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I’m making a bow – would anyone like to watch?
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whatwasithinking
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Joined: 26 Jan 2013
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PostPosted: Mon May 13, 2013 11:33 am    Post subject: Reply with quote

I wish there was some kind of definitive "best practice." There are many methods, and they all seem to work for the makers who use them. I quickly reviewed a number of sources, and summarized what I noticed:



W.C. Retford speaks of a bunsen burner, although it is known that a heat gun was eventually widely used at Hill and Sons during the 20th Century. He says not to wear gloves, evidently to aid in sensing the temperature of the wood. He also says to avoid the blue part of the flame. Other makers clearly wear gloves. One maker told me that the ideal temperature for a heat gun is 642 degrees F. That may have come from some IPCI papers. If you look at Robert Morrow's blog, you'll see an example of a beautiful piece of Pernambuco that simply snapped during cambering, with no obvious cause. Stuff happens.
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Janito
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PostPosted: Mon May 13, 2013 9:16 pm    Post subject: Reply with quote

whatwasithinking wrote:
I quickly reviewed a number of sources, and summarized what I noticed:


Don't forget Regh's pressure cooker.

Surely the important thing is to understand the 'intent' behind a particular method.

For example, the difference in the heating tools used may relate to the thickness of the wood at the time of cambering.

Disclaimer - I know little, but I spent 3 years close to a maker in the UK.
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whatwasithinking
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PostPosted: Mon May 13, 2013 11:40 pm    Post subject: Reply with quote

There's no doubt a lot more going on than I could observe, in many of the sources I looked at. e.g., perhaps most of the makers speed up the motion of the stick as it heats up--at least it seems reasonable. The video of Lev Sobol is unique in many respects. He uses a machine to shape the stick, and then he attaches a cambered metal jig of some kind to the stick before heating it. I'd kind of expected to see the French-method makers using mostly alcohol flames, but that's clearly not the case. They use a variety of heat sources. A lot of the European makers seem to use bunsen burners, but I don't really know whether they're using natural gas, butane, or possibly propane. One shop--Raffin, I believe--evidenced both bunsen burners and alcohol flames. I guess it must depend on the particular maker, or perhaps the task. So far, I've only used a heat gun, but I still have a lot to learn...
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Mat Roop
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PostPosted: Mon May 13, 2013 11:55 pm    Post subject: Reply with quote

Janito wrote:
whatwasithinking wrote:
I quickly reviewed a number of sources, and summarized what I noticed:


Don't forget Regh's pressure cooker.

Surely the important thing is to understand the 'intent' behind a particular method.

For example, the difference in the heating tools used may relate to the thickness of the wood at the time of cambering.

Disclaimer - I know little, but I spent 3 years close to a maker in the UK.


Janito, Do you know what pressure he sets the cooker for?
Thanks, Mat
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Andres Sender
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PostPosted: Tue May 14, 2013 1:10 am    Post subject: Reply with quote

whatwasithinking--I think Janito's point about intent is the key here.

Regardless of what tool you use, there are things which need to happen to the wood, and things which need to not happen, and how you use the tool is what gets you there.

Using any of the usual methods requires the kind of skill that is ultimately built on trial and error, even for people with access to a teacher. Cambering is probably the arch example of this since it's all about feel and timing.
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Ed Shillitoe
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PostPosted: Wed May 15, 2013 9:23 am    Post subject: Reply with quote

How do you get a bow into a pressure cooker?
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ctviolin
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PostPosted: Wed May 15, 2013 9:40 am    Post subject: Reply with quote

Ed Shillitoe wrote:
How do you get a bow into a pressure cooker?



Mislead it by sweet-talking it?
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Janito
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PostPosted: Sun May 19, 2013 9:42 am    Post subject: Reply with quote

Mat Roop wrote:


Janito, Do you know what pressure he sets the cooker for?
Thanks, Mat


Kun & Regh - Fig 31
280 Celsius for 20-25 min. No pressure - that was my artistic license (it does look like a P cooker).

Comment in book: "Be mindful, though, that 280 Celsius can turn Pernambuco into charcoal".
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Mat Roop
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PostPosted: Mon May 20, 2013 9:53 am    Post subject: Reply with quote

Janito wrote:
Mat Roop wrote:


Janito, Do you know what pressure he sets the cooker for?
Thanks, Mat


Kun & Regh - Fig 31
280 Celsius for 20-25 min. No pressure - that was my artistic license (it does look like a P cooker).

Comment in book: "Be mindful, though, that 280 Celsius can turn Pernambuco into charcoal".


well, the pressure cooker conjured a vision as to how it might work... With the pressure full up, and open vent, then the hot escaping and blasting vapour would do the work of heating the stick with no burning. Sort of like using a flame but no flame... I'll have to try it.
BTW... I don't have the Kun & Regh book... is an image of Fig 31 available anywhere ( without buying the book)?
thanks... Mat
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ctviolin
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PostPosted: Mon May 27, 2013 11:30 am    Post subject: Reply with quote

Mat Roop wrote:


I don't have the Kun & Regh book... is an image of Fig 31 available anywhere ( without buying the book)?
thanks... Mat




Ok, Mat, here's the photo you asked for. It's black and white and quite non-distinct in the book also.

http://www.flickr.com/photos/85680750@N05/8852854099/sizes/l/in/photostream/

ct

(BTW, sorry about having to post links - I still have not put in the hours necessary to decrypt things on the flickr site yet... <G>...)
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wm_crash
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PostPosted: Mon May 27, 2013 1:49 pm    Post subject: Reply with quote

Seems like a steam bending type of approach. I like that, since it's a lot closer to "generic" woodworking - even if it's somewhat niche if you're splitting hairs.

cheers,
wm_crash, the friendly hooligan
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ctviolin
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PostPosted: Mon May 27, 2013 3:38 pm    Post subject: Reply with quote

wm_crash wrote:
Seems like a steam bending type of approach. I like that, since it's a lot closer to "generic" woodworking - even if it's somewhat niche if you're splitting hairs.

cheers,
wm_crash, the friendly hooligan


wm,

you've got it! splitting hairs is one of our "things".

ct
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Last edited by ctviolin on Mon May 27, 2013 9:45 pm; edited 1 time in total
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Mat Roop
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PostPosted: Mon May 27, 2013 8:06 pm    Post subject: Reply with quote

ctviolin wrote:
Mat Roop wrote:


I don't have the Kun & Regh book... is an image of Fig 31 available anywhere ( without buying the book)?
thanks... Mat




Ok, Mat, here's the photo you asked for. It's black and white and quite non-distinct in the book also.

http://www.flickr.com/photos/85680750@N05/8852854099/sizes/l/in/photostream/

ct

(BTW, sorry about having to post links - I still have not put in the hours necessary to decrypt things on the flickr site yet... <G>...)


Thanks CT... greatly appreciated. I considered the purchase of the Regh books... expensive!
Looks like a pretty expensive setup.
I am going to try the standard pressure cooker (...provided I get permission from the cook!) using the escaping steam from the vent.
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wm_crash
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PostPosted: Mon May 27, 2013 11:10 pm    Post subject: Reply with quote

I am still trying to figure out if the pressure cooker method uses steam inside or just dry heat. The text around the figure doesn't quite jive with a steam bending approach (e.g. 280C temperature), but my mind naturally associates bending with steam. Steam bending does give rise to all sorts of springbacks and gotchas - that'd be fine fine for Windsor chair armrests, not so much for bows.

But as far as reproducing the approach in the book . . . .

If it's dry heat, I guess a grill on low heat may do the job. Maybe even an oven.

If it's a steam bending jig, the cooker is just a holder for hot steam - granted the steam gets hotter than in a non pressurized box. To that effect, there are quite a few DIY and affordable commercial options (most of them really being just a wallpaper steamer with an attachment for the steam box - see Woodcraft or Rockler).

cheers,
wm_crash, the friendly hooligan
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Mat Roop
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PostPosted: Mon Jun 10, 2013 4:59 pm    Post subject: Reply with quote

Mat Roop wrote:
...well, the pressure cooker conjured a vision as to how it might work... With the pressure full up, and open vent, then the hot escaping and blasting vapour would do the work of heating the stick with no burning. Sort of like using a flame but no flame... I'll have to try it....


Well I tried the pressure cooker today.... It does not work at all... the problem is the bow gets wet and as you heat one spot the other cools real quick... and the heat does not rise much above boiling.
Ah well, another great idea to the trash heap!
Cheers, Mat
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