Homebrew_PCBs

>
> --- In Homebrew_PCBs@y..., Russell Shaw <rjshaw@i...> wrote:
> >
> >
> > n4onl wrote:
> > >
> > > Hints? Tips? Insight?
> >
> > There's a home-brew cnc yahoo group: cad_cam_edm_dro.
>
> I found this group from a post in CCED. I hoped I'd get info here
> since Bill (list mom) might consider this Off Topic in that group.

>
> Hi everyone.
> Just found this group and I have been skimming through the posts.
> I'm interested in building a CNC PCB mill/drill. Stepper motors,
> linear bearings/rods, antibacklash nuts on Acme rod... and a Black
> and Decker RTX. The resolution works out to 0.0005" per full step and
> 0.00025" if I half step.
>
> Is 1/2 or 1/4 of a thousands a good resolution for this project?
>
> Does anyone have links to similar projects?
>
> Hints? Tips? Insight?

>
>
> n4onl wrote:
> >
> > Hi everyone.
> > Just found this group and I have been skimming through the posts.
> > I'm interested in building a CNC PCB mill/drill. Stepper motors,
> > linear bearings/rods, antibacklash nuts on Acme rod... and a Black
> > and Decker RTX. The resolution works out to 0.0005" per full step

> > 0.00025" if I half step.
> >
> > Is 1/2 or 1/4 of a thousands a good resolution for this project?
> >
> > Does anyone have links to similar projects?
> >
> > Hints? Tips? Insight?
>
> There's a home-brew cnc yahoo group: cad_cam_edm_dro.

> -----Original Message-----
> From: n4onl [mailto:umrk@...]
> Sent: Saturday, March 30, 2002 8:21 PM
> To: Homebrew_PCBs@yahoogroups.com
> Subject: [Homebrew_PCBs] Re: PCB Mill/Drill Project
>
>
> --- In Homebrew_PCBs@y..., Russell Shaw <rjshaw@i...> wrote:
> >
> >
> > n4onl wrote:
> > >
> > > Hi everyone.
> > > Just found this group and I have been skimming through
> the posts.
> > > I'm interested in building a CNC PCB mill/drill. Stepper motors,
> > > linear bearings/rods, antibacklash nuts on Acme rod...
> and a Black
> > > and Decker RTX. The resolution works out to 0.0005" per full step
> and
> > > 0.00025" if I half step.
> > >
> > > Is 1/2 or 1/4 of a thousands a good resolution for this project?
> > >
> > > Does anyone have links to similar projects?
> > >
> > > Hints? Tips? Insight?
> >
> > There's a home-brew cnc yahoo group: cad_cam_edm_dro.
>
> I found this group from a post in CCED. I hoped I'd get info here
> since Bill (list mom) might consider this Off Topic in that group.
>
> Thanks
> mike
>
>
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> No, your question would not be considered off topic on the
> CAD_CAM_EDM_DRO group. It directly deals with the design and

> a hobby CNC machine.

> No direct experience with anti-backlash acme screws or a machine

> on linear bearings and rods, but I have done some PCB drilling on my
> Shoptask and on my Bridgeport. My resolution was on the Shoptask at

> time was .00025" and that worked out just fine. I would actually

> a guess that you could get by with resolution in the .0005" - .001"
> range.

>For the spindle I am a big fan of using a collet style Foredom
> flexshaft hand piece. This lets you mount the motor remotely so you

> a small light spindle on the machine and gives you a spindle speed

> 15,000 - 20,000 RPM depending upon the motor and handpiece you use.

> worked well for me when I used one in my Shoptask. I am now using a
> Precise 40,000 RPM spindle in the Bridgeport and that works even

> but can be a little spendy.
>
> Tim
> [Denver, CO]
> Back-up CAD_CAM list mom

> Hi everyone.
> Just found this group and I have been skimming through the posts.
> I'm interested in building a CNC PCB mill/drill. Stepper motors,
> linear bearings/rods, antibacklash nuts on Acme rod... and a Black
> and Decker RTX. The resolution works out to 0.0005" per full step and
> 0.00025" if I half step.
>
> Is 1/2 or 1/4 of a thousands a good resolution for this project?
>
> Does anyone have links to similar projects?
>
> Hints? Tips? Insight?
>
> Thanks
> mike

>
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> Are you really able to get a repeatable and accurite resolution of
> 0.0005" on your ACME screw? What about motor oscilations and over

> (gotta love steppers)? Then there is the question of your guides

> play in them. You might be asking a lot to fabricate that. Take a

> Dadel / Parker and see thier specs. Then remember they are doing

> for a living, granted in larger quantities with out the TLC. I am

> asking the question.
> John

> Hi John, All questions comments, ect. welcome.

> Resolution and repeatibility (accuracy): Good points, and no I
> don't
> expect extreme accuracy and repeatability out of this setup,
> especially using Acme rod, but i think it will be rather
> accurate.
> What Accuracy (resolution and repeatibility) is Really Needed?

> Going by lathes, mills... stiffness of the frame lends to
> accuracy,
> this is why i'm using 8020 and aluminum plate ($0.35/lb scrap
> price).
> It will be rather hefty. Also backlash is a factor so I'm going
> to
> use antibacklash nuts that I will make out of Delrin (for reduced
> friction and wear of the Acme rod lead screws).

> My Guides: For X and Y axis (right and left), Thompson TWN 10
> (5/8")
> Super Pillow Block Bearings and Precision Ground Rod. their used
> but
> are in Excellent mechanical condition, smooth and tight.

> For Z axis (router verticle), used Robohand Inc. model PS-4-4-SH
> (similar to these http://www.robohand.com/dlbb10.htm) with 12mm
> shafts and 4" travel. Very smooth and tight. I also have some
> 3/4"
> supported linear rods and bearings but I think they would be
> overkill. :)

> The part that I have the least knowledge about are the stepper
> motors
> themselves, so I'm going a bit larger than the ones I've seen on
> commercial equipment I've found on the web. I have 2 new (old
> stock)
> Vexta 83 oz/in, 1 used 100 oz/in and 1 used 120 oz/in, all 200
> full
> steps per rev and NEMA23 frame. This one ( http://www.t-
> tech.com/products/quickcircuit/ ) appears to be using 60 oz/in
> motors, .00025" resolition and .00025" (one halfstep ?)
> repeatibility. Check out the PCBs it makes. :)

> Speed of the cut is also a big factor in accuracy, so I intend to
> keep my cutting inches/sec on the slow side, at least until I see
> how
> fast I can move and not affect accuracy to a great degree.
> What Accuracy is Really Needed?

> BTW using a RTX for the spindle has been changed to using a small
> laminate trim router. I found one (and a spare) at Harbor Freight
> for
> half the cost of a RTX ($20 ea.). Thats cheap enough to replace
> as
> needed. :)

--- In Homebrew_PCBs@y..., Steve Greenfield <alienrelics@y...> wrote:
> --- n4onl <umrk@b...> wrote:
>
> > Hi John, All questions comments, ect. welcome.
> -
> > Resolution and repeatibility (accuracy): Good points, and no I
> > don't
> > expect extreme accuracy and repeatability out of this setup,
> > especially using Acme rod, but i think it will be rather
> > accurate.
> > What Accuracy (resolution and repeatibility) is Really Needed?
>
> Good point. Anyone have the answer? Repeatability I would imagine
> will be mostly affected by backlash and stiffness. Resolution by
> the thread pitch and whether you use pulleys to "gear down" the
> steppers, and if you use full step or half. Using pulleys to gear
> the steppers down has the advantages of both higher resolution and
> more resultant power, at the cost of speed. For me, I can take the
> cost in speed. Accuracy is not just repeatability or linearity. It
> is also important that if the calculations say X steps move the
> head 4 inches, that it not be 3.9 inches.
>
> > Going by lathes, mills... stiffness of the frame lends to
> > accuracy,
> > this is why i'm using 8020 and aluminum plate ($0.35/lb scrap
> > price).
> > It will be rather hefty. Also backlash is a factor so I'm going
> > to
> > use antibacklash nuts that I will make out of Delrin (for reduced
> > friction and wear of the Acme rod lead screws).
>
> Boeing Surplus... Yeah! I live about 30 minutes from Boeing
> Surplus. What they don't have, there are metal sheet suppliers all
> around them.
>
> > My Guides: For X and Y axis (right and left), Thompson TWN 10
> > (5/8")
> > Super Pillow Block Bearings and Precision Ground Rod. their used
> > but
> > are in Excellent mechanical condition, smooth and tight.
>
> http://www.smallpartsinc.com for new stuff. I had a project
> cancelled to build an ultrasmooth sliding door, I did a lot of
> research for bearings like this. I should dig out the catalogs
> again and post the links.
>
> > For Z axis (router verticle), used Robohand Inc. model PS-4-4-SH
> > (similar to these http://www.robohand.com/dlbb10.htm) with 12mm
> > shafts and 4" travel. Very smooth and tight. I also have some
> > 3/4"
> > supported linear rods and bearings but I think they would be
> > overkill. :)
>
> Hey, if you have them already and don't have another project for
> them, why not?
>
> > The part that I have the least knowledge about are the stepper
> > motors
> > themselves, so I'm going a bit larger than the ones I've seen on
> > commercial equipment I've found on the web. I have 2 new (old
> > stock)
> > Vexta 83 oz/in, 1 used 100 oz/in and 1 used 120 oz/in, all 200
> > full
> > steps per rev and NEMA23 frame. This one ( http://www.t-
> > tech.com/products/quickcircuit/ ) appears to be using 60 oz/in
> > motors, .00025" resolition and .00025" (one halfstep ?)
> > repeatibility. Check out the PCBs it makes. :)
>
> What makes you think they are using 60 oz-in, besides the size of
> the steppers?
>
> Here's that link fixed:
> http://www.t-tech.com/products/quickcircuit/
>
> BTW, here's my secret source of good battlehardened 60 oz-in
> steppers- Apple Imagewriter II! Two per printer. I checked them
> with a constant current power supply and a balance, at 60 oz they
> held, at 61 oz they'd slip one or two notches.
>
> > Speed of the cut is also a big factor in accuracy, so I intend to
> > keep my cutting inches/sec on the slow side, at least until I see
> > how
> > fast I can move and not affect accuracy to a great degree.
> > What Accuracy is Really Needed?
>
> From the CAD_CAM_etc list, I think it is important to match cutter
> speed to movement speed. IE, while it is bad to move too quickly
> and so take too big a bit on each pass of the cut, it is also bad
> to move to slowly and take too small a cut. So it would follow that
> you'd need to slow down cutter rotation if you slow down inches per
> second.
>
> Don Lancaster http://www.tinaja.com has a great idea for
> lightweight milling heads- dental turbines. Tiny flexible air hose,
> tiny dental turbine, and you have a cutter head that is extremely
> lightweight. Very high speed but the cutting head is small so
> cutting speed isn't quite as high as it might seem. Maybe something
> that could even be retrofit to an HP flatbed plotter? Very cheap so
> when they wear out you just toss the turbine and install another.
> Perhaps use the exhaust air to make a vacuum system to suck the
> particles up.
>
> > BTW using a RTX for the spindle has been changed to using a small
> > laminate trim router. I found one (and a spare) at Harbor Freight
> > for
> > half the cost of a RTX ($20 ea.). Thats cheap enough to replace
> > as
> > needed. :)
>
> Makes sense. A friend of mine bought a very expensive sabre saw a
> few years ago. Since it was so expensive, he felt obligated to
> repair it when various parts wore out. In that time, he's spent
> twice the cost of the saw on parts. He's cutting 3/8" aluminum with
> it, so it is hard on it. In that time I wore out three $25 sabre
> saws and spent a fraction of what he did.
>
> Steve Greenfield
>
>
>
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--- In Homebrew_PCBs@y..., Steve Greenfield <alienrelics@y...> wrote:

[edited for size]

>Accuracy is not just repeatability or linearity. It
is also important that if the calculations say X steps move the
head 4 inches, that it not be 3.9 inches.>

Hi Steve,
Dialing in that 4.0" = 4.0" is done in the driver software. So that
parts easy.


>Boeing Surplus... Yeah! I live about 30 minutes from Boeing
Surplus. What they don't have, there are metal sheet suppliers all
around them.<

I see a new project in you future. ;)


> http://www.smallpartsinc.com for new stuff.<

Did you mean http://www.smallparts.com ?

>What makes you think they are using 60 oz-in, besides the size of
the steppers?<

Just the size, from the movie I can tell their NEMA23 size and from
the pics I can see they are the shorter single stack. The largest
rated ones I have (or found ) in that size are 60 oz/in, the ones I
mentioned before are all longer and or square frame. If they were
that size and square they might be 83 oz/in, and if they were
octagonal, they would probably be PacSci and even higher rated. I
think 60 oz/in is giving them the benifit of the doubt. Of course if
their being driven dual coil then that might increase to abt 75-80
oz/in.

As smooth as the boards curves looked they might be driven with
microstepping drives. I dont really want to dedicate my Gecko 201s to
driving this project but I might. ;)

Also if you watch the movie you'll see their in no hurray either to
mill the board. It doesn't take a lot of power to move that slow, and
that slow the steppers are going to have a lot of power.

Also, 60 oz in steppers, through a 10:1 drive (10tpi Acme) will have
a holding force of over 200lbs...

60 oz/in X 10 (drive ratio) X 2pi (6.28) / 16 (oz/lb) = 235.5 lbs of
holding force.


>Don Lancaster <http://www.tinaja.com> has a great idea for
lightweight milling heads- dental turbines. Tiny flexible air hose,
tiny dental turbine, and you have a cutter head that is extremely
lightweight. Very high speed but the cutting head is small so
cutting speed isn't quite as high as it might seem. Maybe something
that could even be retrofit to an HP flatbed plotter? Very cheap so
when they wear out you just toss the turbine and install another.
Perhaps use the exhaust air to make a vacuum system to suck the
particles up. <

Interesting, and I have 2 - HP 7475A's collecting dust in the
closet. :)
I might try that later, this project can double as a light duty CNC
Router, Signmaker... :)

Thanks
mike

>only found one problem. That is getting a good high speed spindle
>to run the bit. I can't seem to find anything better than the Dremel
>MultiPro. Let me know if you find one! Run out is the problem. Most
>cheap routers have too much play in them for circuit boards. The also
>have a problem if you run them too long. I have some boards that take
>an hour to mill.