End grain splitting

[jefferson]

I turned the lid and base of a lidded box yesterday. Out of Northern Mahagony which seems pretty stable in my shed.

Cutting the end grain on both the top and base, slight splitting appeared, particularly after I power-sanded and hit both with EEE and Shellawax. The wax certainly highlighted the cracks. And they seem worse a day later.

I'm thinking maybe that I over-heated the end grain with the power sanding, thus causing the cracks. Only fine ones but they are quite visible with the topcoat of wax.

Any thoughts?

Jeff

[Skew ChiDAMN!!]

In order of likelihood, I'd say the most likely culprit is the sanding, followed by overheating tools during the cut and the heat from applying the Shellawax at last place.

When end-grain hollowing I frequently remove any residue from the tip of the tool by finger, not just to clean it up but also to see if the tool tip is getting hot. If it is, so is the wood. That's when I have a 5 minute break to let things cool down a bit.

When applying Shellawax there's probably more heat generated but it's typically for only a short time and doesn't heat deeply into the wood. Long cutting with slightly blunt (or even sharp tools on certain woods) may cause less heat per second, but it's applied the whole time you're cutting...

[woodwork wally]

I second that motion of skew You will cop similar from blackwood also . Sanding in short bursts with 5 minute spells will help eliminate a lot of problem Jeff Believe me I know when we can see the end is nigh it is bull at a gate to finish and I come undone everytime I forget.Better to slow down and finish once than having to sell seconds or refinish the endgrain Keep turning and practice as these things are able to be overcome Cheers WW.Wally

[Robomanic]

I too have questions in this area. Splitting in end grain is something I have been tinkering with a bit recently. What do you guys think about dabbing a bit of water on to replace a bit of lost moisture? Obviously it is not going to fix the grain structurally, but it does seem to close it up again. Closing it up seems to buy more time, where as with the splits I would have thought that once they open up the drying is accelerated.

I have found myself interrupted half way through a project and have hit it with water in this way - seems to buy another 24hours or so.

Any thoughts?

[jefferson]

Thanks Wal and Skew.

I thought the problem (after the event) was the power sanding. Lots of heat there. At first, I blamed the Ubeaut, as it really showed up my lack of skill with the chisel, so I sanded some more (and more).

I tried cutting the mahogany end grain with my Ci1, followed by the big scrapers, then the oland from Ern, but it just wouldn't cut clean. All are sharpish, so I'm thinking the wood was a bit soft.

Patience? The hollowing was going so well at the time....

thanks Jeff

[joe greiner]

All of the above.

Most often, cutting end grain is substantially chopping the fibers. The closer you get to a slicing cut, the less distress to the wood. Try cutting stationary end grain crosswise with a hand chisel, first by smiting it directly, and then by a paring cut at about 45 degrees or so to the perpendicular. The difference is amazing. Drill bits, including Forstner bits, have pretty much the same deficiency in end grain.

When the tool or the wood get hot, take a break. "Tool" includes sandpaper.

Joe

[OGYT]

Jeff, what they said. Heat is your enemy. As is fast moisture loss.

Shannon, I too, spray my pieces with soapy water at times when turning.

Wet sanding also will aid the cooling.

[Ed Reiss]

Ditto :wts::exactly:

Unanimous opinion!

[hughie]

Yep heat is the killer. :~ some times I use compressed air when power sanding inside the bowl. A bit messy but it blows the dust away to boot.

Or do as I do build one of these, the vortex will produce sub zero temps instantly from compressed air. I must warn you that the other end of the vortex will produce temps in excess of 100C. But as a spot cooler its the best.

http://www.southstreet.freeserve.co.uk/rhvtmatl/

http://www.eskimo.com/~billb/wirbel.txt

http://www.pdbuchan.com/ranque-hilsch/ranque-hilsch.html

http://www.southstreet.freeserve.co.uk/rhvtmatl/rhvtinfo.htm

[RETIRED]

When sanding end grain vessels or thin wall bowls slow the lathe down to about 1/3rd of turning speed which should be high.

Hold the paper in your fingers, do not use a pad between the paper and your fingers.

If your fingers get hot, the timber is hotter and will surely crack.

[rsser]

Also bear in mind that as you remove stock the timber may move with the changed stresses.

With bowls some folk leave them a little thick and come back the next day for the finishing cuts. I can't be bothered. Sand and be damned!

Added re bowls: contrary to 's advice, for the first few grits sanding the inside of a bowl I often use the paper with an equiv size bit of Scotchbrite backing. Seems often to produce a more reliable surface than a power sander at that stage (ie, more consistent line between hard and soft grain). I can feel the high bits. And then get the PS out. Talking about 80 to 120 grit by hand.

[jefferson]

I've been back reading the R. Raffan book on lidded boxes (again). He suggests doing batch lots of 6 boxes out of the same material, that way you learn more about the timber and how to turn it.

The Northern Mahogany really tore on the end grain, thus necessitating hard power sanding. Unlike the Antartic Beech box I turned last week, which drank up the Danish like no tomorrow.

I think the solution for the Mahonagy is to have curves inside both the lid and base, cut with a gouge? That will test me no doubt.

Suggestions as always more than welcome.

(Ern, I think I gave you a lump of that mahogany. Perhaps you can try to hollow and let me know how you get on. Ta).

Jeff

[rsser]

Jeff,

The prob you mentioned in the first post was checking.

Now you're talking about tear-out.

Are both happening??

You need to be clearer.

[jefferson]

Ern, sorry for any confusion.

When I hollowed the box, I had tear-out in the base using the Ci1 and the Oland. I tried a few scrapers without luck to correct.

So I then power-sanded to remove the tear out. That worked fine, until I over-heated the end grain, which seems to have caused the cracks. These were only noticable when I applied the EEE and Shellawax.

I have some margin for error in base thickness, so may try to resurrect the project by deepening a fraction. No idea how deep the cracks go, but they aren't visible on the outside. ie the chuck end.

Hope this clarifies my earlier messages.

Jeff

[rsser]

K, well I'm no box-hollowing guru. If it were a bowl, I'd resharpen the Oland or whatever scraper you have that will fit and take some very light cuts, pref at 45 degrees or so.

Deep tear-out is a pain to sand out so getting back to HSS is cooler and quicker.

btw, if you're using a round end scraper, don't use more than a third of its cutting edge; as above, get a nice burr on it with the grinder, and try to get it coming across at a shearing approach. The latter is a little demanding. I'd opt for the Oland first and see how that went.

Hate to suggest more tool expenditure to you, but in a case like this I'd reach for my Sorby multi-tip tool (tear-drop scraper, with a shaft that's flat on one side and round on t'other).

[OGYT]

What Ern said. Teardrop scraper at shear. Heck, look at his avatar. He's gotta know what he's on about. :D

[rsser]

LOL.

Maybe not Al.

The beard's nearly all grey now.

What day is it again??