Thursday, 4 June 2015

Trials and tribulations when making a new prototype gear making machine

Some time ago I decided to attempt to design from scratch a new gear making machine.  Some 50 years previously I  read about a commercial gear making machine which made use of a simple cutter in the shape of a rack. That machine was a Sunderland Gear Planing machine.  It utilised a cutter in the form of a rack to generate the exact involute curve applied to each gear tooth to enable perfect meshing irrespective of gear size.  In the case of a very large gear, say of infinite diameter, the gear becomes a rack and the involute curve becomes a straight sided 'V' shape with the pressure angle determining the angle of the 'V' form.  This was the fundamental approach used by Sam Sunderland who first built a prototype machine using a cutter in the shape of a rack in circ. 1905.   Operationally, a reciprocating rack cutter makes a cutting pass to a gear blank whilst also moving vertically as if it were in mesh with the gear blank.  Thus as long as the cutter rack moves vertically a small amount after each cutting pass and the gear blank rotates a small degree in absolute synchronisation then the process will ultimately result in generating gear teeth with the exact involute curve required.

To me this was a beautiful simple and elegant method to manufacture a complex involute curve which is specific to the number of teeth in the gear being made and its PA and DP or Mod specification.   The prototype machine I wanted was to be a small bench top machine which once set up would run automatically and the end result would hopefully be a correctly generated spur gear.

The individual mechanisms required would adhere to the basic Sunderland operational principles but be totally different to that of the Sunderland (of which I had no detailed knowledge) and would therefore provide a very challenging design project.  Fortunately I had the use of 3D modelling software to make a digital machine but ultimately it is only when it is made from steel etc. and the trials begin you see if it will  produce a spur gear with a correct involute curve.  Making the prototype in steel was the simple bit and during the many trials it became clear that despite me being the designer and builder I would have to learn how this machine worked to get the best consistent results.  From the outset I decided the true test of success would be if the machine could produce an acceptable spur gear using hard steel for the gear blank as this is normally difficult to machine and meant that the prototype machine would have to overcome this problem but also meant that in less hard materials the quality was likely to get considerably better. 

This project has certainly proved to be a challenge but the end is now in sight and recent gears made using hard steel are good and the rack cutter seems quite resilient showing no sign of wear.  What is pleasing is the design processes used, which in no way are similar to the Sunderland, have been shown to work and also provide sufficient scope to produce gears of a wide variety for very minimal little cost.  The making of a rack cutter is both simple and very inexpensive as compared to the commercially available alternatives there is a massive saving (1:160 for single gear specification)

For more details see my website  -

Tuesday, 23 December 2014

Preventing Rusting in the Workshop

It is a sad fact of life that where there is moisture in the air then there is a real possibility that valuable machine tools will succumb to rusting.  In my workshop I am fortunate as I have not had any problems with rusting over the last 30 years and I thought it may be of interest to see why.  In my opinion the key things are environment, constant temperature, few windows, low moisture, cover machinery and use of an oily rag on machine surfaces.

The workshop environment is key and my workshop is a double car-sized garage which is part of the house with the main living room above.  The garage has a single large window on one side which is away from any machinery and a wide north facing up-and-over door.  The door is a commercially made unit which is fully internally insulated and has rubber seals.  This door is remarkable in that it is just over 1" thick yet heat loss is minimal.  As it faces north there is no sun to warm it up so by and large the workshop keeps to within a 10-16deg. C range year round.

Maintaining a constant temperature is essential and changes should occur very slowly.  If temperature changes happen quickly by using external heating then moisture will condense onto colder metal surfaces and rust will soon appear.

Maintaining a low level of moisture inside the workshop is ideal and the use of a dehumidifier will help however I do not use a dehumidifier and also park the car inside the garage even when it is covered with rain drops.  So why do my machines not rust when there is evidently a lot of moisture in the air?  The constant temperature is again a major reason but I also cover my machines with these 'blue' polyethylene woven tarpaulin water resistant sheets which are readily available and very low cost.  These sheets are arranged so that they prevent any moisture droplets getting onto a machine surface but crucially allow a free passage of air.  Never use cotton or any covering that absorbs water!

If there is a need to raise the temperature of the workshop then this must be done very gradually to allow the cold metal to also heat up. Never use propane or similar heaters as they produce a lot of water.

The final step is to keep an oily rag available and give the machine surfaces a quick wipe if the workshop is not going to be used for a week or so.

See my website for more information:

Monday, 22 December 2014

So what is gh creative engineering

So what is creative engineering?

I studied engineering many years ago but got side tracked into a computing career mainly because engineering jobs were low paid and difficult to find. The creative aspects within this new and emerging world of computing stayed with me until I retired.  Unfortunately, whilst computers were and are fascinating, my true passion was always engineering.   Despite a demanding job I had a basic home workshop and whenever there was time I was able to spend time making models and tooling.  Now retired, my hobby is my main interest and decided to build some models and workshop tools.  This brings me on to explain the 'creative' aspect of my engineering hobby.

It is quite enjoyable to build a model from acquired plans but sometimes the tools available in my workshop were 'limited' which often presented difficulties.  The answer was to adapt my equipment and 'create' tools to overcome as far as possible the build of models.  This aspect of the hobby is, for me, the most interesting because it is creative.  To design tools and machines to meet a requirement presents many challenges but is very rewarding.

My most significant 'creative engineering' design and build is that of an automatic spur gear involute profiling machine.  This machine operates using the concept used in the Sunderland gear machine.  My starting point was just  a single paragraph in one of my old text books describing the operating concept and a picture of the Sunderland machine.  The operating concept is simple and by means of a 'generative process' it produces accurate complex involute curves.  My machine is a small bench top version which adopts the same operating concept but thereafter the design is unique and all created from just a few words in a book.  The journey from design to completion has taken several years with many obstacles needing to be solved but this is the best part of creating a new machine and then making it so that it works.

See my website for more information: