Jigs and Fixtures?

[5artist5]

I am planning a jig to hold a small 3"x5.25" sheet metal panel that I am going to make several of. I am using this project to learn about making jigs and fixtures.

Are there any resources around that have tips and ideas for making milling jigs/fixtures? I have some ideas about how I want to do it, but I would like go beyond what I have come up with so far and try out some fancy stuff with this project.

I would love to see any pictures of jigs/fixtures that you have come up with.

[escott76]

Jigs and fixtures are a whole art in themselves. So much depends on the work you want to do, and the part in question. The speed necessary to complete the work is a factor, as is the time needed to make the jig versus the amount of parts to be made.
I work in sheet metal a lot professionally, and holding it is frequently a challenge. A LOT depends on the thickness of the part. When I can I'll use soft jaws, but I've made specialized clamps to hold areas of the part. I also like using 90 degree angle aluminum stock with the "mouth" of the V pointing down towards the part. I have a bunch of big rollers at work so I'll frequently put an intentional bow in it so that the ends won't touch until clamp pressure is put on it. This gets more even pressure across the part.
Another thing I do a lot is to mill out a very shallow depression in a piece of sacrificial stock, and drill and tap holes around the periphery to hold small strap type clamps. These usually stay well out of the way of the tool and holder.
Many use vac chucks with thin parts like these, it's something I keep meaning to put together at work but never seem to get around to it.

[5artist5]

Originally Posted by escott76 Jigs and fixtures are a whole art in themselves.

Yes I agree. I was hoping to find a section here on the forum devoted to the topic and I was surprised not to find one.

The material i'm working with this time is .080 aluminum. I'm drilling several holes in it and milling out a slot also.

I am planning to do pretty much what you were saying with a shallow depression and some straps or clamps in this case.

I would love to see some examples if anyone has them handy.

[stevespo]

There is an area for fixturing: Work Fixtures and Hold-Down Solutions

[escott76]

Originally Posted by 5artist5 Yes I agree. I was hoping to find a section here on the forum devoted to the topic and I was surprised not to find one. The material i'm working with this time is .080 aluminum. I'm drilling several holes in it and milling out a slot also. I am planning to do pretty much what you were saying with a shallow depression and some straps or clamps in this case. I would love to see some examples if anyone has them handy.

How deep a slot, what material, and what size mill? Where in the part is the slot? Depending on the answer to these questions, a soft jaw style setup will be quick, easy and repeatable.
I routinely hold down to 0.04 in soft jaws, but it depends a lot on the part in question and the operation.

[5artist5]

Well in this case the material is .080 I think it is 7075. I do not know the T condition other than it is not 0.

The slot is ...Actually I will just attach a jpg.


While I can see doing it with soft jaws there are two reasons why I am lookign to do it another way. The main reason is that I really want to start learning how to make custom jigs. The second reason and the much crappier of the two is that my vise does not open wide enough to hold it.

[escott76]

Originally Posted by 5artist5 Well in this case the material is .080 I think it is 7075. I do not know the T condition other than it is not 0. The slot is ...Actually I will just attach a jpg. While I can see doing it with soft jaws there are two reasons why I am lookign to do it another way. The main reason is that I really want to start learning how to make custom jigs. The second reason and the much crappier of the two is that my vise does not open wide enough to hold it.

That would be an easy job in soft jaws, or similar, but as you have said your vise doesn't open that far.
7075 is great stuff, machines awesome, but it is awful expensive. It's a relatively easy part, shouldn't provide too much difficulty whatever method you choose to hold it with.

[5artist5]

I actually ran the part already. I attached it to a 1"x1"x8" block of wood I had laying around with some hot melt glue. It worked ok, but not great. Not enough support at the edges so I had to apply counter pressure by hand when it was drilling the outboard holes.

(I also need to work on my plunge rate and spindle speed for the drills I was using)

[5artist5]

I have another question, what is the difference between a jig and a fixture?

[Geof]

Originally Posted by 5artist5 I have another question, what is the difference between a jig and a fixture?

Way back in the Dark Ages when I did my apprenticeship the difference was drilled into me:

A fixture just holds the part.

A jig both holds the part and guides the tool; as in a drill jig where the drill is guided by a hardened steel bushing.

Which is why a "Jig Borer" would be used to make the jig; the holes for the hardened steel guide bushings had to be very precisely positioned.

Jigs are never used on CNC machines, fixtures are.


Regarding your fixturing for something 0.08" thick. It depends how many you are doing and how elaborate you want to get. Many times for thin sheet material I make an overlay piece out of thicker material which overlaps the thin stuff and is secured around the edges with a few bolts. All the machining is done through the overlay piece. Normally what I do is simply run the program for the part using a slightly larger tool and slow down the rapids. This machines away the overlay plate and then when the correct size tool is used it has plenty of clearance to work on the part.

For siginificant volume, i.e. many hundreds or into the thousands, I have made fixtures where the overlay plate is very thick and forms part of a bridge affair. Under the overlay bridge there is a plate with an air cylinder (a short one). The stock is slid in, the air turned on and the stock is clamped up against the underside of the overlay plate.

[5artist5]

Oh ok.

That air cylinder setup is pretty fancy!