# Homebrew NC Mill

R

#### Rich Grise

Jan 1, 1970
0
My office opens onto a machine shop. I was just now chatting up the
machinist, and idly musing on the workings of the transport mech or
whatever it's called - it's got motors to drive the bed in X and Y.
This is a Bridgeport end mill, with electric motors to slew the bed.
And I was wondering about turning it with a stepper motor - with
the gear ratio, it looks like you could get about .0005" per step.
"Hmmm ..." I mused to myself, and the machinist (Jimmy) was talking
about closed loop and open loop and the accuracy of servos because
they use the sine and cosine, and that a stepper motor can miss a
step, and so the feedback comes up. "How does the controller know
if you've missed a step?" And I start thinking about position
sensing, and asking about where's the best place to put a pot,
and he says, "Well, you could just use the readout." I slaps
meself in the haid - "Boy! Am I Stupid!" "What? For not thinking
of that right away?" "No. For slapping myself in the head like
that. That really hurt!" And I went, That's trivial. I've written
stepper motor controllers in Z80. You can get a driver for a few
bucks. And I have not only THREE computers (I inherited the one
that they replaced in the front office), but an M68ICS05P in-circuit
simulator/development system in my office.

I'm gonna _BEG_ the boss to let me do that. (slap together a
68HC705P6A and a stepper motor driver, hack into his Bridgeport,
and have NC on a beer budget!)

Wish me luck!

If I get the project, I promise to make frequent progress reports,
so everybody think good thoughts!

Cheers!
Rich

G

#### Garrett Mace

Jan 1, 1970
0
Rich Grise said:
My office opens onto a machine shop. I was just now chatting up the
machinist, and idly musing on the workings of the transport mech or
whatever it's called - it's got motors to drive the bed in X and Y.
This is a Bridgeport end mill, with electric motors to slew the bed.
And I was wondering about turning it with a stepper motor - with
the gear ratio, it looks like you could get about .0005" per step.
"Hmmm ..." I mused to myself, and the machinist (Jimmy) was talking
about closed loop and open loop and the accuracy of servos because
they use the sine and cosine, and that a stepper motor can miss a
step, and so the feedback comes up. "How does the controller know
if you've missed a step?" And I start thinking about position
sensing, and asking about where's the best place to put a pot,
and he says, "Well, you could just use the readout." I slaps
meself in the haid - "Boy! Am I Stupid!" "What? For not thinking
of that right away?" "No. For slapping myself in the head like
that. That really hurt!" And I went, That's trivial. I've written
stepper motor controllers in Z80. You can get a driver for a few
bucks. And I have not only THREE computers (I inherited the one
that they replaced in the front office), but an M68ICS05P in-circuit
simulator/development system in my office.

I'm gonna _BEG_ the boss to let me do that. (slap together a
68HC705P6A and a stepper motor driver, hack into his Bridgeport,
and have NC on a beer budget!)

Wish me luck!

If I get the project, I promise to make frequent progress reports,
so everybody think good thoughts!

Cheers!
Rich

Could be simple, could be tough. These mill retrofits vary. If you've got
the motors and drivers lying around already, half the battle (and 75% of the
expense) is over.

But then you need software to run the thing. TurboCNC
(http://www.dakeng.com) will let you read G-Code files and generate all the
pulses you need with only a Grandma-grade computer. No need to mess with
HC705's or anything.

M

#### Mark J.

Jan 1, 1970
0
In news:[email protected] (Garrett Mace):
Could be simple, could be tough. These mill retrofits vary. If you've
got the motors and drivers lying around already, half the battle (and
75% of the expense) is over.

But then you need software to run the thing. TurboCNC
(http://www.dakeng.com) will let you read G-Code files and generate all
the pulses you need with only a Grandma-grade computer. No need to mess
with HC705's or anything.

Technically, this isn't "Homebrew NC", it's "Workbrew NC". :")

The nicest (cheap, fast, simple) driver board I've seen is:
http://www.hobbycnc.com/driverboards.htm

One of these days I'm gonna get one or three of those, and build a zippy
little PCB driller. And NC the lathe, and NC the mill... one of these days.
Maybe.

S

#### Spehro Pefhany

Jan 1, 1970
0
My office opens onto a machine shop. I was just now chatting up the
machinist, and idly musing on the workings of the transport mech or
whatever it's called - it's got motors to drive the bed in X and Y.
This is a Bridgeport end mill, with electric motors to slew the bed.
And I was wondering about turning it with a stepper motor - with
the gear ratio, it looks like you could get about .0005" per step.
"Hmmm ..." I mused to myself, and the machinist (Jimmy) was talking
about closed loop and open loop and the accuracy of servos because
they use the sine and cosine, and that a stepper motor can miss a
step, and so the feedback comes up. "How does the controller know
if you've missed a step?" And I start thinking about position
sensing, and asking about where's the best place to put a pot,
and he says, "Well, you could just use the readout." I slaps
meself in the haid - "Boy! Am I Stupid!" "What? For not thinking
of that right away?" "No. For slapping myself in the head like
that. That really hurt!" And I went, That's trivial. I've written
stepper motor controllers in Z80. You can get a driver for a few
bucks. And I have not only THREE computers (I inherited the one
that they replaced in the front office), but an M68ICS05P in-circuit
simulator/development system in my office.

The other reason to use FB is to avoid backlash errors and screw
inaccuracy.. it's also better if the mill uses ballscrews which get
rid of the first, but retrofitting them costs $$. I'm gonna _BEG_ the boss to let me do that. (slap together a 68HC705P6A and a stepper motor driver, hack into his Bridgeport, and have NC on a beer budget!) When/if you get it, consider surplus servos as well. They have shaft encoders and you can even make them mimic steppers if you so desire. Wish me luck! Good luck! Best regards, Spehro Pefhany S #### Scott Stephens Jan 1, 1970 0 Mark said: In (Garrett Mace): I've come across web sites describing DC pm motors used for this, rather than steppers, used. Steppers are more cost-effective for lower powers, if your interested in maximizing torque-speed-$$$It is possible to sense back EMF on the stepper to figure out if your missing steps, but analog methods take tweaking and time. And I start thinking about position Yep, I wondered about hacking my own linear encoder from a laser-printed mylar strip, or magnetic tape. But for my (PCB drill) app, I didn't need to worry. (I inherited the one I love PICs. Far superior to the archaic Motorola chips. Post this to rec.crafts.metalworking for some good advice! There's also a spam'n yahoo group mailing list for CNC too. Don't know about that, I think I tried it & didn't like it. You need an RTOS for milling; Windows can't give you precise time-control for coordinated curves. I'd checked out EMC for Linux. One of these days I'm gonna get one or three of those, and build a zippy little PCB driller. And NC the lathe, and NC the mill... one of these days. Maybe. Checkout my web page for my PCB drill bot. Can hardly do it simpler, but perhaps cheaper if you use acme rather than leadscrew & make your own anti-backlash nuts. -- Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** R #### Rick Jan 1, 1970 0 Post this to rec.crafts.metalworking for some good advice! There's also a spam'n yahoo group mailing list for CNC too. join cad_cam_edm_dro on yahoo groups. they have done everything you want to do and will give you much advice. R #### Rick Jan 1, 1970 0 When/if you get it, consider surplus servos as well. They have shaft encoders and you can even make them mimic steppers if you so desire. If you can get servos with quadrature output encoders (two channels of square waves 90 degrees out of phase) then you can use Gecko G320 drives which are about$100 and allow you to use step/dir from a micro or parallel
port. Get an old PII running linux and download the free EMC software to
drive your motors using industry standard G-code.

If you think the palm sized Gecko drives are too small, consider that I am
using them right now to move the x,y, and z axis on a 7000 lb Shizuoka
bedmill. I can do rapids of 180 IPM. I probably could go faster, but the
mill starts dancing around on the floor!

Rick

R

#### Rich Grise

Jan 1, 1970
0
abundance of great replies, I couldn't pick a weiner. ;-)

The "which motor" problem is solved. While talking with
Jimmy about how to hack into Joe's $1200 readout, http://www.acu-rite.com/index.cfm?PageID=2399B4AB-2CF2-11D5-BC6E00A0CC271CB6 he says "Hey, let's use mine!" It turns out that he's got a drive for _his_ old Bridgeport, well, at least the X. It's got what's obviously a universal motor - both the armature and field windings are coming out on the connector; I'll have to do a little digging to see if it's supposed to be series or shunt. I don't want to try to hack into his control circuit - it looks like just a pot and switch maybe an SCR or resistor or two, but it's covered in about 1/8 thick conformal of some kind. So I'm thinking, like wow! The best of both worlds. If it turns out to be a 115V motor, I can drive it with a MOC3030 and a triac - and I have a whole 1/60 second to decide whether to energize a particular cycle, so it might give a reasonable approximation of a stepper motor. Or I could use phase control, making it more like an analog servo motor. AC? DC? Who Cares? Voltage? Duty Cycle! And he says he can get a position transducer, and kept talking about the sine and cosine. Well, a very little digging shows that the transducer, above, uses "quadrature TTL," which is tantalizingly little to go on. But I told him, "If you can give me a signal that tells me where the bed is to a ten-thousandth of an inch, I can write the software (and build the driver - one 3030 and one triac, big whoop) that will put it there." Another thing - how do we get the data from the computer to the machine? Serial port, of course. What kind of software? Well, lessee - how about list a polyline and paste it to COM1? I could certainly write a parser for " at point X= 0.0000 Y= 0.0000 Z= 0.0000\x0d\x0a". Thanks for the PIC idea, whoever it was, but I already have the Motorola development, and already speak HC11, so O5 shouldn't be much of a stretch. And I _love_ that timer! Oh, and I just inherited a broken motherboard and perfectly good power supply, and there's a floppy lying there - with$30.00 worth of RAM (maybe less) I could run a DOS system
and bitbang the whole thing in MSC 5. (well, it's still
got the com port and the LPT port, heh, heh ...) I once hacked
into Telix or Procomm with some debugger and lifted their
interrupt handler so I could write a comm program of my own,
which I called "dt," for "dumb terminal."

Ah, the good old days brought back to life!

Cheers!
Rich

T

#### Tom Del Rosso

Jan 1, 1970
0
In Rich Grise typed:
The "which motor" problem is solved. While talking with
Jimmy about how to hack into Joe's 1200 readout, http://www.acu-rite.com/index.cfm?PageID=2399B4AB-2CF2-11D5-BC6E00A0CC271CB6 he says "Hey, let's use mine!" Why hack into the readout? I think you want to just hack into the cable and tap into the 2 quadrature signals for each axis. If it has a connector you could do it with a breakout box. And he says he can get a position transducer, and kept talking about the sine and cosine. Well, a very little digging shows that the transducer, above, uses "quadrature TTL," which is tantalizingly little to go on. Little to go on? Obviously it's a pair of signals from a relative shaft encoder. You know, they're 90 deg out of phase, like a sine and cosine. S #### Smiley Jan 1, 1970 0 www.cnczone.com is another great resource for both the pre-made and home-brew. J #### Jonathan Barnes Jan 1, 1970 0 Rich Grise said: that the transducer, above, uses "quadrature TTL," which is tantalizingly little to go on. Some scales have glass grids, these align to give an light sensor a signal, two sets, one alined 1/2 step in front of the other alow for direction to be taken into account. If you contact some scale makers, they will be happy to tell you what their scales output is. But I told him, "If you can give me a signal that tells me where the bed is to a ten-thousandth of an inch, I can write the software (and build the driver - one 3030 and one triac, big whoop) that will put it there." O.K. the mill got there..... pity about the cutter :-( Speed ( feed rate ) control is very important. -- Jonathan Barnes's theorem; for every foolproof device there is a fool greater than the proof. To reply remove AT O #### Oppie Jan 1, 1970 0 This magazine often has ads for home shop automation. http://www.homeshopmachinist.net/ If you haven't seen the magazine but are interested in mill/lathe work, get a copy. There are some impressive projects in it. Back the the original question - Any serious machine uses some type of feedback. We have 5 CNC mills now and they all use AC servomotors with a variety of encoder devices. The most impressive is how a 500 pound machine head (whole machine is about 9 tons) about to tap a 2.5mm diameter threaded hole plunges at warp speed to within a mm of the workpiece, spins up and feeds while tapping. As much as I know about control systems, I am impressed every time I watch the machines. Oppie For correct response address, remove -nospam- ========= G #### Garrett Mace Jan 1, 1970 0 Oh, and I just inherited a broken motherboard and perfectly good power supply, and there's a floppy lying there - with30.00 worth of RAM (maybe less) I could run a DOS system
and bitbang the whole thing in MSC 5. (well, it's still
got the com port and the LPT port, heh, heh ...) I once hacked
into Telix or Procomm with some debugger and lifted their
interrupt handler so I could write a comm program of my own,
which I called "dt," for "dumb terminal."

The DOS bit-banging you speak of has already been fully implemented in
TurboCNC, at http://www.dakeng.com. I probably forgot to mention in my
eariler post that it is free to use, and 20 for the source code. A new version is on the verge of coming out, too, think it's in fourth beta now. Also, since you seem to be in the mood for oddball hacks, I've heard of at least one case where a guy used automobile alternators as stepper motors in his CNC router. S #### Spehro Pefhany Jan 1, 1970 0 Some scales have glass grids, these align to give an light sensor a signal, two sets, one alined 1/2 step in front of the other alow for direction to be taken into account. If you contact some scale makers, they will be happy to tell you what their scales output is. O.K. the mill got there..... pity about the cutter :-( Speed ( feed rate ) control is very important. spindle RPM ~= CS* 4/D CS = cutting speed in surface feet/minute D = diameter of tool FEED rate = RPM * FEED per TOOTH * # of TEETH Eg. aluminum with an HSS (High-speed steel cutter), 300 FPM, 5 thou per tooth. Using a 1/2" diameter 4-flute end mill, Spindle RPM = 2400 FEED rate = 48 inches/minute The above is for cutting (G01/G02/G03). CNC machines also do G00 "RAPIDS", which can be as fast as the machine can move (and often don't follow a straight line between the two points). They are not supposed to be cutting when they do this. Best regards, Spehro Pefhany S #### Spehro Pefhany Jan 1, 1970 0 This magazine often has ads for home shop automation. http://www.homeshopmachinist.net/ If you haven't seen the magazine but are interested in mill/lathe work, get a copy. There are some impressive projects in it. Back the the original question - Any serious machine uses some type of feedback. We have 5 CNC mills now and they all use AC servomotors with a variety of encoder devices. The most impressive is how a 500 pound machine head (whole machine is about 9 tons) about to tap a 2.5mm diameter threaded hole plunges at warp speed to within a mm of the workpiece, spins up and feeds while tapping. As much as I know about control systems, I am impressed every time I watch the machines. Rigid tapping or with a tapping head? Best regards, Spehro Pefhany B #### Bill Garber Jan 1, 1970 0 : This magazine often has ads for home shop automation. : http://www.homeshopmachinist.net/ : : If you haven't seen the magazine but are interested in mill/lathe work, get : a copy. There are some impressive projects in it. : : Back the the original question - Any serious machine uses some type of : feedback. We have 5 CNC mills now and they all use AC servomotors with a : variety of encoder devices. The most impressive is how a 500 pound machine : head (whole machine is about 9 tons) about to tap a 2.5mm diameter threaded : hole plunges at warp speed to within a mm of the workpiece, spins up and : feeds while tapping. As much as I know about control systems, I am impressed : every time I watch the machines. Run them for 20 years as I did. You will cease to be impressed after about 5 years. ;-) Bill @ GarberStreet Enterprizez };-) Web Site - http://garberstreet.netfirms.com Email - [email protected] Remove - SPAM and X to contact me W #### Wild Bill Jan 1, 1970 0 Quadrature TTL is a common standard output for rotary and linear encoders, which is two squarewave signals which are 90 degrees out of phase. You can count pulses, but a better approach is to read (and keep track of) all the transitions. There are also sinewave differential encoders, and some manufacturers make modules for converting the sinewaves to TTL. I dunno about the practicality of approaching .0001" accuracy though. In linear encoders, that's about 400 to500 per foot in length.

For the axis drive unit, you might be able to adapt a rotary encoder to the
leadscrew, but leadscrew backlash will be a factor. Because the motor isn't
a stepper, there might not be good resolution for repeatable accuracy. This
wouldn't be bad for some operations, but it wouldn't work well for
predictable precise positioning.

WB
.....................

O

#### Oppie

Jan 1, 1970
0
Spehro Pefhany said:
On Mon, 19 Jan 2004 17:34:03 GMT, the renowned "Oppie"
..

Rigid tapping or with a tapping head?

No tapping head. Just a tiny tap in the spindle of this huge machine.

Then there is also single point thread cutting where a single pointed
cutting tool is spinning fast in the spindle. It decends slowly as the XY
table moves in a circle. We use this for cutting larger diameter threads on
occasion where it isn't practical to buy a tap.

Machines are all RS-232 but connect into an eternet to RS-232 converter so
the files can be downloaded from the office server. parts are designed in
mill.
Ain't technology wonderful?

G

#### Garrett Mace

Jan 1, 1970
0
Rigid tapping or with a tapping head?

Best regards,
Spehro Pefhany

I think the cool way to do it now is threadmilling. Bore a hole out to the
root diameter, insert a smaller tool with a single row of teeth at the right
pitch, move tool to the edge of the hole and make a one helical rotation
around the inside of the hole. Don't need to sync or even turn off the
spindle, makes accurate threads and you can use one tool to replace a number
of taps, and do non-standard diameters.

J

#### John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Garrett Mace <[email protected]>
I think the cool way to do it now is threadmilling. Bore a hole out to the
root diameter, insert a smaller tool with a single row of teeth at the right
pitch, move tool to the edge of the hole and make a one helical rotation
around the inside of the hole. Don't need to sync or even turn off the
spindle, makes accurate threads and you can use one tool to replace a number
of taps, and do non-standard diameters.

That's 'thread chasing'. It's getting on for 200 years old.

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