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Thursday, 21 February 2013

Gear design software

Following from the last post the following list of sites offer Gear profile generators to create the gears for you.

This first Gear template can be used either on line or you can purchase a fuller more feature rich version for use on your PC. The output is to an HPGL format that can be used for direct printing .
One of the benefits of the paid for version is that it can export to DXF format

This software will provide templates for all manner of gears, ratchets and clock escapements along with the facility to adjust the profiles. Output as DXF files. This is not a free program but you can download a demo version to try it

eMachineShop is a Free 2D drawing package with a module for drawing gears, easy to use, you simply add the basic gear parameters and it draws the gear which can then be exported as a DXF file.
The program is free but unlike the first two programs it lacks the facility to see to the main gear and the pinion on-screen at the same time.
Simple Free program , input gear parameters and then save as DXF.

This is a program to generate tooth profiles in an epicyclic form rather than the more generally used involute form. For a description of the difference see the following:-

Comparison Between Involute and Cycloidal Gears
The output from this program is in DXF format and can be viewed in a browser.

Wednesday, 20 February 2013

Gear Train design for the wooden clock

The gears used in all of my clocks have geometry based on the standard gear profile formulae with some adjustment to the tooth profile to thin them down a little to make it a bit less sensitive to the inaccuracies inherent when using hand cutting methods to produce them.
When designing clock gears I generally use the metric system to define the teeth but both metric and imperial can be used interchangeably. The chart shown below shows the formulae I use for gear calculation.

For the gear teeth to engage with each other they must both be calculated using either the same Diameter Pitch (DP) or the same Module these two terms relate to the way the teeth are spaced around the Pitch Circle Diameter (PCD). You can see from the chart below that as the Mod increases so does the size of the tooth, and visa versa for the DP.
If you are working with metric dimensions you will use the MOD and if you are working in imperial dimensions you will use the DP.
Generally speaking, if you are building a wooden clock then you will be using Mod 1.5 or above.

Once you have decided on the DP or Module you are going to use that to calculate all the other features using the formulae in the chart at the top. Both these charts come from the Technical section of the HPC Gears catalogue 
There are two main gear trains in a clock, the minutes train that requires a total ratio of 60:1 this runs between the shaft carrying the minute hand and the escapement wheel. The escape wheel normally turns once a minute and it connects through the train with the shaft holding the minute hand, which turns once an hour, hence the 60:1 ratio.
The second train runs between the minute hand and the hour hand which requires  12: reduction. This ratio normally has to 2 sets of gears with ratio's of 3:1 and 4:1 and the centre distance of each are normally the same as the gears are mounted on the same pairs of shafts, I always use a 8 teeth and 32 teeth pair along with a 10 teeth and 30 teeth pair, as it allows the shafts to be shared.
With the 60:1 ratio there are many more options open to you and will to a large extent depend on the design you are trying to achieve, so I must leave that up to you to decide. Having said that a simple set of 3 gears using 3 pair sets with ratio's of 3:1 4;1 and 5:1 works quite well as when multiplied together they will give you a 60:1 ratio.
Having decided on the  gear arrangement I normally try to determine the Module value I am going to use and that relates to the size of the gears I want. To determine that I would normally work out on CAD or on paper what size I want the largest gear to be, so in my case this is usually a 60 tooth gear. As an example I have decided the gear needs to be about 125mm (5ins) diameter so from the chart above I can work out a value for the module.
Module = Outside Diameter mm / ( Number of teeth +2)
This gives a value for the Module of 2.016 so round that down to 2.0 and you can now use that value to calculate the sizes for all of your gears.
If you are an organised person you would use a spread sheet to enter all your values to work out the relevant gear sizes, I never got round to doing this so finish up working them out on a calculator.
The chart below shows a typical gear pairing for a 3:1 gear ratio and a Module of 2 using a 60 tooth and a 20 tooth gears. The tooth thickness is slightly less than the normal 50% of the CP value I have used between 44% and 48% of that value depending on what looks to work best in the CAD simulations.

Friday, 25 January 2013

Clock 15 - Latest developments

The design of Clock 15 is now complete, with all the features incorporated. I have attached some renders of the model below to give a proper idea as to what it will look like.
That is really the most enjoyable part of the design process finished, now its mostly hard work to bring the deign to a point where it can be added to the website so that the plans and files can be offered to you.
The next stage is to prototype the clock, to do this I will generate DXF files for machining and do the initial detail drawings for me to machine all the parts that wont be cut on the CNC router.

As this is now the middle of winter there is no way I'm going out to the workshop untill it gets a lot warmer, so further developments on the design will have to wait for a couple of months.
Clock 15 Full Length view
Detail of the Grasshopper
Dial Detail

Detail of winder

Detail of Maintaining power
Visulised with glass inserts

Friday, 18 January 2013

Materials for Wooden Clocks

I have been wondering for a while now what wood to use for the next clock that I build. I used Oak for the Clock 14 and was really quite disappointed with the the quality of cut that I was getting even with new Carbide router cutters, and how difficult it was to get the teeth to clean up properly. The other thing with the Oak is that although it is very hard and stable it is liable to split and splinter so I kept losing bits from the gear teeth and other small detail places.
The problem is the very course open grain structure of the Oak, so this has led me to start looking for an alternative wood with a fine grain, but at the same time hard and strong  and capable of attaining a fine finish. I have visited a few websites in this quest and they are all listed at the bottom of this post if you want to undertake your own study.
I make no recommendations on what is going to be the best choice, mainly because there is no single best choice, but some woods are clearly more suitable than others.
The chart below lists some of the more common species that are available and one that isn't available any more (Lignum Vitae) for its historical use by John Harrison. 
The chart is self explanatory except to say that in the last two columns the lower the number the better.
Ash and Oak are the only ones listed that have a course grain, they are usable but the rest hopefully should be better.

Name  Density Texture Grain Ease of working Stability
Alder Medium Fine Straight 2 1
Apple Hard Fine Straight to Roey 2 1
Ash Medium Coarse Straight 2 1
Beech Medium Fine Straight 2 2
Birch Hard Medium Straight 2 2
Blackwood Hard Fine  Straight to Roey 1 2
Boxwood V Hard V fine Straight to Roey 2 2
Cherry Medium Fine Straight 2 1
Dogwood Hard V Fine Straight 1 2
Red Gum Medium Fine Irregular 2 2
Lignum Vitae V Hard Fine Straight 1 2
Lime Soft Fine Roey 3 1
Maple, Hard V Hard Fine Roey 3 2
Maple, Soft Medium Medium Straight 2 2
Oak Hard Coarse Straight to Roey 2 2
Pear Hard V Fine Straight 2 2
Satinwood Hard V Fine Roey 2 1
Walnut M Hard Medium Straight to Roey 2 1

From this list I will make a choice, I will give consideration to what is available locally, how much its going to cost , and more importantly its suitability to for the different clock parts, as the frames and the gears and the arbors all have slightly different requirements, so will probably finish up with different woods for different parts.

To help with the choice I have made a few notes on each of the different woods.

It is heavy, brittle and has a fine, dense, even texture, and bends easily, and resists splitting. Well suited for carving and turning, as it's extremely hard and limber.

 European Alder has closed pores, and a fine, even grain. The grain is usually straight, but can also be wild or irregular depending on the growth form of each individual tree.
European Alder is very easy to work with both hand and machine tools; it sands especially easy. The wood is rather soft, however, and care must be taken to avoid denting it in some applications, not suitable for gears but could be used for the clock frames.

Ash is a long-fibered, light-coloured, medium-density wood, hard, heavy and with a course ring porous grain. It has a prominent grain that resembles oak, will split and splinter easily.

Beech is a heavy, pale-coloured, medium-to-hard wood used widely for chairs and stools. It has a fine, tight grain and large medulla rays, similar in appearance to maple or birch woods. Beech wood has a high shock resistance and takes stains well. Humidity adversely affects the wood.

The sapwood is generally creamy-white, and the heartwood is a very pale brown. It has an even and straight grain, and has good strength and bending properties. It is stiff, very hard, and holds a clean edge. Suitable for frames, keels, and deck houses. Sharp tools are required. Should be selected carefully and cut to avoid grain patterns. Warps readily if not thoroughly seasoned

Australian Blackwood has small, open pores and a fine to medium texture. Grain is usually straight to slightly interlocked, and sometimes wavy. Colour can be highly variable, but tends to be medium golden or reddish brown, similar to Mahogany. It is easily worked with both hand and machine tools, though figured wood and pieces with interlocked grain can cause tear-out. Australian Blackwood turns, glues, stains, and finishes well. Responds well to steam bending.

A very fine textured hardwood with a strong distinctive tanish cream to yellow colour. Very dense with almost no grain or figure. It carves with great detail. Used for turned parts and small detailed components. Boxwood is relatively hard to cut, even with extremely sharp tools, but the effort is worth the labour. A superior wood for clock parts, as it retains sharp edges and details to the smallest dimensions. Care should be taken as in time it can warp and twist if not supported. 

Has a fine texture with close grain. The grain is usually straight and easy to work—with the exception of figured pieces with curly grain patterns. Cherry is known as being one of the best all-around woods for workability. It is stable, straight-grained, and machines and turns well. The only difficulties typically arise if the wood is being stained, as it can sometimes give blotchy results due to its fine, closed pores.

This is an extremely hard, dense wood with a close and very fine grain. A little hard to machine due to its toughness and hardness. Usually white to cream, but can be found in colours to pale yellow and pinkish-brown. Capable of an extremely smooth finish and can be turned to exacting dimensions. Doesn't take stain well and is difficult to work, but can be carved to delicate detail. Hardness will dull and burn saw.. A substitute for boxwood.

Similar to pear, but slightly darker. Has a close, fine, and even texture, irregular grain, and bright satiny sheen.. Red gum can be used as a substitute in appearance for walnut.

Lignum Vitae
Lignum Vitae has a fine texture and closed pores. Bare wood can be polished to a fine lustre due to its high natural oil content. The grain tends to be interlocked and tight. Lignum Vitae is regarded by most to be both the heaviest and hardest wood in the world. Its durability in submerged or ground-contact applications is also exceptional. Lignum Vitae has been used for propeller shaft bearings on ships, and its natural oils provide self-lubrication that gives the wood excellent wear resistance.
Unfortunately, Lignum Vitae has been exploited to the brink of extinction, and is now an endangered species.

Pale, almost white to pale creamy brown with a straight grain and fine uniform texture. Holds a fairly sharp edge, but frays when drilled and sawed. Bends relatively easy but has poor steam bending properties, and low strength. It finishes well but surface "fur" requires sealing.

Hard Maple
This is a heavy fine grained white wood, stable, and among the hardest of usable clock building materials. Although excellent for small parts, its extreme hardness and occasional irregular grain make work difficult. Grain varies from a bird's-eye figure to straight. Color can be pale yellow to deep honey, and can be dull looking. Has high density, a fine, even texture, and is strong and stable. An alternative to box. Easily worked with hand and power tools. Holds an edge well and takes a good finish. Suitable for turnings, gears and it will ability to take a smooth finish, and show a distinctive sheen.

Soft Maple
Soft maple, on the other hand, is relatively easy to work with. Because of their fine, straight grain, both varieties are more stable than many other woods. They also tend to be less expensive than other hardwoods

Oak is a hard, light to medium gray-brown, tough, short fibred wood with a distinctive grain structure. Like mahogany, because of its coarse grain structure is it not really all that suitable for model building.

 Pear is a fine, close grained wood with distinct pores. Can be worked to delicate detail, bends well, and takes an excellent finish. Selected pieces have a straight grain. Turns and cuts well with a clean sharp edge, and holds sharp detail, but has a slight dulling effect on tools. An excellent wood for clock making, but a little scarce. Domestic pear has a cream to pinkish brown to rose colour and the grain structure is excellent for clock making. Foreign pear is usually of better quality, but difficult to find.

Grain is interlocked, producing an attractive mottle figure, as well as striped or roey patterns on quarter sawn surfaces. Texture is fine and even, with a very high natural lustreDifficult to work on account of its high density and interlocked grain. Most surfacing and planing operations result in tear-out, especially on quarter-sawn surfaces. Pronounced blunting effect on cutters. Turns superbly. Glues and finishes well—able to take a high natural polish.

Walnut is a uniform dark purple brown. Even but coarse, open grain limits Clock making applications. Works easily, is hard, strong, and stiff. Free from warping or cracking. Sands to an excellent finish. Cuts and carves exceptionally well, but usually can't obtain fine detail.

For Turning: Apple, box, cherry, dogwood, holly, pear, maple, satinwood..

Friday, 11 January 2013

Woodenclocks new web posting

This is to be the first of many postings which hopefully follow the development of the new clocks as they evolve through the design and development process.
I will write about that process and all the other peripheral issues that arise along the way.

As each new clock seeks to follow a slightly different route, I will try to illustrate what guides the decisions that are made along the way, and examine some of the technologies used in the design.

Currently I am working to incorporate the Grasshopper design of escapement into the next clock which will naturally be Clock 15. The more elegant lines used in Grasshopper 2 are being picked up and used in the new clock design.
The Art Nouveau style is being used to guide the aesthetic of the clock, this is the artistic period that straddled the end of the 19th and the beginning of the 20th centuries and is characterised  by a naturalist free flowing form  that draws strongly from nature.
The Clock is to be wall mounted and has a Seconds pendulum ie it takes one second to swing in one direction and the another second to swing back again.
There is also a single pulley system added to this clock to double the run time, it is mounted on the rear frame so that the weight is carried close to the wall reducing the twisting that can occur when you hang the large weight at the front, the weight of course has to be doubled in size to compensate for the action of the pulley.
A seconds hand and small dial is fitted, but this I belatedly realised will   run backwards, much as it does on some of my earliest clocks.
The use of the Grasshopper drive causes an interesting problem for the design as it can become somewhat disengaged when the clock is being wound and the driving weight is not fully engaged. If this happens its possible that the clock can start to run free and out of control causing considerable damage to the mechanism. To prevent this I have added a Maintaining Power device that the user engages before winding and releases afterwards.
As the design develops over the next few weeks I will try to keep you informed of the developments.