Myford Change Wheels

I'd like to cut some change wheels for the ol' Super 7 but I was curious what the collective wisdom was about what material to use. I believe genuine Myford ones are iron but can I get away with Meehanite processed iron bar or do I need a harder grade?

Same question for my WM180 - I'm sure I read aluminium change wheels are fine - cany anyone confirm please?

I've got some nylon ones off eBay for my Boxford 280; chap makes them for all sorts of lathes. Not had any problem. Change wheels aren't heavily loaded, so they're OK - like the OEM Myford Tufnol tumbler gears.

Pretty much anything will be probably outlast us but I chose FC steel for these " Myford" gears ( actually for the GHT bending rolls). They cut pretty easily with 2 passes of an RGD cutter.

Rod

Nice work there Rod. OK, I'm sold. FC steel is the easiest option and should do what I want.

Lovely job Rod - only 2 passes?

I wonder how my chinesium cutters will do...

I was thinking that. 2 passes? I think I'm heading to the RDG website.

Two passes? That's pussyfooting Rod!

When I started gear cutting I used a roughing and finish pass, but quickly realised it was a waste of time. It just wears the cutter. Use one pass and be done with it. Like this 6DP helical gear:

And it is an RDG cutter.

Andrew

Alu. wheels will also make noise. But of course nobody will run gear wheels fast enough to make them noisy ?

Clive.

PS. I had an Opel Kapitan one time and the large timing gear was made of fibre which disintigrated. The replacement gear was aluminium and I could hear it when the engine was running.

Seems like Delrin (nylon-like plastic) has been a popular choice for change gear material in the past. Sure there have been threads on it before.

An uncle of mine had one of these some many years ago, two features of which I remember: the speedo was a horizontal ribbon which changed colour to reflect the speed limits and when you opened the driver's door a small spotlight illuminated the ignition, both useful in their own way.

Today's cars are keyless and tomorrow, no doubt, compliance with speed limits will be automatic.

Now that's showing off Andrew. Us mere mortals are more timid.

I think I'm going to machine a couple, one in steel and one in iron and try them out.

Just read this in Gears and Gear Cutting - Ivan Law, p66

"Always try to cut to the correct depth with one cut; nibbling away with a succession of small cuts is not recommended."

I guess that answers the question for me, but I will not be attempting steel or iron with my first attempt - confidence is key!

Chris,

All but the smaller Myford change wheels, from say 30T and less, are all usually supplied in cast iron. I have found that continuously cast material is excellent. The smaller sizes are made in steel to handle the tooth loading.

Andrew is quite right and is not boasting, gears are cut in one pass. The cutters begin to lose their edge when not worked as intended and only need more frequent sharpening as a result.

Regards

Brian

Edited By Brian Wood on 01/02/2019 09:01:08

Chaps,

I accept the collective wisdom of the desirability of cutting the teeth in one pass but can somebody please explain to me the mechanism of more than one pass blunting the cutter?

In my case a combination of the power of my mill motor and the slowest speed of my auto table traverse, not to mention the noise from the back gear, led me to be more comfortable with 2 passes and the cutter (which I assume is Chinesium) still seems to be sharp.

Cheers,

Rod

Logic suggests that a tool that has x number of hours life span will take twice as long doing two passes as one achieving the same result in one pass. I think the description should read that it blunts the tool more prematurely than it needs to rather than the suggestion it blunts the tool beyond usability.

.... and thanks for the info Brian.

At the risk of being accused of boasting, I followed Ivan Laws advice and cut the gears with one pass, but with a gentle feed in terms of feed per tooth.

Most of us are unlikely to wear out a cutter with the number of times that we use it. If we were, it would probably be worth spending the money on an Industrial quality cutter for Industrial use.

Myford gears, or all the ones that I have seen are cast iron. I have made up a couple of compound gears by cutting them in steel and sticking them together with an anaerobic.

As pointed out elsewhere, be aware that Myford gears although 20DP are 14.5 degrees pressure angle, not 20.

Howard

If the tool is applied to cut in one pass, the whole cutting edge is applied to the work once only. Conversely, when the tool is applied in steps, the wear concentrates on the sharp end of the cutter. It's because, when nibbling, the sharp end does most of the work and goes blunt while the other end of the tool's edge is barely used at all.

Provided the machine has enough grunt and the tool can take the strain, using the maximum amount of edge possible per cut will extend the life of the tool. This is important in industry, but even something the size of Bridgeport has limits, which is why hefty horizontal mills are popular.

In practice, because my hobby mill flexes and the motor complains when pushed hard, I usually take more passes to remove metal than is ideal. Compared with the risk of damaging the machine or getting a poor finish the extra wear on the end of the cutters doesn't worry me much.

Rubbing tools with very light cuts is to be avoided at all costs. As well as concentrating the wear, rubbing rather than cutting damages the edge rather quickly. Being over gentle with cutting tools is a good way of reducing their useful lives.

Dave