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    tony bubb
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    Model Engineering especially airguns
    Shooting generally
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  1. tonybubb

    Drulov DU10 lubrication

    What lubricant is best for the DU 10? After long storage have just resurrected mine and am stripping it for a service and possible seal replacement. The moving parts seem very dry. The piston on the hammer looked as though it had traces of moly and I wonder whether to relube with DrySlide or oil such as BreakFree. Any Comments? Tony
  2. tonybubb

    Non mechanical regulator

    Thanks Jon. I can't use a semi balanced regulator as it does not give an absolutely constant output pressure. My valve system Is so sensitive to regulator pressure that even a change of 50 psi during exhaustion of the main reservoir would be unacceptable. My solution is to use an unbalanced gas spring with the pressure of the gas in the spring being almost the same as the desired output pressure. It is also manually adjustable during use so that the output pressure can be adjusted using a built in pressure gauge. This would take account of possible temperature changes. The power output is directly proportional to the regulator pressure so the maximum regulator pressure would need to limited for sub 12ft/lb. Tony
  3. tonybubb

    Non mechanical regulator

    He may be interested if the project comes to fruition as my object is to build something that will equal the GC2 in consistency without the complication, muzzle blast and low shot count. I could even make it semi automatic if that were allowed. Tony
  4. tonybubb

    Non mechanical regulator

    Haven't visited this forum for a while but still continuing my home workshop R&D airgun experiments. Having two workshops in different countries and commuting between the two makes things difficult but at least being in Spain I can experiment with higher powers than UK without needing a RFD. Had to leave a nearly completed Rifle project in UK so have returned to an old shelved project to convert a .177 BSA Ultra to a hammerless self resetting action. My next step is to fit an infinitely adjustable regulator using a gas spring. This is a new design of my own that is tried and tested and is about as non mechanical as is possible. But I have recently learnt that John Bowkett has a non mechanical regulator that sounds very similar. I can't find out how it works. Does any one know? Jon perhaps? Tony
  5. tonybubb

    Good chrono?

    Having just bought the IMBR Chrono R2 I noticed this Thread so thought that I might add my thoughts even if slightly late. I bought mine from forGuns in Poland who are currently selling them on Fleabay for £85.99 including free postage. I didn't know that you could buy direct from the manufacturer so maybe I paid more than needed but it did arrive very promptly. I already have a CED millennium Mk 1 with infra red sky screens that I use in my UK workshop but I wanted something more convenient to take to Spain. To compare accuracy I set up the R2 in front of the CED and fired through both using a Gamo Springer. At a velocity around 600 FPS the R2 consistently read 10 FPS higher than the CED. That seems acceptable bearing in mind the difference in price of the Chronos and the difference in the spacing of the Sensors. The R2 could be re calibrated against the CED if I had the time, but it will do for now. One feature that will be especially useful in Spain is that the R2 will measure rate of fire in automatic mode. Tony
  6. tonybubb

    Machining Polyurethane in the lathe

    Thanks for that, don't think that I could afford them. However for my purposes I have found that the best results are obtained by using a sharp pointed blade with a plunge cut. Thus the tool is not trying to turn off the material but slices into it. That way I have formed both small rectangular section O-rings and also flat washers with a conical bore forming a valve seat. The faces of the Urethane are perfectly smooth. One knife tool is used radially for parting off, the other is used axially like a boring tool but makes a circular plunge cut. When the two cuts meet a complete ring of Urethane is separated from the workpiece. The edges of the blade must be razor sharp and the faces mirror smooth. A low speed of 190RPM and lubricant of water and washing up liquid applied with a brush works best. Tony
  7. tonybubb

    Machining Polyurethane in the lathe

    Still experimenting with the best technique. Found this Utube video. Would love to know how those toolbits are ground. http://www.youtube.com/watch?v=RDB_qS0Gxpg Tony
  8. tonybubb

    Cutting half inch thread.

    Agreed, I was just surprised to find a quality lathe without a register on the spindle. Tony
  9. tonybubb

    Cutting half inch thread.

    But if you are only relying on a face for alignment then the centering is being done by the threads. I was surprised how accurate this can be when I recently bought a small USA made Sherline lathe. The spindle has no register, just threads undercut in front of the face of the spindle. Nevertheless the run out in the 3 jaw scroll chuck proved to be less than one thousandth of an inch! Tony
  10. tonybubb

    Machining Polyurethane in the lathe

    Need something larger section than an O ring even very large sections don't work as I need to form something with a conical valve seat that will also act as a buffer. The Urethane arrived this morning so had a quick play with it and not so difficult as I feared It even drills quite nicely although the rod that I have seems quite soft. No Shore hardness was specified. Tony
  11. tonybubb

    Machining Polyurethane in the lathe

    Thanks for the pictures gives me food for thought. I am still waiting for my material to arrive and shall then give it a try. I am not trying to make piston seals for springers however and shall be working on much smaller ring type seals about 10mm diameter. They have to be very low friction so can't afford too much pinch. Regards Tony
  12. tonybubb

    Machining Polyurethane in the lathe

    Unfortunately I have a need for a seal where Urethane may be the only appropriate material so I shall have to give it a try. May be I shall have to try grinding as Bob suggests but would that give a good enough finish to form a valve seat? Is it possible to mould Urethane in the harder grades in a small scale in the home workshop? Tony
  13. tonybubb

    Machining Polyurethane in the lathe

    I almost always use HSS tools. I have always found Delrin, Acetal and even PTFE easy to machine as they cut cleanly. Softer materials such as Nylon or Nylatron are more difficult and I have had best results with a very narrow bladed tool ground like a parting off tool but with a flat top so that there is zero side or back rake. Approach and clearance angles are also minimal but the edges of the tool are very sharp. Initial deep cuts can be made with the side of the tool, but for finishing cuts I use the tool at a very slight angle so that it just shaves the surface of the material and cuts over the full width of the tool. Tony
  14. tonybubb

    Machining Polyurethane in the lathe

    The Canadian guy reckoned the opposite. Said to use tool rakes the opposite from that for turning steel and that he had learnt from a toolmaker who used polyurethane professionally. Apparently the swarf from the Urethane should be directed downwardly away from the work and in front of the path of the cutting tool instead of over the back of the tool as in cutting steel. it is only the very point of the tool that does the work and this must be kept razor sharp with zero front rake. It sounds like he was using a left to right knife tool for cutting steel but working from right to left on the Urethane. I found it difficult to visualise without his photos but he said that this way he could cut soft Urethane below 90 shore provided that it was held in a collet rather than a chuck. I shall need to experiment. Tony
  15. Have at last discovered a cheap source of polyurethane rod for the home workshop (China via evilbay). Now I can try making seals and piston washers for my experimental projects. I found a very interesting topic on a Canadian airgun forum regarding machining, but his photobucket pictures of the cutting tools were no longer available. It seems that negative top rake is king and I shall try to grind up some cutting tools for myself while waiting for the delivery from China. Meanwhile can anyone on this forum throw further light on the tool angles needed? Tony