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Westline
03-05-2011, 05:28 AM
I just finished grinding my first HSS lathe bit and wow can't believe I spend almost 3 years using carbide on my home lathe.
I was always a bit unsure about the angles and decided to stick to carbide inserts where I know the angles are right.
Got 2 1/2 x 4 blanks from a local supplier just HSS no cobalt just incase I mess it up.
The are Kennedy blanks made in England and it turned out pretty well.
http://i1094.photobucket.com/albums/i460/KobusWestline/64aa27bc.jpg
I just thumb sucked the angles and bounced it between my 2 grinding wheels depending on how I had to hold it ( one is green silica and the other white I assume Alu oxide)
It cuts Alu like butter and even suprised me on hardened 4140.
Now I just need to firgure out how to put a ring on square shank and I can marry it. :D (I know I have a problem)
What type of wheel should I have used for sharpest edge and/or rapid removal?
If somebody sees something wrong with the tip please give me a headsup I still need to do the other one just want to wait for the judges verdict.

camdigger
03-05-2011, 06:10 AM
A job well done, especially for a first attempt.

There are a number of nuances for different materials wrt to clearance angles and rakes. Generally, the harder the material, the lower the angle, and vice versa.

For roughing, not everyone bothers with the radius on the tip. the tip radius varies depnding on finish and feed per rev from sharp to +/- 1/32" radius or larger for finishing.

As far as which wheel, the green one for carbide and the white one for HSS. Wheel wear, within reason, is the means by which the wheel sharpens itself - by exposing fresh aggregate.

form_change
03-05-2011, 06:41 AM
Carbide is certainly over rated for home use, as a lot of the machines used for HSMers are not rigid enough, or have the revs. I have a carbide parting blade that I keep meaning to use but so far I met anything that HSS could not manage...

I'd suggest getting a diamond hone so that once you are finished grinding you can put a final finish on your tool. Hand grinding of tools can (inadvertently) round the edges a little.

Michael

Black_Moons
03-05-2011, 06:52 AM
Get the angles right? you can't really get the angles wrong!

Just have some clearance and it will work. Rake is a trade off beween tip strength, free cutting and finish (sometimes). Some materials like copper/brass iirc don't like any rake. Some plastics don't like excessive rake either. Some plastics/woods/aluminum love lots of rake.

hornluv
03-05-2011, 09:22 AM
Get the angles right? you can't really get the angles wrong!

That's pretty true. Any tool will cut any material for the most part and there's a wide range of angles that will work, so there really isn't any need to fret about getting the angle "correct". If you're going to be cutting lots of brass or aluminum, you might want to grind up some bits for each one (no rake and lots of rake respectively), but otherwise a nice, middle-of-the-road tool with 5-10 degrees on each angle will do most everything.

Shape is much more important to me. Is the tool going to fit where I need it to fit? The end relief has to be able to clear the live center if I need to machine close to it. If that's not a concern, I just do the same 5-10 degrees there too. You also want to make sure that each face is one smooth grind. Lots of facets on the face make it harder to hone. Use the tool rest and that shouldn't be an issue. Lastly, hone the edges with a sharpening stone, just to smooth out the rather jagged edge left by the grinding wheel. I also put the radius on the tip with the sharpening stone rather than the grinding wheel because it is very easy to get too big a radius with the grinder. You only really need a little radius (1/32" or so at the most) to get a good finish.

Carld
03-05-2011, 09:35 AM
The only angles that are important are the relief angles on the leading cutting edge and the front clearance angle.

The front clearance angle can be 0 but is best at about 5 deg. The reason it can be 0 is the work is round and the top of the cutter is at the center line so the front of the cutter should never rub the work.

The side of the cutter that is doing the work has to have an angle that gives clearance in relation to the feed that is being used. A fine feed can use a 2 to 4 deg relief but a heavy feed may need 10 deg relief or more.

The angles you grind on the cutter are dependant on the feed, DOC and material your cutting. There is no exact angle to grind to and experimentation is the best way to learn. Look at the sides and top of the cutter after one pass. Does it look like the cutter is rubbing? Did the chips come off nice or did it seem like the tool was working to hard. Try more relief on the sides and maybe some back rake.

Experiment to learn.

mygrizzly1022
03-05-2011, 09:39 AM
Hi

Tool bit grinding 101

http://www.youtube.com/watch?v=hrDr4rYLiAk

This guy is worth subcribing to. He has posted 100+ videos
A dedecated teacher who just can't quit.

Jaakko Fagerlund
03-05-2011, 11:26 AM
Very nice firs one, congrats :) Usually when i grind HSS bit I grind a small "channel" just behind the cutting edge on the top of the HSS bit instead of giving it a rake angle. This acts as a chip breaker and in most cases prevents the tool from forming long stringy chips as the chip is forced to curl and this usually breaks it in tiny pieces.

There is a place for HSS and for me it is shapes that I haven't ground a carbide bit yet or when working with brass/plastic due to not having carbide bits intended for brass or plastic. Quite often I can't use HSS because of machining something hardened (48-58 HRC).

Elninio
03-05-2011, 11:43 AM
how does it compare to india/taiwan HSS?

vpt
03-05-2011, 11:53 AM
I bought 5 pounds of hss off ebay when I got my lathe. I have enough hss for a lifetime! It is also nice because there is a wide variety of different types of hss in the bunch to play around with. And it was around $20 for the whole deal shipped.

Boucher
03-05-2011, 12:36 PM
how does it compare to india/taiwan HSS?
I don't know about the HSS mentioned but. Most of the new stuff is not as good as the older materials like Rex 95. I have some material from India that is good but others have similar that is pretty poor. I have some of the bits from China in both 5% and 10% Cobalt that are ok. There are still batches of the good stuff around that come avaliable ocassionally. It is worth keeping an eye out for these.

Elninio
03-06-2011, 05:22 PM
I bought 5 pounds of hss off ebay when I got my lathe. I have enough hss for a lifetime! It is also nice because there is a wide variety of different types of hss in the bunch to play around with. And it was around $20 for the whole deal shipped.
how do you find such auctions?

Alistair Hosie
03-06-2011, 05:53 PM
I don't know about not being able to get the angles wrong ! There is a certain geometry to them.I remember the first time I used up the sharpeness/blunted the tool in my flycutter I just couldn't get it resharpened despite being told it was an upside down lathe tool cutter.I just couldn't visualize it despite twisting my neck half off :D
lathe tools are much easier in my opinion .see tubal cains video on youtube where he uses a wooden model a great idea I would advise all to watch it who have a problem with sharpening these tools.Alistair

wooleybooger
03-07-2011, 01:20 AM
i ve got about 60 HSS bits i bought off E-Bay. mostly 1/2" but some 3/8" roughed in but not finish ground. best deal ive found in a while. it only takes a minute or two to finish grind one to a usable tool.one thing explained to me by an old-timer was to imagine your eye as the workpiece and the tool coming toward your eye. much easier visualize looking from that perspective.

Willy
03-07-2011, 08:09 AM
Good job on the HSS bit! You are going to be hooked now.

The thing I like about HSS bits is their versatility.
Need a certain size threading tool, grind one. Need a tool to make a groove for an o-ring or snap ring, grind one. Need a form tool, grind one.
I like to use them for internal threading and boring jobs too, I have a pretty fair collection of boring bars that take HSS bits ranging in size from 1/8" to 3/8", very versatile and economical way to tool up.

Another point I would like to mention is bit size.
While everyone's needs are going to be different, even from day to day, I find that for the most part, the bulk of my work is done either with 1/4" or 5/16" bits.
Not only are they faster and easier to grind, but they are also cheaper to purchase and they don't get in the way as much on smaller jobs.

Ed P
03-07-2011, 08:51 AM
I have a couple of comments about your tool sharpening. First you did a very neat job of it. If you did that entirely by hand on a bench grinder then you did a much neater job than I can. Second I notice that you ground quite a bit from the top of the tool to form the side rake so that the cutting edge is well below the top. As you have found, HSS takes very long to grind so don't grind any more than necessary. When grinding the top, grind until the side rake goes from back to front and then stop. Grinding more will not make it cut any better and just takes more time.
Third, and this is hard for me to tell from your photo, but it looks like your tool has a nose radius, side rake and no back rake. If so, then it has an effective negative back rake and that is generally not recommended for HSS.
Last, your tool looks like it has no side cutting edge angle so it would be good for turning up to a shoulder. For general turning you will want to grind up a tool with a generous side cutting edge angle, this will offer increased tool life, use of increased feed rate and reduced possibility of chatter.

SGW
03-07-2011, 09:49 AM
If you can find a copy of "The Design and use of Cutting Tools" by Leo J. StClair, it will tell you everything you ever wanted to know about lathe toolbits and probably a lot you never imagined. It's 350+ pages on nothing but single-point toolbits.

He makes a couple of points: 1) While it is certainly possible to grind a toolbit by eye that cuts well, you'll get the best balance of cutting efficiency and toolbit life if the angles are correct. 2) Individuals are notoriously bad at judging angles by eye. If you want to get the correct angles, you will have to measure them.

Personally, I don't worry too much about it, although I do have my grinder set up to grind a 7 degree and a 14 degree angle, which gives me a good average starting point that I can adapt.

J. Randall
03-08-2011, 01:18 AM
Ed P, I think the photo is deceiving, and your post is kind of confusing to me. If he had just put side rake on and no back rake(which I think it has) it would have neutral rake in the forward and backward direction, and I think it would have cut pretty well providing the clearance angles are good. Hard to tell from the picture for sure.
James

mf205i
03-08-2011, 05:12 AM
Get a 46 I pink wheel for hand held roughing. If you fixture grind and you don’t mind dressing a lot you could use the softer H wheels. I use the 7 x 1/2 inch wheels on a 6-inch grinder. These are 1 bore wheels so you will need to make a spacer and you could have some guard issues but I assure you that it is worth the effort. Be prepared to be amazed as to what a proper wheel will do.
http://www.use-enco.com/CGI/INPDFF?PMKANO=247&PMPAGE=66&PARTPG=INLMPI&PMITEM=317-1113&PMCTLG=01
Mike

Westline
03-08-2011, 05:20 AM
Thanks
I'll give it a shot.
I don't like using by normal bench grinder to shapen lathe bit but I have nice motor that will soon me recuited as a dedicated lathe bit grinder.
The size is no problem if it does not fit heck I'll make it fit.;)
Thanks for the post.

Ed P
03-08-2011, 10:19 AM
Ed P, I think the photo is deceiving, and your post is kind of confusing to me. If he had just put side rake on and no back rake(which I think it has) it would have neutral rake in the forward and backward direction, and I think it would have cut pretty well... James

James, I NEVER said that it would not cut pretty well, only that negative back rake is not recommended for HSS. That means that there are better ways of doing it. If you look at the sketch below it is a plan view of the tool (nose radius has been exaggerated for clarity). Arrow shows direction of tool travel, therefore "A" is the front, "C" the rear and "B" the finishing point of the tool, i.e. the point on the tool that is last to contact the workpiece. Since the tool has side rake, point "C" MUST be below "A", and since point "B" is between "A" and "C" it must be below "A" too, which means negative effective back rake. That's assuming there was no back rake originally ground in to the tool and in my original post I said that it was hard for me to tell if there was based on that photo. So to repeat, a tool with nose radius, side rake and no back rake will have a negative "effective" back rake.
http://i945.photobucket.com/albums/ad296/Dirigo28/tool.jpg

Ed P
03-08-2011, 11:48 AM
Post deleted.

Ed P

J. Randall
03-09-2011, 12:21 AM
Ed P, Thanks for trying to explain, no matter how many times I look and reread, I just can't see how negative rake is going to be involved. In my mind when you get to that point on the radius, the front relief(not the leading edge)and the side rake are taking that part of the tool out of contact with the work, assuming that the tool is properly set to center height. I always visualize rake from the cutting part of the tool, be it side,back, negative or neutral.The only way I can see negative rake being involved on a HSS tool blank is to grind it in, and I agree negative rake is not productive on HSS tooling. We may just have to agree to disagree.
James