Tearout in the sapwood

[wlcummings]

My problem when turning bowls is tear-out of the sapwood between the growth rings on the end grain. The tear-out becomes somewhat muted when i finish sanding and apply the oil and wax but i know they are there and it bugs me.

I turn on shopsmith at somewhere between 750 and 1000 RPM. I am hoping my problem can be solved by reducing the speed of the lathe. SS sells a speed reducer for $250.

I "think" my tools are sharp I used to get huge tear-out and now only the soft wood in between the growth rings.

 

[mkart]

tearout

Reducing the speed will probably not help you. Reducing your feedrate, or the speed at which you you move your gouge across the wood, may help though. This essentially gives the effect of speeding the lathe up but without dealing with those pesky safety issues. In my experience the major cause of endgrain tearout is falling off the tool bevel as you move around the bowl. When you fall off the bevel your cutting edge loses support and tearout usually occurs. It takes a lot of practice to be able to move across the curve riding the bevel all the way but when you do you will know right away.
good luck
Matt

 

[MichaelMouse]

Yep, sapwood's generally less dense and robust relative to heart, and more susceptible to ripping versus cutting. Then there's that pesky zone where the breadth of the shaving is just about equal to the earlywood between rings. My answer is to roll the gouge back a little bit for better bridging, accepting a tad more pickup when I hit the unsupported portion just after the endgrain passes. With a good edge that's less hassle than trying to work out a pit.

Speed's no big deal. If you had your carving gouge you could make a mirror-bottomed cut across the same area with the right angle, and the piece wouldn't even be moving!

 

[dkulze]

I'm gonna go out on a limb and suggest that the ShopSmith might be part of the problem. My experience with them is that they are not the most precise and accurate lathe out there, as they are part of a larger setup. Even a little bit of variance in the bearing set or spindle alignment can amplify vibrations and make minor problems (sapwood's tendancy to tear) major ones.

My suggestion would be to spend that $250 on a Jet Mini lathe. You'll get 10" swing, a wider speed range, excellent construction (bombproof little sucker), and a purpose-built machine. You can even get a free chuck or bed extension with most purchases these days (from Woodcraft, Craft Supply, or Rockler as a special package). If that is an option, I'd suggest the chuck, as you can still use the ShopSmith for longer spindles.

Once you've settled on a path, track down your local turning club (chapters page on the main site here) and give them a whistle. You'll have more support and mentoring than you can handle before you know it.

Have fun,
Dietrich

 

[Griesbach]

I sure don't want to rain on Deitrich's opinion here but maybe the ShopSmith fits a certain need in this case although it sure would not be my recomendation for a lathe. That being said, we have a member in our club who turns on a ShopSmith and his work is nothing short of outstanding.

 

[dkulze]

No rain taken, Cyril. Shopsmiths are great tools for their purpose. They have the versatility and flexability to cover for most tools quite adequately, sometimes even excellently. My comment comes from experience and anecdotes with Shopsmith lathes. They are, by my experience, quite functional but also quite limited. You'll notice I didn't suggest that the Shopsmith was the cause of the problem, just that it may be a contributing factor.

The tool won't make the turner. A persistant and patient turner can make beautiful work on some pretty basic equipment. Purpose built and well made tools can, however, decrease the learning curve and open up possiblities. If what you have is a Shopsmith, use it to it's very limits and appreciate having such a flexible and well supported tool (wish I had one).

Dietrich

 

[Gretch Flo]

shopsmith

I turned several years on an old shopsmith (1952). Kept breaking expensive ($40 as I recall)belts (also have a machinist come and spend an hour with me helping to change it-the dial speed control was the problem as I recall. (I am not handy that way with machines). Then I got a new motor and a better belt and didn;t beak another as I upgraded big time with my oneway 1640. It worked ok except for the hi speed, but for small stuff it was ok-no lock feature and of course no reverse helpful for sanding. You work with what you got-machines and tools!!!Gretch