Take a look at Gearotic Thought, the successor to Gearotic Motion by Art Fenarty of Mach 3 fame.

**LINK**

This has been updated to have 42 different types of spokes.

As well as all the different styles you can choose how many spokes, alter the rim ratio, leg ratio and boss ratio.

This means that a given design can further be spawned off into unlimited designs by playing with these ratios.

Once designed you can get a DXF from it or even get Gearotic to spit the G-Code out directly.

It's getting to be a very powerful gear design software tool.

Russell

Can I ask what make/size of mill you used? Also what level of 'repeatable' precision/tolerance you achieve?

I have a project that requires a quantity of small brass CNC components but they need to fit together to quite a high tolerance, Is +/-0.01 doable?

The wheel you show looks really good, you going to remove the cutter radii in the corners by filing? It would make a big difference to the appearance

Ian P

Russell I reckon that I can cross out a wheel in about 10 minutes using traditional methods and if done correctly there should be very little cleaning up with files to be done Also an English regulator should run on about 7lb assuming its 7day going and not a monthly one My own regulator runs on 5lbs The only variation in time keeping is because the invar pendulum rod expands with cold and contracts with heat

Roy

Ian,

0.01 is 4 tenths of a thou, can you work consistently to that by hand using home shop machinery ?

If not then why would you expect CNC to better the accuracy of a base machine ?

CNC is good for repeatability it cannot replace basic accuracy.

Thank you Andrew,

This was a most practical post.

One thing to bear in mind is that using Andrews heat sink as an example, he got 0.05 using a high end home shop machine, a Tormach to be exact.

The professionals got 0.03 but and a big but their machine probably cost X 5 times to achieve an increase in accuracy of 0.02.

You can hit 0.01 but it's at a high cost or either time or rejects. Unless that accuracy is absolutely needed Andrews last line is very relevant.

I wonder what tolerance Roy achieves given he does a wheel in 10 minutes ?

John

I suspect that Roy would think that he produces his clock wheels to adequate levels of precision!

Russell

Working quickly and accurately by hand is not something that comes quickly but, like those posting on other threads say, it is a skill developed over time and once learned is not forgotten.

OK using CNC may be accurate and fast – if you are going to make lots of clock wheels the same or , indeed, I guess it might be an interesting exercise in machining / programming. The thing is though nobody NEEDS to build a clock. Visit your local pound store and you are likely to find a clock there which is far more accurate than one you will make. So construction of an English Regulator will test your skills and the outcome will be something of beauty that will out last you and many more accurate "modern" clocks. It will be a modern antique! Do you want your descendants to say "what a skilled old boy he was" or "surprising that the computers could do that in the olden days?

Hey well it's all about enjoying the journey – however you choose to travel.

Regards

Norman

Andrew

'Quite' is high praise indeed from me! It was the first word that appeared on the screen when I typed.

I designed the main part so that it could all be done with one cutter size and did adjust various other bits which to my thinking made it easier to machine. Not having CNC experience though, I might not be looking at the problem from the right direction. I dont know the trade-off between cutter changes for hogging out and finishing.

I presume if a part requires re-mounting for some operations it is the manual aspect that adds to the cost. As a general question, would it make sense to submit a drawing where a whole batch of identical parts were machined out of one bar but left attached, for me to later separate and machine the last face?

Ian P

Andrew,

Seems you were cutting a tad oversize:

0.7495

0.7500 *

0.7505 *****

0.7510 ***

0.7515 *

0.7520

Suspiciously close to a normal distribution for such a small sample

Reminds me of A-Llevel chemistry practical exam "It doesn't matter exactly what readings you get, as long as they are all grouped within 0.1cc"

Norman

Do you want your descendants to say "what a skilled old boy he was" or "surprising that the computers could do that in the olden days?

I just hope mine can tell teh difference between the models and the junk.

Neil

Not really, I was aiming for a decent fit in the slots in the front wheel hubs. A stack of slips gauges measuring 0.750" fits, whereas a stack measuring 0.751" will only just fit, with a bit of a shove. So most of the spokes should be a nice fit, with just a lick of the file needed on occasion.

Ian: It sounds like you're well on the way to designing to make best use of CNC. Had I used a separate cutter for roughing and finishing, the cutters would have been identical, but the one used for finishing wouldn't have been worn away by the roughing. Using separate cutters is fairly common if one is chasing tenths. Having to mount a part in more than one orientation has several cost implications. One, as you say, is the cost of manually moving it. Two, the cost of a second fixture and third, problems with ensuring that the part is accurately located, especially if critical features cannot all be machined in one orientation.

In principle it should be cheaper to have lots of parts machined from one bar for separation as a last operation. However, I'd talk to the CNC house and see what they think. Don't assume they know what they're doing! The company that had a go at machining our heatsink gave us a lot of waffle about their old Ferranti CMM measuring to microns. Given that the room it was in was essentially a corridor between the workshop and offices proper, with people coming and going all the time, I just asked if the room was temperature controlled.

Regards,

Andrew

No … Oxford is not playing ball.

Just search Google for:   instability of invar

The first hit will probably be for a book by Matthys … Chapter 23

Edited By Michael Gilligan on 19/11/2013 22:28:56