Tool bits & quick change toolpost

[Marinesteam]

Hi all,

I have generally used brazed carbide toolbits or insert tooling in my lathe with good results. I am doing a lot of turning for my steam engine project with 1018 CRS and getting a fairly lousy finish. A machinist friend sharpened & honed a carbide bit to a razor edge with a tiny nose radius with good results but the edge didn't hold up well. He also mentioed that HSS may be a better choice. This leads to a few questions which I am too embarrassed to ask my machinist freind (an old workld tool & die guy).

I am purchasing a carbide grinder with better adjustable rests than my bench grinder (which is usually setup for buffing and I don't want to switch back and forth often anyway), so that I can sharpen my own toolbits. Also want to try fly cutting.

The questions are:

I have a 1/4 toolbit which I ground a LONG time ago in machine shop class but we were using lantern (rocker?) toolposts. I haven't used it with the Aloris toolpost 'cause it seems to small to fit into the Aloris holder. What is the proper way to hold a sqare stock toolbit in a Aloris type (BXA) toolpost? Do I need an adapter and a small piece of square stock or do I grind the cutting edge from a larger, longer piece of HSS stock (1/2"?). Does the geometry need to change? I seem to remember needing to angle the cutting bit upward in the rocker toolpost but won't be able to do this in an Aloris.

An additonal question....What's the best speed, feed & cutting geometry for 1018 CRS?


Thanks in advance

Ken

 

[Davyboy]

Hi Ken, good questions. Generally, 1018 does not give a really good finish with carbide tools. My sense is that HSS gives a better finish with light cuts and a little cutting oil. I sometimes rough with carbide and finish with HSS. Cutting speed-surface feet per minute- is much more critical with HSS. Too fast will ruin your edge quick!

hand grinding of lathe bits takes a LOT of practice. There are a ton of variables to consider. Many flame wars have been started over just this issue. GENERALLY, softer materials means sharper, more acute( more top rake) cutting edges; harder tougher materials means more blunt and less acute ( less top rake)cutting edges. Think about heat CONCENTRATION (on an acute edge), that will break down a HSS tool faster than anything. Also think about extremes- scalpels as compared to cold chisels, and their durability. Experience will help you to see what works better in certain situations. Pay attention to side and front clearance angles UNDER the cutting edge. Generally, 5-7 degrees is plenty. I've seen too many tools ground with no support underneath.
On Aloris tool holders, sometimes I use a (1/4 X 1/2) shim under a smaller tool bit, whatever it takes to get the job done safely is OK. Generally, length is more of an issue than size.
I'm sure others have more advice to offer. Good luck.

DB

 

[Maryak]

Ken,

My take on getting a good finish is that the cutting edge of the tool needs to be wider than the feed rate. When you think about it the feed is really a very fine thread, so your tool must remove the peaks of the cut. The easiest way is to angle a freshly sharpened HSS tool so that it begins to rub, slow speed for 1018, say 30-50fpm and no more than 0.005" depth of cut - 0.002" is better IMHO.

Hope this helps ??? ???

Best Regards
Bob

Edit - and plenty of suds

 

[rake60]

1018 steel is great to rough but not so great when it comes time
to finish. It is so soft that it wants to tear of smear rather than cut.
Slower speeds for heavier roughing cuts work well but
for me slow speeds and light cuts just don't work well for finishing.

These are my favorite finishing tools for 1018.

A brazed carbide tipped bit and a little sctochbrite.

I was actually just finishing up a roller blank made from 1018 and the camera
was close by so here's my finish cut.

[ame]http://www.youtube.com/watch?v=08qATRG-PNQ[/ame]
(Just noticed that I had reached in and grabbed that chuck before the motor
came to a complete stop. That was stupid!)

Spindle speed is 600RPM (160SFM), .012" depth of cut at .003" feed.
I think it turned out OK.

It is a 32RMS surface finish that could easily be polished to 16.

My standard notice:
I won't say it's the best or even the right way but it works
consistently for me.

Rick

 

[Tin Falcon]

Ken:
Some steels are hard to get a good finish. I recently made a bushing out of a piece of water pipe. I used my Warner Co tolls with HSS inserts. Then polished with 320 grit 3-M strip paper from a yard sail came out near polished finish and within a couple ten thousands in size.
I generally clamp tools right into the QC tool holders even with HSS, carbide is supposed to have Zero back rake.
Proper tool geometry is for the ideal situation for max performance on a given material . In the home shop close counts. Use a nose radius larger than the feed rate.
Hope this helps.
Tin

 

[David Morrow]

Choosing lathe cutting tools is part science, part art, part experience, and part black magic. I spent a huge amount of time reading forum archives from all over comparing and arguing the merits of HSS, Carbide, and Inserts. In the end, I found that the carbide and inserts are not really suited to my home machining and that HSS was the answer. I am learning to grind my own and hone them after the grinding process. I was extremely happy with my first one. Once you learn to grind your own, you don't need to worry about breaking your last cutter on Saturday night or not having quite the right shape for a particular cut. I do need to get proper grinding wheels - the right material and the right grits. I do have a felt wheel and honing compound already.

 

[Kermit]

1018 steel is great to rough but not so great when it comes time
to finish. It is so soft that it wants to tear of smear rather than cut.
Slower speeds for heavier roughing cuts work well but
for me slow speeds and light cuts just don't work well for finishing.

These are my favorite finishing tools for 1018.

A brazed carbide tipped bit and a little sctochbrite.

Spindle speed is 600RPM (160SFM), .012" depth of cut at .003" feed.
I think it turned out OK.
[IMG]
It is a 32RMS surface finish that could easily be polished to 16.

My standard notice:
I won't say it's the best or even the right way but it works
consistently for me.

Rick
[/quote]

I'll be using 1018 for my first project Rick. MOstly because that's 95% of what is available to me through work. A smart and small selection of the right bronze would be a good working compliment to it I'm thinking.
So ends the reading of the facts....now a question. ;)

Is your finishing speed faster then? Faster than the speeds you use to rough out the stock?

Edit: rereading it for the umpteenth time I think I'm the only one who didn't see that was what you were saying all along

 

[Loose nut]

Sometimes you just have to experiment.

I recently turned a piece of 3" pipe (3.5" OD) with carbide insert tooling and wasn't getting a really good finish, pipe isn't really any good for that, so I did a finish cut at 1300 RPM's but only 1 or 2 thou deep with a .004 feed rate. Yes the RPM'S where too fast but with the light cut it worked, a near mirror finish.

Other types of material like 4140, need heavier cuts to get a good finish or sometimes a fast light cut but you have to try different techniques to see what works. A light machine may also give you trouble, rigidity is a big plus in turning.

 

[rake60]

There is no perfect answer.

Every machine is different and the material varies.
Cold roll steel is usually formed from a large lump of stock that is
rolled to a nominal size in a continuous process then cut into 20 foot
lengths for ease of handling and shipping. If you happen to buy the the first
4" section of that bar and the last 4" section of that bar, it is all 1018.
Is it the same? Probably not. Will it cut the same? Positively not!

Cutting that changing material is where you become a machinist.
The books offer guidelines. The old buzzards who have been doing it
awhile can kick in their experiences. That is all good to take that in but when
it comes right down to cutting the metal it becomes personal.
In time the spark of a chip, the smell of the smoke and the sound of the
tool will tell you just what the material wants. I know how stupid that sounds
but you will find out it's true and you won't even know it happened.
It will become as automatic as pressing your right foot down to make the
car go faster. No black magic. It's just letting the metal tell you what it
will yield to.

Rick

 

[steamer]

Found this on the net...Check the attachment.


Dave



View attachment Toolbitsharping.pdf

 

[Marinesteam]

Thanks all for the information.

An extra shout out to Dave for the excellent chart, it's sure to go up on the wall along side the drill/fraction/decimal/speed&feed chart.

I've generally had pretty good luck with carbide (brazed and insert) tooling with 12L14 and tool steels but the 1018 has been a real bear to get a decent finish on. So down to the shop over the next few days to try out the ideas you all have given.

The purchase of a decent grinder, some HSS bits and your help will get me started "rolling my own".

P.S. I'm also trying out an insert that I got from work. It's an Iscar CCGT (CCMT) IC-20 grade which is a positive rake carbide insert that has been micro polished for an extremely sharp edge. It's meant for cutting aluminum but the first cuts on 1018 also seemed promising. The high polish on the insert should prevent the chips from welding too. Still need to work on the speed & feed and DOC needs to be kept down but looks promising. I'll keep everyone posted.

Ken