Gearbox pinion: smooth teeth to be machined?

And if they were repairing rather than throwing and change? Rediscover the pleasure of the repairs yourself. How to diagnose a problem or find spare parts? Repair itself is way to save money generally!
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Gearbox pinion: smooth teeth to be machined?




by Forhorse » 16/05/21, 10:23

Hello everybody
I'm asking the question here in case someone is knowledgeable about machining or has faced the same problem before.
Currently I am trying to renovate an old farm tractor from the 70s, the biggest problem I have is with the reverse gear. The dog clutch teeth are completely worn.
20210515_190837b.jpg
20210515_190837b.jpg (323.82 KiB) Viewed 1604 times


The spare part costs 1800 euros, the complete overhaul of the reverser (forward and reverse dogs + 2 players) would cost more than 4000 euros just for these 4 main parts (to which must be added a whole bunch of gaskets and other supplies)

Does anyone know if it would be possible to have the pinion unscrewed to remove the dog clutch and to re-fret there instead a socket with new teeth (either cut to order or taken from another part of the same? cheaper dimension that will be sacrificed)
Because frankly such a repair cost for such an old tractor seriously calls into question the relevance of the renovation.
Knowing that the reverser is the "disease" on this type of tractor (non-synchronized reverser) and therefore that on occasion all the available parts will be in the same condition (and that all second-hand tractors of the same type still "in working order" already have the same underlying problem)
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Re: Gearbox pinion




by Ahmed » 16/05/21, 11:19

You should post a message on usinages.com, there may be a passionate amateur not too far from where you live, equipped with everything you need to get this back to normal ...
Probably not too complicated to cut out this part to fit a new toothed crown. For this last operation, you need a milling machine equipped with a divider ...
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Re: Gearbox pinion




by Forhorse » 16/05/21, 12:10

Thanks for the address, I asked the question there.
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Re: Gearbox pinion




by Christophe » 16/05/21, 12:51

Ah it's heavy there as I like!

I think you can have a wear insert machined: a ring gear that will be force-fitted but this requires the machining of the original part and more of the crown to do ... the big problem is to find the exact dimensions of the toothed part.

Why do you think so much wear and tear? The age? Forcing?

I think you could get by for less than 1000 € (500 € if you still come across a nice craftsman ... less black with a passionate) ... which remains high anyway!

How big is the part?

I will still dig more in the second-hand market for you ...

edit: you see Ahmed, we reason the same!
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Re: Gearbox pinion: smooth teeth to be machined?




by Forhorse » 16/05/21, 13:58

Wear is the conjunction of 3 factors:
- the age, the tractor at 45, and I think it exceeded 30.000 hours of operation. (the counter stops at 10.000 then returns to zero, so it is impossible to know how many full turns he made)
- The design is an unsynchronized inverter, so it necessarily takes more mechanical constraints.
- In use, because the reverser is not synchronized, it is normally necessary to wait for the tractor to come to a complete stop and fully disengage it before handling it ... but this is the theory, in practice c is far from always being respected.

For the occasion it is dead, all the tractors equipped with this reverser have this problem in a more or less marked way. From the 80s they switched to a synchronized inverter of a totally different design (the arrangement of the gearbox is different) so everything we find is at least 40 years old and 20.000 hours on the clock (excluding a few very rare which have had the chance to be repaired with a new part in the meantime)
Those that are still functioning well do not serve as a parts bank *, and those that are scrapped are usually precisely for a reverse gear problem that is somehow a wearing part for which the manufacturer did not plan. replacement and which suddenly costs particularly expensive to repair!
I have already spent 30 hours to dismantle this part, it will take at least 40 to reassemble ... I do not spend 70 hours to reassemble a half-worn part! If I go back, it must last at least 20.000 hours.

Finding the exact dimensions is not particularly problematic. We can already base ourselves on the reverse gear which is also worn but much less than this one. We can also rely on the player which contains the female part. We can also base ourselves on a similar part of a more recent tractor and therefore with cheaper parts (the manufacturers easily "recycle" the design of a lot of parts from one model to another ... is a dog, no need to reinvent hot water with each new box)

* It is a basic tractor, very common, very easy to repair, whose engine is even more widespread (mounted on several different brands). Any other problem other than that of a breakage of the gearbox (and more particularly of the reverse gear) can be repaired at a lower cost and does not justify sending it to the breaker.
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Re: Gearbox pinion: smooth teeth to be machined?




by Flytox » 16/05/21, 15:10

For your problem there is, among other things, the plasma recharge. You have to turn / grind your dogs then reload "with plasma" (exists with different names and different processes). The refill can be several cm thick if necessary, without ruining the base metal and presenting characteristics as good or better than the original. Then you have of course the re-machining of the dogs.

It is a common practice in aeronautics where the price of parts is very high. Chui not sure that the handling is very cheap ... at least in aero quality. : Wink:

http://www.surfatec.org/rechargement/

Reloading
Definition and preparation
Rappel

Originally, metallization was only used for the protection of surfaces by the projection of metallic coatings. Quickly, thanks to the quality of the sprayed metals, the resistance of the deposits and the technical development of the means of spraying, metallization was extended to other fields.
Thus, the possibility of making very thick deposits made it possible to reload worn parts.
Later, this new technique gave rise to other applications such as the manufacture of parts by metallization (electrodes, foundry models, industrial impressions, etc.).
We will only talk about reloading here.
Reloading

As explained previously, wear and degradation create deterioration that affects the dimensions and strength of parts. The surfaces in contact lose their mechanical properties and the part its original qualities. The hardfacing and re-machining of surfaces therefore makes it possible to prolong the life of the parts. Still used today, hardfacing by welding has the major drawback of greatly heating the part and thus of deforming it. The metallization does not heat up and also provides a choice of superior filler metals.
The preparation

The surface preparation of the parts is done mechanically by machining. Either with a lathe or grinding machine for cylindrical parts, or with a grinding wheel or milling machine for flat parts.
In both cases, it is done for three purposes:
- Regularly reduce the dimensions of the part to leave a sufficient thickness for the metallization deposit;
- realize on the surface an anchoring network for the deposited metal;
- increase the bonding surface and consequently the adhesion of the deposit.
Whether the part is flat or cylindrical, it is necessary in all preparation cases to respect the minimum wear dimensions to avoid subsequent breakage.
By convention, we will respect the 1% rule which is defined as follows:
“The final thickness after machining of the coating must not be less than 1% of the diameter or thickness of the part which receives the deposit”.
This rule is applicable for diameters or thicknesses between 50 and 500 mm. It must be reasoned for the other dimensions. As a precaution, the cutting tools should be checked so as not to work hard, thus increasing the surface hardness of the machined surface. This will reduce the intensity of the final sanding (this operation is not compulsory, but recommended). The use of cutting lubricant should be avoided, dry work being better suited.


Reloading and machining
Choice of filler metal

The choice of filler metal must take into account the difference in the expansion coefficients of the part and the material to be sprayed. If the difference is important, it is necessary to provide one or more superimposed sub-layers of different metals having progressively variable coefficients of expansion.
Pre-metallization

When the coating thickness does not exceed 1 mm and mechanical preparation is impossible, a simple sandblasting followed by pre-metallization can be carried out.
It is made by spraying a special thin deposit with a high molybdenum content. The bonding property of the latter allows good adhesion of the final coating on the part. It also makes it possible, in certain cases, to obtain laminated coatings several centimeters thick, by superimposing pre-metallization passes with steel layers 1 mm thick.
This bonding process is economical due to its rapid execution, the elimination of preparation operations by machining and the smaller amount of filler metal deposited.
This technique is not used on cuprous metals or alloys containing more than 20% chromium.
Finishing

The finishing of the hardfacing work consists in upgrading the metallization deposit. This is done either by tool machining or by grinding with a grinding wheel. Due to oxide formation on the deposit, the sprayed coating is often harder than the homogeneous material.
Machining by tool
For so-called machinable coatings:
- use of tungsten carbide tools with clearances adapted to the material to be machined.
For so-called non-machinable coatings:
- use of tools with boron nitride pellets with cutting oil concentrated at 20%.
In both cases, tool machining can be supplemented by stone lapping.
Abrasion machining
Common grinding wheels clog quickly when removing surface oxide. This is why special silicon carbide grinding wheels will be used. For the hardest coatings, the use of diamond or boron nitride grinding wheels will be essential. The grinding of the bores will be done dry, while that of the exteriors will be lubricated.
In any case, you must not start machining the part before it has completely cooled, ie 24 hours after metallization.
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Re: Gearbox pinion: smooth teeth to be machined?




by Forhorse » 16/05/21, 15:43

It is a lead, but not sure that it is cheaper than buying the original part ...

I found a pinion that seems to have the same dog teeth (same brand, same diameter, same number of teeth) sold 240 euros, that makes a good candidate for a donor ... the rest is just a question conventional machining.

And if I manage to redo this damn inverter, I think I will seriously think about "robotizing" it so that the inversion is facing electrically or hydraulically only when the gears are at a standstill. So it should gain a lot in life! (there is plenty of room in the housing to place a cylinder and 2 sensors ...)
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Re: Gearbox pinion: smooth teeth to be machined?




by Macro » 17/05/21, 10:25

Even robotic ... If the teeth of the dogs are not in front ... It will be necessary to give a rotation stroke to dog ...
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Re: Gearbox pinion: smooth teeth to be machined?




by Macro » 17/05/21, 15:18

Adapt a piece of pinion by conventional machining .... It will at most be a rescue The torques to be transmitted are all the same important on this kind of machines ... Your photo taken from loan does not show us the "machinable environment" "around your pinions ... The photo of your adaptable pinion could also allow us to discuss coupling solutions ... One sure thing is that we will need material available on both sides ... if the assembly of the pinion in force (cold shaft and hot pinion) is possible a solution can be expensive is to drill and insert streaky screws which will act as keys .... But for this you need material on both sides ... c did I repair my lift ...

I suppose that you have done more research than I could do ... By making google inverter broken tractor ... We come across Renault tractors ... By looking a little more some have mounted synchronized inverters of more models powerful (or more recent) ....
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Re: Gearbox pinion: smooth teeth to be machined?




by Forhorse » 17/05/21, 18:04

Macro wrote:Even robotic ... If the teeth of the dogs are not in front ... It will be necessary to give a rotation stroke to dog ...


No because the profile of the teeth of the 2 ribs (at a point) means that in any case it fits and it is the translation of the player which turns one or the other part so that it fits. This is precisely the problem here, it is that the reverser should only be operated with the tractor completely stationary, i.e. the pinions completely stopped, otherwise it is the end of the teeth (precisely the tips that help that it fit) which morflent ...
And since we are in the context of an inverter, if it turns, the player turns in the opposite direction of the dog, so the relative speed is double.
On the other hand, as it is a reverser without a neutral point, there is always a dog clutch engaged, so if the system is at a standstill, everything is at a standstill, no risk of a part turning by " licking "of the clutch or other component (typically PTO clutch shaft that is around)

The torque to be transmitted is not great either ... it is a 75hp tractor and the maximum torque of the engine is given for 27daN.m and the reverser is the first component just after the clutch, so it does not. will never support more than the maximum torque of the engine. it does not seem to me to be a couple which is too important for an assembly by hooping ... moreover the original part is already constituted thus. The splined clutch shaft is force-shrunk into the hollow shaft of the pinions.

Modify the inverter to fit that of a more powerful equivalent tractor I had thought of. The version that came out later had a synchronized reverser, and the kit to restore it costs 700 €, so it's much more valid than the 4000 € for my model. But the design is different (not the same arrangement of the box to use only one player like what is done for a synchronized gearbox) I looked a little and it seems hardly possible to me on mine, there's no room to fit a synchronizer or you would have to sacrifice a range.
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