Bench Grinder Question

[YYCHM]

Today I'm attempting to grind a HSS threading tool from a 3/8" blank on my little 6" Bench Grinder. I've got a lot of grinding to do.
After working for about 45 minutes the motor was almost too hot to touch. Is that normal for these things? The motor appears to be completely enclosed. How long can I run it without damaging it?

Thanks,

Craig

 

[CalgaryPT]

If that is the 6" model there is no overload protection on it, so yes you can damage it if you don't take breaks. Craig, I'll let others chime in as I don't make many tools, but that seems a long time even for a 6 inch grinder. It's hard to tell from the pics, but the wheels seem glazed. Are you dressing them? They look a little clogged up.

 

[YYCHM]

If that is the 6" model there is no overload protection on it, so yes you can damage it if you don't take breaks. Craig, I'll let others chime in as I don't make many tools, but that seems a long time even for a 6 inch grinder. It's hard to tell from the pics, but the wheels seem glazed. Are you dressing them? They look a little clogged up.

I just dressed it and things are going faster now, but it's going to take an hour or two at the current rate.


…… Ok things are going 10 X faster after dressing the wheel LOL. Maybe a 40 min job now.

 

[RobinHood]

Another thing you can do, before you get to the bench grinder, mark your tool steel for the approximate shape you want and cut the excess off with an angle grinder cutoff wheel. Saves a lot of time. Then do the fine tuning on the bench grinder with your nice angle block set-up.

 

[YYCHM]

Another thing you can do, before you get to the bench grinder, mark your tool steel for the approximate shape you want and cut the excess off with an angle grinder cutoff wheel. Saves a lot of time. Then do the fine tuning on the bench grinder with your nice angle block set-up.

Aaaaa…. this blank is a little small to be attacking with an angle grinder. Maybe my Dremel but those cutoff blades are sooo fragile. What angle block set-up?

 

[CalgaryPT]

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....

 

[RobinHood]

Sorry, your tool grinding attachment that you made which is installed on the angle plate on your grinder in the picture.

 

[YYCHM]

Sorry, your tool grinding attachment that you made which is installed on the angle plate on your grinder in the picture.

Ok, that's for sharpening endmills. Works well for 2 and 4 flt endmills. But, Ya, I guess I could set that block up for 60 deg and use it as a guide. Good observation.

 

[YYCHM]

Here is an observation. After grinding for say 20 min, the wheel stops throwing sparks. Is that the indication that it needs dressing? Sparks start again after I dress it.

Craig

 

[CalgaryPT]

Yup.

You're not side grinding are you?

 

[Janger]

You guys rock.

 

[YYCHM]

Yup.

You're not side grinding are you?

What do you mean by side grinding? As in the side of the wheel?

 

[Janger]

Yes. Read up on that. Big safety hazard. wheels are apparently quite weak in that direction and can fail throwing debris at you. Another thing to check for is cracked wheels. They have a different sound when you tap on them if they are cracked.

 

[CalgaryPT]

Yes. Side grinding can heat up a grinder fast because the bearings aren't designed (in all but some grinders) for lateral pressure. Also, side dressing a wheel is pretty unsafe. I'm guessing you aren't doing this though.

Here's a few tips on HSS grinding http://www.chaski.org/homemachinist/viewtopic.php?t=75985

 

[YYCHM]

Nope.... not side grinding.



Man this is tedious, but I'm getting there. Let's see... I started this thread at 5:30. 3 hours later and 3 shutdowns to cool the grinder down so far.

How pointy does a threading tool need to be?

 

[RobinHood]

It depends on the thread pitch. Look on this site under “root flat” of the thread you are cutting.

http://theoreticalmachinist.com/Threads_UnifiedImperial.aspx

Generally, carbide insert threading tools have a very narrow point with just a bit of radius so they can cut a wide range of thread pitches.

I would make it very pointy and then just round over the point. The cutting forces decrease that way - at the expense of the point dulling faster... everything is a trade-off.

 

[DavidR8]

I’d say that you need a better wheel.
It should not take that long to grind a 60 degree bit. Even if it was a 5/8” blank it would take maybe 30 minutes.

I grind my HSS bits on a 2x48 belt grinder and a silicone carbide belt. Works like a charm.


Sent from my iPhone using Tapatalk

 

[trlvn]

The wheels that come with a cheap grinder are...cheap. I suspect it will work OK-ish if you dress it often. What are you using to dress?

If you want to upgrade, Lee Valley Tools has a selection of good quality grinding wheels. For example:

https://www.leevalley.com/en-ca/sho...heel-dressers/62012-norton-3x-grinding-wheels

For shaping tools from a blank, the 48 grit wheel is a good choice. You'll need to use a hand-held diamond hone or similar to tune up the edges. Remember, only a tiny portion of the edge actually does the cutting. That is all that needs honing.

When you need to touch up an edge, an 80 or 120 grit wheel will produce a finer surface--but still should be honed. In fact, a minute of honing every now and then will keep a HSS tool dead sharp for a very long time.

Do you have a fishtail gauge to check your angles? From the picture, it looks like you have ground the top of the tool to produce a negative rake. That is very uncommon. BTW, it is common to grind a threading tool so the cutting tip is closer to the leading edge. Thats to let you get closer to a shoulder without interference.

Craig

 

[historicalarms]

Goodness, I cant feature taking 3 or 4 minutes long to grind a 60 deg. to a HSS cutter let alone 3-4 hours.

I have 3 six inch grinders in the shop with various grades of wheels on them and any of them can form a thread cutter in a very few minutes....on a new sq. HSS cutter I remove the bulk with the coarsest wheel I have ( a cooling tray of water at hand for periodically cooling the tool) and then final form to a thread gauge on the finest wheel I have. Then dress the edge with an old hunting knife stone I keep in my lathe tooling tray.

 

[YYCHM]

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, then start again.

I'm using a threading gauge to check the 60 deg profile.