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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michael
 
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Default slowing my drill press

Bruce wrote:

I use my drill press mostly to drill metal...very little wood, yet my
press, which I was given, was intended to drill wood, so it really
runs too fast. I have it set at its slowest ratio setting, but still
I think it is too fast. I am planning on switching out the belt
pulleys to achieve the speeds I should be running for metal. Thus
the questions.....what is a good speed range to target for and what is
the formula for pully size? I would like to stay with a set of three
step pulleys and have a nice range of metal speed cutting. Most of my
drilling is 1/2 inch thickness or less. Too slow is better than too
fast....I would guess...right??

Thanks


I don't recall having seen a drill press that went too slow. Most all of
them are damn scary at upper speeds. One of mine is an older Rockwell and
I tried the fastest of the 4 speeds but didn't cut anything. I don't ever
use the next fastest speed either. I've had that press since 1978 IIRC.

michael


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clare @ snyder.on .ca
 
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Default slowing my drill press

On Thu, 17 Jul 2003 08:31:24 -0700, michael
wrote:

Bruce wrote:

I use my drill press mostly to drill metal...very little wood, yet my
press, which I was given, was intended to drill wood, so it really
runs too fast. I have it set at its slowest ratio setting, but still
I think it is too fast. I am planning on switching out the belt
pulleys to achieve the speeds I should be running for metal. Thus
the questions.....what is a good speed range to target for and what is
the formula for pully size? I would like to stay with a set of three
step pulleys and have a nice range of metal speed cutting. Most of my
drilling is 1/2 inch thickness or less. Too slow is better than too
fast....I would guess...right??

Thanks


I don't recall having seen a drill press that went too slow. Most all of
them are damn scary at upper speeds. One of mine is an older Rockwell and
I tried the fastest of the 4 speeds but didn't cut anything. I don't ever
use the next fastest speed either. I've had that press since 1978 IIRC.

michael

Put the "motor" pulley on a jackshaft and put another set of pulleys
between the motor and the other end of the jackshaft. If you duplicate
the current setup, and have a 5:1 ratio now, you can get 25:1.
  #3   Report Post  
Michael
 
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Default slowing my drill press

I'd say 100 sfm is close to a maximum. if you scan machinery's handbook,
you'll see numbers from 60-100 for HSS in steel. using a factor of 4
instead of 3.14 grosses up the speed by almost 30%. You also forget to
convert the dia into feet.

@ 100 sfm
..5" = 760 rpm, .125" = 3000
@ 60 sfm
..5" = 450 rpm, .125" = 1800

there's always lots of reasons why the practical speed is less than the
theoretical. I find this especially true on drill presses which are less
rigid than most of our other machines and (comparatively) often take larger
cuts. I agree, there is nothing wrong with running slower, theoretical
maximums guide commercial ops where time=money.

as a reference, on my 18 buffalo, speeds (with at 1725 rpm motor) are
400,700,1100,1750 & 2800. For anything over 1/2 inch, I'm more comfortable
using the mill.

cheers

"Gary Coffman" wrote in message
...
On 17 Jul 2003 06:17:56 -0700, (Bruce) wrote:
I use my drill press mostly to drill metal...very little wood, yet my
press, which I was given, was intended to drill wood, so it really
runs too fast. I have it set at its slowest ratio setting, but still
I think it is too fast. I am planning on switching out the belt
pulleys to achieve the speeds I should be running for metal. Thus
the questions.....what is a good speed range to target for and what is
the formula for pully size? I would like to stay with a set of three
step pulleys and have a nice range of metal speed cutting. Most of my
drilling is 1/2 inch thickness or less. Too slow is better than too
fast....I would guess...right??


RPM = SFM/(4 * dia)

Where diameter is in inches and SFM (surface feet a minute) for mild steel
is about 100 (different materials have different SFM requirements). So the
smaller the drill diameter, the faster it should turn. For example, a half

inch bit
should turn about 50 RPM, but an 1/8 inch bit should turn about 200 RPM,
a 1/16 bit should turn about 400 RPM. Etc. Aluminum would be about 8
times faster, cast iron about 20% slower, etc, because they have different
SFM cutting speed requirements.

In other words, cutting speed is determined by the diameter of the hole,
not the depth. If you drill more than about 4 diameters depth, it is

called
deep hole drilling, and you may have to "peck" drill to deal with chip
extraction.

The speed reduction formula for pulleys is simply the driven pulley
diameter divided by the driving pulley diameter. So a 6 inch pulley
driven by a 2 inch pulley would have a 3:1 reduction ratio. Thus if
the motor turns 1750 RPM, the spindle will turn at 583 RPM.

Gary



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Michael
 
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Default slowing my drill press

ok, didn't pick up on 4 being both pi and inches - feet, but I think
there's still something missing cuz the speeds you came up with are way to
low (imo)- ie 50 rpm for 1/2" drill.

Moltrecht gives the formula for cutting speed as rpm=12*fpm/pi*D". if you
factor out pi, you are left with rpm=4*fpm/D", not fpm/4*D which for the
1/2" hole = 800 rpm. Personally i find cutting a 1/2 hole at 800 rpm a
little hairy and would run my drill press at its slowest speed 400, giving a
fpm rate of about 50.

Michael

"Gary Coffman" wrote in message
...
On Thu, 17 Jul 2003 12:20:48 -0700, "Michael"

wrote:
I'd say 100 sfm is close to a maximum. if you scan machinery's handbook,
you'll see numbers from 60-100 for HSS in steel. using a factor of 4
instead of 3.14 grosses up the speed by almost 30%. You also forget to
convert the dia into feet.


No I didn't. The "factor of 4" as you call it is actually 1/4 which is

close to 3.14/12.
So both the diameter to circumference conversion and the inches to feet

conversion
is taken care of in that one number. It is a standard machinist formula

you'll find in
most of the texts, Moltrecht for example.

Gary



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Roy Hauer
 
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Default slowing my drill press

You have a choice between.a VFD drive or adding a jackshaft to the
existing drillpress. I had this problem, but had difficulties in
getting another pulley that matched what I had. I could get the
diameters, but the spacing between the steps was wrong. Anyhow, I made
a pulley. You can see how I added a jack shaft to my drill press on my
website under my Projects Page. There are a number of ways you can add
this jackshaft, and its not a hard project to do. Cheaper by far than
a VFD drive.

I don't think there is such as thing as being too slow, especially
with a drill press.

Have fun


On 17 Jul 2003 06:17:56 -0700, (Bruce) wrote:

x-I use my drill press mostly to drill metal...very little wood, yet my
x-press, which I was given, was intended to drill wood, so it really
x-runs too fast. I have it set at its slowest ratio setting, but still
x-I think it is too fast. I am planning on switching out the belt
x-pulleys to achieve the speeds I should be running for metal. Thus
x-the questions.....what is a good speed range to target for and what is
x-the formula for pully size? I would like to stay with a set of three
x-step pulleys and have a nice range of metal speed cutting. Most of my
x-drilling is 1/2 inch thickness or less. Too slow is better than too
x-fast....I would guess...right??
x-
x-Thanks


--
Visit my website:
http://www.frugalmachinist.com
Contents: foundry and general metal working and lots of related projects.
Regards
Roy aka Chipmaker // Foxeye
Opinions are strictly those of my wife....I have had no input whatsoever.
Remove capital A from chipmAkr for correct email address
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tomcas
 
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Default slowing my drill press



Bruce wrote:

I use my drill press mostly to drill metal...very little wood, yet my
press, which I was given, was intended to drill wood, so it really
runs too fast. I have it set at its slowest ratio setting, but still
I think it is too fast. I am planning on switching out the belt
pulleys to achieve the speeds I should be running for metal. Thus
the questions.....what is a good speed range to target for and what is
the formula for pully size? I would like to stay with a set of three
step pulleys and have a nice range of metal speed cutting. Most of my
drilling is 1/2 inch thickness or less. Too slow is better than too
fast....I would guess...right??



That is exactly correct. Going very slow will naturally increase your
machining time but unless you a drilling a lot of holes you will
typically spend much more time in handling then cutting. If you go too
fast then you have to make sure you are feeding quick enough to produce
a chip. As soon as you fail to feed quick enough to produce a chip the
drill bit will begin to abrade instead of cut and your cutting tool
life will be drastically reduced. Besides this you have to contend with
keeping the drill bit from overheating. The only real downside of going
too slow for someone not on the clock is that your surface finishes will
typically suffer from the higher feed rates. This is usually offset by
the fact that your cutting tools will be sharper and potentially last a
long time. One word of caution- low speeds usually mean high torque and
when you are using a drill press you frequently hold the parts by hand,
so be careful, especially when the drill breaks through and wants to
thread up on the helix of the bit. If you frequently drill thin parts I
would highly recommend the varibit drills.



Thanks


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jim rozen
 
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Default slowing my drill press

In article CyIRa.85723$H17.27201@sccrnsc02, "Bob says...

Probably an 1100 rpm motor would be hard to come by in an AC machine.
That'd be a 6 pole machine, synchronously speaking. Pricey?


Actually it was not much more expensive than the 1725
standard motor. I almost went that route when updating
the drill press at work, but I do a fair amount of small
stuff, and the slower speeds on the VFD still give plenty
of torque. I think the slower motor was maybe 20% more
money.

Jim

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Dan Caster
 
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Default slowing my drill press

"Bob Swinney" wrote in message news:CyIRa.85723$
If real slow speeds are wanted, then a 1100 rpm motor can
be used.


Probably an 1100 rpm motor would be hard to come by in an AC machine.
That'd be a 6 pole machine, synchronously speaking. Pricey?

Bob Swinney


Depends on where you shop. I have picked up several at the scrap yard
for the same price per lb as any other motor. New they are also about
the same price per lb. They do weigh more for the same horsepower,
but weigh about the same for the same amount of torque.

Dan


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Dale Randall
 
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Default slowing my drill press

I want to pass along a tip my wife's 80 year old uncle showed me in his
work shop. It was simply an old wash machine motor mounted vertically on
drill press so that pulley on motor lined up with 4 speed pulley on
drill press motor. The regular motor is not turned on but is turned by
aux. motor. giving quite a speed reduction. I am now rigging one up on
my drill press to slow down drill for over 3/8 " drilling. Aux. motor
will be fasten to 1 1/4 pipe that will slide over smaller pipe with a
pin to hold it at right height for pulley size I want to use. A spring
will keep tension on belt. For regular drilling of smaller holes the
regular motor will be turned on to use. I think the aux. motor just
runs idle. If not I will just unbelt it. This is what I posted in 1998 and since
then have used it several times with good success. Dale




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jim rozen
 
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Default slowing my drill press

In article , Dale says...

I want to pass along a tip my wife's 80 year old uncle showed me in his
work shop. It was simply an old wash machine motor mounted vertically on
drill press so that pulley on motor lined up with 4 speed pulley on
drill press motor. The regular motor is not turned on but is turned by
aux. motor. giving quite a speed reduction.


If I get this, it sounds like the regular motor is being used
as a jackshaft for speed reduction. Cute idea!

Jim

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