30cc Inline Twin 4-stroke Engine based on Westbury's Wallaby

Help Support HMEM:

Eccentric

Well-Known Member
HMEM Supporter
Joined
Dec 29, 2020
Messages
99
Reaction score
161
Location
Southern California
I have been developing the capability to cut the gears for the Wallaby. I will be using the tools and techniques I picked up from Chris over at ClickSpring. If you are not familiar with his work, look him up on YouTube, he is very talented and makes beautiful videos. I will not repeat his instructions here as I could not do them justice. To make a gear you need to be able to cut the spaces between the teeth with a properly shaped cutter, and to make the cutter you need special lathe cutters, mandrels, cutter blanks, and sharpening tools. This is where I started. Below is a picture of the print for one of the spur gears and an aluminum test gear, the final spur gears will be made of brass and the pinions of steel.
1631390122816.png



This is the print for one of the two pinions
1631390140352.png



Sheet two has the information necessary to create the cutter to cut the space between the gear teeth.
1631390165940.png



Below I am practicing making gear tooth cutter blanks from 01 tool steel.
1631390186260.png





Below is the beginnings of one of the button cutters that will cut the profile into the gear tooth cutter. these are precision diameter made from 01 tool steel and hardened. In the back ground is a tool that allows the proper relief angle to be cut into the button cutters and is also used to precicley sharpen them.
1631390204199.png



As seen below two of these button cutters are mounted in a holder and cut the proper profile into the cutter on the lathe.
1631390218525.png


Then the mill is used to create the face of the cutter.
1631390240323.png



Below is the gear tooth cutter ready for heat treatment.

1631390254168.png








This is a rotary table that I picked up from Amazon and uses the same chucks as my lathe. I use some Arduino code and a PC to advance the gear blank the correct amount so the mill can cut each tooth space.
1631390267400.png



I cut the gear blank to diameter on the lathe, then move the entire chuck and work piece to the rotary table on the mill. then I cut each leaf (the space between the gear teeth).
1631390290280.png



Finally I move the chuck back to the lathe and perform the other operations to finish off the gear.
 

Richard Hed

Well-Known Member
Joined
Nov 23, 2018
Messages
1,157
Reaction score
263
Location
Seattle
I have been developing the capability to cut the gears for the Wallaby. I will be using the tools and techniques I picked up from Chris over at ClickSpring. If you are not familiar with his work, look him up on YouTube, he is very talented and makes beautiful videos. I will not repeat his instructions here as I could not do them justice. To make a gear you need to be able to cut the spaces between the teeth with a properly shaped cutter, and to make the cutter you need special lathe cutters, mandrels, cutter blanks, and sharpening tools. This is where I started. Below is a picture of the print for one of the spur gears and an aluminum test gear, the final spur gears will be made of brass and the pinions of steel.
View attachment 129021


This is the print for one of the two pinions
View attachment 129022


Sheet two has the information necessary to create the cutter to cut the space between the gear teeth.
View attachment 129023


Below I am practicing making gear tooth cutter blanks from 01 tool steel.
View attachment 129024




Below is the beginnings of one of the button cutters that will cut the profile into the gear tooth cutter. these are precision diameter made from 01 tool steel and hardened. In the back ground is a tool that allows the proper relief angle to be cut into the button cutters and is also used to precicley sharpen them.
View attachment 129025


As seen below two of these button cutters are mounted in a holder and cut the proper profile into the cutter on the lathe.
View attachment 129026

Then the mill is used to create the face of the cutter.
View attachment 129027


Below is the gear tooth cutter ready for heat treatment.

View attachment 129028







This is a rotary table that I picked up from Amazon and uses the same chucks as my lathe. I use some Arduino code and a PC to advance the gear blank the correct amount so the mill can cut each tooth space.
View attachment 129029


I cut the gear blank to diameter on the lathe, then move the entire chuck and work piece to the rotary table on the mill. then I cut each leaf (the space between the gear teeth).
View attachment 129030


Finally I move the chuck back to the lathe and perform the other operations to finish off the gear.
This should work for steel as well as alu, right?
 

petertha

Well-Known Member
HMEM Supporter
Joined
Jun 24, 2010
Messages
1,713
Reaction score
393
Thanks for showing these details!

Post 61 shows the Cad diagram of the gear & then on separate sheet looks like you are developing the resultant button diameter & spacing. Did you import the gear solid model from a vendor website or develop it yourself? Just wondering because there was a good YouTube video showing gear tooth generation for Solidworks (which looks like you are using?) entirely using equation driven dimensions for the tooth profile. I don't have it handy but could locate it. But taking it to the next step for cutting tool buttons is very crafty. I was told to be wary of manufacturer downloads because they can vary in their details depending on the source. Some are quite accurate with important details like relief & fillets etc. Others are just meant for spotting into assemblies with no real intent to make the gear itself.

Can you show some more details of the fixture that cuts the relief angle? How did you determine how much to off center the cutter? Then you mentioned re-sharpening - how is this accomplished
 

Eccentric

Well-Known Member
HMEM Supporter
Joined
Dec 29, 2020
Messages
99
Reaction score
161
Location
Southern California
Steamchick - thanks for the kind words. I don't think there is anything I am doing here that is not standard machining practice and well within your abilities.

Richard, you are correct, this will work for steel. My two pinions will be made from steel and the two spur gear will be made from brass. I am working in aluminum now to refine my technique. But the smaller gears (pinions) will be cold rolled mild steel, then I will case harden them with the case hardening compound available from Brownell's. It is difficult cutting steel gears so as not to harm the cutter, it is very important to keep the chips cleared and to progress slowly, both the cutting speed and the spindle speed. I will make several passes to cut each leaf. Brass is different, one pass works well.

Peter - you are correct, I used the built-in SolidWorks gear tool to create the drawing, BUT I am NOT using this profile to make my cutters. Involute gears have a complex tooth shape that can be closely approximated with a constant radius arc. I am using Chris' spreadsheet (Clock Making and Home Machining) to calculate the dimensions shown on the second sheet of my gear drawing. The button cutters are turned on the lathe from 01 tool steel as shown in my last post, and bonded into a block of steel as shown in the following fotos. The button cutters are mounted with a 15 degree relief angle, and they themselves are cut at 15 degrees.

The following picture shows the formed cutter fit into the forming tool.
1631482371167.png





Here is a closeup of the cutter tool for the gear cutter, you can see the 15 degree relief marked in red.
1631482387771.png



Below is the mandrel used to cut the gear cutter. the gear cutter is mounted off center in order to create the 15 degree relief angle when actually cutting the gear. The pin holds the cutter in the proper position as the cutter profile is turned on the lathe, then the cutter is rotated to the next position and the lathe operation is repeated. This mandrel is also used in the mill to cut the notches which reveal the cutter faces.
1631482411987.png



Below is the setup for sharpening the gear cutter. It presents the face of the cutter perfectly to the grinding stone. This same set up is used to sharpen the button cutters. I have highlighted in red the holes that the button cutters are mounted in while they are sharpened.
1631482433163.png



You asked the question: How did you determine how much to off center the cutter? Below is a drawing of the gear cutter blank, I have circled in red the desired 15 degree relief angle that is presented to the gear as it is cut. Then I have also circled in red a small point that represents the rotational axis the cutter blank needs to be turned on in the lathe to create this relief angle.
1631482452824.png



Below is a test fit of the practice aluminum gears on the engine. How do you like my precision carbide 1/4" gear shafts? The top right gear is connected to the cam shaft and the bottom gear drives the oil pump.
1631482515387.png



Below is a mega close up of the two small gears meshed. The leaf cut depth is .07" for scale.

1631482563128.png
 

Richard Hed

Well-Known Member
Joined
Nov 23, 2018
Messages
1,157
Reaction score
263
Location
Seattle
Steamchick - thanks for the kind words. I don't think there is anything I am doing here that is not standard machining practice and well within your abilities.

Richard, you are correct, this will work for steel. My two pinions will be made from steel and the two spur gear will be made from brass. I am working in aluminum now to refine my technique. But the smaller gears (pinions) will be cold rolled mild steel, then I will case harden them with the case hardening compound available from Brownell's. It is difficult cutting steel gears so as not to harm the cutter, it is very important to keep the chips cleared and to progress slowly, both the cutting speed and the spindle speed. I will make several passes to cut each leaf. Brass is different, one pass works well.

Peter - you are correct, I used the built-in SolidWorks gear tool to create the drawing, BUT I am NOT using this profile to make my cutters. Involute gears have a complex tooth shape that can be closely approximated with a constant radius arc. I am using Chris' spreadsheet (Clock Making and Home Machining) to calculate the dimensions shown on the second sheet of my gear drawing. The button cutters are turned on the lathe from 01 tool steel as shown in my last post, and bonded into a block of steel as shown in the following fotos. The button cutters are mounted with a 15 degree relief angle, and they themselves are cut at 15 degrees.

The following picture shows the formed cutter fit into the forming tool.
View attachment 129076




Here is a closeup of the cutter tool for the gear cutter, you can see the 15 degree relief marked in red.
View attachment 129077


Below is the mandrel used to cut the gear cutter. the gear cutter is mounted off center in order to create the 15 degree relief angle when actually cutting the gear. The pin holds the cutter in the proper position as the cutter profile is turned on the lathe, then the cutter is rotated to the next position and the lathe operation is repeated. This mandrel is also used in the mill to cut the notches which reveal the cutter faces.
View attachment 129078


Below is the setup for sharpening the gear cutter. It presents the face of the cutter perfectly to the grinding stone. This same set up is used to sharpen the button cutters. I have highlighted in red the holes that the button cutters are mounted in while they are sharpened.
View attachment 129079


You asked the question: How did you determine how much to off center the cutter? Below is a drawing of the gear cutter blank, I have circled in red the desired 15 degree relief angle that is presented to the gear as it is cut. Then I have also circled in red a small point that represents the rotational axis the cutter blank needs to be turned on in the lathe to create this relief angle.
View attachment 129080


Below is a test fit of the practice aluminum gears on the engine. How do you like my precision carbide 1/4" gear shafts? The top right gear is connected to the cam shaft and the bottom gear drives the oil pump.
View attachment 129081


Below is a mega close up of the two small gears meshed. The leaf cut depth is .07" for scale.

View attachment 129082
It seems to that your clearance of 15deg on the cutter is not necessary. Would 6 or 7 work just as well? If it would, as you sharpen it it would not be used up as quickly. Maybe this is moot as how often will it be used? Not likely every day, probably not more than once or twice in a year.
 

xpylonracer

Well-Known Member
Joined
Dec 23, 2010
Messages
340
Reaction score
86
Location
Norfolk, UK
With aluminium the cutting forces are not as great as when cutting gear steel so I wonder if the stepper will have sufficient torque at standstill to prevent the workpiece moving away from the cutter, recently there was an article on the Emco F1 cnc mill iO group detailing the addition of a brake to prevent movement should the need arise.
 

Eccentric

Well-Known Member
HMEM Supporter
Joined
Dec 29, 2020
Messages
99
Reaction score
161
Location
Southern California
Hi,

The torque of the stepper in the rotary table is reasonably secure, but I can grab the chuck and rotate it using both hands using some effort. I do not think what you describe will be an issue though (but we will see, I'll let you know). To turn the chuck when the stepper is energized and holding position I need to apply a fair amount of radial force to the chuck. However, when cutting the leaf (the space between gear teeth) the forces are not radial to the chuck, that is they do not try to turn the chuck. The cutter is attempting to push the work piece into the chuck (an axial force vector) and at the same time pushing the work piece away from the cutter (a longitudinal force vector). Because of the force pushing away from the cutter, using a tail stock is a good idea.

You have made a good observation, there is quite a bit of vibration cutting steel due to the nature of the interrupted cut, and the chuck cannot move even slightly or the shape of the gear teeth will be compromised. A solid chuck brake would address this. I am hoping my small gears do not give me this problem, but we will see.
 
Top