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Here’s a Quick Way to Figure Out Whether to Build a Fixture

Jul 17, 2015   //   by Bob Warfield   //   Blog, Business, Manufacturing, Software, Techniques  //  5 Comments

It’s been said more than once that great fixtures are the secret to profitability for machine shops.  But that’s not always true.  There’s the shops that leave a couple of vises permanently mounted to the table, set their work offsets to the corner of a fixed jaw, and swear by that.  Not much of a fixture in that, yet many of these shops seem to do just fine.  Sometimes a fixture pays handsomely, while other times it is an additional expense that won’t pay for itself.  How do you tell whether a fixture makes good economic sense or not?

It turns out that it is tragically knowable whether spending time to create a fixture makes sense or not.  We’ve just added a Fixture Calculator to G-Wizard Estimator that’s designed to help you answer exactly that question–whether a particular fixture makes sense or not.  All you have to do is answer a few question and it cranks out the answer for you.  Here’s what the Fixture Calculator looks like:

FixtureCalculator

The Fixture Calculator from G-Wizard Estimator…

The idea is to fill out some basically information on two fixturing alternatives.  In this case, we’re comparing a couple of vises to a custom fixture plate with toe clamps that will hold 10 parts.  So, the vises can do 2 parts per lot and the fixture plate does 10.  Here’s the basic information that has to be filled in:

–   Description:  Just so we can keep the two options straight.

–  Build Time:  How long to build the fixture?  In this case, we already had the two vises so there is no build time.

–  Setup Fixture:  How long will it take to setup the fixture on the machine?

–  Unload/Load:  Time to unload the parts in the fixture and load new material for the next run.

–  Parts per Run:  How many parts will the setup take per run?

–  Part Run Time:  How long to run a single part?

Lastly, we need to know how many total parts are to be made.  In this case, I picked 1200 because it was the number where the two came out equal in terms of total time.

Of course there are some things to think about:

–  The fixture saves quite a lot of Operator load time–360 minutes for this example.  Can you do something valuable with that time?  You may prefer a fixture that doesn’t yield a Total Time Savings just because it frees up an Operator to do something else valuable enough to offset the Total Time Cost.

–  The fixture saves Operator time, but it burns more skilled machinist time because the fixture has to be made.  We’ve budgeted 6 hours for that in the example.  You’ll have to decide whether the Operator Load Time Savings is worth spending some of the more skilled machinist’s time.  In this case, we spend 6 hours of machinist time to save 6 hours of operator time.  That might not be the best trade off.

–  Is the fixture an investment in the future?  Will the customer reorder more of the same parts?  Can the fixture be re-purposed easily for similar parts?  Perhaps a nice vacuum fixture that will see a lot of use is worth investing in even if it doesn’t make sense for the particular job it’ll be used on first.

By playing with some different scenarios, you can get an idea pretty quickly of whether it will make sense on a particular job to take time out and build a fixture.

If you’d like to try the Fixture Calculator, you’ll need to get G-Wizard Estimator.  While it is in Beta, it’s free for anyone who can access G-Wizard Calculator either via Trial or Subscription.  If you haven’t tried our G-Wizard Calculator Software, by all means give it a test drive.  You’re in for a real treat as our many customers will tell you.

 

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Here’s a Quick Way to Figure Out Whether to Build a Fixture
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5 Comments

  • Bob,

    If parts are simple enough that maybe only one tool change is required, if it is a close to net size sawed barstock job, it can be running in 2 or 3 minutes, no fixture or soft jaws required. With a complex / odd shaped part with 3 or more tools, the time savings in doing multi parts per tool change can be the deciding factor. On a machine with a large Z, the chip to chip time can really add up.

    Pt

  • […] One of things that separate profitable machine shops from the rest are great fixtures. However, you have to determine whether or not developing a fixture is worth your time or is a waste. The Fixture Calculator function on the G-Wizard Estimator can help you decide whether or not a fixture is made for you. For more details on the Fixture Calculator and other fixture issues, click here:: Here’s a Quick Way to Figure Out Whether to Build a Fixture […]

  • Although fixtures can be a very profitable venture, i find that with my work (Custom Guns) a fixture is as yet not in my future. When the work comes in and there are several of the same projects coming in at the same time i can see the need to build a fixture, but until it does I’m stuck with 1 off’s.

  • This works assuming 0 tool changes, but what about if you have 10 tool changes and it takes 10 seconds chip to chip? That’s 100 seconds of tool changes per run, so over 600 runs that’s 1000 minutes of tool changing, and over 120 runs that’s 200 minutes of tool changing for the same number of parts. (not certain my math is correct, but I think so)

    Don’t get me wrong, I like this idea, and I guess I could just add it in when I fill this out, but that could get tedious. I think if you added a tool change time and number of changes or something on the next version, that would make this even better.

    • Kevo, the part time is expected to include tool changes. I don’t really want to break it out because there are any number of things we might then want to break out. Better to just figure it into your part time.

      BTW, even if it was broken out, tool changes will vary depending on whether your CAM software can do Tool Sorting for multiple parts. In other words, it does every feature with the tool on every part before changing to the next tool. Some CAM does that, some does not. Makes a big difference as you point out.

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