No updates for a few days.

Going to be a bit before I can work on the clock again.  I'm spending the next few days finishing up a woodworking project.  For those in the SCA, I am working on a new set of thrones for Trimaris.

Some research notes on gear cutting

  With trying to keep this project as authentic as possible, one of my great concerns has been the cutting of the gear teeth.  No documentation that I am aware of exists for how medieval clock makers would have cut the gear teeth.  I have gone back and forth on this but I believe I have a completely feasible production method.  First, the list of the different techniques.

  1)  Filing
  2)  Chisel cut then filed for cleanup.
  3)  Punch then filed for cleanup.
  4)  Sides of teeth cut with hacksaw then hot chisel on bottom of tooth gap to remove material.  Filing for cleanup.

  I think the fourth option is the most likely scenario.

  The first scenario, all filing, works for small gears made out of material like brass.  However, with the large sizes of the wheels and the fact that the material is iron it would involve a lot of filing.  Also, this would wear through many files.  I think this technique would just be too labor intensive and expensive on the files.

  Chisel cutting was a method I have thought about frequently but it has problems.  For those not as experienced in blacksmithing, the metal is heated and a chisel is hammered into the material while it is still hot.  This is usually in the 1400-2000 degree range.  This is a very common blacksmithing technique.  It has some problems as far as the teeth of the gear are concerned.  The biggest problem is that metal is always displaced as part of the chiseling process.  In other words, as I cut one tooth, the adjacent tooth would be pushed some.  I could clean this up with some careful forging.  Another problem is that much hot cutting makes it very easy to accidentally soften the chisel due to the heat.  This would probably require several touch ups and rehardening of the chisels during the work.

  I have briefly thought about punching the teeth.  This would involve creating a punch that matches the exact shape of the gap between the teeth.  While the gear is hot, the punch could be used to knock the gap out.  Problem is that punches also displace some material and they are very easy to not place exactly where you want the punch, especially when talking about a difference of 1/32" of an inch being important.

  So I am now looking at hacksaws.  When I first started this project, I believed hacksawing the sides of the teeth were the way to go.  And when I received a copy of a research article on medieval clocks from the British Museum it also indicated a belief in using hacksaws to cut teeth.  However, when I contacted the gentleman who wrote the article, he indicated that he was no longer sure about using hacksaws.

  Well, it is possible to find hacksaws in period.  Indeed, a search I did over the weekend uncovered several more examples that I was not aware that they existed.  There is one issue to be aware of with this.  Hacksaws can be used for many things.  Examples include cutting for decorative pieces such as horn or bone or cutting softer metals for jewelry.  Hacksaws really are not good for wood because of their tooth size and spacing.

  My research a few years back led me to the Viking tool chest, the Mastermyr Chest.  I made a reproduction of this about 2 years ago with a working lock and key.  In this chest was a hacksaw.  This hacksaw, from what I can see, almost exactly matches a modern equivalent.  The tooth count, tooth pitch and blade thickness all compare to a hacksaw blade that you can buy at a local hardware store.  Also, there are other metal items in the chest that have cuts that match the thickness of the blade.

  Getting the shape of the hacksaw was easy.  The difficult part may have been getting it hard enough.  When cutting iron or mild steel, you need a fairly tough blade.  I think that this was well within the capabilities of the smiths of the later middle ages.  A thin saw blade could easily be case hardened.  If the item was surrounded with carbon material such as bone or fat then wrapped in clay, it could be baked in a fire and case hardened.  I believe that this would give a hacksaw enough carbon to harden it sufficiently to cut the relatively soft wrought iron.  Also, files date back to the Romans and would have needed just as much toughness.

  I also believe that locksmiths probably used hacksaws.  Why so few examples of hacksaws then?  Very simple, they are thin quality steel and blacksmiths are the ultimate recyclers.  Once a hacksaw went dull there was a very good chance that the smith just reused the thin blade as a small spring.  And if the blacksmith did not reuse the blade and just discarded it, the thin material would have easily corroded away.  Most examples of hacksaws from the middle ages come from bogs where the material was preserved.

  So, within the next few weeks I hope to try actually cutting the gears.  I am going to cut the sides of the teeth using a hacksaw.  When I do this, I am going to use a template to make sure all the teeth are at the same angle.  Then the excess material between the teeth will be popped out by heating the gear and using a flat sided chisel to cut the bottom of the gap.  The only metal displaced should be the waste material.

Gear Work

  Well, I could not stand it any longer and I had to start the gears today.  Before I describe the process, some basic information about the gear that I am working on.  This gear is called the great wheel on the going train.  What's so great about it?  It really just means it's the largest gear on that side of the clock.  It has a 12" diameter with 96 teeth.  That comes out to about 3 teeth per inch.

  To start off, I need someway to forge the circle as perfectly as possible.  This is where the layout table comes into play.  This is what the table looks like.  You will notice too circles.  One circle has an outer diameter of 12" and an inner diameter of 9 1/2".  Also in the picture is a piece of 1 1/4" x 3/8" stock that is 34" long.  If you do your basic math you may think that that is not enough (12" x pi = 37.7").  However, the forging process stretches the metal on the outside and compresses it on the inside of the circle.  This means you actual want to use the midpoints between the outside and inside diameter when determining how much metal you need.

p.s. (Thank you Francis Whitaker for sharing this tidbit of knowledge.)

  Anyway, here is the layout table.  You can just make out the circles.  (Click on any of the images to see larger).



So, to make the circle, a portion of the bar is heated and bent using a twisting fork.



  After each heating, the bar is compared to the layout table to make sure it is staying true.  Here are some progression pictures.  I used a technique described by Francis Whitaker in which 1/4 of the circle is made on one end then you switch and work on the other end.  Not quite sure why this is but I think its to help with the tendency of the metal to twist in your hand if there is too much metal out to one side.  Anyway, here are the series of pictures.



 


Oops!  When I closed the circle, I had too much material.  The overlap is about 1 3/4" too much.



I reopened the circle a bit, cut off some material.  The circle was closed back up and welded.  The bulge of the weld can still be seen as this is prior to cleanup.  What is nice is that all around the circle it is only off by at most 1/32" of an inch.  Woo hoo!



  The only minor issue is that during the welding, I accidentally burned a small amount of steel from the edge.  It is a small amount and I think I may try to cut the gear so that a gap between teeth will be where the small amount of metal was lost.

  I next decided to start on the spokes.  This involves taking a rectangular piece of metal, splitting it down the middle on both ends.  These are opened up and draw out.  These work photos give the idea.  (Notice the punched holes, these help with the split being nice and clean.)









  I ran out of time and daylight so I had to stop before I was really done with the spokes.  However, I laid the rough version of the spokes onto the gear just to give an idea.



  So, making some real progress and I hope to start on the arbor soon.  Once the arbor is done, then I can cut the teeth.

Minor update

  I am doing some prep stuff for the gears.  Yesterday I purchased a high quality divider.  This will be used to mark the teeth for the gears.  When dividing the gears up, I will not be dividing by the number of teeth but a larger number.  For example, the main wheel on the going train will have 96 teeth.  I will first divide the wheel into 4 parts of 24 teeth.  Next, those 24 teeth might be broken up into 6 parts.  Then finally into the final four teeth.  This is just easier to lay out then trying to find the exact measurement for the divider that will handle 96 teeth.

  Next I finished cutting off a big hunk of S7 steel.  This will be used to make a top swage to form 1/2" diameter round.  The 1/2" will be the size of the arbor where it goes into the frame.  Most of the arbor will be 1" round stock.  This part of the arbor will hold the winding barrel.  The barrel is nothing more than a round cylinder of wood with a 1" hole in the center.  Other parts of the arbor will be square and this is where the gears will go.  And finally, as mentioned above, the ends of the arbor will be 1/2" round.  That is what I need the swage for.

  Finally, I made my gear layout table.  To call it a table is a bit misleading.  It is nothing more than a thin sheet of 24" x 24" steel glued to a a sheet of 24" x 24" plywood.  In the center is a small pin.  I use the pin to draw two concentric circles.  One circle is the inner diameter of the gear while the other circle is the outer diameter.  As I bend the gear, I will use these circles to ensure my gear is staying true.

  I had hoped to get more done today but it was rainy so I was not able to start until late afternoon.

More parts done...

  Got to the forge again and continued the work on the vertical posts.  These are the ones that are held to the frame using pins.  Also, almost all other clock parts will be attached to these pieces including the arbors (axles) for the clock.

  I also had to make a special shaped punch.  Essentially it is a rectangular punch with rounded ends.  I used it to help make some of holes in the new pieces.

  Anyway, here are some new pictures.  I would have taken some pictures while I was working but I didn't have the camera until the end of day.  In these new pictures you can see the 4 new parts as vertical posts in the middle of the ends and sides of the clock.

In the next photo you can see a pin holding the post on.  I only had time to make 1 pin.  I need to make 7 more for the others posts.  Also, the lettering on the post is "GT" with an up arrow.  That stands for going train which is the time keeping side of the clock.  The arrow and GT let me know where this particular bar is on the clock and its orientation.  The lettering will be removed during final cleaning.

 

Quick update...

  I did not have access to my camera today so just a description of what I worked on.

  I worked on the end uprights for the frame.  These hold the other ends of the arbors (axles) of the clock.)  In a previous entry, I had put in the vertical uprights in the center of the clock.  These uprights go on the end of the clock and are held in by pins.  In order to make these, I need to fix some tools and make a few new ones.  Here is a quick rundown...

  * Made a new rectangular drift to match the size of the pins on the frame.  This will be used to make the holes in the new pieces.

  * Fixed a few chisels.  They had been resharpened enough that the bevel of the chisels was getting too severe.  I reforged their cutting edges and rehardened them.

  * Made a new bolster plate to match the drift made up above.  If you ever do drift work with metal, it is important to have a matching bolster plate if you are concerned about the finish of the metal.

  After doing the bit of tool maintenance, I made one of the end posts.  This was really a fairly acedemic process of punch and drift.  I also made the pins to hold the post in place.  I didn't get to the post for the other end as I had some other stuff to take care of.

Pictures to follow.

Clock is a bit heavier now...

  Today I worked on the center posts.  These will hold the arbors of the clock and they are removed to allow me to create the arbor holes at a later date.  They are held in by gravity and small wedges at the top.  This shows the frame as it is now.  Remember that the center posts are removable.  And actually, any part after this point is removable from the frame.



This shows the detail on the wedges that hold the center posts in place.  The silvery powder is filing shavings from fitting the parts.