m davies Posted October 27, 2009 Share Posted October 27, 2009 Ok, its time to ask the great RMweb oracle again for some help. Try as I might I cannot find a source for gears for my 7mm class 57, gearboxes ? yes, motors ? yes, but just plain gears, not a thing, with a top speed of 75mph and 45" wheels the ABC spread sheets suggest a 15:1 or 14:1 (if I want a little over speed) ratio. I hope to use a Mashima 1833 motor (however clearance is tight so I may need to re think that), thus I'm looking for a set of gears that fit the Mashimas 2mm shaft and the wheels 3/16th shaft please. Any help greatly appreciated Kindest Michael Link to post Share on other sites More sharing options...
bertiedog Posted October 27, 2009 Share Posted October 27, 2009 Ok, its time to ask the great RMweb oracle again for some help. Try as I might I cannot find a source for gears for my 7mm class 57, gearboxes ? yes, motors ? yes, but just plain gears, not a thing, with a top speed of 75mph and 45" wheels the ABC spread sheets suggest a 15:1 or 14:1 (if I want a little over speed) ratio. I hope to use a Mashima 1833 motor (however clearance is tight so I may need to re think that), thus I'm looking for a set of gears that fit the Mashimas 2mm shaft and the wheels 3/16th shaft please. Any help greatly appreciated Kindest Michael Ultrascale do the sizes ratios in the .4 mod range, and would suit 7mm just as well as 4mm. I would go for the 15:1 or towards 20:1 ratio. They appear to do the right holes sizes, best check direct. I believe Tower Models can supply as well, and Slaters have done gears in the past. Stephen. Link to post Share on other sites More sharing options...
m davies Posted October 27, 2009 Author Share Posted October 27, 2009 Ultrascale do the sizes ratios in the .4 mod range, and would suit 7mm just as well as 4mm. I would go for the 15:1 or towards 20:1 ratio. They appear to do the right holes sizes, best check direct. I believe Tower Models can supply as well, and Slaters have done gears in the past. Stephen. Stephen, Ahh, took a while to get to the right section , another supplier to add to the book marks. BTW whats a 2 start gear set ?, I've heard this name before but never worked out what it meant. Its good to have accurate measurments, I can now see how much I need to cut and modify the bogie to fit, or not as the case may be. Its shame they dont do motors as well, you just end up shopping for small bits and pieces all over the place. Kindest Michael Link to post Share on other sites More sharing options...
bertiedog Posted October 27, 2009 Share Posted October 27, 2009 Stephen, Ahh, took a while to get to the right section , another supplier to add to the book marks. BTW whats a 2 start gear set ?, I've heard this name before but never worked out what it meant. Its good to have accurate measurments, I can now see how much I need to cut and modify the bogie to fit, or not as the case may be. Its shame they dont do motors as well, you just end up shopping for small bits and pieces all over the place. Kindest Michael A single start is the normal single threaded screw used for driving a gear, a double start is a twin start dual thread and half the ratio for the diameter, but smoother. Most gears in models are single start, but Tri-ang famously used twin start on their models. Ultrascale and others do twin start if you want, it is a compromise about the diameter being bigger for the same ratio that may be the issue. Stephen. Link to post Share on other sites More sharing options...
m davies Posted October 27, 2009 Author Share Posted October 27, 2009 Stephen, thanks for the description, but for the life of me I cannot visualize this twin start set up , I'm used to gearboxes (big ones on container cranes for rope reeving and power transmission) but this dual start elludes me, its still only one worm and one spur ? so I'm presuming it must be the cut of the teeth that marks the difference ?. Its of no real relevance to 7mm modeling but the engineering side of me is interested to learn more on how this works. Kindest Michael Addendum, belay that, http://www.roton.com/identify_threads.aspx explains all, a twist drill being a perfect example of a dual start thread and a wood screw a single start thread. Link to post Share on other sites More sharing options...
smokebox Posted October 27, 2009 Share Posted October 27, 2009 I cannot visualize this twin start set up , Kindest Michael Try thinking of a drill bit. It has two cutting edges and two "spirals" along it length. A two start worm is the same, it has two spirals, 180 degrees apart. Link to post Share on other sites More sharing options...
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