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Clock wheel cutter

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raynerd:
I fancy having a go at making a clock wheel of course building up to my long term plans of a full clock build but before I can even consider the wheel, I`d need to make the cutter. In my plans that I ultimately want to use, the plans specify the wheel Pitch circle diameter, number of teeth and module cutter to use. Consequently I`ll need to make the specific cutter determined by the "module", so I decided to try and make a 0.8 module cutter and find the measurements to make the cutter! I had some learning to do and this is what I found:



So the most important measurements as far as I can see are:

1. dedendum - the distance between the bottom of the tooth to the pitch circle diameter.
2. addendum - distance between pitch circle diameter to the end of the tooth
3. Distance between tooth = (normally) = width of tooth
4. Radius of arc that forms the tooth.

Obviously this changed a little when your making the cutter as of course your cutting the gap and consequently forming half of two adjacent teeth.

I then found this site which has lots of formula for how the module relates to these dimensions. I can`t find a link to the site but I saved the image, here is the table:



So that kind of helped but now got me a bit hung up on this idea of module, as to me the minute you specified a module I expected that you were specifying or dictating a specific wheel (I thought this due to the link in the formula) needless to say I was wrong. It took me a while but I put together this spreadsheet which gave me examples of using the same module on two different sized wheels - so I used a module 0.5 cutter on a 1 pcd and 2 pcd wheel and then did the same calculations but using a 1 module cutter.

http://www.raynerd.co.uk/images/Gearing.xls

This proved in my head that in actual fact the module DOES dictate the tooth dimensions, simply if you’re using another sized wheel you are just adding teeth onto that wheel but with the same profile. Now I was happy that the module cutter is a specific cutter for a specific tooth form. I then calculated the dimensions for a 0.8 module cutter which is what I wanted to make - this is on the far right of the spreadsheet.
There are currently no formula in the spreadsheet but I am working on adding this (that is what the notes page is for) and if I finish it, I`ll post it up. I used a pen and calc and simply used excel to tabulate the info.

OK, well now I have the dimensions for the 0.8 module cutter:
Tooth arc diameter required would be 2.51968 mm (it was actually worked out as a radius for the arc but the way I`ll be forming it, described later will require the diameter). The addendum for this tooth profile is 0.0424 inches (1.07696 mm) and the dedendum is 0.0496 inches (1.25984 mm). Gap between teeth is 1.25mm

I have heard good things about John Shadle's wheel cutter as it is fully supported. The standard single point/tooth flycutter style is said to often brake and if it blunts during cutting, resharpening often changed the size. John's version is really clever as the forming tooth is fully supported by the body of the cutter:

http://onlineclockbuilding.com/DOWNLOADS/flycut.rtf


....... and sometimes I can do maths, but from here on in I am a novice. I`ll let the pictures do most of the talking:

My slither of apparently silver steel that I picked up from the scrappy. 2inc dia and about 8mm thick. Little bit of steel round stock to be used as the madrel:



Making the mandrel:



Mistake number one - I threaded the mandrel, I think M8 and tried to hold the steel blank. Whenever I hit something a bit tought it just spun the disk. When I tried to tighten the bolt I threaded it and it just spun! Why did I thread it and did I do something wrong?


Steel blank being drilled:


So I had to drill the mandrel fully through and bolt the steel blank on using a bolt pulling it all the way through. It worked a treat but wasn`t as neat as my original idea.......comments appreciated:


Then I used my parting off, grooving tool to cut the dedendum on each side to the correct depth and also gain the correct tooth gap or in this case, width of the tip of the cutter:


Then I needed to put the radius on which I did using a 2.5mm drill bit. I made a template by drilling a 2.5mm hole and cutting it in half. I was going to use that tool next to it but it was too hard to get it to size.


So I used an old 2.5mm drill and hand ground the radius on the end. I`m sure there must be a more accurate way but this is how John described doing it. I got it quite accurate and it seemed to fit the template well, it was just fiddly and very hard to mount in the tool post:


I then prodded the sides to add the addendum that would create the tooth tip profile:


Then dismanltled it all:


Then chopped it in half and started to give it some profile:



Then I drilled the off-set mounting hole and I think you can see the tip profile on this photo. I still have some sharpening and profiling to do but it is there! If you open the link I sent of John's article you will see that by mounting this off set hole in the arbor you automatically create relief below the cut.



So, there we go!

Will it cut a wheel?  Is it silver steel (seems very soft, definitely needs hardening!)?

I`m not too sure but I feel good that I`ve made it! Next job is to harden it and I may even purchase some case hardening compound.

What is the best way to mount this on the arbor? I just think that if I thread a hole on a mandrel it will spin and not hold properly like when I tried mounting the original blank earlier in the post. I could do with a key way or perhaps bolt it in two places...any suggestions?

All the best.
Chris

sbwhart:
Nice going Chris

You've certainly jumped in with this one. Makeing a clock is something I wan't to have a go at, I've read a number of diferent methods for making the tooth cutter, one thing that struck me is the crudness of the methods. I think of a clock as a presition instrument, but when you read how they made early clocks you realise that even using crude methods and the minimum of tooling you can make an intrument that will keep accuratle time.

Any way if it is silver steel the fly cutter is made of it won't case harden. What you need to do is heat it to cherry red and quench it in water, then polish it up, then yoo need to aneal it back a bit, to do this heat it up again on a bed of sand (this slows the temp rise) until its a straw colour then quench it again in water.

You need to make the arbour with a plain diameter thats a nice fit on the cutter with a short threaded length to take the bolt it will look like this



Hope this helps

Stew

raynerd:
Stew, thanks for the help. So basically I need an external thread that I can slip the cutter onto it and then bolt up. Would you bolt up directly against the cutter or would you slip on a washer to give more surface contact against the cutter. I can just imagine it not locking it tight enough and when it comes to cutting the wheel it spinning the cutter around rather than making the cut. I know commercial cutters have a notch or keyway in the mandrel and cutter to stop it spinning.

Chris

sbwhart:
Yes a washer would be a good idea  :thumbup:

Stew

raynerd:
Thankyou  :wave:

Got half term week off so I should give this a go over the next few days.

I`m still questioning whether this was silver steel - seems on the softer side.

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