When you’ve been in the steel grinding business as long as we have, you begin to see patterns… or “Frequently Asked Questions” that we receive from our newest clients or companies who request quotes from us. PGI has been in the grinding business for 45 years, but we realize some of you may be new to these terms. When our experienced estimators ask questions to provide you with the most competitive quote that delivers a product that matches what you need, you may be caught like a deer in headlights.
So we thought we’d share some of the questions we receive most often and give you some definitions for words we use regularly. Hopefully this information will help you – and that you’ll let us help you answer any other questions the next time you’re looking for custom steel plate work.
Surface grinding is a process that moves a grinding wheel or segment in a plane while the wheel contacts the work piece and removes material to create a flat surface. Parts may require surface grinding to achieve a flat surface, a very accurate thickness, a very smooth surface, material removal for hard materials and when material needs to be removed quickly. There are two types of surface grinding: vertical spindle grinding (also called Blanchard Grinding) and horizontal spindle grinding. Horizontal spindle surface grinding is, in most cases, a secondary process to improve surface finish, flatness or parallelism after Blanchard grinding is complete.
- Base plates – when setting equipment, a flat base plate will eliminate shimming and minimize labor cost.
- Machine table tops – when building an automated machine, it is important to start with a flat surface to mount critical close tolerance components.
- Stamping components – when building bolsters, die shoes, parallels and other components, it is important your parts be flat or restrained in the flat condition to eliminate stack up errors.
- Machining set up – Sometimes your print does not call out flatness. It is still important to make you machining set up easier and will help hold machining tolerances.
Parallelism is the relationship a surface has to another surface or datum. As it relates to ground plate, a plate is parallel if its thickness is consistent all over the plate. Parallelism is normally checked using a micrometer or caliper.
Parallelism is different than flatness because it is the relationship between two surfaces, while flatness describes a single surface. Parallelism is critical when consistent thickness is required.
The symbol for parallelism is // and is usually follow with an allowed deviation and a datum surface callout.
When two surfaces are square, they are at 90˚ of each other. This will usually be written as □. Normally one surface is the datum (fixed point) and a tolerance is specified for how a second surface relates to the datum. The datum can be a surface on the part, the centerline of a bore or a surface off the part on a mating structure.
The squareness tolerance is normally written as the amount of variations over the length of the second surface (Ex: ⊥ .005 in.) The second surface could be greater than or less than 90˚ no more than .005 in. over the length. Another way squareness or perpendicularity tolerance can be written is the amount of degrees a surface can vary.
- Plate Thickness and Material Type
- Surface Area and Stock Removal Requirements
- Thickness Tolerance
- Flatness Tolerance
- Parallel Requirements
- Quantity Requirements
These are just a few of the questions we receive every week. Do you have a question about a drawing or a project that you’re working on that we didn’t answer? Let us help! Contact Us today.