Member postings for Steve Crow

Thank you Andrew that makes sense

So is the 30 degree rack profile in the drawing correct? I realise that I can fettle the dedendum ratio.

I've been looking at 30 degree pa gears.

Here is a drawing of a rack form and hob to cut it. I've followed the usual formula for the 20 degree rack but it just doesn't look right at 30. Not much in the way of crest and the root is almost non existent.

Is there a reduction in addendum and dedendum for increased pa?

I've trawled through all the excellent links you have recommended but I can't find anything. Maybe it is buried amongst some of the impenetrable (for me) maths.

Cheers

Steve

Thank you all for you replies and information. Just a couple of points.

I understand that this is not the ideal method for gear cutting but it's my only chance of making the gears I require. With mod 0.20 or 0.25 a single point cutter of any description is going to be tricky to make to an accuracy to improve on the hob forming method.

Also, the "relief" on the drawings aren't the finished profile, just a guide for milling. I intended to go past the centre for rake and get the files out for relief.

I have a CNC dividing head so I have given thought to going round more than once and adjusting tool height but with teeth this small accuracy would be paramount. I have got a DTI mounted to Z axis so I might get away with it.

I've made the blanks and rough grooved them with a threading insert. I just need to finish the grooves with my home made 40 degree insert.

Steve

Hi Dave, what a fantastic thread. I've not taken it all in yet but there is some great stuff on there.

I intend to make a number of small gear forming hobs as described on the Helicron site and discussed here before.

I milled an insert type 40 degree cutting tool from GFS, hardened, tempered and sharpened it with a crocker jig and an arkansas stone. I can't see any tip radius under 12x magnification.

I realise that it won't stay like that for long but I will only need the sharpness for indexing for depth of cut once on the first hob. After that it is indexed for subsequent hobs.

To prolong tool life further, I intend to rough out the grooves as much as possilble using a 0.1 mm radius tip threading insert I have.

I want try to do three hobs, starting with the smallest mod where things are more critical.

I've attached some drawings. Please have a look at the relief forms and let me know if you think that they will work.

I look forward to any comments.

Steve

Cheers Ian, with a forum name like that I know where to go to for info!

I'm not sure I want to try to mill a dovetail that size. Did you make them as small as this?

Steve

I need to retain a compression spring on a 1.2mm shaft using a small e-clip.

And boy, are they small.

I need my finest point watchmakers tweezers to handle them. They are 2mm od, 0.2mm thick and fit a 0.8mm dia groove. Despite their size, they need a fair bit of pressure to engage.

I made a tool to both depress the spring and fit the clip. It was milled from 3mm silver steel, hardened, tempered and polished. Works a treat.

The photos are self explanatory.

Now I need to make a tool for removing them without the "ping"!

Steve

Here is one similar to Nicholas's first pictures - Link.

Ebay link

Words fail me.

Hi Pete

Do you mean like this one?

This is a drawing of my Champion No1. Made in England from the 30's to the 50's. They come up on ebay occasionally, prices vary hugely according to condition. The rear pulleys were missing on mine so I made my own. The handle isn't shown on this drawing.

Steve

Edited By Steve Crow on 06/04/2020 09:06:27

I've just got round to looking at the KHK site. Very useful indeed, the best gear resource I've seen.

I don't have CNC apart from my rotary table but Gearotic looks interesting anyway as a design tool.

Thanks for the tips.

Steve

Thank you for your replies.

I'm interested in this method as I'm looking at making gears with a mod going down to 0.2

Making single point cutters of that size sounds tricky and I don't have access to a grinder. This seems a relatively simple way to make a cutter.

Has anybody tried this method?

I thought that the minimum teeth for involute gears was 12?

Good point about roller chain sockets - I didn't know that the minimum tooth count was so high.

Steve

Hello,

I've been looking at the Helicron site (don't know how to link) and his method of semi-hobbing gears.

My question is this- if I was to cut the grooves in the hob using a VCMT insert, I would end up with a pressure angle of 17.5 degrees.

I know that this is not a conventional angle but is there any reason that it wouldn't work when mated with similar gears?

Also, what is the smallest amount of teeth practical in an involute gear of this type?

Thanks,

Steve

I've just seen a used PP Thornton escape wheel cutter sell for £71 inc. postage.

The Thornton list price is £58 + VAT. Which route would you rather take?

A couple more drawings. A Champion No1 bench drill and an IME watchmakers lathe, both driven by the big Proxxon.

I have not dimensioned these but they are both drawn to half scale on 5mm squared paper, so each square represents 10mm.

Steve

Ok, this isn't a Wild tool unless I missed it in the book.

While making a MT1 cutter arbor I decided to make some brass spacers and a steel bush to hold a slitting saw at the same centre height as the cutter.

The idea is that when cutting a pinion , it can be gashed with the slitting saw and finished with the cutter without changing the set up.

I've not used it yet, I still have to make a centering micrometer.

I use 3 Proxxon spindle machines, the small ones as a Dremel and the larger to drive other tools via pulleys.

To help me make attachments for them, I've jotted down their vital statistics.

I'll share them here as they might be of help to someone.

Steve

Another useful thing is that the tool has a 5/8" shank so it fits right into a Panavise base.

Good for holding small parts at any angle when filing and finishing.

Steve

Edited By Steve Crow on 26/02/2020 17:30:59

In his book on wheel and pinion cutting, Mr. Wild uses some very interesting and useful tools.

I have started to replicate some of them, adapted for use on a Sherline.

Here is a support tool that fits in the adjustable tailstock holder.

It can be locked with the screw for milling or cutting or left free to revolve (with lube) for turning. Take the tommy bar out first though!

This is it partly disassembled.

I will post pictures of other tools as I make them.

Steve

Very nice! Could you tell me what is the diameter of the motor?

Steve