M42 blunting fast

[Maurizio]

Hi again all,

So. Until now, I've been turning with a half-size 1/2" set of Marple carbon steel tools that came with my second hand lathe. They've been absolutely grand for learning on and practicing my sharpening. I've recently bought my first full size tool , a 1/2" Crown M42 bowl gouge. I've spent time getting used to it - but today finally confirmed something odd: it seems to blunt really quickly.

I was turning a small cherry bowl, about 20cm in diameter and getting tearout. So, I sharpened the gouge and got a perfect clean cut - but it only took 2 passes before I started getting tearout again. This is pretty similiar to my experience with the carbon steel tools, so I'm a bit disappointed. Could there be something wrong with my technique? Is it possible I've just got a funny gouge? (after all there are variances in all manufacturing processes).

Any thoughts would be much appreciated!

 

[CHJ]

How 'fine' is your cutting edge, what is the nose angle of your gouge.

Not sure if it's relevant but some harder cobalt 'steels' are more brittle and can suffer from edge chipping if the fine edge is not well supported.
What does the cutting edge look like when magnified, blunt(rounded) or ragged?

 

[Honest John]

In my experience tear out can can occur for many reasons some related to technique and tool sharpness, but also can be caused by particularly cantankerous pieces of wood. Some woods can be really abused and will never tear out, others you cannot cut cleanly no matter what you do to them. I suspect you have a difficult piece of wood. Decent tool steel such as you have bought should not lose its edge like that. Has the tool lost its edge, or are you making that assumption just based on your observation that tear out reoccurs after two passes? You could lower the handle of your bowl gouge, and try some fine sheer scraping. It is a useful technique, you may have to explore it on youtube, but may completely solve your problem. When you can get very fine woolly shavings coming from the cut, often referred to as “Angel Hair” you will know you are cutting right. ...... there again you could just have duff gouge. :roll:

 

[Maurizio]

The cutting edge was sharpened to 240 grit - I'm off to sharpen it to 1000 and log the difference, the edge is a relatively steep angle (will need to check the precise angle). The edge dosnt appear chipped, but I lack the magnification to look at it any closer - is a cheap usb microscope a worthy investment, or perhaps an older magnifying tube?

Hi honest John - you're right there, I recently turned some green cypress, I have never experienced tear-out so badly before, 'orrible stuff. I find that wood that has been left damp after being cut down had a greater propensity to tearout than wood that has dried just once.

I'm making the assumption on two factors: the renewed tear out and the increased force required to cut. The force only ramps up after a few more passes. There is also a chance that this is a characteristic of using a larger gouge? As in, the larger cutting edge could be 'digging more' when taking a cut, and to me this feels like more pressure as I'm still used to a 1/4" gouge? Yes, sheer scraping works well, but I'm not very good at it with this new tool - practice time methinks.


I've read some of the papers surrounding manufacture of M42 and various hardening processes, so I'm confident that the metal should retaining a sharper edge. A quality control issue would show up fairly quickly on forums, hence me asking. Given the paucity of responses it's likely user error - who saw that coming! :lol:

 

[finneyb]

I'd speak with the supplier. I have heard of instances in the past of these not being heat treated by mistake.

Brian

 

[gregmcateer]

If Mark Sanger is your supplier, I would imagine he'd be super-helpful regarding your situation - and give very sound, experienced advice

 

[Maurizio]

Thanks Brian and Greg - I've sent an email to my supplier with the caveat of my situation to see what they say! Will update here afterwards.

 

[gregmcateer]

Any news, Maurizio?

 

[MarkSanger71]

The gouge was collected and returned to Crown Tools where Rockwell hardness testing was carried out near the cutting edge and found to be middle of the tolerance for M42 Cryogenic HSS, the gouge being correct hardness. In the mean time a new M42 Razor Edge gouge was Rockwell tested, again close to the cutting edge and found to be at the higher end of tolerance for M42 Cryogenic HSS. The gouge was sent to the customer who was happy with the outcome. The gouge in question was found to be of the correct hardness with no manufacturing or material defects being found during test. There is a no quibble satisfaction guarantee on all Crown Hand Tools as well as a life time guarantee for material defects in correct use.

 

[deema]

Top marks to Crown Tools, what superb customer service. It’s so nice to see this kind of customer service and acceptance that although the tool was perfectly made, for what ever reason the customer wasn’t happy and their priority was to have a happy customer.

 

[Hornbeam]

My experience with crown tools is similar. Top customer service and very responsive to feedback. Really nice people
ian

 

[Trevanion]

I’d be interested in knowing what the lower and upper thresholds of the hardening of the Cryo M42 is :| It’s all well and good saying halfway to the tolerances but your lower limit could be 0HRC and the upper limit at only 45HRC.