Andy Holder Posted January 6, 2012 Share Posted January 6, 2012 I recall a recent discussion about making screws for straps. Here's my first attempt (well actually, the second, the first one exploded!) I needed extra long threads as the first thumbstraps I've made are a bit thick and normal screws won't reach. I got some lovely brass cheese head screws from ebay with a 6BA thread. Here are the bolts The heads are very sharply cylindrical so my first thought was to drill a blind, flat bottomed hole with a milling cutter and set the heads in very tightly, then silver solder. BAD MISTAKE! The watery flux paste must have created steam and, because it was such a tight fit, it took a little heating with the torch before it exploded loudly and shot the red-hot head across the workshop like a bullet! Pretty stupid idea really. Then I thought that the blind hole idea was an unnecessary complication if I wanted to make more, just for the sake of a clean top. In practice, a through hole is barely noticeable. Consider the difficulties. I wanted to end up with 3 mm thick heads. There is no way of holding this in the average lathe chuck to do the faces. Also, how on earth could I do the knurling round the edge? You can't hold it by the screw because the knurling tool applies so much sideways force. Here are the steps I did, there may well be a better way but this seemed to work quite well with a low-tech hobbyists lathe. 1. Put a short piece (2") of 3/4" brass rod in the chuck. 2. Knurl the last 1/4" of it 3. Face the end and bevel the corner 4. Drill into the end about 1/4" deep 5. Hacksaw a little more than the required thickness off. This is the head! 6. Tap the hole (6BA in my case) 7. Saw the head off the bolt and coat the end of it and the threaded hole with flux. 8. Screw it into the head so it just protrudes through the rough side. The smooth side is now the underneath of the head. 9. Hold the end of the screw in the chuck or a vice, not too much, don't want a heat sink 10. Heat with a gas torch until cherry red, then apply silver solder sparingly to both sides of the joint 11. When cool, push the screw right into the chuck and tighten 12. Very carefully, in small passes, face off the end and bevel the corner.(There's a lot of pressure on that bolt!) 13. Take off protective clothing, ear defenders, safety goggles and have a stiff drink! I then polished the head with various grades of lapping film (in my other life I polish optical connectors) I use 40 micron then 15, then 5, then 1. It's available from Workshop Heaven. They are obviously still much too long, I need to trim them, but I think they're good enough for the Wheatstone. Hope you like the result. Did you see how I used the old fashioned measurements for our American cousins? Andy Link to comment Share on other sites More sharing options...
SteveS Posted January 6, 2012 Share Posted January 6, 2012 (edited) Nice job!! It looks terrific. Edited January 6, 2012 by SteveS Link to comment Share on other sites More sharing options...
Andy Holder Posted January 6, 2012 Author Share Posted January 6, 2012 Nice job!! It looks terrific. Thanks Steve. Link to comment Share on other sites More sharing options...
varney Posted January 6, 2012 Share Posted January 6, 2012 Hey Andy, lovely work! You're certainly coming up with some great results on both this and your french polishing ( which I have yet to attempt, though I now have the pigment ). One thing - does 'silver soldering' require oxy-acetylene? I believe it does, so this and the necessary lathe leaves me out of having a go! ( oh yeah... and the knurling tool...) Your step by step instructions were great though, and really explain the procedure well. Keep up the great work! Michael. Link to comment Share on other sites More sharing options...
Andy Holder Posted January 6, 2012 Author Share Posted January 6, 2012 Hi Michael. Thanks for that. I just use a plumbing blowlamp with propane. With something this small it doesn't take long to heat it to a dull cherry red. A small nozzle helps. I'm afraid a lathe is probably a must for the knurling, unless you were to go round the edge and cut tiny slots with a Dremel. The knurling tool I use is a very cheap thing, not terribly good actually, but it is a couple of wheels on a sort of scissor mount that just clamps into the tool post. Just like this one: Here Andy Link to comment Share on other sites More sharing options...
JimLucas Posted January 6, 2012 Share Posted January 6, 2012 I love the photo. Size comparison leaves me wondering whether you could use the 5p coin as a screw head. Then you wouldn't have to worry about knurling, though avoiding damage to the coin's surface relief would surely be a much more difficult task. Link to comment Share on other sites More sharing options...
Andy Holder Posted January 7, 2012 Author Share Posted January 7, 2012 I love the photo. Size comparison leaves me wondering whether you could use the 5p coin as a screw head. Then you wouldn't have to worry about knurling, though avoiding damage to the coin's surface relief would surely be a much more difficult task. Thank you Jim. Could make a range of "novelty screws" I suppose! Otherwise, I'm not sure how you'd flatten the face. Oh, and of course, I think it is treason to deface a coin of the realm, mind you, they probably have excellent facilities in the prison workshop Andrew Link to comment Share on other sites More sharing options...
Chris Ghent Posted January 8, 2012 Share Posted January 8, 2012 I love the photo. Size comparison leaves me wondering whether you could use the 5p coin as a screw head. Then you wouldn't have to worry about knurling, though avoiding damage to the coin's surface relief would surely be a much more difficult task. The late Pierre Hooft used to do exactly that to make his thumbscrews, though he would file off the relief design. He was just using the coin as stock. If you have the thing on a lathe to knurl it, why not just chuck a piece of 1/2" brass rod and make the screw in one piece? It takes less than 10 minutes per screw. Chris Link to comment Share on other sites More sharing options...
Andy Holder Posted January 9, 2012 Author Share Posted January 9, 2012 I love the photo. Size comparison leaves me wondering whether you could use the 5p coin as a screw head. Then you wouldn't have to worry about knurling, though avoiding damage to the coin's surface relief would surely be a much more difficult task. The late Pierre Hooft used to do exactly that to make his thumbscrews, though he would file off the relief design. He was just using the coin as stock. If you have the thing on a lathe to knurl it, why not just chuck a piece of 1/2" brass rod and make the screw in one piece? It takes less than 10 minutes per screw. Chris You're right Chris, but I didn't have a 6BA die! Just had the taps. Also, I'm not sure how easy it is to cut a thread right up to the shoulder. Is that the way you do it? You would definitely need a live tailstock in place when it started to get very thin. Link to comment Share on other sites More sharing options...
Theo Posted January 9, 2012 Share Posted January 9, 2012 No need for the thread to go right up to the shoulder. There is the thickness if a leather strap below the screw head. Link to comment Share on other sites More sharing options...
Chris Ghent Posted January 10, 2012 Share Posted January 10, 2012 Not sure why you might need to involve the tail stock. If the bar stock is the size of the thumbscrew it won't go anywhere. Cut the stock down to the threading size, make the thread, start to part it off after the top of the thumbscrew, stop and knurl the edge, clean up the edges of the knurl, finish the part off. I have a mandrel with a centred threaded hole in it (I use 7 BA rather than 6 BA, though I am in the process of converting to unc 4-40) which I put in the chuck, screw the new thumbscrew into the hole and then clean up the presentation face. Make another one. As Theo says, don't worry about the thread not going to the shoulder. Theo always gives good advice... Chris Link to comment Share on other sites More sharing options...
Andy Holder Posted January 11, 2012 Author Share Posted January 11, 2012 No need for the thread to go right up to the shoulder. There is the thickness if a leather strap below the screw head. Good point Theo. Link to comment Share on other sites More sharing options...
Andy Holder Posted January 11, 2012 Author Share Posted January 11, 2012 Not sure why you might need to involve the tail stock. If the bar stock is the size of the thumbscrew it won't go anywhere. Cut the stock down to the threading size, make the thread, start to part it off after the top of the thumbscrew, stop and knurl the edge, clean up the edges of the knurl, finish the part off. I have a mandrel with a centred threaded hole in it (I use 7 BA rather than 6 BA, though I am in the process of converting to unc 4-40) which I put in the chuck, screw the new thumbscrew into the hole and then clean up the presentation face. Make another one. As Theo says, don't worry about the thread not going to the shoulder. Theo always gives good advice... Chris I will give that a try Chris. It sounds logical. The mandrel's an excellent idea. It prevents crushing the thread, although I guess it could be threaded as the last operation. Andy Link to comment Share on other sites More sharing options...
Chris Ghent Posted January 12, 2012 Share Posted January 12, 2012 I gave the mandrel a slight dishing in the front face. This means the thumbscrew always is held to the mandrel at the widest point, so it won't bend the thread if there is any slight imperfection in the back face... Chris Link to comment Share on other sites More sharing options...
Geoff Wooff Posted January 12, 2012 Share Posted January 12, 2012 Looking at the strap screws on an old Wheatstsone,where most of the Nickel plate has worn away, I notice that they have been made from two parts soldered, or Peened, together. When you make a lot of parts like this then the saving in material costs might be significant but my main thought was that in the 1800's Labour was perhaps cheaper than materials. Link to comment Share on other sites More sharing options...
Andy Holder Posted January 12, 2012 Author Share Posted January 12, 2012 Looking at the strap screws on an old Wheatstsone,where most of the Nickel plate has worn away, I notice that they have been made from two parts soldered, or Peened, together. When you make a lot of parts like this then the saving in material costs might be significant but my main thought was that in the 1800's Labour was perhaps cheaper than materials. If you're machining from solid, the swarf is probably 80% of it, which, even if material is cheap, is a helluva waste! Link to comment Share on other sites More sharing options...
Chris Ghent Posted January 13, 2012 Share Posted January 13, 2012 Even with the most expensive materials the cost of a concertina is mostly time... Chris Link to comment Share on other sites More sharing options...
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