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Author Topic: One tooth gear hobber  (Read 6089 times)
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Chuck
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« on: November 07, 2010, 04:41:32 PM »

Years ago I wrote a DOS program to calculate the dividing head settings and Y offset to simulate a HOB.

I am stuck inside with a bad cold on a WONDERFUL fall day and spent the last 2 hours convertin g the old DOS program into a G code generatin g 4 axis CNC windows based program.

The program uses a hand ground fly cutter shaped like a rack tooth or a rack formed milling cutter.

It starts by slicing the center of each tooth cut to the full depth then works it way up each side of each tooth by simulatin g the rolling involute action of a rack running against the gear.

You will need to make or buy a rack tooth cutter for each pitch but it should mill any number of teeth.

Please let me know what you think of this.  It worked well with a manual dividing head years ago. Counting turns and holes really got interesti ng!

The big advantage of this over the endmill 2.5D cutting is it can do very fine pitch gears.

Chuck

Feel free to download the program below.  And please let me know what you think!

Update:  I made some changes and have posed an updated version 0.01
Update:  I added Horizonta l/Vertical Milling machine selection and rack tooth formed endmills
            version 0.02.  It is still needs work to remove some air cuts but looks like it is working.
Update: Added tooth tip clearance control with a "Whole depth" calculati on and a variable to widen
            the cut for a formed cutter too narrow for standard tooth. Version 0.03

* onetoothhob0_03.zip (23.72 KB - downloaded 534 times.)
« Last Edit: May 01, 2011, 02:43:03 PM by Chuck » Logged
John S
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« Reply #1 on: November 07, 2010, 05:41:55 PM »

Looks interesti ng, I'll give it a run
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John S.
Nottingha m, England
Chuck
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« Reply #2 on: November 09, 2010, 02:58:10 PM »

I was thinking about this program  and one thing I may need to address is whole depth vs working depth and clearance .

If the cutting tool is a true rack tooth form with NO clearance the program will make nice involute gears.  BUT without clearance at the bottom.

If the cutting tool has the clearance added to the tip then it may undercut as the gear is formed.

I see 2 possible solutions:

1) Simply make a deeper slicing cut with standard tooth formed cutter and then backoff as the tooth forming is done.  This would not be a problem on gears with low tooth count but may be on larger gears.

2) Require a two cutters one for clearance slicing and a second to form the gear.

Of course simply making the formed cutter a bit longer would create the clearance and may not cause enough undercut to worry bout.

Another concern is using formed involute cutter designed for 135 to rack (#1) stock gear cutter.  This cutter has the clearance built into the form and will cause some undercutt ing. This is in addition to the fact that the form is NOT a rack it is closer to the 135 tooth gear's involute.

If I add a length and width adjustmen t to the program a thinner than normal tooth form cutter could do both the clearance and form the sides of the gear teeth.

I will look into this in the next few days.

Chuck

 
« Last Edit: November 09, 2010, 03:06:14 PM by Chuck » Logged
Chuck
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« Reply #3 on: December 27, 2010, 06:50:58 PM »

Here is an old B&W photo of a 8DP gear I made in 1981 using this process with a double fly cutter and a dividing head. NO CNC on this job just lots of counting holes and turns for 15 passes per tooth.

This was a 2 gear compound cluster for a milling machine main drive on a sliding spline shaft.  The hole was cut using a slotting head on a Bridgepor t and rotary table.  I am happy to say the gear is still running quietly nearly 30 years later!

Chuck


* TH_compoundspur.JPG (29.39 KB, 605x480 - viewed 714 times.)
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Mike
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« Reply #4 on: October 09, 2015, 09:45:44 AM »

 Grin Thanks
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BobL
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« Reply #5 on: October 10, 2015, 05:46:33 PM »

Thanks for posting Chuck, I'll give it a try..



Cheers
Bob

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Gearotic Motion
Bob
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