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View Full Version : _ Will this gear cutter work (pic inside) ???



iMisspell
06-08-2013, 05:45 PM
Ive only cut one gear (ever) and made a "fly-cutter" type tool to do so... now just made a multi-point cutter (images below) and would like opinions before i harden it.

My concern, releaf... there is none. I was gonna take a dremal and releave both the top and sides of each cutter before hardening it, but if there it no need to then i wont.

Made from O-1, OD = 2.5" around .300 thick and will be cutting delrin (will keep the cutter for future use also, dont know what material that will be so i want the most versatility from this, long lasting and the ability to re-sharpen).

http://i1284.photobucket.com/albums/a570/iMisspell/Projects/Metal/Gear_Cutter/DCP_1550_zps1cdf85e3.jpg (http://s1284.photobucket.com/user/iMisspell/media/Projects/Metal/Gear_Cutter/DCP_1550_zps1cdf85e3.jpg.html)

http://i1284.photobucket.com/albums/a570/iMisspell/Projects/Metal/Gear_Cutter/DCP_1551_zps04df56ae.jpg (http://s1284.photobucket.com/user/iMisspell/media/Projects/Metal/Gear_Cutter/DCP_1551_zps04df56ae.jpg.html)

http://i1284.photobucket.com/albums/a570/iMisspell/Projects/Metal/Gear_Cutter/DCP_1552_zpsbd51ad98.jpg (http://s1284.photobucket.com/user/iMisspell/media/Projects/Metal/Gear_Cutter/DCP_1552_zpsbd51ad98.jpg.html)

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Elninio
06-08-2013, 06:09 PM
Needs relief.

rohart
06-08-2013, 06:26 PM
I'd have thought you could cut delrin if you take it slow and you have plenty power. The problem is the high friction you'll get as the unrelieved trailing land forces its way past the just cut profile of the gear. The friction in the case of a metal gear might be prohibitive.

While the friction from delrin will be less, you don't want it to melt. As well as this, delrin will to some extent accomodate to the pressure of the cutter, cut less cleanly and then result in higher friction pressure. But if you don't melt the gear, you should manage.

Since you won't be able to use it for many gears, why not reduce the friction by shortening the lands. The only reason for long lands, other that strength, is so you can keep sharpening the cutter. You're not going to be doing that.

John Stevenson
06-08-2013, 06:26 PM
You will get away with this in Delrin.

Harden it off but don't temper it, plastic is quite abrasive and hard works best, no chance of this shattering on Delrin.
When you come to sharpen it feed in from one side and do each alternate tooth, then do the other teeth from the other side.

The idea is to throw opposing burrs over the sides.
Believe it or not these burs will give some relief.
Try not to get it hot when grinding but the bit of heat that goes into the cutter makes up for not tempering.

John Stevenson
06-08-2013, 06:38 PM
Another alternative is to read this thread from post # 58 onwards.

http://bbs.homeshopmachinist.net/threads/41591-Involute-shaft/page2

Change the three teeth to 6 and using your original tool you should be able to put relief on and make a cutter that can be used up until the last regrind.

Hopefuldave
06-08-2013, 07:32 PM
I've made gear cutters (and even a couple of gear and - trickier - worm hobs) with relief by a similar method, but 4-tooth / 4-flute, by moving the blank off-centre in the 4-jaw, using a dial indicator to get the required eccentricity each time (I guess the cutter could also be rotated / indexed in the chuck?) - the gear cutters were pretty good, if I say so myself, and had a dozen resharpenings that I know of, still cutting the same tooth form. The hobs worked ok, but for worm-wheel hobs cutting the same thread 4 times to get the relief with the blank offset got a bit tedious... I drawed a lickle picture in a thread a few months ago, damned if I can find it...
Assuming no CNC / hobber, a cutter / dividing head is easiest, but I'd like to try "automating" the process a bit - it occurred to me that rotating the blank while traversing a rack-form hob doesn't *need* CNC/gearing, a wire and a pulley pcd diameter could rotate the blank to match the hob teeth... Hmmm.....

J Tiers
06-08-2013, 09:38 PM
Watchmaker trick..... I forget which watchmaking book it is out of, probably the Goodrich book that I got from the now departed Lindsay's books.

Cut in under the back of each cutting section. Bend the whole section down into the cut, tilting the heel of each section down a slight amount.

Now you have a relieved cutter, which will be sharpenable. There is a very slight change in geometry of the cutter from the bend, which is generally not an issue.