I am in the prosses of starting a new project a Mastiff 4-cylinder IC engine. Instead of just jumping in I decided to look at the parts I was likely to have the most trouble with. The gears looked the biggest challenge. After looking at some options and the equipment I have, a small lathe, small mill and a CNC router with a 4th axis I came up with the idea I may be able to cut them on the router.
The gears were drawn up in Fusion 360 using the helical gear+ addon. I decided to try the right angle 2 to 1 ratio helical gears fist. To give you an idea of scale the 8-tooth gear is just under 18 mm diameter.
I managed to model the gears now to machine them. The width of the gap at the bottom of the tooth profile is 1.43mm the depth of the teeth is 2.37mm. I have some 1mm x 8.75 single flute carbide router cutters that will fit the gap. The question is will I still have them after I attempt to cut the gears, as I had a packet of 10 I thought give it a go, I would still have 9 or maybe 8.
The trial was done on aluminum blanks. This is the setup I used. Fusion cutting setup, “Rotary with the spiral option” a 1mm cutter at 18000 RPM, feed rate 500mm/min depth of cut 0.25mm, I was limited in Fusion to get multiple depths I had to use the axial stock to leave option this worked but involved a lot of air cutting. Total time for 10 runs was under 30miniutes, I thought quite acceptable.
With this method the cutter is fed in a spiral action riding up and down the tooth flank.
How many cutters broke – none, what was the cutters condition – no signs of wear. To be honest I was surprised I did not expect it to be so successful.
Pros
• Cheep tooling no gear cutters
• Acceptable machining time
• Reletivly simple setup for a spiral gear
• Acceptable finish, I would run a second finishing cut at right angle to improve finish
Cons
• Fusion 360 uses credits to use the rotary function for a day, this includes editing an existing tool path.
• Cutting a finer gear, I tried to use a tapered tool with a 0.5mm tip, it did not work I created a 0.5 mm strait cutter it worked. It appears with a tapered tool Fusion uses the larger diameter.
To my surprise this appears to be a viable way to cut gears.
To get around the limitations of Fusion credits I pulled out an old version of Aspire. I saved the finer gear I could not cut in Fusion as a stl file and dropped it int Aspire. I unwrapped it using the same tapered cutter I created a toolpath without any issues, I was able set multiple depths with out air cutting. I will give Aspire a go and post on how it goes.
There are 2 videos attached one as the gears turning these are roughly screwed to a piece if angle. The other is a simulation of the cutting. Note in the simulation the cutter rotates not the job.
I hope this has been of interest and would be interested if someone else has tried similar.
Greg
