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Single Point Herringbone

Single Point Herringbone

(OP)
Very occasionally we need to have herringbone gears or pinions cut. These were a part of our product line which was discontinued in the mid 80's but we continue to supply repair parts. Whenever we receive a request for a replacement gear or pinion, the request is almost always for 1 pc. We do not have herringbone capacity and are not interested in adding it so we always contract our herringbone teeth. To reduce the cost per piece we process 3 - 5 pcs. It is usual for this low, but high investment $ quantity to be a 5+ year supply. We have been reading about gear cutting on machining centers and have determined our equipment is up to the task. Now we would like to try producing our own. Finding an involute profile end mill is proving to be an obstacle. One of the companies where we purchase our hobs is a source but the price they quoted is pretty significant. Should anyone know of a source for involute profile end mills we would greatly appreciate any suggestions you may wish to offer. Thanks, K.

RE: Single Point Herringbone

Could you spend extra machine time and generate the gear teeth using simpler cutters?

Mike Halloran
Pembroke Pines, FL, USA

RE: Single Point Herringbone

(OP)
Thanks all. Apparently I've been cutting gears too long on dedicated machines to see beyond the norm. You have provided us a new path. Appreciate the help. K.

RE: Single Point Herringbone

Do you have a 5x simultaneous capable machining Center available? Regarding the Herringbone type: which module?
Take a look on www.depo.de. In the English pages you will find a brochure which describes the 5x gear milling with pictures step by step in practice.
Additionally there is a brochure of the gear calculation Software with 3D Format Output etc.

RE: Single Point Herringbone

(OP)
Thanks verknde, that's exactly what my tech told me. We are 4x, not 5x. We are finding many Sharpeners that say they can produce any shape end mill, just send them a print. When I ask if they are currently grinding the involute curve their answer is always something to the effect that they can grind anything to print. That's not very reassuring. Apparently we are back to looking for someone who is currently grinding the involute curve. The deeper we get into this, the more it seems as if we are simply a bit ahead of the curve. Obviously 5x is the way to go, we just haven't made it to that point yet. Thanks All. Appreciate your input. K.

RE: Single Point Herringbone

I'm failing to understand why you can't generate a herringbone gear using a rack tooth cutter with just the following axes:
Plunge
Translate
Rotate
... with the Translate and Rotate axes being coordinated.

I claim no expertise, as usual.
Could someone please explain what other axes are required and why?

Mike Halloran
Pembroke Pines, FL, USA

RE: Single Point Herringbone

kthree-

These guys developed software that allows them to finish hardened spiral bevel gear tooth surfaces using a carbide ball end mill on a 3-axis CNC machine. They should be able to do the same for a herringbone gear and a 4-axis machine (or 3-axis w/rotary table). The images on their website of spiral bevel gears produced using their process look like they have fairly decent surface finish (they claim AGMA Q12 is possible). It looks like it is a rather time consuming approach, but for 1 or 2 parts made in-house it might be cost effective for you. One advantage of this approach is that you can use readily available ball end mills, and they can be sharpened by any qualified vendor. If you use a form cutter it requires a custom tool for each specific gear tooth geometry, and you will likely need to send them back to the supplier for sharpening.

You might download their demo file of a spiral bevel gear and cut a sample tooth surface on your CNC mill with the correct material to see if it gives the finish quality you require.

Hope that helps.
Terry

RE: Single Point Herringbone

(OP)
Thanks tbuelna. My tech is looking into this now. Appreciate your taking time to consider and respond to my post. K.

RE: Single Point Herringbone

Glad to help.

Please post occasionally to let us know how your project progresses. If possible, some pictures of your gear during/after machining would make this thread a great reference for others looking to use the same approach.

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