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Bench Grinder Question

YYCHobbyMachinist said:
I wondered if it should be taking this long. I've been grinding and dipping in water until the blank is too hot to hold then leaving it in water for a few minutes, come back grind some more and after about 40 minutes of that the grinder motor feels a little too hot for comfort. So shut down and let sit for 10-15 minutes.
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A glazed-over grinding wheel will generate a lot of heat while removing almost no metal. A dressed stone should be pretty much the opposite. Obviously, a coarse wheel (dressed) should remove a LOT of metal in a couple of minutes.

Where did your tool steel blank come from? It is not some ultra-hard cobalt or exotic alloy, is it?

Just in case, remember that grinding dust is BAD for your lungs. Especially cobalt and other exotics. A dust mask is essential.

Craig
 
I have a similar grinder, I can’t see why it should take more than 30 minutes. Maybe it’s the wheel? What grit is it?

Don't apply much pressure, just let the wheel do the cutting.
 
CalgaryPT said:
I think wheel choice comes into play too. I seem to recall there are recommended wheels for HSS that are higher quality that what would come with that grinder. They used to be white methinks....
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I have a white and a grey wheel. I don’t find much difference between them.
 
Johnwa said:
I have a similar grinder, I can’t see why it should take more than 30 minutes. Maybe it’s the wheel? What grit is it?

Don't apply much pressure, just let the wheel do the cutting.
Click to expand...

36 and 60. I've been using the 36 side. Wrong kind of wheel maybe?
 
From Hobby Machinist:

1594065221311.png
 
Given the price point of the PA grinder, you can assume the wheels aren't higher quality AO I think Craig. Most manufacturers of grinders assume you are grinding mild steel. Almost guaranteed your wheel isn't intended for HSS.

So why do some work? On a more powerful machine you'll get a slightly higher grade wheel, albeit still not intended for HSS. Those two factors will get you through in a pinch, but especially on lower power 6" models, you will struggle. FYI, some people have a devoted HSS grinder (like some weldors have one for tungstens). Most of the devoted ones I have seen aren't heavy duty...just 6" like yours. So.........this tells me wheel quality is the bigger factor, not power. Regular dressing will help, but it's a kludge because the composition of the lower quality standard wheels (irrespective of grit) works against you. That's why you're clogging wheels, and that's why the unit is heating up.

1594066305049.png
 
Ok, new wheel it is. Do I dare buy that at PA?

DIAMONDDISK.JPG


The diamond disk was sort of effective but no where near as effective it is on carbide tooling.

…… Well, she still gets pretty warm after 20 minutes running no load.

Going to run the grinder no load for a 1/2 hour. I want to see how warm it gets doing no work.

Well...…. she still gets pretty warm after running 20 minutes no load.
 
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The wheels that grinder came with are way, way, way too hard for what you need to cut HSS with. I have similar sized grinder from old saw grinding attachment about 1/3 hp. I can grind new 3/8 threading tool in around 10 min with it. Maybe faster if I hog it.

To grind HSS you need a very soft wheel, it can be either grade of abrasive as long as it is SOFT.

A soft wheel is held with very weak raisin. It disintegrates like it was a sand stone. This action exposes new cutting edges to the action.

Cheap grinders have hard wheels which have strong raisin which is good for some soft metals & lasts forever. Expensive soft wheels disintegrate fast. I have one that is like 3" in size on a 6" grinder and it is a thick 1.5" wheel. Yup it went down from 6" to 3" in size (!).

Hard wheels are also used for say grinding mild steel for welding.

Order one online - maybe Amazon should be cheapest or eBay. I expect maybe $15 for a new wheel in 6" size.

My grinder also gets warm after 15min no load or light load. I never ground for more then 30 min as even large 5/8 HSS would not take too long. Note there could be few table spun sized pools of dust under the grind wheel after grinding say a 1/2" bit.

Diamond is for carbide not HSS - on HSS diamond will react with metal and disintegrate.
 
What grit Aluminum Oxide wheel should I get? I had actually purchased the grinder for sharpening lathe tools. Come to think of it now the 60 grit side had been working well for sharpening HSS endmills, but you're removing very little material for that operation.

TOOL1.JPG


Looking pretty good to me.

TOOL2.JPG


This needs a relief angle/surface ground on the top surface doesn't it?
 
With the new wheel this took about 40 minutes?

TOOL3.JPG


I shutdown once to take a break and let the grinder cool off and dressed the wheel twice.
 
The tool doesn't appear to have much back rake, if any. That would be fine for brass and bronze if that is your goal. Also, it appears there is no radius on the cutting tip. From this angle, we can't see if you ground in relief for the leading edge.

I found the following page really helped when I was learning to grind lathe tools. It provides a clear, concise description of the process with good diagrams. There is a one page pdf you print out that summarizes his approach:

http://steves-workshop.co.uk/tips/toolgrinding/toolgrinding.htm

Craig
 
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