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dai sensei
12th September 2009, 06:58 PM
Some of you may remember the start of this some time ago, it has been on hold since my operation. It was to be a platter plate with a divided trough for biscuits/onions/dip and an end grain cheese cutting board in the middle. It is made from Tiger Myrtle and Zebrano with Ebony divides made by multiple glue-up segmental turning. It was supposed to be finished as a wedding present when I go down to Melbourne in a few weeks :-.

The final glue-up was before my operation and just last week I got back to it and turned the back face and sanded to 1200 ready for the end grain board base to be glued in (the cutting board is in two parts). Today I went to turn it around and work on the front face when I noticed one of the joints has given way :o:doh::C The bottom is only 2-3mm thick and the edging 10-12mm thick, but obviously not enough even for the epoxy I used.

I was thinking of re-gluing, but wasn't sure how to pull it together again, I can't just push it. I tried strapping, but it tended to just come of as I applied the tension. I then put it in my big bowl jaws, but even they can only pull the gap in to around 1mm.

Worse case scenario, I will compress as much as I can and then fill with resin, just not sure that will even hold.

Any experts out there got any ideas?

Cheers

TTIT
12th September 2009, 07:26 PM
Hmmmmm :? I've got a box with a similar problem stashed away in a cupboard somewhere - it's been there about 8 years now :shrug: :U

TTIT
12th September 2009, 07:30 PM
But seriously, from my experience you are never going to keep it in place with glue. I reckon you'll need to 're-segment' at least that join and flatten it so there's no tension - for the time being. :;

I knew there was a good reason I don't do segmented stuff :no:

joez
12th September 2009, 08:40 PM
5mm's a fair bit, personally i'd slice it right through the middle with a bandsaw and take a very light pass with a jointer then reglue.

good luck

joez

Skew ChiDAMN!!
12th September 2009, 09:21 PM
Ouch! :C

I think I'd go all industrial on this one.

Firstly, I'd turn a round disk of MDF and glue it to the face, to act as a backer. Then I'd run it through a TS with a thin kerf blade, ripping along the failed joint with the MDF facing down. Glue the two halves back together - possibly inserting a thin strip the same thickness as the kerf. Or maybe not. Then turn it to the next joint and rip and glue again.

Repeated until all are matched again.

Finally, of course, remounting and turning away the MDF.

hughie
12th September 2009, 10:31 PM
Or maybe if you can find somebody handy with a Bandit strapping set up, you might be able to pull it together and as for glue perhaps only epoxy will have the strength. Leave it clamped for several days

http://www.westernex.com.au/productsearch.asp?Product+Search=38

Texian
13th September 2009, 09:01 AM
Similar to what joez said. Bandsaw through the center (including the bad joint of course). Sand the cut surfaces smooth and flat, removing any of the existing ebony divide, and glue in a new ebony divide. After cutting and sanding the cut surfaces flat, might want to let the two pieces sit for a couple weeks and see if the sanded surfaces remain flat. Beautiful piece, BTW.

munruben
13th September 2009, 09:12 AM
Similar to what joez said. Bandsaw through the center (including the bad joint of course). Sand the cut surfaces smooth and flat, removing any of the existing ebony divide, and glue in a new ebony divide. After cutting and sanding the cut surfaces flat, might want to let the two pieces sit for a couple weeks and see if the sanded surfaces remain flat. Beautiful piece, BTW.
That's the way I would do it. Good luck with it Neil, It's a lovely piece.

dai sensei
13th September 2009, 10:19 AM
Thanks for the ideas guys, certainly gives me a way forward.

I'll use Skew's idea of glueing a backer to the front, that is still unturned, to give me a flat reference surface for the reglue. I'll then rip through the joint with the bandsaw, sand off the ebony divides, then reglue with new divides.

Hopefully it will remain flat and round, I don't have enough timber left to play with, other joints may then fail.

I must admit I'm a bit worried taking it to Melbourne, although it will be finished then. I was going to finish with paraffin oil all over, but now thinking of using the oil on the cutting board, and use Glass Coat on the platter to completely seal it.

Thoughts?

Thanks again

Alastair
14th September 2009, 12:36 PM
Hi Neil,

This is often a problem with flat segmented platters. The only failures I have had have been with these . Where you have wide flat segments, the problems with wood movement are exaggerated. Usually, the problem lies with shrinkage, which gives a failure in the centre. In your case, I would imagine it was increasing humidity, and expansion which resulted in a rim failure. If you can repair, (and the advice regarding ripping in half along the failure line seems good), the drier Melbourne climate may then "suit" the piece more???

A solution from Cox's book, "Beyond Woodturning", is to turn a recess into the base, (as big around as the design allows), and inset a glued in inert piece, (preferably ply). Because of the large flat glueing area, as opposed to the small segment surfaces, it is better able to resist the stresses from wood movement. Where discussed, it was speciffically directed at the shrinkage failure I described above. I am not sure how effective it would be for your rim failure mode.

FWIW,

regards

dai sensei
14th September 2009, 08:58 PM
I think the problem stemmed from the dry cold period we have had, it was quite damp and humid when I glued it up, so shrinkage being the problem. Yesterday I found the gap had closed back up slightly to around 2mm, so managed to glue it up again without resawing it, clamping in the bowl jaws to clode the gap completely.

I am quite worried about the difference in Melb and was considering reinforcing the edge to "hold" it. I'm thinking of cutting a small rebate in the bottom, epoxy in a stainless steel strand, then cover with some coloured resin. All this while it is still clamped in the bowl jaws.

jefferson
15th September 2009, 11:13 PM
Neil,

I've not got into segmented turning, but have done some thinking on the topic. My view is that even if you used the same wood splayed out like you have, you would have separation problems. The wider the wedge, the more it will expand and contract at the edge than the centre. Glue will not hold, ever. Not unless you do the math on the expansion / contraction rates with changes in humidity and the boards are all from the same stick of wood and you get the angles just right.

Segmented bowls limit the problem as the width of the side grain ends up small. Not so for platters.

Either way, you must use timbers that expand and contract on the same tangential plane. If not, you will have problems that you cannot fix. As you have found out.

In ancient times, stone masons used to drill holes in rock, insert a timber tenon, then wet it. And of course, the stone cracked. Such is the pressure of expanding wood.

It's the same rule for all woodworking, not only turning.

IMHO of course.

Alastair
16th September 2009, 11:01 AM
Neil,

I've not got into segmented turning, but have done some thinking on the topic. My view is that even if you used the same wood splayed out like you have, you would have separation problems. The wider the wedge, the more it will expand and contract at the edge than the centre. Glue will not hold, ever. Not unless you do the math on the expansion / contraction rates with changes in humidity and the boards are all from the same stick of wood and you get the angles just right.

Segmented bowls limit the problem as the width of the side grain ends up small. Not so for platters.

Either way, you must use timbers that expand and contract on the same tangential plane. If not, you will have problems that you cannot fix. As you have found out.

In ancient times, stone masons used to drill holes in rock, insert a timber tenon, then wet it. And of course, the stone cracked. Such is the pressure of expanding wood.

It's the same rule for all woodworking, not only turning.

IMHO of course.

Jeff,

the problem is not just to do with the movement being similar. It is more the difference in movement across and along the grain. It is the same issue which causes the opening up of mitre joints in the middle, (shrinkage) or at the corner, (expansion). While you can get away with it in narrow section, as in bowls/vases, the problem is magnified in platters.

While I have not tried the "inset" solution I mentioned above, it is reputed to solve the problem, by adding a large side-grain gluing surface in addition to the small endgrain joints typical in segmenting, and hopefully "forcing" the timber to conform to the dimensionally stable ply etc.

I'll try it when I get around to doing a segmented platter again.:D

regards

regards

dai sensei
16th September 2009, 08:47 PM
Yep, I concluded I would continue to have problems, so after regluing the joint I have cast a 3mm SS strand (what I had) into a rebate with black resin whilst still in the jaws. The rebate is angled towards the centre from the outside on the base, to avoid the strand and resin from popping out when under stress. The SS strand should more than cope with the forces induced from the temperature/shrinkage etc.

Can only hope it all works :fingerscrossed:

ss_11000
17th September 2009, 01:34 AM
Thats got to suck! hope your fix works Neil!

Manuka Jock
20th September 2009, 07:17 PM
Yep, I concluded I would continue to have problems, so after regluing the joint I have cast a 3mm SS strand (what I had) into a rebate with black resin whilst still in the jaws. The rebate is angled towards the centre from the outside on the base, to avoid the strand and resin from popping out when under stress. The SS strand should more than cope with the forces induced from the temperature/shrinkage etc.

Can only hope it all works :fingerscrossed:

Neil , Looking at the pics in the new thread , It did work :2tsup:
Any WIP shots of that ?

dai sensei
20th September 2009, 09:15 PM
The original idea was a tripple glue up (I mentioned in yet another thread) and was supposed to have 2 separate dishes or deep grooves, one for biscuits and another for the pickles/gerkins etc. On the second glue up, I had a massive dig-in and the two dishes became one. But since it didn't work and tended to fly about the workshop many times, I deleted the WIP to ensure nobody made the same mistakes :U I have attached the orginal plans for the tripple glue-up.

As far as WIP on the last repair, no sorry I didn't take photos, apart from the finished product as I am running out of time before my trip (weekend coming).