How Do I Machine Hardened Steel on the Lathe?

[snub]

I'm working on a Chevrolet engine and my timing chain gears are not aligning. I need to remove .025" from the backside of the crankshaft gear. I have an old gear to practice on before I attempt to destroy the new one. It is hardened steel and I'm not having any luck. I'm using a carbide bit (well they claim it is carbide). All I got was sparks and smoke so I went and bought a new insert. Still no luck. My digital read out said I took off .010" but I actually only took off .005". I believe I took .005" off the bit itself by eyeballing it. Another problem is those darn keyways. You can hear it hitting each one and my new gear has 7.  I'm also wondering if I have the correct angle for the bit. Anyone have a pic of the correct angle when facing with one of these? Here are the bits I am using:





And here is what the gear is looking like. Not very good at all:






So I'm wondering if there is something better than Carbide or is it just that these bits are crap. They are about $10.00 each so maybe I'm expecting too much from them.

[patuca]

Hi snub:

Pretty hard stuff to cut.
If it was me, I'd say it's a job for a tool-post grinder....   I've seen die-grinders in homemade toolpost mounts that would work.

patuca

[markball2]

Hardened steel needs a grinder to remove the material.  Even carbide tools won't cut it without annealing the gear.  That would allow the removal of the material, then the requisite hardening of the gear.

Might be less troublesome to purchase a new gear of the correct thickness.

[Arbalist]

Hi snub:

Pretty hard stuff to cut.
If it was me, I'd say it's a job for a tool-post grinder....   I've seen die-grinders in homemade toolpost mounts that would work.

patuca

Yes, grinding is the way to go I reckon as well.

[chipenter]

How about an oil stone set the tool post square and gently push , with some wood or ply as soffener between the post and the cross slide , as with grinding cover the ways and clean up as soon as its finished .

[DavidA]

Are you sure that the gear is through hardened and not just case hardened ?

If it is case hardened (and you succeeded in removing the case) then you would really have to re-harden it.

Either way, as mentioned above,  it's a grinding job.

Best get a new one.

Dave.

[Lew_Merrick_PE]

1) Materials that will cut fully hardened steel tend to be quite brittle, so cutting across you keyways is very likely to shatter a cutter that would otherwise cut such hard steel.  (You can take a file to the face of the part and, if it slides across without cutting, this is the position you find yourself in.)

2) Roller chain sprockets are more commonly case hardened to reduce wear than full hardened.  Thus, if you manage to cut away the "case," you are likely to be entering yet another world of hurt.

3) The real question is, What changed in the overall engine assembly that moved the sprocket .025 out of alignment?  Is there space to have a (hard-drawn stainless steel) shim made to offset the sprocket on the other end of the assembly?  Many of the "higher end" mechanics will have a punch set specifically for making such shims.  A roll of such shim stock is quite pricey, but somebody who has such material on hand will (usually) let you have it on a "per square inch" basis that makes it a lot less unreasonable.

[Manxmodder]

Cubic boron nitride tipped inserts are the way to go if you want to turn the excess material off.

They are available in 2 different grades suitable for interrupted cutting and uninterrupted cutting.

I use these fairly frequently to turn through hardened and case hardened steel components,here is a link to the supplier I purchase mine from: http://www.shop-apt.co.uk/cbn-turning-inserts.html

I usually use the  DCMW 11T308 CBN300 CBN type for interrupted cutting as this tip will also perform well on component areas of continuous cutting.(Link to this type of tip here below)
 http://www.shop-apt.co.uk/cbn-turning-inserts/dcmw-11t308-cbn300-cbn-turning-insert-for-hardened-steel-45-65-hrc-interrupted-cutting.html

When using these tips the swarf comes off as a bright yellow hot ribbon or yellow hot chips on interrupted areas.

Also when using these tips take care not to bump the tip into anything stationary on the lathe like the chuck as cubic boron nitride is very brittle .

Hope this helps.....OZ.

[snub]

Thanks for your replies.

According to the manufacturer the gear is " induction heat treated billet steel".
The gears only come with one backspacing dimension so getting a new one won't help.
The thrust surface on the face of the block has not been altered, so I believe the cause of this problem is the crankshaft. I tried 3 different timing chain sets and the results were all the same. The crank gear is ahead of the cam gear.

I thought about shimming out the camshaft gear but I believe ( correct me if I'm wrong) that this would move the camshaft ahead by .025" which would put the camshaft lobes out of alignment with the lifter bores.

Apparently the misalignment of the gears is a fairly common problem due to manufacturing tolerances so I would have to believe there is a way to cut this gear. After countless hours on the interweb I found little actual data, just lots of speculation.

[snub]

They are available in 2 different grades suitable for interrupted cutting and uninterrupted cutting.

I'm not familiar with those cutting terms. Could you enlighten me?

[Manxmodder]

Snub, interrupted cut is the terminology used when the tip of the turning tool is not cutting in contact with a full 360 degree component face due to cut outs or splines or keyways as in your earlier photo.

By contrast a continuous cut is when you are cutting a component without any keyways,cutouts or holes on the face being machined hence a continuous contact between tip and component.

For your application I would select a tip designed for interrupted cutting.....OZ.

.....OZ.

[Manxmodder]

Snub, here is a link to a short youtube video showing hardened steel being cut with a ceramic tipped insert.

The effect with a cubic boron nitride insert is very much the same as seen in this video.

Link:
     

.....OZ.

[snub]

Thanks for the video. I actually have already seen that one in my quest for knowledge.

Judging by some of the posts it almost sounds like I would have to re-harden the gear after cutting it. I don't think that's an option.

I thought the process for machining was as follows:

Machine the soft steal, then harden it, then use a grinder to bring it back to the proper dimensions that changed when hardening it.  Seems to me that if I could get someone to grind off the .025", that I would be good to go. I could be wrong.

patuca mentioned a tool post grinder, but I don't know much about the. Please enlighten me!

[75Plus]

The reason the sprocket is hardened is to prevent premature tooth wear. The area that you are working in really does not need to be hard. It is hardened along with the teeth in the hardening process. Once you get the thickness where you need it you should be good to go. Sprockets routinely have only the teeth flame hardened so the hub will still be soft enough to bore and broach the keyways.

Joe

[vtsteam]

75Plus has the key to it, and you may find that using a makeshift toolpost grinder like this:

http://madmodder.net/index.php/topic,9890

mght get you through the skin to soft metal. Generally a toolpost grinder isn't a handheld grinder -- but a precision purpose built tool that attaches to the toolpost -- however John's version is really cool and seems to work for some purposes -- maybe yours...

(btw not all the photos in that thread are loading tonight -- seems to be a Flickr problem -- try it again later if the text doesn't refer to something you can see in the thread.)

[patuca]

Hi snub:

I've seen temporary TP grinders made from small motors belt driving a ball-bearing shaft, dremel tools  (small but if you've got lots of time it will work), laminate cutters and small routers.

Basically any high-speed motor shaft you can clamp to the toolpost at center-hieght that has a collet or chuck to fit a small grinding wheel.  Even if presented at an angle to the gear face it would make a flat recess allowing it to "spark out" with some finish passes and be truly flat.

I've even seen someone use an angle-grinder free-hand on a lathe to  shorten a hardened flange.  Here's a webpage with that trick about 1/2 way down "Grinding on a Lathe"....  not exactly a safe thing to do, but  you could easily rig up a clamp.

http://www.submarineboat.com/lathe.htm


good luck,

patuca

[RotarySMP]

I had that same Made in india set of TCMT carbide tools. The inserts were crap. I replaced them with Sandvik TCT's bought for about $1/insert from ebay, and they work much better.

What you haven't said is what sort of lathe you have available. It makes a huge differnece whether you are trying to cut hard steel with a Hardinge/Monarch/Weiler/DSG etc or with a 7x chinese mini lathe.

When I only had the 7x lathe, I could only use TCMT 1102 (.2mm nose radius) without chatter. With the Boley 4L I now have I can run the TCMT 1108 (and probably even blunter) without chatter.

[Jonny]

The crank gear is ahead of the cam gear.

I would look at the cause first.
Genuine parts? or do you mean timing if so looks to me its 22 teeth with 3 off 120 degree fittings, one should line up and will be marked.
Is this the GM made engine either ZE22SE with balance shaft or 2.4 used in the Cobalt and others globally, there is help available.

[tekfab]

It's not that difficult, i purchased some ceramic inserts of eBay, made a holder for them and machined a Wolhaupter boring head from Int40 to MT4 on my lathe. The information is available on the net and I think you'll find it easier than you might think.

[Mark Rand]

The inserts you've got are suitable for continuous cutting in annealed steel or non-ferrous alloys (very positive leading edge and little distance from the edge to the chipbreaker. Have a look at mcmaster.com or mscjlindustrial.com for inserts in the same size that are more suited for the job.

You don't have a lot of metal to remove, but it still needs a robust insert.

[awemawson]

Mark,


Good to see you here ! Welcome aboard 

[hanermo]

You have the wrong type of insert.
The insert is poor.

A CCMT insert will turn hardened steel on little lathes, effortlessly.
I have turned much harder materials, like ballscrews, with no problems.
Interrupted cuts are no problem.

You should be cutting about 0.1 to 0.07 mm per pass, when using a light lathe and positive-edge hardened steel on interrupted cuts.
Once the skin is off, it goes easier.

[snub]

A CCMT insert will turn hardened steel on little lathes, effortlessly.

So I did some research and found that the CCMT insert is "rhombic" shaped instead of a triangle like I am using. Rhombic is almost square but  more like diamond shaped. I'm wondering why this would be more effective as you are cutting with the tip of the insert, not the side. I am strictly a self taught amateur machinist so I am always looking to improve my knowledge base and I welcome all comments and advise. As I mentioned before, there is a very good chance I don't have the insert at the proper angle to the workpiece. 99% of my work is with aluminum, which is a lot more forgiving if you don't have it right.

[Doc]

I have cut tool steel up to 62Rc but only with a micro 100 carbide tool and no cuts under .02 with a good steady feed can't remember the sf or feed I know it is a pretty heavy feed otherwise tool will not last. The micro 100 carbide is some pretty good stuff.

[snub]

We may have to move this post the "Oooops" section. I got some new inserts from KBC and built a mandrel to hold the gear. I made a washer with a chamfer on the backside so the cutting tool wouldn't be hitting the keyways. Tried again with the new insert but still cutting bad.  Then it suddenly dawned on me. I was cutting from the center to the edge away from me and should have had the lathe running in reverse! What a moron I am. Anyways, once I got it running in the right direction I had no trouble at all cutting the gear.

Here is a picture taken after the cutting. Can't really see the joint between the washer and the gear. There was no chatter at all.





And here is the mandrel I built to hold the gear.