I want to cut my first gear

[devils4ever]

Hi all,

I've been looking for a first project that involves cutting gears and I found one. I'm a homebrewer and want to build a bench bottle capper. I know I could buy one cheaper, but I want a project involving gears.

I've been designing this in FreeCad, but I'm not sure what gear parameters I should use. I have a PM25 mill and dividing head. I plan on buying the rack since I don't have the tools to make a long (~12") rack. I want to only cut the pinion.

Questions:

1. Should I use imperial (DP) or metric (module)? Metric cutters seems slightly easier to obtain?
2. What pitch should I use?
3. How many teeth?
4. Pressure angle = 20 or 14.5? PA=20 seems to be for new designs?

I've been playing with this in FreeCad and it seems M1.5 or DP16 or DP20 is about right? For number of teeth, I'm thinking 24 seems about right?

As to formulae, assuming DP20, N=24:
OD = (N+2)/DP = (24+2)/20 = 1.300"

I see some differences when calculating the depth of cut depending on the PA:

From "Gears and Gear Cutting" by Ivan Law:
Depth of cut = 2.157/DP = 2.157/20 = 0.1079"

From Machinery's Handbook, 25th edition (page 1930):
Minimum Whole Depth = 2.157/DP = 2.157/20 = 0.1079" for PA=14.5
From Machinery's Handbook, 25th edition (page 1925):
Whole Depth (preferred) = 2.250/DP = 2.250/20 = 0.1125" for PA=20

All comments would be appreciated.

 

[Alexander McGilton]

I had a request like this at work a year ago or so. They needed a machine to that would turn this white chemical powder into tablet pills. They would then add them to a chemistry experiment and science happens. They needed upwards of a thousand tablets per month and only one grad student to operate the machine. The machine they drew up was a complex machine to dispense and weigh powder, then press them. Thousands of dollars and many hours making a frame and rack and pinion from scratch. I said this looks a lot like a reloading bench. I emailed them photos and a few cataloger pages. I suggested that they buy a powder dispenser kit and a swaging press. Since no components were specific to a cartridge, there was no need for a firearms license. Then I would make only a punch and die of 316ss for the tablet with an ejector pin looking like a firing pin. Less than 1k$ with a wooden bench. I know that there is an anti-gun culture in Canada, didn't realize that it extended this far. So the prior plan was used, only I got rack an pinion from Master and such.

Tangent over.

20* and 25* Pa are for strength in a compact space, 14.5* Pa are for running with the least friction.

You can make your own rack. Square or rectangular cold roll in the vise, then cut slots with one of the below cutters. Be careful that the round bottom is sufficiently deep and the 20* walls extend deeper then the contact surface of the rack teeth.




For the gear. Do you have a lathe change gear or a scrap gear lying around of a corresponding Dp or module of your choice? Can even be a close yet wrong tooth count. Once you have borrowed gear, hand grind a Hss blank to fit the gap between the teeth. Hold the tool and gear to the light to judge the gap. Place the Hss blank in a horizontal fly cutter.

Rack and pinion are more forgiving of less than ideal shape than gear on gear, particularly in an application low speed and few cycles.


Photo credit, and more reading

Products - Milling Tools - End Mills - Tapered End Mills - Page 1 - All Industrial Tool Supply

allindustrial.com

Gear Tooth Cutter Holder - Sherline Products

www.sherline.com

 

[Alexander McGilton]

If you are looking for the strange flat radial fly cutter like the Sherline. You can buy one of the above, then mill the tool blank seat flat to remove the angle inherent. then add another taped hole and set screw. They are heard but not too hard. 1/4-3/8 carbide standard end mill no problem.

 

[devils4ever]

Wow! I like the idea of using an angled end mill for the rack. That gives unlimited lengths. Is the included angle 20 degrees? Is that what I'm looking for?

I may just buy the cutter for the pinion. I'm not sure I can create my own.

Any thoughts on my questions above? Imperial vs metric? Number of teeth? DP/module?

 

[Alexander McGilton]

 

[WobblyHand]

Wow! I like the idea of using an angled end mill for the rack. That gives unlimited lengths. Is the included angle 20 degrees? Is that what I'm looking for?

I may just buy the cutter for the pinion. I'm not sure I can create my own.

Any thoughts on my questions above? Imperial vs metric? Number of teeth? DP/module?

Module gear cutters are relatively inexpensive. Probably can get a whole set in in M1.5 for $80. Just checked - yeah you can, at least on fleaBay. Kind of hard to cut the rack that way, but, using a shaped endmill like above fixes that issue. You will need to make or buy a gear cutter arbor, but that's not an issue.

 

[Alexander McGilton]

Buy a pinion not the cutter, look in repair parts not necessarily an off the shelf generic gear.

Imperial vs metric? Number of teeth? DP/module?

Before asking that, lets determine what your mechanical requirements are. How much load and Travel is needed to cap a bottle, length of handle throw, force on handle, etc? We want this not to break on first pull of the handle and also not to be so massive to be expensive and time consuming to make.

 

[Alexander McGilton]

Fleabay indeed.
I ordered a set as you mentioned. The laser engraving was indicative of a proper set, though the profile of one cutter was duplicate of the adjacent one.

 

[WobblyHand]

Fleabay indeed.
I ordered a set as you mentioned. The laser engraving was indicative of a proper set, though the profile of one cutter was duplicate of the adjacent one.

Playing the fleabay game, is well a crap shoot. 98+% of the time you come out ahead, at least that has been my experience. If you absolutely have to get it right the first time and you are rushed - then you have to buy "commercial" and pay the man. If you have some luxury of time, fleabay is worth a shot. My opinion. Have I had to return stuff, yes. Have I been "screwed over", a couple of times. Still way ahead of the game. In my opinion, if places like fleabay didn't exist, I wouldn't be in the game at all. Can't afford "retail" on a regular basis. Your experience may vary.

 

[Alexander McGilton]

I'm no stranger to buying items of unknown origin and quality. I have purchased everything from cast iron cook wear, coffee accessories, to camping supplies, and scientific glass wear from aliexpress. And yes it is a mixed bag. What I learned and using some of my privileges and mistakes from my work place. Cast iron sometimes has an exsesive amount of lead, lead lowers the melting point of recycling iron, presumably add some car batteris to the cruseble, less coal needed to make those Dutch ovens. Gl45 media bottle may say they take the full 1.5bar, then explode over the weekend under pressuer since the walls are thinner then advertised. Camping stove? Just replace the fuel orifice from 1.2mm to 0.90mm and it will burn 87 octain without smoke.