Build thread - Blackwood & Bunya Dreadnought

[demonx]

My first journey into side bending is a partial failure. I was worried about breaking it, I burned it instead.

Attempt #1 was stained in blues and greens. I used boiled tap water, apparently that is not enough.

This pic is of attempt #2, I could not find distilled water anywhere, so I used mineral free water. Big difference with only a small amount of water/mineral staining in comparison, however the second time I had the wrong probe hooked up and before I realized my mistake I'd over baked the waist.

After lunch it seems I'll be cutting more Blackwood.



The second attempt I tensioned the screw adjustments a lot tighter and the metal sheet didn't buckle like it is in this first pic.

[kiwigeo]

My first journey into side bending is a partial failure. I was worried about breaking it, I burned it instead.

Attempt #1 was stained in blues and greens. I used boiled tap water, apparently that is not enough.

A wash with oxalic acid will often get rid of the worst of the staining.

[colburge]

I had the same problem with burning the first time I used the blanket too. I wound the temp right down and found that mine easily bent at 200F, I know the recommendations on here are 280F but it started smoking at that temperature for me.

Col

[kiwigeo]

No doubt about it....thats blackwood

[demonx]

All the instructions I've read and videos have said 320F and bake at 260f !!! Are we using the same bender & controller?

I've been doing some test runs using sides I've cut up to practice. The blackwood wasn't meant to be a test run, but it quickly became firewood!

I've solved the burning issue, fingers crossed it doesn't happen again. First time I burned was because I had the probes too far out. Second time was because I had the wrong probe plugged in.

I've "mostly" solved the water discolouration, it is still occurring but not as bad as it was. The third bend I did had zero burn and a little water marking.

The issue I'm trying to eliminate now is I've been getting a warp/buckling either side of the waste. I've just done a practice side with a bit less water and I made sure to let it bake at 260 for 15 minutes and I'll let it cool down a lot longer before I remove it. Actually I'll just leave it in overnight as I'm not going back out there again tonight!

Hopefully that solves the warping. If not then I'm out of ideas

[chappy]

I used distilled water from Supercheap.

After bending the sides I immediately put them into moulds and left them there until needed

Alan

[colburge]

All the instructions I've read and videos have said 320F and bake at 260f !!! Are we using the same bender & controller?

I am using an LMI blanket and the same controller as you. I just bent some uke sides at around 80 thou thick, with a tighter radius then you, and started winding down the waste at 120F and finished when it was at 210F, no problem. i read the same recommendations as you, and it just burnt the wood. I have practiced on lots of different woods with the same results, the only one I can't get to bend, no matter what is qld maple.

Col

[demonx]

I'll have a mess around with that on Monday and see what the hundred less degrees does with some blackwood

[demonx]

I pulled the last side out of the bender this morning and it was more warped (only behind the waste) than all the others, so that rules out the bake & cool time.

Next one which I'll do tomorrow I'll try the lower temps as suggested above.

[rocket]

IMG_1726.JPG (174.69 KiB) Viewed 22106 times

All the instructions I've read and videos have said 320F and bake at 260f !!! Are we using the same bender & controller?

I am using an LMI blanket and the same controller as you. I just bent some uke sides at around 80 thou thick, with a tighter radius then you, and started winding down the waste at 120F and finished when it was at 210F, no problem. i read the same recommendations as you, and it just burnt the wood. I have practiced on lots of different woods with the same results, the only one I can't get to bend, no matter what is qld maple.

Col

i don't know if i have more ass than class but i use a home made bender, a LMI blanket no controller, turn it on for a minute or so, turn off for a while and back on , just go by feeling how hot it is, don't rush to bend the stuff, let the heat penetrate the timber . and bend gradually, this is the most sophisticated method i've used so far, before this i've used, hot pipe, heat gun,halogen globes to heat bender, i find the silicone blanket the best heating method so far, bent blackwood,purple heart,Qld maple, curly maple, no problem, i just spray a little tap water on the sides wrap in brown paper then alfoil then whack it in the elcheapo home made bender.
Must be more ass than class i think!!

IMG_1726.JPG (174.69 KiB) Viewed 22106 times

Cheers,,

Rod.

[kiwigeo]

Nice arse on that guitar Rod

I'm using a blanket without controller. I get up to close to 300deg for blackwood but I'm using a slat/wood/slat/sprign steel slat sandwich. The metal is probably absorbing a fair bit of the heat. I wrap wood in brown paper and then aluminium foil after spritzing it with a little bit of distilled water.

I didnt realise that the waist caul assembly on that LMI machine is fixed to the assembly on one side only.....surely this must result in uneven pressure across the waist when its clamped down?

[demonx]

I didnt realise that the waist caul assembly on that LMI machine is fixed to the assembly on one side only.....surely this must result in uneven pressure across the waist when its clamped down?

It's quite rigid and allows you to pull the sandwich straight out the side.

The attached image is the latest (the one I did last night) - you can see where the water marks are in ripples (inside the low spots) where it has buckled behind the waist.

This is my current obstacle as it's happening to every side and I don't know why.

[demonx]

A wash with oxalic acid will often get rid of the worst of the staining.

I missed this post until now

Where abouts do you buy the oxalic acid? I've never heard of it.

[kiwigeo]

A wash with oxalic acid will often get rid of the worst of the staining.

I missed this post until now

Where abouts do you buy the oxalic acid? I've never heard of it.

Bunnings or Mitre 10 should have it. I actually used an Intergrain product that I had sitting around my garage...used for preparing wood surface prior to treatment with their other products.

[kiwigeo]

A wash with oxalic acid will often get rid of the worst of the staining.

I missed this post until now

Where abouts do you buy the oxalic acid? I've never heard of it.

http://www.bunnings.com.au/cleaner-bric ... r_p0960276

[colburge]

A wash with oxalic acid will often get rid of the worst of the staining.

I missed this post until now

Where abouts do you buy the oxalic acid? I've never heard of it.

http://www.bunnings.com.au/cleaner-bric ... r_p0960276

If you have a Masters, they sell it too, in a smaller size. If you don't have one of those, look at your local for any deck cleaning product and check the ingredients for oxalic.

Col

[demonx]

Thanks guys. I'll have to look into that next week.

I've just bent another blackwood side, this time at around 210F. If I don't go back to the workshop tonight I'll post a pic or results tomorrow.

It seemed to bend "nearly" as easily. I also used a touch less water. Fingers crossed it removes the ripples.

[demonx]

Test piece at 210F.

Still getting the ripples as you can see by the attached pic with the straight edge on it.

For now I'm out of ideas.

[Trevor Gore]

Still getting the ripples as you can see by the attached pic with the straight edge on it.

For now I'm out of ideas...

Quarter sawn bends a lot flatter. What you have looks pretty "slabby".

[demonx]

Quarter sawn bends a lot flatter. What you have looks pretty "slabby".

For practice pieces I've been cutting pieces off inch board, so no, it's not quarter sawn.

Surely flat sawn should bend flat though and there's more than flat vs quarter to this rippling problem

[lauburu]

Could this be something to do with the way the bender is made combined with uneven clamping pressure across the wood being bent? There are 3 vertical components (2 sides and a middle bit). Do the ripples coincide with these?
Ripples could occur if the sides were constrained in their ability to move/swell/expand laterally but were relatively free to move vertically.
Miguel

[demonx]

On all the pieces the ripples have been behind the waist, not in the area where the wasit screws down. Where the waist screws down has been flat every time.

On the last piece where I tried the lower temp it also had ripples on the widest part of the body, which is the only time it's happened there.

The rest of the areas have been pretty smooth. I wish LMI had a trouble shooting chart for the bender so you could look up your problem and solve it.

[jeffhigh]

As Trevor said, flatsawn will do this, especially if you use lots of water

[demonx]

As Trevor said, flatsawn will do this, especially if you use lots of water

I've cut the water back to being next to none.

Guess I'll have to hunt down some cheap quarter sawn timber to experiment.

[Woodsy23]

For cleaning "water stains" off blackwood after bending, I used Cabot's Deck Clean. It contains oxalic acid and is available is a smaller 1l container for around $12.65 at Bunnings. It worked pretty well on my blackwood sides.

I did my first trial bends on some timber (silky oak I think) that was flat sawn and it cupped a lot accross the grain. After trying again on some quarter sawn timber of the same species, it came out flat.