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first side bending attempt
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=10996		 Page 1 of 1
Author:  gratay [ Sun Feb 18, 2007 3:33 pm ]
Post subject: 
Although this went fairly well apart from a bit of cupping in the lower bout I found a fair amount of springback....to the point of their being large gaps between the side and my mold especially at the bottom and top bouts with the spreaders in....as can be seen in the photos..I'm a bit hessitant to just try and clamp it to mold in these areas for fear of breaking the side.

i was using a blanket and found a lot of resistance to getting it into the bend ....the waist went to the form fairly easy but the top bout i had to put a lot of weight behind it to get it into position...which was fairly stressful....and seemed to take a lot longer than what i've read about blankets..I thinned the side out to around .085"-.090" ...

I'm just wondering what people do to get their sides snug against their mold once they've taken it off the bending form?

are my sides still to thick if they offer to much resistance when bending?

and is the cupping because of to much water? I sprayed the side to the point of it dripping wet and waited till it stopped dripping before wrapped in alfoil.

overall I'm very happy with the first attempt....just wondering what i can do to minimise springback and get it snug against the form.
cheers and thanks for any advice






Author:  John Mayes [ Sun Feb 18, 2007 4:03 pm ]
Post subject: 
You want the side to fit into the mold as good as possible. While it is easy
to press the side to shape and glue the blocks in that creates internal stress.
I think the issue is either your mold did not match up just right with your
form, or the wood was not cooked hot enough to set the bend. Never the
less what you have WILL work. Nice job for your first time bending.
Author:  gratay [ Sun Feb 18, 2007 4:29 pm ]
Post subject: 
[QUOTE=John Mayes] You want the side to fit into the mold as good as possible. While it is easy
to press the side to shape and glue the blocks in that creates internal stress.
I think the issue is either your mold did not match up just right with your
form, or the wood was not cooked hot enough to set the bend. Never the
less what you have WILL work. Nice job for your first time bending.[/QUOTE]
Thanks for your reply John......My mold is exactly the same shape as the bending form other than being offset 3mm to allow for the thickness of slats and blanket....
quite possibly not cooked enough.....I haven't got a temperature control only a thermometer to gauge things so there was a lot of switching the blanket on and off ......
i guess i can always put it back on the form and cook it some more .....hopefully that will work?

I was finding that depending where i placed the thermometer was a big difference in temp...i placed the thermometer under the timber to make sure that the temp of the timber was getting up there but the temp on top was over 100 degrees hotter....so I don't know what to do about that situation....
cheers
Author:  John Mayes [ Sun Feb 18, 2007 5:00 pm ]
Post subject: 
While cooking it again it will set the bend a little better, it makes the wood
more brittle, but maybe not so much to really have much of an adverse
effect so maybe it's worth a shot. You wanna keep it around 300 degrees
for about 5 minutes (but remember to wet the wood again before cooking or
else you will scorch it)
Author:  John Mayes [ Sun Feb 18, 2007 5:03 pm ]
Post subject: 
oh I just also realized where the springback is..I always offset the butt end of
the guitar way more than the rest. the butt end tapers in on my molds
about a half inch as springback is the worst in that area.
Author:  Martin Turner [ Sun Feb 18, 2007 9:19 pm ]
Post subject: 
Grant,

Glad to see youve finally taken the plunge and joined the esteemed League of Sidebenders.

If youre anywhere near Adelaide then drop in with those sides and well have a session on the bending iron to get the sides fitting the mould like a glove.

Hot here in Adelaide but nothing a few beers wont fix

Cheers Martin
Author:  KiwiCraig [ Sun Feb 18, 2007 9:52 pm ]
Post subject: 

Hi Grant,
           Hey I snapped my first side , and scorched the next ! At least you haven't done that ,so don't feel too bad . Like John, I have adjusted my bending form to overbend the wood slightly on the lower bout and the upper . Also just a hint in the waist .
As Martin said ,the hot pipe would fix it up . Good to learn how to do it anyway , as you'll probably need the experience for future builds ( cutaways etc.)
Practice on scrap first ~! . Well done mate , your on your way .
Author:  Irwin R [ Mon Feb 19, 2007 1:07 am ]
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Great job Grant , I just cracked my 2nd side on my #2..and had to order another set..must be a great feeling to get both sides done!!My inexperience doesn't tell me what shape your baby is ...OM?...nice mold..
Author:  Bruce Dickey [ Mon Feb 19, 2007 2:11 am ]
Post subject: 
Grant, Great job, looking like half a guitar there. Congratulations.

I take my molds in at the butt in as well. The way you determine how much is to bend a few with it the precise size as you have and see how much springback you have. John takes his in 1/2 inch, I do mine at 3/8". So in MM's around 10 to 13 mm would be about right. A lot of folks leave 'em full and it seems to work as well for them.

Good luck on the "other side".
Author:  Bruce Dickey [ Mon Feb 19, 2007 2:13 am ]
Post subject: 
Edit: That should say, "I take my BENDING molds in as well."

(that makes a difference which mold, bending or outside)
Author:  crazymanmichael [ Mon Feb 19, 2007 2:24 am ]
Post subject: 
it sounds like a combination of too little heat and not enough over bend at the lower extremity of the bout.

too little heat because eir is an easy wood to bend and your finding the need to use a lot of force is totally untypical.

you really need to have some other method of heat control than simply turning off and on. a heavy duty dimmer, a router speed controller or a variac will all work well. the problem is a heating blanket will readily get too hot and scorch wood. you need to be able to get it to bending temp and hold it there for a while.

as others have said, the mold should over bend the lower 1/3 or so of the bout and 13mm/1/2" is about right.
Author:  bob_connor [ Mon Feb 19, 2007 8:31 am ]
Post subject: 
Hi Grant

Looking good mate.

I got a motor speed controller from Dick Smiths.

Cost about $130 but was in a kit form.

Luckily I teach at the TAFE here in Geelong so I got some of the electronic students to assemble it. (cost me a slab)

If you've done any soldering before you should be able to do it yourself.

I had a lot of trouble finding anything else in Oz to do the job but it certainly makes bending them sides easier.

Timbecon were advertising one for about $80 assembled and I ordered one but their supplier pulled out of the deal. It might be worth keeping an eye on their website in case they find another supplier.

If you decide to get one of the Dick Smith ones get in touch with me. I seem to remember that one of the teachers made some modifications to the assembly as one of the components ran quite hot so they lifted it up from the PCB to give it a bit more airflow.

Cheers

Bob

Author:  gratay [ Mon Feb 19, 2007 12:25 pm ]
Post subject: 
cheers guys thanks for the info.
I did a lot of reading on the forum about the bending form before i built it but didn't read or take into account building an overbend into the form....I just offset it....you live and learn...i can modify it I guess.

Bob....I have seen the dick smith motor controller and i wasn't sure if it would handle the wattage ..but sounds like it does...so I might get in touch with you to find to modification for the heat problem on the PCB...that would be great.And yes I to have been searching around for something that will work but 220v isn't easy unless your willing to spend big dollars....if we we're 110v in this country would be no problem..

Irwin.....yes its an OM from the LMI plans..the mold is basically the same idea as robbie o'briens DVD...

Martin.... I would take you up on that offer if it wasn't 800km's between where we live.....and yes the heat got to me also on the weekend ...38 and 39 in melbourne....so what do i do ..decide to stress out hovering over a heat blanket....you gotta earn that cold beer I guess.
and thanks for all the help from everyone else.
Author:  crazymanmichael [ Mon Feb 19, 2007 1:37 pm ]
Post subject: 
grant, 220 variacs are often available on ebay for anywhere from us$10 to us$45. variacs, well actually powerstats, but the same thing only different brand, are what i use and they work very well.
Author:  crazymanmichael [ Mon Feb 19, 2007 1:48 pm ]
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oh, i wish we still had our edit buttons. this is the sort of thing i referred to above:

   http://cgi.ebay.com/VARIAC-POWERSTAT-25AMP -250V-NO-RESERVE_W0QQitemZ270090626772QQihZ017QQcategoryZ731 53QQrdZ1QQcmdZViewItem

this one would control two blankets with headroom aplenty.
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