Grinding lathe bits

[gitmkr]

Hello everyone. Ive been on the sidelines for a while and have really enjoyed and learned a good deal from everyone, so thanks for that, I have a problem trying to "break" the cutting edge of my hss lathe bits. I can sharpen them to a point and get good cutting results but the resulting finish is not as good as i would like, it leaves a "phonograph groove type of end result. When I try to slightly round the end of the tooling all I get is chatter and a very rough finish. Ive tried to read everything I can find and I think I am following the methods laid out but to no avail. I wonder if my lathe is to light to sustain the seeming heavier cut ( although I can take a .050 cut with a sharp pointed tool fairly easily).
The lathe I have is an Atlas 6" with the timken bearings and has had very little use. Any help would be welcome.
Thanks,
Rick

 

[pjf134]

Try taking lighter cuts and make sure your tool is on center and radius your tool with a stone to get a better radius. 0.050 seems a bit much for a 6" atlas for steel, but might be ok for softer metals. The atlas was not made for heavy cuts I think, but someone else who has used one or has one might chime in on this, since I never used one like yours. Try taking it slow while you cut into the metal might help too, since I do not know which metal you are cutting I am just guessing and just pointing out some things to try. I hope this helps.
Paul :headscratch:

 

[havnfun]

I was having trouble getting a smooth finish when I first got my lathe. Reground countless HSS bits and even tied a carbide insert tool. No improvement. I was using a rocker style toolpost. I was advised to try a quick change tool post and the finish results were amazing. Using the same bits that I was using in the rocker style, the finish improved dramatically.

 

[george wilson]

That is a VERY,VERY light lathe,indeed. If you can,get a heavier machine. Even the 12" Atlas (which was my first lathe) is none too heavy.

 

[ScrapMetal]

Welcome Rick,

I have a similar thread going over on the Lathe section where you might get something useful: http://www.hobby-machinist.com/showthread.php?3842-Tool-bit-grinding-some-thoughts-and-questions I'll be watching this one as well to see what the guys come up with for you. To add a bit to the questions for you, what kind of grinding wheel are you using, composition, etc?

-Ron

 

[gitmkr]

I am cutting mostly"mystery metal",cold rolled some hot rolled? I look in machinery handbook and slowed the carridge speed and that help some using a non rounded tool. I don't know how well this pic will show up.
1/2" diameter workpiece
900 rpm spindle speed
.023 per rev spindle speed ?
I do have that goofy lantern toolpost and am working on making a QCTP, sounds like that will work better.
Is there a sequence to cutting the different angles? Should I cut the back rake last ?
I'm using a generic grinding wheel from Menards or Home depot.
Sorry if these are questions I could find in some basic texts or posts, I am new to this and I love it !
Thanks for everything,
Rick

 

[ScrapMetal]

The first thing that strikes me as being a problem with grinding bits is the wheel you are using. The wheels that come standard on most grinders are generally too hard to do a good job on HSS. The "grain" of the wheel will clog up and instead of cutting the metal will cause it to heat up and thus ruin the hardening of your tip. (Poorly phrased but I hope it makes some sense. Past my bed time. )

Also, here's some reading from Sherline's site that you might find useful: http://www.sherline.com/grinding.htm

-Ron

 

[GK1918]

Ill have a senior moment here, using a lantern tool post there are two kinds of holders, one with a (about) 16* which
you do not have to grind a back rake and a holder that is flat which a back rake may be ground. I recently bought
a axa qchange from Wholesale tools for $155, for my SB 9A. Ill tell ya what a difference even though an import I
love it comes with knurler boring head and two extras. I can not go .050, more like .010 and I turn up spindle speed
with a kind of slow feed. I round of my bits (round nose) and have no phonograft grooves. I may be breaking rules
but I turn & face with it. And as far as threading the quick change made me a believer. Suppose I grew into an old
timer that refuses change, I now think of how I did things with that Lantern tool post? I may be a little radical
like, for internal treading I have even ground a 60* allen wrench for a bit, works for me. All I say is you will not believe
what your machine can do. Keep this in mind, my mentor was an old timer, at this time was to make the thing start
up and figure whats what. I turned a lot of nice stock into junk. He gave me a 3" alum round stock, and told me
to make a square block out of it? I figured that one out myself, then he said make it round again, figured that out.
He then said "I give you a machinist license" Those days I couldnt read a yardstick never mind a mic. Much reading
librarys, no computors back then I got self taught. Just keep with it > lately I am sucsseful making craftman mower
spindals which are junk out of the box. Mine have grease fittings and heavy bearings. I know Ive gone off subject a
little, but my grinding of bits came from grinding soft keystock-then experimenting on PVC. finding what works and
what does not. As of now If I were to go to some night school machining I would get raised eyebrows or get
thrown out. This little story is for encouragement dont be afraid of going a little on the dark side, just dont crash it.
Sam

 

[jgedde]

Hello everyone. Ive been on the sidelines for a while and have really enjoyed and learned a good deal from everyone, so thanks for that, I have a problem trying to "break" the cutting edge of my hss lathe bits. I can sharpen them to a point and get good cutting results but the resulting finish is not as good as i would like, it leaves a "phonograph groove type of end result. When I try to slightly round the end of the tooling all I get is chatter and a very rough finish. Ive tried to read everything I can find and I think I am following the methods laid out but to no avail. I wonder if my lathe is to light to sustain the seeming heavier cut ( although I can take a .050 cut with a sharp pointed tool fairly easily).
The lathe I have is an Atlas 6" with the timken bearings and has had very little use. Any help would be welcome.
Thanks,
Rick

Your radius is one of the following:

1) Too big. 1/64" or so.
2) Affecting the relief angle.

Or, you have too much overhang in the cutter or workpiece...

Or, your gibs need tightening (the Atlas needs 'em fairly tight to work well).

Or, you are running the lathe too fast.

The Atlas lathe is nowhere near rigid enough to take a heavy cut and get a good finish using a radius tool. That was one of the many reasons I got rid of mine. It's a good machine within its limits though.

In any case, try this: Grind the bit to a point like you've been doing, then create a facet on the point about 1/64" wide with a stone whilst maintaining the relief angle. Stop there and make a cut.

BTW, Don't use the stone on the back rake of the cutter or you'll likely round the edge and it'll chatter like mad.

Let us know how you make out. Good luck.

John

 

[george wilson]

Now that I can see a picture: That looks like hot rolled steel. It doesn't cut as smooth as cold rolled,but it doesn't warp from being machined like cold rolled,either,so is preferred for making angle plates and things where you want to keep warping to a minimum.

Next,you never know the composition of "mystery metal". That in itself can cause problems.

Your bit seems to be hardly radiused at all. That can cause grooves,BUT,on a light lathe,the lathe cannot stand much radius at all. You are sort of stuck with that.

The lantern type tool post is not very rigid. Having a Q.C. post will help a lot,as will tightening up the gibs. I made a simple tool holder block of steel for my first lathe,a 12" Atlas,and it helped a good deal. But,even a 12" Atlas is not very rigid.