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I recently purchased a "new" wood violin bow on eBay with a broken tip. I easily repaired the cracked wood using super glue and a short segment of 4.5 mm diameter carbon fiber rod bored perpendicular to the crack.
Once assembled, I noticed that the stick has a slight twist and the hair is not properly aligned. I went to Youtube and noticed that bow makers set the camber of the stick by heating it with an alcohol flame. I think that I can do this to remove the twist, and since I only paid $12 for the bow I can be pretty brave in the attempt. However, I don't want to do a lot of varnish refinishing (assuming success) if I can avoid it. I saw a Youtube video where the varnish was covered with a anti-oxident coating before the flame was used on it, but naturally the material was a trade secret and I don't know what the material was. I hate videos like that.
My first thought is to use a silicone grease since it is stable to about 800 F and the wood becomes limber at about 330 F. I also have a anti-sputter paste that is used on mig welders to protect the electrode that may also work. I have no idea on how to remove these materials from the stick, but Simple Green is my guess. Any suggestions, particularly those having previous successful experience, would be appreciated.
I got some more information. I received a PM from someone that took a bow making and restoration class which "used a brown block of something that looked like buffing compound to run on the stick to protect the varnish during bending and cambering." She gave me the instructor's name and I sent an email today. I will report back if I hear anything.
I figured that it was time to do some experimentation with fire.
I purchased a dual wick alcohol burner from Amazon (wicks are covered with copper tube which produces a lot more heat than the conventional wick alcohol lamps I have used in the past).
The test wood violin bow was an inexpensive one I got from eBay because it had a broken tip. Varnish of unknown variety. I coiled the hair at tip end to keep it from the flame.
The first material I tried was Dow Corning #4 Electrical Insulation Compound. This is a non drying silicone grease that is NSF approved (you can use it on food processing equipment). I applied a light coating on the bow shaft with my fingers and subjected the shaft to about 3 minutes of flame, keeping the shaft in the flame (above the flame is hotter) and kept moving and rotating the shaft. I noticed a slight amount of bubbling of the coating in spots. Removed coating with paper towel. No damage to varnish was noted.
The second material I tried was NAPA Sil-Glyde #76-1351. It has a stated working temperature range of -20 F to 600 F. Same procedure as above. No bubbling of coating was noted. No damage to varnish was noted but the grease took longer to remove. This material is heavier than the Dow Corning #4 and forms a thicker layer.
The third material I tried was Forney MIG Gun and Contact Tip Nozzle Gel #37031. Same procedure as above. After about 30 second within alcohol flame, the coating started to smoke. The varnish was obvious tacky and stuck to paper towel.
I think that the original material I saw was a high molecular weight paraffin wax used to lessen friction on band saw blades. I have a tube of that coming to test.
The NAPA Sil-Glyde looks promising, but I would not try it on an expensive bow unless you practiced a lot on cheap ones first.
Hello Steveduf (and others). I believe that the material originally used was a high temperature paraffin wax used to lubricate band saws. I was never successful in obtaining some to experiment.
I have now used the NAPA Sila Glyde several times on different bows and I am very happy with it. I believe that it is a better material than the high temperature paraffin wax because it will not ignite. It is much easier to heat the bow if the hair has been previously removed. Keep the alcohol flame moving along the portion of the stick to be bent and keep the bow within the flame, not on top of it. I remove the silicone grease with paper towels.
Hi steveduf (and others). I have had more problems with twisted sticks than with flat ones. The wood does get hot (I would say about 300 F but I have not verified that with an infrared thermometer) and it is helpful to wear leather gloves (similar to TIG welding gloves). If you want to recamber a bow, it is helpful to make a wood template of the profile of a known good bow as a guide. The treated bow is heated in 4" to 6" sections and bent over a piece of wood (like the edge of a wood table). The stick is resilient and you will find that you have to subject it to more of a bend than you need because it wants to straighten itself.
When I want to untwist a bow tip back to 90 degrees I heat up about the last foot of the bow, hold the tip and frog end, and twist it back about 20 degrees more than I ultimately want, hold it there for about 30 seconds, release and look down bow to see if I have what I want. It does not seem to cause a problem if you need to repeat the process for small corrections.
There are several Youtube videos on how to put a camber in a bow (they seem to be all straight sticks in the beginning and a shape is put into them by heating with an alcohol lamp). But all of the videos are on new bows before varnish except for the one by Daniels, and he is using what I think is high temperature paraffin to protect the varnish. I found the person he got the material from but I have not been able to get in contact with her.
I think that she must have seen my thread here on the possibility of putting boric acid in violin rosin to prevent bow hair bugs, and shared the horror that affected the other members of this community.
I believe that making small corrections in the camber of a bow is a relatively standard practice of luthiers when they rehair a bow so they must be using something to protect varnish, but I have not been able to find an protective material being sold "in the trade." So I did my own experiments.
Hi Steveduf (and others). Have you attempted to recamber a bow yet? I remembered that Fiddlerman stated that luthiers often rub the bow shaft wrapped in a towel to achieve the heat by friction necessary to recamber a bow (cited earlier in this thread). It may also be possible to obtain the necessary heat (without inducing varnish damage) by the use of a hot air gun.
We just got back from my daughters wedding. Mackenzie also plays travel softball and we’ve been traveling for that,
i amtomorrow going to NAPA to pick up Silas Glide and we will be giving this a whirl.
i own a couple nice heat guns that I’m going to try also. I was also wondering if one of the hot boxes plumbers use to bend pvc is too crude.
we are going to start rehairing bows also.
PVC gets soft at about 160 F (CPVC at a slightly higher temperature), so I don't think that a plumber's hot box is going to get hot enough (although I don't have one to experiment with). I think that you will need about 300 F to 350 F.
The gold standard for this work is an alcohol lamp, and they can be purchased for about $10 (or make your own with a $1 cotton wick). Keep the stick in the flame and not above it.
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