RWL Posted July 12, 2015 Share Posted July 12, 2015 I'd like to add hand straps to my TT Edeophone and possibly to my Wheatstone Model 21. Since I have a metal lathe, I can make my own screws. The question deals with the dimensions of Lachenal vs Wheatstone screws and how to proceed. I've attached a diagram with my measurements of the screws below. They come close to standard 4-48 machine screws, but are smaller in diameter. In addition, my Lachenal's thumb screws are 0.004" smaller in diameter than the Wheatstone thumb screws. The Wheatstone thumbscrews won't screw into the strap holes in the Edeophone, so they are not interchangeable. The Lachenal thumb screws fit the Wheatstone's strap holes, but are a loose fit. Is this true across all Lachenals and Wheatstones? Both are a loose fit on a 4-48 nut, so just retapping the nuts to 4-48 would permanently alter the instrument and original / period thumb screws would no longer fit either instrument. Has anyone made their own thumb screws? I could make the screw threads to match the instrument, but I was wondering if there is a standard I should be working to and whether there's an easy way to make these rather than single point threading them (e.g. is brass threaded rod available in 4-48 and can be altered?). Since I have some 3/32" bronze brazing rod around I was going to use that for the screws. Bronze is harder than brass, so I don't know how well that's going to thread on such a small diameter screw. Link to comment Share on other sites More sharing options...
OLDNICKILBY Posted July 13, 2015 Share Posted July 13, 2015 Why not stick with U N C or U N F , buy some brass screws , make the heads and solder the screws into them. Much easier and taps are readily available Link to comment Share on other sites More sharing options...
Chris Ghent Posted July 13, 2015 Share Posted July 13, 2015 As you have a lathe, here is another technique which would leave you with threads to match the rest of the instrument. Get hold of a low power microscope, something around 10x. Use it to measure the tpi of the Wheatstone original by comparison to an inch ruler. If it is a Tpi you can match with your lathe set the gears accordingly. Grind a lathe tool to the same shape as the valleys in the Wheatstone thread using the microscope to get the shape right. Measure the major and minor diameters of the original with a vernier calliper. Proceed according to the usual methods used to create a thumbscrew. Link to comment Share on other sites More sharing options...
RWL Posted July 13, 2015 Author Share Posted July 13, 2015 Chris, you must have missed it in the diagram. These are 48 threads per inch and the screws are close in size to a 4-48 machine tap. I measured the pitch diameter of the Wheatsone with my thread micrometer, but the size of the head of the Lachenal thumb screw prevented the micrometer from reaching the threads on that one. I was too lazy and needed to grow a third arm to use the three wire system in my toolbox to measure the Lachenal. It certainly would be easiest to just tap the strap holes to 4-48 and use off the shelf screws, but then the holes would be permanently too large to match original thumb screws, should a subsequent owner wish to use originals. I was hesitant to do that unless I heard from the majority of current repairers that that's what they always do. Link to comment Share on other sites More sharing options...
Dana Johnson Posted July 14, 2015 Share Posted July 14, 2015 (edited) Are we back to those BA threads? If you say 4-48 is a loose fit, at that small a diameter you could be easily off a size and if it was a different standard the numbering would mean something different. If they are something like the BA threads, I've seen dies available for some of them then you could thread a short length, cut it off and solder it into a blind hole in the disk, or a through hole if the fit was good enough not to show the solder line. Make it a press fit and don't bother with the solder at all. I made a couple replacement BA end bolts for my old Wheatstone Duet. They worked fine, but at 44 tpi I was lucky I had that setting on my QC gearbox. Everything has to be more accurate at those sizes. Just getting a threading tool with that fine a point and the right tool angles took me a while. Chris does his own end bolts which always amazes me. Sure makes you appreciate geometric dies and screw machines! Edited July 14, 2015 by Dana Johnson Link to comment Share on other sites More sharing options...
Dana Johnson Posted July 14, 2015 Share Posted July 14, 2015 You mention both being a loose fit in a 4-48 nut, but that is going to be around .112" major dia, and you show the Wheatstone at something like .137"? Am I misreading the drawing? It is very fuzzy on my screen. The lach. Looks like .103". There is a BA thread at .110" and 47.9 tpi, which is a closer match to the lachenal. The BA threads are steeper at 47.5 degrees instead of the 60 for UNF. Might be able to see the difference with a magnifier. Link to comment Share on other sites More sharing options...
RWL Posted July 14, 2015 Author Share Posted July 14, 2015 The thumb screws are not a BA thread as far as I can tell. They would fall somewhere between a BA 6 and 7 screw size. They come closest to UNF 4-48. Would that they were a standard size - as you suggest, I could order a few screws of the appropriate size and fit them to brass discs to make the thumb screws. I guess 100 years ago they still didn't have firm thread standards. It's looking more like I'll have to single point them on my lathe. Link to comment Share on other sites More sharing options...
Dana Johnson Posted July 14, 2015 Share Posted July 14, 2015 Have you thought if making modern nuts to go with modern thumb screws? The ones I remember were disks with an off center mounting screw inlaid into the frame with an off center threaded hole. Be more work, but non destructive. Link to comment Share on other sites More sharing options...
RWL Posted July 14, 2015 Author Share Posted July 14, 2015 I hadn't considered making the offset nuts to match UNF threads. For me it would be a dickens to find those tiny wood screws that hold the disk in place. Link to comment Share on other sites More sharing options...
RWL Posted July 14, 2015 Author Share Posted July 14, 2015 Dana. I missed your post about not being able to read the dimensions on the Wheatstone screw. They are 0.107" diameter and the pitch diameter according to my semi-functioning thread micrometer are 0.096" dia. Both screws are about 1/4" long. Link to comment Share on other sites More sharing options...
Dana Johnson Posted July 25, 2015 Share Posted July 25, 2015 Looks like you managed with the threading anyway. I mentioned the nuts because I thought they might already be in place. I don't know what years they were used. Things like this make you appreciate modern standardized threads. If you ever need them, I have found #00 screws at Craft inc. on the web I needed to replace some lost ones on an old Jeffries end plate. I ordered a few sizes to get a match, but it was nice to know they were available. Dana Link to comment Share on other sites More sharing options...
RWL Posted July 25, 2015 Author Share Posted July 25, 2015 I also posed this question on a machinists group and several members there also thought this is more likely to be a BA 6 screw thread. I stand corrected on believing this was not a BA screw. I'm pondering my options at this point. Dana, thanks for the information about where to find small wood screws. I hadn't realized you were in the USA. Link to comment Share on other sites More sharing options...
David Hornett Posted July 26, 2015 Share Posted July 26, 2015 My thumb screws are cut from a single brass off cut (found at engineering works, or on ebay, 'brass rod'). I have made housings to hold the die in the tailstock and press against the rod, held in the chuck, when spun down to size, after which I knurl the head. Holes are also tapped by the same method when I make the nuts to be seated in the casing under the straps. These nuts are not off centre, rather they pressfit and a piece of 1 mm brass rod 3/8th long is run through their casing and the concertina end and snibbed off. All my concertina screws are made in the same manner, driving them through one of these dies held in the tail stock. I attempted to forward a photo but have used up all my allowance. If interested send an email and I will forward. When I repair thumb screws I make new ones and nuts using M3 x50 thread David Link to comment Share on other sites More sharing options...
DDF Posted July 26, 2015 Share Posted July 26, 2015 My thumb screws are cut from a single brass off cut (found at engineering works, or on ebay, 'brass rod'). I have made housings to hold the die in the tailstock and press against the rod, held in the chuck, when spun down to size, after which I knurl the head. Holes are also tapped by the same method when I make the nuts to be seated in the casing under the straps. These nuts are not off centre, rather they pressfit and a piece of 1 mm brass rod 3/8th long is run through their casing and the concertina end and snibbed off. All my concertina screws are made in the same manner, driving them through one of these dies held in the tail stock. I attempted to forward a photo but have used up all my allowance. If interested send an email and I will forward. When I repair thumb screws I make new ones and nuts using M3 x50 thread David I made a few of the Linota style thumbscrews recently .I used the same process except I used some scrap 16mm stainless steel bar instead of nickel.The original nickel ones always suffer with a verdigris build up which the s/s ones shouldn't.David. Link to comment Share on other sites More sharing options...
David Hornett Posted July 26, 2015 Share Posted July 26, 2015 You need nickel silver (German silver) seems pretty robust when it comes to verdigris. I have made 10 or so in the above mentioned manner from half hard brass, then milled the middle out to1mm depth, dropped in a small bead of resin solder, fly punched a nickel silver disk out of 1.62 sheet and tapped it in the end, while heating the screw. When cooled then turned down to 1mm at the sides with a small convex, (1.62 in the middle) has a great effect when polished and is fairly easy to do. David Link to comment Share on other sites More sharing options...
Dana Johnson Posted July 28, 2015 Share Posted July 28, 2015 There are a number of different NS alloys. I've noticed the ones in old concertinas seem to be lower nickel content and are slightly yellow. The alloys used for springs and medical equipment are where I think I'd go if I were going to make end bolts or the like. Any of them if not annealed are pretty tough, but while Nickel makes them tougher ( and whiter ), it also makes for gummy machining. It would be a good candidate for rolled threads which would be a perfect way to make the short screws on thumb screws if they were all one piece. One can dream... I have noticed verdigris build up on NS thumb screws but this seems to come from the oils and fatty acids in the leather of the straps. Most of the crud on NS ends comes from hand oils and acids. When I am cleaning ends, I always start with alcohol ( on a piece of paper towel to avoid contact with wood finishes ). Everything comes off except the etched surface. The build up on the screws is all on the underside and the threads that are in the leather, and is not visible without taking them out. It also takes some years to really develop though the kind of leather makes a difference. Brass is a lot worse, but the verdigris is in the same place. This is all ramblings late at night after playing music all day. Everybody's solutions are excellent. If someone is thinking about offering a stock of spares these might be things to consider. If there were any real call for these things, making them could be fun. Dana Link to comment Share on other sites More sharing options...
David Hornett Posted July 28, 2015 Share Posted July 28, 2015 Yes, Nickel Silver will discolor and tarnish, but certainly not at the rate of brass. The material I use is C75720: Copper 60-65%, Nickle 11-13%, Zinc 21-28%, and preferably C792: 18% nickle. This is used for buttons and end plates. The best way to maintain the shine is not with wax, but buff to a high luster, soak in vingar and water 50/50 for half an hour or so, dry without touching, and then coat with a polymer car polish (NOT WAX) Nu Finish is an excellent polish for this. Bolts made from Nickel Silver are certainly gummy to machine, but if you use the tailstock method for threads are no problem at all. For buttons, use a parting bit ,HSS, ground to 3/32 wide slight spade tip and spin at approx 2400 RPM. Buff with a rag buff and cutting compound, coat with ploymer and the finished product is a joy to behold. David Link to comment Share on other sites More sharing options...
RWL Posted July 28, 2015 Author Share Posted July 28, 2015 I ordered both a 3-48 and a 6 BA die to see which threads work best. I'll report back when I complete some thumb screws. Link to comment Share on other sites More sharing options...
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