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Archive for June, 2010

Making Big Parts on a Small Mill

Posted by Tom Benedict on 25/06/2010

Or how to get a mill table extension without having to add the extension…

I have a Taig 4-axis desktop mill at home.  It’s a great machine for its size, and I’ve used it on countless projects.  If you’re in the market for a small mill, I highly recommend the one from Taig.

But “small” is the operative term.  On small parts, it’s a blast to use.  I stuck a G540 driver on it, and swapped out the stock 1/10HP motor for a 1HP variable speed DC motor, but otherwise mine is stock.  And for small parts it’ll hog material out and still have the finesse to hold +/- 0.001 tolerance, or better if you’re careful.  On big parts?  Well…  Until recently I’d have shrugged and said, “Get a bigger mill.”

A friend of mine is working on a project and needed some parts made.  He sent me the 1:1 drawings, and without looking too closely at them I said, “Sure, I can do it.”  Then I started dimensioning things and realized I was way the heck out of my depth.  16″ wide?  My mill only has 7″ of travel in that direction!

This is actually a pretty common problem to run into in machining.  And there’s a really simple answer:  Reposition the part, re-indicate, and keep cutting.  Tackling a part piecewise like this, you can theoretically make arbitrarily large parts on even a very small mill.  Of course there are still practical limitations, like the throat depth of the machine and the physical constraints of the room the mill is installed in.  But the idea works.  I’ve used it on manual machines a number of times, and each time it saved my butt.

The real kicker with this approach is that you have to re-indicate the part each time you reposition it.  The parts I had to make didn’t have a lot in the way of features that I could indicate off of, so I knew I had to come up with another plan.

I have a tooling plate on my mill that I use almost all the time.  It has a grid of threaded holes that let me bolt down vises, jigs, stop blocks, or anything else I need to use to make parts.  Step one was to take off the tooling plate and add a grid of precision dowel pin holes.  A couple of hours on a manual mill at work over the weekend took care of that.

The mating part is a second tooling plate with two pressed-in dowel pins on the bottom.  These slip into the dowel pin holes on my main tooling plate, and let me reposition the second plate to any number of positions.  Through holes for bolts that line up with the threaded hole pattern on the main tooling plate allow me to bolt it down once I’ve got it positioned.  The dowel pins are regularly spaced, so plate offsets of 2.000″, 4.000″, or 5.000″ are a matter of picking the right set of holes.

With tooling plates in hand, I gave the big parts a try.

Big Parts

It worked perfectly.  The only issues I ran into were because I was cutting the part out of a sheet rather than working with pre-squared stock.  There are tricks for doing this, such as leaving small tabs in strategic locations to make sure the part doesn’t shift as the contour is finished and the part comes loose.  The tolerances for the outside contour on these parts were pretty loose, so I skipped the tabbing and just cut them out.  I’m very pleased with the results.

I’ve got another project lined up where I might want to make parts larger than the work envelope for my mill.  I still like to design inside the capabilities of the tools I have, but now at least I know I can.

– Tom

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Cleaning House

Posted by Tom Benedict on 21/06/2010

So I head off to San Diego for SPIE in less than a week.  We ran out of photo paper for the big plotter at work, so I still don’t have a show-ready print of my poster.  But otherwise I’m ready to go.  I managed to pack my kites, my KAP rig, my camera, and yeah, even clothes and my laptop bag.  Everyone’s poster is going in my kite bag, so the company will foot the bill for the extra bag.  I’m all set!

Right around the time I started to pat myself on the back for this, I realized I had no space left on my laptop.  It’s embarrassing to admit, but I hadn’t cleaned off the hard drive in ages.  I was holding out for a 1TB external drive, but I simply ran out of time.  I had to burn things off to DVD.  So I went to town, picked up a spindle of DVD-R disks, and got cracking.

At first things were slow slow slow.  But after a while they got a little faster.  Then they got a lot slower.  That’s when I realized my drive had been chok full for so long, it hadn’t successfully defragmented the drive for months.  I finally got my 10% free the defragger needs, started it up, and let it run.  And run.  And run.  And RUN!

In all it ran for almost 16 hours.  Ouch.  I picked right up where I left off the night before, and continued to clean until I had at least 1/3 of my drive clear.  That just about got me to January, 2010.  I still have almost six months of photos stacked up on my computer, waiting to burn.  Ugh.

Organization is one of the things I’m working on before I try to go too whole-hog with my photography.  Bet you couldn’t guess.

In any case, my computer is now quite clean, my photos are nicely backed up onto DVDs, and I can start to clean out the space on my mirror machines as well.  I think all three computers will sigh a huge sigh of relief once this cleanup is done!

– Tom

Posted in Photography | 2 Comments »

SPIE Poster

Posted by Tom Benedict on 08/06/2010

As with most of the projects I do for work, the SPIE poster didn’t work out 100% as expected.  Once I started going through the photographs and diagrams I wanted to stick on the poster, and figured in the size everything had to be in order to be readable at a distance, that 36″x45″ started to look awfully small.  And no matter how neat I tried to make it, that background texture of snow was just distracting.  So out went the theme of “cold” and in came the theme of “I have no clue what I’m doing.”

So I ran with it.

SPIE 2010 - Espadons PCC Poster

I really didn’t know how I wanted to lay the poster out, so I gave up and didn’t.  The text blocks were set on a page I tore out of a notebook and scanned on our Xerox Workcentre printer.  The photos were set in Polaroid-like frames I’d used for the KAP talk I gave a couple of weeks ago.  (True Polaroid frames are taller than they are wide.  These were tweaked to fit the aspect ratio of the photos.)  The graph and diagram were superimposed over the graph paper letterhead we use at work, likewise scanned on the Xerox.  The only traditional object on the poster is a JPG reconstruction of our monitoring web site for this cryosystem.  If the poster looks scattered, it’s because I was, too.

But in talking to people around the company, the feedback I got was that the approach actually worked.  The whole job of the poster at a poster session is to draw someone’s interest long enough for them to come over and talk.  Even if they come over to ask what the @#$^ I was drinking when I made the poster, that’s good enough for me.  If they want to talk cryocoolers, that’s fine.  If they want to talk poster layout, that’s ok, too.

The best part was when I brought my 11″x17″ test print of the poster home last night.  One of my kids asked what it was.  “It’s…  It’s my science fair poster!”  And know what?  It’s true.

– Tom

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