Cracks appearing in Brown Mallee Burr pen

[rendauphin]

I turned a Leveche rollerball using a Brown Mallee Burr blank. I used epoxy to glue the blank to the tube and after bringing into the house for a couple of days cracks appeared along some of the burr lines. I finished it using Phil's melamine technique.

Any advice to prevent this much appreciated.
Jim

 

[Terry Q]

I think your blank was not completely dry. I don't finish turn below 6% because I have been there, done that. I would carefully turn the wood of the tube and try again.

 

[Bammer]

Definite case of the wood not being dry. Get yourself a moisture metre if you are going to turn more burr's

 

[wm460]

Move to a warmer climate like here.

 

[Pierre]

Wood for furniture making etc should be between 12 and 18% humidity as you start to make the piece, as you cut and slice it begins to lose some humidity as each piece becomes smaller. Whilst the wood could be cracking due to drying, it is more likely due to stresses relieving after the turning especially in burls which by definition have all sort of stress angles in them. It is also possible that if your wood is too dry then bringing it into a place with a lot of humidity ie a house closed up for winter with a family in it then it can absorb moisture and have a similar effect as being too humid.

For the wood technical buffs among you have a look here Moisture properties of wood | Wood Products.

 

[Frederick]

Hello Pierre,

Maybe the same reason as why when you drill holes in burr pen blanks the tube doesn't fit afterwards but the drill can be reinserted? I think burrs move when cuts are made. There must be a fair amount of stresses in burrs due to thier nature.......different growth rates and densities etc...

Cheers,
Frederick

 

[Phil Dart]

I've metered the moisture in the blanks from the same batch as yours Jim, and they're reading 14%, so I don't think you could describe the blanks as wet or unseasoned, since that will probably be less than the ambient moisture content in most people's workshops at this time of year. It may be the shock of bringing a 14% blank in to a centrally heated house, where the ambient moisture content which will be probably less than 5%. Ordinarily, a sealed blank would cope with that, but as others have said, there are stresses and strains all over the place in a burr. Either way, watch the post on your doormat next week, and you can have a second crack at it (no pun intended. Well, maybe slightly intended) - I'll pop a replacement blank in the post to you on Monday.

 

[Bill Mooney]

It seems like it’s all been said.

 

[Pierre]

Just to make a point on Phil's post, if his blanks are at 14 % then they are at furniture quality, however most houses are at 50% humidity in the UK and in most of western Europe so as I learned from an ebony blank and from a cabinet I made a few years ago, if you move a very dry piece to a humid place then you must expect movement.

I once helped a friend lay a chestnut floor in a very large room, rather than keep the tongued and grooved planks in the same room, as I advised, he chose to hold them in a barn for a year I spent 2 days re-tonguing those planks, the floor area was 60 sq metres.... I know a little bit about wood and relative humidity!!

 

[Penpal]

I know more than most about Brown Mallee Burl,I have 50 yr cut and turned all over the place ,this has never happened to me but I am ever patient with my blanks. You may never know what caused your cracks. Wish you well in the future. Brown Mallee is so stable for me in my 30 yrs of Pens. I once sold from a Burl Getter 2000 blanks to guys on the U Beaut Forum in Australia but I culled them in such a way there were no apparrent defects. I have no reason to doubt all theories but it seemsPhil supplied your blank and I would bet London to a brick he was unaware of potential problems with yours. I turning sometimes you win and others lose,Cut your losses and try again,I confess sometimes moisture traps in the timber.

Peter.

 

[rendauphin]

Thanks for all the advice. I have learnt so much from all of your experience, it is much appreciated
Jim

 

[Phil Dart]

Just to make a point on Phil's post, if his blanks are at 14 % then they are at furniture quality, however most houses are at 50% humidity in the UK and in most of western Europe so as I learned from an ebony blank and from a cabinet I made a few years ago, if you move a very dry piece to a humid place then you must expect movement.

I once helped a friend lay a chestnut floor in a very large room, rather than keep the tongued and grooved planks in the same room, as I advised, he chose to hold them in a barn for a year I spent 2 days re-tonguing those planks, the floor area was 60 sq metres.... I know a little bit about wood and relative humidity!!

Just to be clear (not a pop at you Pierre), moisture content relates to how wet the wood is and with relative humidity relates to how wet the atmosphere is.

A centrally heated house will have a relative humidity of around 50%, but if you jab a moisture meter into your dining table, you'll find that its moisture content is probably around 5%. That is the ambient moisture content and is brought about by it's permanent situation within that particular relative humidity.

A workshop is likely to be in a relative humidity that is greater than 50% - at this time of year maybe 60 or 70%, and if you meter your workbench you'll find that the ambient moisture content is probably around 15%. In other words, it doesn't matter how wet or dry a blank is before it enters your workshop, after a week or two it will be at the same ambient moisture content as your workbench. Taking the blank (or the finished pen) in to an atmosphere that is dryer will cause the blank to become drier too. If that happens too quickly, that is when trouble arises.