Tearout when using Skew Chisel - Help!!

[Grumpy John]

I am roughing out a piece of blackwood to use for a pepper mill. I roughed out from ~80mm sq. to 70mm dia. using a roughing gouge, no problems. Then I had a go at some skew practice and started getting coming from both directions i.e. cutting toward headstock, cutting toward tailstock. I am holding the skew as shown in photo's 3 & 4 and using lower third of the cutting edge. Any advice from the skew experts greatly appreciated.

[Ed Reiss]

John, its a bit difficult to try to diagnose why your getting tearout just by looking at still pictures...but lets give it a go.

Picture 3 - looks like your angle of attack is good and if the chisel's edge is sharp it should be peeling the layers off like butter...remember to keep that bevel rubbing.

Tear out can and will happen under these conditions:
1) dull edge
2) bevel not rubbing
3) using as a scraper

[Grumpy John]

John, its a bit difficult to try to diagnose why your getting tearout just by looking at still pictures...but lets give it a go.

Picture 3 - looks like your angle of attack is good and if the chisel's edge is sharp it should be peeling the layers off like butter...remember to keep that bevel rubbing.

Tear out can and will happen under these conditions:
1) dull edge
2) bevel not rubbing
3) using as a scraper

I can definately rule out 1 & 3
Number 2 is a possibility, I'll pay more attention to that next time and report back.
Thanks for the quick response.:2tsup:

[orraloon]

I cant claim to be great with the skew either but there are a few things that can be tried. the first is the sharpness of the tool so a touch up before you start. The old rule about cutting down hill grain wise is a good thing to follow. Light cuts. Try different lathe speeds. Oil the piece before the final finishing cut. Keep ther rest close to the work. Blackwood is often prone to tearout so it is a case of trying different things sonetimes. And the last resort is 60 grit paper.
Regards
John

[Alastair]

Firstly, blackwood can be a bar steward for tearout. I have seen George Hatfield at a demo resort to a scraper to avoid the problem.

I think the clue also lies in the photos. I notice you are using a very oblique angle on the cutting edge, (as in suggested best practice, pursuing a slicing cut). Blackwood tends to wild grain, however, and this can mean that your 'slicing' cut will in fact be cutting 'uphill' against the grain in places, something blackwood does not tolerate well.
IMO this would be a case for using the skew more 'square-on' (ie closer to a peeling cut) to avoid this. Or revert to a gouge and sandpaper!

I have also had occasions with blackwood and brushbox with quilted grain, where in extreme cases, reducing the cutting area was the only solution, as roughing gouge was bad, detail gouge better, and a small bowl gouge (used on a spindle) gave the best result. Note that by definition this would also give a squarer rather than slicing cut.

Lets hear from Skew and rsser on this

regards

[Skew ChiDAMN!!]

:whs: Go Alisatair!

Mind you, I don't see any particularly wild grain in the photos, but I've had my share of troubles with Blackwood & tearout too.

There are three things I'd try:

changing the "angle of attack" of the skew. (unlikely but may work and you already have the skew in your hand) using a detail gouge. As Alistair said, this presents a smaller cutting edge and thus the grain being cut has more support from the uncut grain behind it. using a freshly sharpened, unburnished scraper. You'll know when the wire-edge wears away as it starts tearing out again. :rolleyes:

I do a lot of scraping on Blackwood. :~

[Grumpy John]

Thanks Alistair, Skew and others. Roughing out was done with P&N gouge (Pictured). I was getting quite a reasonable finish with this tool, but thought with ~7mm till final dia. I'd take the opportunity to get in some practice with the skew. Obviously I've chosen one of the more difficult timbers to practice on :~.

[Manuka Jock]

John ,
that piece of timber looks to be split at one end ? Is that glue and paper we can see there ?

[Jim Carroll]

How fast are you going, you may need more speed as well to overcome this.

If going too slow it will hack instead of cutting.

[dai sensei]

I was trying to demonstrate how to use a Skew to STAR and a friend and I had exactly the same problem turning my Vesi (Kwila) grinders. I found the solution was exactly the same chisel you have pictured :U

[Grumpy John]

John ,
that piece of timber looks to be split at one end ? Is that glue and paper we can see there ?

Yes, thinned Araldite. Wrapped it in newspaper and duct tape to stop it running everywhere.


How fast are you going, you may need more speed as well to overcome this.

If going too slow it will hack instead of cutting.

Full bore low range on a jet 1642 about 1900 rpm I think. I don't look at the readout I just dial it up till it feels right :D. Just checked speed, 1257 RPM, going slower than I thought.

[funkychicken]

Sharp skew, light cuts and high speed. I've turned Dead Finish before and it'll chip and tear unless you take a veeeery light shaving.

[Calm]

Best way to stop tearout on Blackwood is dont use the skew chisel.. Even has told me that.

Cheers

[Mobil Man]

Looks like the skew angle is ok, but rule #1 to spindle turning is always turn 'downhill' as said in previous posts. Picture shows you going 'uphill'. Go from higher points to lower areas small bites at a time. As in using a duplicator on a lathe, they specify many times in bold print, always turn downhill. I've found that true in most instances, even turning acrylics. Some wood has a tenancy to tear out no matter what you do. Sometimes you have to compare a lathe tool's cutting action to the action of a 'thicknesser'. Some wood can be run thru either direction with no harm, while others you have to pay close attention to grain direction. Pine for example, will not only tear out but take out large chunks at times. "Direction of travel". Thing about the skew--buggar takes lots of practice, & can be the wrong tool sometimes.

[robyn2839]

i use my skew upside down to your first pics, have always done it this way, holding it in right hand and flat in the palm of left hand with fingers straight . a little unorthodox but works well and i dont get tearout.............bob

[Grumpy John]

Looks like the skew angle is ok, but rule #1 to spindle turning is always turn 'downhill' as said in previous posts. Picture shows you going 'uphill'.

Which picture MM, picture 1 or picture 2. The piece is parallel, and as I said I've tried cutting in both directions, cutting from headstock toward tailstock and from tailstock toward headstock, I'm getting tearout both directions. I think it's a case of a particularly difficult piece of Blackwood :((.

[Grumpy John]

Best way to stop tearout on Blackwood is dont use the skew chisel.. Even has told me that.

Cheers

Best answer to date I think :2tsup:, don't use a skew chisel :rolleyes:.
Blackwood is obviously not a skew friendly timber, lucky it was only practice and there's plenty of material left to finish the job using more appropriate tools.

[Calm]

Best answer to date I think :2tsup:, don't use a skew chisel :rolleyes:.
Blackwood is obviously not a skew friendly timber, lucky it was only practice and there's plenty of material left to finish the job using more appropriate tools.

I should actually clarify that answer a bit , the skew works ok when laid on the tool rest meeting the timber at an angle of approx 90 deg and using the whole cutting edge at the same time. :D:D








Yep a scraper.

Cheers

[skot]

Is your tool rest a little too low. For skewing, I was told to have the tool rest approx. mid way between the centre and the top of the piece.

My 2c worth

[Manuka Jock]

I'm getting tearout both directions. I think it's a case of a particularly difficult piece of Blackwood :((.

That could be it John .
As Freud said
'Sometimes a piece of firewood is just a piece of firewood'

:U

[OGYT]

I can't help you, GJ, but this is an interesting thread. I use it a little, but I never feel right using a skew. I guess it's because I'm so shaky... it's hard to hold it steady when I get it cutting right.
I'll read with interest, the other posts.