cutting a worm on the minilathe

My apology, posted this to the wrong group. Reminder: check address before sending.

Mike in BC

On Sun, 24 Feb 2008 00:00:21 +0000, Michael Gray wrote: > I have a 7x12 minilathe and a nicely hand-ground Acme profile tool I made. > Right, so I have to cut a worm at 6.4 tpi for Dave Lammas' dividing head, > the change gears with my 16 tpi leadscrew will be: >

My apology, posted this to the wrong group. Reminder: check address before sending. Mike in BC

You beat me to it Mike! uk.rec.models.engineering would have been my bet as actual modelling does not play a big part in this group. Most technical type questions do not generate much interest and the majority is split between those of us who make use of that which is available and affordable and a small group who seem very pleased at spending loads of lolly on the latest flashbang gizmo!

Good luck with your gear train problem.

regards

Gear TRAIN. He was half right then ;o)

Any decent chap would not laugh at a man with 6.5 tpi worm!

Regards

The problem now being of course, to find a lady with matching - and also right-hand thread. You really asked for that one Peter! :-) Mike in BC

On Mon, 25 Feb 2008 16:43:13 GMT, Michael Gray

wrote:

Touché

Regards

Have we been insulted or is this to generate a discussion of what is the definition of a modeller ?

cheers, Simon

Well Simon me ole butt -- there is modelling (ranging from mathematical {digital or analogue} through to the mini engineering with some very high tech stuff) and model railways which can cover an equally wide spectrum. Having enjoyed all the aforementioned at some time in my life it led me to make my observations.

Mike got into the wrong group and I found myself wondering just how many of this group knew what the chap was asking! He certainly did not generate many helpful replies.

Being a retired matelot I am afraid that I cannot claim to have either the intelligence or wit to insult anyone properly -- I just try my best.

Regards

Well I think he will need an idler has he needs a left hand thread. But only having a Unimat I would have to buy a feed screw and cut it down. Based on his use of an Acme thread used for feed screws and the need to move a tool forward by turning clockwise Ect.

Thats ok then - I think.

Cheers, Simon

Also being a retired matelot (Nat.Serv. only ;-) M(E)I) and not needing a left-hand thread (sorry, but where did you get that from? Trev.), but being able to use NthreadP.exe (now where did I find that?), I did try one of the gear-trains with the least error this arternoon - and I got a chunk of metal definitely resembling a worm in form and substance. Jeez this is fun! I'm sure it would be a lot easier in brass though - like for a little locomotive in OO gauge (obligatory mention of model railways). I seem to remember an article on mounting a 3 or 4 start worm in a model loco so that it would coast with the power shut off. Thanks for your patience gentlemen. Mike in BC

Mike,

You might be referring to a article by Sid Stubbs in one of the model railway magazines some years ago. I could try and dig it out if I can remember where it was. I think it was in Model Railways in the 1970s.

Certainly, Sid Stubbs' gearboxes were/are reversible but I can't remember him using as many starts as four on his worm. I'll probably be proved wrong if or when I find the article :-)

I haven't tried machining a worm but I think I remember that when doing multi-start worms, the lead screw gearing required is such a ratio that it is easier to do the machining at low speed, manually, with the lead screw driving the mandrel.

Machining the worm wheel might be a bigger problem and I remember advice to machine a hob in carbon steel in the same settings for making the worm, then hardening the hob and using it to hob the worm wheel blanks.

Jim.

Ah! I'll miss that pleasure. Just going to use a changewheel to mesh with the worm for a projected dividing head. Mike in BC

Mike,

I omitted to notice that we had goit off model railway gearboxes, and returned to acme worms and dividing heads ;-) -- at an angle of course :-)

If you run into a problem with the worm/wormwheel setup, there's always the option to use trains of changewheel gears and index on the teeth of the gears to give a reasonably good dividing setup, provided you make allowances for play in the teeth if you use more than one gear in mesh.

Jim.