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donf
09-20-2015, 08:57 PM
I was hoping for some advise on what the hp requirements are for a bench grinder thats dedicated to grinding hss lathe bits. I searched and there seems to be a lot of advise on how to do the grinding, but no so much for the basic set up.

I restored a 10" Boxford CUD lathe with help from others here about three years ago and its been a great machine. After the restoration I installed a Phase II AXA tool post on advise here and its been a big improvement too over shims. I have been using mostly import carbide inserts, but even with name brand inserts my finish has not been the best. I have tried hacking on a few hss bits, mostly just resharpening a few used bits I got in a box off ebay. The finish did improve noticeably though.

I was sharpening them on a 12" disk grinder as its rest allowed me to control the grinding better than free handing on my bench grinder. I want to set up a dedicated bench grinder with some sort of rest for lathe bits as thats what people seem to recommend. I am not sure what to look for hp wise. There is a 1950s craftsman bench grinder on Craigslist right now that it missing parts but usable. Its a 1/4 hp. Should I look for something rated higher? I use to have an import 1/4 hp bench grinder and that would stall or drastically slow if you pressed the work in at all, so I gave it to a relative. I have found though that older USA made equipment hp rating are lower compared to the hp rating that is put on grinders from importers. I will probably start out using 5/16 and 3/8 hss blanks for now. I do have a few 1/2 too, but they seem to take forever to grind.

lakeside53
09-20-2015, 09:03 PM
Unless you are brutally roughing.. you don't need much hp at all... My Baldor tool grinder is about 1/2 hp, but I've never come close to making it "slow down" so little to no loading/hp..


There is nothing at all wrong with using a disk grinder. Some will argue you shouldn't use a belt for other than roughing, , but the disk doesn't have a any edge roll-over and gives you complete control over SFM (low near center, high near outside).

alanganes
09-20-2015, 09:23 PM
There are lots of people here that can give much better advice than I can, but knowing no other specifics I'd be willing to bet that the main problem with the import 1/4 HP grinder you had was the crappy low-grade grinding wheels these things typically ship with. They are almost always those nasty too-hard dark grey things that should just be replaced with much better and more appropriate wheels.

Stepside
09-20-2015, 09:26 PM
I bought a Jet 6 inch grinder. I put a white wheel on one end and left the factory one on the other end. It works fine if I take the time to "sharpen/dress" the wheels. When I first got the grinder it was much better than what I had before, so I was pleased with the results. Since then I have added two more steps to sharpening the bits. After grinding the next step is using a diamond sharpening stone and this is followed with a few strokes with an Arkansas stone. The last two steps were as big an improvement as was the new grinder.

Bob Fisher
09-20-2015, 09:31 PM
Ditto to he last post, you don't need a lot of power to grind a tool. You really need a good white wheel. Don't take all the angles as gospel, eyeballing is good enough most times. Try it on a blank HSS bit and gage it with a protractor, you will find it easy to grind an angle close enough for most purposes. Bob.

Forestgnome
09-20-2015, 11:38 PM
I suggest watching Craigslist for a vintage Craftsman block motor grinder. Very common, and smooth running. A good coarse wheel will take a lot off without overheating.

donf
09-21-2015, 01:00 AM
Thank you all for the help! :)

Forrest Addy
09-21-2015, 01:44 AM
The HP of your tool sharpening grinder depends much on the amount of rough grinding from the raw blank. Back in the day when I was running a big planer, the OK tool bits we used were M42 HSS, large by comparison and very abrasion resistant. A 10 HP Hammond floor grinder with 14" diameter wheel 3" wide was adequate but it could have used a built in dressing feature and a coolant system. In the course of free-hand grinding off a half cubic inch of HSS it was necessary to dip the tool four times a minute, raising the gallon of room water in the handy coffee can to near steaming. This is probably an extreme example but one that defines the opposite end of the scale from the home shop.

The typical scenario for a home shop lathe using HSS tooling would be a busy time of tool grinding from the rough until an inventory of basic tool shapes is built up. Then the need for grinding is reduced to maintaining and sharpening the existing tools; maybe some heavy tool grinding once a month when some new shape or modification is needed. Depending on scale, the two modes are best served by quite different tool grinders.

I have a 3/4 HP harbor Freight (don't sneer, it's worked great for years - after I re-built the cheesy tool rest) I use for rough grinding and a HF clone of the legendary Baldor #500 face wheel grinder for finish grinding and sharpening.

Wheels for your grinders can be expensive particularly of you hare off pursuing sharpening fads. I use an A 46 O for rough grinding HSS and every other task across the bench. It pays to get suitable wheels for your grinders and not buying wheels if you don't need them. White wheels, "ruby" wheels ect are great for machine tool grinding but far too soft for use in off hand grinders. Woodworkers may tell you different but remember woodworkers have different tools to sharpen

Another point is the cutting edges of a grinding wheel are the abrasive grains. The abrasive grains wear and the space between them may load with debris. You clean and "sharpen" a grinding wheel by dressing it, that is knocking out the dulled surface grains exposing the underlying fresh sharp grains. If the wheel is dull it will rub instead of cut, heating the work while removing little stock.

Use a star dresser to remove the surface trash and if finer than rough ground surfaces are required, diamond dress the wheel.

This process of grinding and dressing reduces a wheel's volume to some unusable condition making it a consumable item. If yours is a busy shop where you use a lot of HSS tooling and drills besides having to tune up lawnmowers, sharpen kitchen knives and scissors etc for the whole damn neighborhood, you may go through a grinding wheel a year. That's OK. You get bang for the buck and because you dress your wheels when needful they cut well which greatly reduces the frustration level.

To the OP question, I suggest a 1/2 HP 10" grinder (1750 RPM) with a good adjustable tool rest as having the power and reach needed for general shop grinding and your in-rush of tool grinding. Later you might invest in a Baldor $500 clone for fine tool grinding. Get spare wheels for both just in case. Also get a star dresser for chewing down your rough grinder wheels and keep it handy - and a diamond dresser mounted in a hand shank. One like any of these:

http://www.ebay.com/sch/i.html?_odkw=diamond+dresser+cluster&_sop=12&_osacat=11804&_from=R40&_trksid=p2045573.m570.l1313.TR12.TRC2.A0.H0.Xdiamo nd+cluster.TRS0&_nkw=diamond+cluster&_sacat=11804

Don't sweat the price. One diamond dresser will last a career of off-hand dressing grinding wheels. Mine has. Don't be sucked in by the low price of the plated diamond dresser with the built-in shanks, They don't last long because they consist of one layer of tiny diamonds easily overwhelmed and stripped off.

One last point and this one is important: grinding and wheel dressing emits billowing clouds of abrasive dust. The dust drifts everywhere. Isolate your grinders from the machine tools or at least cook up a dust collector. If you sharpen a lawnmower blade and later you find white dust on your machine tools located 20 feet away, do not be surprised.

Adding, I've use resin bonded grinding wheels many times sharpening and dressing cutting tools working with portable boring and facing rigs. The usual grinder was a 7" pneumatic producing maybe 5 HP. My objection to the combination was the resin bond was very strong and dense thus generated considerable heat. It was easy to overheat the tool because the changing colors couldn't be readily seen in sunlight or gloom (the only lighting extant for some reason). Overheated M2 will lose edge hardness. M42 poses no problem but being 3x as expensive it was tough to procure from the tool room without a chit from the boss. We had to sharpen the cheap stuff in the bowels of the ship using the welder's 7" BayFlex C-clamped to the staging. We got an edge but it often wasn't very durable.

This experience has carried over to my home shop where grabbing the angle grinder to touch up a drill fetches often unhappy results: a quick sharpening at the expense of an overheated drill. In my experience the practice hasn't been very satisfactory. Your mileage will vary depending on your natural aggression (sharpen already, Damn you!!!)

A beefy belt sander with a fresh belt: very satisfactory but sanding belts quickly wear when grinding the more durable grades of HSS tools. As usual these questions of home shop equipment acquisition hinge on economics and practicality - and what SWIMBO allows.

Paul Alciatore
09-21-2015, 02:57 AM
I think Forrest said almost everything that I had to contribute and then some. I will repeat his statement that if you are going to start with blanks and form (rough out) the tool shapes, you will need more HP. If you are just sharpening already formed tools, then you can get away with fractional HP grinders.

One more thing, I have found that I like a belt sander better for roughing out where it will work. It goes a lot faster than the average home shop wheel style grinder.

And I often just touch up a tool by hand with an Arkansas stone if it is not really dull.

Mike Burch
09-21-2015, 03:29 AM
No-one ever stayed awake wishing he had a less powerful grinder.
On the other hand...

thaiguzzi
09-21-2015, 04:32 AM
I think Forrest said almost everything that I had to contribute and then some. I will repeat his statement that if you are going to start with blanks and form (rough out) the tool shapes, you will need more HP. If you are just sharpening already formed tools, then you can get away with fractional HP grinders.

One more thing, I have found that I like a belt sander better for roughing out where it will work. It goes a lot faster than the average home shop wheel style grinder.

And I often just touch up a tool by hand with an Arkansas stone if it is not really dull.

+1, what Paul said.
As usual, Forrest reads like Gospel.

Doozer
09-21-2015, 09:08 AM
A grinding wheel leaves a hollow grind.
A belt or disc sander does not.
You need a hollow grind to hone and touch up
the edge by hand. Else you get nowhere fast.

--Doozer

spongerich
09-21-2015, 10:20 AM
I suggest watching Craigslist for a vintage Craftsman block motor grinder. Very common, and smooth running. A good coarse wheel will take a lot off without overheating.

I'll second this. I recently picked up a 1HP 8" Craftsman block grinder to replace my little 6" DeWalt and it runs like a dream.

One tip for grinding larger bits is to rough them out with an angle grinder. That'll hog out most of the material in a hurry, then you can finish shaping and sharpening on a bench grinder.

donf
09-21-2015, 07:04 PM
Thanks to all for the advise, it's appreciated. I will hold off on the 1950's 1/4hp Craftsman and look for one a bit newer and larger.

Mcgyver
09-21-2015, 08:54 PM
what Doozer said. a hss sharpening isn't done until after a bit stoning....and the hollow grind makes it oh so much faster.

I agree with you on the small bits, often use 1/4" myself sitting on top a steel bar so its not a 1/4" insofar as overhand goes. Cheaper, faster to sharpen and enough meat for a large number of applications.

if you can afford it, get an 8" delta or something equivalent. The hp only matters in how fast you want to remove material, any hp will grind a bit but a grinder with more umph is to be appreciated.