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View Full Version : Cutting with the side of a tap.



jimsehr
02-19-2008, 09:22 PM
Saw this part on ebay and thought I would try to make one. Used a 1/2 -13 tap. I can rotate it using a piece of all thread rod or a bolt. Or I could just use it cause it looks cool. Kind of like a knurl. It was easy and fun to make.
I might even use it to rotate a ball turner tool. I'll think of something.
Jim



http://i86.photobucket.com/albums/k106/jims_03/IMG_0012-3.jpg

Fasttrack
02-19-2008, 09:29 PM
Hey thats pretty slick! Sort of like a rack and pinion ... i wonder if you could use it like a threading dial on some applications?

So how'd ya make it? :)

A.K. Boomer
02-19-2008, 09:29 PM
Very clever, was it self-feeding? anotherwords , did you just power the tap and allow the other part to rotate free?

Dragons_fire
02-19-2008, 09:36 PM
this is how ive been making gears for a while.. ever since i saw a site like this one:

http://www.bedair.org/Worm/Worm.html

Fasttrack
02-19-2008, 09:56 PM
Cool! I was trying to figure whether you'd have to come up with something like that to let the piece rotate or whether you clever folks had come up with something else.

I'll have to remember that for future projects.

Weston Bye
02-19-2008, 10:02 PM
Yep, used the technique on my "Time Machinery" Clock in the Spring 2007 Digital Machinist. Gave me a 60:1 reduction to get from seconds to minutes. Been running 24-7 now for over a year. that's over a half a million revolutions. I certainly didn't invent the worm wheel "tap hobbing" technique, but I did put it to good use.

jimsehr
02-20-2008, 01:26 AM
Boomer
It is self feeding . I made a base to establish centerline. Then put a pin thru part and base and let it cut. Put a drop of oil between parts and cutting action held part down to base while it cut.
Jim

http://i86.photobucket.com/albums/k106/jims_03/IMG_0006-6.jpg

old-biker-uk
02-20-2008, 03:48 AM
Some discussion about making knurls this way here. (http://www.practicalmachinist.com/vb/showthread.php?t=147728)

John Stevenson
02-20-2008, 04:34 AM
Sometimes pays to gash the teeth first with a slitting saw and a simple form of dividing head, read pointed bolt into gear teeth.

many who have done that to get say 60 teeth for the DH or rotab have reported they have finished up with 61 or 62 because the outer diameter x pi is greater than the pitch circle x pi and there is room for an extra couple of teeth.

Other than that many people have used this method and it does work well.

.

Weston Bye
02-20-2008, 06:11 AM
Sometimes pays to gash the teeth first with a slitting saw and a simple form of dividing head, read pointed bolt into gear teeth.

many who have done that to get say 60 teeth for the DH or rotab have reported they have finished up with 61 or 62 because the outer diameter x pi is greater than the pitch circle x pi and there is room for an extra couple of teeth.
Just so, John. Indeed, even with gashing I was able to generate a unusable 61 tooth wheel.

laddy
02-20-2008, 07:30 AM
Hey,
Is this with a single pass or slowly increasing the depth of the cut??? If with a single pass wouldn't you have to work out the number of teeth with the diameter of the piece in order not to screw up the threads on the next pass?? Thanks Fred

Evan
02-20-2008, 10:22 AM
I've done quite a few experiments along that line. The part shown is one of the best I have seen in such a small diameter. The problem is that the innermost part of the cut is an entirely different pitch circle diameter than the OD. The smaller the diameter in relation to the thread pitch the worse this effect becomes. It becomes impossible for the thread to match the number of teeth being cut both at the root and the crest of the thread. It cuts properly only at the single part of the tap that is in dirict line with the radius of the wheel. The approaching and departing teeth will recut the previously cut teeth since the form of the tooth is not an involute shape.

Wheels that are large in relation to the thread pitch are easy to make sucessfully since the form begins to approximate a rack but then another problem arises. With many teeth it becomes likely that the cutter will accomodate small errors in alignment progressively as the part rotates. This means that it may just as well generate too many or few teeth even though the pitch circle is correctly calculated.

As John pointed out the part should be gashed with the correct pitch before cutting. What he didn't say is that to obtain the best result the gashing should be done at the correct helix angle.

Dragons_fire
02-20-2008, 10:59 AM
when i did mine, i used a 1" diameter aluminum bar, and a 1/4-20 tap, then turned down each end so it was only 1/16" thick.. it gave an ok gear for really low power applications. and like Evan said, the gear teeth are nothing like they should be, since the tap cuts different profiles as its entering the bar, and when its leaving the bar.

Spin Doctor
02-20-2008, 11:06 AM
I've tought about this in the past (basically when Evan posted the worm gear for his telescope drive). I wonder just how difficult it would be to come up with some sort of gearing set-up that would tie the spindle and work together so they would run at the proper speed ratio to allow actual hobbing on the lathe. IIRC this something that may of been posted on the Yahoo gear cutting group or maybe one of the lathe mods groups. A work slide that allowed the blank to be raised or lowered would let the operator cut spur and possiblely helicals provided that you could set the work axis at the lead angle of the hob.

Evan
02-20-2008, 11:10 AM
You will obtain much better results with an acme thread form as that is very close to what is normally used for a worm and wheel. I hobbed the wheel I just made for the 4th axis with a hob I made from a piece of 1/2 x 10 tpi leadscrew stock.

Note, this isn't the one I just made.

http://vts.bc.ca/pics/wormwheel1.jpg

jimsehr
02-20-2008, 02:48 PM
I cut slowly increasing depth of cut.
Jim

laddy
02-20-2008, 04:23 PM
Thanks, really neat results. Fred

John Stevenson
02-20-2008, 04:35 PM
I've tought about this in the past (basically when Evan posted the worm gear for his telescope drive). I wonder just how difficult it would be to come up with some sort of gearing set-up that would tie the spindle and work together so they would run at the proper speed ratio to allow actual hobbing on the lathe. IIRC this something that may of been posted on the Yahoo gear cutting group or maybe one of the lathe mods groups. A work slide that allowed the blank to be raised or lowered would let the operator cut spur and possiblely helicals provided that you could set the work axis at the lead angle of the hob.

http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/hob%20indexer21.jpg


This is the electronic hobbing setup doing worm wheels.

http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/hob%20indexer23.jpg

And a close up showning the cutter, which is the tail end of an old Myford leadscrew fluted and hardened.

.