cracks in turned pieces

[sandingman]

hello,
This is my first post. I registered here primarily because your site looked to be a likely place to find an answer to a question. It looks like a great site in general.

My questio involves an 8x8x3 block of macassar ebony, which I decided to cut into smaller pieces. It's possible (a certainty?) that I should not have tried to use it in the first place in the first place, because I found that the the pieces I cut, developed some small cracks a few days later. I'm assume it was not dry enough. Anyway, I thought if I turned a thick walled object, I might get away with it. ( I know, it was not a very bright thing to do.)

Things actually went fairly well until I was sanding. At which point there appeared 3 hairline cracks. The result of a combination of not-quite-dry wood & heat of over-aggressive sanding, perhaps? ( I thought I'd learned that sand/heat thing at least twice before.)
The cracks, so far, don't appear to have opened any further. My question is: Are there any techniques for making these cracks less obvious? I found that when I wet them, their light color darkened, and they were much less noticable. I'll keep the piece anyway, as it is a very nice black and red with swirling grain.

I guess I should also ask: What can you do if you think you have a block of wood that is not completely dry? This is the first of ~20 blocks I 've worked that appears to have been too wet. Maybe I should invest in a moisture meter?

Thanks, Sandingman (Andy)

[gatiep]

The cracks you have can be sealed with the thin superglue. If you have waxed the piece, run the superglue along the crack and a qiuick wipe with a DRY cloth to remove the excess.


If you turn another block, finish turning it in one session, be gentle on the sanding. If the heat build up is uncomfortable on your hand thru doubled abrasive, u are either pressing too hard or the speed is too high. Pressing sandpaper too hard doesn't really increase the sanding rate because the sanding dust blocks the paper and then the dust causes burnishing thru friction which increases the heat. Once you have turned and sanded the object seal it all over with a finnish, I use a wax, often Hut wax, but make sure that you cover the complete surface, even the area where it was held by the chuck. I have turned lots of bowls from green timber, sealed as close to 100% as possible and so far none have shown cracks.

Maybe I'm lucky, but maybe I'm not.


Regards
Joe

Have fun ..........................keep turnin

[sandingman]

this message is for gatiep/Joe. I can't tell for sure who it will be addressed to.
anyway...thanks much for your response . I just got a few blocks of green spalted maple. I'll let you know what happens.

Andy

[reeves]

Yes, the quality acrylocyante ?( superglue) and acceleerator will do it.


I started turning 6 months ago and have been discovering and learning about woods.

Some woods will split easily, some will tear, others will chip.

Cutting wood will always give it an oportunity to settle, whethe ryr wood is dry or not is alos a big one in terms of cracking.

I have just had a piecs of tassie sasafras open up cracks one week and close the next when the temperature went down. I have seen lace sheeoak boards curl and uncurl with the weather, it's all relavtive to behavouir of wood.

So mate all i can suggets is that you try a few difernet type sof wood and u will see how they behave in different conditions.

I have not used the massassar ebony but i have used osme other ebony and it tend sto be pretty brittle stuff.

please let us know how it turns out for u..

cheeeeeeeeeeers
john

[barnsey]

Not meaning to state the bleedin obvious but yes this can happen with theoretically seasoned timber. As someone mentioned superglue works on some and if you can clamp it in some fashion it can help. ;)

A lot of people adopt differing approaches to season green timber and they are all worth trying to find one that suits. Some turn very green to get the timber to move and distort. Others rough turn and leave it that way and finish when it drys out. It drys more quickly when the thickness is reduced. :rolleyes:

I've had timber turned green that even when it was still 12-20mm thick it has literally exploded off the chuck so be careful because different timbers react differently :eek:

[gatiep]

Exploded off the chuck ?????????????????????? :confused:

Could you please elaborate as I have never seen green timber exploding off a chuck. I am very interested in the explosion bit.

Cya
:)

[Little Festo]

Hello Sandingman,

This may not apply to what you are doing, depending on how "green" your timber is. Several months ago I turned some VERY green timber (two or three days after felling the tree). I turned a few very thin walled vessels and wet sanded the pieces. I actually wet the wood and dunked the sandpaper, ordinary cloth backed, in water and the periodically washed the sandpaper to remove the "gunk". This worked very well BUT they were very thin walled vessels, tranlucent in fact. There was no cracking but as you would expect a bit of warping. I believe that the stresses that cause cracking are greatly diminished due the the wall thickness. I have heard that some turners use this method particularly on end grain to stop cracking due to heat when sanding, can anyone comment?? I suppose a certain amount of care is need not to over heat the piece when sanding.

I turn quite a bit of unseasoned timber and microwave a fair bit. I rough turn then cover the outside and base with wax or end seal but leave the inside bare and microwave with care, not too hot on a medium setting for about 2 to 5 minutes depending on the piece. Care needs to be taken with knots and the heart wood, a bit of super glue works ok . The blank is weighed and the weight noted, when weight loss stops the wood is ok to turn. Fine cracking occurs when the wood is reaching "dryness" but generally this is only surface cracking. Please note that I live in the tropics and humidity is generally quite high here so you will need to experiment, I imagen that it is quite forgiving so if you are in a drier climate you may need to be a bit more carefull. Hope this is of some use to you, please remember my method is not Gospel but it works for me here in the triopics.

Happy turning - Peter

BTW As long as the cracks are stabilised, CA glue works well, the piece can still be acceptable. I have been and still do get disappointed when I cannot turn out cracks from a cracked blank but people will still like a well turned and finnished piece, they say it's part of the nature of wood, but I think it's nice to have a piece that is not cracked, it's a bit more perfect??

[ribot]

Tell me I'm nuts if you like but a different slant on this problem might be to use either common shoe polish or coloured wax sticks.Apparently this is a method used be antique restorers. Depending on the use and finish you want to apply to your bowl then perhaps filling the cracks with wax will do just fine, no one will notice the difference if done with care.

[rsser]

Wax sticks - nice work if it did - I checked this out and apparently it doesn't.

You can also deal with small cracks while you're turning by running some thin CA into one at a time and asap after that sand by hand with the piece turning - the dust and glue will combine to fill the crack. Esp. get the glue into and over the start of the crack.

The heat alone of cutting and sanding can start cracks in properly seasoned timber.

[Little Festo]

I was finnishing a piece last night and was wet sanding (oil) and must have been a bit too agressive with the pressure I was applying to the sandpaper and developed a few fine cracks, how stupid - just after reading this post. The piece will survive but it won't be what it should have been. Ah well, hope this lesson will be indeliably imprinted in my mind.

Peter - slow learner from Darwin

[barnsey]

Exploded off the chuck ?????????????????????? :confused:

Could you please elaborate as I have never seen green timber exploding off a chuck. I am very interested in the explosion bit.

Cya
:)
I started it late in the day and was probably a bit agressive with the bowl gouge to hollow out the inside trying to get it finished. Then thought I would try and put a bit better finish on the inside with a very sharp scraper - no serious diggins but when I started to sand the outside, wound up with four pieces off the scroll chuck. :eek:

Now I reckon it was a combination of that and the fact that I am inclined to tighten the scroll chuck as tight as I think it will stand. :o I've had whole ones come off the lathe and don't like it when that happens :confused:

Nonetheless, dodging 4 bits being hurled at you all at once by Shane Warne is a bit scary much less Casper. :D

Jamie

[rsser]

I was finnishing a piece last night and was wet sanding (oil) and must have been a bit too agressive with the pressure I was applying to the sandpaper and developed a few fine cracks, how stupid - just after reading this post. The piece will survive but it won't be what it should have been. Ah well, hope this lesson will be indeliably imprinted in my mind.

Peter - slow learner from Darwin

Peter, sometimes the piece will crack not because of any excess pressure or heat but just because in shaping and hollowing you change the balance of inherent stresses.

Some turners leave the bowl for a few days before doing the final fine shaping for this reason. This doesn't always work though because it can warp then too :mad:

[Timbo]

I recently attended Woodturn 2004 in Sydney and was surprised to hear many of the presenters strongly recommending wet rough turning (for three main reasons - dealing with fresh timber quickly, reducing storage space and the timber is often easier to turn). A few weeks ago I followed this advice and rough turned a couple of pieces of gum tree which worked quite well and are now dryign ready for finished turning. This week I tried the same with a piece of recently felled wattle. Having spent quite some time turning one piece last weekend I was really disappointed to discover last night that it has split terribly (of no use at all now). Have I done something wrong? I notice mention in some of the above postings to sealing rough turned pieces either completely or in part. I do not recall mention of this approach at Woodturn. What is the best approach? Is my problem simply that I am working with the wrong timber for the wet rough turn approach? The wattle looks great and I am sure will finish really well if I can get it dry without major cracking and splitting.

Timbo

[smidsy]

Hei Tim,
Check out this thread:
http://www.woodworkforums.ubeaut.com.au/showthread.php?t=13090

This is a bowl from some wood that is only about 5 months off the tree. The wood was treated with endcheck as soon as it came down and left to dry.

I rough turned it wet to about 20mm thick, retreated it with endcheck, let it dry for 3 more weeks (should have been longer but I wanted to try out the new chuck) and then turned it to what you see now.

The reason wood cracks is because it dries out unevenly, so it has to be treated at every stage. Treat it as soon as it comes off the tree, and if you rough turn it and let it dry more, retreat it - I scored a trailer load of marri (that's what that bowl is) and the only peices that have cracked are the ones that weren't treated properly.

Cheers
Paul

[rsser]

Timbo: woods vary a lot in their propensity to crack, and sometimes there's little you can do. I finish turned a goblet from a fresh piece of plum that cracked badly the next day while a banksia vase took three months ;-}

Some turners microwave their piece when finished from green - do a google and you'll find tips on how to do this.

Another tip when finishing from green is to try hard to get even wall thickness all over.

[CHJ]

Barnsey:

I guess if the worst happens you can call it Art http://www.woodworkforums.ubeaut.com.au/images/icons/icon12.gif


http://www.bbc.co.uk/bristol/content/madeinbristol/2004/11/wood/xgallery14.shtml

The rest of these shots are worth a look.

Chas