Bevel Gear Machining.

[David Guzman]

Do you actually want a Miter Gear? 1:1 Ratio?

If yes, ignore rest of post.

Martin Sprocket Catalog shows a Bevel Gear with 16P 48 Teeth. But bevel gears work in sets. This particular one is a 3:1 ratio.


Part # BS1648-3

[42!]

Thanks for all the responses guys. In particular the last one. As it turns out this bevel gear does need to have a 3:1 ratio. The small pinion bevel gear (16 tooth) will most likely be a purchased item, However for a variety of reason it would be preferable to machine the large bevel gear ourselves. In particular I was looking into using a three axis process like this http://www.youtube.com/watch?v=vw4ZX8VDIqY which is often used to make large bevel gears. Is this process a feasible one ?

[Seth Mallory]

In 2011 we used the bevel gears from some power tools from Harbor Freight. We needed some angle gear boxes at the last minute. They came with bearings and shafts that we could mount things too and are still going strong.

[sanddrag]

Originally Posted by Seth Mallory

In 2011 we used the bevel gears from some power tools from Harbor Freight. We needed some angle gear boxes at the last minute. They came with bearings and shafts that we could mount things too and are still going strong.

Which particular tool?

[Seth Mallory]

We used a 18 volt angle drill. One of the kop motors was a perfect match and we were able to use the reduction gears. You can look on line at the parts lists and diagram for most tools. If you search you can many different size of gear sets. Also winch and air tools are good sources. In 6 the hours the team had bought and made 2 angle gear boxes for 25$ each.

[Tristan Lall]

There are several different tooth forms for bevel gears; if you're planning to build something using a stock gear and a custom one, make sure you've matched the tooth forms carefully.

I'd say it's usually a lot simpler just to buy an off-the-shelf set of gears.

[DonRotolo]

Originally Posted by 42!

Is this process a feasible one ?

Not as shown, because the bevel gear you are proposing has an angled face. In the video the tool is perpendicular to the teeth. To use a process like this, you'd need to elevate the workpiece at a precise angle, then turn it a precise arc for each tooth - i.e. have the tool perpendicular to the tooth root.

A spiral bevel gear would work OK (duh - they did it!), maybe better, with just a small extra effort in design. But you'd likely have to cut both gears yourself.

[42!]

Alright then, That makes a bit more sense seeing as there's a good amount on the internet related to 3 axis CNC work on Spiral bevel gears.,but not on straight tooth bevel gears. Having to manufacture both gears would be a trade-off we could make. (We have a 4th axis attachment for our Tormach we could use for the pinion.) Does anyone have any knowledge related to the advantages and disadvantages of using spiral bevel gears?

[Aren_Hill]

I've debated doing this myself a few times, but never really had to pull the trigger. I did decide i'd probably take the CNC and a really long runtime route, as you definitely couldn't buy what I was after.

[DonRotolo]

In the car world, the big advantage of spiral bevel gears are their much quieter operation and their somewhat longer life. The disadvantage is their higher production cost.

In your circumstance, I think ease of manufacturing would trump all that.

It is possible to make a flat straight-tooth bevel gear, but strength, durability and efficiency suffer. Really, the big gear is flat, and the pinion looks like a spur gear but with tapering teeth - the tooth profile is not constant, but gets thinner towards the far end. Generally the pinion is not very wide, maybe 1/2" - 3/4" for the kind of sizes I think you're working with.

Maybe try it with some machining wax, machining foam, or maybe soft brass?

[Orangedesign]

Hi FRC teams! As a team with little experience, we are trying to move away from imprecise tools. What would be a good and cheap 3/4 axis mill (~$2000)? Are used ones ok? Are complex parts manufacturable with better manual tools (ie manual lathe/mill)?

Many Thanks

[protoserge]

There are good inexpensive mills that can do the job just fine for most of the work an FRC robot needs.

We have access to a HAAS four axis once in a blue moon, but most milling last year was done using a Grizzly 1007 manual mill with an autofeed table. It goes for ~$1700. Harbor Freight has a slightly lower model as well (different paint and without autofeed) for $1100 (#33686).

Grizzly has some inexpensive endmills (~$90 for a set in R8 collet size). Spend the money on a precision machining vise. Grizzly sells some as well.

I would budget about $2500-3000 minimum for a good size setup considering the clamps, collets, endmills, cutters.

You can also retrofit one of the Harbor Freight mini mills (#44991) with a X2 CNC kit for <$2000. They sell the mini-mill for $600 and they may accept the 20% off coupons that are always floating around.


I'm sure there are plenty of other options out there as well.

I would post links, but I think that sends my posts to pergatory for now while I get my post count up.

[DonRotolo]

Used tools are OK, and can often get you much more machine for your money.
Search ChiefDelphi for many, many mill recommendations. I remember Dave Lavery offering a particularly good choice.

Far more important than the quality of the machine is the quality of the operator. An excellent operator can turn out world-class items from a poor machine, and a poor operator* can fail to turn out usable items from the finest machine on the planet.

Many schools / teams decide that CNC is the way to go, as a way of compensating for their inability to actually operate a milling machine. They let the computer make the decisions, and the result is just fine. I am of the opinion that having one or two kids on the team become excellent operators is a far better method.

So, find a local machinist or three, and see if you can get them to teach someone - ideally a Sophomore (who will be with the team a while) how to use a manual mill. And/or maybe introduce you to someone in the used machinery business who can find a nice machine with tooling (which costs as much as the machine!) that's within your budget.

My 2 cents.

*=almost any high school student who hasn't been taught.