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September 22, 2020, 20:34:49 pm

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Futura SE gear wheel S-4615

Started by paulinfrance, August 07, 2020, 16:18:59 pm

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paulinfrance

Help, I went out to fly My bell 222 with it's Futura SE mechanics in it and lo and behold, I am not the only one loosing my teeth  :'' the tail driving gear has lost a couple of teeth,  :-\  has anyone out there got a couple to sell or has an addressee where I can get a couple ?.
 Thanks Paul.
Mode 2 THE only way to fly

paulinfrance

I have found someone who is willing to make it but he is asking me what sort of module teeth they are,,

 anyone ?.
Mode 2 THE only way to fly

Gaspin

I have just had a tooth extracted, do you want to try that!!

paulinfrance

No thanks for your offer, that is what I already have, I have found 'free' files for someone who has a 5 whatyamacall it milling machine to make one from plastic,,

and an old mate at Nimes sold me a second hand one, when it is f***k I will chuck it,, 
Mode 2 THE only way to fly

PDR

Quote from: paulinfrance on August 09, 2020, 13:58:05 pmI have found someone who is willing to make it but he is asking me what sort of module teeth they are,,

 anyone ?.

There are essentially two systems that define define involute gear tooth dimensions - "Module" and "Diametric Pitch". Mod is mostly used in metric countries and DP was more common in Inferial countries (although Mod is progressively taking over).

Google something like "calculate Gear Module" and "calculate Gear DP" and you will find websites that explain the measurements you need to take - some include on-line calculators. You will find it easier to take the measurements from the small pinion gear than the large ring gear. Simple enough BUT...

The gear in the picture is a bevel gear. These are MUCH harder to measure and cut accurately. Normal gears can be cut reasonably simply with just a gear cutter in a small milling machine and dividing head, because spur gears have parallel teeth. But bevel gears have tapered teeth, which means that in theory they can only be cut with a shaper with a dividing head (or roughed out in a mill and finished in a shaper). Most home-machine-shop people won't have this stuff.

In practice if the gear part is less than a third of the outer diameter of the gear and less than 1/8th of the distance from the rear gear face to the projected apex of the bevel cone you can get an acceptable approximation by cutting the two faces of each tooth separately using a thinner "bevel gear cutter". Home machinists may be able to do this if they can buy the cutter.

It would actually be easier to do if you were making replacements for both pinion and ring-gear. Then you only have to know the gear ratio and you can *choose* the mod/dp/pressure-angle etc to suit the cutters you have available.

€0.00008 supplied,

PDR
There are no shortcuts on the long, hard road to success. But if your dad's rich there could a limo service...

paulinfrance

Yes i found the formula,, I forgot how to work it out when I had my model shop, I remember Tamiya was 0.5 module,,

70mm dia 70 teeth = module 1mm,,,
Mode 2 THE only way to fly

PDR

Quote from: paulinfrance on August 27, 2020, 11:36:11 am70mm dia 70 teeth = module 1mm,,,

Yes, but remember that that diameter is the EFFECTIVE diameter (the involute contact diameter) which is roughly the external diameter minus tooth depth. A good approximation is usually taken as

Mod=(Peak Diameter)/(number of teeth + 2)

PDR
There are no shortcuts on the long, hard road to success. But if your dad's rich there could a limo service...