Gears...

[precisionmetal]

Cut this gear over the weekend -- a sample for someone building a very tiny scale racecar model.

254 DP - 20° PA - 42 teeth.

This was done on an Agie wire edm machine using .0028" diameter wire.

Material was a piece of .025" Starrett shimstock.

 

[dsquire]

precisionmetal

I am glad that you took the close up with the penny because at real size I would have thought that there was a speck of fly s4!t on it. That is amazing, great work. :bow: :bow:

Cheers

 

[Niels Abildgaard]

Hello PM

Can You use a wire edm machine as a measure thing?
I am asking because I want to make a better parting tool.
(Please se under specialist section)
It is obviously possible to glue ,brace or weld buisnes part of a 2 mm Tang-grip insert holder unto a suitable 3.4 mm prismatic steel bar but it lack elegance.
Will it be possible to use the wire to obtain the geometry for wire sparking a new seat from an existing blade?
We mustasume that the prismatic angles of the seat is 15 degree and rest is 0

 

[precisionmetal]

I'm sorry, but I don't understand what you mean by "use a wire edm machine as a measure thing".

As far as cutting -- if the shape can be defined in a computer, I can cut it (within limits of course -- too large it won't fit in the machine, and if the part is so small it can't be seen, that might be a problem as well).

PM

 

[Niels Abildgaard]

Excuse me for being unclear.Not first time and with luck not last either.

What I wanted was to use the EDM as a copy machine.
First using the wire to measure a master form and the duplicate that on a virgin piece of metal.

It is for making a special parting blade holder explaned in a thread close to this.I have asked a friend if this is possible and we will try it tomorrow.

I will post pictures if succesfull.

 

[precisionmetal]

I suppose that's theoretically possible, however I'd think it would be far more efficient to optically inspect your current part and then create a CAD model from that inspection data.

 

[Ken I]

Wire Cut EDM is also my weapon of choice for small gears.

This is a 10T x 64 DP gear (used for Slotcar racing).

When wire cutting the external gear the wire cut MUST start in the middle of a tooth crest as the end leaves an unavoidable "spike" that must be removed - if this is on a tooth flank the gear is useless.

Using EDM you can also cut from pre-hardened and tempered stock.

Also for small numbers of teeth you can moderate the tooth profiles by generating them on Autocad - to eliminate the interference problems.

You can also do non-standard gears such as this 7T 64 DP below.

The profile to the left is a theoretical "Rack-Cut" involute profile - note the severe undercutting in the dedendum and the root diameter is too small in any case (had to run on a 2 dia shaft) - so I generated the profile for an oversize PCD using the 38T gear profile as the "generator".

The illustration above shows the generation steps in a CAD drawing (the hard way).

Once you have developed your profile you go directly via dwg, dxf Solid Edge etc direct to your wire cut machine.

I generally don't approve of non-standard gearing but with small numbers of teeth or through dint of circumstance its sometimes the only thing you can do.

Regards,
Ken

View attachment Dump.dwg

 

[precisionmetal]

If the situation allows it, I will often enter/exit the cut dead center in the bottom of the gullet.

Then just stop the machine a tiny bit before the profile is finished and apply a clamp to hold the gear in position (and give conductivity to the drop) and finish the cut. More often than not, it's near impossible to see where the cut started and stopped.

Many ways to skin the cat.

 

[Ken I]

I'll try that next time - thanks.

Regards,
Ken

 

[DTANNER]

WoW I have only been using a EDM machine for a few months and you pictures have told me, I have a long way to go. I use it for a varity of things but know I must try a minature gear. If you have time I would like to see some more receant things you have managed to cut. :bow:

 

[precisionmetal]

Here you go -- toward the other end of the spectrum:

A rear end spool out of a Trophy Truck. Customer was stepping up in axle size, but wanted to continue using an existing spool. Part was fully heat treated.

The spool, the axle and the drop in the first photo, and just a photo of the drop in the second photo as a size reference.

 

[Ken I]

That's one long cut - I presume one or two finishing passes ? - what was the total cutting time ?

Ken

 

[precisionmetal]

As I recall it took half a day or so. One skim pass after the drop was out.

 

[popnrattle]

Hello, you may be interested in a video I uploaded to youtube of a procedure to draw the components of a planetary.(Both external and internal TRUE INVOLUTE with backlash gears using Autocad '04). A 9-tooth Sun, an 18 tooth planet(3), and a 45-tooth ring(internal). I would make lots of gears if I had one of those wire EDM's. ;D Later, Rick.

[ame]http://www.youtube.com/watch?v=Hvfytr7DuGk[/ame]

 

[Ken I]

Thanks for the video - very illustrative. KP for effort.

How does your CAD develop the involute ? I see how you generate a series of points on the involute path - what happens then - do you use the cubic spine interpolation ?

My very old CAD (steam driven Ver 10) turns everything into an approximation via a number of circular segments - but that's still very close.

Also I see you didn't bother with the corner root radii in the clearance - on very small gears the wire cut can be bigger than this and you need to allow for it (or use a smaller wire - a PITB) on bigger gears you would want the more generous rad for fatigue reasons.

Ken

 

[popnrattle]

Thanks for the kind comments. I connect the "dots" with the "SPLINE" command. It is a curve with no center point. Yeah, depending on the material you can put fillets. At times I have used a full arc to connect teeth at the root as the following link shows:

http://s489.photobucket.com/albums/rr258/popnrattle/?action=view&current=SHEETMETALGEARS.jpg

These laminated gears show the root as being the diameter of a 1/8"dia. drill. I drill all of the roots before I machine the teeth. You may notice the ring gear segments(internal teeth) whose roots had to be drilled to accomodate external tooth tip clearance. I made these laminated gears to insure alignment. Thanks for your input and interest. Later, Rick.

 

[cfellows]

This is probably not news to anyone else, but a couple of days I came to the realization that an internal gear can be made by taking a regular gear and using it as a template for cutting out the waste in a blank to form the internal gear. In other words, the part that is taken out of a disk to form an internal gear looks exactly like a positive gear of the same pitch, number of teeth, etc. Wonder if it would be possible to use a small brass gear, for example, as the profile on the end of an EDM tool to cut an internal gear?

Chuck

 

[Ken I]

Chuck,
Yes and no - a pinnion shaped EDM electrode would need to be "rolled around" A'La a Fellows gear shaper to generate the shape.

Besides we are talking wire cut EDM so its moot.

You could spark erode (plunge) use a properly profiled electrode - but this would not be the same profile as a pinnion.

However if I want to generate the wire cut path on CAD I would indeed generate it from the pinnion.

Think of all gears as a "rack" - then bend the rack to radius of your gear.

My explanations oft degenerate to the clarity of mud on rereading them.

Ken

 

[Maryak]

My explanations oft degenerate to the clarity of mud on rereading them.

Ken

Nah, I don't believe that for a moment

Best Regards
Bob

 

[Charles Lamont]

Also for small numbers of teeth you can moderate the tooth profiles by generating them on Autocad - to eliminate the interference problems.

You can also do non-standard gears such as this 7T 64 DP below.

The profile to the left is a theoretical "Rack-Cut" involute profile - note the severe undercutting in the dedendum and the root diameter is too small in any case (had to run on a 2 dia shaft) - so I generated the profile for an oversize PCD using the 38T gear profile as the "generator".

I generally don't approve of non-standard gearing but with small numbers of teeth or through dint of circumstance its sometimes the only thing you can do.

[/quote]

As I understand it, the normal way of reducing undercut is 'addendum modification', which is subtly different from what you are doing. The pitch circle remains the same but you increase the addendum of the smaller gear and reduce the dedendum, and vice-versa on the mating gear. This will give a slightly different profile.