Grinding Wheel Productivity

Grinding Wheel Productivity

We posed the following question on social media last week and have John Thompson of Pferd to thank for a fantastic answer!!

“4-1/2, 5″, or 6″ what is your favorite size grinding and/or cutting wheel? Jumping from 4-1/2 to 5″ is an easy way to get more bang for your buck with your existing grinder but will a 6″ wheel justify the cost of a new grinder?”

We asked John Thompson of Pferd USA to use his technical expertise and many years of experience running abrasives to answer this questions for us. Though John works for Pferd, this information is applicable across all brands and industries. We really appreciate John spending the time to put this information together for us!! Without further delay, here is his answer to our question…

Improving Productivity and Performance in Grinding and Cutting

Being competitive in any fabrication process requires a continuing process to improve productivity and reduce labor costs. You may have found the right formula for bending, shearing, welding and material handling to reduce labor and improve process flow to keep the bids low and the work coming in. As these improvements can be very expensive a lot of thought goes into the type of product and overall cost. Long term savings are often the result from a logical investment in the math required to determine the return on any investment and the overall payback time from lower labor and material costs. This is how a fabricator stay competitive and keeps the team invested in the company growth.

But some of this savings can be lost when the productivity of grinding or cutting for preparing material for welding or cosmetically finishing material for paint or powder coating is left up to antiquated equipment or ideas about the difference between Price and Cost when it comes to abrasives. This is NOT a discussion about different grades of Bonded or coated abrasive product. That subject has been beat to death by every abrasive supplier with new grain or new special formulas that promise faster grinding and longer life. THIS IS a discussion with a simple math lesson on improving productivity and reducing overall costs based on the extra life of a slightly larger diameter product.

This is a simple look at the increased performance and reduced costs for applying simple math to improve the volume of material going through the fabrication process and shipped to the customer as a finished product i.e. “Payday”.

There are two false ideas that must be addressed.

One: that the shop worker doesn’t care about getting their part of the job done on time and with minimum effort on their part. They do care as they need that job and the pay it offers to live. The faster they can complete a task with minimal effort means they can move on to the next task and complete the job on time so everyone can be paid and secure that the company is competitive.

Two: Constantly applying pressure to a supplier of consumable product such as abrasives, weld wire, band saw blades and other consumables will make the company competitive even if they do not change the process of grinding prep or finishing procedures. This false idea that high consumption of cheap or small diameter product based on price will offset lost productivity and allow a company to be more competitive. It is the Labor to use the abrasive NOT the Price of the abrasive.

  So how can we improve operator productivity and reduce labor costs to keep some of the lost money due to old process issues? Look at the interaction of RPM, Diameter and power tool Weight to work Faster NOT Harder.

Based on Safety Requirements all manufacturers are held to the ANSI specifications or maximum allowed surface feet per minute of 16,000 or 80 meters per second when they make a bonded or coated product for sale in North America. A system of the power tool and consumable product cannot exceed that maximum speed. However the best grinding or cutting is not based on the time to complete a task but how FAST one can compete the task.

Here are several TRUE items about using Bonded or coated product:

One: As long as you do NOT exceed the maximum posted safe operating speed based on the diameter of a bonded or coated abrasive product it is ALWAYS best to run the product as close to the maximum operating speed as allowed.

For example using a 4 ½ inch (115 mm) bonded wheel that is rated at maximum 13,300 rpm (80 M/s) and often used on a properly guarded electric grinder rated up to 12,000 will yield greater stock removal, lighter surface scratch and less overall time in stock removal than any other process.

However, the negative cost is that the ONLY usable working part of a 4 ½ inch (115 mm) is about ½ of the outside diameter of the wheel. Then the power tool actually keeps the operator from using the rest of the wheel.

If the operator used a 5 inch diameter bonded wheel that is rated at 12,200 rpm (80 M/s) on the same properly guarded electric grinder rated at 12,000 rpm the overall speed of the outside of the wheel is 430 surface feet per minute faster. Faster diameter speed means faster grinding and cutting and the job gets done faster with less effort.

BUT Speed is NOT the whole story let’s look at effective life of the product based on Diameter only.

A 4 ½ (115 mm) inch diameter bonded product (on today’s power tool) has an effective life of ½ inch diameter and is often discarded when the product gets to 4 inches overall due to the size of the head of the grinder.

A 5 (125 mm) inch diameter bonded product (on today’s power tool) Has an effective life of 1 inch diameter when discarded at the 4 inch diameter based on the same physical size of the head of the power tool. Actually there is 44% MORE life on a 5 inch diameter wheel than a 4 ½ inch. With the increased surface feet per minute speed (32% FASTER at the outer edge with the same overall wear life) is really a better way to save money by buying less and getting more productivity from less wheel.

The REAL Savings is going to the 6 inch system. The Safe operating speed on a 6 inch diameter bonded product is based on the 80 M/s rule and is listed at 10,200 rpm maximum. However with a grinder that is offered in the same physical size as the 4 ½ and 5 inch versions but rated at 10,000 rpm to stay in safety guidelines offers the BEST performance at the lowest cost. The surface speed of the 10,000 rpm 6 inch example against the 5 inch 12,000 example is EXACTLY the SAME (15,708 Surface feet per Minute). The real saving is in the life of the product. The difference in total life of the 5 inch to the 6 inch diameter consumable is 62% MORE wheel. The difference in total life between the 4 ½ and the 6 inch consumable is 133%!!

Overall the cost of the new 6 inch power tool required to use the 6 inch product safely is easily justified due to the performance and life of the product. If the fabricator changes their fleet of older grinders from 4 ½ to 6 inch the return on the overall investment is less than 1 year. This is one of the BEST ways to improve performance and lower the Overall cost of a necessary process in the shop to really keep the product going out the door.

It is just looking at the process using simple math.

John Thompson

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