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I’m making a bow – would anyone like to watch?
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Mat Roop
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Joined: 24 Mar 2007
Posts: 911
Location: Wyoming Ontario

PostPosted: Fri Apr 26, 2013 10:56 pm    Post subject: Reply with quote

Ed Shillitoe wrote:
.... Or will I lose so much wood from the kerf and from having to plane it straight again that I will end up with no stick at all?....

Ed, if the stick twists... why can you not simply twist it back with an application of heat same as when you camber??

I have not made any bows, but I do repair a fair number and recambering and untwisting of finished old bows is not uncommon for me.
Thanks... Mat
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Ed Shillitoe
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Location: Syracuse NY

PostPosted: Sat Apr 27, 2013 8:17 am    Post subject: Reply with quote

Matt: I'm sure it is possible to straighten out the bow when it is cambered, but I like to make the smallest possible bends under the heat. I'm afraid of introducing some tension in the stick which would gradually relieve itself over time, leading to it warping later. Maybe these are the bows that you have to repair!

Other people do it differently. If you look in the recent Strad magazine there was an article from the Philip Brown shop in England where they cut out the stick following the grain lines, even if these are very wavy, and then straighten out the wavy looking stick in the heat. It looks a little strange to me but evidently works for them.

And again, the cost of the wood figures into this. If I had bought a stick of very nice looking pernambuco for 150 dollars I might be willing to spend time getting it straight. If I have a piece of bloodwood that cost 3 dollars I would be quicker to add it to the scrap pile and start again!
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Mat Roop
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Location: Wyoming Ontario

PostPosted: Sat Apr 27, 2013 9:09 am    Post subject: Reply with quote

Ed Shillitoe wrote:
..... Maybe these are the bows that you have to repair!.....

Hi Ed... Never thought of it that way! Hope I don't lose any business now Smile
I saw that article from Philip Brown... and my immediate reaction was that straightening that bow would be a significant time consuming task, but in the end having no grain runout is a plus.
Thanks Ed... love your posts... Mat
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Ed Shillitoe
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PostPosted: Mon Apr 29, 2013 6:42 pm    Post subject: Reply with quote

Now it’s time to camber the sticks. The heat source a couple of hundred years ago was a pot of burning charcoal. According to Mr. Bolander, the bowmaker held the stick over the pot and controlled the temperature by blowing on the coals. More recently makers have used an alcohol lamp. Some use an electric heatgun. Obviously the actual heat source does not matter very much. I use an electric hotplate turned up to its maximum heat. I don’t know how hot that is, but it is not red hot. I use the same hot plate at 1/3 maximum to heat hide glue to 140 degrees F, if that means anything. I heat the stick by holding it 6 inches above the hotplate moving it left and right by a distance of 3 inches each way every 30 seconds while rotating it at a rate on one turn for every 20 seconds. Actually I’ve never measured these times before but with this stick I did in case anyone asked! If the stick can be held comfortably in the bare hand for 2 and a half seconds it is too cold. If it catches fire it is too hot. What is really necessary is that it is kept at maximum temperature for long enough. I use 10 minutes. Wood is a poor conductor of heat and unless the interior is up to temperature it will still be under tension after the stick is bent and the camber might not last. I don’t actually know the velocity of heat in wood but if I did I suppose I could find out if 10 minutes is really enough. For a thin stick, such as when correcting a warp in a finished bow, less time is necessary.



When time is up I press the stick down on a curved block, and you can feel the wood stretching into a new shape quite easily if it has been heated enough. I don’t’ try to press it into any particular curve – I just curve it as much as possible. I hold it in place for about 10 seconds then quickly lift it up and look along it to see if it has curved left or right. Then I put it back on the block, pressing at a slightly different angle if I have to correct any such bend. I hold it in place for about a minute.



This produces a curve covering most of the heated area of the stick. Then I go back to the hot plate and repeat the process with the adjacent 8 inches or so. After doing this about 5 time there is a continuous bend all along the stick, but not necessarily very even. I hold the bent stick against the template for the camber and note where it needs adjustment. Then I heat that part and bend it again. This seems to be one of the few parts of bow making where you can just do it again and again until you get it right.

In fact even when the cambering is finished it is usually not entirely perfect and the stick is not completely straight, but final adjustments can be made by planing the stick down a bit more. Experience shows how close to perfect it needs to be at this point. I then put the sticks aside for a few days or weeks and come back to work on them later. The camber might change a little in that time, or maybe my standards drop after an hour or two of bending and I can’t see the errors anymore!

Here is one of the current sticks after the first set of bends – it has quite a good curve at the head but needs more down at the handle end. It’s always easier to get a curve at the head end since the wood is thinner there.



And here they both are, with the top one seeming to match the template quite well, but with the lower one needing a little more work. You can see that this is not the modern type of camber – there is more of a bend in the center and very little up toward the head. Some bows of the seventeen hundreds actually have a reverse camber near the head, especially when they are tightened up. Many bows from the early 19th century have been recambered to suit the twentieth century concept of how the camber should be.



And here’s the longways view. Not too good! I’ve managed to get a good sweep to the camber on both bows and to keep them straight, but they both rotated about 20 degrees clockwise at the end! For the thicker bow this is not a problem since I can just plane it square again – firstly on the sides and top and bottom to make them even and at 90 degrees to each other, then the octagonal facets as before. But for the skinny one I don’t have a lot of spare to play with.



I will know better what to do when the screw hole has been drilled as this defines the center of the stick. If the hole is off a little then one side of the stick has to be planed away to compensate. If that makes the stick too thin then I think I will use it to make a more modern bow - they are a couple of mm thinner at the handle end. So, I will start the screw holes before doing any more work on these particular sticks.
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whatwasithinking
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Joined: 26 Jan 2013
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PostPosted: Mon Apr 29, 2013 8:15 pm    Post subject: Reply with quote

Really interesting, Ed. Something I've wondered a lot about is how to avoid causing problems by reheating partially-cooled wood while bending. I know that Bolander discusses this, and I've seen remarks by other makers as well. If I have any doubts, I simply put the stick down for an hour or so before heating it up again, but maybe that's overly cautious. OTOH, I have yet to break a stick--knock on pernambuco. I have also only done this with existing bows, though--not new sticks. So if I'm moving down the stick, heating one section at a time, does that present a risk to the previously-heated section? Do you let the stick rest sometimes between bends, for this reason?

Bob
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Ed Shillitoe
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PostPosted: Tue Apr 30, 2013 8:37 pm    Post subject: Reply with quote

Good question Bob, and indeed there is a school of thought that says you should let the stick cool down completely before heating it up again. I've never heard a reasonable explanation of why that should be so. I've also been taught that to make tea you start with cold water and heat it up - you don't start with warm water. And you add the hot tea to the cold milk - not the cold milk to the hot tea. I don't know the theory behind this either! So the short answer is no, I don't let the stick cool down before moving to the next section. If anyone has more information I hope they will chime in!
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ctviolin
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PostPosted: Tue Apr 30, 2013 9:36 pm    Post subject: Reply with quote

Still here, still following, still pluged in.

So far, Ed, I love this demonstration. Two human hands and some bow wood - and a bow (well two, really) is being made...
This is more like it, though I suppose could be following the Kun and Regh book - but I believe it would be another additional six months or a year of jig building, first.

Hmmm, what to do... what to do...?

Today it was 95 degrees here, so the wife and I planted the first real summer yard (many flowers - many vegetables) all day. It was a really beautiful - hot - summer NM day out. The kind I love to bake in.

Tomorrow is an early dialysis (5:30 am) - then an afternoon doctors appointment, then the next day is a normal crap day - chores, then some free shop time...


So, I hope to be caught up then, and can post a 'nother photo of my progress.

once again, thanks for doing this

ct
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Last edited by ctviolin on Tue Apr 30, 2013 10:08 pm; edited 1 time in total
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ctviolin
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PostPosted: Tue Apr 30, 2013 10:06 pm    Post subject: Reply with quote


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wm_crash
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PostPosted: Tue May 07, 2013 4:26 pm    Post subject: Reply with quote

Well, I gave it all I had:









In the end, a combination of bad grain runout and me being heavy handed put an end to the first bow. I was also very surprised to see how in the process of bending, a rather severe sideways kink developed. Just in case, the wood was bubinga.

I'll try it again in a few weeks after I am done with the wife's storage bench.

cheers,
wm_crash, the friendly hooligan
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Ed Shillitoe
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PostPosted: Tue May 07, 2013 7:35 pm    Post subject: Reply with quote

Too bad! And it was looking so nice!

Maybe bubinga is not a good bow wood? I've used it for a small table and it really makes the tools dull quickly. But you had a nice curve before it broke!

Try again!!
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whatwasithinking
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PostPosted: Tue May 07, 2013 8:00 pm    Post subject: Reply with quote

Thanks for being willing to share--even when things don't go as planned. What kind of heat source are you using? --not that there are good ones or bad ones. A luthier recently asked me what temperature I was getting out of my heat gun at the surface of the wood. I don't really know.
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Ed Shillitoe
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PostPosted: Tue May 07, 2013 9:39 pm    Post subject: Reply with quote

I really don't know how hot my hot plate gets - you can see it in the pictures and its just something that is used for boiling water really. It does not get red hot so it is not as hot as a stove top.

Your pictures seem to show some scorch marks on the wood which means you must have been getting it about as hot as possible. The only other thing you could do is perhaps keep it hotter for longer so that the inside is as hot as the outside. But I don't know how long that would take either! There's a lot of unknowns in bow making!

I suspect you had a bad piece of wood - I think I would try something different next time. I like bloodwood.

How long did it take you to get that far? Probably not too long - so its a faster learning curve than violin making.
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wm_crash
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PostPosted: Tue May 07, 2013 10:47 pm    Post subject: Reply with quote

I admit that I was a bit stoked and rushed through the cambering part. I used the stove and heck, I put that thing right through the flame. It was HOT. I was well aware of the scorching, but I didn't care for the burn marks. Apparently, there is more to overheating than just burn marks.

The other reason I went with such a hot heat source is I didn't expect the wood to become so limp. I wanted to make sure I am able to bend it. I used Reid Hudson's method of freehand bending (as in http://www.youtube.com/watch?v=JgHkCordNo0 ) so I figured I'd need the stick a bit more flexible than if I had used some sort of bending block.

It took me about 5 hours over a one week period. I spent a good deal of time messing with cabinet scrapers. I had this personal theory that cabinet scrapers would work better than block planes (they don't) in getting the square shape. They do a great job on cleaning up the octagon though.

I have 3 more bubinga billets already prepared just in case I make mistakes. I just checked them and they seem to have at least one good side that could become the tip of a bow. I'll give them a fair chance knowing that maybe they're just not meant to be violin bows.

Bubinga is indeed very hard on tools, and it will immediately punish you for misreading the grain direction. Incidentally, that was also the reason is was initially leaning towards the use of cabinet scrapers just so I don't have to pay too close attention to grain.

cheers,
wm_crash, the friendly hooligan
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Janito
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PostPosted: Sun May 12, 2013 9:10 pm    Post subject: Reply with quote

wm_crash wrote:
I admit that I was a bit stoked and rushed through the cambering part. I used the stove and heck, I put that thing right through the flame. It was HOT. I was well aware of the scorching, but I didn't care for the burn marks. Apparently, there is more to overheating than just burn marks.


Have you not seen the Thanksgiving turkey that's scorched on the outside and raw inside.

The key to heating the wood is to use a source that allows the inside of the stick to get as hot as the outside with no scorching. Heat small sections and move the wood against the caul gently.

I copied my teacher's old electric bar heater with the wire guard removed - a hot plate also works well, as Ed shows.
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Chet Bishop
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PostPosted: Mon May 13, 2013 9:09 am    Post subject: Reply with quote

For what it is worth: Lynn Hannings uses the alcohol lamp, as do the French traditional bowmakers.

It strikes me that one potential advantage to using the alcohol flame (over electric heat) is that the there is a great deal of water vapor in the flame. As a hydrocarbon is oxidized, it produces Carbon dioxide and water as byproducts of the desired heat. Possibly the water vapor in the flame is a help, I don't know. I think the electric hotplate is a good idea, but I have no experience with it.

The flame of alcohol is not as hot as that of propane (I think), so that may be an added benefit. I have used the alcohol flame this way myself, in recambering bows and in cambering a new bow; it seemed to work well enough that I did not have any problems. Maybe I have just been lucky.
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