Converting a Tobin-Arp tappet grinder from cup stone to diamond wheel

Greetings,

We are an obsolete engine shop and one of the services is regrinding valve tappets on an old Tobin Arp tappet grinder.

The standard grinding wheel is a 1.25" center hole 6" stone cup. These have to be continually redressed and wear quickly and heat the workpiece.

We decided to try some diamond impregnated face aluminum wheels. Since this was a test, we went with the $35 eBay Chicom wheels. The 320-grit gave a nice finish but cut too slowly. Next, we tried a 280-grit. The initial finish was not acceptable, but we ran several sacrificial lifters through it and got better results as it wore in. After about 200 lifters, it doesn't cut any longer. A nice side benefit of the diamond wheel is parts come out cool.

Going throught the catalogs, it's possible to pay as little as $21 and as much as $600 for the same size and grit wheel.



What guidance can you give us as to the sweet spot for a wheel which will produce finished parts from the first.

jack vines

First guidance is to look for a better abrasive - CBN. Diamond's for glass, ceramics, carbides, etc. - not ferrous materials.

Talk to a superabrasive company like Norton (Saint Gobain) or SuperAbrasives Cbn And Diamond Products | SuperAbrasives, get recommendations based of your needs and wheel type. You may be better off with a plated wheel over a bonded wheel so you can maintain form until end of wheel life, or you may benefit from a dressable wheel. A review with an applications engineer will help figure that out.

How are you dressing the radius into the wheel? Does the TA not require you to do that?

Milland said:

First guidance is to look for a better abrasive - CBN. Diamond's for glass, ceramics, carbides, etc. - not ferrous materials.

Talk to a superabrasive company like Norton (Saint Gobain) or SuperAbrasives Cbn And Diamond Products | SuperAbrasives, get recommendations based of your needs and wheel type. You may be better off with a plated wheel over a bonded wheel so you can maintain form until end of wheel life, or you may benefit from a dressable wheel. A review with an applications engineer will help figure that out.

Click to expand...

Thanks for that suggestion. As you suggest, a bit of research does recommend CBN for our application. I'll be checking with Norton, Action and Goodson.

A bit off my own topic, but we've always used diamond inserts in our cylinder hone. They cut cast iron quickly and last forever; a great improvement over vitreous stones. Maybe the difference is lifters/tappets are hardenable iron and cylinder blocks are just as-cast iron.

jack vines

PackardV8 said:

A bit off my own topic, but we've always used diamond inserts in our cylinder hone. They cut cast iron quickly and last forever; a great improvement over vitreous stones. Maybe the difference is lifters/tappets are hardenable iron and cylinder blocks are just as-cast iron.

jack vines

Click to expand...

Low-heat ferrous operations can work with diamond, as the threshold for starting the chemical solubility of diamond into ferrous-base materials isn't reached. But an actual grinding op can (does) go over that line.

Did you stick the wheel that was working?
Cbn perhaps better choice.
If too rough a finish steel the diamond wheel as it too open.
Weird, you use a stick to open it up and then some steel to close it a bit.