Epicyclic Gears

This Android App is designed to perform an initial calculation of a simple epicyclic arrangement with a sun, ring, planets and carrier.

Define the motion parameters, teeth number of the different elements and the speed and torque to obtain different results as:

• Total ratio of the system.
• Relative motion to the carrier.
• Geometry verification.
• Absolute Speed of each element.
• Cycle counting, Tooth Contact per minute of each gear
• Factorization value of Sun and Ring Gear
• Torque results of each element.

Different animations are included within the app, just click at the image at the right side of the motion selection.

Also, the definition of "factorization" is described in this video (click to the link)

 App Images:

A link to a youtube video created for each motion definition is available when clicking over the gear image.

Three different types of motion were created:

Planetary:

Solar :

Star:

Many links and lectures are recommendable, I have found interesting for basic and intermediate study the following links and Standards:

• Epicyclic Gearing: A Handbook
• Agma 6123. Design Manual for Enclosed Epicyclic Gear Drives
• Efficiency of a Planetary GearBox
• Efficiency of planetary Gear Trains
• Dynamics of Planetary Gear Trains

Machining Tolerances

This application help designers and engineers while designing the parts for any type of mechanical device.
The application will give you a tolerance range, equal bilateral, for a especific manufacturing process selected. Turning, Grinding, Broaching, Reaming... up to 12 different types.

  Machining Tolerances.

As a designer of mechanical components, here are a couple of recommendations I do always consider when assigning tolerances:

• It's very important to define a correct dimension composition in your drawing. Avoid having accumulation of lineal dimensions. They will only add variation in your part and in your assembly.
• Tolerance values below ±0.013 are difficult to maintain under regular conditions, even when talking about bearing bores or bearing supports, requesting values below those 0.013 mm tends to be a problem for manufacturing and quality. If you can live with something avove it, your supplier or manufacturing collegue will appreciate it.
• Face to face location in case of bearings supports (shafts or pinion gears) could be in values around ±0.05 mm. 
• Think always in those features that would need to be machined after heat treatment. In general, it is common to use a grinding operation to compensate deformation and to obtain the desired roughness. Depending on the size of the feature, values below ±0.013 can be achieved adding more cost to the part.(again, cpk requirements could be an issue for quality and for the supplier)
• Try to not assign geometric tolerance values lager than feature tolerances, so think twice about the values you define in your parts.
• Use equal bilateral tolerances in your drawings. It will help you with your stackup calculations (comming soon application) and if you are using 3D models, and your manufacturing does also, your parts will be machined centered always.
• Cost of the tolerances:

• General Tolerance values: This this the tolerance table intended to simplify drawing indications and specifies general tolerances in four tolerance classes. It applies to the dimensions of work pieces that are produced by metal removal or are formed from sheet metal. It contains three tables and an informative annex with regard to concepts behind general tolerancing of dimensions. 

         General tolerances for linear measures according to DIN ISO 2768-1

         Table one - Permissible deviations for linear dimensions except for broken    

         edges (external radius and chamfer heights) 

Designation	Description	Permissible deviations for basic size range in mm
		from 0.5# upto 3	Over 3 upto 6	over 6 upto 30	over 30 upto 120	over 120 upto 400	over 400 upto 1000	over 1000 upto 2000	over 2000 upto 4000
f	fine	±0,05	±0,05	±0,10	±0,15	±0,20	±0,30	±0,50	Nil
m	medium	±0,10	±0,10	±0,20	±0,30	±0,50	±0,80	±1.20	±2.00
c	coarse	±0,20	±0,30	±0,50	±0,80	±1.20	±2.00	±3.00	±4.00
v	very coarse	Nil	±0,50	±1.00	±1.50	±2.50	±4.00	±6.00	±8.00

Table two - Permissible deviations for broken edges (external radius and chamfer heights)

		Permissible deviations for basic size range in mm
Designation	Description	from 0.5# upto 3	over 3 upto 6		over 6
f	fine	±0,20	±0,50		±1.00
m	medium
c	coarse	±0,40	±1.00		±2.00
v	very coarse

Table three - Permissible deviations for angular dimensions

		Permissible deviations for ranges of Lengths in mm of shorter side of the angle concerned
Designation	Description	upto 10	over 10 upto 50	over 50 upto 120	over 120 upto 400	over 400
f	fine	±1.00°	±0.500°	±0.333°	±0.166°	±0.083°
m	medium
c	coarse	±1.500°	±1.000°	±0.500°	±0.250°	±0.166°
v	very coarse	±3.00°	±2.000°	±1.000°	±0.500°	±0.333

General tolerances for form and position DIN ISO 2768-2 is for simplifying drawing and fixes general tolerances in three tolerance classes for form and position. By choosing a special tolerance class exactly the precision level common in workshops should be taken into account.

General tolerances for straightness and evenness in mm

		Permissible deviations for basic size range in mm
Designation	Description	upto 10	over 10 upto 30	over 30 upto 100	over 100 upto 300	over 300 upto 1000	over 1000 upto 3000
H		0.02	0.05	0.10	0.20	0.30	0.40
K		0.05	0.10	0.20	0.40	0.60	0.80
L		0.10	0.20	0.40	0.80	1.20	1.60

General tolerances for straightness and evenness in mm

		Permissible deviations for basic size range in mm
Designation	Description	upto 100	over 100 upto 300	over 300 upto 1000	over 1000 upto 3000
H		0.20	0.30	0.40	0.50
K		0.40	0.60	0.80	1.00
L		0.60	1.00	1.50	2.00

General tolerances for symmetry

		Permissible deviations for basic size range in mm
Designation	Description	upto 100	over 100 upto 300	over 300 upto 1000	over 1000 upto 3000
H		0.50
K		0.6-		0.80	1.00
L		0.60	1.00	1.50	2.00

Source : www.huaxing.com
Links to Information:

•  Typical Tolerances
•  Machining Tolerances
•  Cost of Tolerances

Involute Spline Calculation App

This app calculate the shear stress, contact stress and safety factors of a involute spline shaft under a defined torque. This calculation gives a good direction on design and will help to define sizes and lengths of shafts, and therefore the parts that are assembled on it. Bearings, Seals, snap rings sizes will, in most cases, be defined by the spline torque capacity.
The calculation is based in the document released by Darle W. Dudley, and used in many different engineering books.
The geometry of the inner diameter and the outer diameter is approximated for a quality 6 spline.
This calculation can be used for splines designed under the standard ANSI B92.2M or ISO4561.
This tool is defined for giving you directions and not definitive or complete designs. For that particular purpose, It is reccomended to run more accurate analysis and of course validate your designs with physical parts.

    Involute Spline Torque Calculation

Aditional Information about Splines:

• The function of a spline can be defined as fixed or sliding. Sliding one is oftenly used in synchronizers, shift gears and other similar machine elements.Fixed ones, are designed for not allowing any axial movement, therefore a minimun clearance, side or outer diameter is desired.A good practice on fixed splines is te use of pilot diameters for centering the load distribution and avoid excesive tilting in the connection.
• Splines work better when it is lubricated. Grease or oil will avoid premature failures due to fretting.
• Fillet root splines resist better the torque load, even when the minimun diameter is smaller compared with a flat root spline.
• A minimun taper angle on the outside diameter of the spline, along the overall effective length could help when torque twist the shaft and the contact distribution runs to the front or rear area of the spline. FEA analysis can help yo to determine the amount of taper needed.
• Splines failures would happen due to:
• Wearing of the spline teeth due to high contact stress and poor lube.
• Broken shaft due to high torsional stress.
• Spline fretting due to vibration, axial movement and poor lube
• Bending failure due to a small section under the tooth. Hollow diameter to big.
• If Faiure happen due to shear stress, shock load may be the reason.
• As general rule, use quality 6, according ANSI B92.2, for general purposes splines. Quality 7 allows more geometrical deviations and can be used for low spec requirements or when the safety factors are really high. Quality 4 and 5 are choosen when the spline is grinded and the contact distribution must be controlled.
• If the teeth number is low, you will require the tooth to tooth spline locatin to have more  accuracy to asure that all teeth share a similar torque level. It is more easy for a spline with smaller module and high teeth number to share equally the load.
• It is reccomended not to have parts in contact with a different in hardness > 8.
• Splines and Shaft materials:
• SAE 1010 & SAE 1020  Low cost material, under low solicitations and where part of the shaft is heat treated (carburized)
• SAE 1045  Common steel used for shafts. Low cost material. Can be heat treated and provide high load resistance. It is not a good selection if the fatigue strength is a mayor requirement on your design.
• SAE 4340 Cr-Ni Steel, bonified (Quenched and Tempered) high toughness and tension resistance.
• SAE 4140 Cr-Mo Steel that is commonly bonified and induction hardened. This steel is used for applications under high load requirements.
• Shaft Design (Link).
• Failure modes (link)
• Load Distribution (Link)

Flange Coupling Calculation.

Quick and fast way to determine the torque capacity of a flange coupling,
Calculation is based on the combination between bolt tension and the coefficient of friction between surfaces.

This calculation do not consider, in any case, that bolts could work under shear load therefore all torque must be transfer between the surfaces.
It was observed in many cases, that once any of the bolts that belong to the pattern, starts to work under shear load, the torque distribution changes within the bolt pattern. 
Bolt will start to work also under combined bending loads which at the end will lead into a premature failure.

The tightening torque is determined using an "utilization factor" of 0.8.












































                                                                Flange Coupling Calculation

Additional Information about Flange Couplings:

Lessons Learned:

• A bolt that is not properly tightened can become loose after a short period of time
• If the fasteners are loose, they are subjected to alternating forces and may fail through fatigue.
• Few bolts could work only in tension, ans some of them work also in shear. Do not overload the flange to avoid premature failures.
• If it is possible, tight always the nut and not the bolt.
• Replace locknuts after some installations. Five or six is a good number.
• Try to keep the oil or grease out of the flange contact as well as from the bolt or nut area.
• Assembly instructions:
• Tight the bolt in pairs crosswise, looking for the opposite one each time.
  During all of the following steps, keep any gap between flanges even all around the circumference, and nuts made up approximately the same amount on each end of the bolt.
  • First time around just snug the nuts with a hand wrench.
  • Second time around tighten the nuts firmly with the same wrench.
  • Third time around apply approximately 25% recommended torque.
  • Fourth time apply approximately 75% of recommended torque.
  • Fifth time around, apply 100% of recommended torque.
  • Continue tightening nuts all around until nuts do not move under 100% recommended torque.
  • If possible, re-torque after 24 hours. Most of any bolt preload loss occurs within 24

Fastener Torque Calculation

Developed for designers and engineers that look for more information about the fastener than only the torque value.

This tool uses the concept of "Utilization Factor", that varies from 0.5 to 0.8. This factor is linked to the type of work the fastener is going to do in the joint. From just a quick clamp, no structural, no risk joint to a design where the fastener perfomance is critical.

Here are some screenshots of the application:

 

  Fastener Torque Calculation

    Additional information about joints and fasteners:

• Metric Grade
• Bolt Science
• Futek
• RoyMech
• Metric to SAE socket conversion
• MIT Open Course

   Lessons learned:

• Provide enough clearance for the wrench tools to access to the head of the bolt.
• Be sure that bolt can be assembled and dismounted, specially attention with long bolts that may be replaced without tier down all the transmission,
• Try to standarize all bolt types and sizes in the gearbox, specially in areas where the bolt is working in the same way. (housing calmping bolts for example)
• Do not mix same bolt sizes with different grades in one gearbox position.
• In castings, be sure that bolt head is not contacting an angled surface. Try to clean up always the casting surface, specially in aluminum castings.
• In aluminum, use roll form threads.
• When specifying the hole dimensions, leave at least 3 times the pitch size of gap between the tap drill depth and the thread depth. One way to specify this type of geometry can be done in this way: 
• Speficy the tap drill Max depth and specify the thread Min depth.
• A whaser under the bolt head can promote a better pressure and contact distribution. 
• Find the right location tolerances when defining the joint holes. Keep in mind always the rule of Clearance = Tolerance. An acceptable position value for threaded holes might be between 0.6 - 0.8. The MMC of the bolt is always its Outside diameter. From those values you may find the hole through diameter and its tolerance.
• If your calculations consider the bolt to be dry and without oil, make sure that you are receiveing this from your supplier.
• When the shank diameter of a bolt is less than the thread diameter thus allowing a radiused thread runout which reduces stress concentration - beneficial in fatigue applications.
• Distance between bolts to clamp the gearbox housings toghether should be around at 6.5  - 7 times the bolt diameter. (Example, M12 bolt diameter, distance between bolts should be around 78 mm and 84 mm)
• Avoid curved geometry between bolts in gearbox housings. Always think on designing for the min distace between bolts.
• If you suspect fatigue, a rule of thumb is to calculate the number of cycles a ferrous metal part has been exposed to before it failed:
• Failure at less than 10,000,000 cycles:  suspect fatigue.
• Failure at over 100,000,000 cycles: fatigue is not likely.
• It only takes 3600 rpm motor only 46 hours to produce 10,000,000 cycles.
• A 75 Rpm mixer shaft coupling bolt failing after 2 ½ years has over 100,000,000 cycles.
• From Fatigue Failure in Bolted Joint
• When joining materials with strengths lower than that of the bolt strength, a washer must be used to avoid bearing failure at the bolt/nut-material interface. In this case a washer should be used under both the nut and head of the bolt.
• The larger the washer diameter the thicker and stiffer the washer should be. It is also apparent that the strength of the washer must be at least equal to the strength of the bolt.