Can't Understand What A Tool Post Grinder Is Good For?

[great white]

Yup, noob alert question.

I've been looking at tool post grinders (specifically, the older atlas catalogs) and I can't figure out what a tool post grinder is good for.

Isn't it just another way to do what you already can with HSS/carbide cutters?

Except that it makes a bigger mess?

Please help me to understand what and why you would use a tool post grinder attachment.

 

[Billh50]

I have used my tool post grinder for making stepped pins out of already hardened drill blanks. I have also used it a couple times to get a real nice finish on material that just would not allow me to get a good finish with normal turning. I have used cut off wheels on mine to put grooves in for "C" clips or snap rings on hardened shafting.
They do have some uses. Just not everyone will need one.

 

[pdentrem]

Just be sure to cover the ways as much as possible. The metal dust and grit from the wheel will get into and under everything.

You can think of the tool post grinder as a poor man's cylindrical grinder. Instead of 0.001" now you can achieve 0.0001" or better on some machines. To get that diameter just right, like when sizing shafts for bearing fit OD or ID. Refinishing valves for an engine.
Pierre

 

[planeflyer21]

/\/\/\ Yup, exactly what Pierre said.

I've not used a toolpost grinder but have done work on ID and OD grinders, to be held to 0.0002" tolerance on size and 0.0001" of taper end-to-end on an 8" part.

 

[samthedog]

My advice for what it's worth, is get an old junker lathe, and add a toolpost grinder and leave your accurate lathe clean.

If the part is unhardened, I have seen pretty good results achieved by angling the compound so that you can sneak up on the dimension ever so carefully, which eliminates the need for tool post grinding. If the part is already hardened, then you need to grind.

Paul.

 

[great white]

Ah, so I guess I get the hardened materials part. Although I would think carbide would be the go to for that. I can see how it might allow you to do hardened materials on a smaller lathe (ie: less powerful) though.

But I'm not understanding the "accuracy" part. Would not the grinding wheel "erode" as it traveled along a surface during a cut? Wouldn't this introduce and error like a taper?

 

[Bill Gruby]

The accuracy part is simple. There is no tool flex. The grinder produces a much better and closer tolerance finish.

"Billy G"

 

[RJSakowski]

If the part is unhardened, I have seen pretty good results achieved by angling the compound so that you can sneak up on the dimension ever so carefully, .......

Paul.

If you set your compound at 5.74 degrees, you get a 10x expansion of your crossfeed dimension. I.e., a .001" movement of compound is equivalent to a.0001 on the cross feed.

 

[JimDawson]

.....
But I'm not understanding the "accuracy" part. Would not the grinding wheel "erode" as it traveled along a surface during a cut? Wouldn't this introduce and error like a taper?

The grinding wheel does erode but at a rate much less then you might expect and only on the leading edge of the cut. To illustrate this, here is a picture I took of a surface grinder in action. This wheel has already made a couple of passes across this plate and has removed about 0.030 off of the top and the wear on the wheel is only about 1/4 inch from the leading edge since being dressed. The rest of the wheel is still in it's dressed state and untouched. The cross feed in this case is right to left in the picture, and the depth of cut is about 0.005. I turned the coolant off momentarily to snap this picture. The wheel is 2 inches wide and all of the work is being done where you see the sparks.

 

[pdentrem]

One thing to realize is the surface finish will be will much better compared to regular turning. Think of it as surface grinding on the lathe. It is all about fit and finish.
Pierre