches for everything else.
Makes life confusing, to say the least. Got a imperial micrometer here
I got at a junk sale - no idea how to read it...
Oh, yes - was told to run reamers at the slowest possible speed/feed -
lessens chance of damage to expensive tools...
(photocopying charts and nailing them to the wall behind the lathe/
mill is a GOOD IDEA -)- nomographs? - is that the right term?
Andrew VK3BFA.
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Posted by Stealth Pilot on April 24, 2008, 12:08 pm
Please log in for more thread options On Thu, 24 Apr 2008 05:27:00 -0700 (PDT), vk3bfa@hotmail.com wrote:
>
>At school, we were told where to look in the textbook for the optimum
>cutting speeds - they do vary with the material.
>BUT - these were the max speeds in a production environment and were
>designed to get maximum ECONOMIC life out of the tooling - faster
eons ago there was a guy creating a table for 'model engineer'
magazine giving the cutting speed vs rate of removal. the table was a
rectangular grid of figures. typical sweet spot being in the middle of
the left hand end.
for the simple reason that he wanted to fill in a value in every
square in the table he ran the lathe and made the cuts at all the
speed combinations.
down in the right hand lower corner was discovered a range of speeds
where the cutting rate increased substantially. the tools ran red hot
but the removal rate was far higher.
that bottom right corner is now where most of industry works.
we work at home in the left slower end where it feels right.
Stealth Pilot
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