Now that we have talked about how to hold a round tube with a V-Block and how to create a V-Block in Pro/E 4.0 (Pro/Engineer), now it is time to talk about detailing. How do you make a drawing of a V-Block so that the machinist can understand it, and create it as quickly and accurately as possible.
A Word About Detail Standards
I keep saying that Machine Design is both Science and Art.
When you work for an existing company, they most likely have standards that you will follow for dimensioning.
If you don’t have standards or are confused about how to dimension a part, it is helpful to spend some time getting to know how your parts will be made. When you take a break from the computer, if you can go out and visit the shop and talk to the people who make the parts that you design, it will be time well spent. A helpful CNC operator, or an angry one, can teach you a lot about designing and detailing.
When your company is reviewing their detail standards, be sure to invite some machine operators onto the standards committee. They will bring a perspective that could save the company time and improve the quality of the parts that are made. A couple things you have to keep in mind is that this part might be made again in the future. If so, you want to detail it so not just your current machinists can read it, but future machinists as well.
So. enough about that!
I have detailed the V-Block in three different ways. Let’s take a look.
So there you have it, three ways to detail a V-Block. I am sure there are other ways that I have not covered here.
Do you do it differently? Please tell me by adding your comments below. This is our chance to learn from each other.
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Today we will discuss some of the questions that help you decide the material, modeling method using Pro/E 4.0, and fastener locations.
1) MATERIAL —
First decide what material you will need the v-block to be.
How much will the fixture be used? That means knowing what the product is made of because we need the v-block to be strong enough not to wear down too quickly. We want to be able to produce lots of product before we have to replace any of the parts in the fixture. The more the fixture is going to be used the harder you need to make the v-block relative to the product tube or rod.
Do you need to plan for weld splatter?
If the v-block is located near the weld joint, you will need to consider using a metal that the weld splatter will not stick to as easily, or using a weld splatter shield. Remember that like metals stick better. So if you are welding steel, you may want your v-block to be Ampco 18 bronze or a hardened steel such as 4140 PH or A2. If you are welding aluminum, hardened steel may work just fine.
2) TOLERANCING –
Is the location of the rod or tube critical?
If the tube or rod needs to be located in just the right spot in order to work or assemble easily to the rest of the product parts, then you will want to design in adjustability with shim packs. You will need to look at the product drawing and also know your customer’s preferences.
At Rentapen we design for many different customers. So we have to consider the standards and preferences of each customer when we design. Some of them love to shim every locator in a fixture. Some of them don’t like to shim at all. If you are a CAD drafter, you may be working under more than one designer. Each designer may have their own preferences. But it is up to you to look at the product drawing and then advise them when you think shims will be needed to meet the tolerances of the product drawing. Then do what they say, they are your customer.
If it is a rough location, you may be able to use a purchased V-block from somewhere. Do you have a favorite model or brand you would like to share?
3) FASTENERS –
Once you have decided if your v-block will have shims to fine-tune its location before going into production, you can decide about the location of the fasteners. If the tube or rod location is critical, you will need to use dowels to lock in the location. If it is rough, you can just fasten the v-block directly to the base plate with screws.
4) MODELING —
Locating the Vee in the v-block.
Here is how I model in the Vee cut. Click on the video to see my method using Pro/E Wildfire 4.0.
In this video I dimensioned the construction hole from the BOTTOM of the block. However, the v-cut may fail if I make an adjustment too big in one direction or the other. Some of the project engineers I have worked with prefer that the dimension for the V-cut be from the TOP surface of the block. That way you can change the size of the block without having problems with the cut.
Some like to create planes that intersect at the center where the the construction circle will be located. These planes are created before you start the sketch to cut the Vee. I think your preference depends on your experience and how your brain works when making adjustments to parts while in the assembly.
5) CLAMPING —
Clamping is a whole topic by itself that we will address in a future blog. I just wanted to note that it is something that you need to think about. We always clamp down our parts in weld fixtures, even if it is a table mounted fixture and gravity does its work. You want to be sure that tube doesn’t move when the heat of the weld hits it.
And now I would like to share a couple of things with you.
First, Rentapen’s Holiday Greeting to our customers, vendors, students, and friends.
In this lesson on Jig or Weld Fixture Design we are going to discuss round tubing.
I can think of three ways to locate a round tube off the top of my head. That doesn’t mean they are the only ways. You might be able to think of other ways. So share any ideas you may have down in the comments section, or email me at straley at Rentapen.com and attach pictures or jpgs so I can share them in future blogs.
We often use v-blocks to hold round rods or tubes. A v-block is simply a block with a v cut into it.
If I need to design in adjustment with shims, I often will sketch on paper a rough plan.
Sketching an adjustable V-block
If I am able to use purchased products, like RAPid Tooling Components to locate the V-block, I will sit with the catalog next to me and decide which blocks will work so I can pull those models from the library.
A sketch helps me think about which blocks will have the slip fit dowels and the tapped holes and which ones will have the press fit and the counter bores.
This video kind of explains what I have sketched.
Another popular way to hold a tube or rod in place in a jig or fixture is with a goal post.
Consider the material that the tube is made of and how much use the fixture will get when deciding what material the plates should be. The plates above are RAPid Tooling Components™. These plates come in hardened steel (4140 PH) and Ampco 18. Remember that weld splatter sticks to like metal. Aluminum sticks to aluminum, steel to steel, etc. So if you are welding steel, the Ampco Bronze may be a better choice for the plates of the goal posts.
Sometimes the best way to hold a tube is with a pin that is inserted into the center of the tube. The best method depends on the application, the size and length of the tube, and your customer’s preferences
Here is a little video that goes over some of the ways to locate a round tube or rod.
What have YOU done in the past that worked that I have not discussed here?