# Lathe tool Grinding



## Brian Rupnow

I may be opening a can of worms here, but---I am tired of the horrible finish I get with my cheap Chinese carbide lathe bits. I an beginning to do a bit of research on grinding my own lathe cutting tools from HSS. I have an old 3400 RPM dual end grinder that my father bought when the local blacksmith finally closed up shop.--You can see it in the attached picture, behind all the small engines (Its red).  This grinder is a bit like me---its pretty damned old, but it still works good. In the picture it is set up with 8" diameter polishing buffs.
  I am wondering about tool grinding jigs to ensure that I get the correct angles on the tools I grind, and sources of good information on grinding my own tools from HSS.----Brian


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## Brian Rupnow

Here are a couple of better pictures of the grinder.--(Ignore the little engines---I'm running out of flat places to set things.) As you can see in the pictures, there are "rests" that I can attach a ginding jig to. These "rests" give me the ability to set one of the "approach" angles of the peice I am going to grind, but that is all.


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## kvom

I have been taught to grind the HSS bits freehand, and just use the rests to support my hands. If you use 3/8" HSS blanks it takes only a few minutes to get a nice turning/facing tool. Thereafter sharpening takes mere seconds. For me the hardest part is rounding off the sharp tip; it's easier to do with a honing stone than with the grinder.

In school they had us grind the first "tool" using CRS blanks; easier to cut and no big deal if you mess up. Once you have one with angles that look good you can replicate it with the HSS.

If you still have the guards for the wheels it might be a good idea to put them on. There are numerous horor stories about grinding wheels shattering and throwing shards at high velocity. 

Finally, you need a fairly soft wheel for HSS, and also a means of dressing the wheel.


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## arnoldb

I have to agree with kvom; though still pretty new to machining, nearly all the toolbits I use I free-hand grind from HSS on the bench grinder; no jigs or anything - then you can "feel" the surfaces as you're grinding them. Once done, a couple of passes over an oil stone to clean up burrs/rough edges left by the bench grinder and they work well. Some more passes over the oil stone, and you can get much sharper cutting edges than carbide tips can have, making for nice finishes and very fine cuts. 

I even started using broken carbide tipped tools as "holders" for HSS; Doing smaller work, I buy a couple of 4mm round HSS blanks at a time, and split each into 3 sections. I drilled a 4mm longitudinal hole in the "blank" end of one of the broken carbide tipped tools, with a couple of 3mm grub screws - this then takes the HSS "inserts" - each of which can be made to have 2 different tips.
I keep the "holder" in one of my QCTP holders, and if I grind new HSS tips, I just grind the tip to center line and then profile like I want it for different materials - makes one quick change holder into a very versatile "slower change" holder, but still quick to use ;D
I can post a pic later on if you'd like to see the scruffy, but effective, arrangement.
Regards, Arnold


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## Kermit

So...  I figure this is the wrong way to do things, but I 'll show my ignorance one more time today.  ;D

I have gotten great finishes on 1018 by using a very small fine grained diamond emery file on a carbide insert(triangle style) as a sort of honing stone... Albeit, the shiny surface finish it made slowly became coarse and grooved looking over the course of ab out five minutes of cutting time. But it worked wonderfully for a short time.

 :-\ eh, whatever.  Still lots to learn,
Kermit


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## arnoldb

Kermit  said:
			
		

> So...  I figure this is the wrong way to do things, but I 'll show my ignorance one more time today. ;D
> 
> I have gotten great finishes on 1018 by using a very small fine grained diamond emery file on a carbide insert(triangle style) as a sort of honing stone... Albeit, the shiny surface finish it made slowly became coarse and grooved looking over the course of ab out five minutes of cutting time. But it worked wonderfully for a short time.
> 
> :-\ eh, whatever. Still lots to learn,
> Kermit


Kermit, that is most likely because the carbide inserts are so very hard, but brittle; if you try to make a really sharp cutting edge on it, the edge just "crumbles" away fairly quickly in use. Personally I find carbide OK for non-intermittent and fairly aggressive cuts if you can use lots of speed - but in general I prefer the HSS because it keeps cutting edges longer on fine cuts.
Regards, Arnold


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## jpaul

Brian,
In my opinion, freehand grinding is fine for preparing a basic HSS lathe tool. However to prepare grooving tools , cut off blades, form cutters, and threading tools, a fixture such as this would be beneficial





this fixture was described in 

	T & C Sharpening, by Harold Hull , Work Shop Practice Series #38 , www.specialinterestmodelbooks.co.uk






also Guy Lautard has a plans and a kit for a similar device called the:
	Tinker and Mini Tinker http://lautard.com/tinker.htm 

Nice engines!


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## Tin Falcon

Brian:
 That old grinder should do fine. I just use a jet 6" I picked up 10 plus years ago. There have been several jig designs published over the years. There are probably at least a couple in the old popular mechanics archives. I was taught to grind by hand in trade school. I suggest you get one of the T style protractors to check your angle but unless you are doing a threading tool the angles are not critical. I will say that my bits have a lot less facets than years of yore. 
What type of info are you looking for?

May 1947
Tin


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## Brian Rupnow

Tin Falcon---That it exactly what I was looking for.---Thanks


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## Brian Rupnow

I've been messing about with this issue all afternoon, and after perusing the Sherline website about grinding lathe tooling, I have come up with the following. I'm not certain that its right, but its my interpretation---Brian  (My lathe uses 3/8" square tooling.)


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## Brian Rupnow

IF--I have done this correctly, the first step in grinding a 3/8" tool will look like this.-------


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## Brian Rupnow

Next step will look like this---


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## Brian Rupnow

Fourth grinding step should look like this????


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## Brian Rupnow

Okay Kiddies---If I use the set-ups previously posted, the tool is going to end up looking like this.


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## Tin Falcon

Brian you drawing are great but me thinks your math / logic is wrong. 
machineries handbook cord height formula on a 6" wheel with a cord of .750 (2 x 3/8) you get a height of .023. plug that in to basic trig Tan (Theta) = opposite/adjacent I come up with 3.5 degrees. that is if you hold the base of the tool at center height and zero degrees to the wheel ie level you will be grinding a 3.5 degree hollow ground angle. by placing the top of the tool at center height to the wheel this gives a canceling effect. so in your first drawing you are in effect only grinding a 3.5 degree angle. if you put the heel at center line the angle will be added giving an effective anlgle of 10.5 degrees. Me thinks you want the base of the tool at center height then add angle as needed. 
Brian this may help. 
http://www.metalartspress.com/PDFs/Sharpening_Steel_Lathe_Tools.pdf

What metal ar you intending that for ?? the end radius is a bit large except for fine finishing with a light cut. .015 -030 would be more in order for general work. 
I see Sherline shows the center of the tool at centerline of the wheel this would make sece as it cancels out the angle imparted by wheel diameter. 

Tin


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## Sleazey

That's a nice set of rests on that grinder.

On mine, a Palmgren 8", the aluminum rests are plenty solid enough, but the mountings are kind of flimsy. There were also some casting flaws on the edges (stubs of gates and sprues), that I shaved off manually by sliding the blank HSS blank over it. The edges on the blank were sharp enough to peel off the aluminum from the rest and plane it down flat. (Not the whole surface, just the bumps and burrs around the edges.)

Your grinding plan looks exactly like what I did the first time I ground an HSS tool bit. I had the same source as you, the Sherline page on grinding tool bits. I was pleased at how well my tool worked on 1018 CRS.

I used a bevel protractor to set the tilt on the rest to 7 degrees.

One trick I came up with (but it's probably something everybody else already knows ), was to paint the grinding rest with some layout fluid, and then scribe sets of parallel lines at the correct angles. That helped me keep things at the correct angle (or at least close enough).

I found that 2 sets of parallel lines, one set oriented for the third grind, 15 degrees to rim of the wheel, and another set scribed at 11 degrees to the edge of the wheel, were easy to follow since one set was at nearly right angles to the other. Two sets nearly parallel would probably be confusing.

I used an EZ-lap diamond hone to dress the cutting edges, and to put a small radius on the nose.

With some cutting fluid (Lowe's Kobalt thread cutting fluid), and a very fine manual feed, and an RPM higher than what I used for roughing, I achieved an excellent nearly mirror like finish. Much better than what my commercially made carbide inserts gave me.


Of course, I then strained my elbow patting myself on the back. ;D


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## Brian Rupnow

AWRIGHT!!! enough of this dickin around!!! Its time to grind a tool. The picture shows my first set-up. (Just a disclaimer here--guards are removed only to show what I'm doing.)
  This first shot is somewhat staged. When you buy these HSS blanks, they already have an angle of about 13 degrees on the end. I set the toolrest at an angle of 7 degrees, in a position that sets the heel of the part I am grinding level with the center of the grinding wheel.--It is somewhat coincidental that with the toolrest set this way and using a 6" diameter grinding wheel, the angle on the end of the tool almost matches the angle of the grinding wheel face.---AND--all the grinding that follows is done without changing the angle or position of the toolrest.


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## Brian Rupnow

The first actual grinding I done is shown in this picture. I held the bottom of the tool against the toolrest and angled the tool away from the centerline of the grinding wheel by about 10 degrees as shown. (Same as the drawing I posted). I ground untill I had 1/4" of flat (again like the drawing), but it didn't look like enough on a 3/8" square tool, so I kept on grinding untill I had a flat about 1/2" long. I have a can of water setting by the grinder for frequently cooling the tool as I grind it.


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## Brian Rupnow

Once I had the first grind finished to my satisfaction, I proceeded to the second grind. Again, the bottom side of the tool is resting flat against the toolrest, and the angle I'm holding the tool at was at "about" 60 degrees to the center of the grinding wheel. This ends up giving an angle of 60 degrees between the two ground cutting edges when viewed from the top of the tool. I figured that would be all right, as the Sherline "how to" article only says 'Less than 90 degrees".


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## Brian Rupnow

At this stage, after 2 grinds were completed, the tool looked like this.


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## Brian Rupnow

Moving on to the third and almost final grind, I layed the side of the tool which would be opposite the cutting side against the toolrest, and held the tool at approximately 15 degrees to the centerline of the grinding wheel (Same as the picture I posted), and more or less held the visible line which resulted from the second grind on the tool in line with the side of the grinding wheel. Then I kept grinding and checking untill the resulting flat surface just touched the sharp corner at the end of the tool which had resulted from the first two grinds.


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## Brian Rupnow

Now when I look at the end of the tool it looked like this. I freehand ground a VERY small radius along the apex of the two first grinds at the end of the tool.


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## Brian Rupnow

Now, I'm not going to say if I did that tool right or wrong, but does that sucker ever cut!!!--and smooth as a babies bum!!! I don't think I will be buying any more carbide tooling.----Brian


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## bearcar1

Nicely demonstrated Brian, a textbook example of how to grind a very usable cutter. DyiM, If HSS cutters dull that quickly for you than there is something wrong, either your spindle/feed rate is too fast or the rake angles on your cutters are way off. (or a very cheap grade of cutter is being used) HSS cutters should cut well for long periods of time with only an occasional dressing with a stone being required. Personally I find that carbide cutters, for my tastes are too brittle, but they do have their applications. Whatever you feel most comfortable using is fine I'm sure. ;D


BC1
Jim


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## Tin Falcon

good job brian tool looks great adn seems to be working well.


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## Speedy

Brian, you made that look way to easy!!!
your in ontario right?

just thinking out loud, can a camera tripod head be used for grinding?
wouldnt it provide the swivel to get the angles.


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## rake60

Beautifully documented tutorial Brian!

Rick


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## gmac

Brian;
Nice work. Like you I reached the point of reading material where I too said "enough, lets just destroy some metal". I'd found info on jigs but after freehanding lots of toolbits I'm in no rush to build more tooling - I need to build engines...

One comment - I found that as soon as the wheel is not cutting quickly anymore (1/4" bits) and seemed to be heating up quicker - it's time to redress the wheel. Amazing difference. If the wheel isn't making a nice sizzling sound and staying cool - redress. Not sure how long my wheel will last; but life's too short.

When you fall back in research mode try the FILES section here;

http://groups.yahoo.com/group/ToolGrinding/?yguid=204436884

And thanks for all the effort you've put into adding to this website, making it a great resource for learners like me.

Cheers
Garry


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## kvom

Tool looks very good!

Carbide needs higher speeds than HSS, so if your lathe is not capable of those speeds than HSS will work better.


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## Brian Rupnow

Now---Just so I can do it again with the same success---Maybe a SIMPLE jig.---


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## Brian Rupnow

Something like this---


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## Brian Rupnow

sECOND GRIND---


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## Brian Rupnow

AND FINALLY---


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## Foozer

Really good idea on the jig. Free handing the grinds gives one that multi faceted look  may look like a diamond in the rough but usually ends up cutting squat.

Getting that nice radius on the tip still eludes me, but for sure a good sharp HSS bit cuts like a new razor. When they start acting like a razor the bride has used for "who knows what," getting it back to the wheel in a jig like you've created is just what the doctor ordered.


Now if you can solve the Rat Nest issue. Here's taking 0.050 cuts off AL with fast hand feed, Just peels right off into one long piece of rat nest  



Robert


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## vlmarshall

Excellent idea, and drawings, Brian! :bow: Looks like a good way for me to come close to the quality of the stuff the tool-grinder guys at work turn out, BEFORE I have their 40+ years of experience. Feels like cheating. ;D





			
				Foozer  said:
			
		

> Now if you can solve the Rat Nest issue. Here's taking 0.050 cuts off AL with fast hand feed, Just peels right off into one long piece of rat nest.


Geez, Fooz, break a chip! ;D I'm not sure what the tool-grind solution is, but I'd use more feed, or less spindle speed, or pause every few seconds while cranking that wheel.
That's too big of a pile of razor ribbon.  ;D


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## Foozer

Vernon  said:
			
		

> Geez, Fooz, break a chip! ;D I'm not sure what the tool-grind solution is, but I'd use more feed, or less spindle speed, or pause every few seconds while cranking that wheel.
> That's too big of a pile of razor ribbon.  ;D




I know, just had to do it. Roughing down to size. I was well to the right. Even on light cuts, fine feed, a good sharp bit will leave that long string of curly cues. Read about employing a chip breaker grove into the bit but I cant get the hang of it. Though when first turning metal it was cool, Oh! lookie lookie at the long curlys being taken off, now there just pesky critters 

Robert


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## Brian Rupnow

So---I got up early this morning and did a bit of welding and grinding and "Voila'"--a welded assembly. This looks like it may work alright. I will make up the "Sliders" this weekend sometime and give this thing a test run.---Brian (If you were wondering about that line that appears to be a crack in the jig----It isn't. The peice of plate that I reclaimed from my scrap bin to make the jig had been cut thru with an acetylene torch, then welded up in one of its previous lives. I uncovered the cut when I was machining. It doesn't go all the way though, so it doesn't hurt anything, it just looks kinda ugly.)


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## kvom

For aluminum "chip breaking" I normally just stop/restart the carriage feed when turning down to size when the curlies get too long. 

The jig looks like it will make grinding easier. Does it work for bits that cut left to right?


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## Brian Rupnow

Kvom---I think it will work for almost any kind of tool. The secret will all be in how you grind the angle on the "sliders".


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## Brian Rupnow

Hey---This works really slick!!! In this picture you see Number 1 slider with the 10 degree angle for the first grind. At the last minute as I was making it I decided to leave the entire length of the slider full height, with just a slot to set the tool in---it holds better that way. The slider still has red layout die on it. The mark on the tool is 1/2" back from the end.


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## Brian Rupnow

Here you see it after the first grind is completed. The grind ends at the mark 1/2" back from the end of the tool. It is really easy to use, and as I slide the tool back and forth on the face of the grinding wheel, the Slider moves ahead and back in the jig slot, holding the angle correctly.


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## Brian Rupnow

And this is what the tool looks like after the first jig grind---the left end in the picture.. (I only have one tool, so I am sharpening the other end.)


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## Foozer

Brian Rupnow  said:
			
		

> And this is what the tool looks like after the first jig grind---the left end in the picture.. (I only have one tool, so I am sharpening the other end.)



Am watching with interest. I've started on a few versions of a jig like that, all failures. Sometimes the simplest things elude me. I like what you got going. HSS bits cut like a dream when sharp. Getting them resharpened while maintaining the same profile is tricky by hand. Ruined more bits with the old just touch it up task.

Like your jig goes. Angles are not that critical for the hobby use, Means to sharpen and resharpen with repeatable is more important. Thanks for the time your taking to do the How To

Robert


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## Brian Rupnow

Here we are with the second slider in place and the second surface ground on the tool. Very easy to use, and very repeatable----So far so good---


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## Brian Rupnow

And now--Slider #3 and the final grind. This worked okay, but I think I may make a new #3 slider with an angle of about 8 degrees rather than the 15 on this one, so it doesn't cut quite so deep at the heel of the cut. The arrow on the tool was supposed to be in line with the edge of the grinding wheel, but as you can see I managed to cut beyond the arrow. That doesn't hurt anything, but it SHOULD have been in line. I have also posted a picture of what the tool looks like with the third cut finished, before any "stoning" was done on the cutting edges, and before I "hand bombed" the 1/64 radius on the tip.


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## Brian Rupnow

And this is a cut in 1018 (mild steel) using the tool I just ground on the jig. You can see that the cut has a good finish. The lathe was running at 970 RPM. You can also see that the tool has a shiny area around the perimeter of the top ground face. That shiny area results from "stoning" the ground faces on a flat oilstone. Since the grinding wheel is a diameter, all the faces it cuts are in effect "hollow ground", so stoning flattens the perimeter and leaves a bit of a "cup" in the center of the ground area. I "stone" all 3 cut faces by rubbing them on an oilstone, as it makes the tool sharper.


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## Brian Rupnow

Diymania  said:
			
		

> To rid of the diameter problem, the flat sides of the wheel could be used.


Diymania--You are probably right BUT----Back about a hundred years ago in my apprenticeship, I was taught to NEVER grind on the side of a grinding wheel. Apparently some grinding wheels are made to take grinding on their sides, but many are not. And the ones that are not are prone to EXPLODE when they are used that way. And I ain't sure which kind I have!!!


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## rake60

*OK Safety Notice!*

As Brian has already stated:
*NEVER grind on the side of a standard grinding wheel!*

Grinding wheels are a cemented composite material.
They are not designed to accept a radial load.
I happened to be on the shift when a grinding wheel failed
due to operator error. I was sure we were going to lose him
that night. He looked like he'd been shot point blank with a
shotgun. He did survive but lost his right eye to the incident.

OK I'll kick my soap box back under the couch now...

Rick


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## Maryak

Brian,

Very neat grinding jig :bow: :bow:

To follow up on Rick's *SAFETY MESSAGE* wheel guards might be a good idea for your, (any), grinder.

Best Regards
Bob


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## Brian Rupnow

Maryak  said:
			
		

> Brian,
> 
> Very neat grinding jig :bow: :bow:
> 
> To follow up on Rick's *SAFETY MESSAGE* wheel guards might be a good idea for your, (any), grinder.
> 
> Best Regards
> Bob



Maryak--That was covered in one of my very first posts

AWRIGHT!!! enough of this dickin around!!! Its time to grind a tool. The picture shows my first set-up. _*(Just a disclaimer here--guards are removed only to show what I'm doing.)*_
  This first shot is somewhat staged. When you buy these HSS blanks, they already have an angle of about 13 degrees on the end. I set the toolrest at an angle of 7 degrees, in a position that sets the heel of the part I am grinding level with the center of the grinding wheel.--It is somewhat coincidental that with the toolrest set this way and using a 6" diameter grinding wheel, the angle on the end of the tool almost matches the angle of the grinding wheel face.---AND--all the grinding that follows is done without changing the angle or position of the toolrest.


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## Tin Falcon

Well just reviewed the "Safety Rule" sticky thread somehow I did not cover grinder safety That has been corrected. 
Tin


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## Thad Swarfburn III

Been following this thread with interest. I just finished my tool grinding jig, to the design of Rudy Kouhoupt from his second "Shop Wisdom of" book.










Had it parkerized at work. It will eventually be mounted to the grinder base as well - I've since cut slots in the base to allow for wheel wear. I brainlocked when making it and rounded the wrong end of the slide bevel. I'm sure the grinding wheel will take care of the other end in short order! I'll be getting a coarse wheel for the other end of the grinder; I realise the white ones are a bit soft to make a tool from square. 

What's the best way of dressing one of these? We use diamond dressers at work, but they're a bit out of my league.

Guy at work had a grinder wheel blow up on him when he was an apprentice - still has nasty scars around his mouth. Wear the gear, ALWAYS use the paper washers on the wheel, ensure you're not exceeding rated RPMs, yadda yadda. Rules are there to make your life more difficult. But not as difficult as eating grinding wheels!

Matt
(shop H&S rep)


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## AlanHaisley

Brian,

I really like your jig, but, I keep having this recurring thought that if the "slider" were square stock it might be possible to cut all three angle slots in various sides of a single slider.

Fewer pieces to mislay if it works. Also, If there is need for others, perhaps for threading, cutting brass, Left/right hand, etc., they could be stamp marked for ease of identity and use.

Alan


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## Brian Rupnow

AlanHaisley  said:
			
		

> Brian,
> 
> I really like your jig, but, I keep having this recurring thought that if the "slider" were square stock it might be possible to cut all three angle slots in various sides of a single slider.
> 
> Fewer pieces to mislay if it works. Also, If there is need for others, perhaps for threading, cutting brass, Left/right hand, etc., they could be stamp marked for ease of identity and use.
> 
> Alan



Alan---you are probably right. Remember--I was figuring it out as I went along. I went from not knowing how to grind a lathe tool to making a jig over the span of about 72 hours. ;D ;D


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## Brian Rupnow

I have been using my tool grinding jig since I built it, and I must say I am very pleased with it.--BUT--Since the grinder wheels are round, (6" diameter), I get a real "hollow ground" effect on the flat surfaces of the tool I grind---so they aren't really "flat"--They are concave. This requires a lot of stoning on a hand held stone, which is kind of a pain in the ---uh----fingers!!! I am thinking about keeping my current set-up for roughing in the shape I require on new tool bits, but perhaps building or buying a small stationary belt sander to finish things off so that I do get true "flat" surfaces on the tools, thus avoiding a lot of hand stoning. Any suggestions on what width and grade of belt to look for to do this with?---Brian


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## black85vette

Brian;

I have done this with a disc rather than belt. Nice thing about discs is that you can get them for automotive work at 800 or 1000 grit. Don't know if belts come in that fine of a grit. Also they are adhesive so you can change them out quickly.


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## Cliff

Hey Brian I had a question about your tool grinding- why do you grind the top of the tool so much all it needs is just enough relief to get the chips away from the material? I had a grinding wheel blow up on me once I was doing some tool post grinding and through lack of experience I had to heavy of a load on the grinder even with the coolant running it got hot and blew up and got me on my left shoulder I was lucky I just had to set down for a while it scared me that bad also had to change my shorts the next day I was running it again and the cooling fan on the motor blew up and hit me on the right shoulder again it scared the crap out of me I didn't run the tool post grinder for a while but I considered my self very lucky. Cliff


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## ttrikalin

brian, i read in the army machining manual on the net that a chipbreaker (groove after the cutting edge) avoids the rats nest... but have never seen a tool with a chipbreaker ground on... 

tom


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## Brian Rupnow

Cliff  said:
			
		

> Hey Brian I had a question about your tool grinding- why do you grind the top of the tool so much all it needs is just enough relief to get the chips away from the material? I had a grinding wheel blow up on me once I was doing some tool post grinding and through lack of experience I had to heavy of a load on the grinder even with the coolant running it got hot and blew up and got me on my left shoulder I was lucky I just had to set down for a while it scared me that bad also had to change my shorts the next day I was running it again and the cooling fan on the motor blew up and hit me on the right shoulder again it scared the crap out of me I didn't run the tool post grinder for a while but I considered my self very lucky. Cliff



Cliff---If you read post #46 you will see that I said I was going to regrind the slot in jig #3 to 8 degrees instead of 15 degrees. I did, and that works much better, without such a deep heel on that last cut.---Brian


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## Tin Falcon

> brian, i read in the army machining manual on the net that a chipbreaker (groove after the cutting edge) avoids the rats nest... but have never seen a tool with a chipbreaker ground on...



Tom:
 I do not think I have ever seen a chip breaker ground on either. I have seen some pretty funky angles on hand ground tools these may have a bit of a chip breaking effect. 
I have seen chip breakers in indexable inserts. This makes sense because the carbide inserts are designed for max production. in the home sop you can always break the chip on roughing cuts by feeding by hand.
 If you want to grind a chip breaker the little dremel wheels would likely work well on HSS or a Harbor Freight diamond wheel for carbide. 

Tin


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## New_Guy

Tin Falcon  said:
			
		

> Tom:
> I do not think I have ever seen a chip breaker ground on either. I have seen some pretty funky angles on hand ground tools these may have a bit of a chip breaking effect.
> I have seen chip breakers in indexable inserts. This makes sense because the carbide inserts are designed for max production. in the home sop you can always break the chip on roughing cuts by feeding by hand.
> If you want to grind a chip breaker the little dremel wheels would likely work well on HSS or a Harbor Freight diamond wheel for carbide.
> 
> Tin



WHAT!! do none of you guys grind chip breakers into your tools? i havent seen any info on doing it on the net but its not hard i cant believe none of you guys do it

when i was still in school i did work experience in the machine shop of our rail way and i was asked about what tools we use on the lathe i said we used HSS and they a they were surprised we didn't used carbide, the next week the tool maker brought out a tool he ground after my last visit just to remember what it was like. ti was a big bit 14mm i believe with a chip breaker or curler we gave it a few goes on the Colchester and boy did it love it he then gave it to me and i still have it only been used a few times on the Hercus's at school

if anyone wants a pic i can upload one tomorrow its a nice tool and very easy to grind i think


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## Tin Falcon

NG I am not sure there is a real need for chip breakers in the home model shop at least most of the time. Most of our parts are small and of brass and aluminum. 
Now in a railroad shop taking a .375 roughing cut on a 3 o 4 foot long steel shaft. Yes you want a chip breaker. 
You will find that difference shops have different needs. 
Also I find a bit of disparity between text books and what is done in the "real world".
Se la Vi
Tin


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## kf2qd

When I grind a HSS tool I leave the top flat. (same with carbide, but I don't have much of that in my shop now...) Cutting steel, aluminum, brass, plastic. If you look at a lot of the chipbreakers on carbide inserts you will see that it is back from the edge as much as 1/32". There are times when a positive angle on the top might be beneficial, but I have seen some ridiculous positive rakes that only made the tool get hot and require sharpening more. And a lot of positive rake makes for a tool that is hard to keep on center after it has been sharpened. I did make a special tool with a lot of positive rake but it was only used on cutting some deep face grooves in UHMW plastic.

By only grinding on the edges, and not touching the top I come up with a tool that is easier to regrind and that holds up well. If you really need a positive rake on the tool why don't you modify your tool holder instead of grinding the top of the tool blank? 

I have done lots of cutting on everything from my 7x12 to a 24" production machine. Always ground the edges of the HSS blank and got any positive rake by adjusting the tool in the holder, rather than modifying the top of the blank.


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## doc1955

kf2qd  said:
			
		

> By only grinding on the edges, and not touching the top I come up with a tool that is easier to regrind and that holds up well. If you really need a positive rake on the tool why don't you modify your tool holder instead of grinding the top of the tool blank?
> 
> I have done lots of cutting on everything from my 7x12 to a 24" production machine. Always ground the edges of the HSS blank and got any positive rake by adjusting the tool in the holder, rather than modifying the top of the blank.



I agree same here I've been working in the shop for a long time and I've seen a lot of things done to tool bits and really if you keep the top flat or a slight and I mean slight angle like .5 degree plus on the face of the tool no more than 3 degrees I always used about 2 degrees you tool will hold up much better. Specially on carbide the keener edge you put on the thinner the cutting edge gets the hotter the edge will run. Because now the material isn't shearing away from the tool but up closer to your cutting edge. Not sure how to explane it very good without some pictures which I don't have.


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## New_Guy

Tin Falcon  said:
			
		

> NG I am not sure there is a real need for chip breakers in the home model shop at least most of the time. Most of our parts are small and of brass and aluminum.
> Now in a railroad shop taking a .375 roughing cut on a 3 o 4 foot long steel shaft. Yes you want a chip breaker.
> You will find that difference shops have different needs.
> Also I find a bit of disparity between text books and what is done in the "real world".
> Se la Vi
> Tin



yeah i know what you mean you guys with Tag and Sherline lathes wont see the need for it but its not hard to do and it would be a good experiment to give it a try i know ill be putting chip breakers on my tools but hey its a bigger lathe

i told a lie before i have seen one guy on the net who ground a chip breaker on a tool that was for a 7" mini lathe he liked it

"If you look at a lot of the chipbreakers on carbide inserts you will see that it is back from the edge as much as 1/32"."

if anyone can get a copy of a Seaco or other manufactures insert catalog/book then i would highly recommend it, its a big book with all there insert range and tables comparing everything about them and yeah they do have a flat on the cutting edge if you had the book it could tell you exactly how much and why.


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## ttrikalin

I'll grind a chipbreaker and we'll see how it goes.


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## New_Guy

ttrikalin  said:
			
		

> I'll grind a chipbreaker and we'll see how it goes.



dont forget to show the tool


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## ttrikalin

I'll show it in the BooBoo's and Blunders section -- 

 :big:


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## Brian Rupnow

I have an observation to make, based on my own experience. I have been grinding my own 3/8" HSS lathe bits the last 3 months with a 6" diameter grinder. This of course left a "hollow ground" effect on the top and both sides of the tool, which I would "stone" slightly on a flat stone after grinding.---Just the edges, not the depressed area in the center of the ground areas, which were left in their convave "hollow ground" state. These tools seemed to cut very well. I never had a problem with long stringy chips. I bought a 1" belt sander this week, and ground all the "hollow ground" areas perfectly flat.---Now I do get long stringy chips. It seems that the 'hollow ground" area on the top surface of the tool was actually acting as a chip breaker. Chips coming off the cutting edge followed the depression down into its center then up the other side, which caused the chips to curl and break. Now that the top surface is dead smooth, the chips don't curl and break---they just keep coming off in long strings which turn into big balls of swarf still attached to the piece being turned. I have to stop feeding the tool to "break" the chip.


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## Tin Falcon

interesting Brian I too use a 6: wheel for tool grinding . I have a belt sander but do not grind my bits on it (too far of a walk to the other part of the shop). I also have some HSS inserts that I use a lot that are dead flat on top can not say I have had a chip problem twith them either.
Tin


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## cfellows

As a related question, what are the considerations in using a smaller bit, like 1/4" sq as opposed to 3/8" or 1/2"? Smaller bits are cheaper and easier to grind. What practical reasons would dictate using a larger bit (other than tool height)?

Chuck


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## Tin Falcon

the larger bit bit will give greater stiffness and give a smoother cut also a bigger bit can take a deeper cut.
the bit should be sized more or less to the lathe and tool holder. I use 1/8 to 3/8 for my 7x 10 and 9" south bend.for general work I have used 1/2 for form tools where i need the extra width to make my part. 
A form tool in my case has the entire profile of the small part ground on it so I get a complex shape with a plunge cut. 
The bit size is dependent on preference as well need of the job. 

 you can make tool holders for small bits I have a couple of tool holders I use for 1/8 bits .It is just a couple of pieces of 3/8 mild steel that I cut a 1/8 wide by about 3/32 deep slot in them one is a Zero angle the other I positioned the piece at IIRC 10 degrees or so . One end being deeper than the other, this gives back rake.This system allows me to grind a 1/16 radius cutter without grinding a lot. I then put the bit and holder in the regular tool holder. 
I have a A2Z cnc qctp on the mini and an Aloris AXA on the SB 9.
Tin


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## Brian Rupnow

Interesting question, Chuck. The distance from my tool holder to the center of my lathe headstock is some Bastard size, more than 3/8" (I have to use a 1/32" shim) and less than 1/2". About the only reason for using 3/8" tooling other than that its the "closest" size to being correct, is that I can have more tool cantilevered out past the holder than I could with a 1/4" tool without being afraid of snapping the tool off. EDIT--It just occured to me after reading another post that perhaps my machine is sized for metric tooling---i.e. 10 mm


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## New_Guy

Brian Rupnow  said:
			
		

> I have an observation to make, based on my own experience. I have been grinding my own 3/8" HSS lathe bits the last 3 months with a 6" diameter grinder. This of course left a "hollow ground" effect on the top and both sides of the tool, which I would "stone" slightly on a flat stone after grinding.---Just the edges, not the depressed area in the center of the ground areas, which were left in their convave "hollow ground" state. These tools seemed to cut very well. I never had a problem with long stringy chips. I bought a 1" belt sander this week, and ground all the "hollow ground" areas perfectly flat.---Now I do get long stringy chips. It seems that the 'hollow ground" area on the top surface of the tool was actually acting as a chip breaker. Chips coming off the cutting edge followed the depression down into its center then up the other side, which caused the chips to curl and break. Now that the top surface is dead smooth, the chips don't curl and break---they just keep coming off in long strings which turn into big balls of swarf still attached to the piece being turned. I have to stop feeding the tool to "break" the chip.



wow thats very interesting, traditional Japanese chisels and knives have "hollow" grinds down there length the point of is that there is less material to take out while flattening the bottom of the chisel (not the cutting bevel) i notice it to when i hone my lathe chisels but i have a 8" grinder so its less of a hollow anyway thats sort of off topic 

have you tried experimenting with leaving the hollow grind on the top and flat sides?


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