Fixture/Jig Design

[kevperro]

I'm a newbie and just getting to the point of breaking end mills on my machine.

Anyway... looking ahead to the parts I want to cut, I'm thinking that fixturing and jig work is going to be important in my part design. Is there any good online references for jig strategy?

[Geof]

Thinking about fixturing and how the parts will be made before starting into the detailed design is a very good idea; almost revolutionary. Now if you tell us you are an engineer you will no doubt be responsible for numerous heart attacks.

Not that I have anything against engineers but so often how something is made is left until the very last thing considered.

Now having avoided answering your question I will get serious and say I do not know of any online source that will give you suggestions on fixturing. This question has come up several times and I cannot recall anyone providing any links.

When you have some preliminary ideas post more questions with pictures and you will likely get specific suggestions.

[zephyr9900]

kevperro, you can go to Google Book Search and download PDF's of jig and fixture design books up through the 1920's. The concepts will not have changed radically since then.

Randy

[kevperro]

Originally Posted by Geof Thinking about fixturing and how the parts will be made before starting into the detailed design is a very good idea; almost revolutionary. Now if you tell us you are an engineer you will no doubt be responsible for numerous heart attacks. Not that I have anything against engineers but so often how something is made is left until the very last thing considered. Now having avoided answering your question I will get serious and say I do not know of any online source that will give you suggestions on fixturing. This question has come up several times and I cannot recall anyone providing any links. When you have some preliminary ideas post more questions with pictures and you will likely get specific suggestions.

Ha! I'm almost an engineer. I have a degree in Chemistry, and another one in Computer Science so I'm dangerously close to being over-educated and ill-suited for any real work.

Be that as it may.... I have to figure out how to use this $10K paper-weight to keep the bills paid.

[kevperro]

Originally Posted by zephyr9900 kevperro, you can go to Google Book Search and download PDF's of jig and fixture design books up through the 1920's. The concepts will not have changed radically since then. Randy

Thanks Randy..... that looks like a good place to start. Probably more details than I need for my simple to make parts but I'll scan through and see if that doesn't give me some ideas.

[justgary]

Originally Posted by Geof Not that I have anything against engineers but so often how something is made is left until the very last thing considered.

Not to mention what it's made of. "Geof, did that bar of Unobtainium come in yet? We'll need it soon for the next project..."

Seriously, don't forget that with CNC you now have the ability to pocket a negative impression of your part to help you hold it, or accurately place alignment pins in a fixture plate. Look through some of the recent posts and you will find other fixturing tips, such as Randy's soft jaws for Locomotive drivers, or saabaero's great threaded plate (although he has not showed us anything actually bolted to it). Vacuum plates are also handy for holding thin material such as engraving plastic or circuit boards.

I read recently about using a dowel pin (hopefully located in an area that will get machined away) as a way to accurately machine bars much longer than your mill table. The idea is that you machine what you can reach, then drill, ream, and place a dowel pin into the stock. Grab the dowel pin in a collet or chuck and use the X axis to drag the unclamped piece along the table (against a clamped straight edge). Reclamp the stock and have at it again after adjusting your X offset. You can pull the pin and pocket a feature where the pin was to remove all evidence of your devious method. Your mill table just became nearly infinite in length!

In my opinion, workholding is the greatest challenge you will face when making things on your mill. If you like puzzles, you'll enjoy figuring out how to hold parts as you make them. Sometimes I pick things up and imagine having to mill them, and ask myself how I would hold them to do all of the steps. Avoiding clamps, vices, and mill tables while milling allows them to last much longer...

Right now I'm delaying a fun project because I have not figured out all of the details of the fixtures I will need. I'm trying to walk the tightrope between too much and not enough fixtures; if I were making a zillion parts, an elegant set of fixtures would make a lot of sense. Since I only plan to make a "few" parts, I only want just enough fixturing to remove the big hassles.

Regards,

- Just Gary

[Geof]

Originally Posted by kevperro Ha! I'm almost an engineer. I have a degree in Chemistry, and another one in Computer Science so I'm dangerously close to being over-educated and ill-suited for any real work. Be that as it may.... I have to figure out how to use this $10K paper-weight to keep the bills paid.

I will not comment on the over-educated, etc, but I will say having a degree in Chemistry in no way puts you close to engineer territory; I have a degree in Chemistry, two actually, and I am certainly not going to admit to being anything like an engineer.

[zephyr9900]

Originally Posted by Geof ...having a degree in Chemistry in no way puts you close to engineer territory

And apparently having a mechanical engineering degree in no way puts me close to practical territory. I will say that I've tried to never design anything that I couldn't at least theoretically fabricate myself. Thus nothing that depends on welding. Certainly the moment I first applied endmill to raw material educated me on what was practical vs. what was theoretically possible...

A former boss of mine, who had worked for IBM in the Thomas Watson era (and I think, was an MIT graduate), was fond of a supposed quote from Watson--"New engineers are useless for a year after graduation, except for MIT graduates--they're useless for two years."

Though not an MIT grad, I can look back and see the validity of that concept, at least in my own case.

Randy

[kevperro]

Originally Posted by Geof I will not comment on the over-educated, etc, but I will say having a degree in Chemistry in no way puts you close to engineer territory; I have a degree in Chemistry, two actually, and I am certainly not going to admit to being anything like an engineer.

That is comforting. I've bumped up against my share of worthless PhDs. There is something about a PhD that causes a person to be unable to function in the normal world.

Anyway.... spent the day making aluminum chips. I've been working with my finish cutter, a Mil-Tec "Freedom Cutter" and have gotten pretty good results. I like the big fly-cutter they have on the Tormach video page simply because it would be able to do my work in one pass, avoiding the multiple 1" wide passes that show up differently because of the change of direction. I'd prefer to pull the part off the mill and not have to use another finishing step before anodizing the part. At least that is my hope..... we shall see.

[Geof]

Originally Posted by kevperro That is comforting. I've bumped up against my share of worthless PhDs. There is something about a PhD that causes a person to be unable to function in the normal world.....

Oh dear, I guess I must not be in a normal world because I am functioning quite okay.

Geof; B.Sc., Ph.D.

Maybe I should have mentioned what the two degrees are.

I am also a true Machinist having done a full five year apprenticeship.

[kevperro]

Originally Posted by Geof Oh dear, I guess I must not be in a normal world because I am functioning quite okay. Geof; B.Sc., Ph.D. Maybe I should have mentioned what the two degrees are. I am also a true Machinist having done a full five year apprenticeship.

Ok... I'll stick my foot in my mouth now. ;-)

My best friend is a Phd. and I make fun of him all the time.

[Geof]

You will notice I did not disagree with you.

I just took a perfect opportunity to poke a stick, what smiley should I use?

One of them should be appropriate.