problem with finish cuts

[Fryers]

For the past month or two, I’ve been having trouble getting good surface with finish cuts on my shallow Blackwood bowls, especially at the end grain. (I tried to photograph, but it is too subtle for my photographing skills).

I can't identify anything that changed in the process. I’ve been turning Blackwood from the same source for over a year. The old Woodfast lathe runs true, I sharpen my gouges the same way, and I take as much care and joy turning as I always have, yet I get tears and patches of rough surface that is a struggle and at times impossible to remove by sanding.

Here come the questions…
· Do the cutting edge of tools go out of shape after prolonged use and frequent sharpening?

· Would they benefit from periodical ‘cutting down’ and reshaping?
· And, can that explain the problem I have with finish cuts?

Thanks,
Fryers

[Skew ChiDAMN!!]

Blackwood is notorious for tear-out, so don't be too hard on yourself.

If you're free-handing your tools on the grinder, the shape the shape can - and probably will - change, but that doesn't normally matter too much unless you're having unintentional touches with the 'wrong' part of the catting edge. eg. the wings.

It's more likely the bevel angle has changed, giving you either too sharp an edge - which bluntens too quickly - or too steep an angle.

If you're sharpening with a jig, then... well it's unlikely. Unless you've changed or misremembered the jig settings.

I can't say what the angles should be as these really depend on the type of wood and your turning technique. There are good approximations (basically the default angles) available if you want to check yours and regrind. But be aware that so long as you're within around +/- 10 degrees, it'll be right for someone. :shrug:

The main cause for tearout on Blackwood is blunt tools, so it may just be the quality of your tools. Perhaps only the first inch or two were tempered correctly and you've ground beyond that. (Chaiwanese tools are notorious for this.)

Perhaps, as mentioned, you've changed the bevel angle beyond the envelope or perhaps you simply need to sharpen more frequently... I've had some cantankerous pieces that needed a trip to the sharpening station every 30 seconds or so.

Most likely it's just the wood being a right PITA. It's known for it. ;)

However, Blackwood - in general... because every piece is different, even from the same tree - is usually more forgiving when being scraped.

For finishing it I like to use a scraper with a gentle curve profile. The curve should be tight enough that when used only a mm or two actually cuts... the idea is to remove only very fine shavings, almost hairlike. This minimises tear-out for me, although there's always the occasional piece I turn that just will not play nicely and I have to resort to grits.

In general I'll use my gouges to get within around 3-5mm of final shape, then switch to a scraper to remove the bulk of the rest and then lots of trips to the grinder for finishing cuts. This is to eliminate the chance of 'deep' tear-out, where I'd need to remove more material than I'd planned to get rid of it.

[smiife]

Sanding sealer to "firm up " fibres , then a trip to the grinder with the neg rake scraper every 30 seconds or so .....failing all that 40 grit gouge :cool::cool::cool:

[Fryers]

The answers always center on patience... and some technique. As many others, I am patient with all but myself :no:
The advice seems good. I have just re-shaped a worn skew into just the right shape scraper and will have a go.

Cheers,
Fryers

[LanceC]

Perhaps only the first inch or two were tempered correctly and you've ground beyond that. (Chaiwanese tools are notorious for this.)


Hmmm, I’m currently looking to buy my first HSS spindle gouges. Perhaps this is part of why the mid priced brand name tools such as Sorby and Crown cost more than the generic low cost ones. Sigh.