GearHeads Corner

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 converting the old DOS program into a G code generating 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 simulating 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 interesting!

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 Horizontal/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" calculation and a variable to widen
           the cut for a formed cutter too narrow for standard tooth. Version 0.03

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 undercutting. 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 adjustment 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

;D Thanks

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



Cheers
Bob