A Very Inexpensive Way To Sharpen Brazed Carbide Lathe Cutters

randyc

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Brazed Carbide Lathe Cutting Tools

Although carbide cutters are useful for several performance advantages, brazed carbide lathe tools are often used by hobbyists because they are readily available and inexpensive. Some, new at this craft, might also choose them because they believe that the correct cutting geometry already exists “out of the box”.

The quality may not be optimum but you get what you pay for, right ? Some of them might actually have reasonable cutting geometry from the factory but most are sort of blunt instruments:

P1050085_zpsgv9qdztl.jpg

These tools universally have neutral rake and that’s OK for most purposes, although not optimal for small lathes. Often, there is little or no front or side clearance and the shank of the tool, to which the carbide cutter is brazed, also might need some relief.

Cutting Speed

Older machines have fairly low spindle speeds (as do larger lathes, even of recent manufacture). Carbide cutters perform best at high speeds, low RPM suggests that carbide tooling can’t be used to best efficiency.

I’m an advocate of HSS lathe cutters (and learning to grind them properly, of course). My small lathes are limited to spindle speeds of 1600 and 2100 RPM, correct for HSS tooling, but like most of us I find uses for carbide cutters.

HSM Uses For Carbide Cutters

The most obvious use is cutting hard materials that would quickly wear HSS. The photo shows a hardened tailstock center with a neck, turned with an AR brazed carbide tool.

P1040897_zpsewuitpvh.jpg

In this photo, the cutting surfaces of the broach at upper right was finish machined with a carbide end mill after hardening. There were no issues when cutting the hardened O-1 material.

P1040831_zpse4cdaf05.jpg

There are other applications and the need for carbide cutting tools will likely be obvious at the time. But the main utility of carbide tooling is that it can remove material quickly leaving a good finish. This of course assumes that the spindle speed of the lathe is high enough to be effective. Generally, for steel, this would be around 300 – 500 SFM and about twice that for most non-ferrous material.

A Typical Method Of Sharpening Carbide Cutters

One might get lucky and buy a brazed carbide tool that is sharp and has reasonable cutting geometry. But that’s not always the case and the tool must be ground to the correct geometry and sharpness. The geometry is not within the scope of this thread but you may find some ideas in the following:

http://www.hobby-machinist.com/threads/sharpening-cutting-tools.32987/

Normal procedure for grinding a brazed carbide tool is to first grind away a little of the steel shank underneath the front and under the cutting edge. The reason for this is to better expose the actual cutting edges of the brazed carbide for sharpening.

P1050086_zpsv8i880sf.jpg

After grinding the shank as shown above, a “green wheel” is used to dress the carbide cutting tool, often followed by a few strokes from a diamond lap for finishing. The AL cutter in the second photo has been stroked with the diamond lap on the cutting edge.

P1050088_zpsr15rkm3u.jpg

P1050091_zpsw2rv3bva.jpg

A fine-grit diamond grinding wheel is probably the best tool for dressing carbide cutters but that is a rare commodity among the HSM community. I actually have a diamond wheel and intend to mate it with a motor but the motivation to do so has been eluding me …

Some Considerations of Practicality And Cost

OK, let’s move on, two questions immediately come to mind:

Is it really necessary to sharpen these cheap brazed carbide cutters?

Sharpening the cutting edge (the left side face of an AR tool for turning applications) certainly lessens the requirements of motor horsepower and machine rigidity (and may improve surface finish) but the cutting edge may become fragile and break down in an interrupted cut or when encountering a shoulder.​

Is it really necessary to set up another grinder with a green wheel (not cheap) for carbide?

It depends. If one has the space, the means and the motivation then a separate grinder for carbide – green wheel and/or diamond wheel with vacuumed exhaust – is desirable. Space might be the limitation for many of us so now we come to the point and thank you for being patient.​

Diamond Cutting Wheels For Dremel Tool

P1050093_zpspacgdrtg.jpg

These things are approximately .75 inches in diameter and are available from HF for about $1 U.S. as I recall. I bought a few of them about ten years ago and the price may have risen in that time. The little wheels have diamond grit embedded on the rim and on the face and are especially handy for cutting.

It occurred to me that a little diamond wheel could also be useful for dressing a carbide cutting tool so I decided to give it a try. My first trial simply used the wheel as it was intended: in a Dremel tool. I clamped a carbide cutter in a vise and ground the cutting edge by hand with the face of the wheel.

P1050089_zpsv25ikz1q.jpg

Hey, this worked pretty well, the diamond wheel cut the carbide readily. But thinking that a lot of folks may not have a Dremel tool, I hit on the idea of putting the wheel in a drill press.

P1050090_zpsonu4a4go.jpg

Again, it worked well despite the much lower speed compared to the Dremel. A little care must be exercised since the lower speed tends to make the wheel “grab” the tool.

And that got me thinking again. I put the tool in a small drill press vise at the correct angle, positioned it under the wheel and carefully fed the wheel into the cutter using the normal drill press handle. I think that it would work even better if the vise was secured to the drill press table.

I'm sorry about the poor quality of the photo - you have to look carefully to discern the little wheel and the end of the cutting tool.

P1050092_zpsjdc0gjqk.jpg

This worked best of the three trials and took only a few minutes to grind both cutting edges of the carbide tool. And if a compound angle is required, which would be common, taping a piece of scrap under one side of the vise to angle it would be practical.

In conclusion, I think that this is a perfectly viable way to sharpen carbide cutters with a minimal investment in tooling. :)
 

randyc

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The drill press is a great idea!
I had an old Sherline Lathe and did the same kind of thing.
R
That's really a nice setup; I'm sure that it functions a lot like a standard cutter grinder ! But it's not inexpensive, which was my emphasis :( Nevertheless it's a very interesting grinding tool, a great way to utilize a machine that might be otherwise idle. Thanks for posting the photo !
 

RJSakowski

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I keep one of those little guys next to the lathe for touchup. A local DIY sells a five pack with mandrel for under $5.
 

rustwa

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Thanks for the write up. When I bought my lathe it came with a shoe box of these cutters that I never use preferring to simply grind hss instead. Now maybe I'll give those brazed carbide tools a try.
 

chip maker

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Great idea to use the Dremal tool. I also have a drill press for my Dremal and will surely give this a try. Either way there has to be a good way to get this to work for anyone in their home shop without spending a lot of money. Good ideas. That's why I like this site always getting some good ideas.
 

kvt

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I keep a Dremel hanging on my bench beside the lathe, with one of the HF ones on it, Does a nice job of touch up, Have even used it to touch up a HSS as well.
 

randyc

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I thought this was a new idea but a lot of you guys have been all over it before me :)
 

juiceclone

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I found a diamond wheel at harbor freight intended for tile cutting. I think it was around ten bucks. Very thin, I put it on the shaft of my grinder with the regular wheel so the side of the diamond wheel is accessible. To my surprise, it sharpens carbide very quickly but leaves a very rough "lined" finish on the carbide surface. Follow up with a green wheel takes care of that.
 

kvt

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rwm
seeing you set up the Sherline to do this, reminds me that I have a small variable speed motor that I could build a setup for and use it. It is from an old sherline, when they used DC motors. what grit wheel do you use.
 

Ulma Doctor

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Excellent thread Randy!
great info and you definitely kept the spirit of low cost.
thanks for sharing the valuable information!
 

kvt

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with prim that is almost cheaper than ebay. For some reason I though maybe a 600 or something like that, or would that be to fine, most of the time I'm just needing to put the edge back on them.
 

mattthemuppet2

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that's funny, first time I ever went into a HF store a couple of weeks ago I picked up a set of those diamond impregnated disks and an arbor for $5 or similar, then used one to reshape and sharpen a couple of brazed carbide bits I'd been given. I even ground a chip breaker on one :) After using the diamond disk, I used a diamond lap to hone the edge and they work very nicely. I'll still use HSS bits for most turning but it's nice to have carbide for the occasional tough piece of steel.
 

randyc

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that's funny, first time I ever went into a HF store a couple of weeks ago I picked up a set of those diamond impregnated disks and an arbor for $5 or similar, then used one to reshape and sharpen a couple of brazed carbide bits I'd been given. I even ground a chip breaker on one :) After using the diamond disk, I used a diamond lap to hone the edge and they work very nicely. I'll still use HSS bits for most turning but it's nice to have carbide for the occasional tough piece of steel.
The little wheels are just about perfect for grinding chipbreakers !
 

mattthemuppet2

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they are indeed :) I used one of the brazed carbide cutters last night to face a 3in steel disk. Lower speeds with HSS kept making the belts slip, so I kept cranking up the speed with the carbide until it cut smoothly - around 850rpm. Way faster than I would have cut with HSS and a beautiful finish too.
 

GarageGuy

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Another cheap way to touch up brazed carbide cutting tools is a carbide saw sharpening blade from Harbor Freight. It is a 4" diamond wheel. Here is a photo with part #:

HF diamond blade.jpg

Then make a bushing and mount to a small bench grinder to make it very easy to use:


grinder.jpg

The blade is $10 at Harbor Freight, and the 5" bench grinder was $10 on Craigslist. It also works well for sharpening TIG tungstens.

GG
 

fluvannabear

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Hello all:
I use the larger disc to sharpen TIG electrodes but had not thought about using it on carbide bits. Thanks for the reminder. Do have the HF tool and cutter grinder but still have not figured out how to hold bits using the miter gage that came with it. Think I need to make a proper holder for the lathe bits once I figure out what it should look like. Take care.
Burt
 

juiceclone

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Another cheap way to touch up brazed carbide cutting tools is a carbide saw sharpening blade from Harbor Freight. It is a 4" diamond wheel. Here is a photo with part #:

View attachment 101348

Then make a bushing and mount to a small bench grinder to make it very easy to use:


View attachment 101349

The blade is $10 at Harbor Freight, and the 5" bench grinder was $10 on Craigslist. It also works well for sharpening TIG tungstens.

GG
yes ... that's the one I have mounted alongside the green wheel.
 

randyc

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Another cheap way to touch up brazed carbide cutting tools is a carbide saw sharpening blade from Harbor Freight. It is a 4" diamond wheel...
A most excellent and cost effective sharpening idea and I'm going to imitate your idea for free-hand grinding !

I still like using the small diamond wheel in a drill press with the carbide tool in a drill press vise at the correct angle (which can be set fairly precisely with a protractor). Lowering the drill press handle for a few seconds gives a near-perfect facet. (I have tremors in my hands and grinding by eye is sort of an iffy proposition now) :)
 

59halfstep

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Thank you, a very useful and ingenious use of currently owned tools to help the shop to grow.

Charlie
 

kennyv

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Hey thanks for posting
Thought the same thing about making a cheap carbide grinder... took a few looks at HF and started thinking if that carbide blade sharpener was joke ... and didn't know if those cheap"inexpensive" wheels would hold up . Thanks for confirmation . I was willing to spend $10-20 to find out but not much more .

prob going to go with the Resin Cup Diamond Grinding Wheel.. and mount on something temp before making all the fixings.
Does anyone use this method and what grit a did you find works well ?
thanks
 

JimDawson

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I just use my bench grinder with standard gray aluminum oxide wheels. You just have to push a little harder, and the underlying steel shank won't hurt the wheel. Have had the same wheel on the grinder for about 20 years.
 

LathemanGoody

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Interesting I've been trying to figure out a way to sharpen the broken carbide lathe and mill bits. This will certainly help me save those cnmg carbide inserts from the recycler.

Thanks
 

hman

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I was inspired by the inexpensive HF98862 that GarageGuy mentioned in his post. I do have a Baldor with a diamond wheel, but keep hearing that diamonds and steel don't work together too well at high speed - excessive heat causes the carbon to dissolve in the steel, and goodbye diamonds.

How to get a low-speed grinding setup for steel? I suppose I could have found a way to mount the HF wheel on a drill press, ala randyc, but it wouldn't be a full-time tool. Something like rwm's Sherline-based diamond grinder would be great, but I don't have a spare Sherline kicking around. Then I remembered that I had a motor salvaged from a discarded ceiling fan. These fans run at a nice slow rate. Mine is a single speed motor, rated at 200 RPM. All it needed was an arbor to adapt the motor's 25mm shaft to the diamond wheel's 20mm hole.

Unfortunately, I couldn't get to Industrial Metals before they closed Saturday, and no aluminum of suitable size on hand. Fortunately, I did have some 1 ¾" Delrin - OK for this low speed, low stress application. Got the arbor turned this evening, installed on the motor, and tested. WORKS! All that's needed now is some dust protection for the motor. If the grinder works out, I'll buy the diamond wheel that rwm bought from Amazon and make another arbor.

Thanks to all of you for some fine ideas and great inspiration!
kHPIM3930.jpg
 

LathemanGoody

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The Amazon diamond wheel finally showed up today. I opted to mount it on my variable speed bench grinder. Needed to turn an adapter bushing 1.220 long x .793 diameter with the step length .330 (unknown Alum alloy). Took a bit of time to get the bushing made as I needed it to run true and a pristine finish was desired. Also ended up using some 316 SS bushing material for a washer that would take up space and help secure the wheel and bushing.

I need to make a small table to bolt onto the side of the grinder, needless to say I was excited to use it so out came some lathe bits that were chipped years ago.

Still intend to make a bushing for the lathe so i can mount the diamond cut off wheel in the lathe and take off those busted ends on my endmills. Did have a nightmare last night that prompts me to remember the lathe chuck and ways wont be friends with the diamond and carbide particles that come off-be sure to cover or make a cover for both.

edited to shrink it.

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