Calling All Machinists - Axles Keep Breaking In Lathe

[1reason]

Ok, so I'm a brand new never before worked with lathes or mills before. I know enough that the term is called turning, but not much else.

I did manage to change out the stock three-jaw chuck in my new Harbor Freight 7x12 lathe to a four-jaw chuck so I could lower my run out (ok, I guess I know that term also, thank you Youtube).

I bought an ER20 Collet chuck, again to improve accuracy (picture below is a screen print from a video of me changing out the three jaw for the four jaw), and each time I try to make a notch in a nail, it breaks at the point the nail enters the collet.

It was obvious the run out increased with the nails, which weren't very straight relatively speaking, but what I don't understand, is I have used rotory tools to sand and notch the wheels, but when I try to get the tolerances"really tight", the nails keep breaking.

With my last builds and before I had a lathe, I took axles and wheels to a friend's shop where he lathed the wheels, but also ran into trouble with the nails breaking, and since I was in a rush and he didn't want to "learn how to work with Pinewood Derby", we didn't experiment very much.

Things I think may cause the problem:

I have tried to make the tool level, and I think it's close, but I wonder if it's too high or low

The collet is too tight around the nail, creating some type of pressure point that is more likely to "snap"

I have to get the nail more straight (it was pretty straight, but not as straight as the chuck

I should use a different tool to try to work the nail (open to suggestions either way on what tool to use)

 

[bracketracer]

Disclaimer: I am not a trained machinist

I think what you're seeing there is "work hardening" and why you're seeing it is because you have some deflection in the nail. The nail bends away from the cutter, and because the nail is spinning, it keeps bending away until it breaks off at the collet. Could be because you are presenting the tool too high or too low or if the tool is being forced into the work too hard or the tool is dull. One easy method to check your tool height if you haven't seen it before:

Could also be that you have the nail sticking too far out of the collet?

 

[1reason]

Disclaimer: I am not a trained machinist

I think what you're seeing there is "work hardening" and why you're seeing it is because you have some deflection in the nail. The nail bends away from the cutter, and because the nail is spinning, it keeps bending away until it breaks off at the collet. Could be because you are presenting the tool too high or too low or if the tool is being forced into the work too hard or the tool is dull. One easy method to check your tool height if you haven't seen it before:

Could also be that you have the nail sticking too far out of the collet?

You hit the nail on the head (cheesy pun, I know). Thanks so very much, I appreciate it. The instructional video was exactly what I needed.

I also moved the nail head in as far as I could, and haven't broken a nail since.

Now.....I have a new issue. I'm able to make a speed grove, but I have a lot of metal "scrapings" that are caught on the sides of the nail at the points the tool stopped cutting. I'm not sure if that's normal, and I just need to sand it down (guessing not), or if that means I need a different tool, different speed, different operator (hopefully not that as my only other choice is my six year old).....

I'll take some pictures of my setup as it is now and post

Thanks

 

[BulldogRacing]

You should have very clean cuts with the correct shaped tool.

 

[5KidsRacing]

Sounds like a dull tool... sharpen it.

 

[GravityX]

Throw out the tool bits when cutting a speed groove, just kidding. Actually, I use a Dremel, with a grinding stone, set up in a tool holder to create any cuts/grooves needed in the axle. It's much easier and I don't have to worry too much about being exact center on my tool height. Both items are spinning and I can control the cross feed easily.

 

[1reason]

You should have very clean cuts with the correct shaped tool.

That's what I thought, but didn't know. Any idea how fast I should spin at? I've kept the speed maybe too low as I baby-step into this.

From Grizzly:

The picture is the rod I use to check run out.

 

[BulldogRacing]

I like to have the work piece closer to the collet because the further away you are the less rigid your set up will be. You need rigidity when turning and if you don't you'll have a mess. To put a grove in the axles you need a machine that has very little run out, and every thing you are adding to your late, the 3 jaw, the collet adapter, the collet it's self is adding runout. So I believe you can do it but you'll notice the grove in the axle will not be the same depth all the way around. Most axles you purchase from venders are made on swiss machines that cost a lot more then my house. I tried to zoom in on the pic of your tool and I cant see the profile because of the background. Sorry bud.

 

[GravityX]

The 4 jaw chuck you are using, is it self-centering or independent jaw? There is a way that you could adapt a collet chuck directly to the headstock spindle, then you would only have to deal with headstock bearing runout and not that of the 4 jaw chuck and ER20 collet chuck setup. Here is a picture of what I'm referring to:

 

[1reason]

The 4 jaw chuck you are using, is it self-centering or independent jaw? There is a way that you could adapt a collet chuck directly to the headstock spindle, then you would only have to deal with headstock bearing runout and not that of the 4 jaw chuck and ER20 collet chuck setup. Here is a picture of what I'm referring to:

Thanks and I think that's a great idea. I did look into it, but went with the four jaw chuck because I figured I needed a four jaw anyway for the tires and my costs have ***cough cough*** reached a point that I'm glad my wife isn't looking at the credit card bill if you know what I mean.

My four jaw is independent and I'm learning the "joy" of centering.

If I could have a do-over, I think if I could buy a collet chuck like you're suggesting that was big enough to do wheels and nails (is a ER32 big enough?) I probably would be better off. But the upside is my son is learning right along with me, and that wouldn't happen if I had the "perfect setup", so there is a silver lining.

I could be wrong, but I was thinking maybe the four jaw could off-set the run out on the bearings??

For those wondering, yes I totally agree I could buy the wheels and axles for much less than buying a lathe and tooling, but then my son wouldn't learn all this stuff and I think that's the real value to him in pinewood. That said, I have bought many products from John including his DVD and highly recommend his products.

 

[1reason]

Here's a better picture of what we're doing.

For a "real" nail, we would have it much closer to the collet.

I'm not sure (looking for feedback) if it's a good idea or a bad one, but I found if I push a nail into the collet first, and then tighten down hard, it makes the nail straighter. At least better, but not perfect.

Can these carbide tips be sharpened, and if so, can I use a normal metal file on it?

Lastly, what speed should I turn at? I've been turning at about half dial (I think I have it set at slow gear off the top of my head, and will check next time I'm in the garage)

 

[bracketracer]

Carbide is harder than your metal file so it would ruin the file. You can try to sharpen carbide with a green silicon carbide stone in a grinder.

 

[GravityX]

Bracketracer, do you know if you could use a sharpening stone to hone the carbide edges on these tool bits or would this technique be better left to HSS?

Here is a thread on carbide sharpening over at Practical Machinist.

 

[bracketracer]

GX, I think the carbide would groove your sharpening stone? Do you have a diamond sharpening stone?

I should add that those green wheels give off silicon in use so a mask should be used. You might find that the carbide chips when you try to sharpen it also.

 

[GravityX]

Yes, I do have diamond sharpening stones. I will give that a try, thanks! Dust mask when grinding is a must!

 

[King Racing]

EZE-Lap
These will sharpen carbide and are cheap.

 

[Mazakdad]

Here's a better picture of what we're doing.

For a "real" nail, we would have it much closer to the collet.

I'm not sure (looking for feedback) if it's a good idea or a bad one, but I found if I push a nail into the collet first, and then tighten down hard, it makes the nail straighter. At least better, but not perfect.

Can these carbide tips be sharpened, and if so, can I use a normal metal file on it?

Lastly, what speed should I turn at? I've been turning at about half dial (I think I have it set at slow gear off the top of my head, and will check next time I'm in the garage)

Man, that tool has no front relief in it. You could be heeling out and it's leaving a bad finish. You can use the tail stock center as a guide to place the tool tip center. You'll want the edge of the tool just below it.
You're cutting small diameter mild steel or even 400 series stainless with a carbide tool. Chances are your lathe won't spin at the RPM needed if you were to do the math.

I'm. Thinking if you indicate the collect chuck in. And lock it down tight, you should only be at the mercy of how accurate the collet repeatability is.
Keep the nail in as far as you can, to promote ridged work holding.
Try high RPM and a light feed rate. .003 per rev. Reduce depth of cut, this will reduce push off.

Edit: Words

 

[GravityX]

I can see that now that you pointed it out. Doh!

Here's a PDF on grinding tool bits.

 

[Mazakdad]

I can see that now that you pointed it out. Doh!

Here's a PDF on grinding tool bits.

Nice info right there. Most tools used in a CNC machine have the relief built into the holder now. That is why the insert is straight on its edge. But the old school brazed carbide tools, such as the one above need some front relief ground into them. You may be able to cheat a bit and run it lower than centerline. But be careful with this, the material will want to roll on top of the tool. And his likely will result in a broken axle. Hope this helps!