Imagine that you had an unlimited budget to buy precision surface grinding accessories for a shop you planned on opening. Suppose also that you were highly skilled at injection mold making, knew all the basics and the entire grinding process.
Your shop is well lit and has climate control; including even heating, cooling and relative humidity. It is a secure facility with adequate locks on the doors and the windows provide plenty of sunlight and fresh air. You also had a healthy budget for all the industrial supplies you might need.
Of course, it is always easier to start out with a new floor plan, compared to retrofitting an existing room that was designed for something else.
Choosing a precision surface grinding machine manufacturer
This is certainly the most important decision, after all, no matter how good the grinding wheels are, or what kind of industrial dust collector you have, the real work is done on the surface grinder.
Most mold components will easily fit on a 6×12 or 6×18 magnetic chuck, which helps determine the size of machine you need. Obviously, there are many jobs which require a much bigger chuck, but these are not the jobs you want.
From experience the best surface grinders are: Mitsui, Brown and Sharpe, Okomoto and Parker Majestic. Such things are always debatable, with others preferring a Harig, Elb, Kent, Chevalier, Boyer Schultz or any of the many Chinese manufacturers.
Coolant or no coolant
Using coolant is nearly always advised, but it can be a nuisance and messy as well. Many small mold components, such as WEDM’d inserts, core pins, or ejector pins just don’t need to be ground using coolant.
On the other hand, having the option of using coolant opens the door for more possibilities and jobs. Consider for a moment how much easier it is to grind 420SS or D2 on a wet grinder, compared to a dry grinder.
Considering that the coolant tank, nozzle assembly and coolant is relatively inexpensive it makes sense to include wet grinding as an option. The expense would quickly be justified by the increased flexibility of obtaining work and efficiently grinding difficult steel.
A place for everything and everything in it’s place is the house rule for precision surface grinding accessories.
Surface grinding wheels
Of all the disposable tooling used in a plastic injection mold making shop, the lowly grinding wheel is perhaps the best investment. An 8 inch 32A46-KVBE Norton grinding wheel costs less than $50 and can be used for a wide range of applications for a very long time.
The Radiac K289027 8” X 1/2” X 1-1/4” Ruby RA46-G800-VOS grinding wheel is even less expensive and usually outperforms the typical aluminum oxide wheel. This wheel works quite well for difficult steels, such as M2 or D2.
Surface grinding accessories
A well equipped precision surface grinding shop needs the best quality accessories, without these the job becomes much more difficult. Time spent checking, aligning, calibrating and adjusting is time lost and money lost.
The basis for all precision measurement is the surface plate. With proper care and use the surface plate will last a lifetime, with periodic calibration to maintain accuracy. A Starrett Inspection grade A surface plate has a tolerance or .0001 in. and costs less than $400.
An 81 piece, grade B set of Starrett gage blocks costs under $500. These are more than adequate for a typical precision tool grinding shop. Economy sets cost much less, even under $150, thought the quality is questionable.
A complete set of Vermont Gage Pins, grade ZZ, black oxide, from .011-.500, minus, costs under $500. As with everything else, economy sets are cheaper, but also of questionable quality.
A Starrett offset V-block costs under $300 and is an essential tool for grinding. The Starrett 3” V-block set of matched V-blocks costs under $600, though I’ve rarely needed a matched set. These are often available on Ebay or Craigslist as well.
The Starrett height gage, Digi-Check series 258, .100-12 in. is an indispensable precision measuring tool and costs under $3500 new. These are also readily available on Ebay and Craigslist.
The electronic height gage from Sylvac is a truly amazing tool that can replace most of the functions of the Digi-check, though not all. The 12 in. height gage can measure under/over, diameters, steps, ID, OD and more. It is the last word for a mold making shop and costs from $4300-5,000, depending on the source.
The Hermann Schmidt surface gage does everything required for transferring measurements from the workpiece to the gage blocks, Digi-Check or for comparative measurement. This quality tool costs under $350.
Two types of sine plates are required: a non-magnetic and magnetic one. Generally, the non-magnetic is generally used for inspection and the magnetic sine plate for the acutal grinding.
Radius & angle dresser
There are primarily two stand-alone types of angle & wheel dressers commonly used in a typical injection mold making shop: under the wheel and side of the wheel types. The Kuhn/Hermann Schmidt angle and radius dresser is certainly the most popular. A new one costs around $2,450, which seems expensive, but it is extremely accurate and easy to use.