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Hoffman Amps Forum image Author Topic: DIY 3 axis CNC engraving machine built for 100 USD: Part I, conception  (Read 11782 times)

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Offline vibrolax

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I recently posted in the amp building section about my first results engraving an aluminum preamp faceplate with a DIY CNC machine.
http://el34world.com/Forum/index.php?topic=18907.0

Since the CNC is not a tube amplifier, I'll summarize the machine build story in this section.

First, a disclaimer:  The only reason this machine was able to be built for less than $100 total cash outlay is because nearly every part was obtained by salvaging scrapped industrial components over a period of years.

Manufacturers and industrial laboratories dispose of tons of high-quality completely functional machine components and control electronics every day.  Depending on how much effort a company puts into their surplus disposal process, it ends up (A) in the hands of industrial remarketers, (B) in on-line auction websites, or (C) discarded in a dumpster.

I formerly worked for a business that usually followed method (C).  Periodically, obsolete or scrapped machine components and controls would be collected on pallets near the loading dock.  The disposal manager polled project managers and engineers to inspect and retain any equipment immediately useable by the business.  The rest would be discarded.  Over a period of years, a co-worker (and friend/DIY collaborator) collected an assortment of linear stages, stepper motors, drives, controls, and wiring from the discard pile.  His intention was "someday" to construct a metalworking CNC machine, or to perform a CNC retrofit on a surplus Bridgeport or similar manual mill.

So unless you are lucky enough to have access to a free source of scrap high quality industrial machine parts, you will not be able to put together a machine like this for $100.  The new OEM cost of the components in this machine might easily be more than 10k USD.  The price for similar components offered through on-line auction sites and remarketers is still 1000's of USD. 

My friend and I are both DIY constructors of vacuum tube audio gear and musical instrument amplifiers.  We really like the appearance of machine engraved control panels.  However, we are both afflicted with a pretty bad frugal streak that makes us avoid spending cash for CNC engraving services like Front Panel Express for our hobby projects.  And neither of us felt justified buying a hobbyist-level CNC router in kit or raw-component form.  This past winter, it finally occurred to us that between the two of us, we already had 98% of the components needed to make a very basic CNC engraving machine.  He is by trade a machinist with controls skills, and I am a software engineer with electrical and controls engineering skills.  Since we did this type of work for a living, we had all the skills needed to design, assemble, and integrate the machine, controls, and software by ourselves.

We committed to build a minimal CNC engraving machine using parts already on hand to the maximum extent possible.  We would purchase only what was necessary to engrave aluminum control panels.  Absolutely no money would be spent upgrading parts, tooling, or buying any software before trying to complete a real control panel.  No, version one of the machine would not be capable of general metalworking, carving wood, or even be able to drill/mill holes in 1/8" (3 mm) aluminum.  It was for engraving control panels. We would discuss capability upgrades only after achieving the first objective.

In part II, I'll continue with more build details.

Jon
Jon

Offline vibrolax

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Re: DIY 3 axis CNC engraving machine built for 100 USD
« Reply #1 on: July 10, 2015, 02:46:10 pm »
Part II: some details

The machine work envelope is X 230 mm (9"), Y 115 mm (4.5"), and Z 255 mm (10").  This was simply the result of the length of the linear stages at hand.  Of course we wanted a bigger machine. The X travel is too short to make 19" panels in one pass, but it is a simple matter to segment the design into left and right halves, repositioning the workpiece between halves.  While the X and Y travels are quite limited, the X, Y, and Z stages are all made with ground 5 TPI ballscrews and high-grade steel rail and carrier blocks, straight and true to a couple micrometers.  The motors and drives are capable of microstepping up to 50X, or 10k steps per revolution.  Practical stage incremental motion is good to about about 0.0002" (5 um).  I have it running at 10X microstepping, giving 0.0001" / step, and a top speed of 60 inches per minute at 10K steps / second.  The current step max step rate is low because we're running on a pretty slow computer (2 gHz Celeron J1900 mini-ITX).  The computer runs LinuxCNC on Debian, stock from the LinuxCNC ISO image.  The machine structure (base and Z column) is made of steel Unistrut bolted together.  The steel gusset on the Z column leaves something to be desired.  But we deemed it stiff enough for engraving, so no upgrade before test.  The workpiece bed is a piece of MIC-6 aluminum jig plate mounted to the X axis. It is flat to about 0.001" over the work area.

Since our initial work is engraving 1/8" aluminum, we are mounting our work on the jig plate with machinists double sided sticky tape.  We aligned and clamped a 1U (1.75")  x 19" control panel blank with accurately machined edges to the jig plate to provide a durable alignment fixture.  No need for a spoil board, or T-slot mounting bed on the jig plate.

The spindle is almost a joke.  It is a Dremel-like 1.5A rotary tool that I picked up at Canadian Tire for $30 a few years ago, attached to the machine with a wimpy improvised mount.  We estimated that this spindle would be marginal at best, but that it might be sufficient for our first objective.  Therefore, no upgrade before test!

So the machine was not so much designed, as it was improvised from the parts on hand.  The stages, motors, and controllers are far more accurate and powerful than 99% of the hobby-level CNC's out there, but the structure and spindle are far less capable.  Nevertheless, they would prove sufficient for acheiving our first objective.

Working at a leisurely pace, we accomplished our objective in 4 months for $100 USD additional cash outlay.
The purchases for this project were:
1) 24" x 8" x 3/4" MIC-6 aluminum jig plate               $42 shipped (ebay)
2) 5 axis isolated parallel port stepper interface           $15              (amazon)
3) miscellaneous Unistrut connectors/fasteners          $20              (mcmaster)
4) low-profile M8 bolts to fasten jig plate to x stage    $20              (mcmaster)

Everything else came from our vast garage and closet accumulations of stuff collected over the eons.
I didn't have to buy, pirate, or write any software to create the control panel design file, generate g-code from the design file, or execute the g-code on the machine.  While it was most definitely not plug and play, it was all within my experience as a S/W engineer.

So there you have the one page summary.  There are many more details about the how the mechanics, controls, software, and workflow came together.  I will write it all up for my personal website eventually.  Feel free to ask questions or comment

After we clear our backlog of projects waiting for engraved control panels, we'll start talking about what capabilities we want in the next version of the machine.

Jon
Jon

Offline shooter

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Very nice!

mines about 6-10mths out still, I'm shooting for a 5 axis robotic arm engraver, using pic controllers that I have and gear motors/encoders that I've robbed from my robot bases I've build over the last 20 yrs.
Went Class C for efficiency

Offline vibrolax

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Very nice!

mines about 6-10mths out still, I'm shooting for a 5 axis robotic arm engraver, using pic controllers that I have and gear motors/encoders that I've robbed from my robot bases I've build over the last 20 yrs.

I nearly launched into an anti-robot rant, based on my experience with a work project I was peripherally involved with 15 years ago.  But I'll save it, because a robot arm mechanism might work perfectly well for the engraving application you have in mind.

Actually, you just gave me my own idea for a robot engraver.....there are lots of robot arm drawing projects out there, and the infamous Logo Turtle Bot, going back to 1957.

I look forward to seeing what you develop.
Jon

Offline shooter

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Quote
anti-robot rant
I used part of my GI bill to get an A.S. degree in robotics, just so I'd know how to kill'em :icon_biggrin:
Went Class C for efficiency

Offline vibrolax

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I used part of my GI bill to get an A.S. degree in robotics, just so I'd know how to kill'em :icon_biggrin:

I don't know how useful this knowledge will be, going around with a handle like shooter.
They'll be watching for you....if they aren't already. :icon_biggrin:
Jon

Offline shooter

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Quote
They'll be watching for you

I'm just a little guy, 1 divided by 7 billion, just in case I do line my hats with copper foil :icon_biggrin:
Went Class C for efficiency

 


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