Tempered Glass Is Always Perfect…Except When It Isn’t

This article is written by Paul Bieber of US Glass and Paul.  It is reposted here with his permission.

Every fabricator strives to deliver perfect tempered glass. That is why you buy from them. Most of the time, they succeed in this perfection. Sometimes their in-house quality program will reject glass, but you never know this. What happens when they ship the glass and your foreman says, “Boss, we have a problem!” Could be you and the fabricator are working to different standards of perfect. ASTM C 1048-04 is the standard for Heat-Treated Flat Glass, either Heat-Strengthened or Fully Tempered. This is the puppy we should all be petting.

Last week we learned that flat glass isn’t perfect, so if a fabricator tempers a piece of flagrantly flawed float (say that three times), and it still meets the standards, you own it. Tempering adds even more variables to the mix.

Let’s read excerpts of the standard on distortion in glass:

7.4.1 “Thermally tempered and heat-strengthened glass is made by heating glass in a furnace to a temperature at which the glass becomes slightly plastic. Immediately after heating, the glass surfaces are rapidly cooled by quenching with air from a series of nozzles. The original flatness of the glass is slightly modified by the heat treatment, causing reflected images to be distorted.”

7.4.2 “…Fully tempered and heat-strengthened glass that has been made in a horizontal furnace my contain surface distortion. Distortion will be detected when viewing images reflected from the glass surfaces.

7.4.4 “Sealed insulating glass units also exhibit distortion regardless of glass type. Air or gas, trapped in the sealed airspace between the panes, expands or contracts, with temperature and barometric changes, creating a pressure differential between the the airspace and the atmosphere. The glass reacts to the pressure differential by being deflected inward or outward.”

The standard addresses concerns that we all have. It acknowledges that glass isn’t perfect. Mostly, when it comes to scratches and rubs in glass, the flat glass standard C1036, applies. So if a scratch is not visible from 11 feet away, it doesn’t exist. These standards are critically important to your business. Ask your fabricator for a copy, or go to ASTM.org, where you will pay a fee for a download.

The biggest issues with tempered glass is size tolerance and ‘bow and warp’.
There are special sections that address both of these.

Here is a basic chart for size tolerance that should be adhered to:

Thickness………Finished Size Tolerance, Length or Width, plus or minus
1/8 ……………………. 1/16
3/16 ………………….. 1/16
1/4 ……………………. 1/16
3/8 ……………………. 3/32
1/2 ……………………. 1/8
3/4 ……………………. 3/16

As this is a plus or minus tolerance, one side of a 1/2 lite can be full by an eighth, the other side shy an eighth, making the lite 1/4 out, and it still is acceptable.

The standard for bow and warp is based on the overall size and thickness of the finished lite. Let’s look at the allowable bow in just two thicknesses,

Size(in) 20-35…35-47…47-59…59-71…71-83…83-94…94-106

1/4 ….. (.12)…..(.16) …..(.20)….(.28)….(.35)….(.47)…..(.55)
3/8 ….. (.08)……(.08)….(.16)…..(.20)….(.24)….(.28)…..(.35)

A lite of 1/4 tempered, 48 x 96, can be warped over a half-inch! Do you find this acceptable? The standard does, and if your glass comes in with this warp, what do you do?

Talk with your fabricator early-on in your relationship and understand what tolerances they ascribe to. Do they have a tighter standard for a high-quality piece like a shower door or table top, than they do for general glazing? This is the key. Know what your fabricator expects of themselves and you will know the standard you can promise your customers.

One last thought, these standards are not law. If you make a contract with a customer to provide perfect glass, that is fine. Buy you probably will need to order two or three lites to get one that is dead-on perfect. If you try to always sell perfect, you better adjust your pricing now.

The original posting of the article may be found here.

Create CAD Standards (SolidWorks environment)

Creating a drafting standards within a SolidWorks environment is an important task.  The task may seem daunting to those of us who haven’t done this before, particularly if our company has no pre-existing documentation methods.  These can be new companies, or companies moving from a lack of control into standardization.

Fortunately, there is a lot of help available.  Actual drafting standards already exist.  Also, many of us have been through this before (sometimes multiple times).  ASME provides American National Standards for many of the areas that need to be covered.  ISO provides international standards for these too, however I will focus on the use of ASME since this is what I used myself.  On the other-hand, creating SolidWorks specific standards requires a little more reseach and upfront work.

Here are my very general suggestions for documents and tasks to create a company’s standard.

  1. SolidWorks Templates (basic overview)
    1. Create a basic solid model template.  The setup within this template will become the backbone of everything within SolidWorks. This will be the most used document.  Establish custom properties that detail the part.  (Use of existing properties can be leveraged to simplify this task.)  Creation of this first template does not preclude the creation of other solid model templates. Instead, it will be used to create any others. For details about templates, goto SolidWorks Help and search titles only for the words “document templates”.
    2. Create a solid model assembly template.  Many of the general settings of this template should be duplicates of the settings of the solid model template.  Some planning is required.  Determine the best method of assembly structure for your company.  Several practices exist as guides, such as Top-Down, Horizontal Modeling, Bottom-Up, and Configurations.  It is important to note that there is not one-size-fits-all method for all companies.  Research each and make the determination based on company needs.  Setup the assembly template to support the chosen method.  However, do not become overly reliant on any particular methodology since situations may require flexibility.
    3. Decide how the drawing templates will interact with solid models. This includes deciding to have any pre-defined views, use of custom and other properties, etc.
    4. Create sheet formats and templates for each drawing size that will be commonly used.  Include annotation notes linked to custom properties, such as part number, material, revision, originator, origination date, surface finish number and/or type, etc.  See SolidWorks Help search for “Link to Property”.
    5. If in a network environment, place the templates and sheet formats within a folder where all SolidWorks users will have access.  Point all SolidWorks installs to this location.  This can be done within pulldown menu Tools>Options>File Location>Document Templates and Sheet Formats.
    6. Create a company standard for shortcuts and macros that speed up SolidWorks operations. Set up a network location for the company macros.
  2. Create the following standard operating procedures.
    1. SolidWorks Performancethat covers computer system requirements, Windows settings, SolidWorks installation, working folders, and standardizing files.
    2. SolidWorks Best Practices and Standards
      • Solid models: discussing preferred methods for creating features.
      • Assemblies: cover methodologies (when to use top-down or bottom-up; and what part should be the primary fixed component) and how to avoid circular mating, etc.
      • Drawings: covering how to use templates/sheet formats, shortcuts, common macros, etc.
    3. Drafting Standards, which can rely on ASME Y14.100 (umbrella engineering drawing standard), ASME Y14.5M (GD&T drafting standard) and possibly ASME Y14.41 (3D model drafting standard).  List exceptions to the ASME standards within the procedure.  If relying on these standards, make sure to have copies of them on hand. This will allow the procedure to be short and to the point.  If not relying on a standard, this procedure can potentially be very long.
    4. Source File and Document Control, which covers how to handle file management (SolidWorks files) and documents.  Be sure to cover processes for control of SolidWorks files in folders and/or the PDM application.  This may be a procedure that is supplemental the company’s general document control processes.
    5. Revision Control, which covers how to revise engineering documents.  This can rely on ASME Y14.35.  If the company uses a ERP or PLM, this procedure may be supplemental to those processes.

For references for further research, check out SolidWorks resource links, such as weblinks that can be found here on Lorono’s SolidWorks Resources.  Also, check out Blog Squad sites such as Matt Writes.