Thread: 0.3 Module Gear Cutting Query

Originally Posted by Anorak Bob

I would be thrilled Ray.

Bob.

Here you go.

It went pretty quickly once I got going, so I'll drop it in the mail tomorrow,

107DividingPlate.jpg
About to do the last hole.

The lexan is 8mm thick, I'll leave it square, and you can turn it to whatever diameter you like.

Ray

Thank you very much Ray.

I greatly appreciate your efforts in helping me with this repair.

I am thinking that I will abandon the idea of using an existing indexing arm with its spring loaded plunger and in its place use a simple sliding bolt or pin. The single row of holes will certainly simplify the indexing ( and probably tax my attention too! )

Bob.

Next question Bob - have you the brass for the job?

Michael

Originally Posted by Anorak Bob

I am thinking that I will abandon the idea of using an existing indexing arm with its spring loaded plunger and in its place use a simple sliding bolt or pin.

Hi BT,

An idea I've seen but not used amounts to a piece of wire clamped to the table with a 90 deg bend in it to pick up the plate. Seemed like it would work well enough, easy enough to try.

Stuart

Originally Posted by Michael G

Next question Bob - have you the brass for the job?

Michael

Michael,

Obtaining the brass shouldn't be a problem. There is a place nearby where brass and aluminium can be purchased for a reasonable price -http://www.robertcameron.com.au/

What I need to work out is a way of turning the brass gear blank so that concentricity is maximised ( I can't say ensured ) when the blank is moved to the mill. I'm thinking of an over width gear bored to the correct dimension and incorporating a spigot to fit one of the new-ish W20 collets I have in my collection. I'd bore a centre hole inside the gear's bore to enable the use of the DH's tailstock. I'll post a sketch of what I'm planning.

I can see why a vertical slide mounted milling spindle is a popular watchmaking accessory.

Originally Posted by Stustoys

Hi BT,

An idea I've seen but not used amounts to a piece of wire clamped to the table with a 90 deg bend in it to pick up the plate. Seemed like it would work well enough, easy enough to try.

Stuart

Could be too flimsy Stu. The dividing head has no provision for locking the quill so whatever I come up with must be sufficiently rigid to prevent any rotation.

BT

Originally Posted by RayG

Here you go.

It went pretty quickly once I got going, so I'll drop it in the mail tomorrow,

About to do the last hole.



Ray

Hang on, the gap between hole 86 and 87 is 5 microns out...

Here's what I'm thinking might do the job. The red line suggests the line of parting off and the circle, the arc of the cutter though that probably could be a lot smaller. The 16mm spigot might need to be reduced to 1/2" diameter if the W20 collet drawbar handwheel gets in the way. I have a 1/2" P20 collet that is internally drawbar threaded and the drawbar could become a less intrusive bolt.

BT

SKMC36015082407490.jpg

Hi BT,
Until you mentioned it, I did not know your dividing head did not have a spindle lock. Earlier when I saw the picture of it with all those solid looking gear teeth on the indexing plate I thought what a strange arrangement it was, now it makes sense. Do you think it would be a good idea to use the pin to locate the hole in the Lexan plate only and rig up one of your collection of clamps like a kant twist one to clamp onto the sides of the disc as a lock.This could be a bit of an overkill as it is only a tiny brass gear.
Bob

Originally Posted by krisfarm

Hi BT,
Until you mentioned it, I did not know your dividing head did not have a spindle lock. Earlier when I saw the picture of it with all those solid looking gear teeth on the indexing plate I thought what a strange arrangement it was, now it makes sense. Do you think it would be a good idea to use the pin to locate the hole in the Lexan plate only and rig up one of your collection of clamps like a kant twist one to clamp onto the sides of the disc as a lock.This could be a bit of an overkill as it is only a tiny brass gear.
Bob

Worthwhile overkill Bob.

Originally Posted by Anorak Bob

The dividing head has no provision for locking the quill so whatever I come up with must be sufficiently rigid to prevent any rotation.

This head?
https://www.woodworkforums.com/attach...4&d=1440045987
If it were my I'd just tighten those cap screws(wont need to be very tight). Much like what clamps the spindle on the Wickman.

Is that not the done thing?(or do I have the wrong head?)

Stuart

Originally Posted by Stustoys

...If it were my I'd just tighten those cap screws(wont need to be very tight).

107 times. Hmm. That won't get tiring at all really.

In the meantime, the alignment issue - I keep thinking of that depth of cut (0.65mm) and really there is not much room for error.
Several things that I do that could perhaps be adapted.

• These days for mounting stuff up on the dividing head I use a 4 jaw when I can - makes it easier to dial something in to concentric. I think the dividing head you have is only a 3 jaw, so either a collet or shim the 3 jaw until concentric.
• I have a set of mandrels that I use to hold gear blanks. If you want to size for the bearing after cutting the gear then sometimes (as Dale is soon to find out) I bore an undersize hole that is a tight fit to one of my mandrels and rebore after I've gear cut (use soft material between the chuck jaws and gear teeth though)
• One thing I do a bit is use a long mandrel, both for gear cutting and sizing the blank in the lathe

mandrel.jpg
The centre will always stay in the same place but the chuck or collet may be slightly eccentric. If you keep the distance to the centre short and to the chuck/ collet long then you can reduce the eccentricity by the ratio of the lengths (strictly speaking by a factor of (short)/(short +long))

When cutting (steel) gears I find that these cutters throw up a burr so another thing to think about is sandwiching your good blank between some sacrificial blanks to reduce your burr. Anything will do - some nylon perhaps but the main thing is that it is stiff enough so that a burr does not form on the good blank. If you made them in a hat section, you could bore your blank to the desired size, turn the lesser diameter of the hat to a good fit while boring through.
hat stand.jpg

Hope that gives you some ideas.

Michael

Originally Posted by Michael G

107 times. Hmm. That won't get tiring at all really.

Am I the only one that locks my table every time?
Got to do every thing else 107 times

Stealing the rest of your ideas for future reference!

Stuart

Originally Posted by Stustoys

Am I the only one that locks my table every time?

No, but possibly the only one who would do and undo multiple hex socket screws when there were other ways.

Michael

Originally Posted by Michael G

Hope that gives you some ideas.

Michael

They are great suggestions Michael. Thank you.

I do like the idea of the long mandrel. I'm not overly confident about boring the gear to size post gear cutting. Based on previous experiences, that's probably where I'd come unstuck or more correctly where the workpiece would come unstuck. If the hub of the mandrel matched the bearing size and the gear blank was sandwiched between sacrificial slices of brass I might be able to reduce the risk of disaster. Based on your sketch I'll draw what I'm thinking about and post it here for appraisal.

You are correct, the chuck I have is a 3 jaw and it does have runout. I do have a near mint 4 jaw 4" Burnerd chuck that is backless. While it would be a considerable amount of rooting around, I should either make a backing plate to suit the dividing head's spindle nose thread* or make a P20 arbor to facilitate its installation in the DH with a drawbar. A hollow W20 arbor would be better but cutting the weirdly pitched buttress thread might be more of a challenge than cutting the scope's gear.

It would be easy enough to leave a hex key in one of the cap screws and use it as a lock but beforehand I will check to see if there is any significant quill deflection if one screw is tightened.

BT

* Schaublin incorporate a clamping collar around the threaded section of the backing plate. Without the chuck being clamped to the DH quill, I'm sure the two horsepower would have unscrewed the chuck many a time.