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bartley

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About bartley

  • Birthday February 13

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  1. Glenn, You have clearly solved the problem of fabricating a moulding cutter now but for the record, and perhaps for a later build, this is an escapement file which I used to cut my profile. This is a round one but other profiles are available. The widest part on this one is 1 .5mm and the tip is 0.4 mm - very delicate but with care, especially on brass, very narrow cuts can be made. Cheers, John
  2. Indeed, all of these processes, including the use of selenium blackening, involve the oxidation of copper to copper ions (for example copper sulfate). I did outline the chemistry under the thread "blackening brass". The different effects depend on what chemical species replaces the copper be it sulfur or selenium or other metals. Modelers do not need to know the chemistry of course but there are some important practical consequences. Firstly, aged copper contains an oxide surface coating and, since it is copper which needs to be oxidized, you must remove this oxide coating before any of t
  3. Derek, Far be it for me to provide advice to you. Your work is excellent and I have learnt a lot from your builds. However, I do know a thing or two about chemical blackening since I have a chemical background. This reaction is actually very fast so if your blackening is taking 1 minute the surface is not clean enough. On clean surfaces 10 to 20 seconds is enough. The advantage of a clean surface is that the minimum amount of selenium is deposited (no flaking) and a very uniform blackening results. Have a look at this post of mine which shows an extreme case of poor blackeni
  4. Yes indeed Kurt, boiling Sparex (which is incidentally an expensive packet of sodium hydrogen sulfate) could be dangerous because once dissolved it is sulfuric acid. It is quite dilute initially but if it becomes concentrated by boiling it will produce oxides of sulfur (chemically SO2 and SO3). These are dangerous gases and if inhaled could cause permanent respiratory damage. John
  5. Others may be interested to note that the inscription reads: "Draft for building in the Marchant's Yards by contract two cutters for his Majesty’s Service to carry ten 18 pounder carronades and two 6 pounders for chase guns A copy of this draft was sent to Mr Thomas Johnstone at Dover 30 May 1806 for building two cutters named Cheerful and Surly Approved by the Lords Commissioners of the Admiralty 17 April 1806 " John
  6. Dgbot, I think you might have a nomenclature problem here. I think what you mean is salicylic acid. By "Selinic acid" I think you mean selenic acid which is a more oxidized form of the selenium dioxide (or selenious acid) which we use to blacken brass. Both of these chemicals are quite toxic but salicylic acid is relatively harmless. John
  7. Jim, I placed this order a week or so ago but have not heard about the postage yet: "Thanks for your on-line order #200817MM14633700 at ByrnesModelMachines.com!" I am only concerned because orders from the US can take a couple of months to get to Australia and I don't want to be caught in the Christmas rush. John
  8. Jim,

     

    I placed this order a week or so ago but have not heard about the postage yet

     

    Thanks for your on-line order #200817MM14633700 at ByrnesModelMachines.com!

     

    I am only concerned because orders from the US can take a couple of months to get to Australia and I don't want to be caught in the Christmas rush.

     

    John

  9. Glenn, I am always a bit reticent about providing any advice here as I am a rank beginner at this game. However, for what its worth here is a picture of my scraper and the result. I think I used the one on the left or something like it. I made about 10 of them in the end. The few tests that I did with yellow cedar gave very indistinct results and it was only when I used boxwood that I could obtain a satisfactory profile. I also stuck the strip to my bench with double sided tape to stop it moving. I found that several light strokes were best until the pro
  10. Glenn, I have these scrapers. They are good but I find them far too big for the scale we are working at. I used jewelers files to cut a profile into the back of a annealed hacksaw blade. I think I might have also used a jewelers saw. There are several posts on this site about this technique. John
  11. Justin, Yes, disposal is always an issue. I am a professional chemist and so disposal is part of our trade. Sparex once dissolved is essentially sulfuric acid. So to dispose of it you should pour it slowly into bicarbonate. It will fizz so do it slowly. Once the fizzing stops the Sparex is neutralized and you can dispose of it down the sink, The blackening solution is another matter. This, when fresh, is selenious acid. When you use it it is converted to black selenium metal and copper sulfate That's the blue colour. But you cant neutralise or destroy the selenium. or copp
  12. I actually posted this elsewhere but it is probably more appropriate here. This is an example of a blackening problem which others may have experienced without knowing the reason. These belaying pins were sold as being brass so on the right I used my usual technique of treating for 5 min with sodium hydrogen sulfate then blackening. Even after about 1 min the result was poor. On reflection they were very shiny so were probably lacquered. So on the left the treatment was: - rub with steel wool, soak in acetone for about 1 min, 5 min in sodium hydrogen sulfate then
  13. The continuing saga of the belaying pins! I can make boxwood ones down to close to 1 mm in diameter at the lower end but for me consistency is the problem If I just had to make one I would be quite happy but 20 odd? I am not sure I have the patience or the skill. Here is a pic of mine versus the commercial ones:
  14. Glenn, It sounds like you only do ripping using the slitting blade. Of course that is what your post is about. The blade which comes with the machine is a cross-cut blade which I use quite a bit. Magic for cutting reproducible lengths. Incidentally I found that a zero clearance insert for the slitting blade improved the quality of my ripped planks enormously especial if I was cutting narrow ones, John
  15. Glenn, Thanks for putting this together. It is reassuring to know that what I am doing is more or less the same as what you are doing. I think that a good safety tip is to "rehearse the cut". By which I mean push the wood through without the saw running. Especially if you haven't used the saw for a while or it is a cut you haven't done for a while. A couple of times I found that I had inadvertently moved the saw or stored something at the exit end that would have stopped the wood exiting freely. John
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